Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 759 PM EDT Thu Apr 20 2023 Valid 12Z Mon Apr 24 2023 - 12Z Fri Apr 28 2023 ...A cold pattern is expected through around midweek across much of the mainland... ...Overview... An upper low across the Gulf of Alaska as the medium range period begins Monday will combine with energy tracking east near/over the Aleutians to produce an upper trough/low centered around the eastern Bering Sea as the week progresses, with the trough pattern extending into the mainland finally displacing the initial blocky upper high northwest of Alaska. Cold temperatures are likely across much of the mainland through around midweek, while a persistent wet pattern is expected across Southcentral Alaska to the southeastern mainland, with rounds of rain also possible for the Aleutians/Alaska Peninsula and the Panhandle. ...Guidance Evaluation/Predictability Assessment... Model guidance is in good agreement for the early part of next week, as upper and surface lows meander in the Gulf Monday, while an upper low meandering near the Kamchatka Peninsula looks to send a couple of rounds of energy eastward near the Aleutians Monday-Tuesday along with surface low pressure systems. A blend of the deterministic guidance favoring the GFS and ECMWF worked well for these features with the blending process serving to reduce individual model issues and provide a middle ground. As the week progresses, models are reasonably agreeable with forming an upper low embedded within a trough stretching across the northern mainland southwestward into the Bering Sea, with some shift west late week for ridging atop the Panhandle. But with this trough/low forming from multiple vorticity maxima coming from multiple directions, individual models struggle with the details of these potential interactions and the larger scale evolution, as well as with surface low positions. For the WPC forecast, gradually increased the proportion of the agreeable GEFS and EC ensemble mean components in the blend to over half by days 7-8 amid increasing uncertainty. ...Weather/Hazard Highlights... Colder than average temperatures are likely across much of the mainland behind the Gulf upper low. Expect well below average temperatures by 20-40F in between the Brooks and Alaska ranges, especially for eastern and central parts of the mainland, likely lasting into midweek next week. Colder than average temperatures should make it all the way west to southwestern Alaska early next week as troughing overtakes the late week ridging, but could be shorter-lived than farther east. Cold air (though less anomalous) will affect the North Slope as well, with highs in the single digits and perhaps even staying below 0F in some areas. The Alaska Range is likely to block the core of coldest air from coming into southern Alaska. Southcentral Alaska to the Panhandle may see below average temperatures in terms of highs but closer to, or even above (by late week), normal for lows. Multiple developments of low pressure in the Gulf of Alaska will support a wet and unsettled pattern across Southcentral Alaska to the Panhandle next week. Moderate precipitation should be widespread across that region early next week. Rain is also likely to track east across the Aleutians and Alaska Peninsula Monday with a low pressure/frontal system. This and some combination of energies from the east and north will help produce increasing amounts of precipitation from Southcentral east into the Panhandle around Tuesday-Wednesday and lasting into late week, especially for Southcentral to the southeastern mainland. Heavy totals are possible during this time that is typically the dry season, especially considering the persistence of the precipitation adding up over time. Also of note, a tight pressure gradient will be in place across the mainland early next week given the Gulf lows and a fairly strong surface high to the north of the state. Breezy winds and moderate to high gusts are possible, but relaxing as the week progresses. Tate Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Wed-Thu, Apr 26-Apr 27. - Much below normal temperatures across portions of mainland Alaska, Sun-Wed, Apr 23-Apr 26. 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