Scientific Forecaster Discussion
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Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
428 am akst sun Feb 26 2017
Analysis and upper levels...
There is a large Pacific subtropical upper level high centered
south of the eastern Aleutians with a broad region of low
amplitude zonal flow from the western Bering Sea to the Yukon.
There is a weakening shortwave trough moving across the Brooks
range with the trailing atmospheric moisture river extending from
the Pacific Ocean to the southwest Mainland west of the Alaska
Range. The main region of precipitation, as one would expect, is
located west and north of the Alaska Range with much lighter
precipitation across regions of southcentral. This pattern is
promoting an onshore flow across southwest Alaska with increasing
westerly offshore flow across southcentral.
Model discussion (through Monday afternoon)...
the numerical models are in excellent agreement with the general
weather pattern deep into next week as the region heads into a
dominant northerly flow pattern aloft. Increasing offshore
pressure gradients will be the concern early next week along with
snow chances as a shortwave trough moves through southern Alaska
Sunday night through Monday night. As usual, there are subtle
timing differences with the shortwave trough moving into the Gulf
of Alaska Monday and Monday night with the NAM and GFS depicting
quicker solutions. The European model (ecmwf) and Canadian are a tad (3 to 6 hours)
slower. For now, a middle ground approach on snow chances and
increasing offshore winds was favored.
panc...MVFR cigs will persist into the morning hours. This will
also likely help keep fog away from the Airport, although a little
patchy fog can not be ruled out. Drier air and higher ceilings
should move in during the afternoon and persist overnight.
Short term forecast southcentral Alaska (days 1 and 2)...
an upper level wave moving through the Susitna Valley overnight
will move into the Copper River basin this morning bringing the
chance of snow for that area. The Aleutian Range is doing an
effective job downsloping out the moisture from the front in
Bristol Bay causing just a slight chance of precipitation there.
Anchorage, the Kenai Peninsula and eastward toward Prince William
Sound are between these two systems with no precipitation
expected in these areas today. As a cold upper level low descends
over southcentral Alaska Monday night, there will be another
chance of snowfall over the area but any that occurs looks to be
very light and many areas will not see any. Temperatures will
start to significantly drop Monday night or Tuesday as this very
cold airmass moves into the area to take up residence for awhile.
Short term forecast southwest Alaska (days 1 and 2)...
The front continues to slide southeast today, with cooler air
filtering in from the north. Accumulating snowfall is expected
near Iliamna with snow shower activity over much of the rest of
the southwest. Although one last day of warming above freezing is
possible, most of that will be confined to the Bristol Bay zone,
where snow will briefly mix with rain just north of King Salmon.
Rain will be predominate along the Alaska Peninsula. Cold air
continues filtering into the region tonight and Mon and
precipitation will be limited to snow showers, which will end Tue
night into Wed.
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
High pressure building into the Bering will continue to push the
front south through Mon. Rain over the eastern half of the Bering
and Aleutians will diminish and switch to snow showers on Mon
before ending. A front associated with low pressure moving to
Kamchatka will bring a surge of warm and moist air into the
western Aleutians beginning Mon. This system will bring gales and
rain through Tue night west of Adak.
Long term forecast (days 3 through 7)...
after cold air filters through the southern Mainland early next
week it remains in place through Friday with the upper level
trough situated over the Mainland and ridging in place over the
Bering. Offshore northerly flow will be gusty at times for
channeled terrain, especially along the coasts, through the end
of the week as the upper low provides a continuous tap from the
Arctic. All operational models were in good agreement through the
long range forecast, although the 12z GFS started to break the
Bering ridge down toward Friday which was an outlier on this
solution. Only minor changes were needed today with a weighted
forecast toward the European model (ecmwf) and it's ensembles.
Marine...gales 120 130 131 177 178 351 411.
Heavy freezing spray 160 185 .