Brisk Wind Advisory 20, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
646 PM AKST Mon Feb 3 2020

.ANALYSIS AND UPPER LEVELS...
The general weather pattern consists of an upper level low over
the Bering Sea and Aleutians, and an upper ridge over northwest
Canada poking into southeast Alaska. Southerly flow aloft is over
most of southern Alaska through the eastern Aleutians. There is
an east to west oriented front over the northern Gulf moving
slowly towards the north. Along this front a surface low is
developing just east of Kodiak Island. Precipitation with this
front is reaching the Kenai Peninsula, and tapering off over
Kodiak. Further west there is a fairly strong surface low (around
964 mb) centered over the central Aleutians. This low is slowly
moving towards the east-northeast. Southerly winds are ahead
(east) of this low, with northwesterly winds behind. This is a
fairly mature system without any well defined fronts, but it is
producing plenty of showers over most of the Bering and Aleutians.

&&

.MODEL DISCUSSION...
Models are reasonable agreement through Wednesday. There are some
differences with the handling of surface lows that develop along
fronts over the Gulf. Generally these differences are along a west
to east axis, and are mostly having an impact on wind directions
over the Gulf. Forecast confidence is near normal.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist through this
evening. Conditions are expected to drop to MVFR around midnight
as some snow arrives at the airport. Visibilities will then drop
to IFR as the snow intensifies. Conditions will then improve
around noon as the snow ends.

&&

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

A weak surface low is currently moving just east of Kodiak
Island. As its associated warm front lifts northward overnight
tonight, widespread light snow (and rain along the immediate
coast near Cordova) will develop across much of Southcentral and
persist through late Tuesday morning. Highest snowfall totals of
up to 6 inches are expected east of and including Prince William
Sound, with slightly lesser amounts farther west. Around 1 to 2
inches are likely for Anchorage and the Mat-Su, which will likely
lead to slick roads for the morning commute. After a brief break
Tuesday afternoon through Wednesday morning, a similar synoptic
setup will occur by the afternoon as an upper level shortwave
trough and associated surface low develops near Kodiak. This low
track will be slightly farther east than today's low, thus
Anchorage will be initially downsloped from any precipitation.
However, once the low weakens and moves over Prince William Sound,
snow is likely to develop over the city and the system will overall
bring similar snowfall/rain across the region through Thursday
morning.

These systems will bring the warmest temperatures seen across
Southcentral in over a month. Areas along the immediate coast (as
well as Kodiak) will see highs warm to near 40 this week, while
the Anchorage and the Matanuska Valley will rise to near freezing
by mid-week and slightly above freezing by late-week.

&&

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

Synoptic flow is shifting from southerly to southwesterly over the
Mainland, cutting off warm air advection and causing temperatures
to cool slightly. Precipitation is also transitioning to a more
showery setup. Tuesday and Wednesday look to be a generally
showery pattern as several shortwaves ejected from the Bering low
track northeastward over Southwest. Expect a distinct cooling
trend Wednesday into Thursday as the Bering low exits to the north
and cold flow on its backside encroaches on the Southwest Mainland.
Late Wednesday into Thursday also look to be the driest period in
the short-term.

&&

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

A 960 mb low just south of Adak is gradually filling and shifting
northeastward. Meanwhile, a secondary low is forming in the
central Bering. Widespread cyclonic flow and areas of small craft
advisory level winds and seas will persist over the Bering and
Aleutians Tuesday. Looking upstream, a deepening low near the
Kuril Islands (Japan) can be seen on satellite... it will approach
the western Aleutians Tuesday night into Wednesday. While storm
force winds will likely develop in the periphery of this low, the
track looks to be far enough south that winds over the Aleutians
will peak at gale force. In any case, expect convective
precipitation over the Aleutians and Bering Wednesday into
Thursday with this system.

&&

.MARINE (Days 3 through 5: Thursday through Saturday)...

Gulf of Alaska:

Thursday and Friday are both looking quiet across the Gulf. A
front moves into the western Gulf Friday night, which could
produce south to southwesterly gales across the western Gulf
through the day. The front weakens by Saturday evening, ending the
gale threat.

Bering Sea/Aleutians:

Thursday will be the quiet day across the Bering, with the only
threat of gales being over the far western Bering and Aleutians
late in the day. The gales rapidly increase in coverage Thursday
night with gales overspreading much of the western and central
Bering and Aleutians by Friday morning. After that, model
agreement rapidly diminishes, which in turn casts large
uncertainty on where and how strong the winds and seas get. It's
safe to say that nearly the entire Bering and Aleutians has some
threat for at least gales through Friday night, with areas of
storms possible. As the winds consolidate into one low on
Saturday, the area of gales should diminish, such that it's no
longer the entire basin threatened. However, once again, with such
high uncertainty as to where the low causing the winds will be, it
would not be prudent to guess where the gales are expected on
Saturday.

&&

.LONG TERM FORECAST (Days 3 through 7: Thursday through Monday)...

Normal to above normal temperatures, unsettled conditions,
plentiful cloud cover, and a mix of rain and snow appears to be a
satisfactory summary of the long-term forecast through the end of
this week into this weekend. Model disagreement increases rapidly
by Friday, but the overall pattern will remain active. A low
centered near Unimak Island Thursday morning slowly drifts to near
Bristol Bay late Thursday night. This will bring another round of
precipitation to much of Southwest Alaska Thursday night into
Friday. By the time the low dissipates Friday evening, another
strong low or front will be moving into Southwest Alaska Friday
night. It's at this point that the models all go their separate
ways regarding where the low over the Bering tracks, and by
extension, where the greatest impacts are felt. Saturday will be
very wet (and in some areas, see frozen precipitation) over all of
Southwest Alaska, which will then move into Southcentral for the
second half of the day. The weather turns drier, but with some
shower activity along the mountains for Sunday, as the strong
systems shift to the western Bering. Meanwhile, high pressure
strengthens and builds over the north Pacific and western Gulf by
Monday.

For Southcentral, much of the precipitation that is expected over
the long-term forecast period will be what's left over from
systems that hit Southwest Alaska first, then move over
Southcentral. Thus, nothing stands out as being particularly
strong or causing significant impacts to Southcentral through the
extended period. As alluded to above, a continuation of above
normal temperatures (that will begin in the next day or 2)
appears to be a near certainty throughout the extended. Despite
significant model uncertainty on systems out west, by the time
they reach Southcentral, the uncertainty diminishes, especially
regarding potential impacts. Chances for precipitation appear
greatest on Friday, with greater certainty for everywhere except
the typical downslope areas on Saturday. That said, those
downslope areas, especially along Turnagain Arm, could potentially
see some high wind threats on Saturday. If the Turnagain Arm wind
gets into Anchorage on Saturday, that appears to be the most
likely day for temperatures to rise into the 40s. Drier weather
appears likely for Sunday and Monday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 119 120 130 131 139 178 185.
         Heavy Freezing Spray 185.
FIRE WEATHER...NONE.

&&

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