Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 221242
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
442 AM AKDT Mon May 22 2017

.ANALYSIS AND UPPER LEVELS...
A very dynamic pattern is on deck with broad troughing influencing
much of the region and sustaining two distinct systems. First,
there is a decaying occluded front that has pushed into the Kenai
Peninsula bringing a precipitation shield from Cook Inlet to
Cordova. Second, there is a mature cyclone impacting the western
Aleutians which has strong jet support.

&&

.MODEL DISCUSSION...
Good model consensus for the ensuing 96 hour forecast period as a
series of storms impact the region. The main event will be a
well-organized storm moves across the Aleutians and into
southcentral AK bringing a widespread batch of unsettled weather.
This is a high confidence event. The primary forecast challenge
will most likely prove to be the QPF.

&&

.AVIATION...

PANC...The remnants of a frontal boundary will bring rain and
reduced ceilings to PANC. The primary forecast challenge will be
pin-pointing the timing of the changes in cigs. Winds are
projected to be southerly today.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A brief break from steadier rain today and Tuesday with showers
before rain once again comes back on Wednesday. The previous upper
low is now pushing into the Interior. Lingering cold air aloft,
some clearing of clouds/surface heating today, and convergence
around Turnagain Arm will keep isolated to scattered showers in
the forecast. A weak trough also slides overhead tonight, so
we won`t likely be completely dry, but the widespread rain will be
over. As we lose clouds and wind Tuesday morning, recent low-
level moisture could promote fog development around Cook Inlet.
I`d like to see a bit more ridging aloft and subsidence, but
moisture and slack flow should be enough for patchy stuff.

Tuesday should be mostly dry, but middle and high clouds will
quickly be rolling in ahead of a pattern change for mid-week. A
strong jet stream will punch in from the west, bringing load of
moisture with it. Expect a return of steady rain and even some
wind on Wednesday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The weak frontal system along the coast will continue to shear
apart today as most of the energy from the associated upper level
trough crosses the Alaska Peninsula and tracks away to east
across the Gulf. Showery conditions will continue across Southwest
Alaska this afternoon through tonight as the remnants of the
trough swing across southwest Alaska. The next incoming frontal
system will reach the coast early Tuesday morning followed by
a stronger and rather wet system Tuesday night and Wednesday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The frontal system currently pushing through the western Aleutians
will continue east into the central Bering today and eastern
Bering tonight. A developing wave along the front further to the
south will swing into the central Aleutians tonight, continue
east across the eastern Aleutians and Alaska Peninsula Tuesday and
then cross Bristol Bay Tuesday afternoon and evening. The large
vertically stacked parent low will track across the western Bering
today and tonight, into the northern Bering Tuesday and continue
east to the Y-K Delta through Wednesday night.

&&

.LONG TERM FORECAST (Days 4 through 7)...An amplifying trough
digging through the Bering sea and Aleutian chain will continue to
shift eastward Wednesday morning, with a blocking ridge building
over the Gulf of Alaska slowing the eastward progression of the
trough. This will keep a steady supply of wet and windy conditions
over much of the southern mainland through the end of the week.
Models continue to come into better agreement with bringing this
unseasonably moist airmass (based on forecasted precipitable water
values) to mainland Alaska.

One of the biggest struggles in the extended forecast will be the
timing of when high pressure builds back into the gulf and if/when
showers over the southern Mainland tapper off. Latest model runs
suggest this wet pattern will begin to dissipate during the
Memorial Day weekend, as models remain firm on bringing the ridge
of high pressure over the Northern gulf. However, there still
remains some uncertainty as these models are showing a chance of
some showers making it over the ridge and into the cook inlet
region Sunday. If this ridge builds into the area stronger than
currently progged, there remains some potential to bring warmer
and drier conditions to Southcentral Alaska over the weekend and
into Monday. Given the current model discrepancies, forecast
confidence remains low in a completely warm and dry scenario.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 155 172 174.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...ML
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...TP



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