Heavy Snow in Alaska, March 18 to 19, 2021

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
309 PM AKDT Wed Mar 17 2021

.SHORT TERM...Long wave trough aloft over the eastern gulf will
start to transitioning to the northeast. The closed low at the
base of the trough connected to the quasi-stationary low west of
the Pacific Northwest along 140W. This low will be lifting
towards Vancouver Island by Friday. The low presently offshore the
Cross Sound region will continue to weaken and moves north across
Glacier Bay into Northwest Canada tonight. The warm air at lower
levels is just south Haines/Skagway area as surface temperatures
are 31 to 33 degrees. The snow and then should be rain/snow this
evening will be lessening so expect that the Warning and Advisory
will probably expire this evening. Showers are going to continue
this evening for much of the northern half of the panhandle. A
moisture band will be lifting north from British Columbia and into
the southern panhandle on Thursday where it wills stall with
light rain into Friday. The stronger convection as ceased as well,
so while isolated sleet may fall, shouldn't have any more thunder
with it.

Gusty winds behind the main weather front has resulted in a High
Wind warning for the Juneau area and strong wind headlines for
several other zones in the north central portion of the panhandle.

A new low will spin up near the southern Kenai Peninsula and then
drift east Thursday into Friday. The cold air that had spilled
out in to the northern gulf will be around to allow the low as is
approaches Yakutat pick up 3 to 7 inches of snow starting Thursday
afternoon. So will be issuing an advisory for snow accumulation
there. Confidence in it is fairly good, although these spring
event are notorious to pin down.

The low will track east towards Cross Sound by Friday afternoon,
zonal flow aloft will then run from the central Aleutians into
the gulf by late Friday. This will lead to quick moving systems
moving from west to east rather than out of the south into the
panhandle.

.LONG TERM..../Friday through Wednesday as of 10 PM Tuesday/
Guidance supports an active pattern continuing through the long
term. Latest operational runs as well as ensemble guidance have
improved showing better agreement on a few significant features
through the extended period. The first system exits the Bering Sea
and tracks into the Gulf this weekend. This system will bring
widespread precipitation across the panhandle Saturday and Sunday.
By mid next week, a second low will track north out of the Pacific
Ocean and into the NE Gulf. This system looks to have strong
moisture support allowing for yet another round of widespread
precipitation and may be heavy at times. Integrated water vapor
transport tables show values around 800 along with both NAEFS and
ECMWF standardized anomaly tables showing between 2-3 standard
deviations for this system. Granted this event is a ways out,
continued monitoring will be needed for potential impacts. In
between these features, confidence decreases as timing, strength,
and placement vary from model to model. With this in mind,
forecast changes were limited to Friday and then implementing
better trends with the more significant features.

Used a blend for GFS/ECMWF with fair agreement and ensemble
alignment. Past Sunday, a nudge to new WPC was used.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind until 7 PM AKDT this evening for AKZ025.
     Winter Storm Warning until 6 PM AKDT this evening for AKZ019.
     Strong Wind from 7 PM AKDT this evening through late tonight for
     AKZ019.
     Winter Weather Advisory until 6 PM AKDT this evening for AKZ018.
     Strong Wind from 10 PM AKDT this evening through late tonight
     for AKZ018.
     Winter Weather Advisory from 1 PM Thursday to 1 AM AKDT Friday
     for AKZ017.
MARINE...Gale Warning for PKZ012-013-032>034-041>043.
     Small Craft Advisory for PKZ021-022-031-035-036-051>053.

&&

Bezenek/CC

Visit us at http://www.weather.gov/Juneau

PRELIMINARY LOCAL STORM REPORT...CORRECTED
NATIONAL WEATHER SERVICE JUNEAU AK
1111 PM AKDT WED MAR 17 2021

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

0509 PM     HEAVY SNOW       1 ESE MUD BAY NEAR HAIN 59.15N 135.33W
03/17/2021  M7.0 INCH                           AK   TRAINED SPOTTER

            7 NEW INCHES OF SNOW SINCE 8 AM AKDT MARCH 17TH.
            VISIBILITY IS PRESENTLY AROUND 1/4 MILE IN HEAVY SNOW.

1043 PM     SNOW             5 SSE HAINES            59.17N 135.39W
03/17/2021  M12.0 INCH                          AK   TRAINED SPOTTER

            STORM TOTAL SNOW ACCUMULATION OF 12 INCHES

1107 PM     HEAVY SNOW       4 W KLUKWAN             59.40N 136.00W
03/17/2021  M7.8 INCH                           AK   TRAINED SPOTTER

            12 HOUR SNOW TOTAL FROM 9 AM TO 9 PM MARCH 17TH. LIGHT
            SNOWFALL INCREASED AT NOON AND WAS HEAVIEST BETWEEN 3 PM
            AND 7 PM.

&&

FCF