Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
306 PM EST Tue Nov 05 2019
Valid 12Z Sat Nov 09 2019 - 12Z Wed Nov 13 2019
Most model and ensemble guidance shows a large scale pattern
featuring varying degrees of mean ridging aligned from near the
British Columbia coast north-northwest through the mainland while
troughing (with one or more embedded closed lows) migrates across
the southern Bering Sea/Aleutians/North Pacific. The gradient
between these two features should gradually tighten and shear out
or eject in some fashion the initial energy over the east-central
Pacific and southern Bering. Over higher latitudes by next
Tue-Wed there is some clustering toward the idea of cyclonic flow
settling over the Arctic/Canadian Archipelago with an associated
cold front reaching the northern mainland.
Models and ensemble members display little meaningful clustering
for individual lows over the northeastern Pacific/Gulf of Alaska
for most of the period, keeping detail confidence quite low.
There is a somewhat better signal for a significant low pressure
system over the North Pacific, albeit with typical timing/track
differences for the time frame involved. One big question mark
here is to what extent Super Typhoon Halong plays a role--with
very poor agreement on that aspect. Overall prefer a model/mean
compromise, with the ECMWF mean likely too fast given system
strength. ECMWF runs had been oscillating but the new 12Z run has
maintained a more western path similar to the past couple 00Z
runs. The 12Z GFS is even farther westward. At higher latitudes,
latest GFS runs have joined recent ECMWF runs in bringing an
Arctic upper low to the northeast of the mainland. The ensemble
means keep the feature farther northeastward but still show enough
cyclonic flow to bring a cold front into the North Slope region.
Based on the current array of guidance and continuity the forecast
blend started with an even weight of the 00Z GFS/ECMWF and
NAEFS/ECMWF means through the period. The NAEFS mean was
generally stronger than the 06Z GEFS mean with important features.
This blend and subsequent manual adjustment represented the most
agreeable aspects of the overall pattern while providing some
degree of embedded detail and downplaying other less confident
ideas. For example recent ensemble mean trends toward a modestly
stronger mean ridge aloft question the degree to which CMC and
perhaps even to some extent ECMWF runs have been bringing energy
into the mean ridge early next week. Expect highest precipitation
totals for the period to be along the southern coast and Panhandle
with meaningful amounts also across the Aleutians. Strong winds
may accompany the potential North Pacific storm early-mid week.
Rausch
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
- Much above normal temperatures across portions of northern
Alaska, Sun-Mon, Nov 10-Nov 11.
- Much above normal temperatures along the coastal plains of
northern Alaska, Sun-Tue, Nov 10-Nov 12.
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