Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
130 PM akdt Friday may 17 2013
Analysis and upper levels...
an upper level trough accompanied by much-advertised unseasonably
cold air is moving through southern Alaska this afternoon. A weak low
pressure system in the Gulf has spread widespread precipitation
across all of southcentral Alaska...which is falling generally in the
form of rain at lower elevations and snow at higher elevations.
Satellite imagery shows the upper trough becoming increasingly
negatively tilted...with an upper level low near the Bering Strait
dropping into the base of the trough. Further west...the cold front
has passed through most of the southwest Mainland...clearing skies
and allowing temperatures to drop into the teens earlier this morning
from the Kuskokwim Delta to the western Kuskokwim Valley. High
temperatures this afternoon will struggle to reach the upper 20s in
parts of the Delta...where the average high this time of year should
be upwards of 50 degrees. Way out west...high pressure remains in
command of the Bering Sea region...though high clouds in advance of a
North Pacific low are approaching the far western Aleutians.
Model discussion...
model agreement has continued to improve today with the NAM joining
the other solutions in the timing and evolution of the upper level
trough over the Mainland today (nam had been faster with speed of the
upper trough in previous days). Thus confidence has continued to
increase that an unusual late-season snowfall event will be unfolding
across southcentral Alaska tonight and continuing through Saturday
morning. The NAM was the primary model used today...though no strong
preferences were noted and no models were unusable.
Short term forecast...
east of the Alaska Range...cold air is slowly bleeding into the area
but this trend will accelerate dramatically by late this afternoon.
As the atmospheric column cools the rain/snow mix will turn to all
snow even at lower elevations. Higher elevations will see the most
snowfall...likely approaching 6 inches in some locations...with lower
elevations significantly less. As skies clear on Saturday afternoon
temperatures should drop significantly overnight into Sunday morning.
Record low temperatures in Anchorage are in the middle 20s...and these
records may be threatened if winds diminish enough to allow
significant overnight cooling. Even if the record lows are not
reached...a widespread hard freeze is expected across much of the
region from the inland Kenai Peninsula northward. Temperatures will
start to slowly rebound on Sunday as high pressure moves in from the
west.
West of the Alaska Range...behind the cold front temperatures dropped
well below freezing this morning at many inland locations over the
Mainland. Mostly clear skies will allow temperatures to drop again
tonight into the lower teens...before a steady warming trend ensues
for the latter half of the weekend. High pressure currently over the
Bering Sea will drift eastward...continuing benign conditions and
mostly sunny skies. Marine fog/stratus over the Bering and Aleutians
will start to slowly dissipate Saturday as a gale-force front
approaches the western Aleutians. This weather front and associated
rain shield will move to the eastern Bering by late Sunday.
Long term forecast...
a more progressive weather pattern will move into the region starting
Sunday. This will see most areas return to near-normal temperatures
by the middle of next week...with rain moving into the southwest
Mainland but southcentral remaining mostly dry.
Aer/alu...watch/warning summary
public...Snow Advisory 101 111 145
marine...gale 130 132 150 172 175 176
fire weather...none
Dixon may 13
