546
FXAK69 PAFG 260002
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
402 PM AKDT Wed Sep 25 2024

.SYNOPSIS...
Weather remains rather benign across Northern Alaska
through Sunday with a trend toward more active weather along the
West Coast early next week. A broad arctic trough will keep light
snow over eastern portions of the N Slope and Brooks Range into
Thursday morning. Showers with snow levels between 1500 and 2500
feet will continue across the Interior resulting in a mixture of
rain, snow or rain/snow mix with little if any accumulation. A mix
of showers and mostly cloudy skies are expected across the West
Coast with clearing across the eastern interior this weekend. Toward
the latter part of next week, the next weather maker will bring
another round rain/snow mixture across the forecast area.

&&

.DISCUSSION...

Analysis and Model Discussion...
Overall model guidance looks to be in good agreement with a 500
mb pattern characterized by a series of troughs tracking southeast
across the Bering Sea through Saturday. Ridging builds across
most of Northern Alaska Sunday into Monday ahead of a broad closed
low over Siberia. This closed low shifts east over the Bering
Strait or Chukchi Sea toward the middle of next week. EPS guidance
is a bit faster than GEFS/GEPS, but all major model suites
advertise two separate waves with the first one arriving early
Tueday-ish and the second arriving late Thursday-ish.

Surface analysis shows very broad troughing across the forecast
area. The primary synoptic feature, is a broad, vertically stacked
low centered near 58N/175W which will slowly meander east or
southeastward into the Gulf of Alaska. This results in increasing
ridging and southerly flow across the Alaska Range including gusty
south winds to around 30-40 mph through Isabel Pass. Surface ridging
persists through Monday before gradually weakening through mid-week
as the Siberian low pressure shifts eastward.

Central and Eastern Interior...
Weak cyclonic flow results in persistent cloud cover and occasional
light rain showers -mixed with snow above ~1500 ft- through Friday.
The most persistent precip is across the northeast interior in the
vicinity of Arctic Village where webcam imagery showed a skiff of
morning snow that is gradually melting this afternoon. Satellite
imagery shows a cyclonic circulation lifting north across the
eastern Brooks Range near Arctic Village. There may also be up to an
inch of additional accumulation, mainly at higher elevations of the
Brooks Range east of the Dalton Highway. Patchy nocturnal fog is
also expected to develop and if breaks in cloud cover occur then it
may become locally dense. A similar temperature regime is expected
through Friday with a warming trend over the weekend as ridging
builds aloft.

Anecdote: The latest first freeze of the season on record at
Fairbanks International Airport is September 27, 1974. Cloudy skies
this week will make Saturday September 28th the first day where a
freeze is possible. Models are in good agreement that skies will be
clearing Saturday morning with a mid level dry slot moving north
over the Alaska Range beneath the building ridge of high pressure,
though gap winds through Alaska Range passes may be strong enough to
produce modest adiabatic mixing/heating. At this time, lows in the
low to middle 30s are likely on Saturday morning, but a freeze is
not certain.

North Slope and Brooks Range...The most persistent precip is across
the northeast interior in the vicinity of Arctic Village where
webcam imagery showed a skiff of morning snow that is gradually
melting this afternoon. Satellite imagery shows a cyclonic
circulation lifting north across the eastern Brooks Range near
Arctic Village. There may also be up to an inch of additional
accumulation, mainly at higher elevations of the Brooks Range east
of the Dalton Highway. For the North Slope, light onshore flow
continues into Friday and I expect low stratus and areas of fog to
continue. Winds become southerly/offshore across the eastern slope
this weekend with more easterly flow possibly persisting across the
east. Highs will be in the 30s, except in the 20s over Brooks Range
passes. Lows will be in the 20s and lower 30s.

West Coast and Western Interior...Partly to mostly sunny skies are
occuring along the west coast and mostly cloudy skies across the
western interior this afternoon. This cloud cover gradient is
beneath a weak and elongated 500mb low. Shortwaves pivoting around
this low allow for generally northerly flow transitioning to
southerly flow across the western interior on Friday. Ridging builds
across the interior on Saturday and shears the upper level low apart
along the west coast by Sunday.

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

Extended Forecast For Days 4 through 7...
The main feature of interest is the Siberian low shifting east into
the area on Tuesday-ish. Operational guidance advertises modest
southerly flow ahead of this system. There appears to be enough of
an easterly component to limit coastal flooding concerns along the
west coast. Model uncertainty is large by the middle of next week,
but some guidance lifts the Siberian low into the Chukchi Sea toward
the middle of next week. If that occurs then there may be a period
of westerly flow with a long fetch across the Bering Sea that could
bring coastal flooding concerns.

A note on the first significant snow in the Fairbanks area:
Ensembles show a large spread, but generally agree that the first
measurable snowfall won`t be before the October 4-7 timeframe.
About 70-80% of the GFS/ECMWF ensemble members indicate some
amount of measurable snowfall in Fairbanks by October 7. The ECMWF
is less enthusiastic, but probabilities for measurable snow
increase beginning around October 6. The average first measurable
snow in Fairbanks is October 2 and the average first snowfall of
one inch or greater is October 10.

&&

.HYDROLOGY...No concerns.


&&

.AFG WATCHES/WARNINGS/ADVISORIES...
AK...None.
PK...Small Craft Advisory for PKZ801-802.
     Small Craft Advisory for PKZ850-853.
&&

$$