Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 250750 CCA
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
1050 PM AKST Fri Jan 24 2020

.ANALYSIS AND UPPER LEVELS...

A blocking high at 500 MB is still present, stretching from the
Gulf of Alaska northeast into the Bering Sea. Closed lows at 500 mb
bookend this high, one over the Western Aleutians and the other
over the northern Gulf of Alaska. On the surface, these systems
are reflected as a storm force low in the Bering Sea which is now
exiting our forecast area. In the Gulf, the low is reflected as a
cut-off low spinning snow showers into the north Gulf coast.

Cold air has also moved into Southwest AK as expected and can be
observed on satellite barreling through gaps and passes in the
Western Gulf of Alaska. This is via "streets" or lines of cumulus
clouds on satellite. Interestingly, the cold air moving south can
be observed on IR satellite. Air is so cold over much of the state
that it can be observed on satellite imagery normally reserved
for cold cloud tops located much higher in the atmosphere. Cold
air is also causing gusty winds for some locations in Southcentral
as high pressure over Interior AK and downvalley flow help move
cold air south.

&&

.MODEL DISCUSSION...

Synoptically models are continuing the capture the pattern of a
blocking high with two stalled lows on either side. On the
mesoscale, models are variable in their ability to capture the
weather depending on location. In the Southwest and the
Bering/Aleutians models are performing well enough to be confident
in the forecast. In Southcentral AK, models are having trouble
handling the low in the Gulf of Alaska which is making it
difficult to forecast snowfall along the coast. They are also
having difficulty handling low-level moisture and cloud cover.
This reduces our confidence for Southcentral AK.

&&

.AVIATION...
PANC...VFR conditions will persist. Northeasterly flow coming down
the Susitna Valley is expected to create gusty conditions for the
airfield this evening and going through tomorrow.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Low pressure over the Gulf of Alaska will advect cold air across
Southcentral through this weekend. Gusty conditions are expected
through channeled terrain and across the western areas of the
Gulf. Freezing spray will be a challenge for marine areas and wind
chills will make temperatures feel much colder. Chances for snow
increase along coastal areas and Copper River Valley this weekend
The upper low over the Gulf begins to shift northwest. There is
high uncertainty on how much moisture is pulled inland from the
Gulf, so details on this weekend`s forecast will likely be updated
for the next front expected to move up on Sunday. Added slight
chance for snow to make it across to the Anchorage Hillside and
eastern areas of the Matanuska Valley Saturday night as models all
show a fairly strong short wave moving across the Chugach Range.
Cordova to Valdez will have the best chance to accumulate snow
this weekend as a front moves up from the eastern Gulf. Blowing
snow was added to the forecast for Thompson Pass and Valdez as cold
air drainage continues on Sunday when the weak front pulls north
through the Copper River Valley.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Through Monday Afternoon)...

High pressure continues its residency over the eastern Bering, as
does the low in the Gulf of Alaska. These two features will bring
more cold Arctic air into Southwest Alaska. As the pressure
gradient tightens between these systems, expect gusty winds to
develop over much of the Kuskokwim Delta, Bristol Bay, and the
AKPEN. Thus, dangerous wind chills will encompass much of the area
over the next few days. Expectations are for the low pressure in
the Gulf to shift northward and bring strong offshore winds out
into Bristol Bay which will allow for snow showers to increase
steadily starting Saturday. Monday will see some of the most
vigorous snow shower activity and some areas on the north side of
the AKPEN will likely have some blowing snow.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Through Monday
Afternoon)...

A 970 mb low in the far western Bering will continue to generate
storm and gale force winds through Monday. Storm force winds will
be confine to the western Bering and will diminish by Saturday
morning. Rain showers mixed with snow showers will impact the
western half of the Aleutian chain. Another low will develop in
the north Pacific Sunday morning and maintain the pattern that
we`ve seen there for the past couple of days, including more
shower activity for the western Aleutians through Monday, as well
as gale force winds.

&&

.MARINE (Days 3 through 5: Sunday through Tuesday)...

Gulf of Alaska:

For Sunday and Monday, the interaction between low pressure in
the northwest Gulf and a ridge inland will continue to produce
gusty outflow winds through bays and passes. Gales and heavy
freezing spray will remain likely across Kamishak Bay and the
Barren Islands. A front associated with the low will be situated
along the coast with southerly small-craft winds (and possibly a
small area of weak gales) over the central Gulf, behind this
feature. By late Tuesday, there is an increasing potential for a
strong gale-force (and potentially a storm-force) low (~950mb)
lifting north into the Gulf, reaching the Kenai Peninsula by late
Wednesday.

Bering Sea and Aleutians:

Widespread small-craft winds and some gales will linger into early
Monday as a low near the western Aleutians continues to dive
southwest away from the Chain. Gusty northerly winds will
persist across the rest of the Bering and eastern half of the
Chain through mid-week with the strongest winds and greatest
potential for heavy freezing spray across the far eastern Aleutian
Chain and AKPEN.

&&

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

Moving into early next week, the core of the persistent upper-
level low centered over Kodiak Island will shift slightly west.
This shift looks to be enough to introduce a more southerly flow
over the Gulf and advance a potential storm-force low north from
the Pacific for late Tuesday into Wednesday. As it reaches the
Southcentral coast, its upper-level energy will phase with the
aforementioned low and reestablish the upper-level low back over
Kodiak Island through the end of the week. This pattern would
favor a push of gusty southerly winds, warmer temperatures, and
snow across the Southcentral coast, perhaps pushing inland a bit,
in association with the surface low through late Wednesday. After
that, conditions across the Southcentral coast look to remain
unsettled with a southeasterly flow continuing across the northern
Gulf. Elsewhere across the Southern Mainland, it looks to remain
quite cold as arctic air remains in place at the surface along
with northeasterly winds, especially for the Kuskokwim Delta and
Valley. Some clouds and snow could spill over the Alaska Range by
mid-week as the low in the Gulf nears the Kenai Peninsula. Farther
west, high pressure sliding south across the western Bering and
Aleutians will keep gusty northerly winds and snow showers going
through midweek. A weak surface low then looks to track across the
Bering by the end of the week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisory 155 161
MARINE...Storm Warning 411
         Gale Warning 121 127 130 131 132 150 155 173 174 175 176 177
         178 185 412 413
         Heavy Freezing Spray Warning 121 127 129 130 131 132 138 139
         141 150 155 160 165 179 180 185 412 414
FIRE WEATHER...NONE.

&&
$$

SYNOPSIS AND MODEL DISCUSSION...BB
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...LTB
MARINE/LONG TERM...TM



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