Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
753 PM EDT Fri Jul 08 2022
Valid 12Z Tue Jul 12 2022 - 12Z Sat Jul 16 2022
...Heavy Precipitation Threat for parts of the Alaskan Southern
Tier...
...Overview...
Today's guidance continues to show the establishment of generally
broad cyclonic flow aloft over and west/northwest of the mainland,
with at least a couple embedded shortwaves influencing the wavy
surface front expected to reach the northern mainland by the start
of the period early Tuesday and persist through the week. The
upper low initially near the North Pole may descend to 80N
latitude or so by the end of the period. Farther south, a system
exiting the southeastern Bering Sea should track across the
northeastern Pacific. This feature may end up taking a track
similar to a leading upper low that should cross the southern
Panhandle around Tuesday-Tuesday night (a little faster than
yesterday's forecast). The expected pattern will likely bring a
much cooler stretch of weather relative to the short range period,
while lingering enhanced moisture across the southern tier and
then eventually some moisture arriving from eastern Asia should
allow for areas of at least locally significant precipitation.
Meanwhile a west-central Pacific system should drift far enough
north to reach the Aleutians and southern Bering Sea by
Friday-Saturday, spreading moisture across the Aleutians and
vicinity after midweek.
...Guidance/Predictability Assessment...
Continuity is good in a broad sense for the overall pattern
evolution but there are some notable refinements in specifics.
For the upper low departing from the southeastern Bering Sea,
guidance has trended deeper/better defined once it reaches the
Pacific. As a result the surface low tracking south of the Alaska
Peninsula as of early Wednesday is deeper and wraps farther back
than previous forecast even though the upper center's position
changed less. The majority cluster now suggests the upper low may
remain intact through the end of the week when it could reach near
the southern Panhandle, close to the track of the leading feature
early in the period. GFS runs (including the new 18Z version)
have tended to take a farther south track with the late-week
system, thus far not supported by the ensemble means. Farther
north, operational models are resolving two main shortwaves--one
crossing the mainland Tuesday-Wednesday and another poised to
enter the northwestern mainland around Friday. Models diverge for
details after that time, favoring a trend toward the means then.
Most models/ensembles show better than average clustering for the
west-central Pacific system that should lift into the
Aleutians/southern Bering Sea by Friday-Saturday.
A composite of the 12Z ECMWF/GFS/CMC provided a good starting
point for depicting significant features during the first half of
the period. The blend did not include the UKMET as it was slower
than consensus for the system tracking out of the southeastern
Bering Sea and to the east with the initial west-central Pacific
system. After that point the total weight of 12Z GEFS/00Z ECens
input steadily rose to 30 percent on day 7 Friday and 50 percent
for day 8 Saturday. The latter reflects a balance of preferring
the means somewhat more over the mainland/Arctic and an
operational model blend still providing better detail over the
Pacific/Bering.
...Weather/Hazard Highlights...
Guidance continues to show above normal values of deep moisture
persisting over the southern mainland for the majority of next
week, contributing to a multi-day potential for episodes of
moderate to locally heavy precipitation over some locations.
Other parts of the mainland may see some precipitation as well,
with a wavy front to the north providing some added focus.
Significant totals could be the result of varying combinations of
more intense activity or accumulation of more moderate
precipitation over several days. A shortwave crossing the
mainland Tuesday-Wednesday may promote activity over parts of the
mainland, including over the northeast, and a more pronounced area
of moisture may arrive from the west ahead of a second shortwave
after midweek. It will take additional time to resolve the
specifics of precipitation coverage/intensity with this latter
area of moisture. Meanwhile the Panhandle should see
precipitation linger into Tuesday with the leading system tracking
over/near the region. The system tracking out of the southeastern
Bering Sea will spread a band of precipitation across mainly the
Alaska Peninsula on Tuesday and could eventually bring some
moisture into the southern Panhandle toward the end of the week.
The slowly moving system initially over the west-central Pacific
should drift into the Aleutians/southern Bering Sea toward the end
of the week, spreading mostly light to moderate rainfall across
the region.
Below normal highs should become more common over the course of
the week as broad cyclonic flow aloft becomes established over the
mainland. Coolest will likely be over the North Slope (north of a
persistent wavy front) as well as Southcentral and the Panhandle
(with clouds and precip prevailing). Expect warmer anomalies for
lows in most cases. Moderately below normal lows should be
confined mostly to the North Slope, though possibly expanding a
little southward late week, and to the southeastern
Coast/Panhandle.
Rausch
Hazards:
- Heavy rain across portions of the Alaska Panhandle, Mon, Jul 11.
- Much above normal temperatures across portions of mainland
Alaska, Mon, Jul 11.
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