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Northern Alaska forecast discussion
National Weather Service Fairbanks Alaska
601 am akdt Wed Oct 18 2017

Synopsis...
aloft...
a long wave trough over Mainland Alaska will deepens through the
end of the week. This will keep snowy conditions over northern
Alaska and cause temperatures to fall through the week to well
below normal by the end of the week. The exception if the Arctic
coast where more open water than normal is keeping temperatures
above normal there.

A deep 493dm h500 low 400 nm north of Demarcation Point will move
to 300 nm north of Prudhoe Bay by 4pm Wed, to 150 nm northwest of
Barrow by 4am Thu, to near Point Lay by 4pm Thu, and over the
Seward Peninsula by 4pm Fri. Since this deep low will have very
cold air aloft with it, expect significant amount of snow showers
over water and along coasts with onshore flow. This will also
cause surface features to strengthen more than normal over water.
See surface discussion below.

Surface...
a 990 mb low 40 nm north of Nuiqsut will move over Nuiqsut as a
990 mb low by 4pm Wed, then move to near Barrow as a 993 mb low
by 4pm Thu, and to the Seward Peninsula as a 990 mb low by 4pm
Fri. A cold front stretching from this low to the Yukon Delta will
move to Barter Island to Fort Yukon to McGrath to Bethel by 4pm
Wed, and then move east of the alcan border Wed night. Light snow
showers are occuring along the cold front and could cause 1-2
inches of northwest facing slopes such as the western Alaska Range and
White Mountains. Heavy snow showers are occuring west of the low
where very cold air (850mb temperatures of -12c or colder) is
moving over open water and onto the North Slope west of the low.
This will cause another 2-4 inches of snow through early Thu over
zones 201 202 and 205 and thus the Winter Weather Advisory
continues through 4am Thu. There are also north to northeast
winds gusting to 40 mph in the northwest quadrant of the low which
will decrease today as the low moves inland and begins to weaken.
This has caused high surf in zones 201 and 202 that should
decrease this afternoon.

A second low developing under the deep low aloft will develop 300
nm north of Barrow as a 999 mb low by 4pm Wed, move to near near
Wainwright as a 993 mb low by 4am Thu, to Point Lay as a 994 mb
low by 4pm Thu, and then merge with the first low Thu night near
Point Hope. A second cold front stretching northwest from this low
will move to Wainwright to the Bering Strait by 4am Thu, to Point
Lay to the Yukon Delta by 4pm Thu, to Point Hope to Bethel by 4am
Fri and then dissipating. Expect more snow showers with this low
and cold front, especially along north facing slopes. Also expect
north winds 20-30kt with and following the cold front over the
West Coast tonight through Thu night. This could cause elevated
surf north facing shores of zone 213. Winds could turn northwest tonight
and Thu over Kotzebue Sound and the Chukchi Sea coast but at this
time it looks like strong winds and elevated surf will remain
west of Shishmaref. This will need to be watched.

An occluded front over Southeast Alaska will ride up over the cold air of
the southeast interior tonight and Thu. This will cause 1-2 inches
of snow over zones 223 224 and 226 tonight and Thu along with northwest
winds gusting to 20 mph.



&&

Discussion...
models initialize well at 06z Wed and show similar solutions
through 4pm Wed. After that time, the ecmf moves the low aloft
over the high Arctic to the southwest much quicker than than the
NAM/GFS. Favor the slower movement shown by the GFS as the ecmf
appears to move this deep low much faster than lows of the depth
normally move. At the surface, the GFS maintains the current
strong low over the central Arctic coast, while developing a
second low that develops over open water of the Chukchi Sea this
afternoon through Thu under the low aloft, and then follows the
low aloft over the Seward Peninsula Fri. There is model
disagreement over this second low movement, but we favor the GFS
maintains the double low structure through Thu and does not merge
them until Thu night. This difference leads to uncertainty of wind
direction over Kotzebue Sound and the Chukchi Sea Thu into Fri.

Coastal hazard potential days 3 and 4...
northerly winds gusting to 40 mph over zones 201 and 202 will
decrease today. This has caused high surf in zones 201 and 202
that should decrease this afternoon.

North winds 20-30kt over the West Coast tonight through Thu
night could cause elevated surf north facing shores of zone 213.

Winds could turn northwest tonight, Thu and again Fri over Kotzebue
Sound and the Chukchi Sea coast, but at this time it looks like
strong winds and elevated surf will remain west of Shishmaref.
This will need to be watched.

&&

Afg watches/warnings/advisories...
high surf advisory for akz201-akz202.

Winter Weather Advisory for akz201-akz202-akz205.

Heavy freezing spray warning for pkz230-pkz235-pkz240-pkz245.

Small Craft Advisory for pkz210-pkz220-pkz225-pkz230-pkz245.

Gale Warning for pkz235-pkz240.
&&

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