Gale Warning 582, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
426 AM AKST Sat Nov 16 2019

.ANALYSIS AND UPPER LEVELS...

A mid-level shortwave lifting over coastal Southcentral this
morning is continuing to produce bands of showers from Prince
William Sound to Cook Inlet and north into the Mat-Su Valleys.
Temperatures across the aforementioned areas are sitting in the
lower 30s to lower 40s this morning. With temperatures at or above
freezing, the vast majority of the precipitation is falling as
rain, with a few pockets of mixed precipitation north of
Anchorage.

Over Southwest Alaska, a vertically stacked complex low over
Bristol Bay continues to produce bands of snow from King Salmon
and Iliamna west to Dillingham and Togiak. Temperatures across
the Bristol Bay region are in the mid to upper 20s. Farther north,
a northeast flow is pulling arctic air southward across the
Kuskokwim Delta and Valley where temperatures this morning range
from 0F to 10F.

The broad, cyclonic flow around the Bristol Bay low is also
continuing to drive colder air south across the Bering and the
eastern half of the Aleutian Chain. For the western half of the
chain, southeasterly winds along an occluded front is ushering in
some warmer air and rain.

&&

.MODEL DISCUSSION...

Models are in good agreement overall moving through the weekend
and into early next week. There is still some uncertainty with how
quickly the upper-level low currently over Bristol Bay tracks
east across Southcentral. The evolution of this will dictate how
much, if any, snow develops across the northern half of Cook
Inlet north to the Susitna Valley Saturday night into early
Sunday. The NAM was the outlier with regard to the 00z runs,
kicking the low east faster than other guidance, resulting less
precipitation as the bulk of the moisture exits toward the Copper
River Basin by the time the colder air moves in. The 06z run,
however, has a slower progression and is more in line with other
guidance (00z and 06z GFS). This slower trend would favor the
development of some snow with cold air advection and southwest
flow off Cook Inlet. Thus, although there is still some
uncertainty, the forecast package has trended to the slower
solutions with slightly higher PoPs and QPF, with a higher
likelihood for light snow accumulations for the Anchorage and
Mat-Su areas.

Further out in time, there is decent agreement in the long term
with two weather features bringing another surge of warmer air
back across the southern mainland by Tuesday and again Thursday.
With this influx of warmer air overriding the cold air in place
from the system this weekend, precipitation type will likely be
the biggest challenge again across a large portion of the forecast
area as we move through next week. This is highlighted more in
the long term discussion.

&&

.AVIATION...
PANC...Periodic light southerly winds early this morning will
again turn northerly around mid morning. VFR ceilings will
continue through noon, although lowering to around 4,000ft at
times as scattered showers move near the airport complex. Ceilings
and visibility will lower to MVFR through the afternoon as light
rain develops. Rain will mix with and change to snow mid to late
afternoon, continuing through the nighttime hours as winds turn
southerly again. There is the potential for IFR ceilings late
afternoon and evening during any snow fall. Conditions are
expected to improve early morning Sunday as precipitation exits
the area.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The upper low centered over southwest Alaska will move northeast
today into the area. This will bring in a colder air mass, with
850 mb temperatures over Anchorage dropping about 5 degrees C from
early this morning to late this afternoon. Dynamics near the core
of this low are pretty decent, and the flow aloft will become
southwesterly. This will bring precipitation to much of the area,
especially from Anchorage northward into the Matanuska and Susitna
valleys, as well as along the Gulf coast. Precipitation type
should switch over to snow at Anchorage by early evening, with
some accumulation expected. This system will then rapidly open up
and exit the area to the northeast by Sunday morning. The flow
aloft will remain southwesterly and thus there will still be
chances of snow through Sunday night, but chances of accumulating
snow will be low. The exception to this will over the Susitna
Valley, the Copper River basin and along the coast to the north
and east of Prince William Sound as an upper level trough crosses
Southcentral Sunday night.

&&

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

A weak area of low pressure continues to spin near Bristol Bay,
with satellite and RADAR clearly depicting its center drifting
east as just comes ashore (as of 4AM AKST) near King Salmon. This
low is still producing some light snow showers for southwest
Alaska. Additionally, it did verify the winter weather advisory
for the Bristol Bay area yesterday when it caused bands of snow
to train over the area. Weather will quiet over the weekend after
the low exits to the east today. Cooling temperatures can be
expected as cold air is drawn south on the backside of the low.

The cold air moving in will drop low temperatures to around zero
for interior areas Sunday. This brief break in the weather will
give way to another low pressure system on Monday. We are taking
a look at possible blizzard conditions close to the coast late
Monday into Monday night with this system. Right now its looking
like warm, moist air will override cold air still in place at the
surface, creating snow. A stiff northeast wind will also develop
coming down the Y-K Delta, which could produce blowing snow,
depending on how strong the wind gets. If the setup is just right,
this could produce the first blizzard of the year. It should be
emphasized that we are in the beginning stages of analyzing this
scenario and right now its just a possibility. More to follow as
we take a closer look in the next day, so stay tuned and we'll
issue advance notification if it does look like a blizzard will
occur. So for now, just something to pay attention to.

&&

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

Weather remains quiet in the Bering Sea. Northerly flow continues,
however snow showers associated with have tapered off. This flow
will slacken today and a pattern shift will take place tomorrow
with a low approaching the western Aleutians out of the north
Pacific. This will quickly be followed by another low taking about
the same track on Monday. Expected gale force winds, rain and
warming temperatures with these low pressure systems.

&&

.MARINE (Days 3 through 5)...

Beginning the extended period marine forecast on Monday, there
is high confidence that the Bering Sea will be in an active storm
pattern, with a 950-960 hpa storm centered over the central
Aleutians/Bering Sea with widespread gale force winds. This low
may eventually deepen to near storm force by Tuesday, but
certainty is lower as some of the energy may remain over the North
Pacific. The low will eventually weaken and exit the Bering on
Wednesday with another potential storm force low moving across the
Aleutian Chain on Thursday/Friday. Low track is uncertain, but
there is good confidence that this stormy pattern will unfold with
a strong low sometime Thu/Fri over the Aleutians, so mariners
should stay tuned for this in later forecasts.

Over the Gulf waters, Monday will begin rather quiet with sub-gale
force winds, but a series of strong gale force or possibly
stronger fronts and lows will barrage the Gulf from Monday night
through the remainder of the week as the aforementioned storm
track shifts from the Bering Sea to the Gulf.

&&

.LONG TERM FORECAST (Days 4 through 7)...

Beginning the extended period forecast on Monday evening, a new
storm cycle will be unfolding as another powerful near storm
force low moves east across the Bering Sea/Aleutians. With cold
air in place over Southcentral, and another strong warm front
moving into the Gulf of Alaska, this will set the stage for
another round of very unsettled wintery weather across the
Southern Mainland.

The first warm front plows into Southern Alaska Monday night,
driven by a powerful subtropical/polar jet stream moving into
Alaska in southwesterly flow. This will likely bring snow,
eventually turning to rain and/or freezing rain Tuesday and
Tuesday night, along with heavy snow for higher elevation passes.
The low track will be key for some inland areas on how quick they
turn to rain, but eventually, regardless of which global model you
look at, the low will eventually track far enough north by
Wednesday to erode most of the low level cold air, changing a lot
of low elevation locations to all rain (some exceptions include
the northern Susitna, Copper Basin, and Lower Kusko Valley). Right
on the heels of this first storm will be another on Thursday and
Friday, also plowing inland, although this one may not move as far
north, allowing for possible snow mixing in late week into the
weekend. Takeaway? It is going to be an active weather pattern
Monday night onwards and interested parties should be prepared for
a myriad of impacts, from heavy snow to heavy rain to possible
inland freezing rain.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 173-176.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...TM
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BB
MARINE/LONG TERM...JA

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
150 PM AKST SAT NOV 16 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0125 PM     SNOW             1 S BIG LAKE            61.51N 149.95W
11/16/2019  E1.2 INCH        MATANUSKA-SUSITNA  AK   NWS EMPLOYEE

            SPOTTER REPORTED 1.2 INCHES OF SNOWFALL.
            SAID FLURRIES BEGAN AT 8A, WITH THE HEAVIER
            SNOW STARTING AROUND 11AM.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
206 PM AKST SAT NOV 16 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0147 PM     SNOW             19 NNW HOPE             61.16N 149.83W
11/16/2019  E2.0 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            SPOTTER REPORTED 2 INCHES OF SNOW. SAID IT
            IS SNOWING FAIRLY HARD AND THAT THE FLAKES
            ARE BIG DENDRITES.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
209 PM AKST SAT NOV 16 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0155 PM     SNOW             15 N HOPE               61.12N 149.71W
11/16/2019  E2.0 INCH        ANCHORAGE          AK   TRAINED SPOTTER

            SPOTTER REPORTED 2 INCHES OF SNOW SINCE
            9:00AM.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
225 PM AKST SAT NOV 16 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0220 PM     SNOW             15 S KNIK               61.23N 149.78W
11/16/2019  E3.8 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            SPOTTER REPORTED 3.8 INCHES OF SNOW.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
252 PM AKST SAT NOV 16 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0234 PM     SNOW             13 SSE KNIK             61.29N 149.55W
11/16/2019  E4.0 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            SPOTTER REPORTED 4 INCHES OF SNOW IN 4
            HOURS.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
320 PM AKST SAT NOV 16 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0319 PM     SNOW             1 NNW WASILLA           61.59N 149.47W
11/16/2019  E3.0 INCH        MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            SPOTTER REPORTED 3 INCHES OF SNOW IN
            WASILLA.

&&

ED