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Area Forecast Discussion (AFD)

Issued by Fairbanks, AK (AFG)

                            
000
FXAK69 PAFG 202108
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
108 PM AKDT Sun May 20 2018

.DISCUSSION...

Synopsis...Thermal trough lies from the Middle Yukon Valley to the
Upper Tanana Valley and a weather front swinging northwest into
the interior will bring showers to most interior locations as it
moves through this evening through Tuesday. The Arctic remains
quiet with low stratus ceilings. Trough over the West Coast will 
continue to produce some isolated showers. Breakup has moved to
the Lower Yukon, see below for details.

Models...Surface solutions are similar, and they initialized well
against the 20/18Z analysis. The Canadian is a bit more aggressive
in moving a low to near Central this evening, but they all 
indicate enhanced trough along the north slopes of the Alaska 
Range this evening moving to lie from from the Upper Kuskokwim to 
the Upper Yukon Flats by Monday evening. A second low will develop
near Beaver Creek YT Monday afternoon move north to Chalkyitsik 
by Tuesday morning at 996 mb, then drifts west to Beaver and 
slowly weakens through Wednesday. Stability indicies are not 
great, but there is still some Lifted Indicies around zero from 
Dot Lake to Delta Junction this evening. Solutions indicate some 
non zero CAPE values with the thermal trough, but nothing 
significant. Will use an equal blend for most elements with a 
strong lean toward continuity since there are not significant 
changes expected.

Aloft...At 500 hpa...Troughing over most of the state as the ridge
has moved east with only weak ridging persisting over the
northeast corner and Eastern Arctic/Beaufort Sea. A 530 dam center
over St Lawrence Island will continue to dive south tonight and
merge with a broad 519 dam center that will move to 200 nm
southeast of Kodiak Island by Monday morning, then persists in the
area into Wednesday. A strong shortwave swinging around the low
will move over the Gulf of Alaska Coast, and southern Yukon
Territory this evening, and north over the Central and Eastern
Interior tonight to lie from King Salmon to McGrath to Tanana to
Old Crow YT by Monday morning. By Monday evening the trough will
lie from Kodiak City to McGrath to Hughes to Deadhorse. Weaker
shortwaves will continue to spin across the Eastern and Central
Interior through Monday night. Ridging will build in over the
Alaska Range Tuesday night with a 547 dam center over the MatSu
Valley. Weak trough will persist over the Western Arctic and
Chukchi Sea along 170W through Monday night. At 850 hpa...Zero 
Isotherm has pushed north and west over all but the coastal areas
with the +10C isotherm over the Fortymile Country. Some cooler air
digs south over the Central and Northwest Arctic and Northwest 
Interior Monday afternoon into Tuesday morning, pulls back to the
north. Some cooler air pushed over the Outer West Coast and St 
Lawrence Island Wednesday will bring slightly cooler temperatures
to the area. 

Surface...High pressure will persist over the Arctic with a 1029
mb center 400 nm north of Point Barrow. Broad area of low 
pressure over most of the state with a 984 mb low 200 nm south of
Kodiak Island, a 994 mb low near Northway, and a 998 mb low near
Marshall. By Monday morning the low south of Kodiak has become
quasi stationary, while the low near Northway will be near Central
and a well defined trough will lie along the north slopes of the
Alaska Range, and weak troughing will persist over the West 
Coast. By Tuesday morning the trough will move north to lie from
Dillingham to McGrath to Beaver and east, while the low near
Kodiak weakens as it slides east to 300 nm from the Island. A 1000
mb low will develop in Kotzebue Sound Monday night and move
northwest across the Chukchi Sea Tuesday night and Wednesday. 

Arctic Coast and Brooks Range...Stratus, and more stratus, and 
after that some more stratus, springtime in the Arctic. The 
20/2000Z GOES MVFR/IFR/LIFR Probability products indicate IFR 
conditions over the Eastern Arctic Coast, with MVFR conditions 
over the remainder of the coastal areas, and the Plains. SPoRT LEO
24hr Microphysics shows a large area of stratus over most of the 
coastal areas from MacKenzie Bay west to Point Lay with 
observations showing 400 to 1000 foot ceilings. Not seeing much 
precipitation, but a sprinkle or a flurry is possible. Winds will 
persist from the northeast to east at 15 to 30 mph with the 
strongest winds over the eastern Arctic Coast as the gradient gets
pinched as the low move north to the Upper Yukon Flats over most 
of the area and the 1025 mb high in the Arctic remains stationary.
Temperatures steady to a couple degrees warmer through Wednesday.

West Coast and Western Interior...Cloudy. Trough over the coast is
producing isolated showers up and down the coast, and do not 
expect that to change as a shortwave aloft swings into the area 
and reinforces the current trough. Some isolated thunderstorms
in the Upper Kuskokwim Valley Monday afternoon, and again Tuesday
afternoon. Patchy Dense Fog will return to the Lower Yukon Delta
Monday morning, mainly west of Anvik, with improving conditions
after 10 am AKDT. Winds generally northeast to northwest at 5 to 
20 mph except near the Bering Strait winds to 30 mph. A little 
cold air gets wrapped into the coast Tuesday, so expect some 
cooler temperature in the outer coastal areas, and St Lawrence 
Island, otherwise no significant change. See below for river 
information.

Central and Eastern Interior...Cloudy. Showers swinging north 
through the area tonight and Monday with isolated thunderstorms 
From Dot Lake to Delta Junction in the evening. Rainfall generally
less than 1/4 inch. Showers will continue to swing north to the
Upper Yukon Flats, and west to the Middle Yukon Monday. Winds
generally less than 15 mph will be swinging around from southeast
tonight to north Monday to west Tuesday. Rivers continue to run 
high, but no issues have been reported and the rainfall will no
produce a significant change in the levels. Not much change in
high temperatures through midweek, but overnight lows in the
Tanana Valley will be cooler tonight with the showers. 

&&

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

&&

.Fire Weather...Thermal trough extends from the Middle Yukon
Valley to the Upper Tanana Valley will slide north to the Upper 
Yukon Flats by Tuesday morning. A weather front will spin north
across the area tonight and Monday bringing showers and some
isolated thunderstorms. Some drying behind the front will push
Relative Humidity values to around 25 percent in the Tanana Valley
and along the AlCan Border Monday. Higher values for Tuesday
around 35 percent, then drying again with values around 25 percent
in the Middle Tanana Valley and the Upper Yukon Flats.
Winds generally less than 15 mph through Wednesday. For the 
latest Fire Weather information go to www.weather.gov/arh/fire.

&&

.Hydrology...Yukon ran free of ice at Galena Saturday, should be 
clearing at Kaltag today. Still quite a bit of ice downstream from
Aniak, but there is some open water. No reports of problems in the
Lower Yukon Delta at this time. For the latest breakup 
information go to www.weather.gov/aprfc.

&&

Extended Forecast for days 4 to 7...Temperatures near seasonal
normals with highs around 50 on the West Coast, around 30 on the 
Arctic Coast, and in the 60s in the Interior. Thermal trough will 
be over the Upper Yukon Flats Thursday, then slide south over the 
Tanana Valley for the remainder of the week. A weather front 
moving into the area from the southeast will bring showers with 
isolated to scattered Thunderstorms to all Interior areas Thursday
and Friday. Gusty winds developing near Alaska Range Passes for 
Thursday. If the GFS is correct, then the Northwest Arctic Coast 
may see some strong north winds and High Surf on Saturday.
 
&&

.AFG WATCHES/WARNINGS/ADVISORIES...

Heavy Freezing Spray Warning for PKZ230.

Small Craft Advisory for PKZ210-PKZ230.

Gale Warning for PKZ225.

Brisk Wind Advisory for PKZ235-PKZ240-PKZ245.

&&

$$

SDB MAY 18