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FXAK02 KWNH 072358

PMDAK 



Alaska Extended Forecast Discussion

NWS Weather Prediction Center College Park MD

757 PM EDT Tue May 07 2024



Valid 12Z Sat May 11 2024 - 12Z Wed May 15 2024



...Low pressure will bring moderate to locally heavy precipitation

to the southern coast this weekend, spreading into Southeast early

next week...





...Overview...



A mean trough aloft atop Alaska will be persistent through late

week into early next week, with some embedded energies including

an upper low shifting across the Alaska Peninsula into the Gulf

this weekend supporting a surface low as well. These features are

likely to produce some moderate to heavy rain and high elevation

snow from the eastern Aleutians Friday into the Alaska Peninsula

and Kenai Peninsula for the weekend and eventually into Southeast

Alaska. Precipitation may be less significant for the latter area

but could last multiple days.





...Guidance Evaluation and Preferences...



Model guidance is agreeable with the mid-upper trough expanding

from the westward part of the Mainland into the rest of it into

next week. Models even show better than typical agreement in the

energies embedded within the trough into the middle part of the

period. First a closed upper low with a stacked surface low should

push across the Alaska Peninsula into the Gulf over the weekend

and stay over the Gulf while weakening. Then additional energy

dropping south from the Bering Sea across the Aleutians during the

weekend and into the north Pacific by Monday should positively

tilt the southern portion of the trough. By Monday-Tuesday there

is a bit of spread with a shortwave or possibly small closed low

atop Bristol Bay or nearby, with the 12Z GFS weaker and farther

east. But overall, the model guidance was in good enough agreement

for a blend of the 12Z deterministic runs early on with small

incorporation of the GEFS and EC ensemble means by the mid-period.



The most uncertain feature looks to be upstream, with potential

for a closed upper low to track from Siberia into the Bering Sea

approaching Alaska by next Wednesday or so. The timing and

strength of the 06Z and 12Z GFS and the ECMWF were different but

within typical spread in the upper low and associated surface low,

but the 12Z CMC became out of phase as it took energy eastward

more quickly in the form of an open trough. The flat ensemble

means and the spread in the ensemble members themselves yield low

confidence in these features, so this will continue to be

monitored as it could be impactful to western Alaska later next

week. With the increasing model spread, increased the ensemble

mean proportion to just over half by the end of the extended

period.





...Weather/Hazards Highlights...



For Friday into the weekend, upper and surface lows tracking

across the eastern Aleutians into the Alaska Peninsula toward the

Gulf will lead to rainfall across that region and Kodiak Island

and the southern coast. Typically favored areas of onshore/upslope

flow could see heavy amounts, while higher elevation areas can

expect snow. Winds could be gusty especially for Cook Inlet into

the Gulf on Saturday ahead of the low (helping to bring in

moisture), while moderate to brisk winds are possible behind the

low as well. As the lows weaken over the Gulf, moist flow will be

directed into Southeast Alaska for the first half of next week.

The heaviest amounts there will likely be Sunday-Monday but still

may be below hazards criteria. Some lighter precipitation in the

form of rain showers and higher elevation snow showers could

extend into the Interior as well. Western Alaska may see

precipitation chances and winds increase for the middle of next

week, but with considerable uncertainty.



The unsettled pattern will tend to keep diurnal temperature ranges

more narrow than climatology, with daytime highs most likely to be

below normal and morning lows averaging above normal.  However,

some pockets of modestly above normal highs may be possible over

the Interior, while various locations depending on the day may see

slightly below normal lows.





Tate





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



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