Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 723 PM EDT Wed Jul 24 2024 Valid 12Z Sun Jul 28 2024 - 12Z Thu Aug 01 2024 ...Cooler and rainy pattern across much of Alaska with locally heavy rain totals possible... ...Overview... Rounds of upper troughing supporting surface lows/frontal systems will be the primary driver of sensible weather in Alaska this weekend into next week. The mean troughing pattern will promote cooler than average weather and multiple rounds of rain over the state, with some locally heavy rain. ...Guidance Evaluation/Preferences... As the period begins Sunday, the first upper trough will be located over the eastern Mainland with a brief bout of ridging atop the western Mainland/Alaska Peninsula. Though the first trough moves east away from the state, the low amplitude ridge should be short-lived as another trough sweeps across the Bering Sea into the western part of the state early in the week. This second trough is on the southern side of/anchored by an upper low that will spin for multiple days just north of eastern Siberia in the Arctic. Most model guidance is in reasonably good agreement with these features through the first part of the period. The main exception was the 12Z UKMET, which held the second trough farther west in the Bering Sea. The 12Z CMC was also a bit slow with this second trough compared to other guidance around Monday but not near as slow as the UKMET. The second trough should push farther east and south across Alaska around midweek, but models show increasing spread with its form and placement. Deterministic models generally show a 500mb low closing off at some point as the energy pushes into Southcentral Alaska and the Gulf of Alaska. As a Pacific ridge builds into the Aleutians, there is a possibility that the ridge could extend northeast and pinch off this upper low from its origin Arctic low/trough northwest of the state. Ensemble means keep the Arctic to Gulf troughing more phased compared to the deterministic models, though with lots of ensemble member spread. Had to lean toward the ensemble mean solution for now given the uncertainty. Then the 12Z GFS diverged from other guidance by Thursday/Day 8 in showing Arctic energy diving toward the Bering Strait. Overall, the WPC forecast used a blend of the 12Z ECMWF and CMC and 06/12Z GFS deterministic models early, with quickly increasing proportions of the GEFS and EC ensemble means as the period progressed to well over half by Day 8, amid the increasing spread. ...Weather/Hazards Highlights... A front oriented west-east near the Brooks Range will provide a focus for moisture to pool, with heavy rain possible in northeastern parts of the state into Saturday. A brief break in precipitation is possible for some areas tracking west to east this weekend, before another upper/surface low provides support for another round of widespread moderate to locally heavy rain spreading from the Aleutians and Alaska Peninsula/western Mainland this weekend and across the Mainland for the first half of next week. Much of the Alaska Range looks to see the heaviest rain totals considering the upslope enhancement, with heavy rain chances peaking Monday into Monday night. The highest elevations of the Alaska Range may see some snow with the precipitation activity, with snow also possible in higher elevations of the Brooks Range. Rounds of light to moderate rainfall are possible early in the week for Southeast Alaska, and rain totals may increase by Tuesday-Wednesday as the upper-level support increases. The flip to troughing aloft will cool temperatures to below normal across Alaska during the short range period, and temperatures are likely to cool even further next week with the second round of troughing. High temperatures are forecast to be 10-25F below average, with actual highs generally in the 50s and 60s. Lows are forecast to be less anomalous at 5-15F below normal. The upside to the rain and cooler temperatures will hopefully be the end of fire season for most of the state. 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 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