Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
328 PM EDT Tue Oct 01 2019
Valid 12Z Sat Oct 05 2019 - 12Z Wed Oct 09 2019
Over the past day guidance has continued its recent trend toward
improved agreement for the large scale flow. Nearly all solutions
now show a fairly amplified but moderately progressive pattern
featuring two significant features aloft. The first will be a
mainland Alaska/Bering Sea trough (with closed low over the
northwestern mainland) as of early day 4 Sat, expected to amplify
into the Gulf of Alaska/northeastern Pacific with time. This
evolution will lead to rapid weakening of initial low pressure
near the northwest corner of the mainland in favor of Gulf low
pressure. Then farther upstream an upper trough emerging from
Asia will pick up Tropical Storm Mitag in the short range. The
resulting system should eventually track over or just south of
eastern Siberia around early next week and then approach the
northwestern mainland by midweek, with a triple point wave in the
process of forming over the northern Gulf at that time. The
forecast pattern should favor heaviest precipitation over the
extreme southeast mainland and Panhandle, with somewhat lower but
still meaningful totals over parts of the southern and western
mainland.
Detail and timing differences are generally within typical error
ranges for the time frame of interest with fairly even spread
between opposite sides of the envelope--GFS/GEFS runs generally
somewhat faster than the ECMWF/ECMWF mean with the CMC/CMC mean
offering some support for either depending on the area. The 00Z
CMC likely strays too far north with extratropical Mitag near the
end of the period though. One notable area of spread involves the
weekend/early next week Gulf low, and again individual ensemble
spread seems to favor an intermediate solution. Members vary
considerably in latitude and reflect aforementioned timing
differences (with 00Z CMC members spread among both the GEFS and
ECMWF members).
Based on the favorable guidance comparisons in principle, today's
forecast started with an operational model blend (06Z-12Z GFS and
00Z ECMWF/UKMET/CMC) and was able to keep an operational model
emphasis into early day 7 Tue--with only 30 percent total 06Z
GEFS/00Z ECMWF mean weight at that time. For the rest of the
period the blend went closer to an even weight of models/ensemble
means. This approach yielded better than average continuity with
primary differences being better defined systems per latest
agreeable models and somewhat faster frontal progression south of
extratropical Mitag.
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
- Heavy precipitation across portions of the Alaska Panhandle and
southeastern mainland Alaska, Sat-Sun, Oct 5-Oct 6.
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