Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 625 PM EDT Thu Mar 23 2023 Valid 12Z Mon Mar 27 2023 - 12Z Fri Mar 31 2023 ...Overview... Upper level ridging anchored over the Gulf of Alaska and eastern Alaska will gradually be replaced by more zonal flow to troughing as a series of weather systems move from the Bering Sea eastward next week. The first system late this weekend into early Monday is likely to track into the Chukchi Sea, but its associated cold front will bring locally heavy snow and high winds to parts of western Alaska. Another system mid to late week will likely bring another round of unsettled weather to parts of western and southern Alaska, including the Aleutians. Above a round of above normal temperatures early on, more normal to slightly below normal readings are expected. ...Guidance Evaluation/Predictability Assessment... In general, the synoptic pattern was well clustered and showed average to above average agreement and run to run consistency for early next week. The main longwave trough at the beginning of the period had little variability among the 12Z operational deterministic guidance and showed good agreement with the low track through the Chukchi Sea. As that shortwave trough weakens Tuesday into Wednesday over the mainland, another shortwave trough begins to take shape across the Bering Sea. Here, there was more model spread, as expected in the day 5-7 range, with some of the typical model biases seen. While all of the models have a similar big picture idea, the 12Z GFS was a faster outlier with a more southerly vort max (and associated low pressure) compared to the slightly slower CMC/ECMWF and a north bias in the CMC. As a result, the 12Z ECMWF was considered a pretty good proxy for the consensus and was heavily used in the model blend forecast. Going into day 7 and day 8, there is higher uncertainty with what happens across the Gulf of Alaska with respect to the potential development of another low pressure along the coast. The 12Z GFS showed this scenario the strongest/most and would result in more unsettled weather late in the week into next weekend, while the other global models were less amplified with that idea. Sticking with the ensemble means and accounting for the GFS fast bias, the model blend will hint at the potential for another low. ...Weather/Hazard Highlights... Unsettled weather is expected late in the weekend into very early Monday across the western part of the state, associated with the passing cold front. Areas from the northwest mainland southward into west-central areas are likely to see a prolonged period of moderate to heavy snow, while further south and including the Aleutians, rain and/or mixed precipitation is expected. In addition, a rather tight surface pressure gradient will make for strong/high winds, particularly in the upslope flow region of the Brooks Range. Winds could be as high as 30-50 mph (locally higher gusts). That storm system will weaken as it crosses the rest of the state Monday into Tuesday, gradually washing out by mid week. Attention then turns to the next storm system coming out of the Bering Sea mid to late week. Another area of low pressure looks to move onshore the western mainland, though there remains some uncertainty in location. This system doesn't look too impressive at the moment, but will bring rounds of precipitation and unsettled weather to parts of the western and southern mainland region. By late in the week, another area of low pressure is likely to develop in the Gulf of Alaska and could bring additional rounds of precipitation to southern mainland and southeast Alaska. Too uncertain at this point whether it'll be strong enough for heavy precipitation or other hazards. Temperature-wise, the western mainland into the Brooks Range and North Slope can expect milder than average temperatures as deep layer southwesterly flow brings in warmer and moister air on Sunday-Monday with a fairly expansive area of temperatures above freezing, even perhaps toward the North Slope on Sunday. Then the upper trough and the cold front making their way through the mainland Tuesday-Wednesday should cool temperatures to a bit below normal, particularly highs, though the North Slope should remain milder than average. Though uncertain for now, the western part of the state may see another warm-up by the latter part of the period ahead of the second storm system. For the Panhandle, high temperatures are forecast to be generally below average next week while the lows are nearer to normal. Tate/Taylor 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 Hazards: - Heavy snow across portions of mainland Alaska, Sun, Mar 26. - High winds across portions of mainland Alaska, Sun, Mar 26. 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