Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 759 PM EDT Thu Mar 14 2024 Valid 12Z Mon Mar 18 2024 - 12Z Fri Mar 22 2024 ...Temperatures will rapidly warm up next week across the Mainland, especially northern and western areas... ...Overview... Model guidance is rather agreeable that a significant pattern change will take place next week. After some upper troughing lingers over the Mainland early next week, this feature is forecast to retrograde while a strong northeastern Pacific ridge builds into the Mainland by around Tuesday and lasting through the rest of the week. A pronounced warming trend is likely especially across the northwestern half or so of the Mainland. An active pattern is likely with mean southerly flow in the North Pacific/Aleutians/Bering Sea, with bouts of precipitation and winds, though with 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... At the start of the period Monday, there is reasonable consensus in the model guidance that an upper low should remain atop the northern Bering Sea with trough axes extending into the Aleutians and east to the Kenai Peninsula, where a weak surface low lingers. After that models consistently expand ridging from the northern Pacific into the Mainland and keep it there. 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 show some spread that impacts sensible weather. One trend today has been for a faster surface low track around Tuesday-Wednesday across the Aleutians compared to yesterday. During the latter half of next week, GFS runs, especially the 12Z, indicate a shortwave/small closed low undercutting the ridge and moving toward Cook Inlet or so before retrograding strangely. It seems unlikely that energy will be able to penetrate the strong ridge to do this and it seems more likely that the energy will get shunted toward the northeast on the western side of the ridge, as other guidance indicates. Thus leaned away from the GFS. More generally, models show variability in how much precipitation makes it into the western coastal areas. The ECMWF suite shows more precipitation for areas like the Southwest to Seward Peninsula than the GFS suite. With the lean away from the GFS, this brought more precipitation into those areas. Overall the forecast for today used a multi-model deterministic blend early on but decreased the proportion of GFS and UKMET first and eventually the ECMWF, in favor of the GEFS and EC ensemble means, reaching 60 percent means for Days 7-8. ...Weather/Hazards Highlights... Lingering energy and surface low pressure across Southcentral will provide a focus for heavy rain and inland/mountain snow for the eastern Kenai Peninsula through the northern Panhandle lasting into Sunday, but likely lessening compared to Saturday. Some areas of light snow may extend northward over the Mainland into Monday. 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. Neither winds nor precipitation look to be high enough to cause terribly hazardous conditions at this point. Less certain is the amount of precipitation reaching farther north across the Lower Kuskokwim/Yukon areas into the Seward Peninsula, but 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. Outflow winds may be a concern there. The forecast pattern evolution will bring a pronounced warming trend to the northwestern half or so of the state. After cooler temperatures into Monday, the building Northeast Pacific into Mainland upper ridge will lead to well above normal temperatures. By midweek or so, some locations should see temperatures at least 20-30F warmer than Sunday readings. Meanwhile Southcentral and most of the Panhandle should start out near normal, with Southcentral staying near to above normal through the period but the Panhandle drifting more below normal by midweek 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