Small Craft Advisory 860, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
442 AM AKST Fri Nov 10 2017

.ANALYSIS AND UPPER LEVELS...

Throughout the upper levels, Southern Alaska is essentially split
half-and-half between a strong trough over much of the mainland,
and a sprawling dome of ridging across the central and western
Bering. Between these two features sits a 105 kt jet streak
oriented northwest to southeast. The trough passage across
southern Alaska earlier today was responsible for the 1-2 inches
of snow seen through much of Anchorage and the Mat-Su Valleys.
With the expectation of the trough persisting across eastern
Alaska for the foreseeable future, cold air building in the Copper
River Basin will be the catalyst for persistent offshore winds
blowing through the numerous gaps in the Chugach. Shortwave
passages may briefly enhance these winds from the weekend right
through into the upcoming workweek. Elsewhere, onshore flow from
the Bering will lead to periodic snow showers across portions of
coastal Southwest Alaska, particularly the Kuskokwim Delta. Over
the Bering under the upper level ridge and associated surface
high, fog and low stratus will be the primary concerns.

&&

.MODEL DISCUSSION...

The models are once again in excellent agreement straight through
into the long-term forecast as the pattern has become relatively
stagnant across Southern Alaska. A semi-permanent ridge will
remain across the Bering, while troughing with winter-like
temperatures looks to persist across eastern Alaska. The primary
weather hazards will be the periodic shortwave troughs moving
southeastward in the fast flow causing mainly mountain snow
showers, and the cold air buildup over interior Alaska and Copper
River Basin making for very gusty winds through many of Alaska's
gaps and passes. Forecast confidence is high owing to the very
good agreement both between the latest model runs and from run-
to-run.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist through the
day. During the evening, a developing Matanuska Valley Wind and a
strengthening down-Inlet flow may cause gusty north winds to
impact PANC through the overnight into Saturday morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

High pressure is building into the area again as the upper level
trough is over the Copper River Basin and continuing to move
eastward. The surface low in the Gulf combined with the high
pressure in the Interior will once again increase winds along the
north Gulf coast. This persistent pattern will continue through
the weekend with periods of stronger winds and periods of lesser
winds.
Temperatures, especially at night, will be quite dependent on
winds with the areas with stronger winds causing the inversions
from setting up and keeping temperatures warmer.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Southwest Alaska remains on the east side of a large ridge of
high pressure currently centered over the Western Bering. This is
leading to brisk northwesterly flow and some scattered snow
showers. A disturbance riding over the top of the ridge will sneak
into the region today bringing precipitation to the Kuskokwim
Delta region by late this morning. Precipitation will start out
as snow but begin mixing with rain by the afternoon as warm air is
advected around the top of the ridge into the region at the same
time. Precipitation should remain as all snow further inland up in
the Lower Kuskokwim River Valley. Accumulations are only expected
to be no more than 1-2" with higher amounts in the mountains. Precipitation
will taper off overnight as the ridge axis moves east towards the
coast. Weaker flow and strong subsidence underneath the ridge
will combine with increasing low level temperatures leading to
the development of fog Saturday into Saturday night over the
area, especially near the coast.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The focus for the next couple of days will be the large area of
high pressure currently centered over the Western Aleutians.
Winds will be strong on the periphery of the ridge but weak flow
will be seen underneath the center. Southerly flow on the west
side of the ridge will draw up warm moist air into the Bering,
with 850 mb temps increasing to nearly 8 C by Saturday night. This
should lead to the development of widespread fog across the
region, especially by Saturday night into Sunday. A low pressure
system pushing up from the south will bring gale force winds and
heavy rain to the Western Aleutians Saturday into Sunday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Models remain in very good agreement through much of the long term
forecast, with some minor discrepancies out west during the early
part of next week. Models continue to agree and provide higher
confidence in a long-wave ridge over much of the Mainland and
Bering/Aleutians, and a long-wave trough over Southeast Alaska
and the eastern Gulf over the weekend and into Monday morning.
Several short wave troughs traverse the top of the ridge, and drop
northwest to southeast across the state during the forecast
period. The strongest of these waves drop through the southern
Mainland on Sunday into Monday, providing some strong gusty
outflow winds along the northern Gulf and Alaska Peninsula. there
is a small possibility for some light snow showers to develop as
this system tracks through Southcentral. However, the limiting
factor on snowfall amounts will be dependent on how much moisture
is available, and as of now with the dry outflow conditions
available moisture looks quite limited during this time frame.

The models continue to struggle with regards to the placement and
track of a north Pacific low and its associated front impacting
the western half of the Bering and Aleutians Sunday into the
middle of next week. A middle ground between the faster GFS and
slower EC/Canadian solutions were preferred overall for this
system. There remains lower confidence on the timing and strength
of the system overall, but there is higher confidence in wet and
gusty conditions making their way through the western and central
Bering/Aleutians Sunday through Tuesday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gales: 120 121 127 130 131 132 150 352

&&

SYNOPSIS AND MODEL DISCUSSION...JPW
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KVP
LONG TERM...TP

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1250 PM AKST FRI NOV 10 2017

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

0445 PM     SNOW             PALMER                  61.60N 149.11W
11/09/2017  M0.8 INCH                           AK   PUBLIC

            STEADY SNOW AT THE TIME

0450 PM     SNOW             1 SW ANCHORAGE          61.20N 149.90W
11/09/2017  M0.2 INCH                           AK   PUBLIC

0450 PM     SNOW             1 NE RABBIT CREEK       61.10N 149.80W
11/09/2017  M1.2 INCH                           AK   TRAINED SPOTTER

&&

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1251 PM AKST FRI NOV 10 2017

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

0600 PM     SNOW             2 NE WASILLA            61.60N 149.40W
11/09/2017  M1.5 INCH                           AK   PUBLIC

0645 PM     SNOW             8 SSE EAGLE RIVER       61.21N 149.48W
11/09/2017  M3.0 INCH                           AK   NWS EMPLOYEE

            7 HR SNOWFALL AMOUNT

0826 PM     SNOW             11 E EKLUTNA LAKE       61.40N 148.80W
11/09/2017  M0.8 INCH                           AK   PUBLIC

1000 PM     SNOW             EAGLE RIVER             61.32N 149.57W
11/09/2017  M2.5 INCH                           AK   NWS EMPLOYEE

0745 AM     SNOW             N BIRCHWOOD             61.41N 149.48W
11/10/2017  M2.0 INCH                           AK   CO-OP OBSERVER

            12 HR SNOWFALL

0830 AM     SNOW             SUTTON                  61.72N 148.88W
11/10/2017  M1.0 INCH                           AK   TRAINED SPOTTER

            LESS THAN 1 IN IN LAST 9 HRS

&&

RA