413
FXAK68 PAFC 240146
AFDAFC
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
446 PM AKST Sat Nov 23 2024
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through
3: Saturday afternoon through Tuesday afternoon)...
Calmer conditions are expected from tonight through tomorrow
morning as winds diminish. While no precipitation is expected,
cloud cover will increase ahead of a low advancing from the Bering
Sea. As this low and its front move in, expect a round of snow
from Sunday afternoon through Monday, followed by a downward trend
in temperatures from Monday night through Tuesday.
Snow will likely be the most impactful aspect of this forecast.
There remains some uncertainty with snow amounts, especially as
models continue to shift with timing and precipitation amounts.
Confidence is high that the greatest snow amounts will occur along
the western slopes of the Talkeetna and Wrangell St. Elias
Mountains due to favored upsloping from westerly flow. About 5-6
inches of snow are forecast along the Parks Highway from about
Willow north, while lower amounts (3-4 inches) are expected from
about Glennallen north in the Copper River Basin. For Mat Valley,
Anchorage, Turnagain Arm, and Valdez, up to about 3 inches. Snow
amounts could be a bit higher than currently forecast, but the
quick movement of the front into and out of Southcentral means
that this won`t be a prolonged snow event and, therefore, snow
amounts should remain on the lower end.
Another aspect of the forecast that is subject to lower confidence
is the chance for dense fog to develop again along Cook Inlet and
the Knik Arm. The presence of fog this morning increases the
confidence that fog will redevelop tomorrow morning, especially as
the temperature inversion will not have had a chance to fully
reverse. Still, confidence is low on exactly where and when fog
will form. Incoming clouds will also make fog difficult to monitor
via satellite.
-Chen
&&
.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING
SEA/ALEUTIANS (Days 1 through 3)...
The leading edge of a front associated with a vertically stacked
Bering low continues to move over portions of Southwest Alaska
this afternoon, especially over the Kuskokwim River Delta. With
high pressure settled in over the mainland, a significant
temperature inversion has been in place for most of Southwest.
This inversion has weakened some with warm air filtering in at the
surface as the front moves over, limiting the freezing rain risk
to this point. Areas around Aniak that will remain sheltered from
the wind could experience brief periods of freezing rain during
the morning and early afternoon hours on Sunday.
By Sunday evening and throughout the day Monday, the front will
move eastward towards the Alaska Range, producing light to
moderate snowfall as it shifts towards Southcentral. For Bristol
Bay, a mix of rain and snow will be experienced as the front
passes over Sunday-Monday. Behind the front will be another push
of cold air advection that will again trend temperatures down as
the week progresses. The biggest temperature shift will occur on
Tuesday as far interior portions of Southwest could once again
fall below zero degrees. For the Bering and Aleutians, a shortwave
trough will retrograde to the north and west starting Monday
morning and continuing through Tuesday afternoon. Gale force winds
and moderate precipitation will be felt along the western Bering
and Aleutians as an area of high pressure currently over eastern
Russia builds over the central Bering and extends towards the
mainland by the end of the forecast period, limiting any chances
of precipitation for the rest of the forecast area.
-BS
&&
.LONG TERM FORECAST (Days 4 through 7: Wednesday through
Saturday)...
Significant weather changes are expected over Alaska throughout
the long term period, with evolving dynamics in the North Pacific.
The period begins with a ridge of high pressure over the Bering
Sea and a positively tilted trough digging over eastern Alaska and
the Yukon. A large upper-level low over the North Pacific is the
key player, but models differ in its progression. The GFS
indicates the trough will deepen, allowing the North Pacific low
and additional shortwaves to move northeastward, spreading more
widespread precipitation across the region, particularly along
the coast. In contrast, the ECMWF suggests the initial trough
evolves into an upper-level low over mainland Alaska, shunting the
North Pacific low southward and leaving much of Southwest Alaska
and parts of Southcentral Alaska drier during the period.
Regardless, gale-force winds are expected to continue over the
Bering Sea early in the period. Snow is also expected to spread
across Interior Alaska by Wednesday, reaching near the
Southcentral coast with coastal areas east of Prince William Sound
potentially seeing a mix of rain and snow. Depending on how the
North Pacific low progresses, as suggested by the GFS and other
guidance, moderate rain and snow could develop near the eastern
Aleutians and AKPEN by Friday and potentially spreading towards
Kodiak Island and the Southcentral coast by the end of the period.
However, with model disagreement, there remains uncertainty in
the exact timing and extent of precipitation, though there is a
strong signal for impacts at some point.
Eovino
&&
.AVIATION...
PANC...VFR conditions and light winds will persist through this
evening. There will be a chance for fog and/or low stratus to
develop once again late this evening into tonight and potentially
affect the terminal with IFR to LIFR conditions at times. There is
still fairly low confidence regarding whether or when fog could
redevelop along the Cook Inlet and Knik Arm and how easily it
could clear out on Sunday morning. A weak southeast wind
developing through the Turnagain Arm could reach the terminal as
well, but will likely hold off until late in the afternoon on
Sunday at the earliest.
&&
$$
250
FXAK69 PAFG 240902
AFDAFG
Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
1202 AM AKST Sun Nov 24 2024
.SYNOPSIS...
A warm front is moving inland over the West Coast and Interior,
bringing mixed precip of snow, freezing rain, and rain to the
coastal regions around Norton Sound and into the Lower Yukon
Valley. Heavier snow is falling further northward toward the
Brooks Range. This front shifts east across the Interior and
Brooks Range through Monday, bringing a wide swath of accumulating
snowfall to the N Mainland, with no change in forecast thinking as
widespread 4 to 8 inches of snow is expected. An arctic front
brings plummeting temps Tue night with the deep freeze expected
for Thanksgiving.
&&
.DISCUSSION...
Key Messages by Region:
Central and Eastern Interior...
- Winter Weather Advisories remain in effect for snowfall for most
of the Interior from the White Mtns west, including the Tanana
Valley.
- Warming temps as clouds move across the region and warmer south
winds increase over the Alaska Range today, gusting into the 40
mph range.
- Snow moves into the N Interior across the Upper Koyukuk and
Dalton Hwy Corridor this morning, and then snow increases across
the remainder of the Interior late this evening and overnight.
Snow continues into Monday and will be moderate at times. We
continue to expect a widespread swath of 4 to 6 inches with
localized higher amounts of near 8 inches in the higher
elevation terrain north of Fairbanks and the White Mtns.
- Snow continues into Monday night and tapers off Tue as a cold
front shifts south. Temps are rapidly falling Tue, with
significant blowing and drifting snow in the Brooks Range as the
strong arctic front dives south.
- High pressure settles in Tue night with plummeting temps into
the -20 to -30 F range by Wed morning.
West Coast and Western Interior...
- Mixed precip, including some spotty freezing rain over Norton
Sound, continues through the day today. Gradually precip will
turnover to snow over coastal regions, with heavier snowfall
moving into the Interior.
- Expect an additional 0.05 inches or less of ice accumulation
possible today. Expect widespread 4 to 9 inches of snowfall
across the Interior and toward the Brooks Range, with lesser
amounts over coastal regions. We will issue heavy snow warnings
for the N Interior regions to the S Brooks Range.
- Gales with gusts to 50 mph move across the Bering Strait coast
and the W Seward Peninsula tonight and Monday as a strong cold
front moves across the West Coast.
- Cold high pressure and drying conditions settle in Monday night
through Wed with the exception being Kivalina north where snow
shower threats will persist.
North Slope and Brooks Range...
- Accumulating snow will spread east across the Brooks Range and
North Slope today through Monday. Snow will clip the arctic
coast from Prudhoe Bay east. Snow accumulations will range from
3 to 5 inches over the Brooks Range to less than an inch toward
the coast. It will remain dry around Utqiagvik.
- A strong arctic cold front moves south and will bring blowing
and drifting snow to Brooks Range passes including ANaktuvuk and
Atigun Passes Monday, so a winter weather advisory will be
issued for this. Much colder high pressure settle in Tue and
through the remainder of the week.
Meteorological Analysis and Forecast/Confidence Discussion...
The slow moving trough is now centered just south of the Gulf of
Anadyr with the warm front bringing rain to the YK Delta with a
mixed bag of precip over Norton Sound, and all snow further north
and across the W Interior. The upper low is analyzed around 526
dam with a strong 565 ridge axis over the S Mainland of Alaska.
The 995 mb surface low is centered southwest of Saint Lawrence
Island this morning with a strong 1033 mb high over the Yukon.
No change in forecast thinking as models are pretty locked into
the pattern as the trough and associated front shift east through
Monday, bringing widespread snowfall to the Mainland, with values
of 4 to 8 inches widespread from the Brooks Range south. We
favored the NAM nest for gales and strong north winds as they move
south across the Interior. Forecast confidence is very high.
Extended Forecast Days 4-7...
An arctic trough settles in Tuesday through Friday with rapidly
dropping temps as skies clear out and arctic high pressure moves
over the N Mainland. A weak front will clip the Arctic mid to late
week, otherwise, very quiet weather looks to settle in with the
main storyline being a return to colder than normal temps.
Coastal Hazard Potential Days 3 and 4...None.
&&
.AFG WATCHES/WARNINGS/ADVISORIES...
AK...Winter Storm Warning for AKZ813-819-828-831.
Winter Weather Advisory for AKZ820>822-824>826-830.
Winter Weather Advisory for AKZ832.
Winter Weather Advisory for AKZ834-842.
Winter Weather Advisory for AKZ809-838-843.
Winter Weather Advisory for AKZ841-844-845.
Winter Weather Advisory for AKZ846.
PK...Small Craft Advisory for PKZ801-851.
Small Craft Advisory for PKZ802-852.
Small Craft Advisory for PKZ803.
Small Craft Advisory for PKZ804.
Small Craft Advisory for PKZ805.
Heavy Freezing Spray Warning for PKZ805.
Gale Warning for PKZ806-807.
Heavy Freezing Spray Warning for PKZ806-817-854.
Heavy Freezing Spray Warning for PKZ807-856-857.
Brisk Wind Advisory for PKZ808.
Brisk Wind Advisory for PKZ809>811-855.
Brisk Wind Advisory for PKZ812.
Small Craft Advisory for PKZ816-817-850.
Small Craft Advisory for PKZ853.
Gale Warning for PKZ854-856.
Gale Warning for PKZ857.
Brisk Wind Advisory for PKZ858.
&&
$$
Ahsenmacher
519
FXAK67 PAJK 232352
AFDAJK
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
252 PM AKST Sat Nov 23 2024
.SHORT TERM...Winds across the panhandle today have started to
trend downward but some areas are still seeing strong winds. With
the winds trending down, we have been able to let the high wind
warning expire for Juneau. With the decreased winds and clear
skies for the area, temperatures will remain cold during the
overnight hours. With the continued cold and clear pattern, only
minor changes were made to the wind and left the rest of the going
forecast. The only changes made for the short term was to
increase the possibility of precipitation for the NE Gulf coast as
chances are starting to increase late in the period.
.LONG TERM.../Monday into Thanksgiving/...
Any chance of precipitation returning to the panhandle rests on the
blocking ridge over the western gulf breaking down. Ensemble models
are trending towards a stronger shortwave moving down from the
Bering Sea, successfully bringing some precipitation chances to
the northern half of the panhandle. Current forecast continues to
reflect pessimistic snowfall totals for Monday through Tuesday.
While the forecast leans toward higher snow totals, the story of
snow is actually much more uncertain. While the overall setup for
heavy snow is present, ultimately, what hinges on this forecast is
the available moisture for snow development. 850 mb winds from the
S to SW flowing over a reinforcing stable layer from northerly
winds down Lynn Canal will remain persistent for more than 24
hours. Currently, just north of Icy Strait, impressive
frontogenesis at 850-700 mb looks to stick around, driving
heavier snowfall. Furthermore, maximum omega, around -30 ubar/s at
-10 degrees C. At this point, most moisture is in the lower
levels of the atmosphere with relative humidities above 700 mb
being increasingly uncertain. If the profile is more moist than
expected, then northerly winds along with moderate to heavy
precipitation rates will keep the entire event for the Icy Strait
Corridor as snow.
Following the initial shortwave, a secondary shortwave moving
along the initial ridge Wednesday and Thanksgiving may reignite
snowfall for the Juneau area, may push the main snowfall band
southward, or may be weak enough that northerly dry air will limit
any precipitation from developing. Ultimately, observing upstream
how each shortwave behaves will be paramount to determining how
each system next week will behave. Stay tuned for updates.
&&
.AVIATION...VFR conditions with clear skies and full visibility
will continue here in SE AK through tonight. Still dealing with the
strong outflow winds this afternoon but the LLWS looks to lighten
up this evening. Smoother flying weather in store late Saturday
night into Sunday.
&&
.MARINE...Outflow winds are expected to continue through the
evening but have already started to trend downward across
portions of the panhandle. Elevated winds and seas are still
possible through the Inner Channels as well as along the outer
coast near entrances to the Inner Channels. Winds will continue
their downward trend as the east west channels become more
favored. These channels will still see some strong winds but
should still a trend downward headed into next week before our
next system moves into the panhandle.
&&
.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind until 3 PM AKST this afternoon for AKZ318.
Strong Wind from Sunday morning through Sunday afternoon for
AKZ318.
Winter Storm Watch from late Monday night through Tuesday
evening for AKZ320>322-325.
High Wind Warning until 3 PM AKST this afternoon for AKZ325.
Strong Wind until 9 PM AKST this evening for AKZ325.
MARINE...Gale Warning for PKZ012-013-662.
Small Craft Advisory for PKZ031>034-641>643-661-663.
&&
$$
SHORT TERM...SF
LONG TERM....NC
AVIATION...GJS
MARINE...SF
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