Gale Warning 211, NWS Fairbanks, AK

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
301 PM AKDT Mon Aug 19 2024

.SYNOPSIS...
A large trough has erased summer from Alaska today, with the
remnants of warm air now shifting east into Canada. Cooler temps
and showers today, then partial clearing overnight will support
temps down into the mid 30s over parts of the Interior. A brief
drying out for the West Coast, then the remnants of post-tropical
Ampil will move into the West Coast Tuesday evening through
Wednesday, bringing high winds and minor coastal flooding impacts
to the West Coast, along with more rainfall for the Mainland.

&&

.DISCUSSION...

Upper Levels and Analysis...
There is a massive longwave trough parked over the Mainland today,
with the center of that trough being an arctic low near the North
Pole, with heights around 516 dam. The longwave trough has heights
around 540 dam and it encompasses the entire Mainland of Alaska.
The surface low is moving north into the Beaufort Sea with the
trailing cold front shifting across the Arctic Coast and N Slope.
Temps are substantially cooler everywhere except the West Coast,
with temps a solid 30 degrees cooler over the E Interior.

Forecast and Model Discussion...
Models are locked into the pattern and are clustered well as the
upper trough over the Mainland shifts east, high pressure builds
in tonight, then the next low shifts into the West Coast and an
associated front shifts east across the Mainland, midweek.
Currently, the remnants of ex-typhoon Ampil are the main storm we
are tracking, and the models have been very good from both a
deterministic and ensemble perspective, so we will continue with
an ECMWF and GFS blend for winds and storm track, which takes the
low from the northern tip of St Lawrence Island to Wales Kivalina,
approximately. This will push the strongest southwest winds of
gale force into Norton Sound, the YK Delta, and up to Teller.
Thus, we have changed the forecast little, and the general
thinking remains the same with minor flooding impacts for the
Norton Sound to YK Delta.

Central and Eastern Interior...
Cooler temps along with blustery and showery conditions continue
this evening then quickly taper off tonight, with brief high
pressure building in overnight. Temps drop into the 30s over
clear areas, especially out west toward the lower Tanana.
Elsewhere clouds should keep lows into the 40s. Still expecting
some higher elevation light snow chances above 2200 feet or so in
the Whites. It'll be drier on Tuesday and clearing out some, with
the next front from the West Coast pushing into the region
Wednesday with more rainfall, along with more south winds in the
Alaska Range gusting to 45 mph. Thursday, more southwest winds to
30 mph and showers will pass over the Interior, so it will be
another autumn-like day for the Interior.

West Coast and Western Interior...
High pressure builds in tonight. West winds in the sounds will
end this evening and high surf advisories will end this evening.

All eyes turn to the west where ex-Typhoon Ampil will move into
the West Coast with south winds as early as Tuesday, and then
southwest winds behind the low on Wednesday. These winds will
reach 60 mph and they will be strongest from St Lawrence Island to
the Norton Sound. As the front shifts inland, wind gusts will be
rather strong through Thu, which may eventually require wind
advisories inland. More rain is coming as well, with periods of
rainfall through Thu night. The main impact is going to be coastal
threats, as the low moves inland across the Bering Coast, which
will bring in a range of elevated water levels of 4 to 8 feet,
highest over E Norton Sound around Koyuk, with values 4 to 5 feet
around Nome, and lower values of 2 to 4 feet over the YK Delta to
Kotzebue Sound. This storm is also projected to bring 10 to 15
foot seas to the S facing coasts of northern Norton Sound, so that
will exacerbate the storm surge. We will be issuing coastal flood
advisories with this forecast package.

North Slope and Brooks Range...
Rain showers with a possible isolated thunderstorm today are
possible along the cold front, as it tracks from the Dalton Hwy
corridor and eastward. Rain showers will turn to mixed rain and
snow showers along parts of the Arctic Coast tonight with little
to no snow accumulation. 1 to 2 inches of snow, however, will
likely accumulate along the higher Dalton highway elevations in
the Brooks Range tonight. High pressure builds in tomorrow and it
will be drier, than south winds kick in again on Wednesday with
gusts to 40 mph through the passes from the south, along with rain
chances.

Extended Forecast Days 4-7...
Massive longwave trough with -2.0 sigma anomalies aloft, which
means will likely be much cooler than average with showers over
the Interior and chances for rain and snow showers over the
Arctic. With the large trough in place, the storm track will also
shift south, so there will finally be a receive from the recent
heavy rains over the West Coast and Brooks Range, although it will
still be wet.

Coastal Hazard Potential Days 3 and 4...A strong coastal low, the
former remnants of current Typhoon Ampil, is projected to move
into the YK Delta and Norton Sound Tuesday into Wednesday with
gale force southwesterly winds and potential for coastal flooding.
The current track and strength could bring elevated water levels
of 4 to 5 feet for most areas but the highest water levels near
Koyuk with elevated water around 7 to 8 feet above the normal high
tideline.

&&

.FIRE WEATHER...
Brief drying out on Tuesday with more south winds on Wednesday as
a front shifts east from the West Coast, bringing south gap winds
to the AK Range passes. It will be mostly dry for the Interior
tomorrow and early Wednesday before more rainfall.

&&

.HYDROLOGY...
2-4 inches of rain over past two days will continue to cause
rapid increases in stream levels draining the Central Brooks
Range. Tributaries to the Koyukuk River could reach bankfull
levels and remain so into midweek.

The Koyukuk River at Bettles and Allakaket will rise
significantly over the next 24 hours and crest Tuesday. River
levels at Bettles and Allakaket are currently forecast to remain
below flood stage. The Koyukuk River at Hughes is expected to
crest Wednesday below flood stage.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
AK...Flood Watch for AKZ812-831-832.
     High Wind Watch for AKZ821-827.
     Coastal Flood Advisory for AKZ821-822-824-825.
     Wind Advisory for AKZ832.
     Wind Advisory for AKZ834.
PK...Small Craft Advisory for PKZ801-802-806-817-850-853.
     Small Craft Advisory for PKZ803-807-852-856.
     Small Craft Advisory for PKZ804-805-808-810-855.
     Gale Warning for PKZ809.
     Small Craft Advisory for PKZ811-857.
     Small Craft Advisory for PKZ812-858.
     Small Craft Advisory for PKZ813.
     Small Craft Advisory for PKZ814-860.
     Gale Warning for PKZ815-861.
     Gale Warning for PKZ816-854.
     Gale Warning for PKZ851.
     Small Craft Advisory for PKZ859.
&&

Ahsenmacher