FXAK68 PAFC 200023
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
423 PM AKDT Mon Aug 19 2019
.ANALYSIS AND UPPER LEVELS...
The weakening omega blocking pattern continues with a ridge
sitting over the east central Bering Sea with troughing over the
mainland and also over the northwest Pacific. Unstable air,
associated with an upper short wave which moved south across the
mainland Sunday, produced an area of thunderstorm over the
Southern Gulf of Alaska this afternoon. Another less potent upper
wave and associated surface front is moving south across western
Alaska. Rain with this system was spreading south across the
Delta. Visible satellite imagery shows a fairly extensive band of
smoke, generally associated with the Swan Lake fire, extending
from the Anchorage Bowl to Kodiak Island. Otherwise, generally
fair skies with cooler temperatures and relatively light winds
extended across Southcentral.
Models overall are in good synoptic agreement. However,
differences on the handling of the low complex moving into the
Gulf Thursday does differ a little. That said, differences do not
produce a significant variation in the wind or precipitation
PANC...MVFR to possibly IFR ceiling/visibilities in smoke are
expected this afternoon/evening. IFR ceilings and visibilities in
smoke likely will settle in by midnight. Ceilings and visibilities
are expected to improve Tuesday afternoon, but confidence in
forecasting the exact conditions is not high. Light winds will
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
Winds are finally starting to relax as the shortwave responsible
continues to weaken as it moves farther south across the central
Gulf. This weakening flow, however, has allowed smoke from
wildfires across the Kenai Peninsula and Susitna Valley to build
across the region, reducing visibility and air quality from the
northern reaches of Kodiak Island north to Talkeetna. As winds
aloft turn more southerly tonight, the smoke around Kodiak Island
will track north and diminish. Farther north, the southerly flow,
coupled with a weak Turnagain Arm wind and developing overnight
inversion will keep smoke trapped over the Anchorage Bowl, where
visibilities may drop as low as one mile. Smoke will linger across
these same regions through Wednesday as the flow remains weak and
a heights aloft build. A front does move into the western Gulf on
Tuesday with a chance of light rain for Kodiak Island. Areas of
light rain will push north toward the Southcentral coast by late
Wednesday. Unfortunately, little, if any, of this rain is expected
to push inland and make much difference for the affected fire
.FIRE WEATHER (SOUTHCENTRAL)...
Very dry conditions will continue across all of Southcentral
through midweek. Minimum RH values will range from 25% to 35%
across valley locations, including areas near active fires.
Surface winds are diminishing this evening and will become light
and variable, and should become more of a diurnal slope/terrain
driven wind through midweek. The exceptions to this will be along
Turnagain Arm and the Knik River Valley where a light SE wind is
expected to kick in this evening and linger through early morning
Tuesday. Overnight temperatures will drop into the mid 30s to
lower 40s with the coldest air over the Copper River Basin. This
will help some with overnight RH recoveries. A weak frontal system
will approach Kodiak Island by Tuesday with precipitation moving
toward the coast by late Wednesday. However, little if any
precipitation is expected to advance inland. Any diurnal shower
activity Tuesday and Wednesday afternoon will be very limited and
mostly confined to terrain.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
High pressure in the Bering will continue to shift to the west,
as a shortwave near the Bering Strait dives southward tonight.
This disturbance will bring cooler conditions and a chance for
precipitation tonight and tomorrow for the Kuskokwim Delta then
reaching the Bristol Bay area by Tuesday.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
There is a mature low with an occluded front south of the Western
Aleutians. The latest ASCAT (Advanced Scatterometer) data has
pinged into gale force winds associated with this low. The models
bring this low north towards Amchitka and a triple point low
develops near Dutch Harbor early Wednesday. Expect gusty winds,
rough seas and precipitation with this storm from Shemya to Sand
Point and into the Western and Central Bering this forecast
.FIRE WEATHER (SOUTHWEST)...
On VIIRS imagery, there is a fire west of Levelock and another
fire west of Port Alsworth. In the past 24 hrs the minimum RH
values across SW AK have ranged from 25-50 percent. There is an
upper level disturbance that is moving across western Alaska that
will dive south bringing clouds and showers to the region. Some
locations may just get a trace although places like Toksook and
Kipnuk can anticipate a wetting rain.
.MARINE (Days 3 through 5: Thursday through Saturday)...
A gale force low centered over the Gulf Thursday afternoon tracks
eastward by Friday evening. Behind that low, there is high
confidence that a disturbance forms south of the Alaska Peninsula
Friday evening, however there is low confidence in the strength
and track of the system at this time. By Saturday afternoon, north
to northwesterly flow will likely create gusty conditions through
the usual gaps and passes along the Alaska Peninsula. Meanwhile,
a ridge of high pressure remains in place over the western Bering
for the weekend.
.LONG TERM FORECAST (Days 4 through 7: Friday through Monday)...
The main feature in the extended forecast includes an upper level
trough in place over much of the state, translating into
unsettled weather. By early Friday morning, a low in the Gulf
continues moving eastward. Behind it, several upper level waves
traverse the southern half of the state, bringing cloudy skies and
precipitation, with northerly flow expected in this pattern.
Meanwhile farther west, a ridge builds over the western Bering for
the weekend. Behind the ridge, a North Pacific low travels south
of the Aleutian Chain, approaching the Gulf of Alaska by late
Monday, though models remain in disagreement on the strength and
timing of this low.
PUBLIC...Dense Smoke Advisory 121.
MARINE...Gale Warning 177.
SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
Back to Main Forecast Discussion Page