Alaska Extended Forecast Discussion National Weather Service College Park MD 649 PM EDT Mon Jun 16 2025 Valid 12Z Fri 20 Jun 2025 - 12Z Tue 24 Jun 2025 ...Warm temperatures will persist across the Interior into the weekend... ...Overview... An omega block will be in place over the Alaska domain late this week, consisting of a consolidating upper low centered over the Aleutians/southern Bering, another upper low in the northeast Pacific moving more quickly east, and a persistent and anomalously strong upper ridge/high atop much of the Mainland in between the two lows. The upper high will bring long-lasting warm temperatures particularly to the central/eastern Interior through the weekend and early next week, along with scattered convection. Meanwhile a low pressure/frontal system should lead to a round of rain moving across the Alaska Peninsula Friday. The Bering Sea/Aleutians upper low and the eastern upper ridge look to shift very slowly east while weakening as the extended period progresses. ...Guidance Evaluation/Preferences... Individual model and ensemble guidance is quite agreeable with the large scale pattern described above. A broad and reasonably deep (for June) surface low will be supported by the Bering/Aleutians upper low at the start of the period Friday, with operational models generally showing a central pressure in the 980s. The location is a bit more variable; averaging the model positions puts the low right over the Aleutians, but many models are just south of the Aleutians while the CMC is just north. By early Saturday the models converge with a low position just north of the Aleutians. The upper and surface lows are forecast to meander near the eastern Aleutians while weakening through the weekend into early next week. There is some spread with how far east the upper low will push toward Bristol Bay. In general, ensemble means and many of the AI models are a bit farther east than the operational models for early next week. The 12Z GFS seemed best aligned with the AI/means with its low position, so leaned toward this cluster. By next Tuesday some deterministic models dive the upper low southeast across the Alaska Peninsula into the Pacific, with the CMC most aggressive. Overall the most uncertain forecast area is the western Mainland/Alaska Peninsula at the interface of the trough/low and ridge to its east. But at least the western trough/eastern ridge pattern remains agreeable on the large scale. WPC preferred a multi-model deterministic blend for the early part of the forecast. As the period progressed, used some GEFS and EC ensemble means, reaching over half means by Day 8 to mitigate the increasing model spread. ...Weather/Hazards Highlights... Warm to hot temperatures will be ongoing underneath the upper high as the period begins Friday. The Yukon Flats can expect the highest temperatures, with some 90s possible, allowing for a Hazardous Heat area to be drawn on the Day 3-7 Hazards graphic for Thursday-Friday. Temperatures will be well into the 80s through Interior areas like Fairbanks. These temperatures are above average by around 10 to 25 degrees across the Y-K Delta and Interior toward the North Slope. The multiple days of hot conditions could lead to fire concerns, especially in areas where it does not rain. The slowly weakening upper ridge will allow for temperature anomalies to lessen slightly by the weekend, but remain warm over the central and eastern Interior. The Y-K Delta and Seward Peninsula and vicinity should cool down close to average by the weekend and early next week as upper troughing could finally approach. Meanwhile, temperatures will be rising to above normal in Southeast Alaska as the upper ridge builds in. Temperatures should peak over the weekend, reaching the 70s in many areas. There are some low probabilities of 80F (the new Heat Advisory threshold) especially toward Ketchikan and areas near the Canadian border, which the NWS Juneau office is monitoring. Many Mainland/Interior areas can expect diurnally forced convection given the instability created in part by the hot temperatures. Rain and thunderstorms will likely be scattered from day to day through the period, and there may be locally heavier rainfall amounts in higher elevations of the Brooks and Alaska Ranges with some orographic enhancement. Southeast Alaska is forecast to dry out by Friday as the ridge aloft comes in. Farther west, moist inflow ahead of the Aleutians low pressure system and its associated fronts will spread moderate to locally heavy rain across the Alaska Peninsula into Friday, with lighter amounts reaching Southcentral by the weekend. Winds are likely to peak around 30-40 knots with a front in the Aleutians/Alaska Peninsula vicinity Friday before weakening. Another couple of rounds of rain are possible in the Aleutians early next week as a surface trough moves through and then possibly a system approaches from upstream. 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