Small Craft Advisory 87, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
700 AM AKST Sat Jan 25 2020

.ANALYSIS AND UPPER LEVELS...

This morning's analysis aloft showed a pair of mid-level lows over
the northern Gulf and eastern interior respectively, with a
negatively tilted ridge stretching from eastern Siberia, through
the Pribilof Islands and eastern Aleutians, into the north
Pacific. Another mid-level low was located west of Shemya. All of
these lows have a surface low reflection as well.

&&

.MODEL DISCUSSION...

The numerical guidance remains in great agreement through the
middle of next week in the synoptic pattern aloft, with good
agreement at the surface through early Tuesday. Thereafter, the
main difference lies with a very strong area of low pressure
racing north into the Gulf by Wednesday. The GFS had previously
been an outlier in this as it depicted a surface low around ~940 mb
heading towards eastern Prince William Sound. It had been showing
this off and on (more so on) for a few days. However, it has gained
support from both the European and Canadian models, as they all show
a ~950 mb low (give or take a few mb) heading into the east central
Gulf.

&&

.AVIATION...

PANC...VFR conditions and northeasterly wind gusts to 25 knots will
prevail through the period.

&&

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

Synoptically, the pattern will remain largely unchanged through
the weekend. The net effect for most locations will be continued
cold and dry surface conditions with gusty winds in the typical
gaps. A deep upper level trough remains parked over the entire
southern half of the state. Within the trough remains a broad
cyclonic circulation over the Northern Gulf. To the west of this
circulation, northwest flow over the warmer Cook Inlet and Gulf of
AK waters continues to produce bands of snow over north and west
Kodiak Island. On the eastern side of the circulation, there is
more moisture available which is leading to widespread snow
showers near Middleton Island and Cordova. Over the mainland, cold
temperatures remain largely dependent on exactly where the winds
are blowing and how much cloud cover is drifting through the area.
This forecast package has warmed some of the overnight lows in
places like the Susitna Valley and W Anchorage where winds will
remain breezy.

As we go through the weekend, the biggest change will a strong,
fast-moving low that sweeps up the eastern side of the trough
near Yakutat Sun morning. The forecast models are struggling
greatly with this feature and how it interacts with the current
circulation in the Gulf, so we have kept changes to a minimum
overnight. At the very least, it will enhance snow chances
markedly for the NE Gulf Coast (to include Valdez) where several
inches are expected. Some of that snow looks to pass through the
Copper River Basin bringing some light accumulations there as
well. This strong low will also serve to pull some even colder air
at 850 mb (5000') further south. Temperatures at that level look
to reach down into the 30 below range. If winds and temperatures
continue to line up, this will likely spell wind chill advisory
level conditions (-40F) for Thompson Pass as early as tonight.

&&

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

Southwest Alaska remains currently situated between an upper low
centered in the northern Gulf and a strong upper high over the
Bering. This is leading to strong northerly winds aloft and thus
colder surface temperatures moving into the region. High and low
temperatures will continue to gradually fall as the aforementioned
upper low shifts westward this weekend. Wind Chill Advisories
remain in effect for the Kuskokwim Delta and Bristol Bay zones
through noon Sunday, though may need to be extended further.
Mostly sunny conditions should prevail across the area through
early next week, however onshore show showers/blowing snow are
possible across Bristol Bay and portions of the Alaska Peninsula.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

A surface low becoming vertically stacked near Kamchatka is
leading to the weakening of its associated front. As such,
rain/snow showers and gusty easterly winds will diminish over the
western Bering/Aleutians through today. Subsequent lows will
approach from the North Pacific Sunday and Monday, however will
remain far enough offshore to have any significant impacts. Strong
upper level high pressure will bring more benign conditions
farther east. Isolated flurries remain possible into early next
week.

&&

.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...Gale Warning 119 121 127 128 130 131 138 139 150 175 176
         177 178 185 411 412 413
         Heavy Freezing Spray Warning 119 121 127 129 130 138 141
         150 160 165 179 180 185 412 414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHCENTRAL ALASKA...MSO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP
MARINE/LONG TERM...TM