Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 704 PM EDT Thu Sep 26 2024 Valid 12Z Mon Sep 30 2024 - 12Z Fri Oct 04 2024 ...Strong winds and some moderate to heavy rainfall expected to accompany a strong storm system into the Panhandle Monday-Tuesday... ...Overview... The main system of concern will be early in the period as an upper low through the Gulf early next week spins up a rather deep surface low which tracks into the Panhandle region around Tuesday. This will bring a low end atmospheric river and periods of high wind and moderate to locally heavy rainfall to portions of Southeast Alaska. The pattern remains fairly progressive into mid next week as the next system drops from the Bering Sea/Bristol Bay region into the Gulf, keeping south-central to southeast Alaska somewhat unsettled. Another upper low and deep surface low will move into the Bering Sea late next week, with some rainfall reaching the West Coast of Alaska. ...Guidance Evaluation/Preferences... Models overall show good agreement with the large scale pattern through the period, but plenty of uncertainty in the details. There are some minor placement differences, but the guidance all agree the initial storm into the Panhandle region early week should be modestly strong. The CMC is the fastest with the next system into the Gulf around Wednesday-Thursday, with the GFS and ECMWF slower, but the ensemble means also show something a little faster as well. For a day 7-8 forecast, models show good agreement on the existence of a deep Bering Sea system late next week but a lot of uncertainty in the placement/track of the surface low and timing of the front and weather into the West Coast. The early period WPC forecast was able to utilize a blend of the deterministic guidance with sufficient agreement. By day 6 and beyond, gradually leaned more towards the ECMWF with the ensemble means to help mitigate the harder to resolve detail differences. ...Weather/Hazards Highlights... The early week surface low into the southern Panhandle region of Southeast Alaska will bring with it maritime hazards, rainfall, and gusty winds. While periods of heavy rainfall are possible, the winds will be the true hazard with this storm. Some model guidance suggests likely storm to near hurricane force winds are possible in some locations along with significant wave heights. The storm should move quickly inland late Tuesday. The remainder of the Southeast/Southern Coast area should remain generally unsettled with light rain expected as another weaker system passes from Bristol Bay into the Gulf mid week. A large and deeper storm system should enter the Bering Sea late in the period, with increasing rain chances along the West Coast and through the Aleutians Thursday into Friday. In a broad sense, cooler than normal high temperatures are likely over southern parts of Alaska and warmer than normal temperatures are likely for the northern two-thirds of the Mainland during the period. 40s to low 50s are forecast for highs in most lower elevation areas, with a slight cooling trend as next week progresses. Most areas should see greater coverage of above normal morning lows though, with most of the below normal readings confined to the southwest and the Panhandle. Santorelli Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook 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