Alaska Extended Forecast Discussion National Weather Service College Park MD 746 PM EDT Sun May 11 2025 Valid 12Z Thu 15 May 2025 - 12Z Mon 19 May 2025 ...Overview... An upper low will be present over the southern Bering Sea as the extended period begins Thursday, and troughing should maintain itself through late week into next weekend while the mean upper low weakens, sinks south over the Aleutians into the northern Pacific, and eventually moves east toward the Gulf. Rounds of weak upper ridging are possible to the trough's east, especially through the end of the week. A shortwave and surface low in the Gulf Thursday into Friday could lead to enhanced precipitation from Kodiak Island across the southern coast into Southeast Alaska. After that, rounds of light to moderate precipitation are possible generally over the southern half of the state. ...Guidance Evaluation and Preferences... Model guidance at the start of the extended period is agreeable with the larger scale features of the pattern, including the Bering Sea upper low and a weakening upper high over the North Slope. Smaller scale features such as the shortwaves and surface lows south of the upper low are more questionable with the details. Surface low interactions with across the southern Bering, Bristol Bay, and the Gulf make it more complex, but at least the pattern for low pressure in those areas is generally set. Another surface low pivots through the northern Pacific south of the Aleutians Friday and Saturday with fair model agreement, but there is increasing spread with its track and interactions with other lows once next week begins. Upstream, model guidance shows quite a bit of variability with the pattern in the Bering Sea/Aleutians behind the mean trough/low, especially by early next week. While upper ridging is expected Friday-Saturday, models indicate that upper lows may emerge from the Kamchatka vicinity to flatten the ridge at times. Models vary greatly with the timing and depth of these features, even from run to run. For example, the 06Z GFS had a solidified upper low over the western Bering by next Monday, but the 12Z GFS became quite ridgy. The ECMWF had a generally opposite trend, with the older 00Z run having a ridge while the 12Z run suppressed it with shortwave energy. This aspect of the forecast is very low confidence. This forecast leaned toward a somewhat flat ridge so that it can trend in either direction in future forecasts. The WPC forecast used a multi-model deterministic blend early in the forecast period with the blending taking care of individual model differences. As spread increased, used more ensemble means, with the means reaching over half by Days 7-8 to mitigate the individual model differences. ...Weather/Hazards Highlights... A surface low supported by a shortwave aloft will direct moisture into the Kodiak Island vicinity into Prince William Sound and eastward into Southeast Alaska Thursday and lingering into Friday. Precipitation is likely but should stay at moderate and not hazardous levels. Windy conditions are likely to be decreasing for the Gulf and Cook Inlet Thursday. Rounds of surface low pressure/frontal systems in the Gulf could maintain precipitation chances all across the southern coast from the Aleutians to Southeast through the period, but amounts should not be very heavy. By the weekend and into early next week, light precipitation may also expand farther north into the Interior as the upper trough/low reorients and moist inflow reaches farther inland. Meanwhile, Arctic high pressure will maintain cool northeasterly flow across the North Slope and banking up into the Brooks Range. Temperatures will be cooler than average, with highs in the 20s. Downsloping from the Brooks Range southward and periods of ridging aloft should lead to clearer skies for the Yukon Flats to much of the Interior late this week, becoming more limited in scope to the northeastern Mainland over the weekend. Warmer than average temperatures are forecast for the western Interior late week and spreading eastward with time, as highs reach the 50s and 60s. The southern third or so of Alaska should generally be warmer than average for lows but near to below average for highs in the moist and cloudy pattern. 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