Area Forecast Discussion
Issued by NWS Anchorage, AK

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235
FXAK68 PAFC 300652 CCA
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
1052 PM AKDT Wed Mar 29 2017

Corrected Aviation Section

.ANALYSIS AND UPPER LEVELS...
A large multi-centered upper level low is centered over western
Alaska with a strong negatively tilted trough extending
east-southeast across Cook Inlet and the Kenai Peninsula and into
the northern Gulf of Alaska. The remnants of a surface low in
western Prince William Sound is headed inland across south central
Alaska this morning. Snow intensity has diminished from early
this morning, but areas of snow continue to fall out ahead of the
trough axis from Anchorage north to the Mat-Su. A wave moving
through the base of the trough has led to a development of another
surface low over the central Gulf of Alaska. This low is tracking
toward the North Gulf Coast to the east of Cordova and will help
keep showers going from Cordova to Valdez.

Meanwhile, an even larger complex low south of the Aleutians is
tracking northeast, with the leading occluded front spreading out
toward the eastern Aleutians and the Alaska Peninsula. The main
impact at this point is increasing pressure gradients and winds.
Otherwise, dry weather continues today across most of the Bering
Sea region on up to southwest Alaska.

&&

.MODEL DISCUSSION...
There are some minor timing differences with the upper trough
lifting north across south central Alaska tonight. Based on the
latest satellite and radar trends we prefer the slower timing
which will allow snow to linger a little longer over interior
south central Alaska. No model really picked up very well on the
well defined low approaching the Cordova area, so we will have to
adjust wind and precipitation forecast to account for this.

Models remain in good agreement with handling of the system over
the north Pacific. With fairly deep arctic air out ahead of this
system we prefer the stronger solutions for winds out ahead of
the occluded front as per the 12z GFS. Otherwise, the primary
forecast challenge with this system will be determining
temperatures and precipitation type as much warmer air advects
north to Bristol Bay and all of south central Alaska on
Friday and Friday Night. Overall forecast confidence is above
average

&&

.AVIATION...
PANC...Periods of snow will persist until the upper trough moves
through later this evening. Confidence in ceiling/vis during this
time is low, as it may vary quite a bit as areas of snow move
through the area. In any case, do expect a general improving
trend overnight. Northerly winds will increase Thursday afternoon
in response to an approaching front, with southeasterly winds
through Turnagain Arm and above the mountains. The northerly flow
will initially be fairly deep, so do not expect low level wind
shear.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Periods of light snow will continue through late this evening from
Anchorage into the Matanuska Valley as the upper trough lifts
northward through the region. Snow should come to an end by around
midnight with the passage of the trough, with little or no
additional accumulation expected. Attention then turns to the next
system as a powerful front enters the southern gulf Thursday
morning and races to the north gulf coast by Thursday evening
accompanied by potentially heavy precipitation. The front will
bring much warmer air, allowing snow to change over to rain
fairly quickly across coastal locations and helping to minimize
any blowing snow concerns. Inland locations will remain mostly dry
through Friday due to strong southeast flow across the coastal
mountain ranges. While precipitation will not be a significant
concern for these areas, there will be a favorable setup for
Chinook winds along the western slopes of the Chugach range. This
could allow temperatures to climb well into the 40s in the
Anchorage bowl by Friday, causing much of the recent snowfall to
quickly melt.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Remnant moisture from today`s frontal passage will gradually push
north and east. Expect a short break between lows and then a
formidable low will get kicked out of the Gulf of Alaska and a
deformation zone will set up directly over southwest AK. More snow
is on the horizon.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

A mature low will continue to deepen and push northeastward
steering a fetch of moisture towards the Aleutians. A low level
barrier jet will develop near the central Aleutians to the AK pen.
Sensible weather-wise bumped up pops this package along with
gusts...with some locations expecting to see storm force winds.
A secondary reinforcing low will follow in its wake enabling
arctic air to filter into the region.

&&

.LONG TERM FORECAST (Days 3 through 7)...

Following the chinook on Friday, the possibility of another
chinook on Saturday is growing. Regardless if the chinook happens,
temperatures overnight on Friday will likely remain above
freezing for much of Southcentral Alaska with Saturday high
temperatures in the 40s once again. Southwest Alaska will not see
the extremes that Southcentral will because the storm track
favors the warmer air pushing eastward into the gulf of Alaska. As
the active weather pattern remains entrenched across the region,
a series of low pressure systems will move into the gulf of Alaska
through the upcoming week. This will allow continued pushes of
warm and moist air back toward Southcentral Alaska which could
quite possibly keep high temperatures above freezing for the next
week. The gulf coast should continue to get slammed with rainfall
at lower levels and snowfall toward higher elevations much much of
inland Alaska will remain on the dry side as most locations
should remain downsloped. This pattern really shows no signs of
breaking so until something changes, this warm and spring-like
pattern will continue.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS/DEK
LONG TERM...MC



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