Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
411 PM EDT Sun Jul 29 2018

Valid 12Z Thu Aug 02 2018 - 12Z Mon Aug 06 2018

An initial quasi-zonal flow regime across much of the region will
force a cascade of shortwaves downstream into the northeastern
Pacific by Friday. The ultimate configuration of the synoptic
pattern will be quite amplified with impressive height anomalies.
With a 594-dm mid-level ridge setting up south of the Aleutians
and a mean trough across northeastern Pacific, a pair of 2 sigma
anomalies will be in place. This remains the set up throughout
much of the period although northern erosion of the mid/upper
ridge is likely as upstream heights begin to lower across the
Bering Sea during the Day 6-8, August 4-6, timeframe. The exact
timing of this evolution is uncertain given the number of days out
but seems to be agreed upon by the guidance. Across the polar
latitudes, a deep upper low fixed over northern Nunavut will
provide a grazing band of height falls across eastern Alaska early
in the period. This mentioned low is forecast to drift eastward
but little movement is anticipated early on given the blocked flow
near the pole. Regarding a forecast preference, there is still
uncertainty during the Day 4/5, August 2-3, period with the
initial slug of energy driving down into the Gulf of Alaska. The
00Z ECMWF had shown a tendency to be slow and overly developed
across south-central Alaska on Thursday. However, the latest run
has appeared to have made some quicker adjustments bringing it
closer to the downstream quasi-consensus. Overall, leaned on a mix
of operational and ensemble guidance with more weighting toward
the 12Z/06Z GFS and the 12Z GEFS/00Z NAEFS/ECMWF ensemble means.

A cooling trend is in store across eastern Alaska after a warmer
start to the week. This will be in response to a baroclinic zone
dropping down from the polar regions which brings high
temperatures back into the upper 60s to lower 70s. With
precipitation, a combination of upstream perturbations in the flow
coupled with enhanced moisture will keep daily chances for
rainfall over the region. Models are scattered about with where
the heaviest amounts will congregate but there appears to be a
focus along regions of upslope within the complex topography.


Rubin-Oster


WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can be found at:

http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
http://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html