Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 740 PM EDT Wed Apr 19 2023 Valid 12Z Sun Apr 23 2023 - 12Z Thu Apr 27 2023 ...A cold pattern is expected early next week across much of the mainland... ...Overview... A blocky closed upper high to the northwest of Alaska will take multiple days to slowly lift northwestward farther away from the state. The overall flow will be redirected around this feature to the east and south for an Omega-style blocking pattern this weekend, transitioning to more of a Rex Block next week. By the start of the medium range period Sunday, upper and surface lows will be in place over Southcentral Alaska/Gulf of Alaska region, behind which cold temperatures will spill into the mainland. Then an upper low meandering near the Kamchatka Peninsula looks to send energy eastward near the Aleutians Monday-Tuesday along with a surface low pressure system, leading to a bout of rain for the Aleutians and eventually the Alaska Peninsula. All this should continue a wet pattern at times for the southern coast and Panhandle. ...Guidance Evaluation/Predictability Assessment... Model guidance is in good agreement for the blocky pattern early next week. The last several model cycles have shown a lobe of vorticity diving south to create an upper low centered near the Kenai Peninsula Sunday with some meandering into the Gulf Monday, along with associated Gulf surface lows. 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. Models also show agreement on the large scale that upper-level energy should track eastward somewhere along the axis of the Aleutians but perhaps in the nearby Bering Sea or northern Pacific through the first half of next week. But there are some model differences in timing and strength that affect the accompanying surface lows, as well as variations with the interaction between this incoming energy and the preexisting Gulf energy. Some GEFS and EC ensemble mean components were added to the blend amid increasing uncertainty in the details of the overall pattern, reaching to about half of the model blend by days 7-8. ...Weather/Hazard Highlights... The lobe of energy/troughing moving across the eastern mainland this weekend will lead to chances of light precipitation there, but perhaps more notably, another shot of cold air. 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 to the West Coast early next week as this trough 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 normal for lows. Multiple developments of low pressure in the Gulf of Alaska/northeastern Pacific will support a wet and unsettled pattern across southeastern Alaska/the Panhandle into next week. Precipitation totals do not look terribly heavy on individual days early in the week, but some moderate/enhanced totals are likely especially given the persistence of the precipitation adding up over time. Recent models have trended wetter by Tuesday-Thursday for some potentially heavy rainfall over the Panhandle. Farther west, rain is likely to track east across the Aleutians and Alaska Peninsula Sunday-Monday with a low pressure/frontal system. This and some combination of energies from the east could spread precipitation into Southcentral Alaska around Monday, with increasing amounts possible by midweek. Tate Hazards: - Much below normal temperatures across portions of mainland Alaska, Sat-Wed, Apr 22-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