High Wind Watch 10, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
517 PM AKDT Thu Nov 3 2022

.ANALYSIS AND UPPER LEVELS...
The big, cold, upper level low remains centered over northern
Alaska with a trough extending southward over Southcentral Alaska.
A surface low can be seen on satellite and radar south of Cordova
early this afternoon. This low is moving eastward with cold air
cumulus clouds streaming across the Gulf of Alaska behind the
low. Clearing has come to the western Kenai Peninsula, but until
the 500 mb trough moves east of Cook Inlet overnight, there will
remain some clouds over Anchorage and the Mat-Su valleys with snow
near and close to the mountains where it is upsloping. It has been
interesting watching the radar returns over Anchorage today as
the reflectivity increased as the snow was tapering off over the
Anchorage Bowl. This is due to the north winds and much drier air
moving over the area. It enhanced the lift and therefore caused
more precipitation. However the amount of dry air was greater than
the precipitation do the dew points were dropping so the snow
sublimated before reaching the surface. This dry air intrusion
can be seen with the Anchorage airport (PANC) dew point dropping
from 30 to 17 in about 4 hours today. The corresponding RH dropped
from 100% to 63% during that time.

The Bering Sea in under cold northerly flow which is keeping some
snow showers and stratus clouds over the region. The Kuskokwim
Mountains are blocking the low level clouds effectively today
bringing in widespread clear skies for the Bristol Bay region and
Kuskokwim Valley.

&&

.MODEL DISCUSSION...

Models remain in good synoptic agreement through the weekend. The
main difference to work through will be subtle features such as
the timing of weak upper level waves and how they may impact the
gusty gap winds that will occur the next few days along the Gulf
coast.

&&

.AVIATION...
PANC...Northerly winds will increase this afternoon through the
overnight hours which should help keep conditions VFR. There is a
chance for a brief lowering of ceilings in a snow showers as an
upper level trough passes through late this evening to after
midnight.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 to 3: Tonight
through Sunday)...

Quieter weather is expected tonight as a vertically stacked low
continues drifting southeast across the Gulf of Alaska. Colder,
drier air is filtering in behind the low, leading to clearing
skies along Kodiak Island and Cook Inlet. A Winter Weather
Advisory remains in effect for the Anchorage and Eagle River
Hillsides through 6 PM tonight. As we head into tonight, we could
see some snow showers along the Chugach Front Range and Kenai
Mountains with the passage of a shortwave through Southcentral
Alaska. However, any additional snow accumulations tonight should
be minimal.

Winds will be the big story as we head into Friday and Saturday.
As cold, dense air filters through gaps in the terrain, we could
see some strong and gusty winds. Winds are already picking up
along Kodiak Island, and winds will gradually pick up into
Friday morning as temperatures continue to drop. Drainage winds
through Copper River Basin could lead to gusts approaching 70 mph
along Eastern Prince William Sound, especially through Thompson
Pass, Valdez passages, and the Copper River Basin. Elevated, but
weaker, winds are expected through Matanuska Valley. Overall,
confidence is high that winds will be strong. However, as these
types of events are not well captured by models, there remain some
uncertainty as to the exact magnitude of these winds. There is
also uncertainty with the shortwaves moving around an upper level
low over Mainland Alaska, so there could also be shifts in the
timing of the strongest winds. Overall, we should expect to see
strong outflow winds on Friday and Saturday, with winds gradually
diminishing through Sunday. Otherwise, the weather should be
relatively clear and sunny, with high temperatures ranging from
the single digits to low 20s.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Tonight
through Sunday)...

Broad northwesterly flow will keep much of Southwest Alaska dry
this evening before a developing low crossing the northern Bering
Sea brings the next round of active weather to the region. Winds
will shift out of the west to southwest ahead of the approaching
low, allowing temperatures near the coast to increase into the
lower 30s through the overnight hours. It will also bring a round
of quick-moving snow showers and gusty winds to the Kuskokwim
Delta into Friday. The combination of winds and cold temperatures
aloft will be favorable for blowing snow to reduce visibility to
as low as one half mile on Friday, which has prompted the issuance
of a Winter Weather Advisory. The primarily showery nature of
precipitation expected with this system, combined with its fast
motion may limit the period of low visibility to a short window of
a few hours at any given location during the passage of its front.
Snow then tapers off from west to east in its wake, with freshly
fallen snow having the potential to be lofted in the wake of the
front until winds diminish Friday afternoon. While snow totals for
most of Southwest Alaska are expected to be one inch or less,
a prolonged period of snowfall in the northern Delta and near
Aniak may lead to snow totals as high as four inches.

As the low tracks southeast, snow showers and blowing snow may
become an issue along the Western Capes and the northern half of
the Alaska Peninsula on Friday as well. Behind the low, a strong
surge of cold air streaming southward with some upper-level jet
support will contribute to gap winds gusting to storm force on
the south side of the Alaska Peninsula Friday night into
Saturday. A ridge of surface high pressure moves across Southwest
Alaska on Saturday, allowing a return to colder, drier conditions
through the weekend under mostly clear skies.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 3: Tonight
through Sunday)...

Relatively quiet conditions across much of the Bering
Sea/Aleutians continue tonight and Friday with surface high
pressure in place near the central Aleutians. The periphery of
the high will be the exception as two low pressure systems drive
gale force winds on either side. To the east, one low tracking
across Southwest Alaska strengthens the pressure gradient, driving
gale force northwesterly winds across the eastern Bering for
Friday. To the west, a front approaches the western Aleutians,
bringing gale force southerly winds, but rain is not expected to
move appreciably into the forecast area until Saturday morning,
when the surface anticyclone moves eastward into Southwest Alaska.
Rain and winds in the western Aleutians gradually diminish on
Saturday as the main low supporting the front moves north into
Chukotka. Saturday night, a storm force North Pacific low reaches
the central Aleutians and crosses into the Bering for Sunday.
With a strong southerly moisture tap, heavy rain is likely in the
eastern Aleutians and the southern Alaska Peninsula.

&&

.LONG TERM FORECAST (Days 4 through 7: Monday through
Thursday)...

Strong model agreement in the synoptic pattern for Southwest
Alaska into Southcentral Monday shifts to mild uncertainty by
Wednesday. The cause of this divergence in solutions is a common
culprit, a deteriorating ridge over Southcentral. Models often
struggle on the breakdown of these ridges and tend to break them
down faster than what occurs. This will lead to some uncertainty
in the long term, particularly for how far east precipitation is
able to make it into Southcentral. The 12Z GFS solution breaks
down the ridge particularly quickly, swinging a low from the
Bristol Bay area into the Gulf by Tuesday afternoon. The 00Z
Canadian offers a more resilient ridge that fends off the low,
however swings a surface low bringing elevated precipitation
across Southcentral. Currently, it is difficult to tell how the
low will progress across the Alaska Peninsula due to the ridging.
Questions of how far north/east the low will push remain
debatable. Out west, after the low moves out to the east, much of
the strong precipitation features will have moved out and zonal
flow will set-up. Some models do suggest a North Pacific low
moving into the Central Aleutians by Thursday morning, however
this is not well agreed upon and time will tell. In summary, the
Bering Sea and Southwest Alaska is looking to be warmer and
wetter, while Southcentral will remain colder and drier.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 155.
MARINE...Storm Warning 351 352 120 127 130 131 132
	     Gale Warning 119 121 125 126 128 129 136 137 138 411 414
					  150 155 160 165 177 178 180-185.
		 Heavy Freezing Spray Warning 121 140
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...KC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ
LONG TERM...CL

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