Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 726 PM EDT Mon Aug 01 2022 Valid 12Z Fri Aug 05 2022 - 12Z Tue Aug 09 2022 ...Heavy rainfall possible from the southeastern mainland to the Panhandle late this week... ...Much cooler temperatures will gradually spill into the state from the north through the first half of next week... ...Overview... Strong high pressure in both the upper levels and at the surface is forecast to retrograde and meander across the midlatitudes of the Pacific between Alaska and Hawaii through early next week. This will allow for an initially fairly progressive pattern across southern Alaska to the north of the high, with an upper/surface low forecast to move across the southern mainland for the latter part of the week, bringing some modest to possibly heavy rainfall especially to the southeastern mainland and Panhandle. Then an Arctic upper low is forecast to edge southward toward Interior Alaska over the weekend into early next week, bringing much below normal temperatures and some light to modest precipitation. ...Guidance/Predictability Assessment... Recent model guidance still seems to be having issues converging on a solution for the exact timing of the low tracking across southern Alaska late this week, which also relates to flow upstream with another possible upper low feature (or whether it is more phased with the northern stream trough). The 12Z ECMWF seems to be too fast compared to consensus with the initial low Fri-Sat and then more aggressive with a separate stream low coming in behind it. The (older) 00Z ECMWF and a combination of other guidance such as the GFS/CMC/UKMET seemed to be somewhat closerÂto the ensemble means, so preferred that combination instead for the timing of the initial low and to indicate less potential for a separate system upstream at this point. Some model cycles have shown more potential for another low system upstream though, so confidence is low for now. Despite the timing issues of features late week and detail differences farther north with the troughing, fortunately confidence is good for lowering heights and colder temperatures as the trough stemming from the Arctic low spills into the state early next week. The latter part of the forecast period was composed of over half GEFS and EC ensemble means given the detail differences, with small proportions of the 00Z and 12Z ECMWF and 12Z GFS. ...Sensible Weather... Precipitation should be ongoing across the southern half of the interior as the period begins Friday, with enhanced amounts likely in Southcentral Alaska and the Alaska Range into the southeastern mainland and the Panhandle. Mostly rain is forecast in those areas, though precipitation in the highest elevations of the Alaska Range could fall as snow. Additionally, a cold front moving just ahead of the trough into the northern mainland could cause some showery conditions across the North Slope and into the Brooks Range Friday-Saturday, which in higher elevations could fall as snow. Additional rounds of precipitation are again possible early next week given upper level support from the trough and with possibly multiple fronts at the surface. Temperatures will be starting to cool down on Friday for most areas as troughing spreads eastward from the southern upper low, especially in terms of highs, with just the northeastern mainland remaining above normal. But for the weekend and into next week, temperatures will trend considerably cooler as more potent troughing spreads southward from the Arctic upper low. The largest anomalies will likely be over the northern interior, where high temperatures could be over 20 degrees below normal and lows are expected to be below freezing. 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 the Alaska Panhandle and southeast mainland Alaska, Fri-Sat, Aug 5-Aug 6. - Much below normal temperatures across portions of northern mainland Alaska, Sat-Mon, Aug 6-Aug 8. 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