textproduct: Fairbanks

SYNOPSIS

Wintry weather is ongoing across much of Northern Alaska today as an atmospheric river of snow persists into the Interior. Widespread accumulating snow from this initial system has ended across the Western Alaska as the main axis of moisture has shifted eastward into the Interior. The parent low pressure still remains in place in the Chuckchi sea for now, keeping blizzard conditions along the NW Arctic Coast and show showers along the North Slope through tonight. A cold front extends southward through the Interior, traversing eastward through the rest of the evening. Snow is expected to end from west to east behind the front through the rest of the evening before the next wave of snow showers moves in from the Bering. An additional few inches of snow is possible from these snow showers, beginning this evening in the YK Delta then shifting into the Interior tonight through Thursday. A brief period of arctic air with lows in the -20F to -40F range expected Friday through this weekend before temperatures moderate closer to normal ahead of the next winter storm.

Closely watching the next significant winter storm to impact Alaska Saturday through Tuesday with another round of strong winds and widespread accumulating snow. Wind and heavy precipitation impact the West Coast as early as Saturday, expanding to the North Slope on Sunday then into the Interior by the beginning of next week. As confidence increases in finer details, additional winter weather headlines may need to be issued for a good portion of Northern Alaska in the coming days for this next event.

KEY WEATHER MESSAGES

Central and Eastern Interior...

- Winter Storm Warnings remain in effect through Thursday where widespread total snowfall accumulations of 5 to 10 inches are expected. Highest amounts likely north and west of Fairbanks where isolated spots could see 10 to 15 inches by Thursday evening.

- A brief break in the snow this evening and tonight before another round of snow showers moves in early Thursday morning

- Much colder temperatures Friday through the weekend with lows potentially below -30F Saturday and Sunday mornings.

West Coast and Western Interior...

- Improving conditions for the majority of the West Coast, lingering snow showers continue into tonight

- Much colder air arrives Thursday and Friday with double digit sub zero lows.

- Watching for another significant multi-day winter storm to impact the West Coast from Saturday through at least Monday with strong winds, snow, and potentially mixed precipitation along the coast.

North Slope and Brooks Range...

- Blizzard conditions persist for the NW Arctic Coast through tonight with slowly improving conditions Thursday.

- Scattered snow showers will continue across the Arctic Plains Thursday night with additional snowfall between 1 and 2 inches.

- Watching for another significant multi-day winter storm to impact the NW Arctic Coast and North Slope from Saturday through at least Sunday with strong winds and widespread accumulating snow

FORECAST ANALYSIS AND DISCUSSION

Accumulating snow continues today for the interior of Alaska as the atmospheric river of snow has shifted eastward. Satellite imagery this afternoon shows the main fetch of moisture now stretching from Central Yukon southwestward along the Alaska Range and to the AK peninsula. The parent low responsible for this winter storm is still up in the Chukchi Sea with a cold front southward through the Interior. As of 330PM AKST, the frontal boundary is right near Fairbanks and marching eastward with deeper moisture and steady snow ahead of it, and much drier air aloft with a brief break in the precipitation behind the front. Latest 00z RAOB sounding from Fairbanks shows a strong inversion at 900mb with steep mid level lapse rates up to 7.0C/km within the DGZ. This sounding should support convective snow showers in the vicinity of the frontal boundary over the next few hours in the Central and Eastern Interior, with the heaviest snow showers producing 1"+/hour rates at times. Outside of any convective snow showers, expect light snow ahead of the front and areas of clearing behind the front. As mentioned yesterday, strong wind shear aloft resulted in fracturing of dendrites, leading to lower snow to liquid ratios than initially expected through the day. Convective snow showers may be able to produce higher SLRs locally leading to quick heavier accumulations. But overall, snowfall accumulations today were on the lower end of the forecasted ranges. Drier air and subsidence behind the front will result in a brief break in the snow and even clearing in some areas this evening and tonight.

The winter storm is not over yet as round two is already pushing in from the west as seen on satellite imagery. Aloft, the main 500mb upper low is stacked on top of the weakening surface low in the Chukchi sea with a wave rounding the base of it and into the YK Delta this evening. Since this wave is behind the cold front within a westerly cold air advection regime, precipitation from this next system will likely be more scattered and showery in nature. Forecast soundings support low topped and fairly shallow convective snow showers with the dendritic growth zone in the lowest 5,000ft agl co- located with strong lift and lapse rates of 6-7C/km. While there still is 20-30 kts of low level shear, this set up supports more efficient dendrite production and heavier snowfall rates. Any snow shower has the ability to produce brief periods of heavy snowfall rates with much higher snow to liquid ratios than what was observed today. As this wave traverses the YK Delta and into the Interior overnight tonight, expect much larger snowflakes with these showers with quick snowfall accumulations. A general 1-2" of additional snowfall is expected with higher amounts of 3-4+ additional inches in westerly upslope favored areas and potentially around Fairbanks. Timing for Fairbanks for heaviest snow showers is the 3AM to 9AM timeframe with lingering snow showers persisting into the Thursday afternoon.

Looking farther west, as the ridge continues to build, weather will slowly become more benign with snow pushing farther east and winds weakening. This will allow for low temperatures in the minus 20s across much of the West Coast Thursday night into Friday. The cold snap won't last long as the ridge will push farther east. Another system is looking to move into the Bering, from the SW, later in the day on Friday. This will set up another round of widespread snowfall. Looking over the NW Arctic Coast, winds will begin to tighten once again with an associated low progress up the east coast of Russia and a tightening area of high pressure over eastern Alaska. The strong winds and additional snowfall could provide the NW Arctic Coast with another round of potential blizzard conditions. In addition to the snowfall across the West Coast later in the week, the building ridge is also bringing up a warmer air mass which may result in a wintry mix for the YK-Delta, St. Lawrence Island, and parts of the Seward Peninsula. More of this will be discussed below in the extended forecast portion of the discussion.

EXTENDED FORECAST DAYS 4-7

A much colder and drier airmass settles in over Alaska as strong ridging builds over the Bering Straight and troughing deepens over the eastern Interior and NW Canada. Latest guidance has strong agreement on 850mb temperatures as low as -30C continuing into Saturday before the ridge shifts east pushing the core of the arctic airmass into Canada. Saturday morning is expected to be the coldest morning across Northern Alaska as the core of the cold airmass overlaps with clearing skies...with the best chance at lows at or below -30F, and potentially below -40F in typically cold valleys. The arctic airmass begins shifting eastward by Sunday, however Sunday morning may be another cold one for the Eastern Interior as lows make a run for -30F to -40F once again. A "warming" trend develops across the rest of the interior toward the latter half of the weekend and into the beginning of next week as yet another winter storm impacts the state from the southwest.

Focus now shifts to a significant multi-day winter storm expected to impact much of Alaska in the long term. Across the west, a significant warming trend is underway by Saturday as the ridge axis aloft shifts east, placing Western Alaska in a southwest flow pattern once again with strong warm air and moisture advection from the tropics. Long range guidance has been consistent in showing a long fetch of tropical moisture extending from Hawaii to the Bering Sea, bringing copious amount of moisture into the state. Temperatures rise near the freezing mark for coastal locations this weekend with another round of heavy precipitation for the majority of the West Coast. This set up supports the potential for a wintry mix over the YK-Delta, St. Lawrence Island, and parts of the Seward Peninsula by the mid weekend. The parent low associated with this system moves from western Siberia on Saturday to the NE Arctic Coast by Monday directing the atmospheric river north and east across the North Slope and Arctic Coast. The ECMWF Extreme Forecast Index has highlighted all of Western and far Northern Alaska for significant snowfall amounts well above climatological normals for this time of year, with high agreement among ensemble members. While this storm system is still a few days out and finer details may change, confidence is increasing in a widespread, impactful winter storm this weekend into early next week. Additional winter weather headlines may be needed as confidence increases in the finer details of the next winter storm. Friday may be the one relatively benign day for all of Western Alaska as the parade of storms continue to impact the state.

Coastal Hazard Potential Days 3 and 4...None

AFG WATCHES/WARNINGS/ADVISORIES

AK...Blizzard Warning for AKZ801-815-817. Winter Storm Warning for AKZ831. Winter Storm Warning for AKZ834-838>847. PK...Brisk Wind Advisory for PKZ802. Brisk Wind Advisory for PKZ803-850. Brisk Wind Advisory for PKZ804. Brisk Wind Advisory for PKZ806. Brisk Wind Advisory for PKZ807>812-855>858. Brisk Wind Advisory for PKZ816-851. Brisk Wind Advisory for PKZ817-854. Brisk Wind Advisory for PKZ852. Brisk Wind Advisory for PKZ853.