Gale Warning 363, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
515 AM AKDT Sun May 10 2020

.ANALYSIS AND UPPER LEVELS...

The upper level weather pattern has become much simpler over
Alaska this morning. A large upper level high and associated
ridging persists over western North America and along the Alaska
Canada border. Shortwave ridging extends into Southcentral as an
extension of the upper level high centered over the northern
Yukon. A southeast to northwest oriented jet streak extends over
the Gulf, across the Kenai Peninsula and into the Lower Kuskokwim
Valley. A large upper level trough and low, centered along the
Pacific coast of the Kamchatka Peninsula, extends over the western
Bering this morning. Southerly flow persists over the whole of
the Bering in between these features.

Warming temperatures associated with the ridging have spiked mid-
level temperatures to between 6 and 8 Celsius over nearly all of
Southcentral, while relatively cold air persists over the western
Bering. Partly to mostly cloudy skies are over much of southern
mainland Alaska. The cloud cover, even if broken, combined with
the warm air largely remaining in place, especially over
Southcentral, are tempering nighttime cooling this morning. Most
areas are in the 40s and 50s.

&&

.MODEL DISCUSSION...

The large scale synoptic weather pattern remains in good agreement
among the models. Thus, forecast confidence remains high. By late
Monday night, a few minor discrepancies in the track and strength
of the Western Aleutians low begin to emerge, though with very
little impact. A few challenges: An upper level disturbance will
move northwestward out of the Gulf and into Southwest Alaska
Monday afternoon. The models are very different as to how strong
this wave will be, which in turn will impact how much rain (and
thunderstorm potential there will be across portions of the area).
The Canadian is the strongest model making a closed low by Monday
evening, with the best chances of thunderstorms along the
Kuskokwim Mountains. The EC is the next strongest, but keeps the
upper wave open, though quite distinct. The GFS is next, followed
by the NAM which is weakest and only forecasts a few showers here
and there. Area-wide, temperatures will be a challenge, as they
will be largely dependent on the amount of cloud cover. The more
sunshine, the warmer the temperatures.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. A westerly sea
breeze may move into the airport late this morning into this
evening.

&&

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

Another warm and generally dry day is expected across inland
areas of Southcentral from the Anchorage Bowl north. A
strengthening interior thermal trough combined with generally fair
skies will allow for afternoon temperatures to rise into the mid
60s to mid 70s, warmest over the Copper River Basin and portions
of the Susitna Valley. A weather front moving slowly north will
bring clouds along with and cooler temperatures to the Kenai
Peninsula today along with chances of rain along its southern
coast. The weather front continues to drift north tonight and
Monday bringing cloudier conditions with and chances of
rain/showers and cooler temperatures to Southcentral. The
exception will be the Copper River Basin where warm and dry
conditions will continue with the potential for convection along
the mountains during the afternoon and evening hours. Winds will
be generally light overall inland with sea breezes along the
coasts through Monday.

&&

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

The main story in the short term will be a an upper level easterly
wave moving westward across the Alaska Range into the Bristol Bay
region and then continuing northwestward across the Kuskokwim
Coast. As a result, raised pops in a narrow swath to likely to
account for this wave moving through this morning into this
afternoon. Mainly dry conditions will be expected for late Sunday
afternoon into Sunday night as the region remains in zonal flow
before the upper level shortwave trough approaches.

The next upper level shortwave will be more robust than the first
and further north as well. This places the northern Bristol Bay
region as well as the Lower Kuskokwim Valley over to the Kilbuck
mountains in the path of this next system. Due to an easterly flow
aloft, we expect some downsloping on the west side of the
mountains for the Bethel area to Hooper Bay, though a few rain
showers cannot be ruled out. As a result, pops were increased
across these regions with likely introduced along the Kilbucks
and Lower Kuskokwim Valley. There is a very slim chance of a
possible rumble of thunder or one or two lightning strikes mainly
along the Kilbuck mountain range. Instability is low but still
enough to put isolated thunderstorms into the forecast. With the
amount of daylight this time of the year and a robust shortwave
moving through, the risk is there that enough instability may
develop. Cloud cover will also be key as if the clouds move in
early enough, then just rain showers will be expected as not
enough instability will be able to develop. Heaviest rainfall
amounts will be along the Kilbuck mountains and the Aniak area
with less from Lime Village east to the Alaska Range due to the
downslope component.

&&

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

The front associated with a strong area of low pressure over the
Sea of Okhotsk will continue to slowly move eastward into the
central Bering through Monday morning before stalling and
gradually weakening through Monday night. This front will get
caught up in between an upper level shortwave moving across
Southwest Alaska and another low pressure system driving north
from the North Pacific. The main change for the Bering and
Aleutians was to increase winds to introduce some gale force winds
especially along the northeast side of this low pressure system.
The NAM/GEM regional and GFS all show gale force winds through
the boundary layer. Due to some mixing that may occur and the gale
force winds not far above the surface, some of these winds may
mix down to the surface, especially in rain shower activity.

&&

.MARINE (Days 3-5 Tuesday through Thursday)...
The general pattern through the middle of next week will consist
of low pressure over the Bering Sea and Aleutians, and high
pressure over mainland Alaska and the Gulf. Winds are expected to
stay below gale force, with small craft advisory winds limited to
the Aleutians and Bering Sea.

&&

.LONG TERM FORECAST (Days 4 through 7 Wednesday through Saturday)...
On Wednesday there will be a ridge over eastern Alaska, with a
trough over the Bering Sea and Aleutians. The pattern will have a
negative tilt, with the interface between the ridge and trough
roughly over southwest Alaska. The pattern will slowly shift
through the end of next week, with the ridge retrograding (moving
west) into the Bering and trough sliding eastward into the
southern Gulf. This will leave room for a trough over northern
Canada to slip into mainland Alaska. There are considerable
differences in how the models handle this Canadian low, so
forecast uncertainty increases towards next weekend. In general,
conditions over southern Alaska will be fairly dry and warm.
Increasing chances of precipitation moving from east to west are
possible Friday into Saturday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Warning: 155.
		 Flood Advisory: 155.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JPW
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MV
MARINE/LONG TERM...BL