Small Craft Advisory 987, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
458 AM AKST Thu Dec 13 2018

.ANALYSIS AND UPPER LEVELS...

The main synoptic feature continues to be the elongated trough
positioned from the central Bering to the Kenai Peninsula. This
feature is beginning to shear apart into two closed lows in the
mid-levels. The first of these mid-level shortwaves is lifting
north into the southern mainland from Cook Inlet and as associated
with both an occluded low in the eastern Gulf and a meso-low over
the Kenai Peninsula continuing to produce snow from Kenai north
to Talkeetna. Here, snowfall amounts have been light, on the order
of 2 to 6 inches. However, a locations underneath the center of
the low and areas aided by upslope flow and better dendritic
growth due to cold air advection (upper hillside of Anchorage)
have seen upwards of 6 to 12 inches of new snow. The second
shortwave dropping southeast into the eastern Bering is associated
with a vertically stacked low anchored over Norton Sound. Cold,
arctic air is wrapping around this low and pushing over the Bering
and western mainland where overnight lows in the interior of the
southwest have fallen from 0 to 15 below. Elsewhere, a shortwave
ejecting from the parent low over the eastern Bering is crossing
over the eastern Aleutians and AKPEN bringing a mix of rain and
snow showers, along with gusty small-craft winds from Dutch
Harbor to Sand Point. Farther west, a developing North Pacific low
is pushing clouds and gales across the western Aleutians.

&&

.MODEL DISCUSSION...

Guidance remains in good agreement in the handling of the
synoptic fields. The NAM continues to be a bit faster with the
movement of the low along the eastern Kenai Peninsula late
Thursday. The EC is the weakest of the solutions, favoring more
of an open trough than a closed low. Guidance is also in good
agreement concerning the next low entering the western Gulf late
Friday into Saturday with the first trough moving along the
southcentral coast on Friday and the larger occlusion pinwheeling
through the Gulf into the weekend. Here a blend of the GFS and NAM
is used to resolve subtle differences and take a middle of the
ground approach. The higher resolution NAMnest is used in the
short term to better resolve local-effect winds.

&&

.AVIATION...

PANC...Light snow will continue across the airport complex
through mid-morning with some clearing through the afternoon and
early evening hours. Lower ceilings and light snow returns again
later tonight into early Friday morning. Expect periods of MVFR
and IFR conditions this morning improving to VFR this afternoon.
MVFR conditions return later this evening. Light northerly winds
will also increase this evening.

&&

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

The overall pattern over Southcentral Alaska remains the same
from yesterday with the cold upper level low over Southwest
mainland Alaska. This low continues to send short waves over
Southcentral Alaska which have brought snowfall with them over
land and snow showers over the Gulf of Alaska and Prince William
Sound.

A meso-low could been seen very clearly on the radar over the
northern Kenai Peninsula. This low drifted very slowly eastward
overnight and enhanced the snowfall over Anchorage and into the
Matanuska Valley. As of early Thursday morning, this meso-low is
moving over western Turnagain Arm and as it moves eastward, the
snowfall will end over the Northern Cook Inlet region. There may
even be some partial clearing by the afternoon as the upper level
wave which helped this meso-low develop moves out of the area.

Another upper level disturbance is over southern Kodiak Island
this morning and will track through the Gulf of Alaska today so
the snow with that disturbance will remain only over those areas.

Yet another short wave will move over the Cook Inlet region
tonight bringing another chance of snow to Southcentral.

The pattern begins to change Friday night into Saturday when a
storm force low moves into the Gulf of Alaska from the south.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3/Thursday
through Saturday)...

A deep upper level low over the southwest mainland will continue
to funnel very cold air from the Arctic south into southwest
Alaska. Some limited cloud cover from a weak shortwave moving
across the southern portion of Bristol Bay will help to slightly
moderate temperatures this morning, though areas with clear skies
will see temperatures in the negative single digits to even
negative teens this morning. The upper low center will slowly
shift north and east over the next couple of days, allowing
northerly flow to increase and even colder air to funnel into the
area. 850 mb (5000 ft) temperatures are expected to drop to -20C
by Fri/Sat timeframe. This combined with decreasing cloud cover
will lead to the coldest temperatures of the season so far by
the weekend. Lows right now are expected to plummet to near -20F
for inland areas in the Kuskokwim River Delta and lower Kuskokwim
River Valley Saturday and possibly Sunday morning. Persistent
northerly flow around 10-15 mph will drop wind chills to near
advisory levels (-40F) in these locations, though if winds slacken
a bit these will be not as cold.

On Saturday, a weak deformation zone is expected to form on the
west side of a low pressure system tracking through the Gulf of
Alaska. This will lead to a band of snow developing on the western
side of the Alaskan Range that will slowly push west from Iliamna
towards the Kuskokwim River Valley. As of now, no significant
accumulations are expected, but this should help to keep
temperatures a bit warmer that further west.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through
3/Wednesday night through Saturday)...

A weak shortwave will continue to push east across Southern
Bristol Bay and the far Eastern Aleutians, brining some areas of
snow and rain. As the system pushes off to the east, ridging will
build in leading to cold northerly flow and some scattered
instability snow showers impacting the eastern half of the Bering
and Aleutians today. A sub-960 mb low will track east skirting
just south of the Aleutians on Friday, bringing increased easterly
winds, though precip should stay just to the south. Ridging
builds in rapidly behind the departing system, bringing a return
to cold northerly flow and instability snow showers covering most
of the Bering by Saturday.

&&

.LONG TERM FORECAST (Days 4 through 7)...

The forecast period commences with the longwave trough extending
from Southwest Alaska to the North Pacific and Gulf Of Alaska. On
the 16th of December at 12z the GFS at 500 mb, has a closed low
churning over the Gulf Of Alaska and a second one south of Adak.
Generally speaking, expect this pair of disturbances to push
eastward. The primary sensible weather highlight for this forecast
package will be another round of snow for the Anchorage and
Girdwood Sunday and early Monday. That said, not expecting much
headway towards catching up to the normal climatological snowpack
for the month of December. The ECMWF has come into line with the
GFS and the GEFS ensemble mean early in the forecast period.
However, the consensus begins to erode rapidly by 00z Monday at
least south of the Aleutian Chain. By Tuesday, the global models
ping into another round of cyclogenesis near Kamchatka which will
bring a front into the Western Aleutians actually warming up
places like Attu, Shemya and Amchitka.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gales...132 150 155 172 174 176 177 352.
 		 Heavy Freezing Spray...140 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...TM
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KVP
LONG TERM...PS

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE ANCHORAGE AK
954 AM AKST THU DEC 13 2018

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

0807 PM     SNOW             1 NW SOLDOTNA           60.50N 151.10W
12/12/2018  M2.0 INCH        KENAI PENINSULA    AK   PUBLIC

            DAILY SNOWFALL ON 12/12/2018.

0850 PM     SNOW             EAGLE RIVER             61.32N 149.54W
12/12/2018  E2.2 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            24 HR SNOW TOTAL.

0906 PM     SNOW             EAGLE LOOP RD           61.32N 149.54W
12/12/2018  E2.5 INCH        ANCHORAGE          AK   PUBLIC

            24 HR TOTAL.

0851 AM     SNOW             WICKERSHAM PARK         61.17N 149.85W
12/13/2018  M3.0 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            7PM ON THE 12TH - 7AM ON THE 13TH.

0725 AM     SNOW             EAGLE RIVER             61.32N 149.54W
12/13/2018  M3.5 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            OVERNIGHT SNOWFALL. TOTAL SINCE TUESDAY
            NIGHT IS 6 IN.

0842 PM     SNOW             2 ESE OF POTTER HILL    61.08N 149.82W
12/12/2018  M4.0 INCH        ANCHORAGE          AK   PUBLIC

            NEW SNOW ON 12/12/2018.

0700 AM     SNOW             LAKE OTIS PKWY & 68TH   61.15N 149.82W
12/13/2018  M4.0 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            FROM 8PM ON THE 12TH - 7AM ON THE 13TH.

0712 AM     SNOW             SEWARD/HUFFMAN          61.11N 149.85W
12/13/2018  M4.6 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            STORM TOTAL ROUGHLY A 18:1 TO 20:1 RATIO.

0814 AM     SNOW             STRAWBERRY RD           61.15N 149.93W
12/13/2018  M4.7 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            8:30AM ON THE 12TH - 7:30 AM ON THE 13TH.
            0.24 SWE. STORM TOTAL SNOW SINCE THE 11TH
            6.1 IN.

0742 AM     SNOW             EAST ANCHORAGE NEAR LOR 61.15N 149.81W
12/13/2018  M5.0 INCH        ANCHORAGE          AK   PUBLIC

            24 HR TOTAL WITH THE 3.5 DAY STORM TOTAL OF
            8.3 IN.

0647 AM     SNOW             LAKE OTIS / HUFFMAN     61.10N 149.82W
12/13/2018  M7.0 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            STORM TOTAL STARTING ON THE 11TH.

0813 AM     SNOW             FORT RICHARDSON         61.27N 149.66W
12/13/2018  M7.0 INCH        ANCHORAGE          AK   PUBLIC

            24 HR STORM TOTAL. SWE 0.3 IN (18:1 RATIO).
            SNOW DEPTH OF 13 IN.

0950 AM     SNOW             RUSSIAN JACK SPRINGS PA 61.21N 149.78W
12/13/2018  M9.3 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            2 DAY SNOW TOTAL WITH AVG SNOW RATIO OF
            21:1.

0813 AM     SNOW             CHESTER CREEK           61.20N 149.83W
12/13/2018  M11.0 INCH       ANCHORAGE          AK   PUBLIC

            STORM TOTAL.

0823 AM     SNOW             O'MALLEY TRAILHEAD      61.12N 149.71W
12/13/2018  M17.0 INCH       ANCHORAGE          AK   TRAINED SPOTTER

            15-18 IN STORM TOTAL.

&&

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE ANCHORAGE AK
1003 AM AKST THU DEC 13 2018

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

0452 PM     SNOW             UPPER POTTER VALLEY     61.06N 149.76W
12/12/2018  M1.4 INCH        ANCHORAGE          AK   TRAINED SPOTTER

            FOR THE LAST 24 HRS.

0454 PM     SNOW             NATIONAL WEATHER SERVIC 61.16N 149.98W
12/12/2018  M1.5 INCH        ANCHORAGE          AK   OFFICIAL NWS OBS

            ACCUMULATED SNOWFALL FOR 12/12. STORM TOTAL
            SO FAR 3.3 IN.

0807 PM     SNOW             1 NW SOLDOTNA           60.50N 151.10W
12/12/2018  M2.0 INCH        KENAI PENINSULA    AK   PUBLIC

            DAILY SNOWFALL ON 12/12/2018.

0850 PM     SNOW             EAGLE RIVER             61.32N 149.54W
12/12/2018  E2.2 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            24 HR SNOW TOTAL.

0906 PM     SNOW             EAGLE LOOP RD           61.32N 149.54W
12/12/2018  E2.5 INCH        ANCHORAGE          AK   PUBLIC

            24 HR TOTAL.

0851 AM     SNOW             WICKERSHAM PARK         61.17N 149.85W
12/13/2018  M3.0 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            7PM ON THE 12TH - 7AM ON THE 13TH.

0725 AM     SNOW             EAGLE RIVER             61.32N 149.54W
12/13/2018  M3.5 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            OVERNIGHT SNOWFALL. TOTAL SINCE TUESDAY
            NIGHT IS 6 IN.

0842 PM     SNOW             2 ESE OF POTTER HILL    61.08N 149.82W
12/12/2018  M4.0 INCH        ANCHORAGE          AK   PUBLIC

            NEW SNOW ON 12/12/2018.

0700 AM     SNOW             LAKE OTIS PKWY & 68TH   61.15N 149.82W
12/13/2018  M4.0 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            FROM 8PM ON THE 12TH - 7AM ON THE 13TH.

0712 AM     SNOW             SEWARD/HUFFMAN          61.11N 149.85W
12/13/2018  M4.6 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            STORM TOTAL ROUGHLY A 18:1 TO 20:1 RATIO.

0814 AM     SNOW             STRAWBERRY RD           61.15N 149.93W
12/13/2018  M4.7 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            8:30AM ON THE 12TH - 7:30 AM ON THE 13TH.
            0.24 SWE. STORM TOTAL SNOW SINCE THE 11TH
            6.1 IN.

0742 AM     SNOW             EAST ANCHORAGE NEAR LOR 61.15N 149.81W
12/13/2018  M5.0 INCH        ANCHORAGE          AK   PUBLIC

            24 HR TOTAL WITH THE 3.5 DAY STORM TOTAL OF
            8.3 IN.

0647 AM     SNOW             LAKE OTIS / HUFFMAN     61.10N 149.82W
12/13/2018  M7.0 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            STORM TOTAL STARTING ON THE 11TH.

0813 AM     SNOW             FORT RICHARDSON         61.27N 149.66W
12/13/2018  M7.0 INCH        ANCHORAGE          AK   PUBLIC

            24 HR STORM TOTAL. SWE 0.3 IN (18:1 RATIO).
            SNOW DEPTH OF 13 IN.

0452 PM     SNOW             O'MALLEY TRAILHEAD      61.12N 149.72W
12/12/2018  M8.0 INCH        ANCHORAGE          AK   TRAINED SPOTTER

            24 HR SNOWFALL TOTAL. LIGHTLY SNOWING AT THE
            TIME OF OBSERVATION.

1001 AM     SNOW             NATIONAL WEATHER SERVIC 61.16N 149.98W
12/13/2018  M8.0 INCH        ANCHORAGE          AK   OFFICIAL NWS OBS

            STORM TOTAL SNOWFALL FROM 12/11-12/13.

0950 AM     SNOW             RUSSIAN JACK SPRINGS PA 61.21N 149.78W
12/13/2018  M9.3 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            2 DAY SNOW TOTAL WITH AVG SNOW RATIO OF
            21:1.

0813 AM     SNOW             CHESTER CREEK           61.20N 149.83W
12/13/2018  M11.0 INCH       ANCHORAGE          AK   PUBLIC

            STORM TOTAL.

0450 PM     SNOW             UPPER HILLSIDE          61.10N 149.72W
12/12/2018  M12.0 INCH       ANCHORAGE          AK   TRAINED SPOTTER

            12 IN FOR THE DAY WITH 2 IN THAT FELL ON THE
            11TH. THIS MAKES THE STORM TOTAL SO FAR 14
            IN.

0823 AM     SNOW             O'MALLEY TRAILHEAD      61.12N 149.71W
12/13/2018  M17.0 INCH       ANCHORAGE          AK   TRAINED SPOTTER

            15-18 IN STORM TOTAL.

&&