Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
759 PM EDT Mon Jun 12 2023
Valid 12Z Fri Jun 16 2023 - 12Z Tue Jun 20 2023
...Recurving Post-Tropical Cyclone Guchol could affect Alaska
early next week, but likely in a relatively weakened form...
...Overview...
Late this week, upper troughing will remain stretched across
eastern Siberia into the eastern Bering Sea into parts of western
Alaska, while a stacked low tracks across the Gulf of Alaska into
Southeast Alaska and supports enhanced rainfall chances for the
southeastern quadrant of the Mainland and into the Panhandle.
Meanwhile a low pressure system that was once Typhoon Guchol but
will soon be fully post-tropical as it recurves east of Japan
looks to track across the northern Pacific. By early next week,
former Guchol is becoming more likely to affect the Aleutians to
Alaska Peninsula and Southcentral Alaska with rain and perhaps
some gusty winds, though the low should not be terribly deep.
...Guidance Evaluation/Preferences...
Recent model guidance is fairly agreeable that upper-level energy
and likely a small closed low will produce a surface low pressure
system in the Gulf of Alaska, with just some minor differences in
its strength and track as it spins. Farther west, model guidance
still indicates that energy from the far northern latitudes will
drop south into the Bering Sea Wednesday-Thursday and be present
there through much of the medium range period. Centers of upper
lows within the elongated trough vary from model to model--the 12Z
ECMWF/UKMET were more aggressive with a Bristol Bay closed low
around Saturday compared to GFS and CMC runs. While an upper low
center should remain near/just north of eastern Siberia into next
week, the orientation of energy to the south and east varies more
with time, and may get affected by Guchol and any potential
phasing. Speaking of Guchol, models have slowed down the low a bit
to cross the Dateline around Friday, when it will likely be at its
(extratropical) strongest. Guidance shows the low tracking
northeast with time while slowly weakening and has trended toward
a higher percentage of models/ensemble members reaching the
Aleutians/Peninsula next week. The WPC forecast trended north as
well, but keeps the low itself a bit south through next Tuesday,
but close enough to be affecting those regions and beyond with
rainfall. With the exception of the 12Z GFS, which temporarily
around Day 6/Saturday weakened the Guchol low in favor of another
low to the west, most models seemed to be reasonable during the
period. A multi-model and ensemble blend was used with the blend
serving to smooth out too many model differences, with the
ensemble means comprising half the blend by Day 8.
...Sensible Weather and Potential Hazards...
Precipitation is likely to be enhanced across Southeast Alaska by
Friday as low pressure at the surface and aloft move through the
region, and locally heavy rain totals are possible. Lingering
energy will keep rain chances in the forecast there on Saturday
while some moderate precipitation amounts spread into the Alaska
Range and southward as well. Then by early next week, the surface
low that was once Guchol is likely to track toward (if not across)
the Aleutians/Alaska Peninsula and spread rainfall to those
regions and into the Lower Kuskokwim/Southcentral with time. There
may be some gusty winds as well dependent on the track and depth
of the surface low, but likely nothing too strong as the low looks
to be weakening as it tracks northeast. Light showers, mainly
diurnally driven, could remain across the Mainland as well early
next week.
With the persistent troughing over the Bering Sea and beyond, this
will maintain cooler than normal high temperatures across much of
the state, though somewhat moderated compared to the short range
period. The eastern Interior may warm up early next week to above
normal with temperatures in the 70s, while Southeast could flip to
slightly above average as well. Low temperatures are forecast to
be generally within 10F above/below average.
Tate
No significant hazards are expected over Alaska during this
forecast period.
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