Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
338 PM EDT Fri Apr 12 2019
Valid 12Z Tue Apr 16 2019 - 12Z Sat Apr 20 2019
The long wave pattern across Alaska is not expected to change
significantly during the extended forecast period. Upper-level
ridging is expected to persist/expand from extreme eastern Russia
into the western Bering Sea. Downstream of the upper ridge, the
pattern will favor a persistent mean trough across the north
central Pacific, centered generally south of the Alaska Peninsula.
This mean trough will be reinforced through the forecast period by
a number of smaller scale shortwaves traversing the broader
cyclonic flow. With the large scale pattern fairly stable, with
broad consensus among the guidance, predictability of
smaller-scale features generally decreases as a function of time.
Therefore, a deterministic blend very early in the extended to one
comprised mostly of ensemble means later in the period is the
preference at this time.
The ECMWF/GFS have shown some consensus for a couple runs with
respect to a surface low pressure system expected to move north
into the Gulf of Alaska Tue night-Wed night, and then pushing
inland on Thu. This front could bring a round of heavy
precipitation to portions of the Alaska Panhandle as it moves
inland. With increased ensemble spread by later next week,
confidence is low in the specific timing and structure of any low
pressure systems moving south of the Aleutians/Alaska Peninsula
and perhaps entering the Gulf during that time. Farther north,
while models agree that upper ridging should expand east across
the Bering Sea, solutions differ as to whether it also expands
into the Arctic Ocean north of Alaska, which plays a significant
role in whether arctic shortwave energy is able to dive south into
Alaska by later next week. Thus, while confidence is good in the
broad large scale pattern, confidence by later next week is
actually quite poor when it comes to the specifics of individual
systems/features.
Ryan
Bullet points from the WPC Days 3-7 Hazards chart can be found at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
- Heavy rain across portions of the Alaska Panhandle, Wed-Fri, Apr
17-Apr 19.
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