Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 754 PM EDT Tue Jul 23 2024 Valid 12Z Sat Jul 27 2024 - 12Z Wed Jul 31 2024 ...Cooler and rainy pattern across much of Alaska with locally heavy amounts possible... ...Overview... There is high confidence that the pattern across Alaska will flip later this week, and as the medium range period begins Saturday, the first round of upper troughing will be present atop the Mainland. Some low amplitude ridging may sneak across the Aleutians to Southcentral Alaska this weekend, but be short-lived as another round of troughing anchored in the Arctic Ocean will sweep across the Bering Sea into the Mainland during the first half of 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... Model guidance is within reasonably good agreement with the pattern, with typical differences in timing and placement of upper and surface lows. 12Z models agree that the initial upper trough should be centered atop the Mainland by Saturday. This will move east by Sunday, with the 12Z CMC seemingly a southern outlier in the extent of the trough and closing off a 500mb low farther south. There is also agreement for an upper low to spin for multiple days just north of eastern Siberia in the Arctic, with somewhat more spread in the placement of troughs/lows extending on its southern side that will affect the Bering Sea into Alaska. While models generally indicate another round of troughing to pivot east into the Mainland by around Monday, there is some timing spread with this feature. Most guidance favored a faster/farther east position compared to the previous WPC forecast, especially the GFS runs and particularly the 06Z GFS that was among the fastest guidance. The 00Z ECMWF also was faster but the 12Z ECMWF slowed again. The CMC was on the slower side but not as slow as the 12Z EC. WPC's forecast tried to take a middle ground approach of the recent guidance, which resulted in a faster trend compared to the previous forecast. Then another model diagnostics issue arose by next Wednesday/Day 8 as the GFS spills another round of energy into the Bering Sea unlike other guidance. Did not favor this solution since it was on its own for now. Overall, the WPC forecast used a blend of the deterministic models favoring the 12Z ECMWF and GFS early, with increasing proportions of the GEFS and EC ensemble means as the period progressed to about half by Day 8, amid the increasing spread. ...Weather/Hazards Highlights... A surface low/frontal system tracking across the southern half of the state as well as another west-east front oriented farther north near the Brooks Range will provide foci for moisture to pool and promote a rainy pattern late week into the weekend. Some of the rainfall could be heavy in spots, especially along/near the Brooks Range and much of the south-central Mainland. 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 early next week. Southcentral Alaska looks to see the heaviest totals, especially into the Alaska Range with upslope enhancement. Given multiple days of rain, a heavy rain area is drawn on the Hazards graphic for Sunday-Monday over Southcentral Alaska given the possible sensitivity of this region after Friday's rain, though at this point rain totals seem to be lower than the late week rain event. The highest elevations of the Alaska Range may see some snow with the precipitation activity, but this looks more probable farther north in the higher elevations of the Brooks Range. Rounds of generally moderate rainfall are forecast across Southeast Alaska as well. The flip to troughing aloft will cause temperatures to quickly fall compared to the warm short range period. Below normal temperatures especially for highs are likely across the Mainland by the weekend, with anomalies of 10-20F below average and actual highs in the 50s and 60s. Lows are forecast to be less anomalous of 5-10F below normal. Cooler than normal temperatures will persist into next week, even perhaps cooling more over the Mainland by Tuesday-Wednesday under the next round of troughing. 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