503
FXAK69 PAFG 212332
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
332 PM AKDT Fri Jun 21 2024

.SYNOPSIS...

Upper-level ridging extending across northern Alaska will
continue to bring warm temperatures and thunderstorm chances
across portions of the Interior. High temperatures will hover in
the 70s across the Interior through Saturday, with cooler
temperatures along the coast. The Eastern Interior will see high
temperatures closer to 80 on Sunday and Monday. Isolated to
widely scattered thunderstorms across the Interior today become
more limited to areas along the Alaska Range and in the Western
and Central Interior this weekend. For the North Slope, expect
winds to relax this weekend with a reprieve from fog and stratus
through Saturday, though they make a return for Sunday and
Monday.

&&

.DISCUSSION...

Upper Level Analysis...

A ridge extends northwest from Western Canada, across Interior
Alaska, into the Chukchi Sea, promoting fairly warm and dry
conditions across much of northern Alaska this afternoon. There is
a weakness in the ridge induced by a strong shortwave trough
over the SE Interior and Yukon, providing upper-level support for
isolated to widely scattered thunderstorms over the SE Interior.
Out west, a second shortwave has stalled along the West Coast,
contributing to cloudy conditions with isolated rain showers.
Additionally, weak troughing continues to slowly sink southward
across the Brooks Range, bringing drier air into the Eastern and
Central Interior.

Surface Analysis...

A thermal trough extends west from Yukon through the far SE
Interior into Southcentral Alaska, with a weak extension northward
into the Western and Central Interior. Surface high pressure is
centered in the Chukchi Sea with a ridge along the Arctic coast.
Between these features, generally light northeasterly winds have
developed across the forecast area. Some locations in the higher
terrain east of Fort Yukon have observed 15 mph winds, while gap
winds through the Brooks Range have gusted as high as 25 mph
(and should continue to be generally lighter than yesterday).
Light winds continue to allow smoke from the McDonald Fire to
linger near the surface between Eielson AFB and Birch Lake. An
elevated unstable air mass moving in off the Arctic Ocean has
brought a reprieve from fog and stratus, instead providing
patchy altostratus and even some light rain showers along the
Arctic coast. Warm conditions with temperatures in the 70s with
dew points in the 40s have allowed for the development of
scattered to widespread rain showers and isolated to widely
scattered thunderstorms across portions of the Interior.

Central and Eastern Interior...

Temperatures will peak broadly in the mid to upper 70s again this
afternoon/evening across the Central and Eastern Interior. Widely
scattered thunderstorms have developed along the high terrain of
the White Mountains and Fortymile Country this afternoon and have
drifted southwest over the Tanana Valley under the influence of
an upper-level shortwave near the Alcan Border. Increased mid-
level moisture brought by a series of shortwaves that lifted into
the SE Interior yesterday will continue the threat of heavy rain
in localized areas from showers and thunderstorms. Rainfall totals
of a quarter to half an inch, or greater, will be possible in
localized areas.

A ridge forecast to build today over the Western Interior will
influence the evolution of showers and thunderstorms this evening
over the Eastern Interior, with some dependence on timing.
Convective activity could be suppressed and storm motion over the
Eastern Interior slowed if the ridge builds in quickly through the
evening, otherwise, expect showers and thunderstorms to continue
to drift southwest off high terrain into the valleys.

Northeasterly winds continue to blow across the Yukon Flats and
are anticipated to spread southward, with impacts to the direction
of smoke dispersal from the McDonald Fire (namely, blowing it
away from the Richardson Highway and out over the Tanana Flats).
However, there is some uncertainty in how persistent the
northeasterly winds will be, as there is some potential for winds
to subside significantly overnight and allow dense smoke to once
again lower visibility tonight and tomorrow morning along the
Richardson Hwy.

This weekend, northeasterly flow brings warmer and drier
conditions as high pressure remains over the Western and Central
Interior. Expecting convective potential to be more limited as a
result, with thunderstorms confined primarily to the far SE
Interior and Central Interior. High temperatures will approach 80
degrees on Sunday and Monday. Thunderstorms make a return to the
Eastern Interior on Monday as a slow moving shortwave trough over
Western Alaska ejects eastward.

West Coast and Western Interior...

Upper-level high pressure builds over the Western Interior today,
leading to another day with high temperatures in the 70s for the
interior valleys of Western Alaska. Warm temperatures and
increased instability will support isolated to widely
scattered thunderstorms today and Saturday across the Western
Interior as a shortwave trough lingers across Western Alaska. An
upper-level low dropping south from the high Arctic will entrain
the shortwave, pulling it northeast. This will begin to shift the
upper-level high and the warmest temperatures to the east
beginning Sunday. Temperatures will therefore cool somewhat along
the West Coast for Sunday and Monday, while highs remain in the
70s in the Western Interior. At the surface, a ridge builds into
the northern Bering Sea this weekend, promoting stronger westerly
flow along the coast. This will increase the potential for
stratus/fog along the West Coast heading into next week.

North Slope and Brooks Range...

An elevated unstable air mass moving in off the Arctic Ocean will
continue to bring a reprieve from fog and stratus for the North
Slope through Sunday. At the same time, a weakening surface high
along the Arctic coast will mean northeasterly onshore flow
relaxes somewhat this weekend. Then, an upper-level low drops
south from the high Arctic and arrives along the Arctic coast by
Monday, leading to a return of fog and stratus, with increased
chances for rain/snow showers as well. Along the Brooks Range,
isolated thunderstorms are likely to develop each day.

Extended Forecast Days 4-7...

Expect a warming and drying trend for the Eastern Interior as an
upper-level high looks to establish over Southcentral Alaska and
Yukon, leading to continued fire weather concerns. A series of
upper-level lows near the Arctic coast, over Far Eastern Russia,
and in the Bering Sea will help to build and maintain ridging in
place through the week. High temperatures next week will likely
hover in the 70s and 80s in the Eastern and Central Interior. Out
west, there are indications that a low in the Bering lifts north
mid- to late-week, bringing southerly to southeasterly winds and
elevated chances of precipitation to the West Coast and Western
Interior. Southerly gale force winds may also produce elevated
surf along south-facing coasts. Thunderstorm potential will extend
across much of the Interior initially, before more stable air
moves up with the Bering low for the latter half of the week. This
will push the bulk of thunderstorm activity into the Eastern
Interior.

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

&&

.FIRE WEATHER...

Temperatures will peak broadly in the 70s across the lower
elevations of the Interior today, with RHs generally remaining
above 25 percent. Isolated to widely scattered thunderstorms
continue this evening as they push slowly southwest off the higher
terrain over Interior valleys. Increased mid-level moisture
brought by a series of troughs lifting into the SE Interior will
lead to the potential of heavy rain from showers and
thunderstorms, particularly from Delta Junction south and east,
leading to increased chances for wetting rains in the area.
Further north and west, storms will be drier with lower
probability for wetting rain.

A shortwave trough dipping south of the Brooks Range combined with
high pressure along the Arctic coast will continue to bring
northeasterly winds with drier air spreading southward across the
Interior. Gusty winds will continue to be possible each afternoon
in and around the Yukon Flats, especially over the higher terrain
east of Chalkyitsik, where sustained winds could exceed 15 mph
through Sunday, though winds diminish heading into the weekend.
Some areas will approach red flag conditions, however there is
increased confidence that hot, dry, and windy conditions will not
coincide, with temperatures peaking in the low 70s in the area.

This weekend, drier air causes RHs across the Eastern Interior
to dip well into the 20s. Isolated to widely scattered
thunderstorms largely focus over the Western and Central Interior
for the weekend, before pushing back eastward for Monday as an
upper-level shortwave sitting over Western Alaska becomes caught
in the flow of an upper low off the Arctic coast. RHs make a
modest recovery on Monday with a shift to westerly flow through
the Interior.

&&

.HYDROLOGY...

Showers and thunderstorms in the SE Interior may produce heavy
rainfall rates of half an inch or greater per hour in localized
areas. This could contribute to rapid rises on creeks in steep
terrain along the Alaska Range and in the Upper Charlie and Upper
Fortymile River Basins this evening.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
AK...None.
PK...Small Craft Advisory for PKZ812.
     Small Craft Advisory for PKZ858.
&&

$$

Quesada