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Area Forecast Discussion (AFD)

Issued by Anchorage, AK (AFC)

                            
000
FXAK68 PAFC 180018
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
418 PM AKDT Sat Aug 17 2019

.ANALYSIS AND UPPER LEVELS...
An anomalously strong upper level ridge remains parked over the 
Bering Sea. A strong short-wave dove southward across the southern
mainland overnight through this morning and is now continuing
southward across the Gulf of Alaska and Southeast Alaska. The
passage of this short-wave combined with a low level cold front
has led to strong gusty northerly winds across much of the region.
As is typical, the strongest gusts are being observed through
mountain passes/gaps and along coastal bays. This includes Cook
Inlet, Seward/Resurrection Bay, and from Valdez down into Prince 
William Sound. Valdez airport reported a very impressive peak wind
of 66 mph this morning. While the air mass is cooling, night-time
temperatures remained elevated due to the arrival of winds, so
high temperatures today won't be much cooler than yesterday.
However, it is noticeably drier and the air may have a bit of a
"fall-like" feel to it. 

The Bering Sea and Aleutians are mostly quiet under the influence
of the ridge. Areas of fog and stratus off of the Southwest Alaska
coast are rotating westward across the eastern Bering and along
the north side of the Alaska Peninsula. A weak front strung out
along the west die of the ridge is bringing areas of rain and
small craft winds to the western Aleutians.

&&

.MODEL DISCUSSION...
Models are in good agreement with handling of large scale 
features over the next few days and forecast confidence is above 
average. The biggest challenge in the short-term will be details 
of the wind forecast as winds fluctuate due to diurnal and upper 
level forcing influences. 

&&

.AVIATION...
PANC...VFR conditions will persist. The wind forecast is quite
challenging. Would expect some decoupling of the surface from the
boundary layer as we lose sunlight and surface temperatures begin
to cool this evening. This will cause winds to trend downward, but
based on the location of the airport right near Cook Inlet, do not
think they will completely decouple and go light. In any case,
northerly winds will then strengthen around noon in response to 
passage of another upper level short-wave.

&&

.FIRE WEATHER...
Winds will slacken a bit tonight with the loss of daytime heating.
However, expect will keep a little bit of wind in most areas.
Thus, RHs will struggle to recover overnight, and where they do it
will likely be for a short period of time. A second short-wave
moving through Sunday morning will help restrengthen winds and
cause RHs to drop back down. Winds will finally lighten up Sunday
night and temperatures will cool quite a bit (with 850
temperatures in the -2 to +2 degrees C range), allowing RHs to 
fully recover.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
With high pressure to the west and low pressure to the east,
northerly winds continue to dominate Southcentral Alaska. A strong
shortwave pushing through the area this morning brought gusty
winds throughout the area. As that shortwave has tracked south of
the area winds will diminish somewhat overnight tonight. On Sunday
another shortwave will move through from north to south ramping 
up the northerly winds again. Winds will diminish Sunday night 
leaving light winds and dry conditions into Tuesday. This setup 
will also allow cooler air to move in over the area. This will 
allow temperatures to drop back closer to normal values for Sunday
through Tuesday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
Strong upper level ridging over the eastern Bering combined with 
breezy north to northeasterly offshore flow will continue to bring
warm weather and mostly sunny skies to Southwest Alaska through 
the weekend. An upper level trough over the Bering Strait Monday 
morning will dig south to the Kuskokwim Delta through Monday 
evening. The trough will then continue slowly south Monday night 
forming into a cutoff upper low centered over northern Bristol Bay
Tuesday. 

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
Upper level ridging over the eastern Bering will shift gradually 
to the north and west through Sunday pushing the frontal system 
currently stretched over the western Aleutians into the North 
Pacific. Upper level ridging will persist over the Bering through 
Monday and then weaken and shift further to the northwest Monday 
night and Tuesday. A frontal system associated with a large 
vertically stacked upper low south of the western Aleutians will 
remain in the North Pacific through Monday and then send a 
weakening frontal system up over the western and central Aleutians
Tuesday.

&&

.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...Gale Warning 127.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
MARINE/LONG TERM...KH