Gale Warning 393, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
541 AM AKDT Sun Aug 18 2019

.ANALYSIS AND UPPER LEVELS...

An upper level jet extends from Siberia across the Bering Sea and
southward over western Alaska. The corresponding broad 500mb low
continues to spin in the eastern Bering, centered near St. Paul
Island. This is leading to strong surface high pressure and
present wide spread low stratus/fog over a large portion of the
Bering and Aleutians. Another upper level low south of Kamchatka
is bringing gusty southerly winds and moderate rain to the western
Aleutians. Looking upstream, a deep upper trough extends across
western Canada through the Alaska Panhandle. Thus, a strong upper
level northerly flow exists over Southcentral as was the case last
night. Strong winds are still occurring across channeled areas in
and around Valdez and Prince William Sound.

&&

.MODEL DISCUSSION...

Models remain in good agreement, particularly regarding the
shortwave through moving over the Anchorage area today. As
previously discussed, localized winds present the greatest
challenge as speed and direction could change frequently.

&&

.AVIATION...

PANC 12z...Gusty NNE winds will persist through the morning and
are expected to peak this afternoon, before diminishing in the
evening. Visibility will be highly dependent on smoke production
from fires to the north. Smoke is expected to persist over
Anchorage through the TAF period, though the aforementioned gusty
winds should lead to mostly VFR conditions. MVFR conditions are
possible this evening as winds diminish.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Another day of plenty of sunshine and gusty winds is in store. The
dry cold front that came through on Sat has now cleared through
the Gulf of AK. Due to the new fire starts in the Susitna Valley
and the reinvigoration of Swan Lake, we have introduced some
smoke back into the forecast. The next trailing shortwave is
moving over the AK Range this morning. It will dive through the
area quickly this morning and clear the coastline by this evening.
As it passes by, it will once again stir up gusty winds and help
to mix down some very dry air. The winds will favor NE to SW
oriented valleys such as the Matanuska and Thompson Pass down
through Valdez. Those planning any sort of outdoor burning
activities should continue to follow burn ban notices and use
extreme caution even outside of burn ban areas.

As we go into Sun night to Mon morning, we will start to see some
reprieve from this pattern. Colder air will truly filter in with
850 mb (5000') dropping to the 0C to 2C range. Winds will also
subside overnight and this should allow that colder air to be
realized at the surface with minimum temperatures Mon morning in
the 30s over the Copper River Basin and the 40s for most other
interior locations. Monday will still feature plenty of sunshine,
but the winds will be much calmer across the area. A chance of
some very light rain could possibly sneak into Southcentral
courtesy of a system over Shelikof Strait by late Tue.

&&

.FIRE WEATHER...A secondary dry cold front moving through will
keep conditions near critical values in many locations again
today. Due to strong winds overnight, many places did not see much
at all in the way of RH recoveries to start Sun morning. By mid
to late morning, this second front will drop through reinforcing
the gusty winds. With good vertical mixing, this will only serve
to exacerbate the very dry conditions already present.
Temperatures should be a few degrees cooler yet again today.
Finally by tonight, winds will begin to die down, especially for
the lower elevations. This should allow temperatures to cool
markedly as a colder air mass settles in. RH recoveries will be
good in the valleys, but could still be relatively poor over the
ridgetops above the inversion.

&&

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

Today will be another warm, dry day with moderate offshore winds
that are gusty at times. The Ethel Creek fire roughly 40 miles
northeast of Koliganek and the Pete Andrews Creek fire roughly 10
miles west of Iliamna remain active and continue to bring smoke
and haze to the Greater Bristol Bay area. Expect cooler conditions
Monday, as a low dives south from the Bering Strait. Showers are
likely along and behind the associated cold front, initially in
the Kuskokwim Delta Monday, then into the Bristol Bay area
Tuesday.

&&

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

Widespread patchy fog persists over the Bering under a strong
upper high. A front bringing small craft advisory conditions and
precipitation to the western Aleutians will dissipate today, but
a stronger low will approach Monday into Tuesday, bringing a
return to strong winds and high seas with possible gales in the
western Aleutians. The associated front will bring another round
of precipitation to the western and central Aleutians.

&&

.MARINE (Days 3 through 5: Tuesday through Thursday)...
On Tuesday...a ridge extending across the Gulf keeps relatively
weather quiet through Wednesday while low pressure over the
western Bering brings active weather. This low to the west will
bring small craft to gale winds before tapering off significantly
late Wednesday night. There is high uncertainty heading into
Thursday, but the main focus will be around low pressure
developing across the Gulf which may bring Gale force winds.

&&

.LONG TERM FORECAST (Days 4 through 7: Wednesday through
Saturday)...
The forecast beginning next Wednesday starts out active with
energy merging together from low pressure over the Southwest and
shortwaves racing across the Aleutians to Alaska Peninsula. The
overall pattern is expected to remain drier and warmer than normal
across the southern mainland as low pressure generally tracks
south of the mainland through the end of the week. A new ridge
developing across the North Pacific builds toward the western
Bering Thursday into Friday. Models are struggling with handling
low pressure which moves to the gulf during this time period;
however, they are in relatively good agreement with the ridge. The
inherited grids were kept for today's package due to the
uncertainty on the track of low pressure mid week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AP
SOUTHCENTRAL ALASKA...MSO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MM
MARINE/LONG TERM...KH