Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 755 PM EDT Wed May 04 2022 Valid 12Z Sun May 08 2022 - 12Z Thu May 12 2022 ...Overview... As next week begins, an upper trough that is looking stronger today is forecast to shift into the western mainland and then across the state for early-mid next week along with some moisture and a low pressure/frontal system, supporting some showers across much of the state. This trough may be strong enough to shunt an eastern Pacific ridge well south of Alaska. Meanwhile an upper low should stagnate well south of the Aleutians with less potential for phasing with the flow farther north in today's forecast, so this feature and an associated surface low may not directly impact Alaska but could provide moist flow into the state for increasing precipitation chances along the southern coast. ...Guidance/Predictability Assessment... As the medium range period begins early next week, most guidance is in fairly good agreement with the overall pattern, with considerably stronger energy (compared to yesterday's guidance) diving into the western mainland. The main exception was the 12Z CMC, which is on its own with an earlier shortwave that is stronger than other models divingÂsouthward, whereas consensus shows that initial shortwave as less impactful and the second shortwave is what creates the larger scale troughing. But the past few runs of the ECMWF, GFS, and UKMET show better than typical overall agreement with this troughing, so the WPC forecast utilized those models early in the forecast as the troughing deepens and shifts eastward. By midweek the trough still shows reasonable agreement the operational GFS and ECMWF and their ensemble means in terms of timing and pushing the eastern Pacific ridge south, as well as the track of a surface low and frontal system that are somewhat stronger and faster moving than yesterday's forecast. An upper low centered well south of the Aleutians in the Pacific (around 40N and the International Date Line) has shown a trend toward slow movement along with less potential to phase with the flow farther north. The 12Z UKMET did show a faster track with the Pacific low which led to some phasing of those features, so it is not out of the question, but preferred the better clustered GFS/EC and their means that keep the Pacific low detached. With the fairly good ECMWF and GFS agreement, was able to keep the deterministic proportion of the forecast blend pretty high through much of the period, just over half (with EC/GEFS means the other half) by day 8. ...Weather and Hazard Highlights... Increasing precipitation chances are likely across the western mainland shifting into and interior Alaska Sunday into Tuesday as troughing and a surface front/trough pass across the area, with perhaps some moderate amounts. The deeper northern trough and sufficient moisture streaming in from the Pacific could lead to light to moderate precipitation spreading from the Alaska Peninsula to Southcentral Alaska possibly becoming moderate to heavy for the Panhandle by around midweek. Chances for particularly heavy amounts have generally gone down over the past couple of days though given the trend toward the Pacific upper low and its associated surface low staying well south. Another round of light precipitation is possible for the interior Wednesday and beyond next week. Another concern during the period will be for river flooding as above freezing temperatures under a significant snow pack will lead to possible flooding in the Tanana basin between the Yukon and Alaska Range of the eastern mainland and westward along the Yukon River until Koyukuk Island. Flooding is also possible due to potential ice jams in the Lower Kuskokwim Valley in southwestern parts of mainland Alaska. Temperatures should be fairly stable and not terribly anomalous during the period. The Panhandle to far southeastern mainland can expect cooler than normal conditions for both lows and highs. Much of the mainland should see around normal to above normal lows, with more of a mix in terms of high temperatures, with the southwestern mainland particularly cool. Tate Hazards: - Flooding possible across portions of mainland Alaska, Sat-Wed, May 7-May 11. 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