Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 751 PM EDT Sat Mar 16 2024 Valid 12Z Wed Mar 20 2024 - 12Z Sun Mar 24 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 to the West Coast next week... ...Overview... Model guidance is rather agreeable that a significant pattern change should take place early next week across the state. A strong northeastern Pacific ridge will build into the Mainland and persist through the week into next weekend. Thus pronounced warming is likely over the Mainland, with the highest anomalies in northern and western areas. To the west of the trough 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 in particular, with more uncertainty farther north in how much precipitation reaches the western coast at times. 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 half of next week into next weekend. 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 lows with a general pattern of tracking northeast show some spread that impacts sensible weather, namely how much precipitation makes it into the western coastal areas. These details are harder to determine, but a Wednesday shortwave is looking more agreeable in the recent model guidance, helping produce Seward Peninsula precipitation. By late week, larger scale troughing with embedded low(s) looks to form across the Bering Sea likely from rounds of Arctic and North Pacific energy combining. This may set up an omega block pattern for late week into the weekend. Embedded lows and shortwaves are even more uncertain with this, but at least the general flow pattern is in place in model guidance, and promotes a possibly large surface low pressure system coming into the Aleutians. The model differences seem actually maximized around Friday, when the EC suite shows focused upper and surface lows just south of the western Aleutians in the north Pacific while other guidance is farther north. By the weekend the models converge better on placement, rotating near the western Aleutians. For the WPC forecast, used a multi-model blend of deterministic guidance early on. Gradually reduced the amount of deterministic guidance as the period progressed in favor of the ensemble means, which reached just over half the blend by Day 8. ...Weather/Hazards Highlights... Expect the most active area for precipitation to be across the Aleutians and Alaska Peninsula, where rounds of low pressure and frontal systems will help focus moist Pacific southerly flow through much of next week. These features could also be accompanied by some enhanced winds. For Wednesday-Thursday, precipitation amounts and winds do not look to be too high, but by late week into the weekend, heavier precipitation and stronger winds may increase in coverage for the Aleutians into the Alaska Peninsula as larger and deeper low pressure approaches. Less certain is the amount of precipitation reaching farther north across the Lower Kuskokwim/Yukon areas into the Seward Peninsula at times next week. Models still have some variability in how much may focus off or onshore. There is some increasing signal for focused precipitation over the Seward Peninsula. This will continue to be monitored, especially since with the warming temperatures some precipitation may be in the form of rain. 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, along with Arctic high pressure extending into western Canada. 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