Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
459 PM akst Tuesday Nov 24 2015
Analysis and upper levels...
The strong storm that was moving through the northern Bering
yesterday has weakened significantly and is now moving toward the
Bering Strait. The associated front stalled over southcentral
Alaska and continues to produce long-lived heavy precipitation
over the far eastern portions of the lower Kuskokwim valley and
Bristol Bay zones as well as over much of the Susitna Valley.
Unofficial reports in excess of 2 feet of snow since yesterday
afternoon have been received from far northern parts of the
Susitna Valley. As expected...warm air has made some progress
northward...with rain and freezing rain mixing in with the snow
from Talkeetna southward and as far east as Wasilla in the
Matanuska Valley. To the south...warm and gusty southerly winds
from Anchorage to the western Kenai have warmed temperatures well
into the 40s.
To the west...showery and gusty southwesterly winds are in order
across the bulk of the Bering Sea and most of the southwest
Mainland. The one exception is east of Sleetmute and east of
Dillingham...where a steady mix of rain and snow continues to fall
associated with the stalled weather front over the area.
The models are coming into better synoptic agreement with the
shortwave and weak surface low that lift northward tomorrow along
the stationary front and impact southern Alaska Wednesday night
and Thursday. The European model (ecmwf) has maintained its further west solution
from yesterday...which now has the support of the Canadian Gem.
With the models in better agreement on a jet streak further west
over the Bristol Bay area...a further west solution makes a bit
more sense. The impact of this will be to spread the precipitation
shield a bit further west over southwest Alaska than the NAM/GFS
would suggest. The European model (ecmwf)/Gem are the preferred model today.
Short term forecast southcentral Alaska (days 1 and 2)...
the warm and windy pattern will continue for the time being. A
moist jet overhead and warm air overriding a cold dome in the
Susitna Valley continue to drive precipitation in the area. The
steadier precipitation is mainly over the valley...with
temperatures cold enough for snow from Talkeetna northward while
the warm nose is overhead south of Talkeetna. The surface warm air
is slowly eroding the cold dome...however freezing rain remains
likely in the southern valley this evening and through the
overnight hours. Heavier snow will continue through early
Wednesday morning north of Talkeetna...especially toward the park.
On Wednesday a North Pacific system will bring a slug of moisture
back over southcentral Alaska as well as a continuation/enhancement
of strong gap winds in the Cook Inlet region. Initially tomorrow
the Anchorage area will remain dry but rain chances will increase
through the day as moisture surges overhead. Precipitation type
will most likely be rain. There is a chance for freezing rain in
the Susitna Valley if the cold pool currently in place holds
steady and does not get eroded overnight. Above average temperatures
and windy conditions will hold through Thanksgiving in most area.
Short term forecast southwest Alaska (days 1 and 2)...
A stalled frontal boundary will keep the bulk of the precipitation
focused over eastern portions of Bristol Bay and the Kuskokwim valley
through Wednesday night. This precipitation will be enhanced by a
potent North Pacific wave riding along the front tonight...with an
even more potent system Wednesday into Thursday. This will result
in several inches of snow possible along and just west of the Alaska
and Aleutian ranges from King Salmon north...with the greatest amounts
north of Iliamna. Elsewhere...persistent onshore flow will keep isolated
to scattered shower activity over the Kuskokwim Delta through Wednesday.
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
broad cyclonic flow will keep a showery regime over the Bering through
tonight in the wake of the departing low moving towards the Bering
Strait. Attention then quickly turns to the next strong low approaching
the western Aleutians early Wednesday. This system will bring another
round of heavy precipitation and storm force winds to the western
and central Aleutians as it skirts the island chain and Alaska Peninsula
through Thursday. An unusually cold and dry air mass just ahead of this
storm will allow for precipitation to start as snow before quickly changing
over to rain as warm air surges northward along and behind the front.
Long term forecast (days 3 through 7)...
Models are in agreement that the large and slowly moving low
pressure center over the central Aleutians Thursday evening will reach
the eastern Bering on Sat and then drift. The second low reaching
the western Aleutians on Sat will remain south of the chain as it
moves to Kodiak Island early Tuesday where it will stall. The
forecast utilizes this general solution...with wpc ensembles
helping to fine tune the trajectory of the second low.
In the east...warm advection on southerly flow will bring warmer
temperatures to much of southcentral Thursday evening through Sat.
Rain will be locally heavy along the coast and upslope sides of
mountain ranges. This will continue with slightly cooler
conditions into early next week.
In the west rain through Sat will be substantial across the chain
and then into SW Alaska as the low transits and then moves over the
eastern Bering, gale and storm force winds will also be associated
with the low. Rain and snow showers...along with slight lighter
winds...will then spread across the chain and into SW Alaska as the
second low moves just south of the island into early next week.
Marine...storms 173 174 175 176 177 178 413.
Gales 119 120 125 131 132 150 155 170 171 172 179 351 352 411 412
Synopsis and model discussion...ad
southwest Alaska/Bering Sea/Aleutians...cirrocumulus