Gale Warning 179, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
540 AM AKST Sat Feb 15 2020

.ANALYSIS AND UPPER LEVELS...

A large area of low pressure over the Bering continues to slowly
drift northward. A weakening front is pushing inland over the
Southwest coast, producing light snow over the Kuskokwim Delta and
Bristol Bay coast. Upper level ridging over the mainland has
become less amplified as it moves eastward. Beneath the ridge, a
weak surface trough over the northern Gulf coast continues to move
eastward as well. Light snow fell across the western Kenai
Peninsula for most of the overnight hours, though is beginning to
taper this morning.

&&

.MODEL DISCUSSION...

Models remain in good synoptic agreement through the short term. By
Sunday night, models begin to show fairly large discrepancies
with the track and strength of a complex low in the Bering, and a
series of lows that spin off of this parent low and propagate
eastward into the Gulf of Alaska. Forecast confidence beyond
Sunday remains low, however it is likely that there will be an
active pattern for the southern half of Alaska early next week.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Sat and
Sun)...
The weekend will continue to feature relatively quiet weather
before things get much more active next week. A very weak remnant
shortwave is lifting over the Western Kenai Peninsula and portions
of the upper Cook Inlet this morning. This has made for continued
light snowfall through the overnight but with very little in the
way of accumulations. This is expected to continue through around
daybreak before tapering off completely from west to east. The
other story in this pattern is the offshore winds through the
typical locations. Whittier, Seward, and Thompson Pass continue to
hold onto gusty conditions with a general thermal offshore
gradient. The winds in Whittier could actually come up a bit more
later this evening into the overnight as an upper-level jet and
mid-level shortwave pass through the area. Besides some very light
snow showers over the coastal areas of the Prince William Sound
and North Gulf Coast, all inland locations will remain mostly dry
through Sun afternoon.

Sun afternoon will start to show the first signs of the pattern
change. An initial (primer) front will slide from Kodiak Island
early Sun afternoon up through the Susitna Valley by early Mon
morning. This front will primarily feature warmer air and some
windy conditions, but it could also spell some precipitation type
woes. While precipitation will start out as snow at Kodiak, it
will quickly switch over to rain. Further north and inland, it
will be a battle between the colder air at the surface and the
warmer air aloft. There looks to be enough southeast flow with
this front to bring winds into the Turnagain Arm/Anchorage
Hillside as well as parts of the Knik River Valley. Temperatures
in these locations should jump fairly quickly. It will be a
different story in the Susitna Valley where cold air should be
able to hold on in the lower levels and allow for accumulating
snow. Turnagain Pass will also be vulnerable to snow and possibly
some blowing snow into Mon morning with this system. Again, this
will be the first of several systems for next week (FEB 17-21), so
please see the Long Term discussion for more details.

&&

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

Snow showers will continue across the Southwest Alaska today
associated with a front from a weakening low over the central
Bering. Areas in the Kuskokwim Delta and Bristol Bay will likely
see an inch or two of new snow accumulation with this system
through this afternoon.  Gusty conditions along the Kuskokwim
Delta coast this morning will cause lower visibility with blowing
snow, which will weaken through the afternoon as winds diminish
and snow showers move farther inland.

Sunday morning, shower begin to taper off before the next
organized system lifting across the Alaska Peninsula moves in for
Sunday afternoon. Widespread precipitation is expected across the
Bristol Bay region, which will initially start off as snow, but
could transition to rain or a mix of rain and snow as warmer
temperatures move in. This system will continue to lift northward
into the Kuskokwim Delta and Valley overnight Sunday into Monday
keeping widespread snow showers in the forecast. Colder air
wrapping around the backside of the associated low will bring the
potential blowing snow for Bristol Bay Monday afternoon, extending
into the Kuskokwim Delta with stronger winds moving in.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

Strong winds over the Bering will weaken this afternoon as a low
continues to lift northward and weaken over the north central
Bering. The next system system will quickly move over the western
Aleutians later this evening, which will bring an area of gale
force winds. However, there is still some uncertainty in the exact
placement and strength of this system, but there will be the
potential for blowing snow for the western Aleutians. The active
pattern continues overnight tonight as the next low system moves
over the central Aleutians, bringing widespread precipitation and
winds to the region. Models are struggling with the strength of this
low as it moves north over the Pribilofs through Sunday afternoon.
The next significant low will move over the eastern Aleutians by
Monday.

&&

.MARINE (Days 3 through 5/Monday through Wednesday)...
Expect multiple deep lows over the eastern Bering Sea down into
the North Pacific on Monday. All of this will shift eastward, with
one or more strong lows tracking into the Gulf of Alaska Monday
night through Tuesday. Forecast confidence remains high in the
overall pattern, with support for gale to storm force lows.
Meanwhile, forecast confidence in the track and strength of each
individual storm is low.

Meanwhile, it is looking likely that another large and deep low
will move to the western Aleutians Tuesday, then quickly track
eastward across the Bering and Aleutians on Wednesday. Once again
expect widespread gales with potential for storm force winds.

&&

.LONG TERM FORECAST (Days 4 through 7/Tuesday through Friday)...
Models have come into slightly better agreement for the
Monday/Tuesday time frame, and there is increasing confidence in
an active pattern for the southern half of the state early next
week. Potential impacts with this active pattern include mixed
precipitation and possible coastal impacts across the Southwest
coast, strong gusty winds for Southcentral and along the northern
Gulf coast, and the potential for a brief warm-up.

Solutions converge upon the same general solution beginning with
a deep low tracking to the western Aleutians on Tuesday. A strong
zonal jet will drive this system quickly eastward, across the
Bering Sea and Aleutians and into the Gulf of Alaska on Thursday.
The GFS solution takes the track a bit farther north, but
ensembles support the more southern track. Based on this, expect
another round of strong winds and heavy precipitation as the storm
system crosses the area. The southern track would keep
precipitation primarily in the form of snow across the southern
mainland of Alaska Wednesday night through Friday.

On the back side of this storm, Arctic air will plunge back
southward across the entire forecast area. Thus, expect well below
normal temperatures to settle back in across Southwest Alaska late
next week, then into Southcentral Alaska by next weekend. Upper
level flow will remain progressive, so it looks like another deep
low will reach the western Aleutians by Friday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales...127, 155, 165, 170, 172, 173, 174, 176, 178, 185, 412,
413, 414.
Heavy Freezing Spray...185.
. FIRE WEATHER...NONE.

&&

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