Graphical Hydro Meteorological Discussion

105
FXAK68 PAFC 220148
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
448 PM AKST Sat Dec 21 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Tuesday)...

A period of freezing rain was observed across Anchorage this
morning. Another round of rain and freezing rain is expected this
evening as low pressure centered south of Kodiak Island pushes
another front to the north Gulf coast. Rain has already overspread
much of the western Kenai Peninsula south of Soldotna as of 4 pm,
with the lifting front and accompanying shortwave aloft set to
bring at least a trace of (freezing) rain to Anchorage and
portions of the Matanuska Valley over the next several hours.
Despite some areas warming above and remaining above freezing,
surface temperatures remain in the upper 20s, which means that any
rain that falls will freeze to snow-free surfaces such as roads
and sidewalks. As a result, Winter Weather Advisories have been
issued for the western Kenai, Anchorage, and the Matanuska Valley.
These advisories last through Sunday evening, during which time
much of the area may remain dry. However, periods of rain/freezing
rain are expected with a series of shortwave troughs lifting
across Southcentral. Some locations, particularly those closer to
the mountains, where temperatures will be warmer (from the mid
30s up into the mid 40s), are expected to see accumulating
precipitation. Where surface temperatures remain below freezing,
up to a tenth of an inch of ice may accumulate.

Along the coast, expect periods of moderate to heavy rain with
each passing shortwave/front. The strongest features pass through
this evening through midnight and midday on Sunday. Ample warm
air will push snow levels as high as 3000 ft. Warm air moving into
the southern Copper River Basin will also lead to freezing rain
potential along the Richardson Highway as surface temperatures
remain below freezing to as low as about 10 degrees. The western
Copper River Basin near Eureka and Tahneta Pass will see enough
instability and moisture with Sunday`s shortwave to receive up to
an inch of snowfall. On Monday, another shortwave lifting through
Southcentral will bring a surge of southerly winds, though
temperatures are not expected to appreciably warm with this. In
fact, temperatures begin to trend downward Monday night as colder
air wrapping in from around the decaying low pressure that remains
quasi-stationary in the vicinity of Kodiak Island and the Alaska
Peninsula begins to work in. By this point, chances of inland rain
and freezing rain will finally be coming to an end, at least
temporarily.

Quesada

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS
(Days 1 through 3: Through Tuesday afternoon)...

The predominant weather feature this afternoon is a low moving
south of Kodiak Island, poised to cross the AKPen into Eastern
Bering by Sunday morning. Gusty north to northeast winds have
continued across the AKPen to Kuskokwim Bay, with the strongest
gusts over open water. Several shortwaves rotating north around
this low will continue to bring bands of precipitation across
Southwest Alaska from this afternoon through Monday.

Precipitation type across Southwest remains the most difficult
aspect of the forecast as precipitation will have to pass through
a substantial warm, dry layer before reaching colder air at the
surface. Due to colder surface temperatures, Bethel may receive a
mix of snow and sleet, with a couple inches of snow possible for
the Pribilofs on Sunday. Precipitation for Dillingham and King
Salmon may remain as rain until Monday, then change to mixed rain
and snow through Tuesday. Winter Weather Advisories remain in
effect.

A second low approaches Bristol Bay from the Gulf between Sunday
and Monday, with more chances for freezing rain and rain/snow mix
across parts of the area through at least Monday morning. However,
both of these lows weaken and dissipate as a strong front
approaches the Aleutian Chain from the west Monday night. This
sends a band of easterly gale force winds and rain across much of
the Aleutian Chain by Tuesday afternoon.


&&

.LONG TERM FORECAST (Days 4 through 7: Wednesday through Saturday)...

An elongated upper level trough extends from the Arctic through
the Eastern Bering into the North Pacific on Wednesday, with
several low centers rotating through the pattern. This trough will
slip over the Central Mainland into the Gulf of Alaska by the
weekend. A ridge over the Bering trailing the trough moves into
Southwest Alaska by Saturday. A second upper trough moves in from
Kamchatka over the Western Aleutians by Saturday. An upper ridge
over Southeast Alaska moves into the Canadian Provinces through
the end of the week. The ECMWF/GFS/Canadian models handle the the
strengths and tracks of the weather producers through the end of
the forecast period.

Most of the jet support rides across the North Pacific to the
South of the Aleutians and Alaska Peninsula. On the surface, a
series of lows and fronts will track over the Eastern Aleutians
and AKPEN over Kodiak Island into the Gulf before pivoting into
the North Gulf Coast. This will bring repeated rounds of locally
heavy rains to the Southcentral and AKPEN coastal zones and Kodiak
Island. Gusty Easterly winds spread over the Northern Gulf
Wednesday, and diminish Thursday. With cold air seeping across the
Interior from Canada, a band of mixed rain and snow or freezing
precipitation away from the coasts along the Northern edges of the
Precipitation areas, with snow mostly further inland. Gusty
Northeasterly winds just below gale force spread over the Central
and Eastern Bering and across the Aleutians and AKPEN through the
forecast period.

&&

.AVIATION...

PANC...VFR will largely prevail for ANC. Two fronts moving across
the Gulf will bring brisk easterly to southeasterly winds aloft,
with wind speeds of around 30 kt. This will lead to low level wind
shear through Sunday morning as surface remains will remain out of
the north. Guidance is trending towards a lower chance of
freezing rain and rain. If any rain or freezing rain occurs, it
will likely happen later this evening and overnight as a trough
moves through.

&&


$$

373
FXAK69 PAFG 212117
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
1217 PM AKST Sat Dec 21 2024

.SYNOPSIS...
Happy Solstice! The first day of astronomical winter comes in with
seasonable temperatures across the Interior and North Slope, and
above normal temperatures on the West Coast. Northerly winds will
be increasing from Point Hope to St. Lawrence Island with gusts of
60-75 mph expected tonight through Tuesday night before gradually
weakening thereafter. We will also be expecting a long duration
snow event from the Brooks Range to the Western Interior

&&

.DISCUSSION...
Key Weather Messages...

Central and Eastern Interior...
- Dry today with seasonably chilly temperatures. A more
significant warm up arrives tomorrow with an increase in clouds
and snow.

- Widespread snow blossoms over the Northern Interior tomorrow
evening from Fort Yukon to Allakaket.
- Areas of intermittent light snow possible from Eagle to Tanana
tomorrow night into Monday morning.

- Snow in the Northern Interior continues into Tuesday, then
shifts westward on Wednesday with most of the snow exiting to
the west.
- Snow totals over the 3 day stretch may be upwards of 6-12
inches in the Northern Interior, and 1-4 inches from Tanana to
Eagle.

West Coast and Western Interior...
- High wind warning from Point Hope to St. Lawrence Island
tonight through Tuesday night with gusts upwards of 60-75mph.
- The strongest winds are expected from Diomede to Gambell.
- Northerly wind continues past Tuesday, but will become
gradually weaker as the week progresses.

- Areas of light snow develop in the Western Interior as early as
Sunday afternoon from Shaktoolik to Shungnak. More widespread
snow is expected Monday afternoon and may be heavy at times from
Holy Cross north.

- The YK Delta, Seward Peninsula and NW Arctic Borough look to
miss out of the heaviest snow from Monday into Tuesday morning,
but the band of snow looks to progress west with widespread snow
moving into the YK Delta and Eastern Seward Peninsula Tuesday
afternoon.
- Snow continues from YK Delta to Ambler and east from there into
Wednesday with significant accumulations over 6 inches
possible.
- There is uncertainty with this! Guidance has been meandering
back and forth with the heaviest snow band, but it is looking
probable that portions of Western Alaska (especially the Yukon
Delta) get their first significant snow of the year.

North Slope and Brooks Range...
- Relatively benign weather for most of the area.

- Northeast winds strengthen in Point Hope today with gusts to 60
mph likely tonight through Monday afternoon.

- We`ll be monitoring snow developing in the Brooks Range south
and east of Anaktuvuk Pass Sunday afternoon. Snow will continue
here through Wednesday afternoon.
- Heaviest axis of snow will be from the Dalton Highway east to
Arctic Village.
- Lighter snows are expected in Anaktuvuk Pass through Monday,
then there is a chance for heavy snow on Tuesday.
- This snow will expand northward to the Arctic Coast between
Deadhorse and Kaktovik Monday night to Wednesday.
- As of now there is still a lot of uncertainty with the exact
placement of the snow, but heavy snow is likely to occur in
some spots from Deadhorse to Kaktovik, south to Arctic Village
and the Dalton Highway.

Analysis and Forecast Confidence
A 1028 mb arctic high pressure in Siberia will be interacting
with a 960 mb low moving into the southern Bering Sea. As the low
moves northwest, a pressure gradient will develop resulting in
very strong northerly winds from Point Hope to St. Lawrence
Island. There is high confidence that these winds will continue
through Monday in Point Hope and through Tuesday night from
Diomede to St. Lawrence Island. Otherwise, these features will
also form in a deformation zone over much of Northern Alaska,
resulting in some widespread, long duration snow. Chances for
heavy snow exist from the Yukon Delta to Kaktovik. The main axis
of snow initially develops from Fort Yukon to Allakaket with
lighter snow expected in the Brooks Range and from Tanana to
Eagle. The heaviest snow will will persist in the Northern
Interior and Eastern Brooks Range through Wednesday. The Western
Interior will get into the snow on Monday, then the West Coast on
Tuesday. There is lower confidence in where the snow sets up
across the Western Interior Monday and Tuesday, but anywhere from
Hooper Bay to Shageluk northward are in play for moderate to heavy
snow. The only spots that may completely miss out on the heavy
snow are the NW Arctic Borough and Central/Western Seward
Peninsula. There will be more details to come on this heavy snow
and where it sets up as we gain more confidence tonight and
tomorrow.

Extended Forecast Days 4-7...
Extended periods of snowfall will continue through the northern
portions of the interior. As the weekend rolls around cold arctic
air will rush down into the western interior as the front moves
through the state. There is significant model disagreements on the
intensity as well as the extent of the coldest temperatures. The
Canadian model is the most vigorous with 850 mb temperatures of
-35 to -40. While the GFS has -20 850mb temperatures. At the
surface low temperatures could approach -20 degrees at Nome and
-35 in the middle Yukon Valley. With limited snowfall currently on
the Seward Peninsula and much of the Y-K Delta there could be
concerns for frozen pipes.

Coastal Hazard Potential Days 3 and 4...
Strong northerly winds in through the Bering Strait through
Tuesday night. Coastal erosion is the main concern at this time.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
AK...High Wind Warning for AKZ801.
Winter Weather Advisory for AKZ814>816-832.
High Wind Warning for AKZ820-821.
High Wind Warning for AKZ827.
PK...Heavy Freezing Spray Warning for PKZ801-807-816-817-851-854.
Gale Warning for PKZ801-802.
Gale Warning for PKZ803.
Gale Warning for PKZ804.
Gale Warning for PKZ805-852.
Gale Warning for PKZ806-856-857.
Gale Warning for PKZ807-811.
Brisk Wind Advisory for PKZ808.
Brisk Wind Advisory for PKZ809.
Gale Warning for PKZ810-850.
Brisk Wind Advisory for PKZ812.
Storm Warning for PKZ816-817-854.
Storm Warning for PKZ851.
Gale Warning for PKZ853.
Brisk Wind Advisory for PKZ855.
Brisk Wind Advisory for PKZ858.
&&

$$

Key Messages...BB
Analysis...BB
Extended...SD

561
FXAK67 PAJK 220010
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
310 PM AKST Sat Dec 21 2024

.SHORT TERM.../ Through Sunday night / The weather front lifts
into the panhandle and shears apart or weakens over the top of the
panhandle. A follow on low rolls northward to the eastern half of
the gulf as a low 960s low move in overnight and pushes a band of
Storm force winds across the gulf. The associated frontal band
will be better organized with brining rain over the southern two
thirds of the panhandle Sunday to Sunday night. Strong winds of 40
to 50 mph across a portion of the southern coastal panhandle
Sunday afternoon.

Only localized pockets of freezing temperatures for the Haines
Highway, higher elevations of Klondike highway and perhaps the
northern arms of Glacier Bay will be cold enough that the p-type
will not be rain.

.LONG TERM.../Monday through Friday/...The mid level low over the
western gulf that has been main steering mechanism that past few
days will finally shift to the east mid week, and then is replaced
by another mid level low over the western gulf by the end of the
week. The development of a low near Haida Gwaii Monday was the
previous forecast question for the start of the week, it is still
a question. There is more consensus that the system will split
into a small fast moving gale force low track up from the south
moving northwestward with second feature remaining over Haida
Gwaii. This complicates nailing down precip for these days as
still timing and location differences. So expect some periods of
moderate precip with breezy conditions and possible breaks
in between. Overall precip with fall a rain due to warm temps and
the SW flow with the exception being boarders along the Haines
and Klondike Highway where at least a few inches of snow will
fall. Pressure gradient keeping small craft to some gales over
the inner channels initially before a general diminishing of
winds late in the week, just in time for another in the series of
lows to move up and start this round of windy and wet weather for
SE AK.

&&

.AVIATION...The next frontal trough to track northward through
the region is causing light rain ahead of it over the southern
half of the panhandle based on radar data. Easterly strong winds
aloft have kept ceilings elevated again today, with a few
exceptions. Satellite imagery shows a spin up along the
approaching trough axis tracking northward into the SE gulf. This
feature will cause winds that have already been gusty to spike up
more as it passes by fairly quickly through the evening...reaching
latitude with Baranof Island around 6z. Expect a brief wind shift
to the SSE and conditions to drop slightly in rain. LLWS remains
the greatest impact to aviation from each of the fronts that are
passing through. VAD wind profiler from the Biorka Island radar
has consistently shown ESE winds of 40kt at 2kft today. Behind the
trough, expect ceilings to lift again and winds to back around to
the ESE ahead of the next front that will be approaching the
southern outer coast Sunday morning.

&&

.MARINE...A large band gale forces in the Gulf of Alaska, and the
next incoming system wind increase up to storm force winds
Sunday for 6 to 12 hours. Gale force wind to the coast and inland
to some of the inner channels like Clarence Strait. Seas of the
gulf waters increase in the continued strong SE-S flow with wind
waves and Swell in to 20 to 30 ft range.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind late tonight for AKZ317-330.
Strong Wind until midnight AKST tonight for AKZ318.
Strong Wind through Sunday afternoon for AKZ323.
Strong Wind from midnight AKST tonight through Sunday afternoon
for AKZ327.
Strong Wind from 9 PM AKST this evening through Sunday afternoon
for AKZ328.
Strong Wind from midnight AKST tonight through Sunday afternoon
for AKZ329.
Strong Wind from 9 PM this evening to midnight AKST tonight for
AKZ330-332.
Strong Wind Sunday morning for AKZ330.
MARINE...Storm Warning for PKZ641-661>664-671-672.
Gale Warning for PKZ033-035-036-642>644-651-652.
Small Craft Advisory for PKZ012-021-022-031-032-034-053.

&&

$$

SHORT TERM...Bezenek
LONG TERM....PRB
AVIATION...Ferrin
MARINE...Bezenek

Visit us at http://www.weather.gov/Juneau