Avalanche in Alaska, May 10 to 17, 2022

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
527 AM AKDT Tue May 10 2022

.ANALYSIS AND UPPER LEVELS...

A longwave trough has settled in across much of mainland Alaska
this morning as several embedded shortwaves rotate into the base
of the trough across Southwest and into the western Gulf. Strong
north to northwest flow has developed on the west side of the
trough, with a roughly 125 kt meridional (north-south) jet streak
now positioned over Bristol Bay. A small low has spun up
southeast of Prince William Sound just ahead of one of the
stronger shortwave perturbations aloft, with a few showers
swirling around it near Middleton Island and Cordova. Very cool
and dry air has filtered into most land areas to the north, with
temperatures in the mid 20s to mid 30s across most of Southwest
and no higher than 40 for most of Southcentral. Gusty northwest
winds yesterday evening have slackened for most inland areas with
boundary layer decoupling. A clear exception has been near Kodiak
and the northern Alaska Peninsula, where hefty gap enhanced winds
continue with gusts near 50 mph observed in Kodiak City at times
overnight. Out west, a blocking ridge continues to set up shop
over the Bering, with a blob of marine stratus starting to creep
back into the Aleutians after the welcome break of sunshine. All
indications are that this ridge will be sticking with us for quite
some time.

&&

.MODEL DISCUSSION...

Model agreement continues to stay on track overall through late in
the week. There is very high confidence at this point for the
blocking pattern over the Bering to stay firmly in place for the
foreseeable future, keeping everywhere downstream across the
mainland/Gulf in persistent north to northwest flow. Models are
now keying in on a fast-moving northerly wave to move across
Southwest and down into the Gulf from Wednesday to Wednesday
night. This could help briefly reinvigorate the ongoing gap winds
along the Alaska Peninsula and across Kodiak Island on Wednesday
afternoon. In addition, continued cooler than average low level
temperatures across Southwest could make precipitation type
challenging once again for areas of showers moving through with
the passing trough.

&&

.AVIATION...
PANC...VFR conditions will persist. Gusty northerly winds could
ebb and flow a bit this morning before they increase this
afternoon with daytime heating. Gusts to 25 knots are expected
with the peak in strength this afternoon. Winds should subside
again near or after sunset through early Wednesday.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3...Tue
through Thu)...We are now behind the cold front and will sit in
the middle of a broad, longwave trough through the middle of the
week. Overall this will spell quiet weather for most areas. The
biggest concern will be very gusty outflow winds through many of
the coastal locations. The parent low will take shape in the SE
portion of the trough near Yakutat. As a ridge builds over the
Bering Sea, it will allow for several pieces of energy to dive
from north to south into the base of the trough. In general, this
will favor bringing the strong winds in the gaps oriented in a
north to south fashion. The strongest winds are expected this
morning through Thompson Pass (into Valdez), Kodiak City, and
Seward. They will slowly start to relax this evening through the
overnight. Winds will be much calmer on Wed.

This pattern will not support much in the way of any
precipitation. Weak instability with the passing waves could
trigger a shower or two, especially over the mountains. The only
spot that could see any sustained precipitation and QPF would be
the far eastern Copper River Basin. The airmass will remain
cool with 850 mb temperatures (5000') hovering between 5 to 10C
below zero. However, a decent amount of May sunshine will still be
able to make it through, which will help to moderate any effects
of the cool airmass. The next chance for any real precipitation
will be associated with a wave dropping through the Aleutian Range
towards Kodiak Island Wed afternoon. While most of the low level
moisture will be stripped away by the higher mountains to our west,
we still have elected to increase the PoPs Wed afternoon for
Kodiak.

&&

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

An unsettled but benign pattern will continue across Southwest
Alaska over the next couple of days. The biggest story will be a
shortwave trough moving through tonight and on Wednesday which
will bring precipitation to the area. Rain is more likely across
lower elevations and coastal locations while snow is more likely
across the mountains. Precipitation will then taper off Wednesday
afternoon and dry weather continues through Friday.

&&

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

A fairly quiet weather pattern is expected across the
Bering/Aleutians over the next few days. The biggest story will be
northwesterly gale force gap winds throughout the coastal waters
south of the eastern Aleutians and western Alaska Peninsula. These
gap winds will then ease on Wednesday. Otherwise, winds will
remain below gale force with no high seas expected as high
pressure extends across the area.

&&

.MARINE (Days 3 through 5: Thursday through Saturday)...

Bering Sea and Aleutians: A Central Bering high slips across the
Southern Bering for Saturday. Forecast confidence is good. Gusty
Northerly gap winds along the Pacific side of the Eastern Aleutians
and Alaska Peninsula through Saturday. Seas less than 10 feet.

Gulf of Alaska: A weak low center exits the Southwestern Gulf for
late Thursday. High pressure extends across the Gulf through
early Friday. A low forms over the Kenai Peninsula early Friday
and moves to the Central Gulf for Saturday. Gusty Northwesterly
gap winds along the Pacific side of the Alaska Peninsula through
Saturday. Seas less than 10 feet.

&&

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

Ensemble forecasts are in good agreement that a high amplitude
blocking ridge will remain in place over the central Bering
through the extended time period. Deterministic model guidance
varies considerably with the breakdown of the ridge, but due to
high confidence in ensemble forecasts the long term forecast will
represent that of the blocking ridge pattern. In this pattern the
main features will be the large area of high pressure over most of
the Bering Sea and northwest flow with multiple embedded shortwaves
that will ride over the ridge and over the southern Mainland. For
the Bering Sea and Aleutian Chain, low stratus and fog will be
the main weather feature for the forecast period. Some of this
stratus is likely to move over coastal areas of Southwest, with
slightly clearer skies inland and over northern Bristol Bay where
the Kuskokwim and Ahklun Mountains downslope and dry the airmass.
Two upper level waves are expected to move over southern Alaska
from the northwest to southeast Friday and Monday. The exact
timing remains uncertain, but generally these waves will increase
chances for mid to upper elevation snow and low elevation rain for
most of the southern Mainland Friday and Monday.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning...127 130 131 132 138 150.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AS
SOUTHCENTRAL ALASKA...MSO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ED
MARINE/LONG TERM...KZ/CJ