Area Forecast Discussion
Issued by NWS Anchorage, AK

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672
FXAK68 PAFC 221721 CCA
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
521 AM AKST Fri Feb 22 2019

.ANALYSIS AND UPPER LEVELS...

The main feature to note is a ridge that spreads from the Bering
Sea to the western Gulf of Alaska. At the mid-levels cold air is
advecting over the mainland around the ridge. With this cold air
advection, northerly offshore flow dominates mainland Alaska. To
the west of the ridge, southerly flow is pushing warm, moist air
over the western Aleutians. At the surface, an occluded front is
finishing its progression through the Gulf and intensifying the
offshore flow through Southcentral. The offshore flow is enhancing
gusty conditions through Thompson Pass, Prince William Sound and
the western Gulf. A nearly stationary surface high pressure ridge
is keeping much of Southcentral clear and dry. To the west of the
ridge however, a large swath of clouds can be observed in
satellite imagery over the western Aleutians. This region is
associated with the remnants of a strong low that progressed
through the Bering yesterday. Gusty conditions persist through
the Bering and western Aleutians. The next Bering storm is
advancing from the North Pacific towards the central Aleutians
today.

&&

.MODEL DISCUSSION...

Numerical models are in good agreement through Saturday. At that
point, models begin to diverge as a North Pacific low moves
into the southern Bering on Saturday morning. At this point, the
American models are moving faster while the ECMWF and Canadian
trail behind through Saturday morning. By Saturday afternoon, the
models diverge further with a large spread between the solutions.
The American solutions, once again, are producing stronger winds
through Sunday while the EC and Canadian, while fairly strong
themselves, are depicting this storm slightly weaker.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist as high
pressure builds through the area. The chance of fog becomes higher
Friday evening. Clear skies through the day, temperature drops
overnight and calming winds will aid in the fog formation.

&&

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

Outflow winds will slowly diminish across the eastern Kenai
Peninsula and North Gulf Coast through this afternoon. Although
considerably weaker, high pressure and cold air inland will
sustain outflow winds across the North Gulf Coast. Stratus and
fog become the main weather challenge tonight through Saturday
night as the upper ridge builds over Southcentral. Fog will likely
develop over interior valleys, along Cook Inlet, and across Knik
and Turnagain Arm during the overnight hours and could persist
into the late morning to early afternoon hours. Otherwise,
generally fair skies and cooler temperatures are expected over the
next couple of days.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2...Friday
through Saturday night)...

A front associated with a departing low moving over Siberia will
continue to bring scattered snow showers to coastal areas along
the Kuskokwim Delta through the morning. Meanwhile, a ridge
building over the Gulf will favorably influence conditions across
the AKPEN and areas further inland through this evening. This will
allow for generally quiet conditions and mostly clear skies,
though areas of patchy fog are likely for low lying areas across
Bristol Bay and the lower Kuskokwim Valley.

A second North Pacific low moves into the Bering this evening
bringing a large area of moist southerly flow to the eastern
Bering. This front will slowly push eastward over Southwest for
Saturday morning, bringing precipitation across the area for
Saturday evening. Temperatures will be warm enough for rain across
the AKPEN while a rain/snow mix or wet snow will be possible
along the northern Kuskokwim Delta coast.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2...Friday
through Saturday night)...

A departing low continues to influence the Bering with a lingering
occluded front oriented north to south over the Pribilofs. This
front continues to advect warm southerly flow over the southern
Bering. In its wake, a second low forms along a fertile
baroclinic zone in the North Pacific. This second gale force low
will move over the western Aleutians this afternoon, continuing to
advect warm southerly flow and moisture across the Bering. By
Saturday morning, the low moves northward and is centered
northwest of Saint Paul Island. Southerly gales persist,
continuing the stream of warm moist air into the eastern Bering.
As the low lifts northward out of the Bering Sat evening, its
associated front pushes eastward. Meanwhile, cold air moves in
over the western Bering as a weak ridge attempts to build over the
central Aleutians. This attempt is quickly stifled by an incoming
storm force low, bound for the western Aleutians for Sunday.

&&

.MARINE (Days 3 through 5)...
Once again, the main area of active weather with strong wind will
be over the Bering Sea Sunday through Tuesday. Sunday begins with
a ridge extending across the eastern Bering Sea with a large
strong storm crossing the western Aleutians. This storm should
pack storm force winds in advance of it with the potential for a
brief period of hurricane force winds possible in the central to
western Aleutians as well as the western Bering Sea offshore
zones. By monday the low weakens but we should still see some
storm force winds close in to the low over the Central Bering Sea
with gales across much of the eastern Bering Sea to the southwest
coast. By Tuesday, this storm continues its northward trek as yet
another gale to storm force low crosses the western and central
Aleutians.

Meanwhile the Gulf of Alaska remains under high pressure and we
are not anticipating any significant wind for the Gulf region
Sunday through Tuesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
For the extended period, Sunday through Saturday, high pressure
over the Gulf of Alaska and southern mainland will result in
benign conditions for the southern mainland. The large upper level
high will likely lead to the development of inversions through
Southcentral and may result in more foggy conditions. Also, we
are expecting very warm 850 mb (~5000 ft) temperatures over the
southern mainland that could result in some unseasonably warm
temperatures along with large diurnal fluctuations for areas that
aren`t trapped under an inversion. The southwest mainland will
see temperatures running 10 to 20 degrees above normal with
persistent southwesterly flow through the week.

Out west, we have a very active pattern on tap for next week. We
start off with a strong storm to hurricane force low over the
western Bering and western Aleutians that treks north across the
Bering as a ridge over the eastern Bering gets pushed east over the
mainland. After this low moves out of the Bering, another strong
storm force low is on tap for the western and central Aleutians. By
the later half of the week the lows are a bit weaker as they trek
across the Aleutians and Bering Sea. A weak ridge pokes up across
the central Aleutians to the eastern Bering Sea Friday. Lastly,
another storm force low will impact the western Aleutians and
western Bering Sea Saturday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 131.
MARINE...Gales: 121 127 128 130 131 150 155 165 170 172-177 179
                180 181 185 411-414.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...RJA
SOUTHCENTRAL ALASKA...RC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK/KO
MARINE/LONG TERM...SA/KVP



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