Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
730 PM EDT Sat Mar 27 2021
Valid 12Z Wed Mar 31 2021 - 12Z Sun Apr 04 2021
...Guidance/Uncertainty Assessment...
The 12 UTC GFS/ECMWF/UKMET, the 12 UTC GEFS mean, the 00 UTC ECMWF
ensemble mean and the 19 UTC National Blend of Model solutions are
reasonably well clustered day 4/5 (Wed/Thu) and a composite blend
seems to provide a good starting point for the forecast process in
a period with above normal predictability. However, forecast
spread increases dramatically at longer time frames as guidance
seems quite sensitive to upstream feature effect on flow evolution
and amplitude. Given rapidly rising uncertainty, the WPC Alaskan
medium range product suite into days 6-8 (Fri through next
weekend) was primarily derived from the still reasonably
compatible GEFS/ECMWF ensemble means and the 19 UTC National Blend
of Models. These blends maintain good WPC continuity in difficult
flow.
...Weather/Hazards Highlights...
Short range Bering Sea storm energies moderate over the mainland
into mid-later week, but along with lingering upper trough support
the pattern should favor a period with unsettled/cooled weather to
include some threat for locally heavy snows. Meanwhile, an
amplified upper trough will settle over the Gulf of Alaska and be
periodically be reinforced by progressive/uncertain upstream
energies and surface systems digging from an also unsettled Bering
Sea/Aleutians. This may anchor a mean surface low position over
the northern Gulf of Alaska and a risk of high winds/waves and
lead/favorable onshore flow to fuel a threat for a prolonged
periods with terrain enhancing precipitation over Southeast Alaska
midweek into next weekend.
Schichtel
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