Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 650 PM EDT Sun Jul 21 2024 Valid 12Z Thu Jul 25 2024 - 12Z Mon Jul 29 2024 ...Increasing heavy rain threat across parts of Alaska late week to next weekend... ...Overview... A strong upper ridge over the mainland as the period begins Thursday should break down and shift east with time as a deep upper low/trough reaches the West Coast by Friday. This will flip the switch from dry and very warm to a much colder and wetter pattern, with a threat for heavy rainfall in some locations. This general pattern will maintain itself into at least early next week as another trough digs south and east out of eastern Russia and into the northern Bering Sea. ...Guidance Evaluation/Preferences... Overall, the latest guidance shows fairly good agreement on the overall synoptic pattern/evolution, but some significant differences in timing, especially later in the period. The initial low/trough into the West Coast is trending better, but the GFS remains a little faster to break down the ridge and given how strong and anomalous the ridge will be, it seems more plausible to favor the slower solutions. Model timing and strength diverge even farther upstream by the weekend as a deeper trough/eventual closed low drops south from eastern Russia. The GFS is again significantly faster with this bringing it into northwest Alaska by Sunday. The CMC and ECMWF at the same time are back in the far western Bering Sea. The ECMWF does eventually track it eastward (as a very strong compact upper low), but the CMC hangs it back in the western Bering early next week. The ensemble means are naturally quite washed out with this feature, but does suggest some sort of troughing to move through the Bering again next week. The blend for today's WPC progs was able to use a general operational model blend the first half of the period, with slightly greater weighting towards the ECMWF. Late in the period, leaned heavily on the ensemble means, with some operational ECMWF to help add some detail and system definition where feasible. ...Weather/Hazards Highlights... As a cold front associated with the initial deep Bering low reaches the West Coast around Thursday or Friday this week, the threat for widespread rains progressing steadily eastward with time increases across the Mainland through at least the weekend. Some of the rainfall could be heavy in spots, especially along/near the favored terrain and the southern coast as a surface low develops in the northern Gulf. Gusty winds may accompany this system, depending on exact strength, but should remain below hazards thresholds. The next trough through the Bering early next week will continue to favor an overall wet pattern, but rainfall intensity at least by Sunday-Monday should be lessening. Well above normal temperatures, with values near or above 80 degrees, will continue through Thursday for the North Slope and eastern Alaska. As strong troughing approaches from the west, this will usher in much cooler temperatures across the Mainland, progressing steadily from west to east Thursday-Saturday. Much of Western and Central/Northern Alaska could be 10 to 20+ degrees below normal lasting into at least early next week. The Aleutians to the Southeast should be mostly below normal the entire period. Santorelli 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