Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
401 PM EDT Thu Apr 11 2019
Valid 12Z Mon Apr 15 2019 - 12Z Fri Apr 19 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 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 these
smaller-scale features generally decreases as a function of time.
Therefore, a relatively simple transition from a heavily
deterministic blend early in the extended to one comprised mostly
of ensemble means later in the period is the preference at this
time.
The ECMWF/GFS/CMC showed relatively good consensus and clustering
with ensemble members with respect to a surface low initially over
the Gulf of Alaska on Mon, with only modestly higher spread for a
second low entering the Gulf late Tue. After Tue, ensemble means
suggest another surface low crossing the Gulf late Wed/Thu, with
the associated frontal system pushing inland by late Thu/Fri. This
front could bring a round of more widespread/heavy precipitation
to portions of the Alaska Panhandle as it moves inland. With
increased ensemble spread by that time, however, the timing and
structure of any low pressure systems crossing the Gulf by mid to
late next week are certainly subject to change in future model
cycles. Farther north, arctic shortwave energy sliding around the
eastern periphery of the upper ridge will areas from the North
Slope to the Bering Coast through the period, with one such wave
diving southeast Mon-Tue showing good consensus in the guidance,
and perhaps another by the middle of next week (albeit with much
more uncertainty in the guidance).
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, Thu, Apr 18.
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