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Area Forecast Discussion (AFD)

Issued by Fairbanks, AK (AFG)

                            
000
FXAK69 PAFG 131349
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
549 AM AKDT Mon Aug 13 2018

.DISCUSSION...

Synopsis...
Longwave troughing encompassing several low pressure systems will
bring unsettled weather across the state for the next several 
days. A low pressure center associated with the remnants of 
Typhoon Shanshan will move northeast into the Interior and
facilitate locally heavy rain across large portions of the state 
south of the Brooks Range. Strong Chinook winds through the Alaska
Range will wind down through today as the low center draws near, 
thus allowing rainfall chances to increase across the lower Tanana
Valley. Finally, continued northerly flow across the Arctic coast
will hold cold air in place and support wintery precip across the
region, particularly across the central and eastern Brooks Range.

Aloft 500 mb...
Several distinct height minima exist across the Alaska region as
part of a broad longwave troughing pattern. A 528 dam low situated
100 nm north of Banks Island will slowly drift southeast and 
continue to deepen through mid week. A 539 dam vertically stacked
low associated with the remnants of Shanshan is situated roughly
over the Yukon Delta and is expected to track northeast into the
central interior and weaken into an open wave mid lvl trough by
Tuesday. A second 544 dam low over the north-central Bering Sea
will swing southeast to Bristol Bay by early Wednesday. By mid
week, the result will be an elongated trough axis spanning the
Canadian maritimes to the northeastern Brooks Range, western
Interior, south to Bristol Bay, and across the Aleutians into the
north Pacific. By this time, a high-amplitude ridge axis 
extending east from central Asia will exploit a weakness in the
trough and cut into the northwest portion of the state. With
significant model disagreement regarding this feature, we will 
lean towards a more GFS based solution with a stronger longwave 
trough remaining in place through the weekend.

North Slope and Brooks Range...
A weak front running parallel to the Beaufort coast approx 100 nm
offshore will move south, brining mix of rain and snow across the
region. Colder temperatures will infiltrate the eastern 
coastline, resulting in mainly snow showers across the eastern 
Brooks Range and Beaufort coast with more of a rain/snow mix west 
of Deadhorse. Snow accumulation of up to 2 inches is possible 
across the central and Eastern Brooks Range through Tuesday. An 
arctic low near the pole will dive southward Wednesday and graze 
the coastline as it then tracks east. Warm southwest advection 
ahead of the front will keep precip mostly rain. A second low will
follow an identical track Thursday. Strong west winds can be 
expected along much of the Chukchi coast from Point Hope to Point 
Barrow. A sea level rise of up to 1.5 ft is possible by Thursday.

West Coast and Western interior...
A broad swirl of moisture constituting the remnants of Shanshan
will move northeast across the Y-K Delta and into the Western 
Interior. Deep saturation with this system will bring rain to most
areas south of the Brooks Range with total amounts through 
Tuesday varying between 0.25 to 0.50 inches in the Valleys to over
1.00 inch possible in the higher terrain of the Kuskokwim 
mountains and middle Yukon Valley. Strong north winds across the 
Bering will cause high surf along north facing shores from St. 
Lawrence Island north to Diomede. Strong winds along the immediate
Chukchi coast near Point Hope have prompted a strong wind 
headline for this area as well. By late Tuesday, weak ridging will
build east across the Chukchi and force most of the shower 
activity south near a sfc boundary spanning Holy Cross to McGrath 
and east across the Alaska Range.

Central and Eastern Interior...
Chinook conditions across the Alaska Range will gradually wind 
down through the day today, supporting an increase in shower and 
thunderstorm activity across the lower Tanana Valley this
afternoon. Rainfall will persist through Wednesday along a
stationary boundary spanning much of southeastern Alaska from the
Kuskokwim Valley across the Tanana Valley into Fortymile country.
Rainfall amounts through Wednesday will generally fall between 
0.25 to 0.50 inches with up to 1.00 inch or more possible for 
favored upslope areas. Weak convergence along the boundary and 
modest daytime heating will support isolated thunderstorm 
development this afternoon. Cooler temperatures Tuesday should 
mitigate this effect. Weak Chinook conditions will remain steady
for the upper Tanana Valley east of Tok through mid week, 
resulting reduced chances for rainfall in this area.

Models...
Good initialization against the 13/1200Z sfc analysis, 
particularly near the low center over the Y-K Delta. Reasonable 
agreement holds through Friday, though significant variability 
becomes apparent by Saturday. For now we will favor a holding a 
longwave troughing patten through the weekend as run to run model 
consistency has been sorely lacking.


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

&&

.FIRE WEATHER...
A large swathe of wetting rains is expected to inundate much of
the state, as fire weather remains suppressed by a broad troughing
pattern. However some dry spots will remain somewhat immune to
this system over the next few days. Areas of the upper Tanana
Valley east of Tok will remain Chinooked out of much of the
incoming moisture, though chanced for wetting rain does increase
Tuesday as the low center nears and downsloping diminishes. 

&&

.HYDROLOGY...
High water will gradually decrease over the next couple
of days. An additional 0.50" to 1.00" of rainfall across much of 
the Interior over the next few days. Expect rises in river levels
across the Interior this week with the rainfall. For the latest 
information go to www.weather.gov/aprfc.


&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Wind Advisory for AKZ217-AKZ224-AKZ227.

High Surf Advisory for AKZ213.

High Wind Warning for AKZ223-AKZ225-AKZ226.

Small Craft Advisory for PKZ200-PKZ215-PKZ230.

Gale Warning for PKZ210-PKZ220-PKZ225.
&&

$$

COWMAN AUG 18