textproduct: Juneau

SYNOPSIS

Key Messages:

- Widespread cold temperatures and cold wind chills last through the middle of the week.

- Increasing potential for a pattern change for the end of the week into the weekend.

- Potential for snow event for the central and northern panhandle; southern panhandle could see snow turning to rain.

LONG TERM

We continue to watch the potential for a slight shift in the weather pattern that would give the next round of significant snow to Southeast Alaska along.

The long range computer models, both deterministic and ensembles, are trying to put a a couple low pressure centers in the northern and eastern Gulf of Alaska later this week. The first low would allow for the flow to switch to a more onshore pattern, or at the very least a weaker outflow. This would weaken the pressure gradient over area, allowing for wind speeds to decrease a bit beginning around the Wednesday/Thursday time frame. When the low continues its journey southeastward Thursday into Friday morning, the pressure gradient would tighten up again, allowing for wind speeds to pick back up ahead of the next low that is forecasted to move northeast into the Gulf. In particular, the N-S gradient will increase across the northern half of the panhandle as the low slides to the south of the panhandle, bringing near gales down Lynn Canal Thursday. As the low moves southeast, before the larger low approaches from the west Friday night, there will be another brief lull in the winds into Friday particularly along the southern panhandle. Winds begin to pick up across the entire panhandle Friday night into the weekend as the stronger low approaches, and a gale force front begins to move in from the southwest. These southerly winds moving into the panhandle will allow for some warming across the panhandle alongside bringing precipitation through from W to E into the start of the weekend.

As far as snow potential, the EURO and GFS have come into greater agreement over low tracks and 500mb flow. The Canadian has become the outlier. The current forecast leans towards the story that the EURO and GFS tell. The biggest difference in the Canadian is the overall positions of the upper level flow and surface level pressures would keep the cold air in place longer, giving southeast Alaska much greater amounts of snow. But there is more confidence on the story in the EURO and GFS, so for now, the forecast thinking leans heavily on the EURO and GFS.

Moisture amounts are hinting at light snow on Thursday, with a break on Friday. Friday night into the weekend is looking like another significant weather event that could produce significant amounts of snow for parts of Southeast Alaska.

For Thursday into Thursday night, the 75th percentiles are giving the area around a tenth to about a third of an inch of QPF, with the greater amounts in the EURO, which would give around 1 to 4 inches of snow over 24 hours. Greatest amounts along the coast.

For Friday into Friday night, the 75th percentiles are less than previous runs, giving the area around half inch to 1 inch of QPF, with the greatest amount along the coast, which would give upwards of 10 inches of snow over 24 hours if it all falls as snow. The 50th percentiles are giving the area around a quarter inch to half inch, which would give around 4 to 7 inches of snow.

Saturday's QPF is even greater with the 50th percentile around one to two inches, which would give over 12 inches of snow and the 75th percentile is well over 2 inches, which would be well over 15 inches of snow if it all falls as snow. The issue with Saturday's snowfall forecast is warmer air aloft may slide in, which would lower total snowfall amounts and some areas in the far south may even see a total switch to rain.

So what are the main takeaways off all this data? For starters, the 75th percentile is an upper bound. So the amounts mentioned above are on the high-end for current estimates. The 50th percentile is a middle-ground estimate. Thursday's snow is looking like a quick-hit of light snow with a break in the snow for Friday. Friday night into the weekend will be a challenging forecast with the surge of moisture and warmer air coming up from the south. The farther south you are, the greater chance of seeing a full transition to rain. The Farther north you are, the greater chance of seeing another long duration snow event.

Either way, stay tuned into the forecast but be prepared for a snowy weekend.

AVIATION.../through Tuesday afternoon/

Generally VFR flight conditions expected with mostly clear skies and outflow winds continuing. Some mid to high level clouds AOA 6kft, mainly across the southern panhandle. A few light snow showers are possible across the far southern panhandle, including PAKT and PAPG, which could briefly bring MVFR CIGs. While outflow will remain, low level turbulence and LLWS will also persist with winds 1-2kft aloft 20-30kts.

MARINE

Outside (Gulf and Coastal Waters): Outflow winds continue across the Gulf. The strongest winds will continue to be out of gaps in terrain such as Cape Spencer and near Dangerous River. These winds continue to weaken somewhat but some locally stronger winds remain possible as we head into the middle of the week before starting to weaken. Wave heights are expected to diminish for most of the Gulf but the largest waves will persist in the areas where the outflow winds continue to remain high. The N-NE swell is expected to weaken going into Tuesday before shifting to a S-W swell component by the time we get to Wednesday.

Inside (Inner Channels): Outflow winds continue this afternoon as the wind speeds continue to remain elevated with gales to strong gales continuing for Lynn Canal and Stephens Passage. Outflow winds are expected to persist through the start of the week before starting to diminish as we get into the middle part of the week. With the diminishing wind speeds, wave heights and freezing spray concern will start to trend down as well. Until then, the strongest winds are expected to continue down Lynn Canal as well as Stephens Passage and down towards Five Finger lighthouse. With a system moving in for the end of the week, the winds will come down before increasing again.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...Extreme Cold Warning until 6 AM AKST Wednesday for AKZ318. Extreme Cold Warning until 6 PM AKST Tuesday for AKZ319. Cold Weather Advisory until 6 PM AKST Tuesday for AKZ320-326>331. Cold Weather Advisory until noon AKST Tuesday for AKZ321-332. Extreme Cold Warning until 6 PM AKST Tuesday for AKZ323. Cold Weather Advisory until 9 AM AKST Tuesday for AKZ324. Extreme Cold Warning until 6 AM AKST Tuesday for AKZ325. Strong Wind from 9 PM AKST this evening through Tuesday afternoon for AKZ325. Cold Weather Advisory from 6 AM to 6 PM AKST Tuesday for AKZ325. MARINE...Heavy Freezing Spray Warning for PKZ011-012-031. Heavy Freezing Spray Warning for PKZ013. Heavy Freezing Spray Warning for PKZ013. Heavy Freezing Spray Warning for PKZ021. Heavy Freezing Spray Warning for PKZ021. Heavy Freezing Spray Warning for PKZ032. Heavy Freezing Spray Warning for PKZ032. Heavy Freezing Spray Warning for PKZ034. Heavy Freezing Spray Warning for PKZ053. Heavy Freezing Spray Warning for PKZ053. Gale Warning for PKZ011>013-022-031-643-644-651. Small Craft Advisory for PKZ021-032>036-053-641-642-661>664-671.