Heavy Freezing Spray Warning 40, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
420 PM AKST Wed Jan 25 2017

.ANALYSIS AND UPPER LEVELS...

A powerful 190 knot North Pacific jet stream is carving itself out
across the Eastern Pacific. Strong left exit cyclogenesis has
already developed a 967 hpa low which is now centered south of the
Eastern Aleutians. Water vapor and IR satellite imagery depict a
well defined closed circulation typically associated with marine
occlusions of this type. Farther east, a weak warm front is moving
toward Kodiak Island while a second and stronger low is forming
along the left exit of the Pacific jet stream along a triple
point. Closer to Alaska, a remnant upper trough axis is moving
inland across Southcentral with rain along the coast and snow
across parts of Northern Prince William Sound. Farther west over
the Bering, an inverted trough axis stretches north from the low
south of COld Bay into the Eastern Bering Sea with cyclonic
northerly flow over the remainder of the Bering Sea. Early morning
snow showers across parts of Southwest Alaska have given way to
drying as brief transitory shortwave ridging builds in this
afternoon.

&&

.MODEL DISCUSSION...

The suite of numerical models are in excellent synoptic agreement
through the weekend, but they remain in very poor agreement with a
series of lows moving into the Gulf of Alaska through Friday. The
first low/front is expected to move toward the coast Thursday then
move inland into Southwest Alaska. Models have come into better
agreement with a southward track of that low, so confidence is
higher. Confidence drops off quickly as another low moves toward
the Gulf coast Friday then another on Saturday. The precipitation
distribution and local wind impacts are of low confidence,
especially for inland locales where downslope patterns are
dependent on low track. With that said, expect continued heavy
coastal precipitation with continued warmer conditions inland.

&&

.AVIATION...
PANC...Southeasterly winds will increase rapidly through
Turnagain Arm this evening making low level wind shear a concern
for some PANC approaches/departures. With a strong northerly down
Cook Inlet gradient the stronger southeasterly surface winds are
expected to bend away from PANC through midday Thu but do have the
potential to reach the terminal Thu afternoon or evening.

&&

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

Warm air and strong winds will accompany the weather fronts as
they move to the North Gulf coast tonight and Thursday. Gale and
storm force winds will affect much of the marine area, and
channeled flow through Turnagain arm will peak Thursday morning
with 60 to 70 mph gusts. Temperatures will warm well above
freezing along the coast and as far north as the Matanuska valley,
reaching the upper 30s and lower 40s. Although Anchorage and the
Matanuska valley, and much of the western Kenai will be
downsloped and little precipitation is expected, there will be a
few rain showers falling on frozen surfaces. Expect very slippery
conditions when this occurs. At higher elevations of the Kenai
and Chugach mountains, well above the lower level warm air,
significant snowfall is expected through Friday.

Thursday night into Fri will have slightly cooler overnight and
daytime temperatures as the flow of warm air diminishes.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The mainland forecast will feature several disturbances rotating
over the area from the north Pacific. The first comes in late
tonight from the western Gulf of Alaska. A band of precipitation
will set up from Kamishak Bay northwestward and will be fairly
intense for a few hours. Precipitation type will likely be rain
toward the north of the band, mixing with or changing to snow
toward the south. The disturbance will push northward out of the
area bringing most of the mainland into a warmer
easterly/southeasterly flow with high temperatures well into the
30's except for the Kuskokwim Delta. On Friday, the same flow
pattern remains with weaker embedded disturbances keeping the
chance for light snow across the mainland. Late Friday night, a
compact system from the Bering will bring a quick shot of snow and
wind to the Bristol Bay coast.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The Bering will be characterized by a snow shower regime as cold
northerly flow streams over the relatively warmer Bering water.
Visibility will be intermittently reduced in snow snow showers.

&&

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

An active pattern ensues this weekend as new low centers form within
a broad longwave pattern centered over the Bering. Cold air
advection from the west moderates temperatures below freezing
across the southern mainland through the weekend. Multiple
shortwaves keeps the wetter pattern into the middle of next week.
Models are in general agreement with the highly active pattern,
however there are large differences in timing and placements of
the projected fronts. Models are starting to hone into a
significant pattern change for the beginning of next week that
could lead to a less active weather regime. This change would
start as a powerful storm system organizes in the North Pacific on
Monday, which then lifts north on Tuesday and becomes negatively
tilted. This potentially allows a ridge to it's east to amplify
over the Bering and possibly cut off near the Bering Strait
heading into the middle of next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm 119 351. Gale 120 125 129 130 131 139 140 165 170
172 175 179 185 352 412 413 414.

&&

SYNOPSIS AND MODEL DISCUSSION...JA
SOUTHCENTRAL ALASKA...DS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ML
LONG TERM...KH

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1248 AM AKST Thu Jan 26 2017

AKZ101-111-121-261900-
Anchorage-Matanuska Valley-Western Kenai Peninsula-
Including the cities of...Anchorage...Eagle River...Indian...
Eklutna...Palmer...Wasilla...Sutton...Chickaloon...Kenai...
Soldotna...Homer...Cooper Landing
1248 AM AKST Thu Jan 26 2017

...Slippery conditions possible tonight through Thursday morning...

Warming conditions are allowing scattered rain showers to spread
across the eastern Kenai Peninsula, Eagle River area and Matanuska
Valley tonight. These rain showers have the potential to cause
very slick conditions when they fall on frozen surfaces. In a few
areas, such as Anchorage metro area where temperatures remain
below freezing, isolated pockets of freezing rain mixed with
scattered snow showers also have the potential to worsen slippery
conditions.

Additional travel concerns are possible in the Kachemak Bay area
where areas northeast of Homer have been reporting snow and
blowing snow this evening above 1000 ft or so. While precipitation
is expected to change over to rain through the early morning hours
the combination of rain on top of the recent new snow could
produce challenging travel conditions.