Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 753 PM EDT Wed May 18 2022 Valid 12Z Sun May 22 2022 - 12Z Thu May 26 2022 ...Overview and Guidance/Predictability Assessment... Today's guidance continues to forecast a blocky regime with only slow evolution of the large scale pattern, but with some trends compared to yesterday. Most solutions have gravitated to the previous minority GFS idea that initial northwest-southeast upper ridging over the mainland will take a little longer to retrograde over the Bering Strait and ultimately open/merge with another ridge building over the western Bering Sea, while the system to the south of the eastern Aleutians and associated wavy front are likely to meander a little farther north for a time. This would lead to greater rainfall focus over the Alaska Peninsula and Kodiak Island through the weekend. A weak upper trough may pass through the eastern mainland early next week as the upper ridge reaches the Bering Strait, but then latest trends yield better agreement toward a stronger ridge extending into the mainland from the Bering Sea by Tuesday-Thursday. There is still considerable spread and variability for flow details around the top of the ridge, from Siberia into the Bering Sea and approaching the mainland, late in the period. From Sunday into early Tuesday, the 12Z GFS/ECMWF/CMC offered the most compatible clustering for the overall forecast and had reasonable support from the ensemble means. Blending these solutions toned down the strength of the GFS frontal wave near Kodiak Island and the Alaska Peninsula, with other guidance recommending a weaker depiction to varying degrees. The UKMET had an alternate scenario consisting of its main frontal wave tracking near Haida Gwaii. By Wednesday-Thursday, guidance maintained yesterday's theme of rapidly increasing late-period spread and run-to-run variability for details of flow around the top of the elongated Bering Sea/Mainland Alaska ridge. Confidence is also low for waviness that could reach the northeastern Pacific. Incorporating a modest (up to 30 percent total) weight of the 12Z GEFS/00Z ECMWF means and splitting the ECMWF component among the past two runs maintained some detail for the most agreeable aspects of the pattern while offsetting low-confidence details elsewhere yielded a solution closer to the means. ...Weather and Hazard Highlights... Expect rain associated with the North Pacific system and its wavy front to affect the Alaska Peninsula/Kodiak Island and eastern/central Aleutians at least through the weekend. Brisk easterly flow could lead to some moderate to locally heavy rain over favored terrain on Kodiak Island and the Alaska Peninsula. Moisture with the front may also extend farther east to the southern coast and Panhandle by late Sunday or Monday with lighter totals. There is still uncertainty over coverage/timing of precipitation over those areas. The combination of moisture from the (eventually dissipating) Pacific front and arrival of a mainland front into southern areas early next week could support scattered rainfall at times. River flooding will continue to be an issue over some locations in the middle latitudes of the mainland due to snow melt and ice jams. Below normal high temperatures should prevail over the North Slope for most of the period, though departure of Arctic high pressure after the early part of the week may allow for some moderation. A brief episode of upper troughing over the eastern mainland, and the cold front pushing southward over the Interior in response, should expand the coverage of below normal highs over eastern areas. Southwestern areas may stay above normal but with a trend closer to normal. The Panhandle should see mostly below normal highs. Anomalies for lows should be somewhat warmer, with more localized areas of below normal readings especially over the east. Rausch Hazards: - Flooding likely across portions of mainland Alaska, Sat-Sun, May 21-May 22. 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