Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 544 PM EDT Wed May 05 2021 Valid 12Z Sun May 09 2021 - 12Z Thu May 13 2021 ...Overview and Guidance Evaluation... Most guidance continues to show a deep-layer mean low over the Aleutians/southern Bering Sea that persists through the weekend before weakening early next week. Shortwaves ejecting from the mean low should produce a series of wavy frontal systems that cross the Aleutians through the Alaska Peninsula and Gulf of Alaska. Although the consensus clusters a little better than average, individual solutions suggest numerous uncertainties with the forecast that would keep confidence in any one solution low, given continuing run to run changes. On Sunday, the next of the series of waves forms east of the parent low and moves from the Aleutians to the open waters southeast of Kodiak Island. On Monday, this low north towards the Gulf of Ak, where the low stalls and decays on Tue 11 May. On Monday, the next forming ave of low pressure moves south of the Aleutians, with better than normal clustering, without unanimity. On Tue and Wed, the system moves slowly northeast, possibly reaching the AK peninsula or even into the adjacent southeast Bering Sea before decaying and merging with the upper low. By mid week, the next 500 mb low moves from south of Kamchatka east near 50N, spawning cyclogenesis, with the low approaching the lower Aleutians and possible arriving by the middle of next week. There is better than typical agreement the low will develop, with timing differences on Wed and Thu 13 May, as the GFS and Canadian global are about half a day faster than the 00-12z ECMWF and it ensemble mean. The agreement lead to a blend of the last 2 ECMWF runs and ECMWF Ensemble Mean to mitigate the differences among solutions, as usually with closed lows the slower solutions are more correct. ...Sensible Weather... Expect the highest probability of precipitation and moderate totals to extend from along the Alaska Peninsula to the Kenai Peninsula, with another max in southeast Alaska/panhandle in tandem with each wave of low pressure/associated fronts. Scattered diurnal convection is possible inland as a quasi-stationary front lingers over interior AK. The Aleutians will likely see unsettled conditions with periods of rain with each low later this week and again in the middle of next week. With above normal heights across interior and northern AK, temperatures are favored to be above normal in most areas. Persistence of the arctic high to the north should maintain cold air along coastal north Alaska, where below normal temperatures are possible next week. The Panhandle and coastal areas west to the Aleutians may see temperatures near normal in periods of clouds and showers (but below normal highs on cloudier days). Petersen No significant hazards are expected over Alaska during this forecast period. 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