Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
748 PM EDT Thu Apr 14 2022
Valid 12Z Mon Apr 18 2022 - 12Z Fri Apr 22 2022
...Deep cyclone transitioning from western Pacific Typhoon Malakas
likely to affect the Aleutians early next week...
...Overview...
Expect the primary focus of significant systems during next week
to be near the Aleutians and over the northeastern Pacific. Deep
low pressure originally associated with Typhoon Malakas should
track over and then southeastward from the Aleutians early next
week, bringing strong winds/enhanced precipitation and maritime
threats. Another potentially strong system could track near the
Aleutians later in the week but with lower confidence in the
details at this time. Meanwhile an area of mean low pressure will
likely exist south of the Panhandle for most of the period, with
an initial system ultimately being replaced by a somewhat weakened
form of the leading Aleutians storm. The combination of these
features may bring some moisture northward into the Panhandle.
Farther north, an upper ridge centered near the northern coast of
the mainland should weaken somewhat but lingering ridging could
persist into late week, while lower heights with troughing/one or
more weak upper lows may prevail near the southern coast.
...Guidance/Predictability Assessment...
There is reasonable large scale agreement for the overall
Aleutians and northeastern Pacific pattern but there are
meaningful differences for some details. Some timing spread
develops for the first Aleutians storm associated with Typhoon
Malakas by Tuesday, with the 12Z GFS a bit on the faster side and
12Z CMC becoming slowest. An intermediate solution looks
reasonable and provides good continuity. There are greater
differences for the next system that may affect the Aleutians
later in the week, including details of evolution as well as
timing. Overall the latest GEFS/CMC/ECMWF ensemble means support
a slower system than forecast by the GFS. The 00Z and 12Z ECMWF
runs differ in the specifics while an average of their runs fits
well with the means. Thus after midweek the forecast blend
excludes the GFS and emphasizes the past two ECMWF runs and 12Z
GEFS/00Z ECMWF means. The new 12Z ECMWF mean supports this
approach. The 18Z GFS has slowed a little while becoming somewhat
of a deep extreme. Within the general area of low pressure south
of the Panhandle, predictability for specifics appears to be on
the moderate to low side given the small scale of initial low
pressure and then eventually some dependence on timing of the
second Aleutians system. A blend approach reflecting upstream
preferences should provide a reasonable starting point for the
time being.
Guidance has displayed various ideas for specifics of upper flow
over the mainland after the initial ridge centered near the
northern coast weakens. These include energy drifting up from the
south as the ridge retreats, some eventual influence from cyclonic
flow to the northeast, or persistence of ridging to some degree.
The favored blend leans a little more to the latter and the new
12Z ECMWF mean has trended more to the persistence scenario as
well.
...Weather/Hazard Highlights...
The extratropical reflection of Typhoon Malakas tracking near the
Aleutians around Monday will produce a broad area of strong
winds/maritime threats and precipitation from the Bering Sea
through the North Pacific early next week. Another strong storm
may track near the Aleutians by Thursday-Friday with associated
enhanced winds and precipitation. This system could extend its
influence at least as far east as the Alaska Peninsula. Relative
to the first system, there is greater uncertainty with details of
the late week system so continue to monitor latest forecasts for
updated information. After Monday a couple surface systems to the
south of the Panhandle may push moisture far enough north to bring
precipitation to portions of the region. Confidence is fairly low
for exact amounts/coverage but most activity should be on the
lighter side. Much of the mainland should be fairly dry with at
most very light/scattered precipitation. In general expect above
normal temperatures over most of the northwestern half of the
mainland and below normal readings over the southeastern half of
the mainland and the Panhandle. Some areas may see slightly
warmer anomalies for morning lows relative to daytime highs.
Rausch
Hazards:
- Heavy precipitation across portions of the Aleutians, Mon, Apr
18.
- High winds across portions of the Aleutians, Mon, Apr 18.
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