Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
418 PM EDT Wed Aug 21 2019
Valid 12Z Sun Aug 25 2019 - 12Z Thu Aug 29 2019
The upper-level pattern will remain relatively consistent across
Alaska during the extended period, with an area of negative height
anomalies south of the Aleutians and active westerlies from that
region toward the Gulf of Alaska, keeping chances for
precipitation relatively high across the Panhandle. Meanwhile,
persistent weak ridging across eastern Russia and the Bering Sea
should allow negative height anomalies to extend from the Arctic
across the northern half of Alaska, with a stream of shortwaves
affecting the North Slope.
Began the forecast for the extended period with a 06Z GFS/00Z CMC
blend days 4-5, before gradually transitioning to heavier
weighting of the ensemble means during days 6-8 due to somewhat
better consensus among those solutions relative to the ensembles.
The GFS/CMC showed much better consensus and consistency with the
ensemble means throughout the forecast period than the 00Z ECMWF,
which had an outlier solution with a deep low in the Gulf of
Alaska Mon-Tue (with little ensemble support). The preferred
solutions also maintain a forecast relatively close to continuity,
with a low pressure system approaching the Alaska Peninsula
Tue-Wed, and a second low pressure system crossing the Aleutians
during the Wed-Thu time frame next week. The Tue-Wed system may
bring the potential for heavy rainfall to portions of southern
mainland Alaska. Farther north, a cold front should sweep across
the North Slope Sun-Mon with a second one arriving Wed-Thu,
bringing a couple rounds of potential rain/snow.
Ryan
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
- Heavy rain across southeastern Alaska, Sat-Sun, Aug 24-25.
- Heavy rain across portions of the southern mainland Alaska, Wed,
Aug 28.
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