Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
729 PM EDT Fri Apr 12 2024

Valid 12Z Tue Apr 16 2024 - 12Z Sat Apr 20 2024

...Synoptic Overview, Guidance Evaluation, & Preferences...

An upper level ridge axis is expected to be in place across the
eastern mainland and into the Yukon Territory and southeast
panhandle region for the beginning to middle of next week. 
Meanwhile, a storm system over the North Pacific tracks in the
general direction of the AK Peninsula by late Wednesday and brings
a return to more rain and snow for southern coastal areas of the
state.  Meanwhile, a second low pressure system is forecast to
track across the Bering and weaken with time through midweek, and
some of the shortwave energy from this may interact with the low
moving north across the western Gulf. 

The 12Z model guidance suite features improvement overall in terms
of agreement compared to the unusually high differences noted
yesterday.  The CMC has trended more in line with the model
consensus across the Bering Sea region with a weakening surface
low even though it is depicted farther south, whereas its run
yesterday featured more surface high pressure over that region. 
Another big change from yesterday is the more northerly placement
of the main surface low in the ensemble means, compared to the
much more suppressed solutions from yesterday.  Upon examination
of the ML guidance from the ECMWF, there is more support for the
stronger GFS solution over the Bering early in the period, and the
ML guidance indicates a faster northward track of the low towards
Kodiak Island by 12Z Wednesday, which is also closer to the 12Z
GFS position.  The CMC and operational ECMWF support the idea of
the Gulf low moving on a more northeasterly path, with the low
south of the Aleutians becoming the dominant low by Thursday
morning.  The tricky part of the forecast is how much an
approaching weaker low south of the Aleutians and the stronger
Gulf low potentially phase, and this is where the model guidance
continues to struggle in resolving.  The fronts/pressures forecast
was based on a multi-model blend as a starting point through
Wednesday with more weighting towards the GFS given its solution
more in line with the ML guidance, and then increasing percentages
of the GEFS and EC means to close out the week and into Saturday.


...Weather/Hazards Highlights...

Coastal rain and mountain snow is likely to increase going into
the Wednesday-Thursday time period from Kodiak Island to the
Prince William Sound region as moist onshore flow increases ahead
of the Pacific low moving northward, there has been a slight
westward trend with the highest QPF from this event.  Strong
onshore flow over this region is expected to produce high waves
and gusty winds over 40 mph at times.  Light showers are possible
farther inland across southern mainland Alaska.  Temperatures are
generally expected to be in the 40s for highs across most Interior
locations, and some lower 50s for east-central portions of the
state.  The Brooks Range will be the demarcation for much colder
conditions across the North Slope and extending to the Arctic
Coast, with highs struggling to reach the freezing mark. 

Hamrick


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