Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
316 PM EDT Fri Oct 25 2019
Valid 12Z Tue Oct 29 2019 - 12Z Sat Nov 02 2019
...Heavy coastal rain and mountain snow for southeastern coastal
areas and much above normal temperatures for the central and
northern mainland early next week...
A highly amplified upper pattern will be in place at the start of
the medium range period, with a strong closed low in the eastern
Bering Sea and a well-defined ridge downstream from the panhandle
northward through the Yukon. The amplified nature of the pattern
will allow moisture from the subtropics to be transported
northward, and where it impinges on the southeastern coast, there
will be heavy rain and high elevations snows. In addition to the
precipitation, the southerly flow will allow warmer than normal
air mass to overspread the southeast and Panhandle.
Starting Day 4, the models diverge in handling the closed low in
the eastern Siberian Sea. The 00-12Z ECMWF shows the low and
associated frontal boundary drifting east, while the 12z GFS and
Canadian Global are slow to move the low. In fact, with the 12z
GFS on the western fringe asna outlier solution,
the 06z run was used as a blend with the more highly weighted
ECMWF and ECMWF Ensemble Mean. An amplified upstream ridge would
help to keep the closed circulation in place.
The middle of next week sees the weakening Bering Sea closed low
move onshore across southest AK and then further inland as it
deamplifies. Given overall good agreement among the ECMWF Mean
and 06z GFS, a blend of these solutions was used in conjunction
with the operational ECMWF.
During the middle to latter part of next week, a new circulation
forms and moves south of the lower Aleutians Wed and middle
Aleutians Thu. The 12z ECMWF trended west to match the prior ECMWF
Ensemble Mean and 06z GFS, so a blend of these solutions was used
due to better than average clustering. The 12z GFS was a
faster/north outlier, thus not used in the overall blend. The low
lingers in the Gulf of Ak Sat 02 Nov as it weakens.
This system may bring a renewed outbreak of widespread
precipitation for the southern coastal sections Thursday into
Friday.
Petersen
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
Alaska Hazards...
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