Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 311256
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
456 AM AKDT TUE MAY 31 2016
.ANALYSIS AND UPPER LEVELS...
Stacked low pressure is centered in the far southern Bering about
150 nm west of Dutch Harbor and has become nearly stationary
overnight. The dominant cut-off high aloft that was over Alaska
this past weekend is now centered over far northeastern Russia and
the Chukchi Sea, with ridging extending southeast through the
Alaska Interior. Between these two features resides deep east to
southeast flow with numerous disturbances moving west to northwest
through the flow. One disturbance that will impact sensible
weather today is located over the northwestern Gulf and is moving
toward the Cook Inlet region towards Southwest Alaska.
Models are generally in good agreement with the transitioning pattern
through the remainder of the week. Not many changes were needed
with the afternoon package; the main adjustments were made for
winds along the front associated with the Aleutian storm system
and to refine precipitation and thunderstorm coverage.
Warm and dry conditions with northeasterly flow will impact the
southern interior today, especially toward the Middle Kuskokwim
Valley and far inland locations of the Kuskokwim Delta, with
winds and humidity remaining just outside critical fire weather
thresholds. Any lightning today will be confined to Southwest
Alaska and will be extremely isolated and most likely confined to
higher elevations toward the Kilbucks and Alaska Range. Gusty
winds will also impact many locations especially toward the
southern coastline, especially through east- west oriented terrain
gaps from Bristol Bay east through the Knik Valley and points
Temperatures warm even more through the mid- to upper 70s and
humidity values begin to approach the 25 percent threshold
Wednesday over the Middle Kuskokwim Valley and inland Kuskokwim
Delta, but winds will be below warning thresholds. Isolated
lightning thunderstorms are possible across the southern interior,
especially toward, but not exclusive of, the mountains.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The upper level high will remain to the north through Wednesday
with low pressure over the Gulf. This will keep most of
south-central Alaska dry through Wednesday morning. An upper
vort-max over the Kenai Peninsula this morning will cross into
southwest Alaska this afternoon. A trailing surface front in the
northern Gulf will continue to move westward today and tonight
into Kodiak Island. The associated surface low will pass south of
Kodiak tonight, after which the surface front will weaken. On
Wednesday night the upper high will push west, leaving
south-central Alaska in a "col". This will allow more shower
coverage on Wednesday afternoon and evening, and the instability
will be high enough for possible thunderstorms over the Copper
River and Susitna River valleys.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 3)...
An upper level wave will cross over the Aleutian/Alaska range
this morning and quickly track through the Southwest Mainland by
this evening while weakening. This wave will coincide with peak
daytime heating, causing showers and isolated thunderstorms to
develop over the Kuskokwim/Kilbuck/Ahklun mountains and the
Western Alaska range this afternoon. These thunderstorms will then
quickly push northwestward over the Kuskokwim Delta and western
portion of the Lower Kuskokwim Valley by the early evening. A
frontal system will also begin to push into the Alaska Peninsula
and Bristol Bay coast today, bringing gusty winds to the Southwest
coast along with a chance of showers to the area.
Showers and thunderstorms will then remain in the forecast into
Thursday as a cold upper level trough dives southward from the
interior through the Kuskokwim Delta and western Lower Kuskokwim
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 3)...
The near stationary low slowly moving into the Eastern Aleutians
will spread Gale force winds and rain into the Eastern Bering and
Pribilofs today before dissipating overnight tonight. This low
will remain nearly stationary through Wednesday, then start
tracking back into the North Pacific Wednesday evening as it
dissipates. This will keep widespread Small Craft winds and a
chance of rain for much of the area through mid-week.
.LONG TERM FORECAST (Days 3 through 7)...
Models are in agreement that Wed night into Thu a front will dive
south to the Alaska range where it slowly dissipates through Fri.
This front will be associated with showers and some thunderstorms
west and south of the Alaska range Wed and Thu afternoons and
evenings. Otherwise showers can be expected over the rest of
mainland Alaska through this period. Persistent north flow across
the Bering will also bring some showers through Thu night. The day
3 forecast utilized the 12z NAM for continuity with the short
Beginning Thu evening the EC and Canadian hemispheric models dissipate
the front along the AIaska and Aleutian ranges. A North Pacific
low begins to weaken as it approaches the Akpen. This feature
continues weakening into a separate low in the northern gulf,
which rapidly dissipates, and another near Cold Bay Sat morning.
The Cold Bay low weakens and is then reabsorbed by a third low
that remains south of the Eastern Aleutians beginning on Sunday.
This pattern will keep showers over mainland AK through the
weekend, with fairly dry conditions across the Aleutians and
Bering. When the low redevelops south of the chain on Sun, the
chance of precipitation will increase across the islands. The
forecast utilized the ensemble approach of WPC guidance which also
included the EC and Canadian models.
MARINE...Gales...120 131 138 165 170 180.
SYNOPSIS AND MODEL DISCUSSION...CC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP