Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 606 PM EDT Mon Sep 28 2020 Valid 12Z Fri Oct 02 2020 - 12Z Tue Oct 06 2020 Heavy rain and windy conditions likely for coastal areas of Southcentral and the Panhandle late this week into the weekend. ...Overview and Guidance/Predictability Assessment... Upper low is forecast to wobble around southwestern Alaska/Bristol Bay later this week into next week, bookended by ridging over NW Canada and the NW Pacific/northeastern Russia. Several embedded disturbances will rotate through/around the upper low, deforming it as the trough axis slowly moves eastward. The 12Z guidance offered a reasonable starting point for the forecast, transitioning toward the 12Z GFS/ECMWF and their ensemble means. Lead system will be a robust area of low pressure Friday just south of Kodiak, perhaps as low as the upper 960s mb. Parent low will rotate across the AKPEN to the northwest as the frontal boundary moves northeastward into the mainland/Panhandle and then Canada. Next system will lift toward Kodiak again by late Sat into early Sun. This system stems from the current tropical storm (Kujira) well east of Japan today (Monday). As the 12Z Canadian/UKMET drifted away from the GFS/ECMWF/ensemble consensus, their inputs were phased out. Lastly, next system from the central Pacific may rotate into the Gulf, a bit farther east than the previous ones, early next week. To the west, GFS/ECMWF and their ensembles were split slower (GFS/GEFS) vs quicker (ECMWF/ECENS) with the next system (far western Bering next Tue). Split the difference for now given the lead time and lack of meaningful trends. ...Weather/Threats Highlights... Lead system may bring in several inches of rain to coastal areas (especially southeast-facing) with strong S to SE to ESE flow off the Gulf. Several inches of rain are possible over southeastern Kenai, stretching to the Panhandle. Wrapped-up low will produce strong winds over Kodiak/southeastern Kenai/Prince William Sound as well as over southwestern areas. Showery weather will follow behind the lead system Saturday in advance of the next system by early Sunday. That will spread additional rainfall over nearly the same area but perhaps a bit farther east with the flow more S to SE (except immediately around the low). Total rainfall between the two systems may surpass ten inches over favored areas. Temperatures are forecast to be near to well above normal over most of the mainland in southerly flow. Near to below normal temperatures are forecast for the Aleutians under the upper low and perhaps over parts of the Panhandle. 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 mainland Alaska, Thu-Sat, Oct 1-Oct 3. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Fri, Oct 2 and Sun-Mon, Oct 4-Oct 5. - Heavy precipitation across portions of mainland Alaska, Thu-Mon, Oct 1-Oct 5. - High winds across portions of mainland Alaska, Thu-Fri, Oct 1-Oct 2. 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