Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
637 PM EDT Fri Jul 10 2020
Valid 12Z Tue Jul 14 2020 - 12Z Sat Jul 18 2020
...Overview and Weather/Hazard Highlights...
A relatively progressive flow pattern looks to persist across the
North Pacific through much of the extended forecast period, with
Alaska on the northern periphery of this area. Ensemble guidance
suggests a gradual amplification of the flow over time, with
troughing becoming more prominent across the Aleutians, and
ridging building north into the Gulf of Alaska and Southeast
Alaska by late next week. An area of low pressure over the Gulf of
Alaska Tue will bring showers to Southeast Alaska before the
system moves inland. Farther west, another low pressure system is
expected to cross the Aleutians through the mid to latter part of
next week, bringing an increase in showers and perhaps some gusty
winds - although model spread with respect to this feature was
relatively high and confidence in the details of the forecast is
below average. Farther north, the setup across the North Slope an
portions of the Interior will be a rather chaotic one, with an
arctic upper low initially north of the Bering Strait retreating
westward through time, and a rather murky picture of what happens
in its wake, but with some potential for additional arctic
shortwave energy to move southward and affect northern Alaska,
keeping some risk for scattered showers and below average
temperatures in place.
...Guidance/Predictability Assessment...
Model/ensemble guidance showed relatively good consensus early in
the extended forecast period, but this degraded quickly at the
smaller scales over time, despite some consensus on the described
amplifying large scale pattern across the North Pacific next week.
The 12Z CMC/ECMWF showed perhaps the closest fit with the overall
consensus early on, and a blend of these solutions served as a
basis for the WPC forecast during days 4-5 (Tue-Wed). After that,
weight placed on ensemble means (ECENS and NAEFS) was increased
through time, and served as a majority of the forecast blend from
day 6 (Thu) through day 8 (Sat). This ensemble-heavy blend later
in the forecast period served to smooth out what were some rather
large differences among the deterministic guidance when it comes
to the timing/intensity of individual, smaller-scale systems with
low predictability.
Ryan
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: No significant hazards are expected over Alaska during
this forecast period.
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