Monday, April 19, 2021

Archived 2021 Anchorage Ski Outlooks


Thurs – Fri: mostly sunny, moderate temps, lovely (high confidence).
Moderate temps. Sunniest at Thompson Pass. Warm in sun with sun effect. Moderate winds for Seward, the Thompson Pass road corridor, and the Anchorage Front Range; light ridgetop winds elsewhere. Good days to get powder fever.

Weekend: warm, snowy, windy (high confidence).
Moderate/heavy snowfall for Hatcher decreasing as you go towards Turnagain; moderate snow for Thompson Pass; rain at sea level. Clearing first at Turny and last at Hatcher.

Early Next Week: moderate temps, some sun/clouds/snow (low confidence).
Monday partly sunny. Tues/Wed snow possible for the Prince William Sound mountains and drier inland with winds for the Anchorage Front Rage, Seward, and the Thompson Pass road corridor. Warm in sun with sun effect.

Dirty Details
This is my last outlook of the winter,'re on your own own! Muahahahaha. Not really - here's how I'd go about about figuring out where to ski:

1 Minute
Turnagain/Girdwood - Girdwood on Wunderground

5 Minutes
Use Meteoblue Multimodel to see differences in magnitude and timing between models for sun and precip. For wind, different models have different resolution - think number of pixels in a picture - resolution affects wind forecast, so just look for relative windiness over a week.
Use the Southcentral Alaska Mountain Forecast for the Rain/Snow line.
15 Minutes
  • 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 Girdwood Valley storms are better captured by high resolution models (NAM & ECMWF).
  • Winds @ 3000 ft - Surface winds. These require high res, so NAM is best, GFS is worst.
  • Winds @ 250 hPa - Jet stream elevation. The weather conveyor belt. When it hits us from the SE it brings precip (and warm air) to western Prince William Sound mountains. From the SW it brings precip to Hatcher, Anchorage Front Range, and Thompson Pass. From the N it brings cold and often wind.
Should I fly into the High Peaks???
Use Meteostar Compare Model QPF. 
Lots of zeros - GO! 
Some zeros - feeling lucky? 
Lots of colorful numbers - prepare to shovel.

Archived Outlook - 3.24.2021
Thurs – Fri: heavy snow, warm temps, ridgetop winds (high confidence).
Thursday heavy snow for Hatcher Pass decreasing towards the Prince William Sound (PWS). Friday dropping temps and partly clearing skies as storm moves out. Solar effect on southerly slopes hit by sun.

Weekend: moderate temps, warm in sun, mostly dry (moderate confidence).
Partly sunny with clouds arriving Sunday evening with the next approaching storm. Confidence decreased b/c amount of sun vs. clouds is uncertain. Moderate winds for the Anchorage Front Range, Portage, Whittier, Seward, and Thompson Pass. Sun affect on southern slopes. Inversions for Portage, southern Turnagain Pass, and East Anchorage.

Early Next Week: snow, warm temps, ridgetop winds (low confidence).
Mon/Tues snow favoring Hatcher Pass decreasing towards the PWS. Then, Tues/Wed snow possible favoring the mountains around the PWS with rain at sea level.

Dirty Details
As we speak, the refresh we've needed is riding the jet stream into our zone out of the southwest. When the jet stream rams directly into our mountains like this it helps to squeeze extra snow out of the storm.

And, when the wind blows out of the SW it particularly favors Hatcher and the Anchorage Front Range. The Tordillos and Neacolas will also do great, but that is of less interest for most of us blue collar skiers.

For the weekend I've downgraded the forecast confidence to Moderate b/c there is poor model agreement on how sunny it will be; as is exemplified below by comparing modeled sunniness for Kickstep. However if the only uncertainty is sunny vs. partly sunny vs. cloudy its really small potatoes which is why confidence isn't Low.

Late Sunday into Monday, a large low pressure system in the Bering Sea will again crank more moisture into our zone on southwest flow. This will (you guessed it) favor Hatcher and our Front Range.

Archived Forecast - 3.17.2021
Thurs – Fri: cold mornings, warm in sun, gap winds (high confidence).
Cloudy Thursday (clearer inland) clearing into Friday. Ridgetop winds for the Kenai and 'Gach plus gap winds for Crow Pass, Portage, Seward, Thompson Pass and Turnagain to a lesser extent. Sun affect on southern slopes. Strong inversions in the usual cold holes like Portage and Granite.

Weekendcold mornings, warm in sun, lovely (high confidence).
Partly sunny (clearer inland) Saturday clearing into Sunday. Ridgetop winds. Sun affect on southern slopes. Strong inversions in the usual cold holes.

Early Next Week: moderating temps, mostly dry (low confidence).
Light snow possible for the mountains near the Prince William Sound. Dry and clearer inland. Stronger sun affect. Strong inversions.

Dirty Details
MARCH. What a month! And more good weather to come! I have high confidence in this because across different models, and between models runs there is strong agreement in dry weather. For example, the GFS has been forecasting little to no QPF (precip) for the Susitna Valley run after run:

Looking into the weekend, a low pressure system in the Gulf of AK will brush against the mountains of the PWS on Saturday. Depending on how close the low comes to us we could see clouds and snow showers for Turnagain or most likely partly cloudy skies; as you move towards Anchorage then Hatcher it will get progressively sunnier.

As we move into a typically dryer time of year our snowpacks are in great shape! Across Southcentral SNOTELs are near or above average!!!

Archived Outlook - 3.10.2021
Thurs – Fri: windy, clearing, cold (high confidence).
Snowfall tapering Thursday as the north wind brings in cold air and then clearing skies Friday. Winds worst for the Anchorage Front Range, the gaps of Crow Pass, Portage, Seward, and Thompson Pass, and the Kenai Mountains. 

Weekend: cold, clear -> cloudy (high confidence).
Saturday clear and cold with moderate winds for the Anchorage Front Range and Thompson Pass; sun affect on low elevation southern slopes. Sunday temps and wind increasing and clouds arriving with the next incoming storm; clearer and dryer inland.

Early Next Week: moderating temps, light snow (low confidence).
Monday into Tuesday light to moderate snow favoring the mountains near the Prince William Sound with possible clearing into Wednesday. Rising temps and increasing winds with each pulse of snow. Clearer and dryer inland. 

Dirty Details
We can already see the trend of temps dropping at our weather stations as the north wind picks up:

Like has been the case for the last month, the upcoming days will be a game of hiding from the wind. These winds will continue to be worst in and near long channels and passes where they can flow unobstructed towards the ocean. Getting away from the road corridor, and back into dead end valleys will be where the snow least impacted. We did this last weekend in the Girdwood Valley; you can even see where the wind has scoured the pass below Dmitry in the pic:

One last note. After an early season that brought feet upon feet of snow to Turny/Gird and left Hatcher high and dry, February saw a changed pattern where snowstorms favored Hatcher; and many of us took advantage of the improving conditions there! Check out the plot below to see SWE jumping at Hatcher and plateauing at Turnagain:

Archived Outlook 3.3.2021
Thurs – Fri: rising temps, warm in sun, light coastal snow (high confidence).
Cold, clear, and inverted temps then clouding up with arrival of Friday's small storm. The storm will favor mountains closest to the western Prince William Sound; no rain concerns. Sun affect on steep, low elevation southern slopes. Light ridgetop winds. Colder, clearer, dryer inland.

Weekend: clearing skies, dropping temps, mostly dry (high confidence).
Clouds depart replaced by cold, clear, and inverted temps. Sun affect on steep southern slopes. Ridgetop winds and gap winds for Seward, Portage, Crow Pass, and Thompson Pass. Colder, but clearing last inland.

Early Next Week: mild temps, moderate snow (low confidence).
Likely multiple pulses of snow first arriving late Monday, followed by more Wednesday. Snow favoring mountains close to PWS. Rising temps and increasing winds with each pulse of snow. Colder, clearer, and dryer inland. 

Dirty Details
The big story is the rain event at Hatcher that no one saw coming. Several models did show the rain happening, but I disregarded it as impossible for it to rain well below freezing. The key is ice melts at 0 °C, but water doesn't necessarily freeze at 0 °C. Water needs microscopic particles to freeze to and build an ice lattice. Close to freezing there is no ice in the air, and particles like clay, dust, or bacteria need to be present. Without such a nuclei, "supercooled water" can exist to -40 °C! What happened at Hatcher is a combination of C and D:

The rain crust was actually thickest at highest elevations (C), and thinner lower as the rain began to freeze as it fell thru the cold air (D).

Looking forward, Friday's small storm will favor mountains right next to the PWS and Seward as is clearly visualized on Windy.

Finally, another point on my sun infatuation - diurnal temperature swings are becoming clear on the weather stations (and our faces) as the sun warms the air, then the heat escapes into the clear atmosphere at night.

Archived Outlook - 2.24.2021
Thurs – Fri: showery inland, moderate temps, approaching storm (high confidence).
Thursday clearer towards Turnagain and showery moving inland to Hatcher. Sun affect on steep, low elevation southern slopes. Ridgetop and gap winds for Whitter, Seward, and Turny to a lesser extent. Friday, increasing clouds and snow with the approaching storm. Colder inland. 

Weekend: Snowfall favoring Hatcher, then dropping temps & clearing skies (high confidence).
Fri night storm favoring Hatcher and Thompson Pass with moderate to heavy snowfall then clearing into Sunday; no rain concerns. Clearing first and more completely towards Turnagain. Warm in the sun. Ridgetop and gap winds Sunday for Whitter, Seward, Thompson Pass, and Turny to a lesser extent. Colder inland. 

Early Next Week: some sun, some snow, cool temps (low confidence).
Multiple small storms bringing snow. First is Monday, followed by another around Wed. Both look to favor mountains close to the Prince William Sound. Ridgetop winds. Colder inland.

Dirty Details
Last week's weather was challenging for skiing in the sun, especially for weekend warriors. People skied lots of good snow at Hatcher which has continued to deliver lately. On Sunday we got lucky, cracked the code, and found the sun above Girdwood:

When the sun is out, its really feeling brighter, and my fascination with it continues. This week its cool 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 and tilted axis.

Looking towards the coming weekend, Hatcher and Thompson Pass will do well as SW winds wring snow out of the air as its lifted over the mountains. This SW flow is very visible on Windy:

The ECMWF is currently predicting 1.5 inches of SWE for Hatcher by the end of the weekend. Remember, to use "Rain accumulation" for forecasting Hatcher instead of "Snowfall" as Windy simply uses a 10X multiplier which lowballs cold, light Talkeetna snow.

Archived Outlook - 2.17.2021
Thurs – Fri: snowy, then clearing skies and dropping temps (high confidence).
Widespread light to moderate snow Thursday. Clearing first for Gird/Turny and last for Hatcher/Thompson Pass. Inversions, warm sun, and gap/ridgetop wind event for the Kenai and Gach mountains Friday. Colder inland. 

Weekend: mostly dry, cold mornings, inversions (high confidence).
Partly sunny with showers possible for mountains close to the PWS. Warm in the sun. Light gap and ridgetop winds. Colder, clearer, dryer inland. 

Early Next Week: cold, some sunny, snow possible (low confidence).
Mostly clear/cold/dry Monday with inversions, warm sun, light ridgetop/gap winds possibly extending into Tuesday. Then another smaller storm is possible which would bring rising temps, winds, and clouds. Colder inland.

Dirty Details
We have one more round of precip before the next cold/dry period arrives. Snowfall at Hatcher will be boosted by cold temps and lower density snowfall. In this situation on I look at "Rain accumulation" (SWE) instead of "New snow" because Windy just multiplies by 10X to convert from rain to snow which is not accurate when expecting low density snow as is often the case for Hatcher.

The wind has not been kind to the Kenai and Chugach mountains and this will continue with another wind event Friday. The below wind accumulation figure for the ECMWF highlights this, and the other models agree.

Like discussed last week, its hard not to notice the rapid return of the sun. Not only are the days getting longer, the sun is also rapidly getting higher in the sky. In fact, as shown below, the 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. 

Archived Outlook - 2.10.2021
Thurs – Fri: clearing skies, dropping temps, calming winds (high confidence).
Wind and snow showers for the Kenai and 'Gach on Thurs with more snow immediately near the western PWS. Sun affect on solar slopes with inverted temps/valley fog on Fri. Colder, clearer, dryer inland. 

Weekend: moderate temps, sun affect, inversions/valley fog (high confidence).
Sun affect on solar slopes, light winds. Snow showers Sunday for Gird/Turnagain/PWS mountains. Colder, clearer, dryer inland. 

Early Next Week: moderate temps, showery, overcast (low confidence).
Showery Mon/Tues. Snow possible Wednesday. Light winds. Colder inland. Good couloir skiing weather.

Dirty Details
We've all been noticing the glorious return of the sun, it feels noticeably longer every day. Here's a cool plot from showing the dramatic percentage change in daylight that's happening in northern latitudes right now:

We all know that the length of day varies much more up here in the north, but this animation from Visual Capitalist really hammers it home:

Outside of our region, its probably worth noting that Kodiak (and the Alaska Peninsula) are about to get clobbered with precip. Maybe a ski trip is in order???

But for us, looking into next week, we have a lot of quiet weather coming up. There's a couple reasons for this, but a main one is because the jet stream-storm conveyor belt will be to our south. Another impact of  this is that it will not bring the strong winds or cold arctic air that we often see during dry midwinter periods.

Archived Outlook - 2.3.2021
Thurs – Fri: cool, dry, light winds (high confidence).
Sunnier Thursday. Snow showers possible Fri night for Hatcher. Light ridgetop winds. Strong inversions especially for the cold holes (Portage, Granite Creek, East Anchorage), valley fog. Colder inland.

Weekend: dry, dropping temps, windy (high confidence).
Wind event Saturday for the Kenai and Chugach; particularly bad on ridgelines and channeled terrain. Temps drop over weekend as the skies clear, it will be cold by Sunday with strong inversions; colder inland. 

Early Next Week: mostly dry, cold temps, ridgetop/outflow winds (low confidence).
Some clouds and snow showers possible. Winds increasing Tues/Wed. Strong inversions. Colder, clearer, dryer inland. 

Dirty Details
We are staring down the barrel of a clear and cold period. These midwinter clear and cold periods often bring wind. There are two main reasons for this: First, is the cold, dense and high pressure air of the interior flowing "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); hence Gap Winds. Here's a cool figure from UBC illustrating this:

On Saturday these gap winds will be in full force (particularly visible in the graphic for Seward, Whittier, and the Copper River).

Second, on Saturday the winds will be reinforced by the jet stream blowing over us from the northwest. This arctic air is also what's bringing in the clear and cold.

Looking into the next work week we can expect to see these winds kick up again.

Archived Outlook - 1.27.2021
Thurs – Fri: snow, moderate temps, windy (high confidence).
Moderate snowfall favoring mountains closer to the western PWS; snow totals will be boosted by lower temps and low water content. Colder, clearer, and dryer inland. No rain concerns.

Weekend: dry, dropping temps, ridgetop/outflow winds (moderate confidence).
Temps drop over weekend as skies clear; it will be cold by the end of Sunday. Wind increasing Sunday for ridgetops and channeled terrain. Colder/clearer inland. 

Early Next Week: mostly dry, cool temps, ridgetop/outflow winds (low confidence).
Light snowfall/clouds are possible (low confidence) Tuesday as a storm brushes against us to the south; no rain concerns. Dry Mon and Wed. Colder, clearer, and dryer inland.

Dirty Details
Wow, Alaska is awesome - how quickly we forget weeks of gray when the sun comes out! On that note, the last week went largely as we expected. Last week I said it was possible that a small storm could brush against our coastal mountains bringing clouds on Tuesday, instead we just got sun, sun, sun. Everybody took advantage of it with some great days including this one in Virgin Creek:

Something I noticed after this last clear period was the patchy spatial formation (and reporting) of surface hoar. This video does a good dweeby job of briefly describing the reasons for its spatial variability:

For the rest of the work week we have a really nice storm headed our way. With colder temps expect stellar dendrites as opposed to the dendrites we often get during warmer storms. It should produce great snow quality. Check out this cool plot that showing how snowflake type is dependent on air temp and humidity:

After the storm clears out temps will drop over the weekend as clear skies combine with the jet stream bringing in cold arctic air from the northwest. 

Of note, cold temps and the jet stream overhead are great for producing outflow winds. If the jet stream does indeed move overhead on Sunday you know the drill for avoiding the wind: get away from the main terrain channels like the passes proper, Turnagain Arm, Portage, Seward, Whittier, etc.

Looking into next week, on Tuesday a storm will brush past us to the south. Depending on the exact path of this low, it will either bring light snow, clouds, or totally miss us.

Archived Outlook - 1.20.2020
Thurs – Fri: snow showers, ridgetop winds, warm (high confidence).
Snow showers favoring mountains closer to the western PWS (Whittier, Turnagain, Girdwood), with rain mixing in near sea level. Colder, clearer, and dryer inland. Winds ramp up Fri with approaching storm.

Weekend: snow Sat, clearing Sun, windy (high confidence).
Moderate snowfall Saturday favoring mountains closer to the western PWS, with rain mixing in near sea level. Sunday expect clearing skies, dropping temps, and ridgetop and gap winds. Colder and dryer inland. 

Early Next Week: some sun, some clouds, moderate temps (moderate confidence).
Temps bottom out Monday morning, then rise with approaching nearby storm. Into Tuesday, light snowfall favoring mountains closer to the western Prince William Sound possible; no rain concerns; likely dry with some sun Mon and Wed. Colder, clearer, and dryer inland. 

Dirty Details
The stormy period sure went out with a bang! The last week was largely as I expected with the one exception of heavy precip in Anchorage on Monday. This heavy rain was due to the jet stream blowing up Cook Inlet from the SW; when it blows from the S or SE it turns off precip for the inland side of the Chugach. Below is an example of this SW upper level wind:

Now we are into the quieter period that we expected. Its not the endless high pressure we all dream of, but there are nice days tucked in there! Jordan and I got out for lovely alpenglow pow yesterday:

As a skier, the thing that worries me for the upcoming Sunday is the wind. As is often the case when its dry and cold here, gap winds will be an issue. These winds can be visualized as water behind a reservoir (cold, dense, high pressure air from the interior) going thru a gap in the dam (wind thru Thompson Pass) and flowing downhill (towards relatively warm and low pressure air in the Gulf of AK). Here's a cool figure from UBC illustrating this:

The key to skiing during Sunday's winds will be to target mid-elevation terrain that is below the ridgetop winds and away from channeled terrain. The worst gap winds will be the usual offenders of Seward, Whittier, Thompson Pass, Tordillos, and Neacolos, and to a lesser extent the Turnagain Pass corridor:

Temps will bottom out Monday morning as cold air air rides into our zone on the north wind:

One other exciting thing is that Windy had added the ICON model!!! As many of you know, one of the keys to weather forecasting is comparing between models, so its really nice to have another point for visual comparison on Windy. Also, ICON updates six times a day which is more than the other models!

Its worth noting that not all models are created equal, and each have their own strengths. For example, the NAM has smaller grid cells so it does better forecasting snow for small mountains like Hatcher as opposed to the GFS with its big grid cells which has a hard time "seeing" Hatcher.

Archived Outlook - 1.13.2020
Thurs – Fri: Snow for Turny/Gird, dry inland, warm (high confidence).
Moderate snowfall favoring mountains closer to the western PWS (Turnagain, Girdwood, Whittier, Seward) with rain line near sea level on Thurs. Friday is the in-between day with temps rising before the next storm. Colder, clearer, and dry inland.

Weekend: stormy, warm, windy (high confidence).
Heavy snowfall favoring mountains closer to the western PWS. Rain line rising above Turnagain road level. Storm tapering down Sunday. Colder, clearer, and dry inland

Early Next Week: stormy/warm/windy then drying (moderate confidence).
Heavy snowfall favoring mountains closer to the western PWS with rain line rising to Turnagain road level for Monday, followed by drying and cooling Tue/Wed. Colder, clearer, and dry inland likely thou snowfall for Anchorage/Palmer/Hatcher is possible.

Dirty Details
Wowwwww!!!! That went about as we expected. But. Still. WOW! As can be seen in the below figure of SWE as percent of median, the Kenai is doing great this year. Turnagain Pass is at 159% of median, Seward approaching 200% of normal, and Cordova and Thompson Pass both above average! With 9 inches of SWE in the last week at Center Ridge imagine how much fell on the big mountains that its sheltered behind! 

There are consequences of the more northerly storm track - it has left most of the western US very dry:

Looking ahead, we have high confidence in another stormy period. This confidence is due to good agreement between model runs and between models. For example, the GFS model for the Kenai Mountains has been predicting this stormy period for days now:

We likely won't see as giant of snow totals as last week, but they will still be good. Again the mountains close to the western PWS will do best, less snow as you move towards Anchorage and Hatcher.

Long term, it looks like we have another weather window headed our way! Given how far away it is confidence just can't be that high, but good run-to-run model agreement makes it seem promising as can be seen in all the zeroes (or small numbers) in the GFS SWE model runs for the wet side of Kenai Mountains:

Archived Outlook - 1.6.2020
Thurs – Fri: stormy, warm, windy (high confidence).
Heavy snowfall favoring mountains closer to the Prince William Sound (PWS); snow tapering off Fri with dropping temps. Rain to Turnagain road level. Colder, clearer, and dry inland.

Weekend: stormy, warm, windy (high confidence).
Heavy snowfall favoring mountains closer to the PWS; increasing snowfall and temps by Sunday. Rain rising above Turnagain road level. Colder, clearer, and dry inland with Chinook event in Anchorage/Palmer Sunday.

Early Next Week: decreasing storminess, warm, dry inland (moderate confidence).
Moderate snowfall Monday decreasing to light snow/showers for mountains closer to PWS. Temps, rain line, and winds dropping. Colder, clearer, and dry inland.

Dirty Details
Well. Well. Well. We got the weather window we'd expected. I don't have to remind y'all how awesome it was. But I will anyways. Here's Neil Liotta celebrating New Years in Goldpan:

At one point we counted 22 people/dogs and 60 sets of tracks in Goldpan. Its awesome to see everyone out enjoying their public lands, but a good reminder to be careful, patient, and considerate of each other in avalanche terrain.

After our New Year's treat, the weather has slowly degraded as we forecast. And now we are into another big storm cycle (note the Five Day forecast for SEVEN feet of snow below). Like we've seen so far this season, these storms will feature southeast flow which favors the Prince William Sound (Turnagain, Girdwood, and Thompson Pass to a lesser extent), Tordillos, and the Neacolas while leaving Hatcher cloudy and dry and the Anchorage Front Range blustery and dryish:

Speaking of inland areas, I have high confidence that Hatcher will continue to stay dry. This is because run after run of the GFS model is forecasting zero or near-zero precipitation for the Susitna Valley:

By Monday forecast confidence degrades for Turnagain/Gird. This is because of increasing differences in output between the different weather models. Modeled accumulated precipitation for Turnagain is shown below; the models (purple lines) stay tight until next work week when they start to rapidly diverge.

Archived Outlook - 12.30.2020
Thurs – Fri: clearing, cooling, calm (high confidence).
Moderate temps with colder and clearer inland. Inversions in the usual cold pools (Granite Cr, Portage, East Anchorage) with valley fog. Light gap winds thru the worst repeat offenders (Thompson Pass, Copper River, Seward).

Weekend: Saturday lovely, moderate temps, calm (high confidence).
Snow showers near the PWS Sunday. Colder, clearer, and dry inland thru the weekend. Inversions in the usual cold pools with valley fog. Light gap winds thru the worst repeat offenders.

Early Next Week: dry inland/snow near coast, moderate temps (moderate confidence).
High confidence in colder and dryer inland. For PWS: light snow Monday, low confidence in snowfall intensity Tues/Wed - light or possibly moderate. Moderate ridgetop winds kicking up with snowfall. Warming temps.

Dirty Details
As we forecast last week, we are entering a quieter period with clearing skies. We have high confidence in this period because of good agreement between models:

This dreamy weather is courtesy of the storm track moving to the south:

Starting Sunday and heading into next week we are back to snow near the PWS and dry inland. I've been using "dry inland" a lot lately. Its a pretty safe bet to make as Hatcher and the Anchorage Front Range just average less precip then Turnagain, Girdwood, and the coastal mountains as can be seen in this Alaska Annual Precipitation Map:

Archived Outlook - 12.24.2020
Thurs – Fri: light snow Thurs, warm temps, light winds (high confidence).
Snowfall will be measured in the low inches with more precip and warmer temps closer to the Prince William Sound (PWS). Wind for ridges and channeled terrain. No rain concerns. Friday will be the better ski day.

Weekend: light snow, moderate temps, dry inland (high confidence).
Warmer and snowier closer to the PWS (ie. Turnagain/Girdwood), cooler with clouds for Hatcher and inland. Weekend snow total around 12". No rain concerns. Ridgetop winds increasing Sunday. 

Early Next Weekmoderate snow Monday, dry inland, cooling temps (low confidence).
Medium-sized storm Monday for the mountains close to the PWS, with rain at sea level. Dry inland Mon-Wed. Low confidence drying Tuesday into Wednesday for Turnagain/Gird - if this occurs expect inversions and valley fog.

Dirty Details
We are entering a quieter period after Tuesday's well advertised storm. Pretty cool to see the storms's firehose of moisture flowing north on sat imagery:

Another bonus of this big storm is that the rain stayed below the road at Turnagain. Last week I forecast the rain line rising as high as treeline, so a good place to be wrong!

Meanwhile temps in Anchorage made it into the 40s as Chinook winds ate our snow in town. These winds are caused by air that has dropped some of its moisture and rapidly warms as it descends over the mountains.  From Accuweather.

Looking past next Monday's storm, there is low confidence in a dry period for Turn/Gird. The low confidence is because of poor disagreement between different models, and between runs of the same model. This is exemplified by the GFS model's precipitation forecast for the Kenai Mountains shown below. Although there are a lot of zeroes, their timing and presence is inconsistent.

Archived Outlook - 12.17.2020
Thurs – Fri: light snow for Turnagain/Girdwood, moderate temps, light winds (high confidence).
Warmer and snowier closer to the Prince William Sound (PWS), cooler with clouds for Hatcher and inland. Snowfall in inches. No rain concerns.

Weekendlight snow for Turnagain/Girdwood, moderate temps, light winds (high confidence).
Warmer and snowier closer to the PWS, cooler with clouds for Hatcher and inland. Snowfall in inches. No rain concerns. Sunday will be nicer across our zone.

Early Next Week: stormy, heavy precip for Turnagain/Gird, warm temps (high confidence).
Temps rising with arrival of large subtropical storm bringing heavy snowfall to the mountains around the PWS, and heavy rain likely reaching treeline. Snowfall in alpine will be measured in feet. Hatcher Pass will be dry, cloudy, and windy.

Dirty Details
The week's weather will be controlled by a pattern of southeasterly winds blowing into our region. For example here is next Tuesday:

Southeast winds produce precip near the coast (ie Turnagain/Girdwood/Whittier/Valdez) and leave the inland side dry and cloudy, which is nicely explained in this figure I edited from the Teton Valley News:

The resultant wet near coast/dry inland is seen in the modeled snowfall from now into the weekend:

Archived Outlook - 12.10.2020
Thurs – Fri: clear, temps dropping, calm (high confidence).
Colder towards Hatcher than Turnagain. Inversions especially strong in the typical cold holes like Granite Creek, East Anchorage, and Portage.

Weekend: moderate temps, calm, quiet (high confidence).
Colder and clearer towards Hatcher. Strong inversions Fri night. Some snow showers and clouds for Turnagain/Girdwood, but insignificant snow accumulation.

Early Next Week: moderate temps, light snow (low confidence).
Generally more clouds and snowfall near Turnagain, less so towards Hatcher. Light accumulation.

Dirty Details
Clearing skies are forming strong 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 without winds there isn't much to mix out the inversions. Here's an old textbook graphic of the process:

Like discussed last week, another consequence of cold and clear temps is faceting, scroll down for an animation of that process!

For the weekend, temperatures will moderate with the arrival of warmer air from the Pacific:
Confidence in timing for snow next week is low. This is because the models aren't agreeing between runs as shown below (each run is a vertical column)

That said, the first half of next is likely to be mostly cloudy with waves of light snowfall and moderate temps.

Last Week
This last week went largely as we expected. Everyone got out and enjoyed the sun late last week into the weekend. Its incredible seeing the alpine filling in at Turnagain. We had a nice day at Sunburst on Friday:
Photo Neil Liotta

By the end of the weekend the next storm moved in. Temperatures immediately rose as the cold clear air was replaced by warm air blowing off the Gulf of Alaska:

The storm peaked Monday, before petering off on Tuesday and Wednesday. Like we forecast, snowfall heavily favored mountains closest to the Prince William Sound and the Gulf of Alaska with the Seward Mountains picking up about three feet of snow! 

Speaking of which, its great to see the snowpack for the western Chugach and Kenai Mountains looking so good on the SNOTELs!

Archived Outlook - 12.3.2020
Thurs – Fri: clearing, temps dropping, calm (high confidence).
Clearer/colder and happening sooner as you move from the Prince William Sound towards Hatcher Pass.

Weekend: clear & cold ­čá× stormy & warm (high confidence).
Temps bottom out Saturday then rise with the arriving storm. The most precipitation will be closest to the Prince William Sound and dry out as you move inland to Hatcher. Turnagain/Anchorage Front Range/Hatcher will all see some wind. Precip type should stay all snow thru Sunday.

Early Next Week: warm, stormy near coast (moderate confidence).
Stormiest with the most precipitation closest to the Prince William Sound and drying out as you move inland to Hatcher. Snow possible for Hatcher, but low confidence. Rain line rising Monday, possibly to Turnagain Pass Road level. Heaviest precip and warmest temps likely on Monday/Tuesday.

Dirty Details
The wild week of weather is wrapping up with a snowglobe here in Anchorage. These big fluffy dendrites are produced when the right temperature and humidity meet:

As the weather shifts from wet and warm to cold and clear our snowpacks will start faceting as the moisture is sucked out of the snow. Just like everything else in the world, faceting is driven by gradients. 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 causes snow metamorphism. has a good description and fun animation of the process:

By Sunday low pressure spinning in the Gulf of AK will pump moisture into the mountains surrounding the Prince William Sound. When the winds blow out of the southeast like this they turn off precipitation to Hatcher Pass as it is in the "shadow" of the Chugach.

Although temps rise for the Sunday - Tuesday precipitation, don't expect major rain concerns for our ski terrain. The reason for this is that the Jet Stream's "Pineapple Express" carrying tropical temps will again be focused on southeast AK:

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