Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
636 PM EDT Sun Apr 26 2020
Valid 12Z Thu Apr 30 2020 - 12Z Mon May 04 2020
...Guidance/Predictability Assessment...
Upper pattern across Alaska during the extended forecast period
shows an upper high over northwestern areas meandering near the
North Slope through next weekend. An upper low initially in the
Bering Thu is forecast to move east-southeastward into the
backside of a deepening system south of the Gulf. The 12Z
GFS/ECMWF (and UKMET through Saturday) showed relatively good
consensus with the ensemble means during the period, and a blend
of these solutions was used as a forecast starting point.
Southern/split portion of the former Aleutian system in the short
term is forecast to lift back northward toward the southern Gulf
late in the week though its occlusion will likely push northward
through the Panhandle. Upper pattern would prevent much northern
movement of the surface low toward Southcentral as the upper high
shows no signs of budging until at least next week. Models remain
in good agreement on curling the low back northward then
northwestward, but disagree on the track and northward extent of
the low (ECMWF farther north than most). Ensemble means were close
to their deterministic counterparts (GFS/GEFS a bit farther south)
so split the difference as there was no reason to favor one
camp/cluster over the other at this point.
...Weather/Threats Highlights...
Pattern remains rather unsettled for the Panhandle with lingering
rain/snow Thu as an old parent low dissipates in the Gulf. System
next weekend to the south would bring in at least some
precipitation near/ahead of the occlusion with the heavier
rain/snow likely being forced into British Columbia but perhaps
into the southern Panhandle, too, depending on triple point
development. The Interior, by contrast, will be nearly
precipitation-free owing to the upper and sfc high. The Aleutians
will see generally light rain after Thu-Sat as the sfc low slowly
weakens, but at a slower pace than forecast 24 hrs ago. After a
couple lingering cooler than normal days at the start of the
period over the eastern part of the mainland, temperatures will
moderate back to within several degrees of normal for most of the
state with the better chance of sustained above average
temperatures near the Bering Sea near the upper ridge axis.
Fracasso
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can also be
found at:
https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html