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000 
FXAK69 PAFG 172312
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
312 PM AKDT Tue Sep 17 2019

.SYNOPSIS...
A low pressure center over Bettles that is causing heavy snow
there, will move to near Barter Island tonight. Heavy snow over 
the Dalton Highway from Finger Mt north to Sagwon will be 
diminishing late this afternoon, and heavy snow in zone 218 east 
of the Dalton Highway will diminish late tonight. 

A weather system moving north over southwest Alaska tonight will 
bring rain to the southwest Interior and western Alaska Range 
tonight, and then bring rain to much of the Interior on Wed and 
Wed night, except for the southeast Interior which will be under 
southwesterly chinook wind conditions Wed and Wed eve. Thu will
see scattered showers over the Interior.

Fri will see another low pressure system move north into the Gulf
of Alaska, and then continue north over the Eastern Interior on
Sat. This will bring rain to most of the Eastern Interior Late Fri
into Sat, with snow over higher elevations.

Aloft...
A long wave pattern consists of a trough that stretches from 
Mainland Alaska southwest over the Bering Sea, and a long wave 
ridge over the Gulf of AK and South Central Alaska. The ridge will
push east over Western Canada and SE Alaska by Thu and then remain
there through the weekend. H500 Heights will remain low over
NW Alaska, and gradually fall through the weekend over the
remainder of Northern Alaska. What this means on the big picture
is that conditions will cool to seasonal norms in most areas, and
be mostly wet. Expect snow from the Brooks Range north, with mixed
rain and snow along the Arctic Coast and West Coast, while the
Interior has rain, which could be mixed with snow at times, 
through the weekend, but could see accumulating snow at elevation.

A low aloft near Coldfoot will move to Arctic Village by 10 pm
Tue, to Barter Island by 4am Wed, then move north of the Arctic
Coast Wed and Thu. This feature has strong vertical motions and
Mountain with it and is causing heavy snow. Expect another 
several inches of snow along its track northeast of Coldfoot 
tonight. Snow should be ending SW of Coldfoot in the next several 
hours. This scenario has led us to continue the snow advisory for 
zone 218 east of the Dalton Highway through midnight, while the 
snow advisory for the Dalton Highway West in zone 218, and zone 
219 will end at 4pm. The Snow warning for zone 206 will continue 
through 6pm as the area from Atigun Pass north will likely get 
upslope snow for several more hours. 

A second low aloft over the Chukchi Sea will move over Point Hope
tonight, and then persist there into Fri. This will cause isolated
to scattered snow showers over the area from Point Hope to the
Bering Strait as the cold air associated with this low. This
feature will also induce a surface low under it which will be
addressed in the surface section below. 


Surface...
A 1002 mb low will develop near Point Hope tonight and then
persist into Fri. This will cause some N-W winds of 15-20 kt over
the Chukchi sea late tonight through Fri. Winds are expected to 
be light enough to not cause any significant waves or surf. 

A 1006 mb low 100 NM north of Barter Island will deepen to 998 mb
by 4pm Wed, then move to 60 NM north of Utqiagvik as a 1002 mb low
by 4pm Thu. Snow occuring with this low will taper off to
Scattered showers showers Wed. 

A 1005 mb low near Coldfoot will move to Arctic Village as a 1005
mb low by 10 pm Tue, then move north an merge with the previously
mentioned low north of Barter Island on Wed. An Arctic cold front
that extends from Old Crow to this low near Coldfoot, then to 
Fairbanks and to the Yukon Delta, will move by 4am Wed to Inuvik
to Eagle to Fairbanks to the Yukon Delta. The front will then
retreat north over the Interior to the Brooks Range as the next 
incoming system pushes it now on Wed, while the portion of the
front along the West Coast drops south of the YK Delta on Wed. 
Snow will track northeast with the low center tonight, giving
another several inches of snow northeast of Coldfoot, while
isolated to scattered rain and snow showers occur along the cold 
front tonight.

A just west of St Paul Island will move to Kuskokwim Bay as a 986
mb low by 4am Wed, to McGrath as a 991 mb low by 4pm Wed, to near
Tanana as a 1007 mb low by 4am thu, and to near Battles as a 1004
mb low by 4pm Thu. An occluded and warm front stretching NE from
this low NE over SW Alaska will move to Bethel to Denali to
Northway by 4am Wed, to McGrath to Old Crow by 4pm Wed, to Tanana
to Old Crow by 4am Thu, and to Bettles to Arctic Village by 4pm
Thu, then dissipating. The Arctic cold front will extend south 
from the low near Tanana at 4am Thu, then from Bettles to Denali 
by 4pm Thu, then remain stationary into Fri. 

Expect rain to spread northeast over the SW Interior and Western
Alaska range tonight with the low and front, and over the
remainder of the southern and Eastern Interior on Wed and Wed
night, then linger as scattered showers into Thu. Precip may start
as snow north and west of the Arctic front, then change to rain as
the Occluded/warm front overrides the arctic air. Rain may mix 
with snow Thu along the returning arctic cold front.

On Fri...A strong low moving north to the northern Gulf of Alaska 
will spread clouds and a chance of rain to the Eastern Interior. 
This low will continue north into the Eastern Interior by Sat, and
will likely cause rain and high elevation snow across the Eastern
Interior on Fri night and Sat. 

&&

.DISCUSSION...
Models initialize well aloft at 12Z, and show similar solutions
through 4pm Fri. Models show precipitation fields in general 
agreement, and we prefer to use a blend of the NAM and GFS precip 
fields for both areal coverage and precip amounts. 

At the surface at 15Z, models verify a few mb too weak on the 
surface trough north of the Eastern Arctic Coast. As a result, 
models verify winds directions almost 180 degree off in direction.
Since this trough will likely persist, and intensify tonight and 
Wed as the low aloft moves northeast over it and helps to 
intensify it, expect winds to remain Westerly in zones 203 and 
204 and to be 3-5 kt stronger than models would indicate for 
tonight and Wed. Otherwise, models show similar solutions through
Fri and we will go with a blend of the GFS and NAM for winds. 

Bottom line is we will use a blend of the GFS and NAM, but keep
west winds in zones 203 204 tonight and Wed and bump up speeds
from what models indicate. 

FIRE WEATHER...
Temperatures cooling to near normal this week. RH values should
remain above 40% this week. Could see winds conditions Wed in zone
226 and 224 between Dot Lake and Tok with winds southwest gusting
to 40-50 mph on Wed. 

Coastal Hazard Potential Days 3 and 4...None.

&&

.HYDROLOGY...
Rivers continue to slowly fall or have leveled off. No areas of 
concern at this time.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Wind Advisory for AKZ224-AKZ226.

Winter Storm Warning for AKZ206.

Winter Weather Advisory for AKZ218.

Small Craft Advisory for PKZ200-PKZ210.

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