Small Craft Advisory 215, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
421 AM AKDT Tue Mar 13 2018

.ANALYSIS AND UPPER LEVELS...
The latest satellite image has an occluded low over the Gulf Of
Alaska with a warm front pushing towards Southcentral. The Kenai
radar (PAHG) has a band of snow pushing into Anchorage while the
Middleton Island radar (PAIH) has both stratiform and convective
precipitation moving over different portions of Prince William
Sound. All the while to the west, there is a developing surface
low with a front over the Aleutians that is moving eastward.
Strong westerly winds and rain associated with this feature as
observed over the western and central Aleutians.

&&

.MODEL DISCUSSION...
Models are in agreement with the synoptic features the first 24
hrs, and then some divergence is introduced which gets amplified
with time. In the near term, the devil is in the details. Most
notably the timing of the QPF over the North Pacific and the Bering.
On the east domain, the GFS is the way to go with the timing and
the coverage of the QPF with the disturbance moving across PWS.

&&

.AVIATION...
PANC... As of 12z or 4 AM AKDT, the VSBY at PANC was reduced to
1 SM with light snow. The cigs and visibilities will bounce
around the next precipitation shield moves into the area. MVFR to
IFR conditions possible.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
An upper level front over the area this morning will mostly
dissipate later today. Snow over much of the area will diminish
to scattered/isolated showers this afternoon, briefly becoming
completely dry over the areas around Cook inlet. Another system
will approach Prince William Sound from the southeast this
afternoon. Precipitation with this system will spread over
Cordova, Valdez, and the Copper River basin later today into
Wednesday morning. An upper level trough approaching from the
southwest will bring some showers to the Cook Inlet area tonight
into Wednesday morning, but not much is expected as this system
does not contain much moisture. This upper trough will then push
most of the moisture east of the area Wednesday afternoon and
evening, for a brief dry spell. A rather more robust system will
approach from the southwest Wednesday night, with chances of
precipitation reaching Kodiak Island in the evening, then
spreading across the Kenai Peninsula and into the Anchorage area
as well as the Matanuska and Susitna Valleys late.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...

A very weak upper level wave is spreading mostly cloud cover over
SOuthwest Alaska this morning. There are a few rogue flurries and
light snow showers scattered about, but otherwise, the weather is
currently quiet. The next weak system moves into Southwest today
and tonight as a reinforcing shortwave trough helps spread light
snowfall over the region. However, this system looks weak and
quite moisture starved, so snowfall amounts look to be around an
inch or less. On Wednesday night, a more substantial low and
associated warn frontal will bring in widespread rain and snow to
Bristol Bay before spreading northward Thursday.

&&

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

A warm front and associated weak surface low is currently tracking
east along and just north of the Eastern Aleutians, bringing light
rain showers along with it. However, it is weakening and will
continue to do so as it skirts eastward into Bristol Bay tonight
before weakening. A stronger warm front and associated low will
move into the Central and Eastern Aleutians/Bering Sea Wednesday
through Thursday, bringing gale force winds and widespread rain as
it tracks into Southwest Alaska. A gale force occluded front will
move into the western Bering Sea Wednesday night.

&&

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

Models are coming into better agreement at the start of the long
range forecast period beginning on Thursday as a system develops
near the central Aleutians and tracks NE into mainland Alaska. A
longwave trough will dig south across the Bering as a strong
southerly jet helps support the formation of a surface low with a
decent tap of sub-tropical moisture. Models are generally showing
this system moving across SW Alaska and into southcentral Thursday
afternoon through Friday morning. Based on the track of the low,
snow could be heavy along the Bristol Bay coast and up into the
lower Kuskokwim River Valley on Thursday, though a more northward
track would allow warmer air to push up past the coast changing
precip over to mostly rain. Precipitation will spread east into
southcentral by late Thursday night or Friday morning, depending
on the model solution, bringing snow to inland locations and a
mix, or all rain, to the coast. Due to better run-to-run
consistency over the past couple of days, the forecast for days 3
and 4 were hedged more towards the slower Euro/Canadian solutions,
which would bring precipitation into southcentral late
Thursday/early Friday morning.

Past Friday, the models again show a wide range of solutions,
though generally an upper level low over the NW Bering Sea will
continue the active pattern into the weekend and at least early
next week. Therefore, the forecast incorporated mostly ensemble
means after day 4.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...GALE 174. Heavy Freezing Spray 180 and 181.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...KVP

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE ANCHORAGE AK
1038 AM AKDT TUE MAR 13 2018

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

1000 AM     SNOW             NATIONAL WEATHER SERVIC 61.16N 149.98W
03/13/2018  M2.0 INCH        ANCHORAGE          AK   OFFICIAL NWS OBS

            STORM TOTAL SNOWFALL.

0900 AM     SNOW             LAKE OTIS & O'MALLEY    61.13N 149.83W
03/13/2018  M2.0 INCH        ANCHORAGE          AK   PUBLIC

            OVERNIGHT SNOWFALL TOTAL. SNOW DENSITY
            MEDIUM AND MOIST.

&&

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE ANCHORAGE AK
1049 AM AKDT TUE MAR 13 2018

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

1048 AM     SNOW             2 SE EAGLE RIVER        61.30N 149.53W
03/13/2018  M1.4 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            STORM TOTAL.

1000 AM     SNOW             NATIONAL WEATHER SERVIC 61.16N 149.98W
03/13/2018  M2.0 INCH        ANCHORAGE          AK   OFFICIAL NWS OBS

            STORM TOTAL SNOWFALL.

0900 AM     SNOW             LAKE OTIS & O'MALLEY    61.13N 149.83W
03/13/2018  M2.0 INCH        ANCHORAGE          AK   PUBLIC

            OVERNIGHT SNOWFALL TOTAL. SNOW DENSITY
            MEDIUM AND MOIST.

&&

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE ANCHORAGE AK
1253 PM AKDT TUE MAR 13 2018

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

1253 PM     SNOW             14 NNW HOPE             61.08N 149.78W
03/13/2018  E2.0 INCH        ANCHORAGE          AK   PUBLIC

            A LITTLE OVER 2 INCHES OF SNOW OVERNIGHT.

1048 AM     SNOW             2 SE EAGLE RIVER        61.30N 149.53W
03/13/2018  M1.4 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            STORM TOTAL.

1000 AM     SNOW             NATIONAL WEATHER SERVIC 61.16N 149.98W
03/13/2018  M2.0 INCH        ANCHORAGE          AK   OFFICIAL NWS OBS

            STORM TOTAL SNOWFALL.

0900 AM     SNOW             LAKE OTIS & O'MALLEY    61.13N 149.83W
03/13/2018  M2.0 INCH        ANCHORAGE          AK   PUBLIC

            OVERNIGHT SNOWFALL TOTAL. SNOW DENSITY
            MEDIUM AND MOIST.

&&

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE ANCHORAGE AK
115 PM AKDT TUE MAR 13 2018

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

0113 PM     SNOW             OCEANVIEW/OLD SEWARD    61.10N 149.86W
03/13/2018  M2.5 INCH        ANCHORAGE          AK   PUBLIC

            STORM TOTAL.

1253 PM     SNOW             14 NNW HOPE             61.08N 149.78W
03/13/2018  E2.0 INCH        ANCHORAGE          AK   PUBLIC

            A LITTLE OVER 2 INCHES OF SNOW OVERNIGHT.

1048 AM     SNOW             2 SE EAGLE RIVER        61.30N 149.53W
03/13/2018  M1.4 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            STORM TOTAL.

1000 AM     SNOW             NATIONAL WEATHER SERVIC 61.16N 149.98W
03/13/2018  M2.0 INCH        ANCHORAGE          AK   OFFICIAL NWS OBS

            STORM TOTAL SNOWFALL.

0900 AM     SNOW             LAKE OTIS & O'MALLEY    61.13N 149.83W
03/13/2018  M2.0 INCH        ANCHORAGE          AK   PUBLIC

            OVERNIGHT SNOWFALL TOTAL. SNOW DENSITY
            MEDIUM AND MOIST.

&&