621
FXAK69 PAFG 192217
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
217 PM AKDT Thu Sep 19 2024

.DISCUSSION...

.SYNOPSIS...
There will be a few spotty showers possible this evening over the
Mainland, with the main brunt of the showers remaining over the
White Mountains. These will continue to taper off through the
overnight hours with skies remaining mostly cloudy to overcast.
Weak troughing remaining in place will help to develop a few
showers again tomorrow. An arctic front will begin to dig
southward going into this weekend with some colder air advection
and the possibility of snow making it down into portions the
valley floor of the Interior this weekend. There will also be more
significant snowfall amounts expected for the northern slope of
the Brooks Range beginning tomorrow and especially by Saturday
through Sunday. Overall weak troughing to the north and another
major shortwave trough moving into the Gulf of Alaska early next
week will help to provide some instability for additional showers,
and accumulating snow showers above 1000 ft, to continue through
the mid part of next week with the colder temperatures still
locked in place.

&&

.DISCUSSION...

Upper Levels and Analysis...
The decaying low pressure system well to the southeast will
continue to propagate eastward. There will be an Aleutian low
undergoing cyclogenesis well to the south, which will track into
the northeast corner of the Gulf. This will provide some wrap-
around moisture, which will help for shower development over the
Upper Tanana by later in the evening on Friday. Meanwhile, a weak
arctic trough will begin to deepen over the North Shore and into
the Interior this weekend. Another major shortwave trough with an
associated strengthening low pressure center will move south and
into the Gulf early next week, along with weak upper level
troughing remaining over the Mainland through the mid part of next
week.

Forecast and Model Discussion...
The weak instability in place over the Mainland, due to weak
troughing, and the exiting low towards the southeast, will allow
for some spotty showers to be possible through tomorrow. The low
pressure moving into the northeast Gulf by tomorrow evening will
increase the probability of showers by tomorrow evening and
through Saturday morning over the Yukon-Tanana Uplands, with snow
accumulations for the White Mtns. As the troughing over the North
Shore deepens this weekend with an associated arctic front moving
southward into the Interior and advecting in colder air from the
north, it will bring about the possibility of snow occurring at
lower levels this weekend. The NAM and GFS have been the more
reliable model with resolving this features, and most of the blend
has incorporated these models. The NBM has been the more heavily
relied on for temperatures.

Central and Eastern Interior...
Spotty light rain showers will continue to be possible throughout
the day tomorrow, and then the probability will begin to increase
going into Saturday as the arctic front continues to dive south
and advect in colder temperatures. Most of the snowfall will occur
above 2000 ft through tomorrow, although these snow levels will
continue to drop down around 1000 ft and possibly lower for some
locations by Saturday. Depending on whether skies clear out and
get cold enough for some locations Saturday night, there could
even be light accumulations occurring for portions of the valley
floor.

West Coast and Western Interior...
Light onshore winds out of the west will continue to keep some
periodic light rain showers in place. The will eventually begin to
mix with some snow showers over the NW Arctic and W Brooks Range
by Friday and through early Saturday colder air begins to settle
in, then there will be some drier air moving in with the north
winds with weak high pressure building in behind the trough, which
will help to limit the amount of shower activity and just keep
skies mostly cloudy to overcast, with patchy fog possible.

North Slope and Brooks Range...
As the arctic trough continues to deepen this weekend, initial
accumulating snow will be possible for the W Brooks Range by
Friday of a few inches, by even more so going into the weekend,
with 48 hours totals of being anywhere from 6 to 12 inches
expected. At this time, it is going to be close on the timing and
intensity of snowfall amounts to reach Winter Storm Warning
criteria, and will continue to be analyzed as a result.
Accumulations of a few inches or more will also be possible for
the lower elevations, although likely remain more on the drier
side over the W Arctic.

Extended Forecast Days 4-7...
For early to mid part of next week, the arctic troughing will
remain in place, and there will also be a low pressure system to
the south which will also help to increase the instability and
keep the possibility of rain/snow showers in place over the
Mainland, and especially for the eastern half of the Interior. The
W Interior does look to be more on the drier side with the
continuation of more prevailing northerly winds.

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

&&

.HYDROLOGY...
No concerns.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
AK...Winter Storm Watch for AKZ809.
PK...None.
&&

$$

Steward