Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 757 PM EDT Thu Sep 02 2021 Valid 12Z Mon Sep 06 2021 - 12Z Fri Sep 10 2021 ...Pattern Overview and Model Guidance... The main large-scale upper-level feature affecting Alaska through the period will be a broad upper low spinning west of the state, possibly meandering a bit southward into the Bering Sea as the workweek progresses. While this feature's existence has good agreement among model/ensemble guidance, shortwave troughs and thus surface low pressure systems moving around this broad gyre are less consistent. First, the shortwave lifting northward through the western part of the state on Mon/Tue has some timing/strength differences. But another shortwave tracking across the southern side of the upper low could cause even more forecast issues in terms of the surface pattern as well. The shortwave is generally expected to move eastward from the northwestern Pacific somewhere near the Aleutians and the southwestern mainland, but with ample differences in timing and the degree of interaction with the main upper low from model to model and run to run, lessening confidence. Surface low tracks vary quite a bit with possibilities for lows north of the Aleutians into the Bering Sea as well as south into the Gulf of Alaska. The 12Z GFS and ECMWF came in farther north with this surface low compared to previous runs, which aligns better with the ensemble mean solutions. Thus the WPC forecast leaned toward a forecast into the Bering/southwestern mainland for now, but changes in future forecast issuances are quite possible. Additionally, for the early part of the workweek, a potent shortwave will push a surface low through the northeastern Pacific toward the Panhandle. The current 12Z model cycle and the previous 00Z model cycle have both trended much stronger with the surface low among basically all reliable guidance, and deepening this low is the main change to the previous WPC forecast. The low is forecast to fill/weaken midweek as it approaches the Panhandle. The WPC forecast utilized a mainly operational model blend early in the forecast period, trending toward the GEFS and EC means later in the period. The 12Z CMC was excluded after Day 4/Mon, as its pattern especially in the northwest Pacific pushed the aforementioned shortwave eastward more quickly than consensus as it phased more with the persistent northern low. ...Sensible Weather... A wet pattern is likely across the Panhandle for the first part of the workweek given moist inflow ahead of the potent surface low moving toward the region, and rainfall totals could be modest to locally heavy there. Precipitation is also expected in the northwest part of the state early in the week with the initial shortwave, with higher totals in terrain enhanced areas, some of which could fall as snow. Then, despite the uncertainty in the exact track of the southern shortwave and low, enhanced rainfall seems possible for the Aleutians and then likely across the Alaska Peninsula and eastward toward the Kenai Peninsula for the latter part of the week. With general southerly moist flow across the state, cloudy conditions are likely. High temperatures are expected to be around or below normal across all but the eastern part of the mainland especially for the early part of the week. Meanwhile, low temperatures are likely to be around or slightly above average for most of Alaska other than the western mainland. Tate No significant hazards are expected over Alaska during this forecast period. 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