Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 646 PM EDT Tue Mar 19 2024 Valid 12Z Sat Mar 23 2024 - 12Z Wed Mar 27 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 of the Mainland... ...Overview... By this weekend, an amplified pattern will be well established across Alaska, as a strong northeastern Pacific to Mainland ridge is overhead. 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, fairly active weather, especially this weekend, 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 western coastal areas. Meanwhile, the northerly flow on the east side of the ridge axis should produce a cool and dry pattern for Southeast Alaska. The ridge is forecast to gradually weaken and shift east early next week, but the general pattern should remain in tact much of the period. ...Guidance Evaluation and Preferences... The latest model guidance shows general agreement on the large scale pattern of reinforced troughing/upper low over the Bering/Aleutians and slowly retreating ridging across the Mainland. There remains plenty of uncertainty in the details though, especially concerning individual systems moving south of the Aleutians and into the Gulf. The GFS is quite a bit stronger with one system Monday-Tuesday that breaks off the parent upper low and moves into the Gulf, while the ECMWF and CMC show better agreement on just a weak shortwave through the region. Behind this, the ECMWF gets really fast with another shortwave south of the Aleutians. Given the uncertainty in these smaller scale lower predictability systems, the WPC blend for today trended from a purely operational blend on Days 4 and 5, to an increasing reliance on the ensemble means later in the period to help mitigate and smooth out these differences. Overall, this maintains good continuity with the WPC forecast from yesterday as well. ...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 this weekend and into early next week. These features could also be accompanied by some enhanced winds. Mainly Saturday, 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 and southwestern Alaska. 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 through about 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 should 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 mostly dry, though with perhaps some increasing chances for light amounts by Monday-Wednesday. Much warmer than average temperatures will likely last through the entire period for much of the Mainland due to the ridge aloft and warm mean southerly flow underneath/on the western side. The greatest anomalies should be across parts of the North Slope to Brooks Range, where temperatures may be greater than 30 degrees above normal into at least this weekend. Temperatures look to gradually moderate early next week but remain well above normal. The rest of the Mainland should also be near or above normal, but to a lesser extent. On the other hand, Southeast Alaska can expect near to slightly below normal temperatures initially 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