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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 2247Z Mar 20, 2024)
 
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Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
647 PM EDT Wed Mar 20 2024

Valid 12Z Sun Mar 24 2024 - 12Z Thu Mar 28 2024

...Much warmer than normal temperatures expected especially for
northern and western parts of the Mainland...
...Moderate to heavy precipitation potential for parts of
Southwest and coastal Alaska through the weekend...

...Overview...

The pattern across the Alaska domain should stay fairly amplified
through the period with a strong ridge across the Mainland, mean
troughing across the Bering, and several shortwaves rotating
through the mean flow south of the Aleutians and into the Gulf.
This should result in warmer than average temperatures across much
of the state, with precipitation mainly confined to coastal areas
as well as into southwest Alaska. Most systems look to stay far
enough south to keep most of the precipitation light in nature,
but an early period low pressure system may bring more enhanced
rain/snow this weekend. The ridge over the mainland is forecast to
gradually weaken next week, but the general pattern should remain
in tact much of the period.


...Guidance Evaluation and Preferences...

The latest model guidance shows general agreement on the large
scale pattern of reinforced troughing/upper low over the
Bering/Aleutians and slowly retreating ridging across the
Mainland. There remains plenty of uncertainty in the details
though, especially concerning individual systems moving south of
the Aleutians and into the Gulf. The 12z GFS and ECMWF are the
most consistent through the period with each other, as well as the
ensemble means and formed the majority basis for today's blend.
The UKMET was a little different early on with the placement of a
surface low in the Bering as well as a system sliding well south
of the Aleutians into the southern Gulf Monday-Tuesday. The CMC
for the most part was consistent enough with the ECMWF and GFS on
southern stream systems, but was an outlier with dragging a cut
off low south along the western Alaska coast and a stronger
surface reflection. There are some timing differences with the
next system south of the Aleutians on Wednesday (especially the
CMC), and another stronger system behind it on Thursday, but for
the most part the agreement on these systems is very good for the
day 7-8 time frame.


The GFS is quite a bit stronger with one system Monday-Tuesday
that breaks off the parent upper low and moves into the Gulf,
while the ECMWF and CMC show better agreement on just a weak
shortwave through the region. Behind this, the ECMWF gets really
fast with another shortwave south of the Aleutians. Given the
uncertainty in these smaller scale lower predictability systems,
the WPC blend for today trended from a purely operational blend on
Days 4 and 5, to an increasing reliance on the ensemble means
later in the period to help mitigate and smooth out these
differences. Overall, this maintains good continuity with the WPC
forecast from yesterday as well.


...Weather/Hazards Highlights...

Expect the most active area for precipitation to be across the
Aleutians and Alaska Peninsula and the western coast of the
Mainland, where rounds of low pressure and frontal systems will
help focus moist Pacific southerly flow this weekend and into
early next week. The most active day should be Saturday-Sunday
with some potential for moderate to heavy rainfall across parts of
southwest Alaska into the Kenai Peninsula. Given warm
temperatures, much of the precipitation should be rain, but snow
is possible in the higher elevations. After this, the general
pattern should stay unsettled and showery from the Aleutians to
the Southern Coast and Panhandle, but most systems should be weak
enough or far enough south to limit anything in terms of hazardous
weather.

Much warmer than average temperatures will likely last through the
entire period for much of the Mainland due to the ridge aloft and
warm mean southerly flow underneath/on the western side.
Temperatures look to gradually moderate early next week but remain
well above normal, especially across northern and western parts of
Alaska. The eastern interior may trend back towards normal/below
normal by mid next week, and Southeast Alaska may be near or below
normal much of the period due to influence of multiple systems
weakening as they reach the coast.


Santorelli


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