Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
757 PM EDT Tue Oct 3 2023

Valid 12Z Sat Oct 7 2023 - 12Z Wed Oct 11 2023

...Multi-day heavy precipitation threat from southern to Southeast
Alaska along with windy conditions and freezing rain and snow
potential for Southwest Alaska and the Alaska Range into the
Interior...


...Overview...

A rather active weather pattern will likely be in place for the
end of the week and going into the weekend with a couple of
organized Gulf low pressure systems affecting the southern coastal
areas, principally from the Kenai Peninsula eastward to especially
include the southeast Panhandle region.  Several inches of
rainfall from atmospheric river events is expected, and result in
enhanced run-off and elevated stream flows.  Temperatures are
expected to drop steadily going into the weekend and beyond with
generally below normal readings for much of the mainland.

...Guidance Evaluation and Preferences...

The 12Z model guidance suite generally indicates near average
forecast spread through the weekend and the beginning of next
week.  A general deterministic blend of the 12Z GFS/ECMWF/CMC and
some UKMET and previous WPC continuity seems to offer a good
forecast starting point through Sunday with seemingly average
predictability and continuity.  With greater mesoscale differences
becoming apparent by next Monday and Tuesday, use of the ensemble
means increased to about 50%.

...Weather and Hazards Highlights...

There will likely be a strong surge of lower latitude
moisture/atmospheric river later this week into the weekend across
southeast Alaska as a warm front lifts north across the Gulf of
Alaska in advance of a developing Gulf system.  This moisture
should produce heavy rainfall and mountain snows from the
Panhandle back to portions of the southern mainland coast. 
Details for additional potential systems reaching the Gulf of
Alaska become more uncertain over the weekend into next week, but
there is a growing signal for a subsequent deep low approaching
from the northeastern Pacific into early next week as a maritime
threat and as a focus for onshore flow and additional rain. 
Confidence decreases with respect to precipitation coverage and
amounts, but the overall pattern seems to offer a continued
potential for enhanced rainfall and mountain snows extending
across the broad southern mainland tier, including south-central
and the Alaska Range as well as the Panhandle region.  Lingering
cold temperatures may pose a threat for impactful freezing rain
into Southwest Alaska for the Lower Kuskokwim and vicinity, and
across the southern Interior including the Copper River Basin,
with snow over other areas.  For the five-day period, the highest
precipitation totals will likely be over the Southeast.  Between
low pressure east of the Alaska Peninsula and high pressure
forecast over or north of the North Slope, a broad area of the
mainland into the eastern Bering Sea should have a fairly tight
gradient supportive of brisk to strong winds and gaps winds to
monitor.

Hamrick


Hazards:
- Heavy rain across portions of Southeast Alaska, Fri-Sat, Oct
6-Oct 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