Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 722 PM EDT Thu Apr 24 2025 Valid 12Z Mon 28 Apr 2025 - 12Z Fri 02 May 2025 ...Overview... For much of next week, a mean upper low is forecast to spin atop the Bering Sea, pinned in place by an Arctic ridge to the north and rounds of ridging over eastern Alaska and western Canada. Spokes of the trough may poke into western parts of the state at times. Meanwhile the storm track on the southern side of the upper low will lead to a few surface lows and frontal systems moving through the northern Pacific. This will spread rounds of moderate precipitation to the southern coast. At the surface expect a persistent temperature gradient between a wavy Interior front and Arctic high pressure, allowing for cooler than normal temperatures in the north and warmer than normal temperatures in the south, aside from cooler coastal areas. ...Guidance/Predictability Assessment... Recent model guidance displays a somewhat typical pattern of okay agreement on the large scale with considerably greater differences in specifics that could have sensible weather implications. There is general agreement for weak low pressure to move into Southeast Alaska Monday. Meanwhile a shortwave rounding the southern side of the Bering upper low will support surface low pressure moving eastward through the northern Pacific. The ECMWF seemed most agreeable with the ensemble means' position of the low south of the Aleutians/Alaska Peninsula around Monday-Tuesday, so this seemed like a favorable cluster. GFS runs were a bit east and the CMC a bit west, so the EC and EC mean was a good middle ground. This low is forecast to interact with low pressure over Bristol Bay and vicinity by midweek and overall produce lower pressures in the southwestern Mainland. One negative with the EC was that energy crossing the Aleutians on Tuesday appeared to combine with this feature to produce a deeper/farther west trough moving through the northeast Pacific into late week. It was not too dramatic but at the surface this caused a relatively deep low to track north in the northeast Pacific near Southeast Thursday and reaching near Southcentral Friday, unlike consensus. Then upstream, another low is forecast to track south of the Aleutians Wednesday-Friday. Once again the models showed a pattern of the CMC as slowest, EC in the middle, and GFS runs the fastest --but more dramatically with this low. The middle ground EC seemed best. The WPC forecast was based on a blend of the deterministic models favoring the ECMWF early in the forecast period. As model spread increased, reduced the proportion of deterministic models in favor of the ensemble means since the means were more agreeable, with the means more than half the blend by Days 7-8 to minimize individual model differences. ...Weather/Hazards Highlights... Weak surface low pressure is forecast to track into Southeast Alaska Monday, while moist inflow spreads light to moderate precipitation from Southcentral to Southeast. The next, somewhat stronger, low moving through the northern Pacific will spread rain to the Aleutians Monday and continued precipitation chances in the Alaska Peninsula and southern Mainland Monday-Tuesday. Later Tuesday into Wednesday, precipitation looks to become enhanced in Southcentral as the low approaches, with the heaviest amounts from the Kenai terrain into Prince William Sound. Precipitation is likely to spread into Southeast Wednesday and Thursday. These precipitation totals of a couple of inches of rain/liquid equivalent with locally higher amounts are not currently expected to be hazardous, but will continue to monitor if amounts trend upward. Lighter precipitation is possible farther north into the Interior. Another northern Pacific low is likely to produce additional rain chances in the Aleutians midweek and reaching the Alaska Peninsula late week. Wind-wise, easterly winds could be breezy along the North Slope due to the Arctic surface ridge in place to the north. The Monday-Wednesday surface low coming across the northern Pacific may enhance northwesterly gap winds behind it and southerly/southeasterly winds ahead of it. Still, 30 to 40 knots of wind are expected rather than hazardous winds of 50 knots or greater. Cooler than normal temperatures are likely for northern Alaska into the Yukon Flats through much of next week due to persistent flow around the southeast periphery of the Arctic ridge. Meanwhile warmer than average temperatures are expected for western Alaska and across much of the Interior early next week. Anomalies will generally be warmer for morning lows relative to those for daytime highs. Southern coastal areas into Southeast Alaska should see near to above average lows and below average highs much of the period during rounds of wet weather. 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 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