Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 757 PM EDT Thu May 05 2022 Valid 12Z Mon May 09 2022 - 12Z Fri May 13 2022 ...Overview... A potent upper trough is forecast atop much of the mainland as the workweek begins, and this trough should shift eastward and deepen through around midweek along with some moisture and a low pressure/frontal system, supporting showers across much of the state. Then an upper-level ridge/high is expected to set up over the Bering Sea, north of a persistent upper level and surface low in the Pacific well south of the Aleutians. Additional troughing may come into the mainland during the latter part of the week with some chances of additional precipitation, but with uncertainty in the details. ...Guidance/Predictability Assessment... As the medium range period begins Monday, most guidance is in fairly good agreement with the overall pattern, continuing with considerably strong energy diving into the western mainland to create troughing that continues to deepen Tuesday and possibly split off an upper low in the Gulf of Alaska near the Panhandle by Wednesday. The 12Z CMC seemed a bit south and aggressive with forming the upper low earlier than consensus. Meanwhile recent guidance shows an upper high incoming stationed a bit farther east than the previous forecast, centered to the north of the Aleutians with surface high pressure near Bristol Bay. An upper low and an associated surface low show good consensus hovering well south of the Aleutians (around 40N and just east of the International Date Line). The WPC forecast utilized a multi-model deterministic blend but favoring the ECMWF and GFS for the early part of the medium range period. The latter half of next week becomes more uncertain with the overall flow over Alaska, as possible shortwaves moving into the northwestern part of the state could impact the extent of the ridging from the Bering Sea upper high. The GFS runs have been persistent in showing some suppression of the ridge due to shortwave energy, and the 12Z ECMWF and CMC did start to trend toward stronger shortwaves as well. However, there are ample differences in the timing and strength of such shortwaves that grow to be pretty significant by Thu-Fri. Gradually increased the proportion of the GEFS and EC ensemble means through the period to about 60 percent by day 8 given the model differences. ...Weather and Hazard Highlights... Increasing precipitation chances are likely across interior Alaska Monday into Tuesday as troughing and a surface front/trough pass across the area, with perhaps some moderate amounts. Given the trough movement, precipitation should spread into southeastern Alaska and the Panhandle Tuesday and Wednesday, but heavy totals are generally not expected. Another round of light precipitation is possible for the interior Wednesday and beyond next week. Another concern during the period will be for flooding, as above freezing temperatures atop a significant snow pack could lead to river flooding and ice jams could develop in parts of interior Alaska. One short to medium range flooding concern is an ice jam along the Kuskokwim at Crooked Creek. Much of interior Alaska can expect cooler than normal high temperatures through the period, with low temperatures more of a mix of somewhat below and above normal. The Alaska Peninsula could gradually warm through the week as ridging builds in. Meanwhile, the Panhandle has the best chance of seeing below average temperatures for both highs and lows. Tate Hazards: - Flooding possible across portions of mainland Alaska, Sun-Thu, May 8-May 12. 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