Brisk Wind Advisory 50, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
538 AM AKDT Mon Mar 9 2020

.ANALYSIS AND UPPER LEVELS...

In the upper levels, a positively-tilted upper trough over the
western Bering/Aleutians is slowly moving eastward. A high
amplitude blocking ridge is currently over the central North Pacific
south of Alaska. Despite the high amplified ridge to the south,
the flow remains relatively zonal (from west to east) over the
Alaskan mainland. A deep positively-tilted upper trough currently
extends southwestward from the Canadian Rockies to the subtropical
eastern Pacific. The jetstream is oriented northeastward from the
western subtropical Pacific to the southern Gulf of Alaska and
then sharply extends southward into the subtropical eastern
Pacific. Simplfied, this means that temperatures across the
Alaskan mainland will remain cold in the near term with the
predominant storm track being over the Aleutians and extending
northeastward into eastern Alaska.

At the surface, a 999 mb low over the eastern Bering continues to
move eastward toward Bristol Bay. A 997 mb low over Prince William
Sound continues to move eastward. A strong 1032 mb surface high
extends northward from the subtropical central Pacific to near
50N. The Middleton Island radar is showing isolated rain/snow
showers moving northeastward across the Gulf into Prince William
Sound. Kenai radar shows snow showers moving northeastward across
Cook Inlet into the Mat-Su Valleys. Freezing drizzle was observed
at NWS Anchorage during the break in between snow showers. Across
the Anchorage Bowl, snowfall amounts were highest on the west
side and lowest on the eastside due to the easterly flow over the
Chugach causing downslope (air warming and drying due to
compression) on the eastern side of the bowl. King Salmon radar
shows snow moving eastward from Bristol Bay to over the northern
AKPEN. Observations across western Alaska show a northeasterly
flow pattern which will allow for cold temperatures across the
area.

&&

.MODEL DISCUSSION...
Models are generally in good agreement at both the surface and in
the upper levels throughout this week. Some amplitude differences
in the upper levels and differences on the exact placement and
intensity of surface highs and lows develop towards the middle of
the week. However, there is a consistent trend throughout the
forecast period between guidance, thus forecast confidence remains
above average.

&&

.AVIATION...
PANC...IFR conditions will gradually become VFR throughout this
TAF package as light snow and mist taper off allowing for ceilings
and visibility to rise. IFR visibility conditions will exist
before 09th/16z as visibility will remain near 2SM while ceilings
remain MVFR. Visibility will increase to near 5SM after 09th/16z
with MVFR ceilings. VFR conditions then begin after 09th/20z as
visibility will be at least 6SM and ceilings rise above 3000' AGL.

&&

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

An upper-level trough axis over Southwest Alaska will continue to
push east today. As it does, the light snow, along with a few
pockets of freezing drizzle this morning, will taper off to
higher elevation snow showers across the Susitna Valley south over
the Kenai Peninsula. Farther east, snow will develop across the
Copper River Basin later today as a low-level southeasterly flow
ahead of the trough advects moisture across the region. 3 to 6
inches of snow is expected across the Copper River Basin through
Tuesday.

As the upper-level trough and its associated surface low over the
northern Gulf slide east, northerly outflow winds will begin to
set up due to the increasing north/south pressure gradient between
the trough and a ridge inland. These winds will first ramp up
through the bay and passes along Shelikof Strait north to the
Barren Islands and for locations such as Seward and Whittier this
evening. The winds will then increase for eastern Prince William
Sound, including the Valdez waterways and Thompson Pass by
Tuesday. These winds are expected to peak in intensity through
Tuesday (with areas of blowing snow likely) before slowly winding
down on Wednesday.

In addition to the strong winds, the northerly flow will lead to
clear and dry conditions spreading across Southcentral from west
to east through the next several days. Colder temperatures will
also return with the overall northerly wind flow.

&&

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

Cloudy conditions across Southwest Alaska this morning will start
to clear out this afternoon. A few lingering snow showers near the
Bristol Bay coast will taper off this morning, resulting in a dry
pattern across the Southwest mainland throughout the next several
days. Colder air will continue to spill into the region, with
high temperatures today in the teens across Bristol Bay, dropping
to single digit highs for Tuesday. These single digit temperatures
and low wind chill values will also continue through Wednesday
for the Kuskokwim Delta and Valley.

&&

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

A low over the central Bering will track into the Gulf for this
afternoon. This will keep snow showers in the forecast this
morning from Dutch Harbor to Port Heiden, which will taper off by
the afternoon. As high pressure builds in behind the departing
low, the pressure gradient will strengthen between these features,
resulting in strong northwesterly winds for the eastern Aleutians
and Alaska Peninsula. This gradient in conjunction with the cold
air advection could bring gusts of 50 kts for bays and passes
south of these locations today through early Tuesday.

Out west, a quick moving front over the western Aleutians will
move towards Adak by Tuesday afternoon before the associated low
center dives south into the North Pacific. By Wednesday morning,
the next strong system approaches the western Aleutians and
Bering, which could potentially bring a brief period of storm
force winds to the region. This warm system will also bring
widespread rain as it moves eastward.

&&

.MARINE (Days 3 through 5/Tuesday through Thursday)...
Forecast confidence in the advertised marine forecast is high.
The only question is with strength of winds as a front tracks from
east to west across the Bering Sea Wednesday through Thursday. For
now, forecast advertises high end gale force southerlies, though
there is potential for storm force southerlies, particularly for
the western Bering and western Aleutians.

&&

.LONG TERM FORECAST (Days 3 through 7/Tuesday through Saturday)...
Beginning Tuesday, an Arctic trough will cross Southcentral and
the Gulf of Alaska, with cold and dry air settling in across the
entire southern mainland. Offshore gap winds will be in full
force along the Gulf coast and Prince William Sound, including the
communities of Seward, Whittier, and Valdez. While low level cold
air advection and pressure gradients look fairly impressive, the
upper level jet is much weaker than in the wind event this past
week. Thus, expect overall winds to be weaker than what was
observed last week, particularly in the Valdez to Thompson Pass
corridor. Blowing and drifting snow and low visibilities will
likely plague Thompson Pass again as winds kick up Monday night
and Tuesday. This may necessitate issuing a blowing snow advisory
or blizzard warning, depending on how much new transportable snow
is in place. There will also be some localized gusty winds across
the rest of Southcentral and Kodiak Island, as winds accelerate
through mountain gaps and bays. Winds will gradually diminish
across the region Wednesday through Thursday, while temperatures
continue to fall.

The Bering Sea and Aleutians will start out quiet on Tuesday as a
high amplitude upper level ridge builds in from the west. The
ridge will then shift eastward through Friday, with a storm system
tracking from near the Kamchatka Peninsula on Thursday way up into
the high Arctic on Friday. A trailing front will bring gale force
southerly winds to much of the Bering Sea, with potential for
storm force winds over the western Bering and Aleutians. With the
high amplitude ridge holding over the Gulf and Southcentral and
another ridge likely building into the Bering Sea next weekend,
the forecast looks dry (and quiet) for much of the forecast area.
In particular, after the current snow event ends over the southern
mainland, it could be dry for a week or more. After temperatures
bottom out Thursday and Friday of this week, expect steadily
increasing temperatures after that.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Heavy Freezing Spray Warning 121 127 129 130 138 139 150
         155 165 179 412 414.
         Gale Warning 121 127 129 130 131 132 138 150 170 172 173
         174 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ED
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...SEB

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
155 PM AKDT MON MAR 9 2020

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

0154 PM     SNOW             1 W PALMER              61.60N 149.13W
03/09/2020  M3.0 INCH        MATANUSKA-SUSITNA  AK   NWS EMPLOYEE

            3 INCHES SINCE 7AM MONDAY MORNING. MODERATE
            TO HEAVY SNOWFALL OCCURRING AT 1:40PM.

&&

KO

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
310 PM AKDT MON MAR 9 2020

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

0309 PM     SNOW             10 MILES SE             61.10N 149.78W
03/09/2020  E1.0 INCH        ANCHORAGE          AK   TRAINED SPOTTER

&&

KO

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE ANCHORAGE AK
314 PM AKDT MON MAR 9 2020

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

0154 PM     SNOW             1 W PALMER              61.60N 149.13W
03/09/2020  M3.0 INCH        MATANUSKA-SUSITNA  AK   NWS EMPLOYEE

            3 INCHES SINCE 7AM MONDAY MORNING. MODERATE
            TO HEAVY SNOWFALL OCCURRING AT 1:40PM.

0309 PM     SNOW             10 MILES SE             61.10N 149.78W
03/09/2020  E1.0 INCH        ANCHORAGE          AK   TRAINED SPOTTER

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
345 PM AKDT MON MAR 9 2020

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

0317 PM     SNOW             SUTTON                  61.71N 148.87W
03/09/2020  M3.5 INCH        MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            CURRENTLY SNOWING, TEMPERATURE OF 32.

&&

KO

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE ANCHORAGE AK
346 PM AKDT MON MAR 9 2020

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

0317 PM     SNOW             SUTTON                  61.71N 148.87W
03/09/2020  M3.5 INCH        MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            CURRENTLY SNOWING, TEMPERATURE OF 32.

0154 PM     SNOW             1 W PALMER              61.60N 149.13W
03/09/2020  M3.0 INCH        MATANUSKA-SUSITNA  AK   NWS EMPLOYEE

            3 INCHES SINCE 7AM MONDAY MORNING. MODERATE
            TO HEAVY SNOWFALL OCCURRING AT 1:40PM.

0626 PM     SNOW             5 NNW HOMER             59.70N 151.59W
03/08/2020  M3.0 INCH        KENAI PENINSULA    AK   CO-OP OBSERVER

0309 PM     SNOW             10 MILES SE             61.10N 149.78W
03/09/2020  E1.0 INCH        ANCHORAGE          AK   TRAINED SPOTTER

&&