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PMDAK 



Alaska Extended Forecast Discussion

NWS Weather Prediction Center College Park MD

805 PM EDT Fri May 03 2024



Valid 12Z Wed May 08 2024 - 12Z Sun May 12 2024



...Overview...



The leading upper low over the northeastern Pacific/Gulf of Alaska

(associated with an impactful system during the short range

period) is expected to weaken and open as its energy lifts

northward with time, pushing into mean ridging over Canada into

the northern mainland. This feature will be accompanied with

meaningful precipitation to the south-central and eastern parts of

the state. Meanwhile, the combination of a northern Bering Sea

upper low and a system emerging from the northwestern Pacific

should ultimately support an Aleutians system whose surface

reflection with mean upper low may settle over or near the Alaska

Peninsula by late next week.  This system will likely bring

increasing precipitation to the southern coast and Panhandle

during the middle to late part of next week.  With lower

confidence, another system may have some influence on portions of

the Aleutians by next Friday.



...Guidance Evaluation and Preferences...



Followed a similar model blend approach as the previous forecast

to provide some continuity with the average to below average

confidence pattern evolution. Initial weighting was 40 ECWMF/30

UKMET/30 GFS since the overall handling of the leading low

weakening/lifting northward was decent, although did include two

runs of the GFS to help fine tune the location of the system near

the Aleutians as it progressed. The EC ensemble means and GEFS

means will added in by Day 5 and increased weighting to 30% for

days 7 and 8. This helped reduce some of the noise, particularly

the Aleutians/western Gulf region.



Overall, there was decent clustering with the weakening upper low

as it drifts north and the northeast from the Northeast

Pacific/Gulf of Alaska, with the initial surface reflection

weakening in place. By midweek, there is a general consensus for

upper trough with an embedded low  along with best emphasis for

surface low pressure near the Aleutians and into the Alaska

Peninsula; however there continues to be a fair amount of spread

with any specifics for this feature. There is better than average

agreement toward the overall upper/surface low reaching near the

Alaska Peninsula by Friday. Between the initial Northeast Pacific

feature and Aleutians system, guidance shows a very wide spread

for the potential track of a mid-latitude wave forecast to be well

south of the Aleutians as of early Monday. The majority of

solutions would keep the wave near or south of 50N latitude and

have no effect on Alaska.  There has been trends from the CMC

ensemble mean to track it to Kodiak Island while the past couple

CMC runs have brought it into the northeast Pacific.  Such a

solution would yield an earlier increase of moisture along the

southern coast and/or Panhandle. At this time, use of the CMC/CMC

ensemble means were not utilized. 



...Weather/Hazards Highlights...



Episodes of locally heavy rainfall will be possible across parts

of the eastern and southern Mainland initially and into midweek as

the initial upper low offshore the southern coast/Panhandle

gradually opens up and lifts northward/northeastward. PW values

will be in the 0.25 to 0.50 range which will be 1 to 2 standard

deviations above average for early May. Currently the details are

too uncertain for evaluating how this activity may influence any

river flooding due to ice jams and snowmelt. Light precipitation

may hang around the southern coast and Panhandle early in the

week. The system tracking near the Aleutians should bring that

region mostly light precipitation during the first half of the

week.  As the surface low reaches the eastern Aleutians and Alaska

Panhandle, leading flow will likely bring increasing moisture to

the southern coast and eventually Panhandle. A burst of PW values

0.5 to 0.75 inch (about 1.5 standard deviations above average)

will help bolster rainfall amounts and intensity for portions of

the southern Coast and the Panhandle. A heavy rain area spanning

from portions of the Alaska Peninsula through Kodiak Island, along

the southern coast and covering a majority of the Panhandle in the

Days 3-7 Hazards Chart. The Aleutians may see another episode of

rainfall by next Friday with another system but confidence in

specifics is fairly low at this time.



Given the increased cloud cover and potential for rain early in

the week for southern and eastern portions of the state the daily

maximum temperatures are expected to be below normal for much the

extended period; with the eastern Interior tending to have the

best chance for some above normal readings. Elsewhere, the weather

pattern would support mix of both above and below seasonal average

temperatures over the far western reaches of the state. Morning

lows will tend to be more above normal over most of the state

(highest anomalies over the North Slope), though still below

normal over the far west early in the week. The Southcentral coast

and Panhandle may see some localized below normal lows as well.



Campbell/Rausch





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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