Graphical Hydro Meteorological Discussion

000
FXAK68 PAFC 090203
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
503 PM AKST Sun Dec 8 2019

.ANALYSIS AND UPPER LEVELS...
A brief clearing over Southern Alaska from this morning is
quickly giving way to the next rapidly moving low out of the
North Pacific. Satellite shows this system approaching Kodiak
Island with a front extending to around 25N. This pattern is
strengthening the surface low which will move into the eastern
Bering Sea early tomorrow morning. This will also bring the strong
front associated with this low through the Gulf and into Southwest
and Southcentral Alaska tomorrow.

&&

.MODEL DISCUSSION...
Models remain in relatively good synoptic agreement the next few
days as the differences are of the type where they are not
disrupting the forecast very much. What is the biggest question
mark is the way the winds will move around the Anchorage area.
This is due to the complexities of the terrain and therefore the
high-resolution models are preferred.

&&

.AVIATION...
PANC...Winds will be the main concern around the terminal
tonight. Specifically the low level wind shear. Winds should
increase from the north at the surface, but winds aloft will
increase from the southeast this evening creating some wind
shear. These southeast winds aloft will increase more after
midnight with northerly winds persisting at the surface therefore
increasing the wind shear. Late Monday afternoon the strong southeast
winds will move over the airport at the surface.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2: Tonight
through Tuesday)...

High Wind Warnings will go into effect along Turnagain Arm, higher
elevations of the Anchorage Hillside, and through Portage Valley
starting at midnight tonight and continuing until 9pm Monday
evening. A strong east-west oriented front will move north across
the Gulf tonight. As it approaches the north Gulf Coast, southeast
winds will increase ahead of the front from Prince William Sound
through Portage Valley, Turnagain Arm, and the Anchorage Hillside.
For the Anchorage Bowl, 10 to 20 mph winds will remain out of the
north or northeast, likely coming into town as remnants from a
gusty Matanuska Valley wind. That Mat wind will impact Palmer and
Wasilla with gusts up to 45 mph from around midnight tonight
through the day Monday.

Precipitation-wise, we have drastically reduced expected rainfall
totals across the Anchorage Bowl and the Mat-Su Valleys over the
next 24 hours or so. The aforementioned southeast winds moving
down the Chugach mountains should dry out as they descend, which
will evaporate most of the rainfall. Portage and Whittier will be
the wettest communities from this rainfall event, with around 6
inches of rain possible from this evening through Monday evening.
For Seward, 2 to 4 inches are possible. These reduced amounts are
primarily because the winds with the front will have a significant
easterly component to their direction. Thus, instead of moving up
the valley, the winds will be directed somewhat across the valley,
which will reduce rainfall totals in town. However, higher
precipitation amounts will be possible towards Exit Glacier on the
eastward facing mountain slopes.

The front will move inland Monday evening. After frontal passage,
the winds will diminish dramatically, which should coincide with
the end of the High Wind Warnings Monday evening. As the front
crosses the area, increased lift will give the Anchorage Bowl its
best chance of rain from this event, though amounts should remain
under a quarter of an inch. Monday evening will also be the
Anchorage Bowl`s best chance of getting the Turnagain Arm wind
into town, which will spike temperatures well into the 40s.
Behind the front on Tuesday, the winds will be significantly
diminished, but the Turnagain Arm wind will continue through the
day, but should not affect the Anchorage Bowl. A return to
northerly winds for Anchorage and the Mat-Su will bring high
temperatures down into the mid to upper 30s on Tuesday. A front
associated with another low will move into the southern Gulf
Tuesday evening. This will be the next chance of precip for much
of the area through midweek.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Tonight
through Wednesday evening)...

A strong low will approach the Alaska Peninsula this evening.
Easterly winds with gusts exceeding 60 mph are likely in terrain
gaps of the Aleutian Range near Iliamna by early Monday morning. A
brief period of snow is possible over the Bristol Bay area over
the same time period, however temperatures will quickly rise
above freezing as the warm front lifts northward, changing
precipitation to rain. Snow and blowing snow are expected across
the Kuskokwim Delta Monday morning as well (see Winter Weather
Advisory for further details). As the associated low departs to
the northwest, strong southerly flow on its east side will lead to
well above average temperatures in the low 40s over much of
Southwest Alaska by Monday afternoon. After a brief break between
systems on Tuesday, another front will track near the Alaska
Peninsula by Wednesday with gusty easterly winds redeveloping near
the Aleutian Range though precipitation looks to be minimal at
this time.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Tonight
through Wednesday evening)...

A low will track northward over Bristol Bay through Monday
morning, bringing rain and gusty northerly winds to the eastern
Aleutians. Scattered rain or snow showers will continue across the
entire Chain through Wednesday in a broad northwesterly flow.

&&

.MARINE (Days 3 through 5)...

...Bering Sea and Aleutian Coastal Waters...

A pair of low pressure systems will affect the region. The first
low moves from the Northern Bering towards the Kamchatka Peninsula
on Wednesday as it retrogrades (moves west), with sustained gales
likely north of 60N and west of 175W. Further east, a north
Pacific low moving towards the Alaska Peninsula (AKPEN) will also
bring sustained gales to the Bristol Bay and coastal waters of
the AKPEN. The winds will then subside for both locations on
Thursday and Friday. Seas look to generally remain at or below 15
feet through the period.

...Gulf of Alaska...

A front will move from south to north across the region on
Wednesday, with sustained gales preceding it. Given a long fetch
length, seas are expected to build into the 20 to 25 feet range
ahead of this feature. The winds will subside for Thursday and
Friday, but, the waves will take more time. We expect seas to
remain near 20 feet for the southern and eastern Gulf on
Thursday...before decreasing more on Friday.

&&

.LONG TERM FORECAST (Days 3 through 7)...

Models continue to struggle with the specifics of the long term
forecast, but some general signals can still be gleaned in the
noise. Synoptically, a progressive pattern will persist over the
Bering and Alaska. A vertically stacked low in the northern Bering
Sea Wednesday will continue steering modified Arctic air over the
Aleutians and Bering. The low will continue to gradually weaken
and shift towards Siberia, but in the meantime expect scattered
showers over much of the Bering/Aleutians through Thursday.
Meanwhile, a low that is currently roughly 400 miles southwest of
Shemya will quickly traverse the North Pacific over the next few
days. As this low tracks northeast of 50N 150W it will push a warm
occluded front towards the North Gulf Coast, likely in the
Wednesday to Thursday timeframe. This should trigger a healthy
round of precipitation along the North Gulf Coast and
Alaska/Aleutian Range. South/southeast facing slopes should get
the heaviest precipitation, while areas in the lee (e.g.,
Anchorage Bowl, western Kenai Peninsula, Bristol Bay) will be more
of a challenge with shadowing. While it`s early to get into
specifics with respect to precipitation type, this looks like a
fairly warm system... the mountains should get snow but in lower
lying areas precipitation type will be a challenge. Friday into
the weekend, models indicate a strong low or series of lows
traversing the Aleutians, bringing a round of strong southerly
winds and precipitation.

In short, temperatures will largely be near or above average with
a southerly component to the flow over southern Alaska for much
of the Wednesday through Sunday timeframe. In addition,
precipitation will mostly be focused along the North Gulf Coast.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NPW 101 125. WSW 155.
MARINE...Storms 119 120 130-132 138 160 180 351 352.
Gales 125 129 139-141 150 155 165 179 181 412.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP
MARINE/LONG TERM...PD/MM

240
FXAK69 PAFG 082318
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
218 PM AKST Sun Dec 8 2019

.SYNOPSIS...
An area of low pressure will bring strong winds, snow, blowing
snow and freezing rain to the west coast Monday and Tuesday,
primarily to areas south of the Bering Strait. Strong southerly
gap winds are expected Monday in the Alaska Range, with a strong
easterly winds expected near Delta Junction.

&&

.DISCUSSION...
Overall the models initialize well and are in generally good
agreement through the middle of the week. There are still some differences
in the track and placement of a strong low that will move move
through the Bering Sea Monday and Tuesday.

Central and Eastern Interior: A northward moving front will bring
snow to areas north of the Yukon River this evening, with an inch
or so of accumulation. Strong southerly flow aloft will develop
over the Alaska Range tonight. This will limit chances for
precipitation for for most of the Interior for the first part of
the workweek. The southerly flow will help to bring above normal
temperatures for Monday and Tuesday. Strong southerly gap winds
are expected near passes on the north side of the Alaska Range.
Gusts of 60 to 70 mph are exepcted with the strongest winds
expected from the Parks Highway west. Strong easterly Tanana
Valley Jet winds are expected to develop as well on Monday with
gusts up to 50 mph expected near Delta Junction. We opted to
issue a High Wind Warning for zone 225 and Wind Advisories for
zones 223 and 226. Northeasterly winds will develop elsewhere
across the Interior. We will likely see gusts up to 40 mph with
blowing snow over summits along the Dalton and Elliott Highways.
Monday afternoon into early Tuesday.

West Coast and Western Interior: Gusty southeasterly winds
continue will continue along this evening over St. Lawrence
Island and coastal areas south of the Bering Strait. These winds
may cause some minor rises in water levels along the coast of
Norton Sound this evening, generally up to two feet above the
normal high tide line. Winds will quickly become more
northeasterlyin direction after midnight as the next system
approaches. This system, a 960 mb low will move into Bristol Bay
from the south around midnight tonight. This low will move to the
northwest Monday into Tuesday. This low will bring strong winds,
snow, blowing snow and freezing rain to areas. Winds will begin to
increase early Monday morning, with strong winds continuing into
Tuesday. St. Lawrence Island and the Yukon Delta will likely see
gusts of 60 to 70 mph on Tuesday. Warm air is expected to push up
north with this system. Therefore, while we expect precipitation
to initially begin as snow, we expect a transition over to
freezing by noon on Monday. Precipitation will taper off for most
places along the coast Monday evening; however, strong winds will
persist after the precipitation ends, into Tuesday.

North Slope and Brooks Range: Gusty easterly winds and blowing
snow continue will continue into this evening along the Beaufort
Sea Coast. Winds will die down late this evening as the strongest
winds push offshore. The pressure gradient will tighten up north
of the Brooks Range Monday evening. As the pressure gradient
tightens up, southerly gap winds with gusts up to 40 mph are
possible near passes on the north side of the Brooks Range. These
gap winds will persist into Tuesday evening. Another round of
gusty easterly winds and blowing snow is expected to begin Monday
evening and will persist into Tuesday evening.

Coastal Hazard Potential Days 3 and 4...The low moving through the
Bering Sea has the potential to bring elevated water levels to the
west coast on Tuesday. Right now there is still some disagreement
between the models how fast the low will track to the northwest.
If the low moves slower, it will allow for more time with winds
from a favorable direction to cause elevated waters. We will have
to continue to monitor this situation.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Wind Advisory for AKZ223-AKZ226.

High Wind Warning for AKZ225-AKZ227.

Winter Storm Warning for AKZ213.

Winter Weather Advisory for AKZ203-AKZ204-AKZ210-AKZ211-AKZ212-
AKZ214-AKZ215-AKZ217-AKZ219-AKZ220-AKZ221.

Heavy Freezing Spray Warning for PKZ210-PKZ220-PKZ230.

Gale Warning for PKZ200-PKZ210-PKZ240-PKZ245.

Brisk Wind Advisory for PKZ200-PKZ215-PKZ220-PKZ230-PKZ235.
&&

$$

DEC 19

010
FXAK67 PAJK 082348
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
248 PM AKST Sun Dec 8 2019

SHORT TERM.../Sunday evening through Tuesday evening/ Weakening
and nearly stationary front draped across the northern Panhandle
today. Light rain or drizzle continues in these areas with some
light snow still hanging on in far northern Lynn Canal. Freezing
rain in Haines and along the Haines highway expected to continue
into this evening.

To the south, a strong storm system is taking shape over the NPAC
as a negatively tilted shortwave on the nose of a 170-180kt
Pacific jet begins to interact with a strong baroclinic zone over
the western Gulf. This low will rapidly deepen today and lift
north-northwest to a location south of Kodiak Island tonight. Warm
front associated with this low will combine with the leftovers
from our current front and lift northward through the Panhandle
today into this evening. With continued WAA and moisture in the
low to mid levels, kept higher precipitation chances from Icy
Strait northward through the day today with much lesser chances
south where the low to mid levels are drier.

Snow levels have risen abruptly across the entire Panhandle today.
One exception is the Chilkat Valley where stubborn low level cold
air will be tough to scour out with almost no surface gradient in
a stable WAA regime.

Winter Weather Advisory has been issued for Haines and along the
Haines highway for freezing rain and minor ice accumulations under
one quarter inch through 9PM AKST tonight. Expect the precip to
move out of the region as a ridge builds over the Panhandle
tonight and into Monday.

One thing the strong storm to the southwest will do is to build
the mid/upper ridge over the Panhandle tonight. This will
effectively direct the best moisture transport back to the west
and allow any remaining rainfall to decrease once the warm front
passes. With height rises aloft and a cool moist boundary layer
present, think low clouds and fog are a good possibility across
much of the area through Monday morning. It will be quite warm
aloft on Monday with 850mb temperatures approaching 4C. If there
are any areas that are able to mix briefly Monday afternoon in any
enhanced easterly flow 50 degrees is not out of the question.
Places that do not mix at all may not see low cloud cover break
out much which could keep temps much cooler. Needless to say, some
major bust potential for high temps on Monday. Either way Monday
should be a dry day with any rainfall from the next front holding
off until late Monday night.

Winds over the Gulf will increase to gale force by tonight as the
strong low and associated occluded front lifts northward. Gales
will continue through Monday night which will lead to high seas
of 20 to 25 ft over the offshore waters by Monday night. Winds on
the inside waters will be much lighter, but will begin to increase
on Monday night as the occluded front approaches.

.LONG TERM.../Tuesday through Sunday as of 10 pm Saturday/ The
long range features a period of change in the upper level pattern.
First off, the upper ridge just east of the panhandle will break
down by Wed. Meanwhile the broad trough upstream over the Bering
Sea will be breaking apart into various weaker upper low centers
through mid week. One of these upper lows will settle into the
Western Gulf by Wed and generally remain there into early next
weekend.

The Panhandle, which will be suffering through the remains of a
gale force front that entered the panhandle Mon night, will be
subject to another gale force front as soon as Wed. Wide spread
gales expected in the gulf and more gusty winds and rain for the
panhandle expected. Warm southerly winds will also continue,
keeping snow levels between 1000 and 3000 feet so rain is expected
for most sea level areas. Model consensus was reasonable with few
forecast changes noted compared to yesterday (main change was
increasing land and inner channel winds during frontal passage on
Wed).

Forecast confidence falls to low past Wed night as various
troughs rotate around the western gulf low and into the panhandle.
Little consistency between models for the position and timing of
any one of these troughs, so extended forecast is mainly a broad
brush of the general trends expected. Those general trends favor
wide spread shower activity and a slight cooling trend in the post
frontal environment. This cooling trend will be enough to lower
snow levels to a few hundred feet in the north, but if it will be
enough to get snow at sea level again remains to be seen. Favored
WPC and NBM for any updates.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Weather Advisory until 9 PM AKST this evening for AKZ019.
MARINE...Gale Warning for PKZ041>043-051-052.
Small Craft Advisory for PKZ012-022-053.

&&

$$

CM/EAL

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