Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 111352
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
452 AM AKST Sun Dec 11 2016
.ANALYSIS AND UPPER LEVELS...
The weather over much of Mainland Alaska is beginning to move into
a much quieter weather pattern under widespread high pressure.
This high pressure has pushed the persistent trough of low
pressure that had been over the Gulf since late last week south of
the area. It has also brought decreasing clouds and diminishing
winds throughout the south Mainland and Gulf Coast. As the ridge
approached, a weak mountain wave over Southcentral created from
E-NE flow the Talkeetna Mountains, but this is beginning to
quickly dissipate this morning as stronger stability and weakening
winds move into the area. Over the eastern Bering a trough
stretching from the AK pen northward towards Nunivak Island is
bringing a narrow area of snow showers, especially near Cold Bay
where over an inch of snow has fell overnight. This trough is
beginning to lift to the north as a gale force front moves into
the western Bering. Without the protection of the persistent
ridging that had been over the eastern Bering last week this
front will then spread through the Bering today and make landfall
over the southwest coast on Monday.
With high pressure descending into the Mainland into early next
week, forecast confidence is above normal with good model
consensus. Starting late Monday some uncertainty in the speed and
strength of a Western Aleutian low begins, especially when
looking at the NAM which a much weak outlier and was ignored.
Instead the forecast preferred the stronger GFS to increase winds
over the western Bering, which is also slight faster in a strong
southerly jet. This system has little impact overall to the
mainland however, leading to good forecast confidence with
continued high pressure into mid-week.
PANC...High pressure will lead to VFR conditions and light and
variable winds into Monday morning. There is a outside chance of
fog/stratus development tonight, however this was left out of the
TAF due to dry low levels and light offshore flow.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Offshore persists across much of the Southcentral mainland, with
broad low pressure system in the southern Gulf of Alaska, and a
persistent upper level high pressure system encompassing the
mainland. Moisture was sufficient at upper levels to support a few
upper level clouds across the Susitna Valley due to weak mountain
waves, but generally clear skies dominate. At the surface, air
remains dry enough to prohibit the formation of low stratus and
fog. As a result, temperatures continue to plummet, especially in
valleys protected from even light winds in the Copper River Basin.
Generally benign weather conditions will persist through the short
term, as the current weather pattern remains in place. Some patchy
fog could develop in protected valleys over the next few nights,
but generally conditions will be too dry for fog.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The Southwest Alaska region remains under offshore northerly flow
bringing in cooler temperatures with high pressure dominating the
upper Kuskokwim Valley northward through the Brooks Range. By
Monday a weather front approaches the Southwest coastline. Look
for the winds to shift to a southeasterly direction accompanied
by warmer temperatures as the front moves inland before washing
out as it tries to move into the interior by Monday afternoon.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The Bering/Aleutians is influenced by southerly flow as a storm
force low tracks just west of the Western Aleutians this morning.
The associated weather front will move from west to east as it
tracks from the western Bering/Aleutians eastward. By Sunday
evening a triple point low develops, and will be located in the
central Bering. This synoptic feature moves farther north into
the northern Bering before dissipation by Monday morning. Look
for the Bering Sea/Aleutians to have warmer temperatures heading
into Monday as this front moves through the region. Meanwhile, a
rapidly intensifying storm force low will develop south of the
Western Aleutians by Monday morning. This system looks to track
across the chain near Kiska by Monday afternoon. Therefore, look
for strong gusty storm force southerly winds through the Central
Aleutians, and storm force easterly winds in the Western Bering as
this system tracks into the Bering. This will bring widespread
rain/stratus as we heading into Monday.
.LONG TERM FORECAST (Days 3 through 7...Fri through Tue)...
Monday night will begin a transition period to a stormy regime
over the Bering Sea as the cold Siberian high reestablishes
itself. A blocking high over Southcentral will weaken Tuesday as
an undercutting Bering shortwave trough moves across the area
bringing some rain and snow to Southwest Alaska...and clouds to
Southcentral. After Thursday, uncertainty grows with respect to
another shortwave trough moves through the ridge with the GFS much
more bullish than the ECMWF/Canadian GDPS. That uncertainty is
already considered in this forecast which calls for increasing
chances for precipitation late week. Thereafter, the possibility
for increased storminess and multiple precipitation chances
increases as the ridge over Southcentral shifts east and weakens,
allowing for a series of shortwave troughs in southwest flow to
impact the southern mainland through the weekend. This should
usher in a return to above normal temperatures along with an
active weather regime across the forecast area.
MARINE...Gale 173 174 175 176 177 178.
Heavy Freezing Spray 127 181 185.
SYNOPSIS AND MODEL DISCUSSION...DEK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD