Area Forecast Discussion
Issued by NWS Fairbanks, AK

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000
FXAK69 PAFG 212042
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
1242 PM AKDT Thu Sep 21 2017

.DISCUSSION...

Models...Very good agreement in the near term. Some minor height
differences of 2-5 hpa for the major features, and they continue
into the mid range. At the surface the solutions initialized well
against the 21/18Z analysis with pressure differences less than 5
mb. For the short term forecast will be utilizing a equal blend
for most elements. For precipitation will use the NAM because it
it handles the downslope effect better than the other models.
Precipitation type will continue to be the biggest challenge until
winter fully sets in next month.

Aloft at 500 hpa...Main longwave trough lies from high in the
Canadian Archipelago to a 546 dam low over the eastern Arctic
Coast, to a 535 dam low over Norton Bay to a 548 dam low south of
Adak this afternoon and will remain relatively stationary through
Friday afternoon. A broad area of low pressure with a 500 dam low
remains over the North Pole. By Saturday afternoon the low over
the eastern Arctic moves east over MacKenzie Bay at 542 dam, and
the low over Norton Bay moves south over Nunivak Island at 528 dam
with the trough extending south to a 554 dam low over the north
Pacific. Weak ridging over the southeast interior will remain in
place as heights fall a few dam tonight, then builds back to the
northwest Friday night with heights rising a few dam. Ridging over
Siberia will push east over Wrangel Island over 73N with weak
ridging extending east to Banks Island by Friday morning. The
longwave trough will remain over the state in a similar
configuration through the weekend. At 850 hpa...Zero isotherm has
started drifting back to the north and lies from Dawson YT to
Livengood to McGrath lies from Ft McPherson YT to Delta Junction
to Wasilla to Nunivak Island, and will push back to the north
tonight to lie from Dawson YT to Livengood to Anvik to the
Pribilof Islands by Thursday afternoon, and continues to slide
slowly back to the north through Friday.

Surface...Leeside trough is developing north of the Alaska Range
this afternoon and a bubble high developing over the Copper River
Basin has the gradient over the Central and Eastern Alaska Range
tightening up a bit. Weak downslope conditions developing, and
will persist into Saturday morning before breaking down. A weather
front lies from Burwash Landing YT over the Alaska Range then
southwest to Bristol Bay and will be quasi stationary through
Sunday morning as it weakens. High pressure will persist north of
the Brooks Range with a 1026 mb high 200 nm north of Point Barrow
Friday morning. The high center will move east Saturday, but high
pressure will persist over the offshore waters. A weather front
will move southeast across the Arctic Saturday with the tail of
the front approaching the northwest coast Sunday morning, but will
be held offshore by the high pressure over the area as it
continues east. The inverted trough over the west coast extends
north over Point Hope, and will remain stationary as a 1000 mb low
moves to King Salmon by Friday morning, and a broad area over low
pressure develops over mainland Alaska.

Arctic Coast and Brooks Range...Not much change as high pressure
remains over the area with the high center just offshore, so the
tale of two Arctic coasts will continue for another day or two.
From Point Barrow east expect low clouds, some light rain or snow
and patchy fog with the onshore flow. Winds will be north to east
at 10 to 20 mph east of the high. To the west some clouds, but
periods of clearing skies with winds east to south at 10 to 25
mph. Over the Brooks Range and Plains the northeast flow will
produce mostly cloudy skies with occasional light snow or rain in
the Plains and occasional light snow in the central and eastern
Brooks Range. No significant snowfall is expected. Winds will be
northeast to east at 5 to 15 mph. Temperatures warming into the
mid to upper 30s during the day, and in the 20s at night.

West Coast and Western Interior...A mix of clouds will range from
cloudy north of the Seward Peninsula, and in the middle Yukon
Valley, to partly cloudy over the lower Yukon Delta. Expect a mix
of precipitation from north to south with some light snow north of
Galena near the inverted trough, and light rain from Galena
south, but areas may see a mix at times. Weather system to the
south will send some light rain into the Upper Kuskokwim Valley
tonight as a low moves into Bristol Bay and a weather front pushes
north. Light rain south of Ambler, and east of Golovin with the
exception of the Lower Yukon Delta on Friday. A shortwave moving
southwest around the low will spin some rain over the Lower Yukon
Delta coast Friday night, and another wave will spin some west
over Norton Sound on Saturday. Winds northeast to east 10 to 20
mph along most of the coast, with winds to 35 mph near the Bering
Strait. Inland winds northeast to east 5 to 15 mph. Temperatures
steady with lows in the 30s, and highs in the 40s.

Central and Eastern Interior...Cloudy conditions will prevail the
next day or so. Light rain will be moving north across the area
this evening, but downslope effect will limit amounts from
Fairbanks south and southeast in the Tanana Valley to 0.10 or
less. Rainfall amounts to the north and west of Fairbanks will be
up to 0.25 inch. Slight chance of snow on higher elevation summits
north of Fairbanks, but it will be wet snow that melts rapidly as
freezing levels are around 4000 ft and will be rising a little as
the system pushes north. In the Alaska Range expect snow
primarily above 4000 ft, but those levels may fall a bit as the
atmosphere is cooled by the precipitation. Areas along the Parks
and Richardson Highways may see some snow, but expect it will melt
rapidly on contact as surface temperatures remain well above
freezing. Northeast to east winds across the area will range from
5 to 25 mph with the strongest winds north of the Yukon River.
Locally winds may be gusting near 40 mph. The exception will be
the Alaska Range where gap winds near passes are developing and
will peak overnight from the south at 35 to 45 mph.

&&

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

&&

.Hydrology...Rivers continue to run high in the northwest
interior, but are slowly falling. They are expected to remain high
into next week. No significant rain is expected through the
weekend.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...

Small Craft Advisory for PKZ200-PKZ210-PKZ225-PKZ230-PKZ240
-PKZ245.

&&

$$

SDB SEP 17



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