Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
630 PM EDT Mon Oct 19 2020
Valid 12Z Fri Oct 23 2020 - 12Z Tue Oct 27 2020
...Heavy rain possible for portions of coastal Southcentral later
this week into the weekend...
...Guidance/Predictability Assessment...
Model guidance today agrees reasonably well that a robust cyclone
engulfing southwestern Alaska, the Aleutians, and the Bering Sea
late this week will gradually weaken as low pressure waves on the
trailing cold front lift toward southern Alaska and eventually
across the Panhandle by the weekend and early next week.
Meanwhile, the upper pattern is forecast to trend toward a flatter
flow as another system nears the western Aleutians by early next
week. The 12Z GFS/ECMWF formed a good cluster with the 12Z GEFS
mean and 00Z ECMWF ensemble mean for most of the medium-range
period. A blend of these model components yielded a surface
pressure pattern quite compatible with yesterday's WPC prognostic
charts. By early next week, the next cyclone nearing the western
Aleutians now appears to take on a more southern track, which is
the main difference from yesterday's forecast.
...Weather/Threats Highlights..
Rainfall around the Aleutians system could be locally heavy from
the Alaska Peninsula to the Kodiak especially the southeast-facing
areas Thu-Fri before gradually moderating during the weekend. By
early next week, low pressure waves lifting northward along the
trailing front from the weakening cyclone should deliver periods
of heavy precipitation from west to east across southern Alaska
into the Panhandle. Models are indicating varying degree of
intensities associated with these low pressure waves heading
toward the coast.
Upper ridging will bring above normal temperatures to much of
western coastal Alaska and the Interior, especially over the North
Slope, with dry conditions along the Arctic coast. Temperatures
may be 10-15 degrees above normal along and north of the Brooks
Range, and 5-15 degrees above normal north and west of the Alaska
Range. Areas of eastern/southeastern Alaska and especially the
Panhandle will see near to below normal temperatures as high
pressure (around 1045mb) delivers easterly flow to the region
Thu-Sat. Temperatures will moderate just a bit next Sun-Mon across
the Panhandle as onshore flow picks up.
Kong/Fracasso
Hazards:
- Heavy precipitation across portions of mainland Alaska and the
Aleutians, Thu-Fri, Oct 22-Oct 23.
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Sun-Mon, Oct 25-Oct 26.
- Heavy snow across portions of mainland Alaska, Thu-Fri, Oct
22-Oct 23.
- High winds across portions of mainland Alaska and the Aleutians,
Thu-Fri, Oct 22-Oct 23.
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
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