Gale Warning 633, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
456 AM AKST Wed Nov 20 2019

.ANALYSIS AND UPPER LEVELS...

A large cutoff low sitting off the coast of Cape Newenham
continues to be the primary weather maker for Southern Mainland
Alaska. A separate front is moving across the western Aleutians
as well, but the winds around the front are not particularly
strong. Meanwhile nearly all of Southern Mainland Alaska is on the
warm (southerly winds) side of the low. Now, the low is thoroughly
occluded by this point, so cooler, recycled air has fully
encircled the Bering low. This has allowed for the atmosphere to
become more unstable, and showers have broken out in a number of
areas, including Bristol Bay and the Kuskokwim Delta, and a wave
of shower activity is moving north up the Susitna Valley as well.

The Turnagain Arm wind has finally moved into Anchorage, and
temperatures are rapidly rising through the 30s and into the 40s
across town this morning. Temperatures are well into the 40s along
the coast as well. Any sub-freezing air is in the Susitna Valley
and northern and western portions of the Copper River Basin. Above
freezing air has overspread all of Bristol Bay, and southern areas
of the Kuskokwim Valley and Delta. Only areas from Bethel north
and west remain below freezing at this point.

In the upper levels, an amplified trough and upper low are
vertically stacked with the eastern Bering surface low. A strong
jet is helping amplify a ridge downstream across eastern Alaska
and the Panhandle. An even stronger jet streak is approaching the
western Aleutians.

&&

.MODEL DISCUSSION...

The models are in somewhat better agreement today compared with
yesterday. There is a strong piece of upper level energy from the
western Aleutians that gets caught up into the eastern Bering
low on Thursday. There is a fair level of disagreement on the
details of how those pieces of energy phase. However, the result
of that phasing results in the models coming back into decent
agreement that the resulting low center moves into Bristol Bay
Thursday night. Thus, differences in the timing and strength of
the associated winds as the western Aleutians impulse races
eastward at the leading edge of a strong North Pacific jet is
about all that those model differences result in, which are fairly
minor. Strong winds associated with fronts rounding the eastern
side of the low over the Gulf required increasing forecast winds,
especially during the day on Thursday along the coast into Prince
William Sound. Precipitation-type will be less of a problem as
many areas have warmed well above freezing and are expected to
remain there. Thus, only where pockets of cold air remain is where
any precipitation-type concerns will persist. Forecast challenges
will include the strength of the winds through the gaps, amount of
precipitation in the northern Susitna Valley and over portions of
Southwest Alaska where snow may persist and continue to pile up,
and temperature trends. Forecast confidence is about average.

&&

.AVIATION...
PANC...Turnagain Arm winds are likely to persist for much of the
next 24 hours across the airport and west Anchorage. These winds
will keep temperatures about where they are now (mid 40s) for the
next day or so. A front moving into Southcentral this afternoon
will cause rain showers to develop which may lower ceilings into
the MVFR category. MVFR ceilings will persist behind it, but
there is very high confidence that any precipitation that falls
will be plain rain.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2/Today
through Thursday night)...

Upper level flow will remain progressive over the next couple
days, leading to continued active weather across Southcentral
Alaska and the Gulf of Alaska. A surface cold front just east
of Cordova this morning will be slow with its eastward progress
today, thanks to a wave moving up the front and into the far
southeastern Copper River Basin. Heavy precipitation will
continue in the mountains north and east of Cordova, with rain
across the lower elevations of the southeastern Copper River
Valley, including the McCarthy area.

Meanwhile, a vertically stacked low over the eastern Bering Sea
will head inland across Southwest Alaska today through tonight,
while a series of short-waves rounding the upper low cross
Southcentral. This will lead to rounds of showers, with steadier
and heavier precipitation in upslope areas of the northern Susitna
Valley and Prince William Sound. Gusty south to southeasterly
winds have already caused temperatures to rise well above freezing
across most of Southcentral. The one exception is the western
Matanuska Valley and the Susitna Valley. As the low moves into
Southwest Alaska today expect a little bit of southerly wind to be
funneled northward into these areas, causing temperatures to rise
above freezing. Any showers which move through this morning,
which shouldn't be much, could produce some patchy light freezing
rain in the colder areas. The bulk of precipitation across
Southcentral today through tonight will be in the form of rain.
The one exception will be the northern to western Susitna Valley
where temperatures look like they will remain just cold enough to
support snow. Colder air aloft will move into Southcentral tonight
as the upper low passes just to the west. However, with continued
gusty winds, expect surface temperatures to remain above freezing
and precipitation to fall mainly as snow. Broad Pass in the
northern Susitna Valley could see additional advisory level snow
accumulation tonight into Thursday morning. With a warning still
in effect early this morning for heavy snow, will wait until this
has expired before considering a new advisory.

Thursday through Thursday night a couple of fast moving fronts
will cross the Gulf and move onshore across Southcentral. The
second front will be notably stronger, with support of a strong
upper level short-wave and jet streak. Once again expect
impacts from strong winds and heavy precipitation. In particular,
there is potential for high winds for Portage, Turnagain Arm and
Anchorage. Some forecast soundings indicate a strong inversion
above mountain top with winds coming down the hillside into the
Anchorage Bowl. Pattern-wise, this looks like a favorable set-up
for high winds with a strong front and a surface low passing just
to the west of Cook Inlet. However, models have been anything but
consistent of late with track and strength of synoptic scale
features. Therefore, will hold off on issuing any High Wind
Watches and closely monitor future model runs to see if this
solution holds.

&&

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

Showers will continue across much of Southwest Alaska today
associated with a mature low positioned south of Nunivak Island
this morning, which will move inland and weaken through the
afternoon. Temperatures above freezing across the greater Bristol
Bay area has kept precipitation falling as rain, but this could
turn over to a rain/snow mix heading into the late morning and
afternoon hours. In the Kuskokwim Delta, areas north of Bethel
are already reporting snow associated with this system and will
continue to see snow as cooler temperatures stay in place.
However, there could be a brief period of a rain/snow mix if high
temperatures rise near or just above the freezing mark.

Another round of precipitation will move into Southwest Alaska
early Thursday morning with a new front moving in, which will
bring the heaviest amounts of precipitation near Dillingham and
surrounding areas. Precipitation will likely start off as snow,
but could switch over to rain or a rain/snow mix by Thursday
afternoon for the Bristol Bay region. Northerly winds over the
Kuskokwim Delta, associated with a new low center moving inland,
will reinforce cold temperatures across the region. Snow will
continue to be the dominant precipitation type as the showery
pattern weakens through Friday with the surface low diminishing.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

Small craft winds across the Pribilofs and central Aleutians will
weaken as a low in the eastern Bering moves inland this
afternoon. As this low continues inland, a small area of gales
will move into Bristol Bay and then quickly diminish by this
evening. By this afternoon, a complex low near Kamchatka moves
into the western Bering and Aleutians, which will bring strong,
northerly flow to much of the Bering through Thursday. High end
small crafts, and gale force over the northern Bering, can be
expected with this system as the complex low moves into the
eastern Bering and AKPEN through Thursday evening.

&&

.MARINE (Days 3 through 5)...

A vertically stacked area of low pressure in the eastern Bering
responsible for gales and storm force winds will be the main event
for early Friday morning. The 957 mb low will just be moving
ashore near 60N Friday morning with gales and a few storm winds in
the central Bering and gales across the Western half of the Gulf
to include the coastal waters of Southern Alaska and the AKPEN.
The surface low remains fairly stationary, drifting slightly
north, and fills to 970 mb by late Friday night with the gales in
the Gulf diminishing to a small area in the southern Gulf, while
northerly gales will persist across much of the Central Bering and
into the eastern Aleutians until late Saturday night. While the
upper level flow remains rather active with zonal flow through
Sunday, an area of ridging builds into the Central Bering on
Sunday before another low moves in from the Kamchatka Peninsula.
The expected low will deepen to 953 mb by Monday morning bringing
gales and storms into the western Bering and Aleutians. Early
guidance suggests this low will track north of 60N again, with
some ridging in the Gulf of Alaska, but model discrepancies in
this active pattern leave some uncertainty 5 days and beyond.

&&

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

By Friday, a deep vertically stacked low will be centered over the
Kuskokwim Delta with the upper level portion of the low extending
to cover Southwest Alaska as well as the central and eastern
Bering. To the west of the low, cold north to northwesterly flow
from Siberia will continue to spread south across the Bering,
Aleutians and Alaska Peninsula. Supported by a strong west to
southwesterly jet stream south of the Aleutians and shortwave
troughs rotating around the south side the upper level low will
continue to swing a series of fast moving frontal waves along the
Alaska Peninsula and into the Gulf.

The low over the Kuskokwim Delta will lift north over the Yukon
Delta Friday evening to be replaced by a second surface low
developing along the northern Kuskokwim Delta coast Friday night
and moving inland Saturday. A surface trough associated with this
second low will swing from north to south across the eastern
Bering Friday night through Saturday morning. A surface trough
will push east across the Alaska Peninsula and into Southwest
Alaska Saturday afternoon through Saturday night as the upper low
opens to a trough. The upper level trough will then rotate away
to the northeast Sunday with a colder air mass pushing into
Southwest Alaska behind it.

A transient upper level ridge will build into the western Bering
Saturday night followed quickly by an initial frontal system
swinging of the Kamchatka Peninsula and reaching the western
Aleutians Sunday morning and central Aleutians Sunday night. A
stronger frontal system supported by a rapidly developing and
rather deep surface low will follow quickly behind, reaching the
western Aleutians and western Bering late Sunday night through
Monday morning and central Aleutians and Bering by Monday
afternoon. The front will reach the eastern Bering Monday night
and push onshore into Southwest Alaska Tuesday morning. The front
will continue east into the Gulf and Southcentral Alaska Tuesday
afternoon and evening. A new surface low will spin up just
offshore of the Kenai Peninsula Tuesday evening and strengthen
rapidly as it rotates trough the northern Gulf Tuesday night
through Wednesday morning.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 119 120 125 130-137 139 141 150-165 175-178
					   185 351 352 412.

&&

SYNOPSIS AND MODEL DISCUSSION...JPW
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...LB/JR

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1126 AM AKST WED NOV 20 2019

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

1124 AM     SNOW             7 E SKWENTNA            61.98N 151.20W
11/20/2019  M6.0 INCH        MATANUSKA-SUSITNA  AK   PUBLIC

            6 INCHES OF NEW SNOW. TOTAL SNOW DEPTH IS 14
            INCHES.

1119 AM     SNOW             2 ENE KIPNUK            59.94N 164.04W
11/20/2019  E5.0 INCH        BETHEL             AK   PUBLIC

            ESTIMATED 5 INCHES OF SNOW. WHITEOUT
            CONDITIONS OBSERVED TUESDAY MORNING. CHANGED
            TO RAIN AROUND 1PM TUESDAY.

1118 AM     SNOW             TOKSOOK BAY             60.53N 165.10W
11/20/2019  E5.0 INCH        BETHEL             AK   PUBLIC

            ESTIMATED 5-12 INCHES OF SNOW. VERY WINDY,
            SNOWED ALL DAY ON TUESDAY BEFORE CHANGING TO
            RAIN TUESDAY NIGHT.

1115 AM     SNOW             4 ENE MEKORYUK          60.39N 166.19W
11/20/2019  E2.0 INCH        BETHEL             AK   COUNTY OFFICIAL

            ESTIMATED 2-4 INCHES SNOW. WINDS GUSTING
            45-50 MPH ON TUESDAY.

1103 AM     SNOW             3 W BETHEL              60.77N 161.86W
11/20/2019  M6.0 INCH        BETHEL             AK   LAW ENFORCEMENT

1033 AM     SNOW             1 NNE CANTWELL          63.39N 148.90W
11/20/2019  E8.0 INCH        DENALI             AK   DEPT OF HIGHWAYS

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1254 PM AKST WED NOV 20 2019

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

1109 AM     FREEZING RAIN    3 MI SW BIG LAKE AIRPOR 61.51N 149.89W
11/19/2019  M6.00 INCH       MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            CORRECTS PREVIOUS FREEZING RAIN REPORT FROM
            33 NW ANCHORAGE. 6 INCHES SNOW 27F LGT-VRBL
            WINDS SNOW FALL 1 INCH/HR.

1105 AM     SNOW             25 NE VALDEZ            61.39N 145.82W
11/19/2019  M6.0 INCH        VALDEZ-CORDOVA     AK   TRAINED SPOTTER

            CORRECTS PREVIOUS SNOW REPORT FROM 25 NE
            VALDEZ.

1003 AM     SNOW             KENAI                   60.55N 151.21W
11/19/2019  M0.5 INCH        KENAI PENINSULA    AK   TRAINED SPOTTER

            CORRECTS PREVIOUS SNOW REPORT FROM KENAI.
            1/2 INCH SNOW, TRACE ICE PELLETS.

&&