Flooding in Alaska, May 9 to 13, 2024

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
523 AM AKDT Thu May 9 2024

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

Areas of showers that developed along and ahead of a now weakening
shortwave trough lifting into northern Southcentral this morning
managed to change over to mostly snow across parts of Anchorage
overnight. Half an inch to an inch or more was able to accumulate
on elevated surfaces, with 0.7 inches recorded at the official
observation site at the Anchorage forecast office. This brings us
solidly into 2nd place for the snowiest season on record in
Anchorage, with our total for the 2023 to 2024 snow year now
sitting at 133.3" as of 5 AM this morning. While it probably won't
be much, we might be able to add a touch more to this total
today.

A secondary, weaker trough showing up well near 700 mb is now
lifting into the Kenai Peninsula from the Gulf this morning. This
feature is helping to focus bands of snow showers across the Kenai
Peninsula and up into Anchorage, though precipitation is staying
quite a bit lighter thus far in the band of snow set up near and
just west of Anchorage compare to what moved through yesterday
evening. This second shortwave should continue to shift north
towards the Talkeetnas today as another push of cooler air follows
in tow behind it up the Cook Inlet, helping additional areas of
light rain/snow develop across the Kenai Peninsula and Anchorage
initially. This activity will shift north towards the Mat-Su as
the cooler and drier air rushes in behind this next trough moving
past. Confidence for precipitation type is very low through this
evening due to the combination of seasonably cool low level
temperatures and long daylight hours, so have generally stuck with
a rain/snow mix for most of the western Kenai up into Anchorage
for remaining precipitation potential through this evening.

Meanwhile, a low moving near the AKPen will move northeast past
Kodiak Island as it becomes and open wave in the upper levels
today. This stronger resulting trough axis will swing north into
Southcentral by tonight, solidly ending the threat for lingering
snow/rain for interior locations once the trough axis nears the
Alaska Range early Friday morning. A shortwave ridge will move
into much of the region behind this stronger trough passage,
yielding drier and perhaps even a bit sunnier conditions for at
least the first half of the day for some. By Friday afternoon, a
stronger low moving up along the AKPen will extend it's front into
the Gulf as strong southeasterly flow begins to pick up out ahead
of this feature. Gusty south to southeast winds will spread from
Kodiak Island back into the remainder of Southcentral through
Saturday as the front slowly lifts north and the parent low shifts
into the western Gulf. Steady low elevation rain and mountain snow
will primarily be focused along the coast and across Prince
William Sound, while strong cross-barrier flow keeps most of the
inland portions of Southcentral mostly dry. Temperatures will
remain cool, but will begin to rebound closer to seasonal norms in
the low 50s over interior valleys by Saturday afternoon.

-AS

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA, THE SEA AND THE ALEUTIANS
(Days 1 through 3)...

A compact polar low moves up the Alaska Peninsula Thursday
morning. Gusty winds and snow showers continue through the day but
dissipate as the low weakens by the afternoon. A larger low
advances eastward over the western Aleutians, pushing a broad
front of widespread precipitation and gale force winds. Warm air
along the front should raise temperatures above freezing along
the chain, and change precipitation over to rain. The low reaches
the Southwest mainland by Friday morning before a new low
consolidates south of Shemya Saturday morning.

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

The Alaska weather map shows a very broad upper level trough
stretching from the Western Bering to the Canadian border. A
number of occasionally vigorous troughs work through the pattern,
picking up energy from the North Pacific and helps relax the
overall amplitude of the trough into a more or less zonal flow
through midweek. A couple of weakening low centers slip across
from Bristol Bay along the North Gulf Coast through Wednesday,
with most of the active weather production in their tracks. A
moderate ridge over the Russian Far East flattens out with help
from troughs moving out of Siberia late Monday into Tuesday.

A surface low near the Shumagin Islands with its front extending
into the Gulf of Alaska pushes most of its precipitation ahead of
the front. Locally heavy rainfall is expected from the Eastern
Kenai Peninsula, and diminishes over Prince William Sound to the
Canadian Border through Monday. Lesser amounts will occur further
inland to the Alaska Range. A well developed low near Kodiak
Island and its front spreads another period of rainfall across
Southcentral Alaska through Wednesday. A moderately strong trough
drags another area of precipitation across the Aleutians and
Alaska Peninsula Sunday and Monday. A new front out of Russia
enters the Western Aleutians and Bering Tuesday, moving across the
Central Aleutians by Wednesday. A third weather producer out of
Russia approaches the Western portions for Wednesday.

- Kutz

&&

.AVIATION...

PANC...Predominantly MVFR ceilings and visibilities with
intermittent periods of IFR ceilings are expected to diminish and
lift by the early afternoon. Rain/snow showers over the area
possible, however will become increasingly sparse by the early
afternoon, but could make a resurgence by the mid-to-late
afternoon. Gusty southerly winds over the terminal early this
morning will weaken, becoming variable by noon, then shifting
back southerly by the late afternoon.

&&

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
656 AM AKDT Thu May 9 2024

AKZ102-103-112-126-132-100200-
Anchorage-East Turnagain Arm-Matanuska Valley-
Western Prince William Sound-Northeast Prince William Sound-
Including the cities of Anchorage, Eagle River, Indian, Eklutna,
Girdwood, Portage, Palmer, Wasilla, Sutton, Chickaloon, Whittier,
Seward, Moose Pass, Valdez, and Thompson Pass
656 AM AKDT Thu May 9 2024

...SNOW LIKELY FOR HIGHER ELEVATIONS AND PASSES WITH MIXED SNOW
AND RAIN FOR LOWER ELEVATIONS THROUGH EARLY FRIDAY MORNING...

Periods of snow will continue through early Friday morning
for higher elevations above 700 feet and for passes such as
Thompson Pass, Turnagain Pass, Summit Lake, Hatcher Pass and the
Sutton area. An additional 2 to 4 inches of snow is possible for
Thompson Pass and Hatcher Pass, the Anchorage and Eagle River
Hillsides, Turnagain Pass, Summit Lake, and the Sutton area
through Friday morning. Locally higher amounts are possible,
especially across the Upper Hillside of Anchorage and Eagle
River. Accumulation on roadways will be difficult due to warm
temperatures and standing water following the rain, but the
higher elevations may accumulate snow on roadways during the early
morning and overnight hours when temperatures are coolest.

Additional snow amounts of up to 1 inch are also possible for
lower elevations; however, any additional snow will be highly
dependent on precipitation intensity and timing of precipitation.
The light rain/snow mix this morning is expected to become
heavier, and potentially transition back to all snow, this
afternoon. The heavier precipitation will then move east over the
higher elevations this evening before tapering off by late
THursday night or early Friday morning.