Small Craft Advisory 37, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
534 AM AKST Fri Jan 14 2022

.ANALYSIS AND UPPER LEVELS...

Southcentral Alaska remains under deep southerly to southeasterly
flow this morning as what was once a very strong storm system
continues to weaken. The low continues to move northwestward
towards Bristol Bay opening up into a trough as it does so. Even
though, the flow is southerly, Seward has been reporting light
snow for much of the night with temperatures hovering right near
freezing. Visibility has dropped to as low as 3/4 mile at times
as well overnight. Portage continued to receive rain overnight
with temperatures in the mid to upper 30s and southeasterly winds
gusting as high as 55 mph. Turnagain Pass snotel reported snowfall
of 21.4 inches so far with this system with snow still falling
there as of this writing. Elsewhere across Southcentral,
conditions remained rather quiet overnight with most areas in the
20s and 30s except for the Copper River Basin where Gulkana was
mostly in the teens.

Much of Southwest Alaska currently remains under general weak
synoptic flow aloft. Though, when looking at water vapor imagery
with the 500 mb height lines of various models overlaid, we see
what was once a vertically stacked low earlier in the night
opening into a upper level trough as the surface low weakens as it
continues moving northwestward towards northern Bristol Bay.
Ahead of this feature are just sporadic light snow showers across
Southwest with Aniak, New Stuyahok, Dillingham, and Chevak
reporting light snow earlier in the night. All in all though,
conditions remain rather quiet with temperatures mostly in the
teens across the Kuskokwim Delta and the Lower Kuskokwim Valley
with 20s to low 30s for Bristol Bay. Iliamna is one of the warm
spots in the mid to upper 30s this morning.

An upper level low is present moving southward through the Bering
Sea. Underneath this upper level low the flow is predominantly
northeasterly/northerly. As a result, Arctic air continues to flow
off the ice edge and over the relatively warm water of the Bering
creating unstable conditions. This can be seen on the nighttime
microphysics imagery this morning as stratocumulus dominates much
of the Bering. Underneath some of these clouds are occasional snow
showers that are affecting the marine waters of the Bering as
well as the Pribilofs Islands and the Aleutian Chain. Heavy
freezing spray is also continuing mainly near the ice edge.

&&

.MODEL DISCUSSION...

Overall, model guidance remains in good agreement on the synoptic
scale features out through Day 3. Where differences continue to
arise is how exactly the upper level low center over the Bering
plays out as it moves eastward into Southcentral. The
EC/Canadian-NH/NAM all seem to show a more consolidated and
concentric look to the upper level low as it moves into Southwest
and then east into Southcentral. Therefore, these were the models
of choice for this forecast package. The GFS seems to be the
outlier with the energy associated with this upper level low
center too stretched out and too far south. Out west, model
guidance maintains the status quo on a storm force low moving
northward towards the Bering for tonight through the weekend.
Therefore, only small changes made here mostly to fine tune the
corridor of where storm force winds will be.

&&

.AVIATION...

PANC...VFR conditions are expected for the entire TAF package.
Light winds mainly out of the north or northwest are expected to
continue through around 17-18z this morning. Though, expect
southeasterly winds around 2000 ft causing wind shear over the
terminal. A southeasterly Turnagain Arm wind is expected to bend
over the terminal around mid-morning (17-18z) as the surface low
currently over the Barren Islands region moves up Cook Inlet. Any
precipitation that tracks up the Inlet with the low could fall in
the form of rain as temperatures climb above freezing with the
southeasterly wind. Any rain that does fall, however, would be
light in intensity and short in duration.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Sunday night)...

A rapidly weakening low in southern Cook Inlet this morning will
track quickly inland across interior Southwest Alaska and
dissipate this morning. At the same time, a series of upper level
short-waves will lift northward across Southcentral this morning
then exit this afternoon. Strong south to southeast flow behind
the surface low will focus precipitation over upslope areas of
the eastern Kenai Peninsula and northern to western Susitna
Valley, with continued downslope drying from the western Kenai
to Anchorage and the Matanuska Valley. Pressure rises behind
the surface low and shifting of the pressure gradients favors
winds coming into Anchorage this morning, especially along the
upper hillside and south to west Anchorage as the Turnagain Arm
jet bends toward the city. This will cause temperatures to jump
into the mid to upper 30s. With all key features exiting the
region, winds and precipitation will quickly diminish this
afternoon through this evening. As winds die down, temperatures
across most of Southcentral will drop back below freezing.

Another deep storm system moving out of the Pacific will take a
much further east track into the eastern Gulf of Alaska and toward
Southeast Alaska tonight, with wind and precipitation along the
western periphery of the storm impacting the central Gulf. The
next feature of interest for Southcentral will be a large upper
level low and short-wave trough currently over the Bering Sea. It
will approach Southcentral Friday night and Saturday, likely
bringing snow to much of Southcentral. However, at the moment
there is quite a bit of uncertainty in the track of this low and
accompanying short-waves, making it difficult to nail down timing
of snow and snowfall accumulation. The low will progress steadily
eastward across the region, so it generally looks like a quick
shot of snow and amounts will generally be light. However, the
leading short-wave looks fairly robust and cold air advection
will contribute to vertical motion and a transition to dendrites
as we head through the event. Thus, there is potential for
localized higher amounts for which ever areas end out ahead of
that short-wave. Conditions will dry out Saturday night-Sunday
in the wake of this low, with colder temperatures settling in.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2: Today
through Saturday night)...

Scattered showers are the main story across Southwest Alaska this
morning. One region of mixed snow and rain showers is occurring
over the eastern interior Bristol Bay region, on the west side of
the low-level center of a strong low now quickly weakening as it
tracks northward into the mouth of Cook Inlet. The region of
showers will move northward along the Aleutian/Alaska Range from
Bristol Bay into the Kuskokwim Valley through this evening. Warmer
air wrapping around the core of the low has allowed for surface
temperatures to rise above freezing and for some precipitation to
fall as rain, especially along the western slopes of the
Aleutian/Alaska Range. Above freezing air will quickly retreat
eastward this morning, meaning this rain will begin to mix with
and eventually become all snow through the morning hours.

A second batch of snow showers lingers in the Kuskokwim Delta as
a broad surface low moves slowly northward through Saturday.
Northerly flow will shift to southwesterly flow this evening
behind this low, pushing colder air over the Bering into
Southwest Alaska. This colder air will usher in a strong upper-
level low which will make for the next round of active weather
beginning early Saturday morning. Model solutions have trended
toward increased snowfall for portions of Bristol Bay and the
Kuskokwim Valley as a cold front aloft and divergent flow enhance
lift ahead of the strong upper low. Areas from Iliamna northward
can broadly expect 1 to 3 inches of accumulation as a band of
light snow develops early Saturday morning and pushes north
through Saturday night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2: Today
through Saturday night)...

Broad northerly flow across the Bering Sea to the central and
eastern Aleutians continues through this afternoon. A low over
Southwest Alaska will elongate and stretch into the Bering Sea,
drawing this colder air from the central Bering eastward. A North
Pacific low tracks toward the western Aleutians. Winds shift to
easterly tonight ahead of the low as a front brings snow which
quickly transitions to rain for the western and central
Aleutians. Winds increase to storm force through the western
Aleutians by Saturday afternoon. The front progresses slowly
eastward, reaching the eastern Aleutians by Saturday night and
bringing primarily rain on warmer, southeasterly flow. Heavy
freezing spray over the Northern Bering and near the ice edge will
continue.

&&

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

Gulf of Alaska: A weak area of high pressure will maintain winds
less than 35 kts and seas less than 20 ft for the Day 3 through 5
period.

Bering Sea: A broad area of low pressure settling across the
western Aleutians to the North Pacific will remain stationary
through early next week. Small, embedded disturbances circulating
around the broad low will bring gale force winds and seas above 20
ft at times for south of the Aleutians and much of the Bering Sea
through Tuesday.

.Long Term Discussion (Days 4 through 7: Monday through Thursday)...

Overall, the latest operational model runs are in decent agreement
with the evolution and progression of the synoptic scale features
for early next week but diverge in the specific details towards
the end of the period. For Southcentral, high pressure building
over the Gulf of Alaska will leave a brief period of dry weather
from Monday through Wednesday. The rest of the mainland, including
coastal and interior Southwest, is expected to be relatively dry
with near to below normal temperatures as the ridge axis extends
north of the Alaska Peninsula to the eastern Bering Sea. Beginning
on Wednesday, models seem to key on a frontal boundary extending
from the center of a North Pacific low, bringing precipitation and
wind from Kodiak Island northward to the southern mainland. If
this scenario were to materialize, there is a potential that a
barrier jet will develop along the northern Gulf coast from Prince
William Sound to the Copper River Delta area. Where the
uncertainty emerges is the track, position, and timing of the low
and front that still needs to be ironed out with subsequent model
runs. Out west, a broad trough will settle across the western
Aleutians to the North Pacific. Weak, embedded shortwaves and
surface lows moving upstream of the trough will bring a wintry mix
of rain/snow and gusty winds at times along the southern portion
of the Aleutians into the Bering Sea. Depending on the track and
positions of these shortwaves, this could also bring widespread
precipitation to the eastern Aleutians and the southwestern
mainland later next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 178
Gale Warning 411 413 119 120 125 130 174 175 176 177. Heavy
Freezing Spray Warning 185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MV
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ
MARINE/LONG TERM...MF

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE ANCHORAGE AK
1038 AM AKST FRI JAN 14 2022

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

0700 PM     SNOW             20 SSW TONSINA          61.35N 145.31W
01/13/2022  E12.0 INCH       VALDEZ-CORDOVA     AK   DEPT OF HIGHWAYS

0604 PM     SNOW             TURNAGAIN PASS          60.79N 149.17W
01/13/2022  M14.0 INCH       KENAI PENINSULA    AK   PUBLIC

            SNOW FROM THE PAST 24 HOURS AT 1600 NEAR
            TURNAGAIN PASS. 18; AT 2400. SLIGHTLY LESS
            RIGHT AT THE ROAD. HEAVY RAIN UP TO ABOUT
            750 AROUND NOON. VISIBILITY AT THE TOP OF
            TURNAGAIN PASS WAS ABOUT 1/2 MILE AROUND
            3:00 P.M. AK TIME.

0326 PM     SNOW             UPPER POTTER VALLEY     61.06N 149.76W
01/13/2022  M1.7 INCH        ANCHORAGE          AK   TRAINED SPOTTER

            SPOTTER MEASURED 1.7 OF SNOW.

0801 PM     SNOW             UPPER HILLSIDE          61.12N 149.72W
01/13/2022  M1.0 INCH        ANCHORAGE          AK   PUBLIC

0700 AM     SNOW             MID HILLSIDE            61.11N 149.78W
01/14/2022  M1.0 INCH        ANCHORAGE          AK   PUBLIC

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1207 PM AKST FRI JAN 14 2022

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

0900 PM     SNOW             26 S TONSINA            61.27N 145.28W
01/13/2022  M14.0 INCH       VALDEZ-CORDOVA     AK   DEPT OF HIGHWAYS

&&

JPW

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1209 PM AKST FRI JAN 14 2022

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

0900 PM     SNOW             13 S TONSINA            61.45N 145.11W
01/13/2022  M6.0 INCH        VALDEZ-CORDOVA     AK   DEPT OF HIGHWAYS

&&

JPW