Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
755 PM EDT Thu Jul 11 2024

Valid 12Z Mon Jul 15 2024 - 12Z Fri Jul 19 2024

...Heavy Rainfall Threat across Southern Alaska this weekend...

...Overview and Guidance Evaluation/Preferences...

The latest guidance solutions seem reasonably agreeable in
depicting a slow-moving upper air pattern, with an initially deep
cyclone centered near the west coast of mainland Alaska weakening
and opening up with time toward the end of the medium-range
forecast period.  Deterministic solutions indicate that shortwaves
will spin around the mean center of the cyclone at various speeds
as the center of the cyclone drifts farther inland and
de-amplifies over southwestern Alaska through next week.  The
ensemble means from the GEFS, ECMWF, and CMC show very good
agreement in depicting the mean position of the weakening cyclone
through Day 8.  Therefore, the WPC forecast package today was
based a blend of 40% from the 06Z/12Z GFS and 12Z GEFS, 40% from
the 12Z ECMWF and EC mean, and 20% from the CMC/CMC mean for Days
3-5, increasing to more than 2/3 from the ensemble means by Day 8.
 This blend maintains reasonable WPC continuity.  WPC manual edits
were applied to better depict the strength of the main organized
surface systems that seem to have the most favorable mean upper
support as an offset to inherent smoothing from the blending
process. 


...Weather/Hazards Highlights...

The southern portions of Alaska will be in the midst of a wet
period as the medium-range period begins next Monday.  The wettest
day will probably be Sunday along the southern coastal areas and
down through the Panhandle as depicted on the WPC Hazards Outlook
map.  Winds could reach gale force in the Bering Strait and on the
back side of the surface cyclone across eastern Aleutians on
Sunday.  Cumulative heavy rain, 1-3" areal average amounts and
local amounts in the 3-5" range are possible in the Panhandle. 
The heavy rain threat will generally decrease by midweek as the
cyclone weakens but the rain can be expected to linger through
late week with a period of enhanced rainfall possible in the
Panhandle with the arrival of a low pressure wave.  The remainder
of the state will remain unsettled with scattered showers and
perhaps some embedded thunderstorms.  High temperatures will be
more evenly distributed, with 60s and 70s in the central Valley,
40s on the North Slope, and 50s and 60s elsewhere.  Subfreezing
lows should be constrained to the higher terrain of the Brooks
Range and the various ranges across south-central and southeast
Alaska.  The next round of rain should reach western Aleutians
late next week ahead of the next low pressure wave.

Kong/Roth


Additional 3-7 Day Hazard Information can be found on the WPC
medium range hazards outlook 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