Gale Warning 681, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
922 PM AKST Wed Nov 8 2023

.Update...
Latest webcams, observations, and reports show that snow, heavy in
many areas, continues to fall across much of southcentral Alaska.
Have increased snow totals across the board given current trends
and observations. Whittier, Portage, and much of the area adjacent
to the Turnagain Arm remain receiving snow or a rain/snow mix with
temperatures hovering near the freezing mark. A slight wind shift
back to an easterly wind is expected for the Turnagain Arm and
Whittier this evening, which should result in the lower elevations
changing back to snow.

As for much of Anchorage, increased snow totals as latest high-
resolution model guidance suggests colder air will continue to be
in place as the low center is expected to move right over or just
north of the Anchorage Bowl. Our office, the official measurement
for Anchorage, has received 6.2" as of the 9PM measurement. An
additional 6-12 inches is expected through the morning hours, but
there remains some uncertainty given temperatures continue to
flirt with the freezing mark and are expected to do so for the
next 12 hours. Higher elevation areas in Eagle River and the
Anchorage Hillside will likely remain snow, while lower / more
coastal elevations such as by Potter Marsh and downtown Anchorage
may changeover to a rain/snow mix, which would stifle additional
accumulation.

Regarding the Mat-Su Valley, snowfall rates upwards of 1"/hour are
currently being observed as of 9PM for much of the valley, with
reports suggesting around 3 inches has fallen thus far. Latest
guidance suggests a strong, warm easterly wind out of the
Matanuska River Valley will warm low/mid-level temps just enough
for a changeover to rain tonight. An additional 2 to 4 inches may
fall before that transition occurs, with some light snow
accumulation on the backside.

Earlier today, reports from the DOT up at Thompson Pass reported
approximately 48 inches of new snow at the pass with temperatures
hovering near freezing and a rain/snow mix occurring. North of
the pass by milepost 46, a measurement of 65 inches of snowfall
was reported. It should be noted this is an area that receives a
lot of snowfall.

Confidence is lowering regarding flood potential for Anchorage,
though the "moment of truth" will occur late overnight with the
potential of warmest air. Confidence is higher of a transition
back to rain across areas adjacent to the Turnagain Arm such as
Portage and lower elevations of Girdwood. Rain on accumulated snow
may result in a combination of slick, icy conditions as well as
ponding water. As a result, have kept the watches hoisted for now.

We continue to monitor this complex storm system closely. We've
launched additional balloons/soundings at 21z, 03z, and 06z to
monitor the vertical thermodynamic environment.

-Brown

&&

.PREV DISCUSSION... /issued 506 PM AKST Wed Nov 8 2023/

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

The well-advertised major winter storm is currently underway for
Southcentral Alaska. Snow has overspread Anchorage, Girdwood, the
northwestern Kenai Peninsula, and the Mat-Su Valley this
afternoon. Snow also continues in the Copper River Basin. The
forecast for these areas has been nothing short of a challenge.
This is due in part of trying to time out a warm air push aloft
early tomorrow morning. A plethora of Winter Weather and High Wind
products have been issued for this system. However, Anchorage has
been upgraded to a Winter Storm Warning to address greater
impacts with somewhat higher snow totals than the previous
forecast. The thought is that a transition to rain will occur
sometime overnight tonight into very early tomorrow morning.
However, there is uncertainty with this and there is a chance that
precipitation remains mostly as snow throughout this event due to
precipitation intensity maintaining the cold air just enough
through the column as well as a light northwest wind also helping
to maintain the cold air. Regardless of this uncertainty, this
storm will still be impactful whether it remains mostly snow or
with rain falling on top of snow.

To address the latter, a Flood Watch also remains out for
Anchorage and Girdwood/Portage. Precipitation should begin to
taper off later in the day Thursday. Another low pressure is
expected to lift into the Gulf through the day on Friday. There is
uncertainty with the track currently on this system. As of now,
most precipitation appears to be confined to the north Gulf Coast
and Prince William Sound with maybe some precipitation making it
over the mountains and into Anchorage and the Mat-Su Valley Friday
afternoon. Stay tuned for forecast updates on this current storm
and for updates for Friday as the active weather pattern
continues.

DAN

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

An occluded low is pushing into the Central Aleutians this
evening. Its front is bringing showery conditions to Shemya and
Adak. The front will sweep across the Eastern Aleutians before
dropping southward into the North Pacific on Thursday. Northwest
to northerly gales over the southwestern Bering tonight into early
Thursday become widespread over the central/southern Bering by
Friday. The overarching theme for the west side of Alaska has been
cool, northerly flow across the Bering with weak high pressure
and drier conditions over Southwest Alaska. Southwest will see a
slight pattern change on Friday as a trough works its way into the
Kuskokwim Delta, resulting in areas of light snow through the
morning hours. Otherwise, nighttime lows across Southwest should
continue to dip into the single digits and teens while daytime
highs will climb into the teens and mid 20s. In the short term, a
small wedge of warmer air within the warm sector of the Aleutian
occluded low will maintain rain for the Western and Central
Aleutians. As soon as the front drops south of the Aleutians any
remaining precipitation should transition to all snow. Elsewhere,
convective snow showers will be common across the Bering as cooler
temperatures aloft keep convective instability over the warmer
Bering Sea waters. The next frontal system does not enter the
western Bering until the weekend.

BL

LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)...

More active weather is on the menu through Wednesday, and
forecast models slip into a better consensus through the period.
The low center in the Gulf slides to the Southeast, and the
shortwave ridge moves across the Southern half of the Mainland by
midweek. Gale force winds are expected along the Alaska Peninsula,
around Kodiak Island and the Southern Kenai Peninsula for Sunday.
The first well developed low center tracks across the Northern
Bering into Northwest Alaska for Monday. This brings locally heavy
precipitation, gale force winds with storm force gusts and the
potential for coastal flooding to Western Alaska through Monday.
On its heels, a second strong low enters the Western Bering from
the North Pacific, spreading locally heavy rainfall, widespread
gale force winds and large areas of storm force gusts across the
Bering and Aleutians through Wednesday. These winds spread across
the Southern Bering into Western Alaska, increasing the chances
for coastal flooding through Wednesday. The leading edges of this
low also spread locally heavy precipitation along the Western
Alaska Range, and from the Eastern Kenai Peninsula to the Canadian
Border through Wednesday.

KZ

AVIATION...

PANC...Low-end MVFR to IFR conditions will prevail through at
least the first half of the TAF period as snow continues across
the Anchorage bowl. Snow rates will increase to an inch/hour or
more by around 06z, further decreasing visibility. LIFR vis is
likely, but may be intermittent with stronger bands. There is
still some uncertainty with warmer air once winds become southerly
around 12Z, which may allow for a transition to a rain snow mix
or periods of rain tonight.

Snow totals for Anchorage Ted Stevens and Lake Hood are likely to
be in the 6 to 10 inch range, though may vary depending on the
changeover to rain. Regardless, temperatures hovering around the
freezing mark will result in low snow ratios and a somewhat heavy,
wet snow.

Brown

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
1053 PM AKST Wed Nov 8 2023

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

1038 PM     Snow             Anchorage Hillside      61.06N 149.76W
11/08/2023  M10.2 inch       Anchorage          AK   NWS Employee

            Moderate to heavy snow falling at time of
            observation.

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
1103 PM AKST Wed Nov 8 2023

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

0500 PM     Snow             Thompson Pass           61.13N 145.72W
11/08/2023  E48.0 inch       Chugach            AK   Dept of Highways

            About 2 feet of snow on the Richardson
            Highway through Thompson Pass as of
            approximately 5 PM AKST.

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
1109 PM AKST Wed Nov 8 2023

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

0500 PM     Snow             NE of Thompson Pass     61.21N 145.49W
11/08/2023  E65.0 inch       Chugach            AK   Dept of Highways

            Several feet of new snowfall in less than 24
            hours reported along portions of the
            Richardson Highway northeast of Thompson
            Pass at of approximately 5 pm AKST.

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
1115 PM AKST Wed Nov 8 2023

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

1107 PM     Snow             Anchorage Hillside      61.07N 149.77W
11/08/2023  M12.5 inch       Anchorage          AK   Trained Spotter

            Heavy snow still falling at time of report.

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
1139 PM AKST Wed Nov 8 2023

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

1129 PM     Snow             Butte                   61.53N 149.01W
11/08/2023  M2.6 inch        Matanuska-Susitna  AK   Trained Spotter

            Snow changing over to a rain snow mix at
            time of report.

&&

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