FXAK68 PAFC 260046
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
446 PM AKDT Sun Jun 25 2017
.ANALYSIS AND UPPER LEVELS...
Two potent upper level lows continue to drive much of the dynamics
across Southcentral this morning, with one low centered in the
western Bering, and another low centered in the far eastern Gulf
of Alaska. IR satellite imagery indicates a front draped across
the Alaska Peninsula which is progressing eastward slightly faster
than models have indicated. East of this front a broad shield of
cirrus covers much of Southcentral. While some convection is
already starting to form across the Kuskokwim Valley and into
the Susitna Valley, currently the cirrus seems to be keeping
temperatures cool enough to prohibit too much convective
development. In addition, the sounding this morning indicates
several layers of dry air.
Models are in generally good agreement depicting the eastward
inland propagation of the Gulf low, and the progression of the
Bering low into the eastern Bering over the next several days.
Currently models are indicating that the front approaching the
Gulf of Alaska on Tuesday afternoon will be stronger than
previously indicated. Due to the increased model confidence as
well, winds were trended upward especially in the Gulf of Alaska
PANC...VFR conditions and light winds will persist.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
Widespread high clouds that have moved into Southcentral will help
keep conditions slightly cooler than initially expected this
evening. This will limit the wet thunderstorm potential mainly to
the Susitna Valley, Talkeetna Mountains, and Copper River Basin.
Further south over the Chugach Mountains convection should be weak
enough to produce mainly showers, though there is a slight chance
of a few strikes as far south as northern Kenai Peninsula.
A front approaching the Gulf will then usher in a pattern change
stating Monday, bringing increased moisture and cooler
temperatures - which should persist into mid-week. Most
importantly on Tuesday, the models have come into much better
agreement in the timing of a barrier jet that will develop along
the North Gulf Coast, and as a result winds from Prince William
Sound to Turnagain Arm and West Anchorage were significantly
increased with today's forecast update. This front will be
widespread rains to most areas. For the typical downslope prone
areas such as the Anchorage Bowl, Matanuska Valley, and Copper
River Basin, the only chance of widespread rain from this system
will come Monday night before strong cross barrier flow develops.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
A warm front will move inland tonight, bringing widespread light
rain to the coast with that rain making it into the interior by
Monday afternoon. The strongest southeast winds will occur this
evening along the coast, especially the Kuskokwim Delta, where
gusts close to 40 MPH will be possible. The front will stall and
weaken before the main upper trough supporting the front moves
toward the coast Tuesday morning. This trough will support waves
of moisture moving across the region through Wednesday with
widespread rain and showers. Expect cooler temperatures and rain
chances to continue Wednesday night as the upper trough begins to
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
The low in the Bering will continue to maintain its strength but
slowly meander eastward over the next several days. Its associated
front is fairly potent for this time of year and has been
bringing gusts above 40 mph in areas of channeled terrain such as
Cold Bay. As the front progresses eastward today, it will diminish
in intensity. However, with the low lingering, unsettled weather
is expected to continue over the short-term.
.LONG TERM FORECAST (Days 4 through 7)...
The extended forecast beginning next Thursday is a progressive
pattern with a long wave trough over the Bering and Gulf of Alaska
which continues clouds streaming inland along with higher chances
for rain into the weekend. Models are struggling with the
multiple shortwaves moving through the expansive trough leading
to higher uncertainty through the long range forecast. One of the
main challenges on Thursday into Friday is the development of the
next low in the North Pacific which quickly moves into the southern
Gulf. Models differ with how they build a ridge ahead of this
system over the southern mainland, which has large impacts on the
progression of the Gulf low. Kept the inherited forecast intact
for this package as models still lack consistency from run to run.
There is a better signal over the Bering that the broad trough
remains focused over the central Bering waters while weakening
through the end of the week.
SYNOPSIS AND MODEL DISCUSSION...EN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
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