Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 754 PM EDT Thu May 19 2022 Valid 12Z Mon May 23 2022 - 12Z Fri May 27 2022 ...Overview and Guidance/Predictability Assessment... As has been the case in recent days, guidance shows fairly slow evolution within a blocky Bering Sea/Mainland Alaska into North Pacific pattern. The most stable part of the forecast is for the upper ridging that should extend across the Bering Sea and farther east into the mainland after departure of an eastern mainland trough on Monday. Lower heights will prevail to the south, consisting of a vertically stacked system initially south of the eastern Aleutians and a weaker upper low (or at least elongated trough) to the northeast. These two features may consolidate over the northeastern Pacific by next Friday. Flow to the south could bring a wave close to the southern Panhandle mid-late week. At the same time the flow around the top of the upper ridge may gradually become more progressive as a high latitude upper low drifts southward to some degree. A western Pacific system should come into the picture well south of the Aleutians late next week. Today's forecast started with a blend of 12Z operational models for the first half of the period, the exception being that ECMWF input was split between the past two runs. This is due to the 12Z ECMWF differing from other guidance in holding a nearly stationary surface low to the southeast of Kodiak Island, plus differing interaction of Aleutians energy with the emerging western Pacific system to yield a relatively northern track. Then the forecast quickly transitioned to 40-50 percent total weight of the 12Z GEFS/00Z ECMWF means with lingering input from operational runs. Even among non-ECMWF runs, guidance has not fully decided on specifics of early-week waviness that anchors a weakening front. Then there is meaningful spread for the mid-late week wave that could track anywhere from south of Haida Gwaii to offshore the southern Panhandle, and spread/run-to-run changes for the system eventually tracking well south of the Aleutians. The favored blend provided a reasonable intermediate solution for these systems. As for flow around the top of the mean ridge aloft, multi-day trends have been away from occasional solutions that had been on the amplified side with any shortwaves. Now differences later in the week are more due to various paths of an initial North Pole upper low, with ECMWF/CMC runs bringing it farther south than most other models/means. A model/mean blend provided a conservative decrease in northern mainland heights while awaiting better agreement. ...Weather and Hazard Highlights... Mostly light precipitation will be possible along coastal areas and the Panhandle early in the week with modest waviness and its dissipating front. Some of this moisture could interact with an inland cold front (turning stationary) to produce slightly more enhanced totals over Southcentral. The front will weaken/retreat northeastward after initial Arctic high pressure weakens while tracking southeastward. River flooding may continue to be an issue over some locations in the middle latitudes of the mainland through at least the first part of next week, due to snow melt and ice jams. A wave may bring some moisture to the Panhandle by mid-late week but with low confidence in precipitation coverage if any. Parts of the mainland could see scattered activity later in the week as upper ridging weakens. Low pressure emerging from the western Pacific mid-late week will most likely track far enough south to bring minimal wind/rain effects to the Aleutians. Northern and eastern areas, along with the Panhandle, will see the best potential for below normal high temperatures during the period. The eventual decline of upper heights later in the week could expand the coverage of below normal highs but generally with moderate anomalies. Expect somewhat warmer anomalies for lows, with below average readings tending to stay confined to eastern areas. Rausch Hazards: - Flooding likely across portions of mainland Alaska, Sun-Mon, May 22-May 23. 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