Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
712 PM EDT Thu Apr 09 2020
Valid 12Z Mon Apr 13 2020 - 12Z Fri Apr 17 2020
...Overview and model guidance...
Upper ridging over the Gulf and Panhandle early next week will
slowly weaken by the end of the week as the flow strengthens over
the North Pacific and across the Beaufort/Arctic Sea. The models
and ensembles have struggled with the several features over the
northeast Pacific to start the forecast period due to slight
changes in the shape/strength of the upper ridge to the east and
how they either lift up and over or slip underneath the upper
ridge. Consensus of the 12Z deterministic guidance again today
(though a bit different than yesterday) should be a good starting
point with a few detail differences in the system
progression/depiction. By midweek, North Pacific system may slide
more easterly before turning northeastward toward the Gulf before
weakening/dissipating. That system may be a catalyst for the ridge
breakdown, in concert with a stronger northern stream flow across
the Interior than was shown yesterday. By the end of the week,
ensembles still indicate a more robust system to approach the
Aleutians, though the 00Z ECMWF ensemble mean was quicker than all
the rest of the guidance. Preferred the slower 12Z GEFS mean with
the GFS/ECMWF/Canadian. Farther east, unclear how the ridge breaks
down or tries to hang on in pieces across portions of western
Alaska, but a blended/consensus solution (such that it was) would
allow for some ridging ahead of the Aleutian system next Thu/Fri
but confidence is low given the spread.
...Weather/Threats Highlights...
Rather wet few days for areas of the AKPEN and favored upslope
regions of Kodiak Island eastward across the southern Kenai into
Prince William Sound (with snow in marginally colder air).
In-house ensemble-based QPF shows several inches (4-6") liquid
equivalent over the 5-day period. Otherwise, rain/snowfall will be
on the lighter side over the rest of the stateexcept for
southwestern areas and along the cold/stationary boundary through
the Interior. Along the North Slope, temperatures perhaps 10-25
degrees above normal (but still below freezing around Utqiagvik)
will trend a bit cooler (back to typical mid-April values) as
heights lower and the surface boundary settles across the Tanana
Valley. Over southeastern areas, temperatures will generally be
below normal as high pressure remains overhead or to the northeast
and east.
Fracasso
Hazards:
- Heavy precipitation across portions of mainland Alaska, Sun-Mon,
Apr 12-Apr 13.
- High winds across portions of mainland Alaska, Sun-Mon, Apr
12-Apr 13.
- High winds across portions of the Aleutians, Tue-Wed, Apr 14-Apr
15.
- Much above normal temperatures across portions of mainland
Alaska, Sun-Wed, Apr 12-Apr 15.
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