Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 545 PM EDT Sun Sep 13 2020 Valid 12Z Thu Sep 17 2020 - 12Z Mon Sep 21 2020 ...Heavy rain Thursday for coastal southwestern/southern Alaska... ...Overview and Guidance/Predictability Assessment... An upper low will meander near the Bering Strait during the period, with shortwaves or upper lows rotating around it generally over the Aleutians and into the Mainland. Lead system on Thursday will likely be the most potent, traveling into the AKPEN/Gulf (parent/triple point low) Thursday and through the Interior Friday. Models continue to waver on the evolution, but still prefer the parent low track toward Bristol Bay/SW Alaska with triple point development just east of Kodiak as the whole system lifts northeastward on strong southwesterly flow. Blend of the GFS/ECMWF (which favored the farther west or east low) seemed to get a good starting point which carried northward. Higher latitudes will remain in weak troughing, modulated by the lead system. Trend has been just a bit quicker overall with this first system. Next system should dive through the Bering, across the Aleutians, and find its way to the Gulf late Sat into Sun. Ensembles still lose this system due to the spread, but GFS/ECMWF and some Canadian blend maintained a feature that has actually kept good continuity the past few days. Finally, last system out of the NW Pacific showed good agreement between the 12Z GFS/ECMWF and 00Z ECMWF ensemble mean (12Z GEFS mean farther south). This could affect southwestern areas next week as the upper pattern may retrograde a bit as can be the case. ...Weather/Threats Highlights... On Thursday, potential exists for much several inches of rain along the southern coast from the AKPEN/Kodiak through the Kenai Peninsula into Prince William Sound. This could be enhanced by triple point development just off the coast. Pattern should turn more showery after the system moves northeastward/eastward into/past the Panhandle late Friday. More focused rainfall may return with the third system next Sun/Mon over the Aleutians per the forecast of a defined low. Max temperatures will be near to above normal over the Interior but generally near to below normal over southern coastal areas into 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 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