Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
349 PM EDT Sat Jul 20 2019
Valid 12Z Wed Jul 24 2019 - 12Z Sun Jul 28 2019
Trough/ridge pattern will only slowly shift eastward late next
week through the weekend as a Gulf upper low fills. The
models/ensembles remain in good agreement to start the forecast
but then diverge from Friday onward. Preferred to stay closer to
continuity rather than introduce a change while confidence is low.
The 12Z GFS and 00Z ECMWF offered reasonable clustering with their
ensemble means and each other to use as a starting point. This
takes a northeast Pacific system toward the Panhandle Wed-Fri
(good agreement here) with continued (but not continuous)
rainfall. Upstream, a system will push through the Bering and
reach the western coast of Alaska where it may either lift
northeastward (12Z GFS) or have its southern extent (sfc wave)
move across the AKPen into the Gulf (00Z ECMWF and somewhat the
06Z GFS) or get left behind in the Bering (00Z GFS, not too
likely). Ensembles suggest somewhat of split, with the lead
weakening low lifting northeastward but the trailing low becoming
the deeper feature as it slides into the west side of the Gulf
upper low. Given the uncertainty, opted to side with continuity
and the 00Z ECMWF until a more meaningful ensemble signal emerges.
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
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