Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 642 PM EST Wed Feb 28 2024 Valid 12Z Sun Mar 03 2024 - 12Z Thu Mar 07 2024 ...Very cold temperatures over much of the state lasting into Saturday... ...Overview... Cold surface high pressure will be atop the state this weekend, but weakening and pushing east while an upper ridge tracks over the Mainland. Model guidance is now more agreeable that this ridge pattern should last into around Tuesday. Rounds of upper troughing and energy along with surface low pressure/frontal systems are likely across the Bering Sea and Aleutians next week, which could erode the Mainland ridge by midweek with more progressive flow. ...Guidance Evaluation and Preferences... Fortunately, recent model guidance has come to a more agreeable position for the early part of next week, indicating that the upper ridge stretching across the Mainland will remain over the state. Some slight shifting of the axis is likely with time, from positively tilted across the Alaska Peninsula northeastward on Sunday, to neutral from Southcentral northward on Monday, to negatively tilted from Southeast Alaska toward the northwestern Mainland by Tuesday. This arises due to potent energy with troughing and perhaps an embedded upper low tracking across the Bering Sea into western parts of the state and eventually displacing/eroding the ridge. This first round of Bering energy (with some spilling southeast into the northern Pacific by Tuesday) is reasonably agreeable in the model guidance. However, model spread increases by Wednesday-Thursday with an additional round or two of troughing from upstream. The GFS runs break away some energy that is near the Kamchatka Peninsula Tuesday and the small closed upper low that it forms tracks quickly eastward, along with the associated surface low. The ECMWF/CMC deterministic runs track this feature more slowly east as more of the energy stays together. The ECMWF and CMC means are slower as well, while the GEFS mean is faster but not to the same extent as the deterministic GFS runs. In this somewhat progressive flow pattern, the differences lead to problems with blending models, as the various solutions become out of phase with each other. Favored the slower solutions at this point, but the details are likely to change with time. Given these considerations, the WPC forecast used a model blend of the 12Z deterministic guidance early in the period, but then phased out the GFS by Days 7-8/Wednesday-Thursday while slightly decreasing the proportions of the other deterministic models. Introduced the EC mean in the blend by Day 6 and increased the weighting of the EC mean to almost half for Day 8, while including a lesser proportion of the GEFS mean. ...Weather/Hazards Highlights... Northerly mean flow, lingering troughing in the eastern Interior, and cold surface high pressure will promote very cold temperatures lasting into Saturday across a majority of the mainland to the south of the Brooks Range, as highlighted on the Days 3-7 Hazards Chart. This will be from a combination of actual air temperatures (possibly reaching -40 degrees over the typically coldest eastern Interior locations) or wind chills farther south and west. Much below normal temperatures are also likely for Southeast Alaska in the northerly flow. Temperatures should gradually moderate from west to east through the weekend into early-mid next week, especially considering the trend toward a sustained upper ridge. Northwestern areas of the state look to reach above normal temperatures this weekend and last into much of next week. Some gap/outflow winds may persist into Saturday across portions of Southeast Alaska in northerly flow, which do not look to be too extreme but could be hazardous per the Juneau Weather Forecast Office. Farther west, a couple of low pressure/frontal systems tracking across the Alaska Peninsula to southwestern Mainland along with persistent mean southwesterly flow should promote precipitation chances early next week. This precipitation activity should spread north and east with time, with some light snows potentially impacting much of the Interior by around Tuesday, while moderate precipitation shifts east into Kodiak Island and the Kenai Peninsula and surrounding areas. The flow pattern across Southeast Alaska on the other hand should be relatively dry, until perhaps a wetter shift around midweek. Winds and precipitation may be enhanced for the Aleutians next week when frontal systems pass through. There could also be concerns for localized gap/outflow winds farther east across the southern coast of the state at times, but without good consensus at this point. 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