Heavy Snow and High Wind in Alaska, March 17, 2021

Southeast Alaska Forecast Discussion...CORRECTED National Weather
Service Juneau AK 310 PM AKDT Tue Mar 16 2021

.SHORT TERM...Upper long wave trough at 500 mb in place from AK
interior, south to eastern Pacific. A cut off low lifting north
Tuesday/Wednesday over Eastern Gulf will be supporting the incoming
wave and gusty winds. At the base of the upper level trough, a low
closes off and lifts NE toward Vancouver Island from Wednesday to
Thursday. The long wave trough starts moving NE slowly to the
panhandle by Friday. Weak ridge west of the gulf and a zonal pattern
across the N. Pacific south of Aleutians moves east to the gulf by
late Friday.

A mid 970 mb low moves northward just east of 140 West tonight and
Wednesday, approaching Cape Fairweather Wednesday afternoon. The
associated frontal precipitation band and wind will be moving north
through tonight. A small warm frontal feature will lead the way by
about 6 hours it spreading rain to southern panhandle late this
afternoon. Gusts near the front reaching up to 40 mph for a Sitka
and Juneau zone, and eventually the Skagway zone by Wednesday
afternoon. For much of the panhandle the P-type will be rain or a
mix, although a little cooler air for the northern Lynn Canal will
support snow near sea level especially for Haines as it hangs on to
low level NW flow refreshing cooler temperature.

Lynn Canal area looks as if 3 to 5 inches will likely fall tonight
so will maintain the Advisory for snow amounts. Does look as if will
try to shift to rain in the morning for Wednesday.

Did work on temperature for the next 12 to 48 hrs as initial
temperature is not looking to be a diurnal with steady or warming
for portions of the central and northern panhandle tonight.

Behind that front is a weak surface low moving into the NE gulf
coast area late Thursday, and an old moisture band will be pushed
northward into the southern panhandle by late Thursday. This may try
to react as a warm frontal feature.

The most exciting weather looks to be tonight and early Wednesday
and calm down headed into Thursday. Confidence is above average for
tonight into Wednesday and a little lower for Thursday.

.LONG TERM.../Thursday through Tuesday as of 10 pm Monday/ More
amplified weather pattern for AK for the long range, but as of
now no significant hazards anticipated. Upper level trough over
the AK Gulf mid week will shift to the east through the weekend,
possibly with a ridge moving in, followed by another low/trough.
At the surface, remnants of the low that tracked into the NE Gulf
will weaken then reform near Prince William Sound, and then begin
to move to southward along the panhandle coast towards Cross Sound
through Friday. A second low will move near Haida Gwaii around
the same time as the NE Gulf low reforms but should remain mainly
south of the panhandle. Beyond that time frame about the best
that can accurately be said is more lows will move in from the
west.

The Thursday NE Gulf low has a typical pattern with small craft
winds and precip bands pushing over the northern panhandle.
Meanwhile the Haida Gwaii low moves in precip to the southern
panhandle creating a narrow break over the central panhandle.
Starting to see the early spring diurnal temperature pattern with
highs in the upper 30s to mid 40s and lows near freezing, so have
mixed precip through out the long range, with more rain to the
south. 850 mb temps really show the boundary between arctic air
from the Yukon steered by the NE low moving in with a warm air
over S British Columbia influenced by the Haida Gwaii low. As of
now 12 hour snow totals of only a few inches expected. By the
weekend see a much larger spread in both operational models and
ensembles. GFS indicating a deep low with potential for heavy
precip along with strong winds. However this is the outlier
solution.

Used a blend for GFS/ECMWF for Thursday with fair agreement and
ensemble alignment. For the rest of the long range, a nudge to
new WPC was used. Low forecast confidence for long range beyond
Thursday.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind Wednesday afternoon for AKZ018-025.
     Strong Wind from late tonight through Wednesday morning for
     AKZ023.
     Winter Weather Advisory from 10 PM this evening to 10 AM AKDT
     Wednesday for AKZ018-019.
MARINE...Storm Warning for PKZ042.
     Gale Warning for PKZ012-013-032-033-036-041-043-051.
     Small Craft Advisory for PKZ011-021-022-031-034-035-052-053.

&&

Bezenek/PRB

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE JUNEAU AK
557 AM AKDT WED MAR 17 2021

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

0500 AM     HEAVY SNOW       1 E GUSTAVUS            58.41N 135.71W
03/17/2021  M6.3 INCH        HOONAH-ANGOON      AK   CO-OP OBSERVER

&&