Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
632 PM EST Sat Jan 25 2020
Valid 12Z Wed Jan 29 2020 - 12Z Sun Feb 02 2020
...Well below average temperatures for most of mainland Alaska...
...Active pattern with two deep Gulf of Alaska storms bringing
heavy precipitation to portions of Alaska Panhandle and mainland
next week...
Through the medium range period, the latest models and ensemble
guidance continues to show above average consensus on the overall
synoptic pattern. Upper level troughing should be reinforced
through much of the period, only gradually beginning to weaken and
shift eastward by next weekend. Forecast confidence remains high
for a cold surface air mass settling across much of Alaska well
into next week, with max and min temperatures 20+ degrees below
normal for some places.
An active North Pacific jet will send a series of potentially deep
shortwaves/surface lows across the North Pacific and into the Gulf
of Alaska. The first of such systems, in place across the central
Gulf by next Wednesday, models have consistently shown a central
pressures of at least the low 960s mb, with some runs even lower,
possibly into the 940s. This low should shift north and weaken in
favor of a second deep (970s mb) low just west of the southern
Panhandle on Thursday. These lows should keep precipitation
chances high across parts of the southern Mainland and much of the
Panhandle, with locally heavy precipitation possible. Lingering
deep layered cold air could support locally heavy snows even into
the lower elevations of southern Alaska and the northern
Panhandle. High winds across these regions are also possible.
Beyond Thursday, weak broad low pressure maintains across the
Gulf, being suppressed a bit south and east as surface high
pressure builds across the interior Mainland. In the Aleutians,
wind and precipitation chances increase by next weekend as a deep
surface low moves towards the western islands.
The 12z guidance suite showed very good agreement through much of
the period. The led to a total deterministic model (GFS/ECMWF/CMC)
blend through day 5. After, opted to slowly increase contributions
from the ensemble means to mitigate the smaller scale, less
predictable, detail differences. This maintains good continuity
both with yesterday's Alaska progs and with downstream preferences
over the CONUS.
Santorelli
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards 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