Brisk Wind Advisory 41, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
735 AM AKST Fri Feb 28 2020

.ANALYSIS AND UPPER LEVELS...

A ridge of high pressure aloft was centered over Nunivak Island
this morning, with said ridge extending northwest to Russia, and
through the Alaska Peninsula. A secondary ridge was centered
across the north Pacific, and it was building north into the
central Bering Sea and Nunivak Island as well.

Flanking these ridges were a pair of low pressure systems. The
first of which was a weak 1000 mb low just west of Yakutat, and
this system was quickly trekking towards that location while also
weakening. A stronger 985 mb low was centered a few hundred miles
south of Shemya. Otherwise, colder air continued to filter into
the Kuskokwim River Valley, and the northern Susitna Valley from
the north. Here, several locations were below zero, with many
reporting temperatures in the negative teens.

&&

.MODEL DISCUSSION...

In the short term (through the weekend), the models remain in good
agreement at the surface and aloft in their forecast depictions,
but there has been a change with how they handle a north Pacific
low moving into the Bering. This morning's numerical runs have
shifted the track of this low further east, and not have the low
crossing the Aleutians near Adak, then take it towards Cape
Newenham.

This is at least a couple hundred miles to the east of yesterday's
assortment of solutions. This sudden shift has also resulted in
increased uncertainty to where and if a new triple point low forms
in the northern Gulf or Prince William Sound vicinity.

Heading into next week, the models are in better than average
agreement in the synoptic pattern, with the main difference this
morning being a portrayal of a deeper mid-level low or trough,
diving southeast across the central and southern portions of the
state. Should this verify, another Arctic plunge of air into our
neck of the woods would be likely. Stay tuned.

&&

.AVIATION...

PANC...VFR conditions and light winds will prevail through the
forecast period.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

There will be generally quiet weather over Southcentral Alaska
today with just a few areas of lower clouds near Kachemak Bay and
also the Matanuska Valley early this morning which are expected to
clear out by mid-morning. Some lingering snow showers were in the
eastern Copper River Basin overnight and early this morning, but
they too should move east and out of the area by afternoon. There
is some gusty winds through channeled terrain such as near Seward
and through Thompson Pass, but that is about it for today.

The quiet weather will start to change tomorrow with the approach
of a strong front from the southwest. This will bring some
snowfall to Kodiak by late tonight/early Saturday morning and then
turn to rain by Saturday afternoon. This front will remain over
the northern Gulf and not penetrate inland so even though Kodiak
will turn to rain, the rest of Southcentral should remain all
snow. Some of the snow may be occasionally heavy over the Kenai
Peninsula Saturday night into Sunday, but it is still a little far
out to call for a winter weather advisory as overall snowfall
accumulation rates look to remain under advisory thresholds.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 2)...

One more day of dry conditions. Looming on the horizon, there is a
low in the North Pacific that will move into the Bering tonight
and continue to close in on Southwest Alaska. The models continue
to depict the leading edge of the precipitation shield moving into
Bristol Bay and Y-K Delta early Saturday. Generally expecting
snow but portions of the AKPEN and Bristol Bay will see a mixed
P-type. More precipitation expected Sunday.

&&

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

An active weather pattern is on deck this forecast period. A low
southwest of Adak is going to deepen and sweep across the chain.
The pressure gradient will be strong enough to produce widespread
gales and areas of storm force winds. Looking at satellite
imagery, there is an extensive fetch of tropical moisture
associated with this system. The PWs (precipitable water) ranges
from 1-1.7 inches and the source region for this moisture is
Micronesia. The airmass is being modified as it comes north, but
make no mistake this is a juicy system. As time elapses, cold air
will get entrained into the backside of the low.

&&

.MARINE (Days 3 through 5 Sun through Tue)...
Gale force winds will continue around the low
in the western
Bering on Sunday then diminish to small craft range Sunday night.
Gales are expected from south of the Alaska Peninsula through the
Gulf Sunday and Sunday night associated with a low in the northern
Gulf. Winds are expected to be near storm force in the offshore
waters of the Gulf Sunday evening.

&&

.LONG TERM FORECAST (Days 4 through 7 Mon through Thu)...

An upper level trough will dig into southern Alaska Monday and
Tuesday then slide east Wednesday and Thursday, with the axis near
the Canadian border Thursday afternoon. High pressure over
extreme northeast Russia on Monday will slide eastward behind this
trough, pushing into the western Bering on Tuesday and into
western Alaska by Thursday. The Ensemble means are in fairly good
agreement, but the deterministic models are all over the place on
the details. Therefore the forecast confidence past Tuesday is
rather low.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 191.
MARINE...Gale Warning 127 130 132 150 155 165 170>179 185.
 Heavy Freezing Spray 121 130 150 165 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
MARINE/LONG TERM...BL