Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
527 PM EDT Tue Jul 28 2020
Valid 12Z Sat Aug 01 2020 - 12Z Wed Aug 05 2020
...Overview and Guidance Evaluation...
As the deep upper low currently over the Arctic retreats/weakens
to the northeast later this week, another on from the Bering Sea
will move eastward into Southwestern Alaska with another in the
Gulf this weekend. The pattern will attempt to weaken into broad
troughing next week with smaller-scale features after more than a
week of blockier flow. The latest 12Z deterministic guidance
showed good agreement with the ensembles Sat-Mon with the Bering
system before they dispersed from the ensemble consensus. Could
not rule out much from the models though the 12Z ECMWF/Canadian
were to the south of the means and the GFS/UKMET were to the
north, favoring a broad consensus. This was close to the forecast
yesterday but quicker by about 12-18 hrs. Lead system in the Gulf
showed continued good continuity and a blend sufficed, though the
Canadian was perhaps too low with pressures via a few sfc lows.
By next week, still forecast the sfc system to progress eastward
into the Gulf as the triple point develops east of Kodiak, then
continues swiftly eastward into the Panhandle. Ensembles and most
models show a weaker system in the western Bering late in the
period but with a large latitudinal spread. Favored the ensembles
with some weighting of the ECMWF/GFS/Canadian.
...Weather Highlights/Threats...
The Northeast Pacific/Gulf upper low Saturday will bring a surge
of moisture into the southern mainland/Panhandle with significant
precip totals possible at some locations depending on specifics of
flow aloft, wind direction, and moisture levels. The fairly
vigorous system tracking across the Bering Sea during the weekend
into next week will likely bring a period of precipitation and
winds, with effects reaching the mainland late weekend/early next
week. Best potential for highest totals with this system will be
near the southern coast but other locations may see meaningful
precip as well.
Expect below normal high temperatures across the northern and
southern thirds of the mainland along with the Panhandle, while
warmer readings versus normal will prevail over the central
mainland, especially Saturday. Starting Sunday, the negative
anomalies should expand and yield below normal highs over most of
the state next week, but still with greatest negative anomalies
over the far north and south. Clouds/precip should promote broader
coverage of above normal min temps south of the Brooks Range.
Fracasso
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
Hazards:
- Heavy rain across portions of the Alaska Panhandle and mainland
Alaska, Sat-Sun, Aug 1-Aug 2.
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