Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
541 PM EDT Fri Jul 16 2021
Valid 12Z Tue Jul 20 2021 - 12Z Sat Jul 24 2021
...Overview...
It remains evident that the current blocky pattern will start to
break down and move east next week, but with continued/renewed
troughing into an unsettled Bering Sea/Strait then
western/northwestern Alaska. Meanwhile, ample undercutting storm
energies will increasingly work through the
Aleutians/Southwest/AKpen to the Gulf of Alaska. A lead upper low
initially south of Haida Gwaii will very slowly move into British
Columbia as weakening ridging over the Interior/Southcentral moves
into the Yukon as the pattern relaxes.
...Guidance/Predictability Evaluation...
The WPC Alaskan medium range product suite was primarily derived
from a blend of well clustered guidance of the 12 UTC GFS/ECMWF
and GEFS/ECMWF ensemble means along with the 19 UTC National Blend
of Models days 4-8. Predictability seems to stay above normal
through the period, albeit with a gradual increase in forecast
spread with time as addressed by minority weighted inclusion of
the ensemble means. WPC continuity is well maintained, in part
again due to subsequent manual adjustments to this WPC blend to
ensure offshore low depth consistent with favorable upper support
and lowered uncertainty in this pattern.
...Weather/Threats Highlights...
Precipitation will be focused, especially early-mid next week,
over western/northwestern Alaskan areas during the period under
southwest flow with Bering lows approach/height falls, as well as
across the Aleutians along the tail-end of the frontal boundaries.
Widespread tenth to a quarter inch with focused half to one inch
rainfall (locally more) is possible over these areas over a 1-2
day period with each system. Some precipitation will also
overspread the North Slope/Brooks Range with inland system
translation and weakening.
Meanwhile, ample undercutting energy flow through the
Southwest/AKpen and into the Gulf of Alaska will lead to deepening
northern Gulf low and frontal system genesis. This emerging
pattern will offer unsettled maritime conditions over the Gulf and
some potential for modest rainfall into southern and southeastern
coastal areas mid-later next week.
Schichtel
Hazards:
Heavy rain across portions of northwestern Alaska, Mon-Wed, Jul
19-Jul 21.
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