Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 722 PM EDT Tue Aug 1 2023 Valid 12Z Sat Aug 5 2023 - 12Z Wed Aug 9 2023 ***Very warm temperatures likely over parts of central/eastern Mainland Alaska this weekend into early next week*** ...Synoptic Overview... An overall blocky upper flow pattern is expected to be in place across the Alaska domain for much of the extended forecast period, primarily owing to an anomalously strong upper ridge axis that builds northward across northwestern Canada and into the Arctic. This will support unusually warm conditions for much of the lower elevations of the eastern Interior and even across the North Slope region. The strong ridge axis will also limit the eastward progression of a strong storm system over the Bering Sea this weekend, and an upper low over the Gulf will likely stay south of the southern Alaska coast and weaken by Monday, while a second low tries to develop farther south by Tuesday-Wednesday. These low pressure systems will keep scattered showers in the forecast for western and southern portions of the state, and mainly dry across eastern and northern areas. ...Guidance Evaluation/Preferences and Predictability Assessment... The 12Z model guidance suite has a good overall depiction of the Bering and Gulf lows, and especially the building upper ridge over eastern Alaska for the weekend. Looking ahead to early next week, the guidance becomes a bit more varied across the Gulf with shortwave energy south of the ridge axis and how it evolves. The ECMWF and CMC were more in line with supporting a better defined second upper low developing by Tuesday, whereas the GFS is considerably weaker and even has a weak ridge axis trying to build northward over the southern Gulf. This also holds true going into next Wednesday, and the GFS is quicker with the Bering Sea trough moving across southwestern Alaska. Taking these factors into account, the WPC front/pressures forecast is primarily derived from a nearly multi-deterministic model blend through Sunday, and then less of the GFS by Monday and beyond and increasing use of the ensemble means to about 40% by the middle of next week. ...Weather/Hazards Highlights... The amplifying upper ridge shifting from the mainland into western Canada will promote well above normal temperatures, especially over the Interior and North Slope regions and likely peaking this weekend. Of particular note, highs may reach the upper 80s and even low 90s over parts of the eastern Interior, especially the Yukon Flats, while the North Slope could see readings rise into the low-mid 80s. Temperatures will likely moderate a little from west to east early next week depending on how much the ridge breaks down. Elsewhere, the southwestern mainland and the southern coast will likely see a trend toward slightly below normal highs. Low temperatures should be above normal nearly statewide with the greatest anomalies over the North Slope and a few scattered areas farther south. Guidance continues to show a broad area of mainly light to occasional moderate rainfall during the weekend across the far western mainland as a band of deep-layer southerly flow sets up between the advancing eastern Bering Sea front and the upper ridge farther east, and some heavier thundershowers are possible over favored terrain. Depending on how upper dynamics/surface waviness may evolve near the Alaska Peninsula early next week, the best prospects for noteworthy rain will likely be across that region and farther east along and near the southern coast, but nothing particularly heavy is currently expected. Hamrick Hazards: - Hazardous heat across portions of eastern interior mainland Alaska, Sat-Mon, Aug 5-Aug 7. 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