Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 758 PM EDT Tue Jul 05 2022 Valid 12Z Sat Jul 09 2022 - 12Z Wed Jul 13 2022 ...Heavy Precipitation Threat for the Alaskan Southern Tier... ...Pattern Overview and Weather/Hazard Highlights... An active weather pattern is forecast to persist over Alaska through the medium-range period. This pattern will feature a closed low over the Gulf of Alaska, another closed low digging across northeastern Siberia, with an upper ridge sandwiched in between over the Alaskan mainland. Today's guidance has trended toward a better-defined and more amplified trough/front to dip across northeastern Siberia on Saturday, reaching into the Bering Sea on Sunday. This allows more separation of this trough from the closed low forecast to slide across the Alaskan Peninsula and then into the Gulf of Alaska during the weekend. Sustained and deep Gulf of Alaskan moisture associated with this closed low will provide a prolonged threat for moderate to locally heavy/terrain enhancing precipitation to the southern periphery of Alaska from Kodiak Island eastward. Meanwhile, ejecting impulses and moisture northward through Southwest Alaska and into the Interior on the western periphery of the slowly eroding upper ridge should promote areas of rain/showers. An upper ridge anchored overland will tend to inhibit progression of the closed low toward the coast. Meanwhile, the upper trough over the Bering Sea is now forecast to dig southeastward and interact/re-energize the closed low over the Gulf of Alaska by early next week. Another round of potentially heavy rain is forecast to affect areas farther south into the Panhandle early to midweek, with heavy rain progressing farther inland over interior southern Alaska. Farther north, the Arctic vortex should initially stay well to the north of Alaska. But toward midweek, a forming frontal boundary could focus light to moderate precipitation along the North Slope while moisture from the south could reach northeastern Alaska and interact with the front. ...Guidance/Predictability Assessment... The 12Z ECMWF solution seem best clustered with the pattern evolution aloft of the quite compatible GEFS/NAEFS/ECMWF ensemble means through medium range time scales and a reasonable composite from days 4-8 seems to also offset more evident surface system differences, partially due to less certain smaller scale upper impulse interactions over time. Some manualÂadjustments were applied to ensure Gulf of Alaskan surface lows and wind flow were not too weakened by the mean/blending process,Âconsistent with upper support and system specific uncertainties. The GFS exhibits more run-to-run variability on the timing of the digging Siberian trough but usable. The WPC forecast grids for Alaska were based on 40% from the 12Z ECMWF/00Z EC mean, 40% from the 12Z GFS/12Z GEFS, and 20% from the 00Z CMC/CMC mean, using more ensemble means with increasing forecast lead time. This forecast strategy maintains good WPC product continuity from yesterday in a pattern with seemingly average to better overall predictability. Kong/Schichtel Hazards: - Heavy rain across portions of mainland Alaska, Fri-Sat, Jul 8-Jul 9. - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Sun-Tue, Jul 10-Jul 12. 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