Small Craft Advisory 923, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
539 AM AKST SAT NOV 21 2015

.ANALYSIS AND UPPER LEVELS...
A LONGWAVE TROUGH STRETCHES DOWN THROUGH MAINLAND ALASKA WITH THE
MAIN EMBEDDED LOW NEAR PRINCE WILLIAM SOUND. THE LOW IS SUPPORTED
BY A STRONG VORTICITY MAX THAT IS PUSHING THE LOW TO THE
NORTHEAST. BEHIND THE LOW COLD AIR IS BEING ADVECTED IN FROM
THE NORTH HAVING ALREADY DROPPED TEMPERATURES OVER THE SOUTHWEST.
OVER THE BERING...COLD WESTERLY FLOW WITH EMBEDDED SHORTWAVES IS
BRINGING SNOW SHOWERS TO THE AREA.

&&

.MODEL DISCUSSION...
THE MODELS ARE HANDLING THE PATTERN FAIRLY WELL BUT ARE STRUGGLING
WITH TWO OF THE LOWS. THE FIRST IS THE WEAK LOW OVER THE BERING
THAT IS TRACKING OVER THE SOUTHWEST ON ITS WAY INTO THE GULF
SUNDAY. GUIDANCE IS HAVING DIFFICULTY WITH TRACKING THE LOW ACROSS
LAND BEFORE IT MAKES IT INTO THE GULF. THE OVERALL IMPACT OF THESE
DIFFERENCES IS MINOR BUT IT WILL HAVE SLIGHT CHANGES IN THE TIMING
OF SNOW TO THE SOUTHCENTRAL. THE OTHER ISSUE IS WITH A LOW
APPROACHING THE WESTERN BERING. THE MAIN DIFFERENCE IS THAT THE
EC IS MOVING THE LOW MORE SLOWLY THAN THE CONSENSUS. THE HIGHER
CONFIDENCE IS WITH THE FASTER TRACK OF THE CONSENSUS LOW.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

THE LOW PRESSURE SYSTEM THAT HAS BROUGHT A FRESH BLANKET OF SNOW
ACROSS MUCH OF SOUTHCENTRAL OVERNIGHT IS NOW CENTERED IN PRINCE
WILLIAM SOUND. THIS LOW PRESSURE SYSTEM IS EXPECTED TO CONTINUE
TO BRING LIGHT TO MODERATE SNOW THROUGH THE MORNING HOURS...AND SNOW
WILL BEGIN TO TAPER FROM WEST TO EAST AS THIS LOW WEAKENS AND
SLOWLY DRIFTS EASTWARD. A VERY WEAK UPPER LEVEL DISTURBANCE...AND
PERSISTENT UPSLOPE FLOW WILL ALSO ALLOW SNOW SHOWERS TO LINGER
ACROSS THE ANCHORAGE BOWL AREA INTO THE AFTERNOON. THIS LOW
PRESSURE SYSTEM WILL CONTINUE TO SUPPORT GUSTY WINDS THROUGH
LOCAL GAPS ACROSS PRINCE WILLIAM SOUND...INCLUDING SEWARD AND
WHITTIER...INTO THIS EVENING.

CONDITIONS WILL DRY OUT BRIEFLY SUNDAY MORNING AS A WEAK RIDGE
QUICKLY TRAVERSES THE REGION. ANOTHER LOW PRESSURE SYSTEM QUICKLY
FOLLOWS ON ITS HEELS...WITH THE LOW FIRST MOVING ACROSS KODIAK
EARLY SUNDAY AFTERNOON...AND MOVE INTO THE CENTRAL GULF BY SUNDAY
NIGHT. THIS SYSTEM IS EXPECTED TO BE MUCH WEAKER THAN THE CURRENT
LOW AND ALSO TO HAVE A MORE SOUTHERLY TRACK. AS A RESULT...IT IS
NOT EXPECTED TO BRING MUCH SNOW THREAT TO THE SOUTHCENTRAL
MAINLAND.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
SCATTERED SNOW SHOWERS WILL CONTINUE ACROSS MUCH OF THE SOUTHWEST
MAINLAND TODAY IN BROAD WESTERLY FLOW...WITH UPSLOPE ENHANCEMENT
YIELDING SOME MINOR ACCUMULATIONS ACROSS EASTERN PORTIONS OF THE
LOWER KUSKOKWIM VALLEY. AN UPPER LEVEL DISTURBANCE AND ASSOCIATED
WEAK SURFACE LOW WILL THEN BRING ANOTHER QUICK SHOT OF SNOW TO THE
AREA TONIGHT...WITH THE HIGHEST ACCUMULATIONS FOCUSED OVER THE
KUSKOKWIM DELTA WHERE 2-3 INCHES WILL BE POSSIBLE THROUGH SUNDAY
MORNING. CONDITIONS WILL THEN IMPROVE ON SUNDAY AS RIDGING BUILDS
OVERHEAD IN ADVANCE OF A STRONG BERING FRONT ARRIVING ON ALONG THE
COAST LATE SUNDAY NIGHT.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE AFOREMENTIONED UPPER DISTURBANCE AND WEAK SURFACE LOW SET TO
IMPACT THE SOUTHWEST MAINLAND TONIGHT WILL YIELD ONE MORE DAY OF
SHOWERY CONDITIONS ACROSS THE BERING BEFORE ATTENTION QUICKLY
TURNS TO THE POWERFUL LOW PRESSURE SYSTEM MOVING INTO THE WESTERN
BERING TONIGHT. A STORM FORCE FRONT WILL MOVE ACROSS THE WESTERN
ALEUTIANS LATER TONIGHT...WITH PRECIPITATION QUICKLY CHANGING OVER
TO RAIN AS WARMER AIR IS DRAWN IN FROM THE NORTH PACIFIC. THE
FRONT WILL WEAKEN SLIGHTLY AS IT CONTINUES EASTWARD THROUGH
SUNDAY NIGHT BUT WILL STILL MAINTAIN STRONG GALE FORCE WINDS AS
IT MOVES OVER THE CENTRAL AND EASTERN ALEUTIANS. MEANWHILE...
ANOTHER ROUND OF STORM FORCE WINDS WILL BE IN STORE FOR THE
WESTERN ALEUTIANS AS STRONG COLD ADVECTION COMMENCES ON THE
BACKSIDE OF THE LOW.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
AS PREVIOUSLY DISCUSSED...THE MODELS ARE IN GENERALLY GOOD
AGREEMENT WITH THE HANDLING OF LARGE LOW OVER THE BERING SEA AND
AN ASSOCIATED FRONT MOVING INTO THE GULF EARLY NEXT WEEK. STORM
FORCE WINDS ARE EXPECTED OVER A GOOD PORTION OF THE BERING SEA
ALONG THIS FRONT WITH AN SECOND SWATH OF STORM FORCE WINDS ALONG
THE BACKSIDE OF THE LOW AS IT MOVES INTO THE NORTHERN BERING SEA.
THE STRONG SOUTHERLY PUSH IS STILL EXPECTED WITH THIS SYSTEM...SO
TEMPERATURES OVER THE SOUTHWEST MAINLAND ARE EXPECTED TO QUICKLY
RISE WITH PRECIPITATION TURNING TO MOSTLY RAIN OVER THE REGION BY
MONDAY MORNING. THIS WARM AIR WILL THEN MOVE EASTWARD TOWARDS
SOUTHCENTRAL. THIS WILL BRING TEMPERATURES THROUGHOUT SOUTHCENTRAL
ABOVE FREEZING IN MOST AREAS BY TUESDAY...CAUSING SNOWFALL IN MOST
AREAS TO MIX OR SWITCH OVER TO RAIN IN MOST LOCATIONS.

AT THIS POINT...MODELS BEGIN TO DIVERGE THROUGH THE REMAINDER OF
THE PERIOD. BROADLY...THE MODELS ARE IN GROSS AGREEMENT IN
DEVELOPING A BROAD AND DEEP TROUGH OVER THE EASTERN BERING THAT
EXTENDS ALL THE WAY DOWN TO ABOUT 40N...SETTING UP DEEP SOUTHERLY
FLOW OVER THE SOUTHWEST MAINLAND AND MOST OF SOUTH-CENTRAL ALASKA.
THEY ALSO AGREE IN A DEEP UPPER LOW OVER NORTHEAST RUSSIA...SETTING
UP A BROAD AND FLAT TROUGH OVER THE REMAINDER OF THE BERING SEA
WITH ZONAL FLOW OVER THE NORTHERN PACIFIC. THE DIFFICULTIES ARE
WITH SURFACE FEATURES AS THE MODELS ARE STILL PROVIDING
SIGNIFICANTLY DIFFERENT SOLUTIONS WITH THE REMNANTS OF TYPHOON IN-
FA...WITH A ROUGH LOCATION SOMEWHERE SOUTH OF THE CENTRAL
ALEUTIANS ON WEDNESDAY. MODELS ARE ALSO STRUGGLING WITH A LOW
THAT IS EXPECTED TO DEVELOP ALONG A FRONT JUST NORTH OF HAWAII
SUNDAY NIGHT. IN GENERAL...THE GLOBAL MODELS ARE DEVELOPING THIS
LOW AND MOVING IT NORTHWARD ALONG THE WESTERN SIDE OF THE
NORTHEASTERN PACIFIC RIDGE AND INTO THE WESTERN POTIONS OF KODIAK
ISLAND SOMETIME LATE TUESDAY NIGHT THROUGH EARLY THURSDAY MORNING.
BECAUSE THE WIDE SPREAD OF SOLUTIONS WITH THIS LOW AND ITS
POTENTIAL INTERACTION WITH IN-FA...WPC GUIDANCE WAS USED IN DAYS
4-7...WHICH LEANED HEAVY ON ENSEMBLE GUIDANCE.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY 101 111 141.
MARINE...STORM 119 120 131 175 176 177 178
         GALE 129 130 132 139 141 170 172 173 174 179 185.

&&

SYNOPSIS AND MODEL DISCUSSION...DK
SOUTHCENTRAL ALASKA...EN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...DEK/RF

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
547 AM AKST SAT NOV 21 2015

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

0530 AM     SNOW             4 SSW ANCHORAGE         61.16N 149.93W
11/21/2015  M4.6 INCH                           AK   NWS EMPLOYEE

&&

DKOCHEVA