Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 758 PM EDT Mon Jul 17 2023 Valid 12Z Fri Jul 21 2023 - 12Z Tue Jul 25 2023 ...Wet pattern for much of western and southern Alaska... ...Overview... A stacked upper/surface low over the northeastern Pacific late week into early next week will support rounds of rain across southeastern Alaska. Meanwhile, energy dropping south from the Arctic and separate energy moving east may combine in the Bering Sea, promoting wet weather for western Alaska late week and additional rounds of rain possible especially for the Alaska Peninsula and vicinity into the weekend and next week. By the latter part of the period early next week, a Rex Block is likely to set up with elongated west-east troughing in the Pacific while ridging pinches off farther north across western Canada into the Alaska Mainland. ...Guidance Evaluation/Preferences and Predictability Assessment... Model guidance is in decent agreement with the pattern described above, especially in terms of the initial northeast Pacific low. Models also are indicating two other bouts of upper troughing/energy influencing the pattern late week into the weekend--an upper low near/just east of the Kamchatka Peninsula at the start of the period Friday, and vorticity from the Arctic crossing the Bering Strait and forming troughing near western Alaska late week. However, the timing and location of the troughs/lows are uncertain and dependent on each other. Models are generally in two camps. GFS runs indicate a slower track of the Kamchatka-Bering low, which allows for more Arctic energy to spill well southward across the Bering and then crossing into the Pacific over the weekend. Meanwhile the ECMWF/UKMET track an upper low eastward through the Bering faster, which combines with the originally Arctic energy to form a consolidated low atop the eastern Bering Sea that eventually crosses the Alaska Peninsula around Monday. The CMC is closer to the EC/UK camp but a bit slower with the Kamchatka low for a middle ground. The 12Z GEFS mean was actually unlike the GFS runs and showed a pattern more like the non-GFS solutions. Thus favored the non-GFS deterministic models with a 12Z GEFS mean component for today's model blend, as multiple model suites were going against the GFS solutions. Gradually increased the proportion of ensemble means with increasing lead time to just over half by the end of the period. This also seemed reasonable for the ridge building atop the mainland, though there is some uncertainty with possible shortwaves coming into the North Slope to suppress it early next week. ...Weather/Hazards Highlights... As an upper trough axis sets up over the eastern Bering Sea late week, moist inflow is likely for western Alaska to promote a wet pattern there. The highest rain totals are likely over the Alaska Peninsula around Thursday-Friday, with rain farther north into the mainland as well. Additional rounds of rain are possible over the Peninsula through the weekend. Farther east, moisture will be directed into Southeast Alaska for multiple rounds of rain there. Rain amounts should generally be moderate but may be enhanced to locally heavy on any given day. Particularly by early next week, rain is likely for southeastern parts of the Mainland, with totals possibly enhanced in the Alaska Range with upslope flow. Cooler than normal temperatures are likely for western Alaska late this week under the troughing influence, generally moderating into next week. Southern coastal Alaska is likely to remain cool in terms of highs, with more of a mix of above/normal temperatures in Southeast Alaska depending on the day and location. But as an upper ridge/high gets established farther north across the Interior, temperatures are likely to warm above average. Areas of the eastern Interior are likely to see temperatures well into the 80s. 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 rain across portions of mainland Alaska and the Aleutians, Thu, Jul 20. 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