Anchorage Ski Outlook - 3.22.2023

THURS - FRI: warm, mostly cloudy, snowy (high confidence).
Thursday light snow and winds taper off for the mountains around the PWS (favoring Portage/Whittier), before a moderate Hatcher storm arrives Friday. Rain/snow mix near sea level on Thurs. Winds increase Friday especially for Hatcher where they will be strong.
WEEKEND: dry, warm, sunnier Saturday (moderate confidence).
Colder mornings, warm afternoons, and strong sun affect. Gap winds Fri night & Sat for Valdez, Portage/Whitter, and Seward. Temps warm Sunday as cloud cover increases. Light snow possible Sunday PM for Hatcher Pass and the Anchorage/Eagle River Front Range.

EARLY NEXT WEEK: partly sunny, warm, snow possible (low confidence).
Snow possible Mon/Tues for Hatcher Pass and the ANC/ER FRange (likely light). Partly sunny elsewhere - low confidence in timing of sun. Strong sun affect when its out. Light ridgetop winds. 

Dirty Details
We are past the equinox (March 20th), and its hard not to notice the return of the sun (when its out). Each day feels noticeably longer than the last. Here's a cool plot from showing the dramatic percentage change in length of day that happens in northern latitudes in the spring and fall:

This animation from Visual Capitalist really hammers home how much the length of day varies up here:

Not only are the days getting longer, the sun is also rapidly getting higher in the sky. Just like length of day, percent change in height of the sun is much greater here than farther south. Its also fun comparing the angle of the sun across latitudes. Note that at the equator the sun is directly overhead at noon on the equinoxes. 

Speaking of the equinox: I'd always thought the equinox is when there is equal day and night. Actually there is a little more than 12 hours of daylight on the equinox. Technically, the equinox is when the plane of the earth's equator passes through the geometric center of the Sun's disk - the moment the center of the visible sun is directly above the equator: 

The spring equinox is also when sunrise first comes to the north pole, then the last sunset of the year at the north pole on the autumn equinox - pretty cool!

On the subject of our star, one more cool tidbit: its fun to look at how much the time of solar noon changes over the year. Particularly, from Nov to Feb where real noon changes by 30 minutes relative to clock noon. The reason for this is basically due to a combination of our elliptical orbit, tilted axis, and the human construct of time.
Archived Outlook - 3.8.2023
THURS - FRI: mostly sunny, windy, moderating temps (high confidence).
Temps drop to a more reasonable range with cold mornings and warm afternoons. Strong winds for the Mat Valley (affecting Hatcher), Anchorage/ER FRange, Portage/Whittier, Seward, Crow Pass, our high peaks, and especially VDZ/Thompson. Sun affecting south-facing slopes that are not cooled by wind. 
WEEKEND: dry, moderate temps, decreasing winds (high confidence).
Sunny with sun affect on south-facing slopes and decreasing winds on Sat - winds lasting longest for VDZ/Thompson and the Mat Valley. Mostly cloudy and calmer winds on Sunday. Cold mornings with inversions and warming afternoons.

EARLY NEXT WEEK: cool temps, dry, partly sunny (low confidence).
Low confidence in timing of sun - Tuesday looks the most promising. Moderate winds for the ANC/ER FRange, Seward, Portage/Whitter, and strongest for VDZ/Thompson. Very light snow possible Tues into Wed. I wouldn't bet my office powder-fever sick days on these.

Dirty Details
WOW WOW WOW. Last week I said it would "feel hot in the sun" - I was wrong - it didn't just feel hot it WAS DAMN HOT. Those were crazy temps with some weather stations in our zone measuring (or exceeding) 50 °F! Here's a sample from today - Anchorage Front Range:

Turnagain Pass:

Hatcher Pass:

Temperatures are finally starting to "cool down" as we can see on the ECMWF temp forecast for 5,000 ft below. Its pretty wild seeing the ridge of heat encompassing our zone before it finally breaks down tonight. 

Speaking of the sun, as it gets higher in the sky (and stronger), so much more terrain is getting direct light! You can really see the difference comparing the Shade Map for the winter solstice and the equinox. On the solstice basically just Goldpan was getting sun, while by the upcoming equinox nearly everything gets some sun! Its a good time to focus on all those classy north facing lines!

With the strong spring sun we are going to keep seeing big diurnal temp swings between cold early mornings and warm late afternoons. Today there was a 42 degree temp swing at Granite Creek!

These swings occur because of the difference in incoming radiation from the sun and outgoing energy from the earth. Even more interesting, the peak temp of the day doesn't occur at noon when the incoming solar radiation is the greatest, but later in the afternoon when the earth has had a chance to cook a little longer. This is well explained by the nice figure below:
Archived Outlook - 3.1.2023
THURS - FRI: dropping temps, clearing skies, windy (high confidence).
Skies clear and temps drop into Friday. Clearing will be the most complete for the Kenai Mountains on Fri. Very strong winds for Portage, Seward, & VDZ/Thompson; strong winds for Turny/Summit; and moderate winds for the ANC/ER FRange, the Turnagain Arm mtns, and the Mat Valley. The key for skiing in these conditions is to get away from terrain channels and ridgelines.
WEEKEND: clear, cold, windy (high confidence).
Saturday will be cold and windy before winds decrease and temps moderate on Sunday with the sun affecting south-facing snow. On Sat very strong winds for Seward & Valdez/Thompson; strong winds for the Mat Valley & Portage; moderate winds for Turny/Summit, ANC/ER FRange, and the Turnagain Arm mtns. Sunday should be glorious.

EARLY NEXT WEEK: glorious, moderate temps (moderate confidence).
Mostly sunny with sun effect on south-facing slopes. It will feel hot in the sun. Widespread cold morning inversions, warm afternoons, and light winds. Highest confidence in glory Mon/Tues but possibly lasting Wednesday.

Dirty Details
I heard the aurora was out the other night, did anyone notice? I even saw one or two pix of it social media 😜. Pretty cool to even see it blazing away on the Arctic Valley Webcam:

The weekend sun sure has been so lovely! As my friend Tony put it, it was cold AF in the shade. Here's Nyssa's February entry into the AK hardgirl swimsuit calendar from Saturday in the East Fork of Eklutna - trust me there's a swimsuit under 5 layers of insulation.

We think it was about -10 or -15 °F and blowing 25 mph back there. That's a wind chill of -40 °F...brrrrrrr. With more cold and windy weather coming its fun to take a look at the wind chill chart:

More gap winds - I feel like a broken record! Fortunately these winds will not last for the whole upcoming period, and will be decreasing by Sunday! These midwinter clear/cold events often come with wind. This is because the cold, dense and high pressure air of interior AK flows "downhill" towards the relatively warm and low pressure air in the Gulf of AK. These winds favor terrain channels and gaps (i.e. Thompson Pass, Whittier, and Seward); hence Gap Winds. Here's a cool figure from UBC illustrating this:

To ski during these gap wind events the idea is generally to avoid channeled terrain such as road corridors and long valleys where the wind can easily flow (i.e. the west face of Magnum vs. Goldpan, or Tincan Proper vs. The Library).

As the winds stop stirring the air up on Sunday and early next work week, strong inversions will arrive. These form at night and are driven by cold, dense air flowing downhill while any warmth left at the surface escapes into the atmosphere. Without clouds to act as an insulating blanket more energy escapes into the atmosphere.  Here's an old textbook graphic of the process:

Happy March 🌞🌞🌞🌞!!!!!
Archived Outlook - 2.22.2022
THURS - FRI: heavy snow, warm, windy (high confidence).
Thursday heavy snow favoring Hatcher and Thompson/Valdez with the Anchorage/ER FRange (especially near Turnagain Arm) doing well; windy in the mountains too. Friday the storm moves out, winds decrease, temps moderate, and skies partly clear (the most clearing for the Kenai Mtns).
WEEKEND: dry, windy, cold (high confidence).
Temps plummet over the weekend with the arrival of north winds. Strong winds for the Kenai Mtns, Thompson Pass/Valdez, and the Anchorage FRange. Hatcher will clear last on Sat. Sunday will be the clearest and coldest. Inversions for Gold Mint.

EARLY NEXT WEEK: dry Monday then another storm (low confidence).
Temps bottom out Mon morning with widespread inversions and calming winds. Temps moderate as the next storm arrives Tues into Wed. It looks to be another southwest flow storm favoring Hatcher, the FRange, and Valdez/Thompson with moderate to heavy snow with rain possible near sea level.

Dirty Details
With the last couple months of stormy, gray, and unstable weather I had started to wonder if I don't like skiing anymore....ahahahaha....yeah right. But, this weekend was a reminder of how much we all REALLY like skiing in the sun. Here's Tom ripping steep turns on the west face of Nest Peak on Sunday:

However, the cloud deck was pretty high which is the usual with these clear and calm periods after precip:

Photo: Tom Flynn

Looking into this weekend, the upcoming clear and cold period will bring strong gap winds. These midwinter clear/cold events often come with wind. This is because the cold, dense and high pressure air of interior AK flows "downhill" towards the relatively warm and low pressure air in the Gulf of AK. These winds favor terrain channels and gaps (i.e. Thompson Pass & Whittier); hence Gap Winds. Here's a cool figure from UBC illustrating this:

The key to skiing during these gap wind events is generally to avoid channeled terrain such as road corridors and long valleys where the wind can easily flow (i.e. the west face of Magnum vs. Goldpan, or Tincan Proper vs. The Library). In this bad case the key will probably be to avoid most of the Kenai, Turnagain Arm, and Anchorage Front Range mountains.

Clear and cold periods generally bring inversions. These form at night and are driven by cold, dense air flowing downhill while any warmth left at the surface escapes into the atmosphere. Without clouds to act as an insulating blanket more energy escapes into the atmosphere. Winds can mix out these pools of cold air up, and its going to be windy so expect these inversions to be less widespread than normal. Here's an old textbook graphic of the process:

Lastly, now on the radar you can see the southwest flow that is dumping snow on Hatcher:

As has been well advertised, the Hatcher and FRange snowpacks are fat. But, the Gird/Turny zone is falling behind, and that disparity is only going to get worse with the next couple SW flow events:

Archived Outlook - 2.15.2022
THURS - FRI: moderate temps, light snow, mostly cloudy (high confidence).
Thursday mostly cloudy with snow showers and ridgetop winds before a small storm arrives early Friday bringing increasing winds and light snow. The storm favors Portage/Whittier with moderate snow, but all our mountains see snow. Strong winds for the Anchorage FRange, Turnagain Arm mountains, and Portage/Whittier/Seward. No rain concerns.
WEEKEND: light snow -> drying, moderate temps, ridgetop winds  (high confidence).
Saturday brings light snow favoring the mountains closest to the PWS, but with everywhere getting a bit. No rain concerns. Then on Sunday drying begins!!! Clearing first for the Kenai Mountains and last for Hatcher.

EARLY NEXT WEEK: DRY, cool, gap winds (moderate confidence).
The sun is coming out, and its about damn time. Mon/Tues have the highest confidence of being glorious. Gap winds thru channeled terrain between the interior and the Gulf of AK especially Portage/Whittier, Seward, Valdez, and Turnagain Arm. Inversions for Turny/Summit, Gold Mint, and Anchorage/ER.

Dirty Details
Now time to look into the crystal ball...

Art by Goldpan Owen

Owen made one error here which is that it should say *Mike avoiding work*, but, regardless the MOST IMPORTANT THING HERE IS THE SUN IS FINALLY COMING OUT. There is high confidence in this upcoming dry period because of strong model agreement:

On a slightly less positive note, you all probably noticed that has locked down access to long term forecasts with their Premium subscriptions. We should probably buy a subscription for the backcountry ski group.

This clear and cold period will bring gap winds to the usual spots. These midwinter clear/cold events often come with wind. This is because the cold, dense and high pressure air of interior AK flows "downhill" towards the relatively warm and low pressure air in the Gulf of AK. These winds favor terrain channels and gaps (i.e. Thompson Pass & Whittier); hence Gap Winds. Here's a cool figure from UBC illustrating this:

The key to skiing during these gap wind events is to avoid channeled terrain such as road corridors and long valleys where the wind can easily flow (i.e. the west face of Magnum vs. Goldpan, or Tincan Proper vs. The Library).

This clear period will also bring inversions. These form at night and are driven by cold, dense air flowing downhill while any warmth left at the surface escapes into the atmosphere. Without clouds to act as an insulating blanket more energy escapes into the atmosphere. Winds can mix out these pools of cold air up, so expect the inversions to be weaker where the gap winds are stronger (ie. Portage). Here's an old textbook graphic of the process:

One last thing - I noticed that the Snow Water Equivalent (SWE) at the Wrangell's SNOTELs is at all time highs for the date. Has me thinking about a spring ski trip out there:

Archived Outlook - 2.8.2022
THURS - FRI: cold/clear -> stormy (high confidence).
Thurs crisp and clear with moderate outflow winds for Portage/Whittier, Seward, and Valdez bleeding into Turnagain Pass to a lesser extent. Clearing least complete for Thompson/Valdez. Inversions for Turnagain Pass, Summit, Goldmint, and east Anchorage. On Fri, the next storm arrives favoring the mountains closest to the western PWS (Gird/Turny and especially Whitt/Portage/Seward) with moderate snow. No rain concerns.
WEEKEND: light snow, cloudy, moderate temps (moderate confidence).
Saturday brings light snow favoring the mountains closest to the PWS; decreasing to snow showers on Sunday. No rain concerns. Moderate ridgetop winds for the Chugach and Kenai mountains.

EARLY NEXT WEEK: cool, a little bit of everything (low confidence).
Next work week starts cool, partly sunny, breezy, and showery on Monday. Tuesday dry inland with snow favoring the mountains close to the PWS possibly continuing into Wed; very low confidence in intensity of precip - probably moderate.

Dirty Details
The snow just keeps trickling in and, as you all know, it is doing wonders for surface conditions!!! We went to Hanging Valley yesterday as the fluffy snow continued to come down around us:

It was amazing how much soft snow had accumulated there after it had been hard just days before. Additionally, it was a great reminder of just how local mountain weather and conditions are as winds are funneled by terrain: just a few hundred yards away the main drainage was much firmer and wind-affected.

Tomorrow's clear and cold weather will bring moderate gap winds to the usual spots. These midwinter clear/cold events often come with wind. This is because the cold, dense and high pressure air of interior AK flows "downhill" towards the relatively warm and low pressure air in the Gulf of AK. These winds favor terrain channels and gaps (i.e. Thompson Pass & Whittier); hence Gap Winds. Here's a cool figure from UBC illustrating this:

The key to skiing during these wind events is to avoid channeled terrain such as road corridors and long valleys where the wind can easily flow (i.e. the west face of Magnum vs. Goldpan, or Tincan Proper vs. The Library).

Looking towards next week, the confidence in the weather near the PWS is extremely low. This is because there is such high model disagreement with predictions of everything from sun to heavy snow for the western Prince William Sound mountains:

All this snow trickling in just keeps adding up, with the Independence Mine SNOTEL sitting right near the max SWE (snow water equivalent) on record for the date. For that matter, we're getting very close to the median annual peak SWE.

Probably a good time time to start thinking about those Hatcher and Anchorage/Eagle River Front Range objectives! That is, if you aren't already!!!
Archived Outlook - 2.1.2022
THURS - FRIlight snow, warm, cloudy (high confidence).
Light snow across our zone favoring Hatcher and the mountains closest to the Prince William Sound. Light winds and no rain concerns.

WEEKEND: Saturday drier, Sunday stormier (moderate confidence).
Sat mostly cloudy, showery, moderate temps, and light winds across our mountains except for Thompson Pass/Valdiseased with light snow. Sun temps rise/winds increase as the storm arrives favoring Turny/Gird and especially Whittier/Portage with moderate snow. Light snow for the Anchorage/ER FRange and Thompson/VDZ, but only a dusting and lighter winds for Hatcher.

EARLY NEXT WEEK: snow, cloudy, moderating temps (low confidence).
Moderate snow, winds, and warm temps continue Mon for TurnaGird, Whittier/Portage, and Thompson/VDZ; precip favoring the mountains closest to the PWS and decreasing moving inland to a dusting and lighter winds for Hatcher. Tues into Wed temps/winds moderate and snow turns to showers for our mountains

Dirty Details
Boy oh boy it was nice to see (and feel) the sun on Saturday!!! Also, it sure was unusual to have sun-effected snow in January. Here's Nyssa soaking in the vitamin D amongst some sun-triggered roller balls on the south side of Homicide.

It was warm, but nothing like the upper 40s that the NWS was predicting. I have no idea where they got those numbers from, there was never any model that showed that kind of extreme heat. Use their forecasts at your own risk.

Skiing out of the windf#*$ed Rabbit Creek drainage into the east side of North Yuyanq’ Ch’ex, it was incredible how the snow immediately turned to pow as soon as we were out of the Anchorage Bowl. The Front Range is a windy place. Check out this difference from wind scoured rocks on the west side... Ben ripping pow just a couple hundred yards east from our wind-scoured wasteland:

Past the Sunday/Monday storm it looks like we are in for more of the warm and cloudy weather that has been plaguing our mountains (and my soul) for the last month.

Fortunately you don't *need* good viz to ski the chutes and couloirs that infest the FRange!
Archived Outlook - 1.25.2022
THURS - FRI: clearing skies, moderating warm temps, calming winds (high confidence).
Conditions improve moving into Friday as the last storm departs and weather moderates. Clearing first for the Kenai Mountains and last for Thompson Pass/Valdez and Hatcher. Most sunny on Fri for Thompson and least for the Kenai Mtns with valley fog and widespread inversions Fri morning and eve.

WEEKEND: hot, dry->showers, light winds (high confidence).
Dry, calm, and partly sunny with valley fog on Sat before clouds and showers move in across the zone Sun. Clouds/showers arrive first for the Kenai Mtns and last for Thompson. Rain/snow line near the Turnagain Pass road level. Winds increase a bit on Sun the Turnagain Arm mountains and the Anchorage/ER Front Range.

EARLY NEXT WEEK: warm, cloudy, showery (moderate confidence).
Temps trend down and the cloudy/showery weather continues for our Southcentral mountains.  Moderate ridgetop winds especially for the Turnagain Arm mountains.

Dirty Details
After the latest warm and wet period, high pressure arrives bringing with it widespread inversions. These form at night and are driven by cold, dense air flowing downhill while any warmth left at the surface escapes into the atmosphere. Without clouds to act as an insulating blanket more energy escapes into the atmosphere. And with calm winds there isn't much to mix out the inversions. Here's an old textbook graphic of the process:

With the ongoing disaster created by the last month of weather around the TurnaGird zone we've continued to work the western edge of the precipitation shield. This time we checked out The Sail and Shaman Dome. Turns out Arctic to Indian is a lot of work with 20 miles of trailbreaking and two bonus mountains thrown in there. Who would have thought...

That being said, stability is not perfect around Ship Creek either. Here's a cool picture from The Sail of a smaller skier-triggered windslab avalanche initiating from Austin's skis.

Oh!! For those who haven't noticed - its actually been snowing at Hatcher! This week's snow brings the Independence Mine SNOTEL close to max on record for the date!
Archived Outlook - 1.18.2022
Dirty Details
I saw this cool little summary graphic from the NWS - you maybe did too. What a warm and wet year for Anchorage. Not that that's a surprise to anyone!!!

There's more interesting annual climate stats for Anchorage from the NWS here. Some things that stood out to me for this warm and wet year:
    - 2022 was the 7th warmest year on record with an average temperature 1.6
°F above normal!
    - New high temp records were set for 12 days in 2022, while only one new low temp record was set!

    - The five warmest years on record have all happened since 2015!
- The five coldest year on record all happened before 1974!
    - There were above 0 °F temperatures at the Anchorage Airport EVERY DAY in 2022!
As we're all too aware, we've been stuck in this warm/stormy (and unstable) pattern for awhile now, but we're getting a brief break from it on Saturday! And we have high confidence in a dry and cool day thanks to good model agreement including the GFS and ECWMF ensembles below:

We've been trying to manage this weather by skiing a little farther west to where the edges of the storms are just dropping enough snow to soften surface conditions. Here's Cam looking for that sweet spot above Indian Pass:

Archived Outlook - 1.11.2022
THURS - FRI: partly sunny, warm, ridgetop winds (high confidence).
Quiet weather with the most sun for Hatcher and cloudiest with showers (rain near sea level) for Turnagain/Girdwood and especially Whittier/Portage. Light winds.

WEEKENDlight snow, cloudy, warm (high confidence).
Light showery snow increasing in intensity over the weekend for Turny/Gird while Hatcher, the Anchorage/Eagle River Front Range, and Thompson left dry and mostly cloudy. Rain near sea level. Ridgetop winds which will increase Sunday.

EARLY NEXT WEEKsnow, mostly cloudy, warm (low confidence).
Moderate snow Mon into Tues decreasing Wed. Precip again favoring TurnaGird decreasing moving inland, though the FRange should get a quick shot on Mon. Rain near sea level. Moderate winds for TurnaGird and the FRange.

Dirty Details
Its probably worth noting the surface hoar that formed in our zone late last week. Surface hoar is basically just dew that freezes on the snow surface under clear skies as the snow dumps heat into the atmosphere via long wave radiation. Here's a fun illustration of it from George Manley:

There's lots of examples of mongo surface hoar out there on the interwebz, and we often see particularly large hoar frost crystals around creeks where there is an infinite supply of moist air. I like this example of surface hoar from the Crested Butte Avalanche Center, possibly cause it reminds me of the good old days in Colorado.

This upcoming week looks to be pretty similar to the last couple, with the mountains closest to the western Prince William Sound again getting the most snow.

Hatcher is again the big loser where the dry period is all too visible on the SNOTEL daily SWE plot. Thanks to our very wet December, there's still a lot of snow on the ground there, but surface conditions could be...softer.

This weather pattern of snow for Turnagain, Girdwood, and Portage vs. graybird for Hatcher is courtesy of storms hitting our zone with southeasterly winds. It would be nice to get a storm or two with southwesterly winds to refresh surface conditions around Hatcher and the FRange.

Archived Outlook - 1.4.2022
THURS - FRI: clearing skies, dropping temps, light winds (high confidence).
Skies clear Thurs with the departure of the storm. Clearing first for Hatcher and last for Whittier/Portage/Girdwood/Turnagain. Seward, Whittier, and Valdez with light wind (for those places) on Fri. Valley fog and widespread inversions Friday morning.

WEEKEND: moderate temps, light snow, ridgetop winds (moderate confidence).
Saturday starts clear w/ widespread inversions. Clouds arrive first for Thompson Pass/Valdez then during the day for Turny/Gird in advance of snow Sat eve into Sun. Light/moderate snow favoring TurnaGird and especially Portage/Whittier. Snow decreases moving inland to insignificant accumulation and just clouds for Hatcher. No rain concerns.

EARLY NEXT WEEK: partly cloudy, moderate temps, snow possible (low confidence).
Dry for the FRange, Hatcher, and Thompson Pass with snow possible for TurnaGird and Whittier/Portage. Low confidence in timing and strength of that snow, but probably light with no rain concerns. Moderate winds for Thompson Pass/Valdez and the Mat Valley.

Dirty Details
This week of storms has done great things to build up the snowpack around Turnagain - a great start to the new year!!! It was fun watching on satellite imagery as the low pressure of the last storm spun counterclockwise (lows spin clockwise in the Southern Hemisphere) across the Gulf of AK before crashing into the PWS:

As we all know its been warm down low...which has not helped with alders...unless you are an alder, in which case you're probably very happy.

But, the alpine is filling in with the Center Ridge SNOTEL getting close to average! Its actually a little better than shown below too because the SNOTEL plots are from end of day, so it doesn't account for the inch of SWE that fell on Wednesday.

Looking into early next week there is low confidence if it will snow at Turnagain/Girdwood. This is because the models are all over the place on if, when, and how much it will snow:

Most likely is that some light snow will trickle through during the early part of next work week. On the bright side it should be a little colder, so the precip will go further at low elevations.

Archived Outlook - 12.28.2022
THURS - FRI: warm, light winds, light snow (high confidence).
Light snow Thursday for Turnagain/Girdwood decreasing to showers on Fri with rain near sea level. Drier and clearer moving inland and towards Thompson Pass - Thurs looking mostly sunny for Hatcher. Ridgetop winds for TurnaWood, and the Anchorage/ER FRange decreasing Fri.

WEEKEND: stormy hot wet mess (low confidence).
Saturday starts dry before the next warm, wet, and windy storm arrives with heavy precip by Sunday again favoring the mountains closest to the western Prince William Sound & TurnaWood. Temps peak Sun night with rain to treeline. Moderate precip for Valdez/Thompson with Hatcher missing out completely. Confidence is low for precip totals.

EARLY NEXT WEEK: warm, snowy, cloudy (low confidence).
Moderate precip favoring the mountains closest to the western PWS with Hatcher again high and dry. Precip for favored zones decreasing to showers by Wed. Strong winds for Portage, TurnaWood, and the FRange on Monday then decreasing. Rain line dropping to the Turnagain Pass road level by Wed.

Dirty Details
Well...well...the major thing I missed in last week's forecast was just how high the rain line would go - I should have known better. You probably remember the unusual "drizzle crust" event a couple years ago at Hatcher where supercooled water in the atmosphere had no dust particle nuclei to form an ice lattice around. In contrast, this week's rain crust is a much more classic and simple case of rain falling on a below freezing surface (snow) and...freezing! Or just melting at lower elevations 🤮. Check out the NWS graphic below on the different types of winter precipitation:

Confidence is low for this weekend's storm because there is so much uncertainty in just how much precip it will bring. As the NWS put it in their forecast discussion this afternoon: "If there were ever a weatherman`s wish for a New Year`s resolution, it would be with models to just get along and agree with each other." Maybe next year!!! As can be seen in both the GFS and ECMWF ensembles below there is huge spread in the forecast precipitation range:

Regardless of just how much snow (and rain) this storm brings it will favor the mountains that rise out of the western Prince William Sound. This is pretty typical climatologically (and why there are huge glaciers at sea level in the PWS) as can be seen in this Alaska Annual Precipitation Map:

With these warm storms, Whittier, Portage, Seward, Turny, and Gird need the high winds to wring precipitation out of the air by slamming the moisture into and lifting it over the Chugach/Kenai mountains (orographic lift). Meanwhile Anchorage/Hatcher are in the rain shadow:

Archived Outlook - 12.21.2022
THURS - FRI: windy, clearing skies, dropping temps (high confidence).
Temps drop as the little storm that brought a bit of snow to Turnagain/Gird moves out. Clearing will happen last and be the least complete for Turny/Portage/Whittier. High winds Friday for Hatcher Pass, the Matanuska Valley, and Valdez/Thompson Pass. For Hatcher riders, remember that the Arkose/Government zones get hit harder by the Mat winds than Independence Mine.

WEEKEND: partly cloudy -> light snow, warming temps (high confidence).
Saturday starts cold & partly cloudy w/ strong inversions for East Anchorage/Gird/Turny/Summit. Clouds increase with light accumulating snow by Sun. Precip begins first for Thompson, then Turny/Gird, with little accumulation for the FRange and none for Hatcher. Snow favors Whittier/Portage.

EARLY NEXT WEEK: moderate snow, moderate temps, cloudy (moderate confidence).
Storm peaks Monday favoring Whittier/Portage with Turny/Gird also doing well; rain at sea level close to the western PWS. Snowfall decreases moving inland to no accumulation for Hatcher. Snow likely becoming light and showery Tue & Wed. Probably more Mat Valley winds on Monday.

Dirty Details
We're getting a break from those cold temps while the Lower 48 is tossed into the freezer. Check out this "apparent temperature" map from the National Weather Service - we'd call it wind chill -all the -30s and -40s on there make our 15 °F temps seem quite balmy!

But, the story here over the last week has been the cold temps after the series of storms that pounded our Upper Cook Inlet mountains. These storms have made December 2022 the fourth snowiest month on the record in Anchorage. December will probably finish as the 3rd snowiest month on record, but at this point I wouldn't put any money into bumping into the top two.

The clear skies and cold temps have led to impressive inversions and hoar frost formation:

Weather and terrain factors determine the spatial variability of surface hoar formation. This video does a good dweeby job of briefly describing this:

Time (and gravity) has also led to a lot of settlement in the storm snow. I've really enjoyed watching this settlement in our yard compared to the snow stuck to the fence:

We also classically see this slow deformation and densification of snow in settlement cones around trees, brush, and other veg like in this awesome pic from the Sierra Avalanche Center:

Looking at this coming week, some of our mountains are going to get whacked by the wind on Friday. We are used to the Valdez zone getting the wind, but its notable that the Talkeetnas, which often escape the high, will get hit hard.

And finally, we are past the solstice! My buddy Carp posted this last year, its a hilarious representation of our strange relationship with the sun here in AK.

Archived Outlook - 12.14.2022
THURS - FRI: clearing, temps dropping, moderate wind (high confidence).
One last quick round of snow tonight! Intense snowfall for the mountains of Valdez and Cordova; moderate accumulations for Hatcher, Anchorage/ER FRange, and Gird; light accumulations for Turny and Summit. Then moderate winds for Whittier, Seward, Valdez, Mat Valley, Anchorage FRange, and Kenai ridgetops. Inversions for Turnagain Pass, East Anchorage, Mint Valley, and Portage.

WEEKEND: clear, cold, light winds (high confidence).
A beautiful crisp winter weekend! Moderate winds for the Mat Valley and Valdez/Thompson Pass decreasing Sunday. For Hatcher skiers, remember that the Arcose/Government zones get hit harder by the Matanuska winds than Independence Mine. Widespread strong inversions.

EARLY NEXT WEEK: cold, dry, light winds (moderate confidence).
More beautiful (and cold) weather! Clouds possible Tuesday and Wed. Moderate winds for the Mat Valley, Valdez/Thompson Pass, and Whittier. Low confidence in when/where/how strong these gap winds will be. Widespread strong inversions.

Dirty Details
One last storm, and then we have a major pattern shift! This last blast of snow is the result a shortwave and high altitude low from the Bering joining forces with a firehose of moisture from the south. That atmospheric river of southerly moisture is clearly visible on satellite imagery smashing into Southcentral AK today:

Its going to snow hard overnight, but it will be over quickly and Anchorage, Girdwood, and the Valley won't see anything like the bonkers numbers that some of the weather apps and Wunderground have been predicting. Here's an example of this error:

As of last night Anchorage broke the 1989 record of 27.55 inches of liquid precipitation in a year!!! I'm sure we all remember (or would like to forget) July, August, and September. This last storm should be a cherry on top of our new record before the weather dramatically shifts to clear and cold. I have high confidence in this change happening (and hanging around for awhile) because there is such good agreement between models as can be seen on Meteoblue Multimodel:

Archived Outlook - 12.7.2022
THURS - FRI: cold, clearing, windy (high confidence).
Windy for Thompson Pass, Seward, Whittier/Portage, and to a lesser extent the Anchorage FRange, Crow Pass, Summit/Turnagain and Mat Valley. Temps dropping and skies slowly clearing with inversions Thurs/Fri night for Turnagain/Summit, East Anchorage, and the Mint Valley. Clearing first for the Kenai and last for Thompson Pass & Hatcher.

WEEKEND: dry -> stormy, moderating temps (moderate confidence).
Saturday starts dry, cold, and gap windy before the winds die briefly then temps begin to moderate with the arrival of Sunday's storm. Heavy snow for Whittier/Portage, with Turnagain/Thompson doing well, and all of our mountains receiving snow. Only rain concern is at sea level in Whittier.

EARLY NEXT WEEK: stormy/partly sunny, moderate temps (low confidence).
Moderate snowfall totals when the Sun/Mon storm wraps up (hopefully 2 feet for Turnagain, but more possible!). On Tuesday winds switch from the south to north bringing partial clearing and dropping temps before possibly (low confidence) another storm later in the week.

Dirty Details
Of course the big story is the band of snowfall that focused on Anchorage:

Figure: National Weather Service

I was wrong in my forecast last week when I predicted light snowfall favoring the mountains closest to the Prince William Sound. Not only was the snowfall not light, it didn't favor that zone! In my defense these heavy precipitation deformation zone events are really hard to predict a week out partly because they are such small-scale events. The storm is really visible in the sudden jump in the Anchorage Hillside SNOTEL:

I feel like a broken record here (yes that was a high school nickname), but leading up to the weekend we're gonna get hit by more gaps winds. These winds will pound the usual victims of Valdez/Seward/Whittier/Portage, but as shown below they will also hit the heart of our Turnagain ski terrain and the Mat Valley. When the Mat Valley winds blow like this they'll bleed over into the Arcose Ridge ski terrain as well.

Archived Outlook - 11.30.2022

THURS - FRI: sunny, windy, moderate temps (high confidence).
Strong winds (peaking Thurs) for Thompson Pass/Valdez, Seward, Portage/Whittier, the Anchorage Front Range, Crow Pass, and to a lesser extent Turnagain, Summit, and the Mat Valley. Temps rising towards the weekend with inversions for Turnagain/Summit, East Anchorage, and the Mint Valley.

WEEKEND: dry, warm, calm (moderate confidence).
Partly cloudy for all of our mountains. Moderate confidence because of uncertainty on how cloudy and when those clouds will be. Sunday might be clearer, as might be Thompson Pass.  Light ridgetop winds.

EARLY NEXT WEEK: warm, cloudy, light snow (low confidence).
Snow showers and cloudy for all our mountains. Confidence is low because timing of these showers is uncertain, but accumulation will be light. Most precip for mountains closest to the Prince William Sound (Valdez, Seward, Whittier). Ridgetop winds. No rain concerns.

Dirty Details

These midwinter clear and cold periods often bring wind. This is because the cold, dense and high pressure air of interior AK flows "downhill" towards the relatively warm and low pressure air in the Gulf of AK. These winds favor terrain channels and gaps (i.e. Thompson Pass & Whittier); hence Gap Winds. Here's a cool figure from UBC illustrating this:

The key to skiing during these wind events is to avoid the channeled terrain along the road corridors and long valleys where the wind can easily flow (i.e. the west face of Magnum vs. Goldpan).

This same cold weather also works to facet the snow as the moisture is sucked out. Just like most everything else in the world, faceting is driven by gradients (differences over distance or time). The difference between the relatively warm/wet air in the snow and the cold/dry atmospheric air produces a pressure gradient that drives water vapor through the snowpack and changes round snow crystals into square ones. has a fun animation that describes the process:

Ski season is definitely here and some people have definitely been getting after it (specifically Colin Gordon & William Kincaid). A little bit more snow would always be nice though, so I was interested in how this season-to-date compares to normal for this time of year. Plotting up SNOTEL data for Turnagain and Hatcher, looks like we are off to a pretty average start:

Turnagain (Center Ridge SNOTEL):

Hatcher (Independence Mine SNOTEL):

Archived Outlook - 11.23.2022

Thurs - Fri: moderate temps, light snow, light winds (high confidence).
Thursday starts out clear and calm before snow and clouds arrive lasting into Friday. Clouds/snow arrive first for Thompson Pass/Valdez then the rest of our mountains as the storm moves west. Moderate snow for Thompson Pass with generally light snow elsewhere. No rain concerns. Winds ramp up Friday afternoon as the storm departs.

Weekend: cold, clear, windy (high confidence).
Temps drop thru the weekend with inversions for Granite Creek, East Anchorage, and the Mint Valley. Clearing least complete for Thompson Pass. Strong winds (especially Saturday) for Portage/Whittier, Seward, Thompson Pass/Valdez, the Anchorage Front Range, and Turnagain ridgetops.

Early Next Week: cold, dry, windy (moderate confidence).
Temps keep dropping with a break in the wind Monday. Slight chance of light snow Monday for Turnagain, Portage, and Whittier. Strong winds Tuesday for Valdez/Thompson Pass and to a lesser extent Whitter/Portage and Seward. Ridgetop winds elsewhere. Strong inversions for Granite Creek, East Anchorage, the Mint Valley, and Portage.
This is my first outlook of the winter, so here's how I go about figuring out where to ski:

1 Minute
5 Minutes
Use Meteoblue Multimodel to see differences in magnitude and timing between models for precip/sun, wind, and temp. For wind, different models have different resolution - think number of pixels in a picture - resolution affects wind forecast, so just look how relatively windy your day of interest is versus the rest of the week. Confidence in your forecast will be higher if the different models agree in strength and timing of weather. Check back on Meteoblue every day to see if the models are consistently forecasting the same weather - if the forecast is different each time you check then the confidence in your forecast will decrease.
Use the Forecast Discussion within the NWS Avalanche Weather Information for the Rain/Snow line - its a new product, so we'll see how we like it.
15 Minutes
  • Avalanche Weather Information Forecast Discussion - mountain-specific short-term forecast discussion.
  • Short Term Forecast Southcentral AK - most useful, provides specific weather.
  • Model Discussion - usually useful, informs confidence in your forecast.
  • Long Term Forecast - sometimes useful, provides possible trends.
  • Analysis and Upper Levels, Marine Gulf of AK - details and learning opportunities.
  • New Snow -  Use to figure out what area is favored. Hatcher Pass, Anchorage Front Range, and Turnagain Arm storms are better captured by high resolution models (NAM & ECMWF). Note, Windy uses a 10X conversion from precip to snow, with cold storms (like the recent ones), the Snow/Water ratio will be 15X or higher.
  • Winds @ 3000 ft - Surface winds. These require high res, so NAM is best, then ICON and ECMWF, with GFS the worst.
  • Winds @ 250 hPa - Jet stream elevation - the weather conveyor belt. When it hits us from the SE it brings precip to western Prince William Sound mountains. As it rotates to the SW it favors precip for Hatcher, Anchorage Front Range, and Thompson Pass. Look to see if the jet stream is coming from as far south as Hawaii for warm Pineapple Express storms. From the N it brings cold and often outflow winds.
Long Term - Should I get ahead on work to ski next week???
  • Windy's 10 Day ECMWF and GFS Forecasts - Do the two models agree? Is the forecast changing each time you pull it up? For higher confidence in your forecast look for agreement between the two models and between runs of each model.
  • NWS Forecast Discussion (referenced above) - This product is produced twice daily. Read the long term forecast. Does each new forecast discussion say generally the same thing or it changing? Look for the terms "confidence", "agreement" and "differences" throughout the forecast discussion - this will let you how much the Weather Service is trusting the models.
  • Meteoblue Ensemble - Farther into the future the model spread will generally grow. The bigger spreads there are for temp, precip, and wind, the less confidence you have in your forecast.
Note: the National Weather Service has discontinued their "Southcentral Alaska Mountain Forecast" replacing it with "Avalanche Weather Information". The old site was an imperfect product, but did have some short term forecasting value especially for rain line forecasting. The value in the new site appears to be in the Forecast Discussion in the "Overview" tab - I'm looking forward to seeing how it goes!

1 comment:

  1. Thanks for introducing me to Meteoblu, this seems to improve on Windy's forecast comparison tool.