Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 746 PM EDT Wed Mar 22 2023 Valid 12Z Sun Mar 26 2023 - 12Z Thu Mar 30 2023 ...Overview... The medium range period begins early next week as surface and upper lows trek across eastern Siberia into the Chukchi Sea, providing south-southwesterly gusty winds to the Aleutians and western mainland as well as moist inflow causing precipitation potential, with heavy snow possible for the Seward Peninsula into parts of the Brooks Range. Some lesser precipitation amounts could spread across the rest of the mainland into the Panhandle for Monday-Tuesday as a cold front and upper troughing push through (displacing an upper ridge extending through the mainland on Sunday). Then another storm system looks to track eastward from the Bering Sea around midweek next week, which will likely affect the western part of the state and some way but with low confidence in the details for now. ...Guidance Evaluation/Predictability Assessment... Overall the somewhat progressive synoptic pattern seems reasonably well handled by the model guidance, especially early next week. Models agree that an upper low should track north-northeast across eastern Siberia into the Arctic Circle while troughing extends across the Bering Sea. Meanwhile an upper high centered well south of the Alaska Peninsula will extend ridging into the mainland for an amplified pattern to start the week. There are some minor model differences with where the exact interface of the trough/ridge will set up along with the surface frontal positions. This is not too egregious for this lead time but could affect amounts and timing of precipitation spreading inland across the mainland. The 12Z CMC was perhaps on the faster side of the guidance envelope with bringing the troughing eastward while the 06Z GFS was slow--the 12Z GFS looked better clustered with the bulk of other models. The WPC model blend favored middle ground placement using a blend of the 12Z ECMWF/GFS along with lesser amounts of the 12Z CMC and UKMET. Models indicate the upper-level pattern should likely deamplify a bit by around Tuesday as troughing comes farther into the mainland and displaces and weakens the ridge. Then a potent shortwave along with a surface low is likely to track eastward across the Bering Sea around midweek and perhaps reach the western mainland by next Thursday. While guidance agrees that this feature is likely to exist, there are some notable variations on the timing and placement of the lows in the deterministic models and ensemble members. Given the increasing spread and thus uncertainty, added in and gradually increased the GEFS and EC ensemble means into the model blend for the latter half of the medium range period. ...Weather/Hazard Highlights... Precipitation and gusty winds are likely to be ongoing across the western part of the state on Sunday, while a cold front pushes a round of rain across the Aleutians as well. The southwestern mainland could see messy weather with rain and perhaps precipitation types changing through the event, while the northwestern mainland generally can expect heavy wet snow, with enhanced totals and some possible gusty winds where there is upslope flow across the Brooks Range. Winds could also be high (30-50mph with higher gusts) along the west coast of the state where the surface pressure gradient is tight, and coastal flooding may also be a problem. Light to moderate precipitation is likely to spread across much of the mainland and then the Panhandle around Monday-Tuesday along and ahead of the cold front and upper trough. Then the second low pressure system could provide another round of precipitation to the Aleutians/Alaska Peninsula and the western mainland by next Wednesday-Thursday, but details on this will have to be refined in future forecasts. Temperature-wise, the western mainland into the Brooks Range and North Slope can expect milder than average temperatures as deep layer southwesterly flow brings in warmer and moister air on Sunday-Monday with a fairly expansive area of temperatures above freezing, even perhaps toward the North Slope on Sunday. Then the upper trough and the cold front making their way through the mainland Tuesday-Wednesday should cool temperatures to a bit below normal, particularly highs, though the North Slope should remain milder than average. Though uncertain for now, the western part of the state may see another warmup by the latter part of the period ahead of the second storm system. For the Panhandle, high temperatures are forecast to be generally below average next week while the lows are nearer to normal. Tate 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 Hazards: - Heavy snow across portions of western mainland Alaska, Sat-Sun, Mar 25-Mar 26. - High winds across portions of western mainland Alaska, Sat-Sun, Mar 25-Mar 26. - High winds across portions of the Aleutians, Sat, Mar 25. 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