Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
654 PM EDT Fri Apr 02 2021
Valid 12Z Tue Apr 06 2021 - 12Z Sat Apr 10 2021
...A cold pattern for Alaska...
...Guidance/Uncertainty Assessment...
Guidance over the Alaska region for the extended range period is
mostly in agreement with the large scale/synoptic pattern overall,
though continue to show more significant embedded system
differences later in the period. A deterministic model blend
between the reasonably well clustered 12 UTC GFS/ECMWF/UKMET and
the 19 UTC National Blend of Models seems to serve well as a
forecast starting point days 4-6 (Tue-Thu) and this solution has
good ensemble support. After that, some differences in timing of
ridging across the Bering and the next systems upstream led to
more weighting of the more compatible GEFS/ECMWF ensemble means
days 7/8. Manual adjustments were then applied to the blend to
ensure offshore low system strength and circulation would be
consistent with favorable upper support and to account for
weakening due to the blending process.
...Weather/Hazards Highlights...
An amplified and cold Arctic vortex is slated to dig over an
unsettled North Slope and Interior early next week and
significantly cool the region. The lead pattern underneath for
early next week will feature lows/frontal systems tracking across
the southern Bering Sea and effect the Aleutians/Southwest
AK/AKpen before reforming over the northern to eastern Gulf of
Alaska. These systems will focus moderately unsettled weather
across the region in progressive flow. However, the flow will
amplify significantly upstream next week. Amplification will drive
Arctic energies and cold air sharply down across the state and the
Gulf of Alaska. Stream phasing and low pressure reinforcement
across the northern and eastern Gulf should favor periods of
terrain enhancing precipitation for much of the period for
Southeast Alaska and the Panhandle. The mainland should dry out as
frigid high pressure settles in. This would allow below normal
temperatures to expand across almost all of Alaska, with the
coldest anomalies (as much as 20-30+ below normal) across the
Interior. Upstream surface system and progression entering the
Bering Sea by later in the week is quite uncertain, but may
leading precipitation into the Aleutians and present maritime
issues.
Schichtel
Hazards:
- Much below normal temperatures across portions of mainland
Alaska, Tue-Thu, Apr 6-Apr 9.
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