Area Forecast Discussion
Issued by NWS Fairbanks, AK

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FXAK69 PAFG 202110
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
110 PM AKDT Thu Jul 20 2017

.DISCUSSION...
Progressive weather pattern over northern Alaska through the
weekend and early next week. An upper level ridge over southwest
Alaska combined with a strong upper level low over the Beaufort
Sea will provide strong westerly flow aloft with a series of
shortwave troughs and accompanying surface features over the north
slope and Brooks Range through early next week. A more moist and
cooler weather pattern is on tap for the west coast, western
interior as well as the central and eastern interior.

Aloft at 500 hpa, an east to west oriented ridge over southern
Alaska combined with a series of strong short wave troughs moving
from west to east over the Brooks Range will bring ample moisture
over the north slope, especially over the eastern north slope and
eastern Brooks Range where a special weather statement addressing
expected rises on river levels in these areas has been issued.
The ongoing rain event has already dropped between one quarter and
one half inch of rain with another one half to three quarters of
an inch expected through Friday evening. Westerly flow at the
surface and in the mid levels will bump up precip totals in the
northeastern Brooks Range with upslope enhancement. Another strong
shortwave with attending surface low and fronts will plow onto
the western north slope Sunday and will bring another significant
rain event over the western north slope sunday morning and the
eastern north slope Sunday night and Monday. Will need to closely
monitor rivers especially on the eastern north slope and eastern
Brooks Range Sunday and Monday as ongoing significant rain event will
already have river levels in the area elevated. As a 995 mb
surface low near the Gulf of Anadyr moves north and east on Sunday
heavy rain is expected over the southwestern Brooks Range and
southern slopes of the Seward Peninsula ahead of a strong front
moving over western Alaska. Wetting rains are expected over much
of the interior Sunday and Monday ahead of the front as the front
sweeps inland over the western interior Sunday night and Monday
and over the central and eastern interior Monday.

The thermal trough currently along a Bettles to Fort Yukon to Old
Crow line will be the focus this evening for scattered rain
showers and isolated thunderstorms. The thermal trough will move
south to be along a Fairbanks to Eagle to Mayo line Friday
afternoon and evening and along a Bettles to Northway line
Saturday as a trough extending southward from a low over the
Beaufort Seas sweeps south and east over the the Brooks Range to
near Bettles. Minimum relative humidity levels are expected to be
above 30 percent in all areas of northern Alaska with the
exception of Fort Yukon to Central to Eagle line and points east
this evening. Minimum relative humidity levels are expected to
drop to around 30 percent this evening and to around 35 percent
Friday afternoon and evening. Winds in these areas are expected to
remain below Red Flag criteria.

The 12z model suite initialized well against the 12 surface
analysis and verified well against the 18z surface analysis,
however model spread on feature position and strength increase
rapidly in the short range as the models continue to struggle
with the track and intensity of a low expected to be located 250
nm north of Wrangel Island Friday afternoon. Both the NAM and the
ECMWF have the low 250 NM north of Wrangel Island as a 992 mb low
Friday afternoon however the GFS has the low located 150 nm
northeast of Wrangel Island as a 999 mb low. The GFS takes the low
on a much further south trajectory that would bring stronger west
to northwest winds along the eastern north slope coast Saturday
as compared to a more northerly track as given by both the NAM and
ECMWF. The GFS is also forecasting a 995 mb low to develop over
the Gulf of Anadyr that tracks east northeast over the Bering
Strait Monday while other models forecast a much weaker low over
the Chukotsk Peninsula. These significant strength and track
differences between model families and from run to run for only a
couple days out strongly erode model confidence in the mid and
long range.

Coastal Hazard Potential Days 3 and 4...
Models continue to indicate strong westerly winds in the vicinity
of Barrow Saturday and along the eastern north slope Saturday
afternoon and into Sunday. Surf models continue to indicate
elevated water levels north of Wainwright to Barrow in the 1 to 2
foot range beginning Sunday morning and along the eastern north
slope with momentum transport onto shore Sunday night into Monday.
Continue to monitor.


&&

.FIRE WEATHER...
The thermal trough currently along a Bettles to Fort Yukon to Old
Crow line will be the focus this evening for scattered rain
showers and isolated thunderstorms. The thermal trough will move
south to be along a Fairbanks to Eagle to Mayo line Friday
afternoon and evening and along a Bettles to Northway line
Saturday as a trough extending southward from a low over the
Beaufort Seas sweeps south and east over the the Brooks Range to
near Bettles. Minimum relative humidity levels are expected to be
above 30 percent in all areas of northern Alaska with the
exception of Fort Yukon to Central to Eagle line and points east
this evening. Minimum relative humidity levels are expected to
drop to around 30 percent this evening and to around 35 percent
Friday afternoon and evening. Winds are forecast to remain just
below Red Flag criteria in these areas. Temperatures are expected
to rise into the lower 70s. Fire weather concerns will diminish as
a more moist and cooler airmass moves over central and eastern
interior Friday and through the weekend.

&&

.HYDROLOGY...
Significant rainfall continues along the eastern north slope and
eastern Brooks Range with 24 hour totals in the one quarter to
one half inch range. Moisture ahead of a front currently along a
Prudhoe Bay to Anaktuvuk Pass line will continue to slowly move to
the east. West to northwest flow in the low and mid levels will
enhance rain fall totals in the eastern Brooks Range where an
additional one half to three quarters of an inch of rain is
expected though Friday evening. A special weather statement for
rises on rivers draining the eastern north slope and northeastern
Brooks Range has been issued. Another round of rain possibly heavy
will move into the eastern north slope and eastern Brooks Range
Sunday as another shortwave moves over the area. Continue to
monitor for rises on rivers.


&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory for PKZ220-PKZ225-PKZ230-PKZ245.
&&

$$

CCC JUL 17



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