Heavy Freezing Spray Warning 131, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
409 PM AKDT Thu Mar 25 2021

.ANALYSIS AND UPPER LEVELS...
The upper level jet is nearly zonal, extending along the Aleutians,
Alaska Peninsula, then slightly northeastward across the western
to northern Gulf of Alaska. A broad long-wave trough is situated
over the Bering Sea and mainland Alaska with strong ridging to the
south over the North Pacific. As would be expected in this
pattern, weather is relatively quiet across much of the region.
There are some local areas of snow, with Winter Weather Advisories
in effect this morning for portions of interior Bristol Bay,
Anchorage and the Matanuska Valley. Weak upper level waves
embedded within deep southwest flow have aided in snow production
along the west side of the Alaska and Aleutian Ranges, with
reports of 10" or more snow accumulation in the Iliamna area. An
approaching cold front is helping enhance upward vertical motion
and keep snow going in these areas. Snow is also falling along
the west side of the Kenai, Chugach, and Talkeetna Mountains, with
light snow accumulation in Anchorage and the Matanuska Valley.
In all of the aforementioned areas, the upper level forcing is
fairly weak, while low level upslope flow is moderate to strong,
leading to higher snowfall along the mountains. As seen in water
vapor and infrared satellite imagery, much of the deep upper level
moisture has shifted off to the east. Thus, the snow production
is increasingly due to low level processes of cold air advection
and/or upslope flow. As a result, snow accumulation will become
even more focused right along the mountains. Lastly, snow is also
falling across eastern Prince William Sound (Cordova/Valdez) and
portions of the Copper River Basin. For the remainder of the
forecast area from the southern mainland out along the Aleutian
Islands, weather is quite benign.

&&

.MODEL DISCUSSION...
Models are in excellent agreement with evolution of large scale
features over the next few days. The primary short-term challenges
include snow accumulation as upslope flow lingers over the
southern mainland tonight. Overall forecast confidence is high.

&&

.AVIATION...
PANC...Areas of light snow will persist in the Anchorage area into
the overnight hours. However, with most of the forcing coming
from upslope flow along the mountains, expect the terminal will
be mostly dry. If it does snow this afternoon or evening, it
should be very brief in nature. Low level flow will shift to
northwest around 09Z as a surface cold front arrives. the the
layer of cold and dry air advection will be shallow, think it's
enough to provide for VFR ceilings at the terminal. Suspect there
may be localized areas of IFR ceilings lingering in Cook Inlet
and/or east Anchorage/along the mountains.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (tonight through Sunday
afternoon)...

Upslope flow snow will continue, but gradually taper off
throughout the evening hours. Snow will linger the longest at
higher elevations from the Talkeetna Mountains southward through
the spine of the Kenai Mountains. Colder air filters through the
Alaska Range overnight tonight. The big question is, will it be
enough to erode the shallow moisture that is currently over much
of Cook Inlet through the Susitna Valley. Current thinking is that
the cold advection will not be strong enough to completely erode
the clouds which will stick around into Friday. Otherwise the
incoming cold air, coupled with a weak low pressure in the
northern Gulf will facilitate an uptick in gap winds along the
north Gulf coast Saturday into Sunday. The winds will not be an
high-end event but will get a little gusty in the preferred
locations. Overall, temperatures will continue to be slightly
below normal, especially minimum temperatures. However, it is hard
to deny the sun in March, maximum temperatures will still recover
quickly up to near freezing.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Sunday afternoon)...

A series of upper shortwaves will continue to bring scattered snow
showers to much of the region through Saturday morning. No
significant accumulations are expected. Colder temperatures will
build in Friday night as an upper trough moves over Southwest
Alaska. A trailing ridge will bring brief clearing Saturday
afternoon and evening. A front will move onshore over the
Kuskokwim Delta coast early Sunday morning. Temperatures will warm
with the combination of an upper ridge and strong southerly
surface flow. It is therefore a bit too early to determine
impacts, however if temperatures did remain below freezing, snow
and blowing snow would be likely.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Today
through Sunday afternoon)...

A weakening low moving southward near Saint Matthew Island will
bring scattered showers to the central/eastern Aleutians through
Saturday morning. Gusty winds of up to 55 mph are possible out of
bay and passes on the Pacific side of the eastern Aleutians and
Alaska Peninsula on Saturday as pressure gradients increase
between a Gulf low and a high over the North Pacific. The high
will build over this area through Sunday afternoon leading to
more benign conditions. A front will track across the western
Bering Saturday bringing strong southerly winds and moderate
rainfall, gradually weakening as it tracks eastward through
Sunday.

&&

.MARINE (Days 3 through 5: Sunday through Tuesday)...

Gulf of Alaska: Confidence is high for widespread northwesterly
gale force winds with storm force gusts around Kodiak Island,
diminishing late Sun. Upper level support brings widespread
westerly gale force winds across the Gulf, diminishing Tue. Seas
to 15 feet, mostly across the Southern Gulf, subsiding.

Bering: A wind wrapped Western Bering low moves into Norton Sound
by Tue. Confidence is high for widespread high end gale force
winds and waves with storm force gusts and freezing spray over the
Western and Central Bering, diminishing Mon. Winds will continue
diminishing to northerly small craft over the Eastern Bering by
Tue. Seas to 33 feet Pacific side, 24 feet Bering side, subsiding.

&&

.LONG TERM FORECAST (Days 4 through 7: Monday through
Thursday)...

The upper level flow will become more amplified during the
extended period, though remain progressive. Starting on Sunday,
a large and deep low will track northeastward across the Bering
Sea with a frontal system moving onshore of western Alaska.
Temperatures look cold enough along the Kuskokwim Delta coast to
produce snow and blowing snow as the frontal precipitation first
arrives. However, strong southwesterly flow behind the front
should bring in some warmer air off the Bering Sea. It looks like
a sustained period of long fetch southwesterlies across the
southern Bering and into Southwest Alaska and thus potential for
high surf or coastal flooding Sunday through Monday. Stay tuned
as we get closer and can better evaluate storm surge timing in
relationship to tidal cycles. Meanwhile, Southcentral will be cold
and dry out ahead of this storm Sunday, with gap winds along the
coast. Snow will spread into Southcentral with the frontal system
Sunday night through Monday.

Uncertainty grows Tuesday through Wednesday with handling of the
upper trough as it transitions from the Bering Sea and western
Alaska to Southcentral and the Gulf. With multiple waves embedded
within the larger trough, models differ on amplitude, tilt, and
track of this trough, leading to a variety of solutions for
weather over Southcentral and the Gulf all the way through
Wednesday. All models indicate some snow for Southcentral for
the first half of the week. The question is whether there is
significant snowfall anywhere. In any case, this trough/storm
should exit by Thursday, with another round of cold air advection
and gap winds behind it. Out west, another storm will race across
the Bering Sea in the fast upper level flow.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 165,177,178,179,185,411,412,414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...ML
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP
MARINE/LONG TERM...MK

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
150 AM AKDT FRI MAR 26 2021

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

0900 AM     SNOW             CHICKALOON, AK          61.80N 148.48W
03/25/2021  E15.0 INCH       MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            SPOTTER ESTIMATED ABOUT 15 INCHES OF SNOW.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
151 AM AKDT FRI MAR 26 2021

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

0900 AM     SNOW             INDEPENDENCE MINE       61.82N 149.24W
03/25/2021  E10.0 INCH       MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            SPOTTER ESTIMATED 10 INCHES OF SNOW.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
156 AM AKDT FRI MAR 26 2021

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

0900 AM     SLEET            SKEETAWK, AK            61.74N 149.24W
03/25/2021  M9.8 INCH        MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            SPOTTER MEASURED 9.8 INCHES OF GRAUPEL.

&&

ED

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE ANCHORAGE AK
157 AM AKDT FRI MAR 26 2021

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

0657 AM     SNOW             4 WNW PALMER            61.62N 149.21W
03/25/2021  E1.5 INCH        MATANUSKA-SUSITNA  AK   NWS EMPLOYEE

            OVER PAST 9 HRS. -SN FALLING.

0758 AM     SNOW             1 SSE SUTTON            61.71N 148.87W
03/25/2021  E4.4 INCH        MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            SNOW STARTED 730PM LAST NIGHT. FAST RATE OF
            FALL. CALM WINDS. 25F. HIGH YESTERDAY 39F.

0900 AM     SLEET            SKEETAWK, AK            61.74N 149.24W
03/25/2021  M9.8 INCH        MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            SPOTTER MEASURED 9.8 INCHES OF GRAUPEL.

0900 AM     SNOW             INDEPENDENCE MINE       61.82N 149.24W
03/25/2021  E10.0 INCH       MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            SPOTTER ESTIMATED 10 INCHES OF SNOW.

0900 AM     SNOW             CHICKALOON, AK          61.80N 148.48W
03/25/2021  E15.0 INCH       MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            SPOTTER ESTIMATED ABOUT 15 INCHES OF SNOW.

0934 AM     SNOW             1 NNW PALMER            61.61N 149.12W
03/25/2021  E3.5 INCH        MATANUSKA-SUSITNA  AK   NWS EMPLOYEE

            VIS 3/8SM SN FZFG. CALM WINDS. PERIOD OF
            SNOW PELLETS BET. 7-8AM.

1258 PM     SNOW             1 NNW PALMER            61.61N 149.12W
03/25/2021  E5.8 INCH        MATANUSKA-SUSITNA  AK   NWS EMPLOYEE

            UPDATE VIS <1/2SM SN FZFG.

0105 PM     SNOW             4 ENE MEADOW LAKES      61.64N 149.49W
03/25/2021  M3.1 INCH        MATANUSKA-SUSITNA  AK   NWS EMPLOYEE

            3.1 INCHES TOTAL SINCE LAST NIGHT. 33
            DEGREES AND NOT CURRENTLY SNOWING.

0107 PM     SNOW             1 N PALMER              61.62N 149.11W
03/25/2021  M6.0 INCH        MATANUSKA-SUSITNA  AK   NWS EMPLOYEE

            MEASURED 5.75 INCHES TOTAL. VIS LESS THAN
            ONE HALF MILE.

0222 PM     SNOW             SUTTON                  61.72N 148.88W
03/25/2021  M9.5 INCH        MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

0446 PM     SNOW             14 S TALKEETNA          62.14N 150.03W
03/25/2021  M7.0 INCH        MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            STORM TOTAL 7 INCHES. CURRENT SNOW DEPTH 37
            INCHES. SEASON SNOWFALL TO DATE 103.6
            INCHES.

0515 PM     SNOW             1 NNW PALMER            61.62N 149.13W
03/25/2021  M8.0 INCH        MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            STORM TOTAL 8 INCHES.

0652 PM     SNOW             4 SSW MEADOW LAKES      61.56N 149.66W
03/25/2021  M4.5 INCH        MATANUSKA-SUSITNA  AK   PUBLIC

0811 PM     SNOW             4 WNW PALMER            61.62N 149.21W
03/25/2021  E8.0 INCH        MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            8 INCHES SNOW FELL SINCE 10PM MARCH 24.

0721 AM     SNOW             5 W STERLING            60.51N 150.93W
03/25/2021  E1.0 INCH        KENAI PENINSULA    AK   NWS EMPLOYEE

            LOW OVC. LGT WNDS. 38F.

0600 AM     SNOW             3 S ANCHORAGE           61.17N 149.90W
03/25/2021  E1.0 INCH        ANCHORAGE          AK   PUBLIC

            SNOW PLOW MAINTENANCE INDIVIDUAL ESTIMATES 1
            INCH NEW SNOW.

0630 AM     SNOW             13 SE KNIK              61.30N 149.53W
03/25/2021  E1.7 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            SNOW OVERNIGHT -DZ AT 1030PM. 29F.

0722 AM     SNOW             9 SE ANCHORAGE          61.12N 149.71W
03/25/2021  E1.0 INCH        ANCHORAGE          AK   TRAINED SPOTTER

            OVC. 33F. 10 HR SNOWFALL. VIS E 2 W 10.
            BREEZY.

0931 AM     SNOW             10 SSE ANCHORAGE        61.08N 149.78W
03/25/2021  E1.0 INCH        ANCHORAGE          AK   PUBLIC

            HEAVY WET SNOW. -SN STILL FALLING.

1000 AM     SNOW             5 SW ANCHORAGE          61.16N 149.98W
03/25/2021  M1.4 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            1.4 INCHES AS OF 10AM.

0127 PM     SNOW             2 ESE POTTER HILL       61.08N 149.78W
03/25/2021  M2.0 INCH        ANCHORAGE          AK   TRAINED SPOTTER

            STORM TOTAL 2 INCHES. ONE INCH OVERNIGHT,
            ANOTHER INCH THIS AFTERNOON. STEADY SNOW FOR
            LAST HOUR.

0208 PM     SNOW             9 SE ANCHORAGE          61.12N 149.71W
03/25/2021  M2.0 INCH        ANCHORAGE          AK   TRAINED SPOTTER

0552 PM     SNOW             8 SSE EAGLE RIVER       61.25N 149.44W
03/25/2021  M5.0 INCH        ANCHORAGE          AK   NWS EMPLOYEE

&&