Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
525 PM EST Tue Nov 03 2020
Valid 12Z Sat Nov 07 2020 - 12Z Wed Nov 11 2020
...Guidance/Predictability Assessment...
Successive troughing is forecast to push through much of the state
in progressive flow, squashing upper ridging in the northeastern
Pacific but at times nosing into southeastern areas. The 12Z
guidance offered good clustering to start the period Saturday as a
system lifts northward toward the eastern Aleutians and a boundary
lingers astride the North Slope. By early Sun, 12Z GFS slips the
surface low just east of the other models (closer to Kodiak) that
maintained a more defined parent low across the AKPen into Bristol
Bay and southwestern Alaska. With some wavering in recent runs
east-west, preferred to blend the 12Z guidance which keeps a
modest parent and triple point low before the triple point low
develops into the Gulf late Sun. The will approach the Panhandle
early Monday and head into Canada thereafter. Along the North
Slope, surface boundary may waver north-south as a weak upper
trough dips through late Sun into Mon.
Next system of interest will enter the western Bering around late
Sun, moving eastward next week. 12Z guidance paired the
ECMWF/Canadian closer to the ensemble means as the GFS spun up a
wave along the cold front, but then all diverged from the ensemble
means by late in the period. With no clear signal on which model
may have a better handle on the pattern/evolution, trended to
solely and ensemble mean blend between the 12Z GEFS mean and 00Z
ECMWF ensemble mean for lack of anything better. This would take
the parent low toward the Bering Strait next Wed as its triple
point takes over in the Gulf between Kodiak and the Kenai
peninsula. At the least, this was close to continuity from 24 hrs
ago but is a rather simplified depiction.
...Weather/Threats Highlights...
Approaching Pacific system will bring increasing coastal rain and
inland snow to southwestern portions of the state late Sat into
Sun on southerly to southeasterly flow. Precipitation may be heavy
with several inches (liquid) possible in favored areas. Heavy snow
is possible in some areas that stay cold enough. In-house
bias-corrected QPF shows 3-5 inches over southeastern Kenai
eastward toward Yakutat and some locally higher amounts into Mon
(5-8"). Next system over/near the western to central Bering Sea
Mon-Tue should spread another area of precipitation and strong
winds across the Bering Sea/Aleutians. This will move into
Southcentral by mid week next week but perhaps with less
precipitation than the lead system Sunday. However, this may bring
significant precipitation to western areas from the Y-K Delta
northward to Kotzebue.
Well above normal temperatures are forecast near the Brooks Range
on Saturday (anomalies about +20F) but this will trend less above
normal next week as the boundary slips southward. Above normal
temperatures are expected over the rest of the Interior (generally
west and north of the Alaska Range) next week. By contrast, below
normal temperatures are expected over the Panhandle and
southeastern areas Saturday with high pressure over Canada.
Temperatures will only moderate a bit next week as the lead system
approaches and moves through.
Fracasso
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 precipitation across portions of the Alaska Panhandle and
mainland Alaska, Sat-Mon, Nov 7-Nov 9.
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