Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
658 PM EST Mon Feb 21 2022
Valid 12Z Fri Feb 25 2022 - 12Z Tue Mar 01 2022
...Heavy precipitation along the southern coast of the mainland
through Friday, possibly extending into parts of the Panhandle...
...Overview...
A sharp and amplified upper ridge should gradually trend weaker
and broader as it moves over western Canada and the Arctic. An
area of broadly cyclonic flow behind this ridge will contain
multiple shortwaves whose associated surface systems may serve to
enhance precipitation along the southern coast and Panhandle
through the end of the week and possibly into the weekend. A
leading wave should track rapidly northwestward from just south of
the Alaska Peninsula Friday into Saturday while another system
(with lower confidence) could track into the Gulf of Alaska during
the weekend. By the first part of next week the two primary
features of interest will be a mid-latitude Pacific system
expected to track into the northeastern Pacific and an area of
fairly strong low pressure that may track into the western
Aleutians/Bering Sea next Tuesday. The forecast pattern will
support well above normal temperatures over many areas with
highest anomalies likely over the northwestern half of the
mainland. Temperatures should moderate somewhat by early next
week.
...Guidance/Predictability Assessment...
From late week into the weekend the primary forecast issue
involves the continued uncertainty with small-scale northeastern
Pacific surface lows supported by shortwaves embedded within the
flow around the initially sharp western Canada ridge. In relative
terms the best confidence lies in a wave tracking from south of
the Alaska Peninsula into the northern Bering Sea Friday-Saturday
as a defined impulse aloft follows this path. Latest
GFS/ECMWF/CMC runs form a loose cluster for this system while the
12Z UKMET was a deep and slow extreme. Confidence is much lower
for potential trailing waviness that may reach into the Gulf of
Alaska during the weekend. The last several ECMWF runs have
depicted this wave while a number of CMC runs have also had it and
in stronger form. GFS runs have been inconsistent, with 12Z and
18Z runs vaguely hinting at an ECMWF-like wave but emphasizing one
farther south. Ensemble members display no meaningful clustering
and so do not really reflect this specific wave at all. The 12Z
GEFS/CMC means actually have a weak wave lingering near Kodiak
Island through Saturday, a scenario not reflected in operational
runs and seemingly less likely as height falls extending across
the northeastern Pacific Friday into the weekend should support a
farther east track of any low pressure. The forecast blend tilted
somewhat in the ECMWF direction given a continued southerly
component of mean flow aloft into the weekend, supporting a
reasonable degree of northward progression of any surface wave.
Meanwhile there has been multi-day continuity with the general
idea of surface development across the mid-latitude Pacific and
turning into the northeastern Pacific, but with both the
operational models and ensemble means showing some spread and
run-to-run variability for timing and track. By next Tuesday the
current best guidance cluster includes the 12Z ECMWF/CMC and
latest ensemble means while latest GFS runs have strayed to the
suppressed side of the envelope. Farther upstream the ensemble
means have been consistent and agreeable over the past couple of
days for the system expected to track near the western Aleutians
by next Tuesday. Operational runs have been depicting a general
area of low pressure in the vicinity of the means but with the
possibility of multiple centers.
The forecast blend started with 12Z model guidance, reflecting
greater emphasis on the non-UKMET cluster for the Friday-Saturday
wave and then yielding a slightly weaker version of the trailing
ECMWF wave during the weekend. Input of 12Z GEFS/00Z ECMWF means
increased mid-late period to provide an even model/mean weight by
days 7-8 Monday-Tuesday.
...Weather/Hazard Highlights...
Strong low-level flow to the east of a wave (and trailing front)
tracking from south of the Alaska Peninsula into the northern
Bering Sea Friday into early Saturday will enhance the potential
for heavy precipitation along the southern coast of the mainland
late this week. The Kenai Peninsula should see the highest totals
from this event. The heavy precipitation may extend as far east
as the Panhandle, with low-confidence details for a possible
trailing wave determining amounts and duration of activity over
the southeastern coast/Panhandle over the weekend. Some
precipitation could extend farther north over the mainland but in
much lighter and scattered form. While precipitation along the
southern coast and Panhandle should generally trend lighter with
time, another area of moisture could reach the southeastern
coast/Panhandle early next week if a northeastern Pacific system
tracks close enough. A strengthening northwestern Pacific into
western Aleutians/Bering Sea system and leading front may spread
increasing winds/precipitation across the Aleutians next
Monday-Tuesday.
Coverage of much above normal temperatures will be greatest from
late this week into the weekend. Highest anomalies should be over
the northwestern half of the mainland and some areas could see
readings at least 30-40F above normal, especially for lows.
Temperatures should steadily moderate from south to north early
next week but remain above normal over most areas. The southern
two-thirds of the Panhandle should continue to see moderately
below normal highs.
Rausch
Hazards:
- Heavy precipitation across portions of southern coastal Alaska,
Thu-Fri, Feb 24-Feb 25.
- Heavy precipitation across portions of southeastern coastal
Alaska and northern Panhandle, Fri, Feb 25.
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