Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 755 PM EDT Sun Mar 17 2024 Valid 12Z Thu Mar 21 2024 - 12Z Mon Mar 25 2024 ...Much warmer than normal temperatures expected especially for northern and western parts of the Mainland... ...Active pattern with precipitation and winds for the Aleutians/Alaska Peninsula to the West Coast... ...Overview... By the latter part of the week, an amplified pattern will be well established across Alaska, as a strong northeastern Pacific to Mainland upper ridge takes hold and likely stays into early next week. Warmer than normal temperatures are expected across the Mainland, with the highest anomalies in northern and western areas. To the west of the ridge axis, an active pattern is expected with mean southerly flow in the North Pacific/Aleutians/Bering Sea. Bouts of moderate to heavy precipitation and windy conditions are likely across the Aleutians to Alaska Peninsula as well as farther north across the West Coast. Meanwhile the northerly flow on the east side of the ridge axis should produce a cool and dry pattern for Southeast Alaska. ...Guidance Evaluation and Preferences... Model guidance has consistently shown persistent upper ridging through the latter part of this week into early next week, likely setting up an omega block with troughing coming into the southwestern edge of the ridge. Confidence is relatively high on this larger scale. The main uncertainties through next week include details of the flow to the west of the ridge axis, so from the Aleutians to Bering Sea to West Coast, as shortwaves and embedded upper lows within the general troughing pattern show some spread. Fortunately, recent model guidance was pretty agreeable in indicating a shortwave over Bristol Bay and vicinity early Friday and tracking north across the West Coast toward the North Slope by Saturday, providing a little more confidence in one of the smaller-scale features impactful to sensible weather. Farther west, the details of energy are still murky, but at least there is better agreement in this forecast for a relatively large surface low pressure system to be south of the Aleutians in the northern Pacific Friday and cross the Aleutians by Saturday. By early next week though, increasing spread is seen with the low track, as GFS runs retrograde the low toward the west while the ECMWF/CMC continue tracking the low northeast toward the western coast, though at differing speeds. Not a lot of ensemble members show a low track like the ECMWF/CMC. These differences are also reflected in differences aloft, naturally. The ECMWF also drops quite a bit of energy southward from the Arctic atop the Bering Strait by next Monday, unlike other models. Considering these factors, the WPC forecast utilized a multi-model blend of deterministic guidance early on, and gradually reduced the amount of deterministic guidance as the period progressed in favor of the ensemble means, reaching over half the blend by Days 7-8. ...Weather/Hazards Highlights... Expect the most active area for precipitation to be across the Aleutians and Alaska Peninsula and the western coast of the Mainland, where rounds of low pressure and frontal systems will help focus moist Pacific southerly flow through the latter part of the week into early next week. These features could also be accompanied by some enhanced winds. During late week, a shortwave and onshore flow should produce some enhanced precipitation for western areas of the Mainland in general, and particularly for favored southern parts of the Seward Peninsula. Both rain and snow are possible depending on the area and elevation, considering the warming temperatures. While multiple rounds of precipitation are likely for the Alaska Peninsula, currently the amounts look to be maximized there Friday into Saturday with a favorable surface low placement to the west. The details of the flow pattern make the precipitation totals and placement more uncertain into next week, but generally there is some signal that energy could press a bit east and bring precipitation to parts of the Kenai Peninsula and Southcentral. Meanwhile, the northerly flow east of the upper ridge axis should keep Southeast Alaska cool and dry. Much warmer than average temperatures will likely last through the entire period for much of the Mainland due to the ridge aloft. Parts of the North Slope to Brooks Range can expect temperatures over 30 degrees above normal with some above freezing readings possible (though probably not quite reaching Utqiagvik). Temperatures that are above average but to a lesser extent are likely across the rest of the Mainland too, with highs reaching the 40s on average. On the other hand, Southeast Alaska can expect near to below normal temperatures due to northerly flow aloft to the east of the upper ridge axis. 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