Wednesday, March 13, 2019

Weekly Anchorage Ski Outlook

Thurs – Fristormy, warm (high confidence).
The storm that is already impacting our region will continue into Friday. Another storm will arrive immediately on its heels. These storms are very similar. Areas closer to the western Prince William Sound (Whittier & Seward) will see the most precip with each storm bringing FEET of snow to the Turnagain/Girdwood alpine. The rain/snow line will rise over the storm to at/above the Turnagain Pass road level. The Chugach Front Range will see high winds from these storms; Hatcher will likely also see wind.

Weekend: stormy, warm (high confidence).
The Friday storm will continue into Saturday before being following by ANOTHER powerful storm. Again, areas closer to the western PWS will see the most. The rain/snow line will be high. The Chugach Front Range will see high winds, as will Hatcher to a lesser extent.

Early Next Week: stormy, warm, possible breaks in storminess (moderate confidence).
More western Prince William Sound storms look to be in the lineup. There is less certainty about the exact timing of the storms, and there may be a breaks, but expect more of the same: areas closer to the western PWS favored for precip, high rain/snow lines, and high winds in the Chugach Front Range. Continued storminess is likely for the long term.

Dirty Details
The first of a series of storms is slamming into the western Prince William Sound. This is very visible on the Middleton Island Radar:

Mountains closer to the western Prince William Sound see the most snowfall from this kind of storm (Whittier & Seward) as moisture slams into the mountains from the southeast. Behind this storm there are more storms in the pipeline; these are clearly visible in the model output:

The next storm (Low #2) will arrive Friday. It will be very similar to the last one. More western PWS storms arrive over the weekend. They will bring high rain/snow lines and abundant precip as they carry warm moisture from the Pacific Ocean. Areas in the lee of the Kenai and Chugach Mountains will be downsloped. Below is a nice graphic from the Teton Valley News explaining downsloping (and why Whittier averages more precip than Anchorage):

Long term there is no sign of the stormy pattern letting up. The 10 day forecast for the mountains above Seward is calling for a preposterous 200+ inches of snow. Long term forecasts are notoriously inaccurate, but you get the idea.

Last Week
Snowfall began in our mountains on Thursday afternoon. Areas closer to the western Prince William Sound saw the most with Turnagain/Girdwood picking up 1-2 feet of snow by Saturday morning and with high winds in the Chugach Front Range.

A stormy weekend favored the western Prince William Sound. This time the rain/snow line reached the road at Turnagain Pass. Weekend storm totals for the Turnagain/Girdwood alpine were generally 1-2 feet. The Chugach Front Range saw less snow, but high winds. The Friday and weekend storms were both clearly visible as peaks in the wind record at the Sunburst Weather Station:

Monday saw light snowfall in Turnagain/Girdwood due to continued moist onshore flow visible on the Middleton Island Radar:

Additionally, Hatcher picked up about 6 inches on Monday afternoon/night due to moist winds blowing up the Cook Inlet. This was about 6 hours earlier than I forecast. Up inlet flow shown on Monday's Kenai Radar Loop:

Archived Ski Outlook - 3.6.2019
Thurs – Fricloudy to stormy, warm (high confidence).
Snowfall will begin in our mountains on Thursday afternoon, increasing on Friday. Areas closer to the western Prince William Sound will see the most (Whittier & Seward). The Turnagain and Girdwood alpine will see 1-2 feet of snow by Saturday morning. Precipitation should remain all snow at the Turnagain Pass road level, though there could be a rain/snow mix at sea level. The Chugach Front Range sees less snow, but high winds for this kind of storm.

Weekend: stormy, warm (high confidence).
Precipitation will again favor areas closer to the western Prince William Sound; this time there will be rain concerns. The rain/snow line could easily reach the road at Turnagain Pass, though it shouldn't rise to the alpine. Saturday will be stormier; weekend storm totals for the Turnagain/Girdwood alpine will be 15 - 30 inches. Again, the Chugach Front Range sees less snow, but high winds for this kind of storm.

Early Next Week: cloudy to snowy (low confidence).
Monday will be an in between period with clouds and light snow before another storm arrives on Tuesday. This storm will favor the mountains around the Cook Inlet including Hatcher, the Chugach Front Range, the Peters Hills, and the Alaska Range. Another storm looks to arrive in our region on Wednesday.

Dirty Details
There is good consistency from model run-to-run and between models about the timing and strength of the Thursday/Friday storm. Additionally, recent model runs have trended the storm stronger. The figure below shows the good consistency between the models. The NAM forecasts higher winds because it is higher resolution. Forecast is for Kickstep.

Like the Thurs/Fri storm, this weekend's storm will favor the mountains around the western Prince William Sound. This is clearly seen in the 5 day snowfall forecast. The Tordrillos/Neacolas, Seward, and mountains above Port Wells do particularly well with this kind of storm.

Monday will be a transition day before the arrival of the next storm on Monday night. This storm currently looks to favor the mountains around the Cook Inlet with upper atmosphere winds blowing up the inlet from the southwest. Given that its 6 days away, there is good model run-to-run consistency for this storm. GFS SWE forecast for the Susitna Valley shows this consistency:

Last Week
Springlike high pressure remained over our region last Thursday and Friday bringing with it calm winds and HOT temps; the Sunburst weather station even reached 47 degrees!

Over the weekend an extremely weak storm passed over us bringing clouds and snow showers. Although accumulations were insignificant, visibility was greatly reduced. Here's what visibility was like on Sunday in the Chugach Front Range:


As forecast, sunny skies returned on Monday. Tuesday was overcast, but snowfall was limited to the Susitna Valley. Model runs leading up to Tuesday had trended this event weaker and weaker.

Archived Ski Outlook - 2.27.2019
Thurs – Frisunny, calm, warm (high confidence).
Springlike high pressure remains well established over our region bringing with it calm winds and warm temps. Without winds to scoop it out, high pressure will cause valley fog and temperature inversions. Expect sun impact on solar aspects.

Weekend: partly sunny to cloudy, calm, warm (high confidence).
Expect some clouds and possible snow showers without significant accumulations, Sunday will be cloudier. With nightly cloud cover don't expect fog to develop or strong nightly temperature inversions. The sun won't soften solar aspects.

Early Next Week: partly sunny to snowy, moderate temps (low confidence).
There is moderate confidence that Monday will be at least partly sunny. Confidence drops on Tuesday with a possible storm - exact timing and strength of this storm are uncertain. Do not expect huge snowfall numbers, or snow/rain line issues. It doesn't currently look like the storm will favor the Prince William Sound vs. the Cook Inlet Mountains.

Dirty Details
Wind forecasts show the high pressure still established and spinning in the Gulf of AK.


But, by Friday the high pressure begins to move southeast and out of our region. This weekend the high pressure breaks down allowing a very weak storm to pass over us with snow showers possible. This is exemplified in the figure below showing spotty precip for Kenai Mountains in model runs over time:

Models have trended the Tuesday storm later (see below). There is also good agreement between models that Monday will be at least partly sunny. There is poor run to run model consistency on the strength of the storm, except that it doesn't look huge. Currently, upper atmosphere winds look to be out of the south, which would allow snowfall for both the Prince William Sound and the Cook Inlet Mountains. On the other hand, SE or SW flow would favor the PWS or the Cook Inlet, respectively.

Last Week
Last Wednesday night's storm went south, brushed our region, and rapidly exited. Snow totals were low and favored areas closer to the PWS. Following the quick storm were the gap winds Thursday decreasing by Friday. Thompson Pass saw the worst winds while northern areas like Hatcher were spared.

By the weekend springlike high pressure was over our region with strong inversions, calm winds, and warm sun. Strong solar warming has been very evident in the diurnal temp swings observed at the Sunburst Wx Station:


Inversions at Turnagain Pass produced temperature swings of almost 35 degrees from the top of Sunburst to the Johnson Pass chest freezer:

Archived Ski Outlook - 2.20.2019
Thurs – Fri: stormy -> windy -> sunny (high confidence).
Tonight's storm will exit our region tomorrow followed by strong winds. Snow totals will generally be less than 12" and will favor areas closer to the Prince William Sound. Winds will decrease on Friday to be replaced by warm sunshine. Expect the worst winds along the highway corridors (Chugach Front Range, Turnagain Arm, Turnagain Pass, Seward, Whittier, Thompson Pass). These winds hit channeled terrain and the Front Range the worst.

Weekend: sunny, calm, warm (high confidence).
Springlike high pressure will be well established over our region bringing with it calm winds and warm temps. Without winds to scoop it out, high pressure will cause valley fog and temperature inversions. Expect strong sun impact on solar aspects.

Early Next Week: sunny, calm, warm (moderate confidence).
The warm high pressure is likely to persist into next week. Expect strong sun affect, valley fog, and temperature inversions.

Dirty Details
Tonight's storm will exit our region tomorrow. With its quick passage and minimal support from upper atmosphere winds, don't expect huge snow totals. Cold air should squeeze a bit more fluffy snow out of the atmosphere. As the storm moves east, strong winds will blow from high pressure towards the low pressure of the departing storm. These winds will decrease on Friday as the low moves on and upper level winds decrease. Tomorrow's winds draining through gaps to the coast are shown below:


Models are very consistent in the establishment and persistence of the high pressure ridge over our region. This is exemplified in the figure below showing zero forecast precipitation for the Kenai Mountains in model run after run. Model time is in Greenwich Mean Time (Zulu), subtract 9 hours to get local AK time.

Last Week
Temps dropped with the strong arctic winds last Wednesday - Thursday; they bottomed out Thursday night before warming Friday with solar heating and the arrival of warmer air from the southwest.


Weekend snowfall initially favored the Kenai before switching to the Cook Inlet. By Sunday night the the mountains had picked up a foot of snow. Southwesterly upper level winds persisted thru Monday which continued snowfall in the mountains around the upper inlet. Monday's Kenai radar shows moisture flowing up the inlet.


Snowfall distribution for Sat - Mon is typical of SW upper winds enhanced by cold air. SNOTELs recorded 0.7" of SWE for Turnagain, and 2" for Alyeska, the Chugach Front Range, Hatcher Pass, and the Peters Hills. Multiply SWE by 10 to approximate snowfall. The SNOTELS are at lower elevations, more snow will have fallen at higher elevations.

Archived Ski Outlook - 2.13.2019
Thurs – Fri: clear, cold, windy, no sun effect (high confidence). Winds will be the strongest tonight, temperatures will be coldest on Thursday night. Expect the worst winds along the highway corridor (Chugach Front Range, Turnagain Arm, Turnagain Pass corridor, Seward, Whittier, Portage). These winds hit channeled terrain and the Front Range the worst.

Weekend: warm, stormy (high confidence). Storm totals will likely be less than a foot, snow will begin during the day Saturday, Sunday looks to be snowier (particularly for Hatcher), all southcentral ski zones will see accumulation. Rain/snow line will be at/near sea level. Temperatures will warm thru weekend.

Early Next Week: moderate temps, light snowfall, some sun (low confidence). A small storm front will pass thru our region on Monday night, it will likely clip the Kenai Mountains, and will bring cloud to the rest of the zone.  With moderate temps there will be sun effect on steep south faces when the sun comes out.

Dirty Details
The ongoing strong winds are due to cold, dense air from the interior flowing “downhill” towards the low in the Gulf of AK. These winds are being strengthened by strong upper atmosphere winds blowing out of the arctic and dragging cold air with them. These winds are lazy and favor passes, gaps, and channeled terrain as they funnel to the coast. The figure below shows these upper winds carrying these strong Arctic air south:


On Saturday, a storm front will ride southwesterly upper atmosphere winds into Southcentral. A second low will follow on its heels Sunday. For both of these systems, upper level flow will be from the southwest. Upper level southwest winds allow snowfall for Hatcher Pass and the Chugach Front Range, as opposed to upper level southeast winds which favor snowfall for the Kenai/Girdwood and generally turn off snowfall for Hatcher/Front Range. This upper level wind setup is shown below:


Early week next the storm track will move to our south, turning off significant precipitation to our zone. A storm riding the storm track will likely clip our region on Monday night. Confidence is low because each model run has not consistently predicted the timing or impact of this system on our region, but have generally trended our precipitation forecast down - it is unlikely to be significant. The figure below shows how consecutive model runs are forecasting SWE (snow water equivalent) for the Kenai Mountains early next week.  Model time is in Greenwich Mean Time (Zulu), subtract 9 hours to get local AK time.

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