Anchorage Ski Outlook

1.19.2022
Thurs – Fri: warm, wet, and windy storm arriving (high confidence).
Clouds arrive Thursday ahead of the approaching storm and its rapidly warming temps. Thurs night into Friday precip heaviest for Portage/Whittier/Seward, moderate for Turny/Gird/Thompson Pass then decreasing as you move towards Hatcher. Rain to the Turnagain Pass road level.

Weekend: warm, light snow, cloudy (high confidence).
Light precip all weekend for Turnagain/Girdwood/Thompson - heavier precip the closer you are to the Prince William Sound and dryer towards Hatcher. Rain to the Turnagain Pass road level; hot in Anchorage. Moderate ridgetop winds. 

Early Next Weekwarm and stormy (moderate confidence).
Heavy, windy precip Monday into Tuesday for the mountains above the PWS (especially Whittier, Seward, Portage with Turny/Gird/Thompson doing well too), and dryer towards Hatcher. Rain to the Turnagain Pass road level; hot in Anchorage. Drying out with moderating temps on Wed.

Dirty Details
This evening (Wednesday night) we can see today's storm dissipating and moving off to the east on the Middleton Island radar as snowfall comes to an end for our zone:


After a brief break tomorrow, we are back into the pattern of wet and warm with heavy precip for the mountains close to the Prince William Sound, while the Anchorage Front Range and Hatcher are left out of the fun. Its a 10 day forecast, so the exact numbers are not important, but you can see that the heavy precip is coming and where its focused: 


This ongoing pattern of precip heavily favoring Turnagain, Girdwood, and Thompson Pass over Hatcher and the Anchorage FRange is climatologically typical (and why there are huge glaciers at sea level in the PWS) as can be seen in this Alaska Annual Precipitation Map:


The other big story is how warm its going to get in Anchorage and the Matsu Valley. This will be caused by the relatively dry chinook winds that heat up as they flow downhill over the Chugach after dumping their moisture on the upslope side. From Accuweather:


Finally, as the days keep getting longer its pretty cool to check out the Shade Map that somebody recently posted (in case you missed it) in the Backcountry Ski Addiction Group. It really highlights those special places that get the sun midwinter, and hide from it in the spring!

 
Archived Outlook - 1.12.2022
Thurs – Fri: stormy, warm, windy (high confidence).
Tomorrow's warm storm brings heavy precip and high winds both petering off Fri. Snow heaviest in the mountains above Whittier and Seward decreasing moving away from the PWS. Thompson will do OK, Turny/Gird well, then decreasing moving west 'til leaving Hatcher dry. Rain to near the Turnagain road level.

Weekend: moderating temps, light snow, mostly cloudy (high confidence).
Light snow Sat and Sat night with some clearing Sunday. Rain line near sea level. Ridgetop winds.

Early Next Weekmoderate temps, some sun, some clouds (moderate confidence).
Mon will be the best ski weather of this forecast with high confidence of dry with some sun. Tues likely dry then light snow (low confidence) possible Wed. Driest/clearest for Hatcher. Light winds.

Dirty Details
The Sunday/Monday storm came in a little smaller than I had hoped, but on the bright side the next one is almost here as can be seen on the satellite imagery with the Pineapple Express plume of moisture already approaching from near Hawaii:


Just like last time, this storm will bring the most precip to the mountains closest to the western Prince William Sound. The reason for this is that the storm will have winds flowing from the southeast which smash moisture into the mountains above Whittier, Seward, and Portage and on towards Turnagain:


Meanwhile this SE flow leaves the inland side (Anchorage Front Range/Hatcher) dry, which is nicely explained in this figure I edited from the Teton Valley News:

As the moisture of this SE-flow-storm is wrung out of the air by the mountains it will then warm as it descends over the mountains and into town. From Accuweather.

Looking into the crystal ball, the next chance of significant precipitation probably won't be until late next week.
 
Archived Outlook - 1.5.2022
Thurs – Fri: cold, clear, windy in specific areas (high confidence).
A couple more days of the same before the pattern change. Windy Fri (although not as windy as its been) for the Mat Valley, Thompson, and Hatcher. Ridgetop winds elsewhere. Inversions for the usual cold holes (Portage, Granite Cr, Gold Mint). 

Weekend: moderating temps, increasing winds, snowy (high confidence).
Saturday will be the transition day as clouds and light snowfall arrive and temps begin to rise with Sunday's incoming storm. The storm will favor the mountains closest to the western Prince William Sound - heavy snowfall for Whittier/Portage, moderate snow for Turny/Gird, less for Thompson, and Hatcher left high & dry. No rain concerns.

Early Next Weekwarm, stormy (moderate confidence).
Precip continues and continues to favor the mountains closest to the western PWS. Precip (and wind) likely heaviest Monday then continuing into Wednesday. By Wed the storm totals for Turny/Gird could be several feet of snow. Rain likely at sea level.

Dirty Details
We've talked about it before, but given how extreme the winds hammering the Mat Valley have been its worth mentioning again. These midwinter clear and cold periods often bring wind. This is because the cold, dense and high pressure air of the interior flows "downhill" towards the relatively warm and low pressure air in the Gulf of AK. These winds favor terrain channels and gaps (especially the Mat Valley, Thompson, Seward, and Whittier). Here's a cool figure from UBC illustrating this:


Which area gets hit the hardest is dependent on the specific location of the low pressure that the winds are flowing towards.

Speaking of wind, this is a good time to throw in a wind chill chart. The warm surface of our skin heats the air around it, creating an insulating boundary layer of warm air next to our skin. Wind disrupts this layer, allowing cooler air to replace the warm air against the surface. The faster the wind speed, the more readily the surface cools. 


Of course, wind chill temperature only applies to us living critters. It doesn't apply to inanimate objects like rocks. The wind may increase the rate at which a rock cools off, but if its 20 degrees with a wind chill of -5 then the rock will still behave as if it’s 20 degrees. Your exposed skin, on the other hand, will frostbite as quickly as if the temperature was actually -5 degrees.

This cold and clear weather also works to facet the little bit of soft snow we have left as the moisture is sucked out of the snow. Just like everything else in the world, faceting is driven by gradients (differences). 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. Avalanche.org has a fun animation that describes the process:


Long term its likely that we stay in this warm and stormy pattern favoring precip for Portage, Turnagain, and Girdwood. Precision in a 10 day forecast isn't realistic, but nice to see these big numbers!

 
Archived Outlook - 12.29.2021
Thurs – Fri: moderate temps, light snow, light winds (high confidence).
The rest of the work week will start clear then cloud up with the arrival of light snow Thurs night. Light snow continuing thru Fri. Snowfall won't be enough to improve surface conditions. But at least no rain! Inversions Thursday morning for the usual cold holes (Portage, Granite Cr, Gold Mint). Ridgetop winds. 

Weekend: dropping temps, clearing skies, increasing winds (high confidence).
Cloudy Saturday with partial clearing and cold temps on Sunday. Strong winds (especially Sunday) for the Anchorage Front Range, the Mat Valley (think Castle Mtn coolie), Hatcher Pass, the Thompson Pass road corridor, and Seward. Elsewhere, moderate winds for long valleys, passes, and ridgetops.

Early Next Week: cold, sunny, windy in specific areas (high confidence).
Strong winds Monday decreasing towards Wednesday for the Anchorage FRange, the Mat Valley, Hatcher Pass, and the Thompson Pass road corridor. Decreasing ridgetop winds elsewhere. Cold temps. Inversions for the usual cold holes.

Dirty Details
Well. Well. Well. As our dear friend Neil likes to say: "The Chugach giveth and the 'Gach taketh away"...but, in this case its all of Southcentral AK taking away!!! My forecast last week called for warm temps, but I erroneously used the word "snow". We all know how that went. I missed forecasting last year's freezing rain event too, so clearly need to up my game in this front.

This picture from @sarahmasco sums up what's happened to all of our surfaces:


Its going to snow across our zone tomorrow night, but not enough to significantly soften conditions in our mountains. On the bright side, even a couple inches should go a long way to improve the XC skiing in town! Ice skaters may be less stoked about this.


From Sunday into the next work week, there is rare high confidence in the long term forecast. This high confidence is because of amazingly good agreement across the ensemble forecast.


Another way of visualizing this is EMCWF's Probability of No Precipitation map. For our zone, there is a greater than 95% probability that there will be no precipitation between Monday and Wednesday!


Long term forecasts have such low value, and I am probably going to stick my foot in my mouth for doing this, but it looks like the dry weather will likely stick around at least thru the end of the next week (especially for Hatcher Pass) as is shown by the ENS Meteogram:


Archived Outlook - 12.22.2021
Thurs – Fri: windy, clearing, temps dropping (high confidence).
Light snow for Hatcher tonight will be followed by high winds for all our mountains tomorrow - unusually Thompson Pass will be less windy. Friday skies will clear, temps will drop, and winds will calm. Inversions for the usual cold spots (Portage, Granite Creek, Gold Mint).

Weekend: cloudy, warming, snow (high confidence).
Expect a cloudy weekend with moderate snowfall favoring Hatcher on Sunday. Hatcher will be the snowiest and cloudiest, followed by the Anchorage Frange, then by Turnagain/Girdwood, with Thompson Pass being the driest. Light winds.

Early Next Week: warm temps, mostly cloudy, stormy (low confidence).
Monday will be quiet, calm, and partly cloudy before a potentially strong storm moves in Tues/Wed. Again this storm looks to favor Hatcher, followed by the Anchorage Frange, then by Turny/Gird, with Thompson Pass being the driest. Confidence in timing/strength of this storm is low.

Dirty Details
We are past the solstice! My buddy Carp posted this, its a hilarious representation of our strange relationship with the sun here in AK.


In all seriousness, a bit more daylight sure will be nice! Not only are the days getting longer, the sun is is 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. Also, note that the sun currently only makes it 5.5 degrees above the horizon 😱.


The weather pattern we are experiencing is governed by an Omega block. Its called an Omega block because the jet stream winds around a high pressure paired with two low pressures in the shape of an omega:


As the blocking high pressure wiggles around it lets small storms blowing from the west sneak into our zone. This storm track favors the Tordrillos and Alaska Range, and Hatcher does the best for us...but as you can see the Omega Block doesn't let much snow through.


Next week's storm is promising because it could feature upper level winds at the jet stream elevation blowing out of the southwest and stuffing moisture into Hatcher Pass. These SW winds force the moist air to rise over the Talkeetna Mountains and wring extra moisture out of the sky.

Archived Outlook - 12.15.2021
Thurs – Fri: moderate temps, light snow, light wind (high confidence).
Very light snow Thursday followed by some sun on Friday. Snowfall will be the highest near Whittier.

Weekend: moderate temps, light snow, winds in specific areas (high confidence).
Very light snow Saturday followed by some sun on Sunday. Snowfall will be the highest for Hatcher. Ridgetop winds. Winds peak Sat night: worst for Seward and Thompson Pass road corridor followed by Whittier/Portage then the Anchorage Front Range.

Early Next Week: moderate temps, light snow, increasing wind (moderate confidence).
Some sun Monday followed by light-moderate snow Monday night-Tuesdayish favoring Hatcher. Then increasing winds and dropping temps likely towards Wednesday. Winds will be the worst for the usual spots (Whittier/Portage, Seward, Thompson Pass, Anchorage Front Range), but everywhere looks to be affected.

Dirty Details
Some cloud cover over the upcoming period will be part of the moderate temperature equation, this is because clouds provide insulation for the atmosphere by trapping energy by reflecting longwave radiation:


The next week's weather is pretty boring, so its a good time to look at the status of our snowpack, its about what you'd expect with areas favored by southeast-flow storms (mountains close to the western Prince William Sound) doing well - Alyeska and Turnagain are both around 150% of average! While zones that are favored by southwest flow not doing so well (Hatcher and Thompson).


Interestingly, Hatcher's Independence Mine SNOTEL isn't that far below average at 94% of water year-to-date median precipitation despite the term "low tide" being thrown around a lot lately (and it definitely does look bumpy up there!). But, with as close as we are to "average" the snow depth at Hatcher right now is really just a reflection of how its a pretty continental snowpack that gets less snow as can be seen in this Alaska Annual Precipitation Map:


Despite its relatively thin snowpack, there sure has been some good early season skiing up at Hatcher:


Archived Outlook - 12.8.2021
Thurs – Fri: stormy, moderate temps (high confidence).
Heavy snowfall (with wind) Thursday favoring the mountains closest to the western Prince William Sound and the eastern Kenai Peninsula (Turnagain, Girdwood, Seward, and especially Whittier and Portage). Storm tapering off Friday. No rain concerns. 

Weekend: cold, dry, windy (high confidence).
Skies clearing and temps PLUMMETING thru the weekend. Sunday will be colder and clearer. The worst winds will be through Thompson Pass, Seward, and the Anchorage Front Range. Hatcher will be the least impacted by the wind. Inversions for East Anchorage and Granite Creek.

Early Next Week: moderating temps and winds, possible (moderate confidence).
Monday starts out clear and bitterly cold with strong inversions in the usual spots and with moderating winds for Thompson Pass, Seward, and the Anchorage Front Range. Tuesday and Wednesday temps moderate with the arrival of clouds and likely light snowfall for our mountains. Snowfall likely to again favor the mountains closest to the western Prince William Sound and the eastern Kenai Peninsula. 

Dirty Details
The upcoming storm will favor the mountains of the eastern Kenai Peninsula and those closest to the western Prince William Sound while leaving Anchorage and the Talkeetnas dry. The reason for this is that the storm winds will be southeasterly, as shown in the example below:

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:


Moving into the weekend, it will be freeeeeezing and bringing wind with it. These midwinter clear and cold periods often bring wind. This is because the cold, dense and high pressure air of the interior 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); 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. 

Tuesday into Wednesday my forecast confidence degrades because I am not sure how much snowfall is coming. This is because of increasing differences in model runs. Modeled accumulated precipitation for Turnagain is shown below; the purple lines stay tight until Tuesday when some solutions start to rapidly diverge towards possibly heavier snowfall.

Archived Outlook - 12.1.2021
Thurs - Fri: clearing, cold temps, light winds (high confidence).
Plummeting temperatures as skies clear across our zone. Windy for Seward, the Thompson Pass road corridor, Whittier, and to a lesser extent the Anchorage Front Range; ridgetop winds elsewhere. Inversions and valley fog, especially Portage, Granite Creek, and East Anchorage.

Weekend: increasing clouds, temps, and winds (high confidence).
Saturday starts out COLD and clear with light winds and inversions/valley fog especially in the usual cold pools. Then temps rise and clouds and wind arrive Sunday with the incoming storm.

Early Next Week: moderate temps, stormy (low confidence).
Stormy Monday/Tues drying into Wednesday with everywhere in our zone picking up snow. Precip totals will be moderate, but snowfall will be boosted by cold air in place. Confidence is low, not on whether it will snow, but where will be favored.
 
This is my first outlook of the winter, so here's how I 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, precip, and temp. 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. Confidence in your forecast will be higher if the different models agree. 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 Southcentral Alaska Mountain Forecast for the Rain/Snow line - its an imperfect product, but so is rain line forecasting.
 
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 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.

1 comment:

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

    ReplyDelete