Small Craft Advisory 203, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
401 AM AKST Tue Mar 7 2017

.ANALYSIS AND UPPER LEVELS...

The presence of a high-amplitude ridge axis extending north
through the Bering Strait this morning is keeping the main storm
track over the far Western Bering Sea. Dominant north-northwest
flow aloft remains over the state with a closed upper low near
Haida Gwaii anchoring the longwave trough. Out west, there is an
occluded surface low and weakening shortwave trough moving toward
Siberia. This pattern is holding in place a dominant offshore
pressure gradient pattern with local gap winds along the coast and
clear/cool conditions inland. The upper ridge in the Bering Sea
will shift east and strengthen into a closed blocking high heading
into the weekend. This will keep a dry and stable pattern locked
in place for the foreseeable future.

&&

.MODEL DISCUSSION...
No model discrepancies to note. Global models are in excellent
agreement with the large scale pattern and associated sensible
weather heading into next week. The NAM was favored for this
forecast. Confidence is extremely high.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Cold, dry, and breezy conditions will continue through Wednesday
night and beyond as the highly amplified blocking pattern keeps
dry northerly flow entrenched over Southcentral AK. Winds will
then begin to ramp up again later today into Wednesday morning as
the Bering ridge nudges eastward and shifts the upper level jet
eastward over Southcentral. Winds will diminish again beginning
late Wednesday night as the upper level flow weakens.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The upper level omega block continues to dominate the Southwest
Alaska region with sunny skies and offshore northeasterly flow.
This pattern will remain through the week as the upper level ridge
builds into the Kuskokwim Delta extending northward into the
central interior. Look for large diurnal temperature spreads with
sunny skies during the day, and clear skies through the night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The huge omega block over the Bering keeps storms on the periphery
of the Western Aleutians. Therefore, look for light winds over a
majority of Bering with the strongest winds over the Western
Aleutians associated with storms as they track northward into the
Eastern Siberia region through the week. The biggest challenge
will be where to forecast the development of fog as the omega
block continues to build through the Bering.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The high amplitude upper level ridge running across the eastern
half of the Bering and west coast of Alaska by midweek will tilt
east and widen Thursday and Friday expanding across Mainland
Alaska. As the ridge broadens, warmer air aloft will begin
pushing into Southwest Alaska Thursday and Southcentral Alaska
Friday and Saturday. Initially the higher elevations will warm
first, however with the increasing March sun angle, afternoon
high temperatures at lower elevations will begin a trend upward as
well. With the stable conditions underneath the large ridge,
patchy valley fog and low stratus along the coast will be a
concern although somewhat limited due to the prolonged dry spell.
With an anchoring upper low well south of the high, forming a rex
block, the large scale pattern looks quite stable with the high
remaining in place through at least early next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 127 177 178 411.
Heavy Freezing Spray 121 126-130 138 139 141 150 165 414.

&&

SYNOPSIS AND MODEL DISCUSSION...JRA
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...JR