Brisk Wind Advisory 11, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
702 AM AKST Thu Jan 23 2020

.ANALYSIS AND UPPER LEVELS...

A 1024 mb ridge centered over eastern Siberia extends through the
Pribilof Islands to the tip of the Alaska Peninsula (AKPEN).
Flanking this ridge is a 965 mb low well south of Shemya, and a
983 mb low over the far eastern Gulf of AK.

On a smaller scale, a compact area of low pressure was crossing the
AKPEN towards southwestern Kodiak Island. A low topped layer of
stratus is producing light snow from the Matanuska Valley, through
the Anchorage Bowl, into the western Kenai Peninsula. Interestingly
enough, this stratus deck has cloud bases of 1000 to 2000 feet, with
earlier pilot reports indicating cloud tops only reaching 3500 feet.

To have such a "shallow" cloud deck producing accumulating snow
(so far we've measured 1.8 inches of snow here at the office
between 9 pm and 3 am this morning), aided by lift associated with
a disturbance aloft passing overhead, exemplifies how challenging a
snowfall forecast can be as the interplay between sufficient
moisture versus lift interacts with the various terrain features.

&&

.MODEL DISCUSSION...

The numerical guidance remains in excellent agreement in the
overall pattern aloft through the weekend, before some subtle
difference arise by early next week. Even then, the differences
mainly involve the positioning of a deep mid-level area of low
pressure, somewhere near the AKPEN.

A similar story can be seen with the surface forecasts with the
main differences being location of cyclogenesis (low pressure
development) over the next 48 hours, with models contrasting in
where this occurs over the Northern Gulf, and what track does it
take as the lows meander in this general vicinity through the
weekend. This affects which parts of Southcentral may receive
snowfall.

&&

.AVIATION...

PANC...Light snow will continue to fall out of a stratus deck with
ceilings of 1200 to 1900 feet. Earlier PIREPs indicated tops of
only 3500 feet. The degree of cold air has proven sufficient for
snowfall to reduce visibilities to less than 2 miles. Conditions
should continue to slowly improve through the morning with some
uncertainty on the exact timing of when the snow will stop. VFR
conditions will take over in the afternoon. By 24/05z, wind gusts to
20 KT will develop.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Thu and
Fri)...
A building ridge upstream over the Eastern Bering Sea is causing a
trough to deepen over Southern AK this morning. Within this trough
is some of the coldest air of the season so far with 850 mb
(5,000') temperatures pushing -25C. With some lingering moisture
still hanging around parts of Southcentral, this trough and cold
air are still wringing out every last bit of said moisture. Thus,
very light snowfall continues from Anchorage up to Palmer and over
to Valdez this morning. This snow has extremely low water content
(fluffy) and has been able to accumulate through the evening and
early morning hours. As the trough digs further through the day
and allows an increasing offshore gradient to develop, this should
usher in enough dry air to bring an end to nearly all the light
snow. The next chance for any snow will be starting during the day
Fri as the trough is able to tap into some moisture over the NE
Gulf and sling it into the Copper River Basin.

Attention then shifts to the stout north-northwest winds and cold
air as we head towards the weekend. The ridge over the Bering
will continue to build forcing the low in the N Gulf of AK to "cut
off" from the rest of the flow. This will make for an increasing
offshore pressure gradient and allow winds to really ramp up. The
hardest hit spots will be many of the typical channeled
areas...Seward, Thompson Pass, Whittier, Matanuska Valley, and Broad
Pass. While none of these spots will approach warning criteria, once
the winds start, they will remain quite gusty through this pattern.
There will also be strong winds through many of the bays and passes
in the marine zones. This will help to produce heavy freezing spray
in some of the more treacherous spots like the Barren Islands and
Shelikof Strait. As for temperatures, the places that remain calm
(Glennallen, Skwentna, etc) will see the coldest temperatures.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

A highly amplified pattern is developing over the region. Much of
western Alaska is situated between an upper level low centered
south of Anchorage and a ridge building over the Bering. Embedded
shortwaves are currently bringing scattered snow showers to the
Alaska Peninsula and Middle Kuskokwim Valley. The main impact of
the aforementioned pattern (which will generally persist through
the weekend) will be strong northerly winds aloft bringing in
much colder air to the area. Surface winds, especially near the
Kuskokwim Delta coast could exceed 15 mph and thus, Wind Chill
Advisories have been issued for applicable forecast zones.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

A strong ~965 mb low south of Adak is currently moving
northeastward. An omega block over the central Bering is
inhibiting its associated front from progressing eastward and
thus, storm force easterly winds and locally heavy rain will
continue across the western Aleutians through Friday. This low
will eventually become vertically stacked and gradually weaken
through the weekend. Strong high pressure will likewise persist
over the central and eastern Bering/Aleutians through the weekend.

&&

.MARINE (Days 3 through 5: Friday through Sunday...from Wed afternoon
discussion)...

Gulf of Alaska:

Weak low pressure will persist over the Gulf of Alaska Friday
through Monday and then a second weak low enters the GOA Tuesday
and Wednesday. A strong thermal gradient has set up where brutally
cold temperatures reside over land and mild temperature are over
the Gulf Of Alaska. The expectation is that enhanced offshore
winds and gap winds will develop resulting in areas of heavy to
light freezing spray and enhanced sea states. The areas of concern
at this time are the Copper River Delta along with Kamishak Bay
through the Barren Islands.

Bering Sea and Aleutians:

A strong low centered south of the western Aleutians will keep
widespread gales with occasional embedded storms ongoing across
the central and western Bering Friday. The Gales will likely be over
the western Bering Sea Saturday and Sunday. Seas of 20 to 30 ft are
expected over a large area of the central and western Bering and
Aleutians Friday and Saturday. Heavy freezing spray is expected
Saturday north and east of the Pribilof Islands.

&&

.LONG TERM FORECAST (Days 4 through 7: Friday through Tuesday)...

The big picture will be low pressure persisting over the Gulf of
Alaska and south of the Aleutians with strong high pressure over
the eastern Bering Sea and fierce cold air advection over the
mainland. For the mainland this translates to below normal
temperatures this forecast period. The Climate Prediction Center
which is part of the National Weather Service anticipates that
these below normal temperatures will persist into the 8-14 Day
Outlook. This pattern will result in enhanced offshore flow and
gap winds. Models are in good agreement with the longwave pattern
over the mainland, Gulf Of Alaska and Bering through the forecast
period.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisories 155 161.
MARINE...Storm Warning 175 176 177 411 413
        Gale Warning 119 120 121 127 129 130 131 132 138 150 172 173 174 178
					185 412 414
Heavy Freezing Spray Warning 121 127 129 130 132 138 139 141 150 160
							165 179 180 185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHCENTRAL ALASKA...MSO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP
MARINE/LONG TERM...PJS

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
914 AM AKST THU JAN 23 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0738 AM     SNOW             SUTTON                  61.71N 148.89W
01/22/2020  E2.0 INCH        MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            SPOTTER REPORTED 2 INCHES OF SNOW.

&&

MV

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
917 AM AKST THU JAN 23 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0736 AM     SNOW             2 MILES SE OF EAGLE RIV 61.31N 149.54W
01/22/2020  M3.5 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            SPOTTER REPORTED 3.5 INCHES OF SNOW.

&&

MV