Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 735 PM EDT Sun Aug 21 2022 Valid 12Z Thu Aug 25 2022 - 12Z Mon Aug 29 2022 ...Unsettled weather to persist across the Gulf Coast of Alaska through next weekend, with periods of heavy rain and strong winds expected... ...General Overview... The extended period over Alaska late this week into next weekend begins with a weakening upper trough over the Gulf which should slide eastward into western North America by Friday. This happens as a deep upper low drops into the Bering Sea and skirts western Alaska around Sunday, before crossing the Peninsula into the Gulf. This recurring/reinforced troughing scenario will keep much of the Gulf Coast of Alaska (from the Peninsula to the northern Panhandle) fairly unsettled with periods of heavy rain and gusty winds, with also some locally heavy rains across western Alaska late this week. By Monday, onshore flow may finally shift south and east, with some modest rainfall moving into middle and southern parts of the Panhandle as well. ...Guidance/Predictability Assessment... Guidance today shows above average agreement on the synoptic level regarding the above scenario throughout much of the extended range, though with plenty of differences in the timing and details of individual systems. Models continue to show plenty of uncertainty on impacts to western Alaska with the upper low in the Bering Sea, seemingly flip flopping between more or less QPF. Hence, once again, per the latest trends, WPCs QPF footprint across western Alaska did increase today compared to yesterday. Timing of the front thereafter as it drops through the Aleutians and the eventual evolution of triple point redevelopment in the Gulf are also other areas of uncertainty. Regardless, nothing is too egregious considering a forecast this far out in time and so a general model blend seemed to suffice and serve as a good starting point for the forecast today. Utilized the deterministic runs through day 6, with more ensemble means (along with half of a GFS/ECMWF combo) days 7-8. The CMC was completely removed from the blend by day 8 due to it being significant stronger with a surface low which rounds high pressure in the north-central Pacific and brings it close to the Alaska domain (towards Kamchatka). This isn't a concern per se for Alaska at this time, but it did present some differences farther downstream inconsistent with the GFS/ECMWF and the ensemble means. ...Sensible Weather and Potential Hazards... Multiple storm systems near the Gulf Coast of Alaska is forecast to continue a rather unsettled pattern through much of the period across the southern coast, into the mountainous terrain of far southern Alaska, and the northern Panhandle. Heavy rain associated with a deep low in the short range period should be waning by the start of the period along the Gulf Coast on Thursday, but still some lingering rainfall and maritime threats as weakening troughing shifts east. The next system dropping through the Bering Sea may bring some moderate, maybe locally heavy, rain to western Alaska as early as Thursday-Friday, with another round of moderate to locally heavy rainfall again into the southern Coast/Panhandle next weekend as the system redevelops in the Gulf. In terms of temperatures across Alaska, upper ridging over the central and northern part of the state should keep highs near or above normal through much of the period, while clouds and precipitation keep southern (and western areas for a time) rather cool during the day. 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