NWS Anchorage, AK wrote its last area forecast discussion before the first event at Nov 4, 6:59 PM AKST, 5 hours 41 minutes earlier.
Area forecast discussion, Nov 4, 6:59 PM AKST, 5 hours 41 minutes before
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
659 PM AKST Mon Nov 4 2019
.ANALYSIS AND UPPER LEVELS...
A weak front is stretched out across the Northern Gulf of AK while
quiet weather persists over much of the mainland. Two weak areas
of high pressure are transiting the region trying to usher in some
colder air. The first is over the Kamchatka Peninsula and the
other is along the ALCAN border. This has allowed temperatures to
cool to some of their coldest readings of the year so far with
single digits reported across much of the Interior of SW AK.
However, some warm air continues to flow over this cold layer at
about 1,000' as is evidenced by the 12z Bethel and King Salmon
upper air soundings. This will present significant concerns with
the forecast.
The front across the Gulf is waning but continues to bring warm
air over top of a cool surface in Southcentral AK. The result is
some low stratus hanging on around the Cook Inlet with continued
patchy dense fog across parts of the Matanuska Valley and the
Copper River Basin. High clouds associated with the front are
keeping this low level moisture from dissipating. Some light rain
is making it into Kodiak Island and parts of the coastline
courtesy of the front. However, with a weak offshore gradient,
just about all inland locations remain dry.
&&
.MODEL DISCUSSION...Models remain in very good agreement with the
overall synoptic pattern. This is resulting in high forecast
confidence. The few areas of concern remain the track of the
developing surface low north of the Alaska Peninsula and exactly
what type of precipitation will fall and where over parts of SW AK
later tonight and through Tue. All signs continue to point
to a prolonged period of freezing rain for the Kuskokwim Delta
and portions of the Kuskokwim Valley. The forecast for this area
was mostly adjusted through hand edits.
&&
.AVIATION...
PANC...VFR conditions and light northerly winds will persist.
Ceilings should slowly lower Tue morning as a front moves over
the Gulf Coast and brings the chance for some light rain.
&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Wednesday)...
Fog is expected to continue through this evening in the Palmer
area. There is a high amount of uncertainty thereafter with
regards to how long the fog will persist, however if winds remain
calm, it could last through the entirety of Tuesday morning.
Patchy fog is also possible in the Copper River Basin as the
overall large scale pattern is similar to yesterday.
High pressure over the Yukon Territory and a front over the Gulf
will lead to potentially gusty northeasterly winds in terrain gaps
across Southcentral through Tuesday morning. The associated
pressure gradient will gradually weaken by the afternoon as the
aforementioned front tracks northward, at which time rain is
expected to begin along Prince William Sound and the western
Kenai. As temperature cool overnight ahead of the front, higher
elevation snow is likely north of Valdez and in the windward side
of the Chugach Mountains. Precipitation will continue to move
north on Wednesday. Accumulating snow is likely along portions of
the Denali and Richardson Highways in the Paxson area. Anchorage
and the Mat-Su are expected to remained mostly dry given the
easterly surface flow.
&&
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
As the warm front lifts north over Southwest Alaska, the biggest
forecast challenge continues to be precipitation type. A few
locations saw a brief period of snow as the front initially made
it into interior Bristol Bay, but quickly transitioned over to
rain, which will continue as warm air moves in with this system.
The main focus of the forecast is when this front moves into the
Kuskokwim Delta and Valley tonight through Wednesday morning. On
the front edge of this system, there could be some snow with
little accumulation, if any. The main impact will be the freezing
rain expected with this system as the warm air moves in over the
below freezing surface temperatures. This event is expected to
have a longer duration due to the north-northeasterly winds
bringing more cold air into the region.
Winter Storm Warnings are in effect for the Kuskokwim Delta and
Valley. Areas along the coast are expected to see the highest ice
accumulations (around a half inch or higher), since this is where
the heaviest precipitation will occur. The Kuskokwim Delta could
see up to a half of inch of ice accumulation, including the Bethel
area, which could affect travel conditions and cause power
outages. The Kuskokwim Valley will be on the northern edge of the
precipitation shield and warmer air. Thus, expect less ice
accumulation (two to four tenths of an inch), with potential for
some minor snow accumulation as well.
By Wednesday, a showery pattern will remain across the Southwest
as the front weakens. Any new precipitation should fall as rain
for most areas as the temperatures warm above freezing across most
of the region.
&&
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A strong front, associated with a Kamchatka low, over the western
Aleutians and Bering will bring a brief period of gale-to-storm
force winds through Wednesday morning as it moves out of the area.
By Wednesday afternoon, a ridge will build in over the western
Aleutians. Small craft winds across the central Aleutians this
evening, associated with a North Pacific low lifting towards
Southwest Alaska, will weaken through Wednesday morning. An upper
level love near Nunivak Island will help keep north to easterly
small craft winds across the eastern Bering through Wednesday
afternoon.
&&
.MARINE (Days 3 through 5: Thursday through Saturday)...
Gulf of Alaska: Lingering easterly small-craft winds remain
likely into Thursday across the Barren Islands and Shelikof
Strait. Easterly gales are possible across the northern Gulf and
Southcentral Coast late Friday into Saturday as low pressure lifts
north into the Gulf of Alaska.
Bering Sea: Winds are expected to stay below gales through Friday
across the Bering Sea and Aleutians with only areas of small-
craft advisory winds circulating around a low in the central
Bering. By saturday, a low tracking into the western Bering may
bring southerly gales along a front to the western and central
Aleutians. Confidence in this solution, however, is low given
significant model disagreement with timing and position of the
low.
&&
.LONG TERM FORECAST (Days 3 through 7: Thursday through Monday)...
There is still a quite a bit of model uncertainty moving from the
end of the week through the weekend. For Thursday. a decaying,
vertically-stacked low in the Bering will keep conditions
relatively warm and unstable from the Gulf over to Southwest
Alaska and across much of the southern Bering. On Friday,
conditions look to improve slightly as a ridge over the interior
initiates a clearing and drying offshore flow across much of the
southern mainland. This is expected to be short-lived, however,
especially for Southcentral, as a series of shortwaves lifts north
into the Gulf of Alaska beginning late Friday through Monday.
These features will allow a moist, southerly flow to persist with
periods of rain and high elevations snow across the Southcentral
mainland, especially along the coast.
For the southwest, the aforementioned ridge may hold on a bit
longer, keeping conditions relatively cold and dry into Saturday.
However, a series of troughs looks to impact this region by
Sunday with a switch to a more southerly flow, a slight warming
trend, and increasing chances for rain/snow showers Sunday into
Monday, mainly across the Bristol Bay region.
&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning 152 155.
MARINE...Storm Warning 178.
Gale Warning 127 130 131 138 172 174.
FIRE WEATHER...NONE.
&&
SYNOPSIS AND MODEL DISCUSSION...MO
SOUTHCENTRAL ALASKA...AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...JW