Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 337 PM EDT Tue Jul 23 2019 Valid 12Z Sat Jul 27 2019 - 12Z Wed Jul 31 2019 The most stable and agreeable aspects of the extended Alaska forecast are the shortwave expected to track from near the Alaska Peninsula early day 4 Sat across the Gulf/Panhandle through the weekend and an Arctic ridge that drifts westward with time. Elsewhere guidance over the past couple days has shown a lot of spread and run-to-run variability. Since yesterday model/ensemble clustering has strongly gravitated toward the idea of keeping the short range northern Bering/eastern Siberia upper low on the western side of prior spread--versus a modest majority that had brought it southeastward. Even early in the period there are still significant differences for the initial upper low but loose agreement exists for an elongated trough (with one or more embedded upper lows) over portions of northeastern Siberia and extending into the western mainland. In addition there is spread regarding details of flow to the south of this axis of lowest heights aloft, plus northern Pacific/Aleutians flow along with what interaction may occur between the two. Among the most pronounced differences, 06-12Z GFS runs become slower than other guidance with flow near the Aleutians during the weekend while the past four ECMWF runs through the 00Z cycle have been alternating between high and low pressure at the surface over the Bering in the Mon-Tue time frame. A 70 percent weight toward the 00Z operational models relative to the 06Z GEFS/00Z ECMWF means reflects the most common ideas/detail of guidance while downplaying other less confident specifics for days 4-5 Sat-Sun. With the ensemble means providing the most stable forecast late in the period the initial blend adjusts to an even model/mean blend for day 5 Mon and then goes 90-100 percent to the means thereafter. This approach maintains the forecast of a North Pacific warm front lifting toward/to the western Aleutians while a modest surface ridge covers the Bering. Meanwhile there is a hint of a weak trough aloft settling over the Gulf of Alaska with modest low pressure over the northern Gulf. The Peninsula through Gulf/Panhandle shortwave and corresponding surface low/frontal system this weekend will provide a brief period of enhanced precipitation to areas along the southern coast/Panhandle. Otherwise a fairly broad area will see some precipitation potential for one or more days during the period but with low confidence in location/timing specifics due to the uncertainty in flow details aloft and corresponding surface evolution. Rausch Additional 3-7 Day Hazard information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php No significant hazards are expected over Alaska during this forecast period. 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