Gale Warning 69, NWS Fairbanks, AK

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
111 PM AKDT Sat May 13 2023

.SYNOPSIS...
An impressive atmospheric river is taking direct aim at the West
Coast today. Satellite imagery is showing a moisture tap which is
originating from around the Hawaiian Islands, which is south of
30N latitude. Strong winds and heavy rainfall will accompany this
front as it moves inland. Strong chinook winds will also blow out
of the AK Range and through the Brooks Range. Expect warming
everywhere except near the West Coast, where some snow will also
accompany this front over the Bering Strait Coast and W Brooks
Range. Ice jam flooding is also a current concern over the eastern
half of the Interior.

&&

.DISCUSSION...

Upper Levels and Analysis...
A 491 dam arctic closed low is anchoring the long wave pattern,
with the center over the high arctic north of Wrangel Island. A
powerful shortwave trough is lifting northeast across the N Bering
Sea with the trough elongating southwest across the W Bering Sea.
A very deep atmospheric moisture stream is tapping 25 N around
the Hawaiian Islands. A powerful for this time of year gale force
981 mb low is moving toward Saint Lawrence Island. Snow is falling
along the leading front as it moves up over Saint Lawrence and
the Bering Coast. Farther east there is a skinny ridge aloft
extending across the Interior with a migratory wave over the
Yukon. A coastal front over the N Gulf Coast is supporting a tight
enough pressure gradient to push AK Range gap winds into the 45
mph range.

Model Discussion...
The numerical weather models have settled into great agreement
with the overall idea of how the deep trough over the Bering Sea
will evolve over the next few days. There still remains higher
uncertainty with how far east the frontal system moves into the
Western Interior, as well as the timing if a negative tilt basal
trough moving from Bristol Bay into Norton Sound on Monday and
Tuesday. This affects the eastward extent of heavier precipitation
as it tries to make its way as far east as the Lower Tanana
Valley and Upper Koyukuk. We have mainly trended the front farther
east with this forecast package more similar to the
ECMWF/Canadian/NAM vs the farther west GFS. Currently this
forecast is looking at 2-4" of liquid precip over the higher
terrain out west, with 20+" snow over the W Brooks Range.

Central and Eastern Interior...
Today is the warmest day over most of the Interior with widespread
60 degree temps, and maybe a 70 closer to the AK Range. Gap winds
through the AK Range have already hit 50 mph and will push into
the 60 mph range for Monday into Tuesday. Chinook winds will also
move across most of the Interior by Monday with daytime gusty
south winds 15 to 25 mph. A front over the West Coast moves into
the Central Interior bringing rain to the Upper Koyukuk and Lower
Tanana Valley Monday and Monday night. Upslope precipitation will
impact the south side of the AK Range with snow levels in the
3000-5000 foot range. Showers today will move over the Fortymile
and possibly White Mtns with drying Sunday and Monday.

West Coast and Western Interior...
The long expected front is moving into the West Coast and Bering
Strait, with current conditions depicting snowfall and blowing
snow from Saint Lawrence Island to the immediate Bering coast.
Strong southeast winds of mid range gales move across the entire
West Coast by late this evening then continue into Sunday morning.
Gusts to about 60 mph over the Bering Coast and Yukon Delta slowly
diminish Sunday.

Meanwhile, heavy rainfall along the coast shifts inland, with snow
levels of around 3500 feet over the W Brooks Range falling to 2500
feet Sunday and Monday. Heavy snowfall is expected in the W Brooks
Range higher elevations, probably upwards of 15-20". The front
does shift into the W Interior Monday and Monday night with
steady rainfall, then shifts west again Tuesday as the main low
moves from Bristol Bay to the Y-K Delta coast. Gale force north
winds develop over the Bering Strait with more snowfall and
blowing snow expected.

North Slope and Brooks Range...
The first chinook is already underway as light south winds are
pushing marine stratus offshore. The main chinook reaches the NW
Arctic late this evening and shifts east Sunday, with widespread
south winds of 15 to 30 mph coming off the Brooks Range and across
the plains. Temps will likely rise into the 40s over the Arctic
Coast with low 50s possible. Powerful gap winds through the Brooks
Range passes will likely push 40-50 mph from the south. A cold
front will shift east Mon and Tue with a mix of rain and snow
along this front. This is conjunction with the low moving offshore
Monday with south winds weakening than switching back to a north
component.

Extended Forecast Days 4-7...
The large low over the West Coast Tuesday will gradually weaken
midweek with Yukon ridging building into the Mainland from the
east. The arctic front rapidly falls apart and temps warm again
late week as height anomalies aloft build. ECMWF and GFS both
support 850 temps rising to near 10C over parts of the AK Range
and Interior by Friday. That would mean widespread 70 degree temps
possible, but right now the window does not look long lasting.

Coastal Hazard Potential Days 3 and 4...None.

&&

.FIRE WEATHER...
Fire weather watches have been upgraded to red flag warnings near
the Alaska Range Sun and Mon afternoon and evenings. The watch for
near Denali has been cancelled as temps remain well below 75.

The chinook winds ramp up quickly today and then increase Sunday
and continue Monday. Min RH values and winds will reach criteria
for red flag conditions from the Isabel Pass area north to Delta
Junction. However, since this is a chinook pattern south winds
will also be quite gusty even over areas usually not impacted by
the typical south winds in a gap wind only type event. Expect min
RH values around 21 to 25 percent Sun afternoon and evening,
climbing to around 25 percent Monday afternoon and evening. South
winds should peak on the N end of Isabel Pass to 60 mph, with
gusts into Delta Junction into the 45 mph range. Conditions
improve Sun night with a slight decrease in winds with overnight
RH recovery, with winds picking back up Monday afternoon in
conjunction with dropping RHs.

Elsewhere, it will be dry and breezy over most of the Interior Sun
and Mon. An isolated thunder strike is possible over the Fortymile
Uplands today and tomorrow but looks very very marginal.

&&

.HYDROLOGY...
Flood watches are in effect for the Tanana River and Yukon River
for possible ice jams. A flood warning remains in effect near
Eagle for ice jam flooding. A flood watch is now in effect, as
well, for snowmelt flooding along the Chena River.

A strong front moving east out of the Bering Sea will stall over
the area this weekend and into early next week. This front is
expected to bring strong southerly winds and heavy rain to the
West Coast and Western Interior. The heavy rain combined with an
above normal snowpack over higher elevations, will cause an
increase in snowmelt. Runoff into rivers along the south faces of
the Brooks Range southward to the Lower YK Delta over the weekend
and early next week will cause water levels to rise and possibly
begin the breakup process on many rivers. The potential exists for
local ice jams to form and result in elevated water levels. The
increased runoff may also cause smaller streams and creeks to rise
to bankfull levels or overbank in low lying areas.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
AK...High Wind Warning for AKZ213-214.
     Wind Advisory for AKZ215.
     Flood Watch for AKZ220.
     Flood Watch for AKZ221.
     Flood Watch for AKZ222.
     Wind Advisory for AKZ223-226.
     Red Flag Warning for AKZ223-226.
     Flood Watch for AKZ224.
     Wind Advisory for AKZ225.
PK...Gale Warning for PKZ801-817-854.
     Gale Warning for PKZ802-853.
     Gale Warning for PKZ803-856.
     Small Craft Advisory for PKZ804.
     Gale Warning for PKZ805-852.
     Gale Warning for PKZ806-807.
     Brisk Wind Advisory for PKZ808.
     Brisk Wind Advisory for PKZ809.
     Gale Warning for PKZ810.
     Gale Warning for PKZ811.
     Brisk Wind Advisory for PKZ812-813-859.
     Brisk Wind Advisory for PKZ814-860.
     Gale Warning for PKZ816-851.
     Gale Warning for PKZ850.
     Brisk Wind Advisory for PKZ855.
     Brisk Wind Advisory for PKZ857.
     Brisk Wind Advisory for PKZ858.

&&

Ahsenmacher