Small Craft Advisory 857, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
410 AM AKST Thu Nov 14 2019

.ANALYSIS AND UPPER LEVELS...

An upper-level trough is anchored across the western half of the
state, stretching south into the northern Pacific where a
vertically stacked 962 mb gale-force low sits well south of the
AKPEN. Downstream of this parent low, a 983 mb low that formed
yesterday along a decaying occluded front sits near Middleton
Island. This low, and its associated surface front draped across
the northern Gulf, continues to lift northwest to the
Southcentral coast this morning. Along with this surface low, a
series of upper-level short waves and mid-level vorticity maxima
is tracking southeast to northwest across the Southcentral
Mainland. These features are the catalysts for the area of
widespread precipitation from Prince William Sound and the Copper
River Basin west over the northern half of the Kenai Peninsula.
As of this morning, the first bands of rain, freezing rain, and
sleet have worked its way over the Anchorage Bowl and Mat-Su
Valleys. For these locations, temperatures are hovering at or just
above freezing. The reason for the mixed precipitation is the
warm nose of air (42 degrees at 1700ft on the 07z PANC sounding)
above the surface.

Numerous winter weather advisories and warnings remain in effect
through the early afternoon across Southcentral as snow continues
to fall in the Copper River Basin and along Thompson Pass and a
wintry mix of precipitation becomes more widespread from Kenai to
Talkeetna.

Farther west, a second, potent upper-level low is diving
southwest across the Kuskokwim Delta while a weaker shortwave is
lifting north across the AKPEN. Between the two, a stationary
surface boundary has set up with a band of snow falling from Cape
Newenham and the northern coast of Bristol Bay, across the
Kilbuck Mountains to the middle Kuskokwim Valley. Arctic air is
also spilling across Southwest Alaska with temperatures in the
single digits across the Kuskokwim Valley and teens and 20s along
the coast where northeasterly winds are stronger.

Colder air is also diving south across the Bering behind a cold
front draped just south of the Pribilof Islands. Gusty northerly
winds also continue across much of the eastern half of the
Aleutian Chain as colder air wraps around the backside of the main
surface low.

&&

.MODEL DISCUSSION...

Although there continues to be some minor differences between the
numerical models (e.g. precipitation intensity and type), there
is above average confidence in the current forecast given the good
agreement and performance of the hi-res models with the initial
event yesterday and development of the first bands of
precipitation across the Anchorage Bowl earlier this morning.
Thus, any changes to the forecast, specifically with timing,
precipitation type, and amounts, were done using local edits
using the hi-res model solutions.

Numerical guidance is also in good agreement moving toward the end
of the week before breaking down beyond the weekend. In general,
the pattern looks to remain active through the weekend as the
upper-level trough remains over the state.

&&

.AVIATION...
PANC...Periods of freezing rain will continue through mid morning
before likely transitioning to snow before ending by mid
afternoon. Precipitation type will also be dependent on
intensity. Thus, any snow that develops may transition back to
freezing rain at times. Ceilings will also drop below 5,000ft this
morning and as low as 1,500ft with any heavier wintry
precipitation. Visibility will also be reduced in conjunction with
any snow development. VFR conditions are expected to return by
this evening. Northerly winds will persist through the day.

&&

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

A mix of wintry precipitation is expected over the area today as
a moist weather system moves through the area. The freezing levels
are rather high this morning allowing precipitation to fall as
rain for most areas from Prince William Sound through the Cook
Inlet area into the southern Susitna Valley. Cold air trapped at
the surface is turning much of this into freezing rain and/or
sleet. For the Copper River basin and northern Susitna Valley,
snow is the predominant precipitation type. Blizzard conditions
are occurring through Thompson pass as strong winds and low
temperatures combine with heavy snowfall. Conditions will improve
this afternoon as the weather system moves north. Also, cooler air
aloft will lower snow levels as well as mix out the surface
inversions. This will mostly end chances of freezing rain.

Another system will move to the Gulf coast on Friday. Most of the
precipitation with this system will fall along and near the coast,
but some will manage to work inland. On Friday night this system
will work its way inland for increasing chances of precipitation.

&&

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

The forecast period starts with a narrow band of snow just
southeast of Bethel. This band of snow is being produced by a
stationary boundary hanging over southwest Alaska. The forecast
was adjusted tonight to account for more precipitation than
initially anticipated. Still, we are only expecting 2-3 inches of
snow in populated areas, with a couple pockets maybe getting 4
inches. This band of precipitation will slowly rotate offshore
later this morning. Some blowing snow will be associated with it
due to stiff northeast winds in the area.

Tomorrow night, a small low pressure system will generate in
Bristol Bay, bringing another round of snow to southwest Alaska.
However, models are doing a poor job of finding a solution for
this low, so where exactly the snow will fall is still uncertain.
Right now it's looking like snowfall will mainly be immediately
around Bristol Bay, especially on the southern side.

Also of note is the arctic front, which lies through southwest
Alaska and is the cause of the aforementioned stationary boundary.
This boundary is separating the arctic air places like Bethel are
seeing and more moderate temperatures to the southeast. It is
good to see that winter exists somewhere within our forecast area.

&&

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

The Bering Sea remains pretty quiet. The arctic airmass that is
being pulled south on the backside of low pressure over the state
is bringing some snow showers with it. This low will move east on
Saturday, allowing high pressure to move into the Bering Sea late
Saturday into Sunday. The ridge of high pressure will slide east
through Sunday, with another low moving into the western Bering
Sea Sunday into Monday. Right now, models do not have a good
handle on this low, with considerable disagreement between them on
low center placement. Therefore, will have to wait a day or two to
see what comes of this low.

&&

.MARINE (Days 3 through 5/Saturday through Monday)...
A series of gale to storm force lows will affect the Aleutians
and Bering Sea Saturday through Monday. There is quite a bit of
uncertainty in the track of individual systems, so it's hard to
say where the worst conditions will be located. The Gulf of Alaska
looks quieter through this period.

&&

.LONG TERM FORECAST (Days 4 through 7/Sunday through Wednesday)...
Beginning on Sunday, an upper level low will approach Southcentral
from the west. Model guidance from previous days has differed on
the ultimate track of this low, but the latest solutions all
depict the same general idea, though there are differences in
timing. They also all show a trailing upper wave immediately
following the low. With arctic air spreading across Southcentral,
this set-up is favorable for snow across most of the region,
sometime in the Sunday through Monday time frame.

Meanwhile, a strong jet stream will drive a long-wave trough
eastward across the North Pacific. Expect numerous fast moving
deep storm systems to rapidly form and move through the trough,
affecting the Bering Sea/Aleutians through at least the middle of
next week. Model guidance is all over the place with depictions
of individual storm systems, but in general agreement on the storm
track which will be close the Aleutian chain. The first of these
storms will begin to impact the southern mainland of Alaska next
Monday or Tuesday. Expect high winds/seas and heavy precipitation
with each storm. It looks like there will be enough arctic air
over the southern mainland to support mostly snow inland, with
rain likely along the coast. Of course, individual storm tracks
will greatly affect this. Bottom line, the extended forecast
period will be characterized by an active storm pattern with
widespread weather impacts likely across the entire region.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning 101, 111, 121, 145.
 		 Blizzard Warning 131.
		 Winter Weather Advisory 141.
MARINE...Gale 119 130 180 181 185 351 352.
		 Heavy Freezing Spray 180.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...TM
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BB
MARINE/LONG TERM...SEB

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1117 AM AKST THU NOV 14 2019

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

1020 AM     SNOW             15 NNW MENDELTNA        62.28N 146.55W
11/14/2019  M5.0 INCH        MATANUSKA-SUSITNA  AK   PUBLIC

            SPOTTER REPORTED 5 INCHES OF SNOW AT LAKE
            LOUISE.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
124 PM AKST THU NOV 14 2019

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

0123 PM     SNOW             23 E VALDEZ             61.13N 145.68W
11/14/2019  E6.0 INCH        VALDEZ-CORDOVA     AK   PUBLIC

            DOT REPORTED THEY MEASURED 6 INCHES OF SNOW
            AT THE STAKE. HOWEVER, SAID THEY ESTIMATED
            8-10 INCHES FELL IN OTHER AREAS AS THE WIND
            HAS CAUSED FOR BLOWING SNOW.

&&

ED

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE ANCHORAGE AK
211 PM AKST THU NOV 14 2019

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

0123 PM     SNOW             23 E VALDEZ             61.13N 145.68W
11/14/2019  E6.0 INCH        VALDEZ-CORDOVA     AK   PUBLIC

            DOT REPORTED THEY MEASURED 6 INCHES OF SNOW
            AT THE STAKE. HOWEVER, SAID THEY ESTIMATED
            8-10 INCHES FELL IN OTHER AREAS AS THE WIND
            HAS CAUSED FOR BLOWING SNOW.

0727 AM     SNOW             25 S TONSINA            61.28N 145.28W
11/14/2019  E3.0 INCH        VALDEZ-CORDOVA     AK   DEPT OF HIGHWAYS

            DOT REPORTED THE MOST SNOW THEY OBSERVED
            BETWEEN THE 42-82MI MARKERS ON THE
            RICHARDSON HIGHWAY WAS 3 INCHES AND THAT
            OCCURRED BETWEEN THE 46-50MI MARKERS.

0658 AM     SNOW             21 E VALDEZ             61.14N 145.74W
11/14/2019  E6.0 INCH        VALDEZ-CORDOVA     AK   DEPT OF HIGHWAYS

            CORRECTION: DOT REPORTED 6 INCHES OF SNOW
            FOR RICHARDSON HIGHWAY BETWEEN THE 12-42
            MILE MARKER.

0616 AM     SNOW             10 SSE PAXSON           62.96N 145.51W
11/14/2019  E8.0 INCH        VALDEZ-CORDOVA     AK   DEPT OF HIGHWAYS

            DOT REPORTED 8 INCHES OF SNOW ON RICHARDSON
            HIGHWAY BETWEEN THE 148-203 MILE MARKERS.

0615 AM     SNOW             10 ENE MENDELTNA        62.10N 146.14W
11/14/2019  E5.0 INCH        VALDEZ-CORDOVA     AK   DEPT OF HIGHWAYS

            CORRECTION: DOT REPORTED 5 INCHES OF SNOW
            ALONG RICHARDSON HIGHWAY FROM THE GLENN
            HIGHWAY TO MILEPOST 148.

1020 AM     SNOW             15 NNW MENDELTNA        62.28N 146.55W
11/14/2019  M5.0 INCH        MATANUSKA-SUSITNA  AK   PUBLIC

            SPOTTER REPORTED 5 INCHES OF SNOW AT LAKE
            LOUISE.

1017 AM     SNOW             34 NNE CHASE            62.89N 149.58W
11/14/2019  E2.0 INCH        MATANUSKA-SUSITNA  AK   DEPT OF HIGHWAYS

            DOT REPORTED 2 INCHES OF SNOW ON THE GROUND
            WITH LIGHT FLURRIES. REPORTED MORE MODERATE
            SNOW TO THE NORTH BUT DID NOT HAVE AN AMOUNT
            TO REPORT AT THIS TIME.

0558 AM     SNOW             25 WSW MENDELTNA        61.94N 147.18W
11/14/2019  E2.0 INCH        MATANUSKA-SUSITNA  AK   DEPT OF HIGHWAYS

            DOT REPORTED 2 INCHES OF SNOW WITH ICY SPOTS
            FOR GLENN HIGHWAY BETWEEN THE 118-176 MILE
            MARKERS.

0530 AM     FREEZING RAIN    11 WNW BIG LAKE         61.56N 150.28W
11/14/2019  E0.25 INCH       MATANUSKA-SUSITNA  AK   NWS EMPLOYEE

            SPOTTER REPORTED 0.25 INCHES OF ICE WITH A
            DUSTING OF SNOW.

1156 PM     FREEZING RAIN    17 SE TRAPPER CREEK     62.06N 150.06W
11/13/2019  U0.00 INCH       MATANUSKA-SUSITNA  AK   DEPT OF HIGHWAYS

            DOT REPORTED AN ICY GLAZE ALONG THE PARKS
            HIGHWAY FROM MILEPOST 52 TO TALKEETNA SPUR
            ROAD.

0900 AM     SNOW             1 NW SOLDOTNA           60.50N 151.10W
11/14/2019  M1.0 INCH        KENAI PENINSULA    AK   PUBLIC

            VERY LIGHT ICE ACCUM ON PLANTS PRIOR TO
            SNOWFALL. 34F CURRENTLY.

0645 AM     SNOW             2 NNW RIDGEWAY          60.56N 151.12W
11/14/2019  E2.0 INCH        KENAI PENINSULA    AK   DEPT OF HIGHWAYS

            DOT REPORTED 2 INCHES OF SNOW ALONG THE
            KENAI SPUR FROM THE STERLING HIGHWAY TO
            MILEPOST 12.

0645 AM     SNOW             5 S KASILOF             60.26N 151.25W
11/14/2019  E2.0 INCH        KENAI PENINSULA    AK   DEPT OF HIGHWAYS

            DOT REPORTED 2 INCHES OF SNOW FOR TUSTUMENA
            ROAD FROM JOHNSON LAKE ROAD TO TUSTUMENA
            BOAT LAUNCH.

1047 AM     FREEZING RAIN    11 SSE KNIK             61.32N 149.57W
11/14/2019  E0.13 INCH       ANCHORAGE          AK   NWS EMPLOYEE

            SPOTTER REPORTED A THIN LAYER OF ICE WITH
            LIQUID ON TOP. ESTIMATED NO MORE THAN 0.13
            INCHES OF ICE.

1044 AM     FREEZING RAIN    11 SE KNIK              61.32N 149.54W
11/14/2019  U0.00 INCH       ANCHORAGE          AK   NWS EMPLOYEE

            SPOTTER REPORTED A LIGHT GLAZE OF ICE ON
            SIDE STREETS, DECKS AND WALKWAYS.

1043 AM     FREEZING RAIN    8 MILES SSE EAGLE RIVER 61.24N 149.44W
11/14/2019  U0.00 INCH       ANCHORAGE          AK   NWS EMPLOYEE

            ER IS GETTING UGLY. HE SAID IT WAS QUITE
            SLICK UP HIGH (HIS HOUSE BY SOUTH FORK EAGLE
            RIVER TRAILHEAD) BUT THE STEEP SECTIONS
            WERENT BAD BECAUSE THERE WAS NO RAIN. NOW
            WITH HEAVY RAIN FALLING, ITS GETTING VERY
            SLICK - INCLUDING DOWN IN LOWER ER.

0915 AM     FREEZING RAIN    17 NNW HOPE             61.13N 149.79W
11/14/2019  M0.10 INCH       ANCHORAGE          AK   NWS EMPLOYEE

            SCHOOL BUSES USING CHAINS.

0645 AM     FREEZING RAIN    17 NNW HOPE             61.14N 149.79W
11/14/2019  E0.05 INCH       ANCHORAGE          AK   NWS EMPLOYEE

            SPOTTER REPORTED 0.02-0.05 OF ICE
            ACCUMULATION ON ROAD SURFACES ABOVE LAKE
            OTIS PARKWAY GOING TOWARD HILLSIDE DRIVE.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
246 PM AKST THU NOV 14 2019

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

0800 AM     FREEZING RAIN    13 NNW HOPE             61.09N 149.74W
11/14/2019  E0.19 INCH       ANCHORAGE          AK   NWS EMPLOYEE

            SPOTTER REPORTED VEHICLE SLID UNCONTROLLED
            INTO A DITCH. REPORTED BETWEEN 0.13 AND 0.25
            INCHES OF ICE ACCUMULATION.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
252 PM AKST THU NOV 14 2019

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

0700 AM     FREEZING RAIN    15 S KNIK               61.23N 149.78W
11/14/2019  E0.10 INCH       ANCHORAGE          AK   PUBLIC

            SPOTTER REPORTED 0.10 INCHES OF ICE AT THE
            BONIFACE ENTRANCE TO JBER.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
300 PM AKST THU NOV 14 2019

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

0221 PM     FREEZING RAIN    15 NNW HOPE             61.11N 149.75W
11/14/2019  E0.13 INCH       ANCHORAGE          AK   PUBLIC

            SPOTTER REPORTED 0.13 INCHES OF ICE
            ACCRETION.

&&

ED