Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
318 PM EDT Wed Sep 25 2019
Valid 12Z Sun Sep 29 2019 - 12Z Thu Oct 03 2019
Latest models and ensembles still show an amplified medium range
flow pattern, but forecast spread with weather focusing systems
embedded within the larger scale flow has increased days 4-8,
lowering forecast confidence closer to average. The WPC medium
range product suite was primarily derived from a composite blend
of the 12 UTC GFS/UKMET and 12 UTC GEFS/00 UTC ECMWF ensemble
means days 4/5, strongly trending blend weightings toward
ensembles at longer time frames amid growing uncertainty. The 00
UTC ECMWF in contrast offered outlier surface system progressions
compared to the 12 UTC GFS/UKMET and was discounted. The newer 12
UTC ECMWF has since trended more in line with the aforementioned
preferred model and ensemble blend. This overall solution
maintains good WPC continuity as coordinated with local Alaskan
WFOs.
In this pattern a significant and warming upper-level ridge will
build over Alaska as an unsettling longwave trough strongly
amplifies upstream over the Bering Sea/North Pacific Ocean. Brisk
low level winds will transport lead precipitable water values of
0.75 to 1.25 inches northward into the state, including some
tropical moisture associated with former tropical system Tapah.
Scattered to widespread precipitation will spread from the
Aleutians into southwest/western/interior Alaska later this week
and then into southern/southeast Alaska on the western periphery
of the slowly eastward shifting ridge early next week as energies
work increasingly into the Gulf of Alaska.
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
Hazards:
- Heavy rain across portions of the Alaska Panhandle and mainland
Alaska, Sun-Tue, Sep 29-Oct 1.
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