Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 658 PM EST Mon Feb 21 2022 Valid 12Z Fri Feb 25 2022 - 12Z Tue Mar 01 2022 ...Heavy precipitation along the southern coast of the mainland through Friday, possibly extending into parts of the Panhandle... ...Overview... A sharp and amplified upper ridge should gradually trend weaker and broader as it moves over western Canada and the Arctic. An area of broadly cyclonic flow behind this ridge will contain multiple shortwaves whose associated surface systems may serve to enhance precipitation along the southern coast and Panhandle through the end of the week and possibly into the weekend. A leading wave should track rapidly northwestward from just south of the Alaska Peninsula Friday into Saturday while another system (with lower confidence) could track into the Gulf of Alaska during the weekend. By the first part of next week the two primary features of interest will be a mid-latitude Pacific system expected to track into the northeastern Pacific and an area of fairly strong low pressure that may track into the western Aleutians/Bering Sea next Tuesday. The forecast pattern will support well above normal temperatures over many areas with highest anomalies likely over the northwestern half of the mainland. Temperatures should moderate somewhat by early next week. ...Guidance/Predictability Assessment... From late week into the weekend the primary forecast issue involves the continued uncertainty with small-scale northeastern Pacific surface lows supported by shortwaves embedded within the flow around the initially sharp western Canada ridge. In relative terms the best confidence lies in a wave tracking from south of the Alaska Peninsula into the northern Bering Sea Friday-Saturday as a defined impulse aloft follows this path. Latest GFS/ECMWF/CMC runs form a loose cluster for this system while the 12Z UKMET was a deep and slow extreme. Confidence is much lower for potential trailing waviness that may reach into the Gulf of Alaska during the weekend. The last several ECMWF runs have depicted this wave while a number of CMC runs have also had it and in stronger form. GFS runs have been inconsistent, with 12Z and 18Z runs vaguely hinting at an ECMWF-like wave but emphasizing one farther south. Ensemble members display no meaningful clustering and so do not really reflect this specific wave at all. The 12Z GEFS/CMC means actually have a weak wave lingering near Kodiak Island through Saturday, a scenario not reflected in operational runs and seemingly less likely as height falls extending across the northeastern Pacific Friday into the weekend should support a farther east track of any low pressure. The forecast blend tilted somewhat in the ECMWF direction given a continued southerly component of mean flow aloft into the weekend, supporting a reasonable degree of northward progression of any surface wave. Meanwhile there has been multi-day continuity with the general idea of surface development across the mid-latitude Pacific and turning into the northeastern Pacific, but with both the operational models and ensemble means showing some spread and run-to-run variability for timing and track. By next Tuesday the current best guidance cluster includes the 12Z ECMWF/CMC and latest ensemble means while latest GFS runs have strayed to the suppressed side of the envelope. Farther upstream the ensemble means have been consistent and agreeable over the past couple of days for the system expected to track near the western Aleutians by next Tuesday. Operational runs have been depicting a general area of low pressure in the vicinity of the means but with the possibility of multiple centers. The forecast blend started with 12Z model guidance, reflecting greater emphasis on the non-UKMET cluster for the Friday-Saturday wave and then yielding a slightly weaker version of the trailing ECMWF wave during the weekend. Input of 12Z GEFS/00Z ECMWF means increased mid-late period to provide an even model/mean weight by days 7-8 Monday-Tuesday. ...Weather/Hazard Highlights... Strong low-level flow to the east of a wave (and trailing front) tracking from south of the Alaska Peninsula into the northern Bering Sea Friday into early Saturday will enhance the potential for heavy precipitation along the southern coast of the mainland late this week. The Kenai Peninsula should see the highest totals from this event. The heavy precipitation may extend as far east as the Panhandle, with low-confidence details for a possible trailing wave determining amounts and duration of activity over the southeastern coast/Panhandle over the weekend. Some precipitation could extend farther north over the mainland but in much lighter and scattered form. While precipitation along the southern coast and Panhandle should generally trend lighter with time, another area of moisture could reach the southeastern coast/Panhandle early next week if a northeastern Pacific system tracks close enough. A strengthening northwestern Pacific into western Aleutians/Bering Sea system and leading front may spread increasing winds/precipitation across the Aleutians next Monday-Tuesday. Coverage of much above normal temperatures will be greatest from late this week into the weekend. Highest anomalies should be over the northwestern half of the mainland and some areas could see readings at least 30-40F above normal, especially for lows. Temperatures should steadily moderate from south to north early next week but remain above normal over most areas. The southern two-thirds of the Panhandle should continue to see moderately below normal highs. Rausch Hazards: - Heavy precipitation across portions of southern coastal Alaska, Thu-Fri, Feb 24-Feb 25. - Heavy precipitation across portions of southeastern coastal Alaska and northern Panhandle, Fri, Feb 25. 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