Alaska Extended Forecast Discussion
National Weather Service College Park MD
702 PM EDT Sun Jun 15 2025
Valid 12Z Thu 19 Jun 2025 - 12Z Mon 23 Jun 2025
...Warm temperatures will persist across the Interior through next
weekend...
...Overview...
An omega block will set up over the Alaska domain later this week,
consisting of an upper low in the Bering that slowly drifts south
while merging with a shortwave, 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
to the Interior in particular through much of the week, along with
scattered convection. Meanwhile a low pressure/frontal system
should lead to a round of rain moving from the Aleutians into the
Alaska Peninsula Thursday-Friday.
...Guidance Evaluation/Preferences...
Individual model and ensemble guidance is quite agreeable with
the large scale pattern described above. Minor model differences
appear with the way the Bering upper low and the northern Pacific
shortwave and surface low interact and combine by around Friday.
At the 12Z Friday timeframe, the surface low shown by the 12Z
ECMWF and CMC is near/just north the Aleutians while the GFS runs
are just to the south over the northern Pacific. The model
averaging puts the low just atop the eastern Aleutians but AI
models are generally favoring a slightly southern solution. The
low positions late this week are a bit farther west than
yesterday's.
Over the weekend, the upper and surface lows are forecast to
meander near the eastern Aleutians. The main outlier appears to be
the 12Z GFS that shows a farther southwest position with the
lows. Preferred to use the 06Z GFS run in the model blend instead,
which was more aligned with consensus, especially because AI
models were east even of the deterministic model consensus. This
continues into early next week, where the AI models and ensemble
means were east with the upper low position closer to Bristol Bay
compared to farther west deterministic models. Overall the most
uncertain forecast area is the western Mainland 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 (including the
06Z GFS) 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 Thursday. The Yukon Flats can expect the
highest temperatures, with some 90s possible, while temperatures
will be in 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 Y-K Delta and Seward Peninsula
and vicinity should cool down close to average by next weekend and
early next week as upper troughing could finally approach. The
slowly weakening upper ridge will also allow for temperature
anomalies to lessen somewhat, but remain warm over the Interior.
Meanwhile, troughing moving across Southeast Alaska should lead to
below normal temperatures there later this week, but by the
weekend temperatures are forecast to rise as the upper ridge
builds in, reaching 70F in some areas.
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. Into Thursday, Southeast
Alaska is forecast to see modest rain as the upper low moves
overhead. Then farther west, moist inflow ahead of a low pressure
system and its associated fronts will spread moderate to locally
heavy rain across the Aleutians Thursday and across the Alaska
Peninsula Thursday-Friday, with more modest amounts reaching
Southcentral by next weekend. Winds are likely to peak around
30-40 knots with a front in the Aleutians/Alaska Peninsula
vicinity Thursday-Friday.
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