Graphical Hydro Meteorological Discussion

000
FXAK68 PAFC 280150
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
450 PM AKST Fri Nov 27 2020

.ANALYSIS AND UPPER LEVELS...

Quite a busy weather day for our forecast area. Three surface low
pressure systems exist, two of which are weather producers for us
today. First, a surface low just south of Prince William Sound has
been creating impactful weather for Southcentral AK. A deformation
band with this low has produced heavy snow for the Western Susitna
Valley and another band of moisture along coastal Southcentral is
producing heavy snow through Turnagain Pass and snowfall in
Turnagain Arm and Anchorage Bowl. The second low is a strong low
in currently in the Eastern Aleutians, with Hurricane Force wind
gusts wrapping around the backside of the low. A front from this
low is currently entering the Western Gulf of Alaska as well. The
third low is in the Western Bering and not yet impactful. The
three are making for some very interesting satellite shots.

All of this active weather is supported in the upper levels by a
complex longwave trough that encompasses most of our forecast
area. Several upper low centers are spinning within this trough,
three of which are associated with the aforementioned surface lows.
This trough extends all the was from Eastern Siberia to Central
Alaska. Induced shortwave ridging is developing between the low in
the Gulf of Alaska and the low in the Eastern Aleutians, which is
the only bit of ridging that can be seen in our forecast area.

&&

.MODEL DISCUSSION...

On the synoptic scale, models are performing well and in good
agreement. They are capturing the overall weather pattern. When we
focus in on the mesoscale, disagreement and performance issues
emerge with our major models. This is mainly the case for
Southcentral AK. They have had difficulty depicting the current
round of snowfall in Southcentral AK and are having trouble
resolving the next frontal system slated to move into the Gulf of
Alaska tonight. This has made for difficulty in forecasting the
finer details, dropping our confidence level for the next couple
of days, specifically along coastal areas. In the western part of
our forecast area, models are performing better and we have higher
confidence in the forecast.

&&

.AVIATION...

PANC...A heavier band of snow moved through this morning reducing
the airfield to IFR conditions. The heaviest snow has moved
through and MVFR conditions can be expected with light snow
showers into the evening. Winds should stay light and variable.

&&

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

The amount of snow will vary across from Kenai Peninsula through
Prince William Sound to Anchorage this evening, thanks to
remaining remnants over the Gulf that are still making their way
inland which will bring additional snowfall tonight.

More mixed snow and rain are heading our way as a result of the
next storm from the Bering Sea. The leading edge of the frontal
system from the storm has already reached Kodiak this afternoon,
and this system will race northward toward Kenai Peninsula and
Prince William Sound through Saturday morning. Along the axis of
the frontal boundary, a couple other lows will emerge from it and
may keep snowy conditions near Anchorage Bowl through the weekend.
For now, the models suggest at least two separate microscale lows
with the first one emerging near Kodiak on Saturday morning and
the other over Cook Inlet on Sunday afternoon. It should not come
as a surprise should the areal coverage for snow increases through
Monday. Although strong winds from the frontal boundary will reach
much of Prince William Sound by Saturday morning, but these strong
winds are expected to be short-lived.

Patchy fog was observed around the Anchorage Bowl this afternoon,
and this situation will continue through late tonight. Freezing
spray is also expected in the next couple days mainly over the Cook
Inlet and Kamishak Bay. The combination of moderate to strong
winds and cold temperatures are favorable ingredients for
freezing spray.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

The cold weather pattern continues across Southwest Alaska this
afternoon, with a few lingering snow showers over interior Bristol
Bay. Cloud cover and the chance for precipitation will increase
this evening for the mainland as a frontal system lifts northward
overnight into Saturday morning. This system has stayed all rain
earlier today for the Alaska Peninsula, which will transition to
snow or a mix of rain and snow as temperatures cool overnight.

The potential for blowing snow across Bristol Bay from Dillingham
to Koliganek is the main focus for this forecast package. As the
front lifts northward, strong winds and gusts are possible, as
well as a few inches of snowfall. Blowing snow is a concern with
these conditions, which could lower visibility to a half mile at
times. Thus, a Winter Weather Advisory for blowing snow has been
issued through Friday morning for these areas.

The Kuskokwim Delta and Valley should stay relatively dry through
Friday, when a chance of snow returns to the Kuskokwim Valley.
Temperatures across the region will continue to fall through the
weekend as northerly flow allows cold air advection to move into
the area.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

High winds across the central Aleutians will continue through the
evening hours as a storm force low positioned just north of Dutch
Harbor tracks over the Alaska Peninsula and back into the North
Pacific by Saturday morning. A High Wind Warning remains in effect
through this evening for the eastern Aleutians, including
Nikolski, which has already seen warning level gusts of 80 mph.

A second storm force low over the western Bering this afternoon
will continue to weaken overnight as it dives south crossing the
central Aleutians Saturday afternoon and into the North Pacific
through the evening hours. Widespread precipitation will accompany
the two aforementioned systems, diminishing through Sunday
morning.

Another storm force system will move into the forecast area by
Sunday morning, with the associated front tracking over the
western Aleutians. This low will skirt the Aleutians, keeping the
strongest core of winds and widespread precipitation for the
Aleutian Chain as it tracks eastward towards the Alaska Peninsula
for Monday.

&&

.MARINE (Days 3 through 5/Monday through Wednesday)...

Gulf: A weak low lingers in the Northern Gulf through Monday
afternoon before moving onshore and dissipating. On Tuesday, a
series of shortwaves troughs move across the Gulf towards the
North Gulf Coast as a second weakening low approaches Kodiak
Island from the south. Winds will be primarily southeasterly on
Monday, transitioning to southerly by Tuesday afternoon as the
low moves north. Storm force winds may result as the front pushes
the North Gulf Coast, with a barrier jet likely to set up late
Monday night. Winds should begin to dissipate by Tuesday evening.

Bering: A strong North Pacific low pushes towards the western Gulf
over the course of a few days. This results in widespread gales
across the Southern Bering and possible storm force winds along
the central/eastern Aleutian coasts Monday into Tuesday. On
Tuesday the low is positioned further east and lingering gales and
small craft winds will be confined to the Southwest coastal
waters. Additionally, flow will be primarily northerly on Tuesday
with colder air being advected along the coast, thus, freezing
spray is likely, with heavy freezing spray possible along parts of
the immediate coast. High pressure sets up over the Central Bering
Tuesday afternoon.

&&

.LONG TERM FORECAST (Days 4 through 7/Tuesday through Friday)...

A strong front pushes the Southcentral Coast late Monday night.
With this, widespread precipitation is likely, with the heaviest
along Western Prince William Sound and Eastern Kenai. Further
inland, snow is likely through Wednesday morning before becoming a
rain/snow mix in the lower elevation. Significant warm air
follows this front, thus, precipitation along the coast should
start as a snow or rain/snow mix Tuesday morning and transition to
all rain by Tuesday afternoon. Rain will likely linger through
Thursday as a second low pushes the coast from the Southern Gulf.
Precipitation transitions back to snow by Friday with colder air
behind the low.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...
Storm Warning 119 172 174 177 178 411.
Gale Warning 120 125 128 130 132 138 139 140 150 155 160 165 170
173 175 176 180 351 352 413 414 .
Heavy Freezing Spray 180 181.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...BB
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...KM

823
FXAK69 PAFG 272134
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
1234 PM AKST Fri Nov 27 2020

.SYNOPSIS...
The weather pattern over Northern Alaska remains relatively quiet
especially as compared to the last couple of weeks with no watches,
warnings or advisories currently in effect nor expected through
the weekend. Gusty winds are expected along the Chukchi Sea
Coastline as well as the Bering Strait through Saturday. Gusty
winds are also expected from Delta Junction to Nenana as a weak
Tanana Valley continues into Saturday. Mostly cloudy skies and
light snow is expected over the Central and Eastern Interior to
the south of the Yukon River Sunday into Monday. Easterly winds
will become northerly for most of the West Coast and Western
Interior and will help limit precipitation chances in these areas.
A stalled and weakening front over the North Slope will produce
low stratus ceilings and flurries as well as gusty southeast winds
along the coast through Saturday.

&&

.DISCUSSION...
Upper Levels and Analysis...
The long wave pattern consists of a deep trough over the Bering
Sea and a ridge over Western Canada and Eastern Alaska. Several
strong short waves making their way around the trough will dig
into the ridge and pull the trough east over Alaska and the Gulf
of Alaska by Sat, then persist there into Mon before retrograding
slightly next week. This means that Northern Alaska will cool to near
normal by Sat, then remain near normal through Mon, with the SE
Interior warming to above normal Tue through the end of next week.


Models...
The 27/12z model suite initialized well against the 12z surface
analysis and verified well against the 18z surface analysis on
synoptic scale features in both location and strength. The model
suite remains fairly consistent in amplifying a the trough ridge
pattern centered over Alsaka over the weekend and into next week.

Central and Eastern Interior... Mostly cloudy conditions will
continue with no large weather system expected to impact the
interior into the middle of next week. A weak front will push
north and west into the Eastern and Central Interior on Sunday and
Monday and will bring a chance of light snow or flurries to the
area mainly south of the Yukon River and to the East of Tanana.
The Tanana Valley Jet is active this afternoon and will continue
to bring gusty east winds in the 15 to 30 mph range to areas near
Big Delta west to near Nenana through Saturday night. Southerly
winds ahead of a low pressure in the Gulf of Alaska continues to
cause moderate south winds through Alaska Range Passes. Expect the
winds to continue through and near the Alaska Range Passes into
Saturday before diminishing some Saturday night.

West Coast and Western Interior...
A strong low in the southern Bering Sea will become very strong
and move into the Gulf of Alaska on Sat and move to the Northern
Gulf of Alaska Coast on Sun. This will cause North winds along
the Capes of the West Coast to increase through Sat and persist
into Sun. Generally dry conditions are expected for the Western
Interior and only a stray snow shower pushing inland along the
coast.

North Slope and Brooks Range... A stalled and weakening front
over the North Slope will produce low stratus ceilings and
flurries along the coast through Saturday. Gusty northeasterly
winds will develop through the Brooks Range Passes, especially the
Western Brooks Range as a deep low pressure system in the Gulf of
Alaska combined with strong ridging over northern Siberia stacks
a strong gradient along the north side of the Brooks Range through
the weekend.

Extended Forecast Days 4-7... A low pushing into the northern
Gulf of Alaska on Tuesday of next week will spin a front north and
west into the Interior and will produce snowfall generally light
south of the Brooks Range. Gusty winds are expected along and near
the northern Foothills of the Alaska Range Monday and Tuesday.
Moderate strong northerly winds will continue along the West Coast
and through the Bering Strait through the middle of next week.

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

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Heavy Freezing Spray Warning for PKZ200-PKZ210-PKZ220-PKZ225-
PKZ230.

Small Craft Advisory for PKZ225-PKZ230.

Gale Warning for PKZ210-PKZ220.
&&

$$

CCC NOV 20

380
FXAK67 PAJK 280008
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
308 PM AKST Fri Nov 27 2020

.SHORT TERM.../Through Sun/ Very active short range period with
a weak short wave tonight, and a storm force front for Sat that
will linger in the southern panhandle into Sun night.

For tonight, The weak low that was forecast to affect the area
this evening has ended up with a much further W and N track then
was previously indicated (heading toward Prince William Sound
rather then the further south and east track of previous
forecasts). That has resulted in more showers expected overnight
tonight as the weak front associated with it moves onshore
overnight. Little wind and not much moisture so any rain and snow
amounts will be somewhat low.

The next front is the major story, as that is rather strong.
Little in the way of changes for this system, other then some
headline updates and accounting for local effects. First the
winter storm watches for the Haines and Klondike highways have
been upgraded to warnings for Sat. Highest snow amounts will be on
the Highways as the towns may start mixing with rain mid day
limiting snow amounts in the towns. A winter weather advisory has
also been issued for Hyder where 7 to 9 inches of snow could
accumulate from Sat afternoon to Sun morning. As for the high wind
watches, we have decided to cancel them as expected wind gusts
are not expected to reach 60 mph at this time. However, widespread
gusts of 45 to 50 mph will be likely for many areas on Sat.

Front moves through most of the panhandle by Sat night with
showers showing up for much of the panhandle into Sun. The
exception is the southern panhandle where the front hangs up
through at least Sun night. So wet weather will continue for the
south through that period. There is the possibility of a wave
developing along the front and moving into the southern panhandle
on Sun, but confidence is rather poor on that at this point.


.LONG TERM.../Sunday through Friday night/...The first of three
strong fronts laden with a low of PW will be over Southeast Alaska
at the start of this extended range forecast period. The others
will impact the region on Monday night through Thursday morning and
then Thursday night through Friday afternoon. Some locations may
see a break from the relentless precipitation Sunday night and
Monday morning. but after that...anybody got an ark handy? The
front that will being to affect SEAK Monday night has indications
that it may be a training event with a wave working its way along
the frontal boundary, causing it to waiver north and south across
the Panhandle before giving way to the follow on low and
associated front Thursday night. At present, locations north of
Cape Ommaney and Frederick Sound will received the majority of
this precipitation. Low level onshore flow and temperatures as
well as mid and upper level thickness values all point to these
fronts being predominantly rain makers (vice snow) for all of
Southeast Alaska except possibly the far northern inner channels -
Skagway, Haines, and the associated highways. By Tuesday night,
the only potential left for snow will be at higher elevations
along the highways.

The eastern Gulf and inner channels will get a break from the
gales and small craft conditions that have been quite common for
the past several days. until Monday night. At that time, the next
high end gale force (possibly storm force) front will push across
the eastern Gulf. Those winds winds may last as long as Wednesday
night as wave rides north along the front and re-invigorates the
front. At least one long range mode is suggesting that more high
end gales are possible Thursday night, but we`ll see what happens.

-Fritsch

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind Saturday afternoon for AKZ025-026-028.
Strong Wind from Saturday morning through Saturday afternoon for
AKZ027.
Strong Wind Saturday afternoon for AKZ024.
Strong Wind from Saturday morning through Saturday afternoon for
AKZ021-022.
Strong Wind from Saturday morning through Saturday afternoon for
AKZ023.
Winter Weather Advisory from 3 PM Saturday to 5 AM AKST Sunday
for AKZ029.
Winter Storm Warning from 6 AM to 9 PM AKST Saturday for AKZ018-
019.
Strong Wind Saturday afternoon for AKZ018.
Strong Wind Saturday morning for AKZ017.
MARINE...Storm Warning for PKZ042-043-051-052.
Gale Warning for PKZ012-013-021-022-031>036-041.
Small Craft Advisory for PKZ011-053.

&&

$$

EAL/Fritsch

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