Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
650 PM EST Fri Dec 01 2023
Valid 12Z Tue Dec 05 2023 - 12Z Sat Dec 09 2023
...Overview...
A low aloft will support a moderately strong surface low moving
into the Gulf of Alaska as the period begins Tuesday, weakening
and gradually pivoting through midweek. This feature could lead to
some enhanced precipitation for Southcentral into Southeast Alaska
as well as some gusty wind potential along the southern coastal
areas. Then by the latter half of next week, a northern stream
upper low with likely some surface reflection looks to track
southeastward into the Bering Sea and over western parts of Alaska.
...Guidance Evaluation and Preferences...
Model and ensemble agreement with the 12Z cycle was reasonably
good considering the time frame. Models show good clustering in
placement and depth of the Gulf surface low Tuesday and its
weakening with time. The details of the upper low and energetic
shortwaves and the associated surface lows moving from Siberia
southeast into the northern Bering Sea/western Alaska are a bit
more nebulous, but without particular outliers at this time, and
the timing on the large scale seems to have improved compared to a
day ago. The eventual depth of the trough by late week and how far
south the centroid of the low goes is more questionable, with the
12Z GFS on the southern side of the guidance envelope but still
supported by its ensemble. These details also impact the potential
for a southern stream surface low to track northeast through the
Pacific toward the Gulf late week. While there is some spread with
this, at least the ensemble means are agreeable about the low's
existence, and hopefully the details will cluster better with
time. Given the reasonable agreement, the WPC forecast used a
blend of the 12Z ECMWF/CMC/UKMET and 06Z/12Z GFS early in the
forecast, gradually increasing the amount of ensemble means with
time as spread increased later in the period, but only to half by
Day 8 as the deterministic models still generally seemed within
the ballpark.
...Weather/Hazards Highlights...
The initial storm system of concern is a reasonably deep surface
low (likely in the low 960s) moving into the Gulf on Tuesday.
Though the most concentrated moisture flux will be focused farther
south, some enhanced moist flow should bring in some moderate to
perhaps locally heavy precipitation totals to Southeast Alaska
into Tuesday and pivoting into Southcentral Alaska later Tuesday
into Wednesday. The precipitation type will vary over Southeast
but snow appears more likely for the land areas of Southcentral.
Additionally, some enhanced winds are a threat with this deep low.
The highest winds on the north and east sides of the low should
generally stay offshore or just skirt the western coast of the
Panhandle, but on the backside of the low some
northerly/northeasterly gap winds could form from around the
Alaska Peninsula to Cook Inlet. These gap winds may be around
30-40kt, but this is still below the criteria for hazardous winds
in those areas. Lighter precipitation may continue across the
southern coast into Thursday.
As surface and upper lows move southeast through the eastern
Bering/western Alaska, they will spread mostly rain to the
Aleutians and some snow to the Alaska Peninsula into the southern
Mainland, but with totals generally on the lighter side. Light
snow accumulations are expected over northern areas in the
interior to the Brooks Range. Additional enhanced precipitation
chances for Southcentral and Southeast are possible by late next
week as these lows come in and as another low may be drawn north
through the northern Pacific into the Gulf.
The Brooks Range and North Slope should maintain above average
temperatures through next week, with highs staying above 0F for
the most part. However, some pockets of below normal temperatures
are likely to traverse southwestern areas into Southcentral, with
temperatures within a few degrees of average in between.
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