Small Craft Advisory 189, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
436 PM AKST SAT FEB 27 2016

.ANALYSIS AND UPPER LEVELS...

ANALYSIS...
CLOUD COVER HAS BECOME EXTENSIVE OVER MUCH OF SOUTHERN ALASKA
THIS AFTERNOON...PARTICULARLY FROM THE MATANUSKA VALLEY SOUTH.
THIS IS THANKS TO THE APPROACH OF A STRONG FRONT TOWARDS THE GULF
COAST FROM THE SOUTH. THE LATEST ASCAT SCATTEROMETER
PASS/SATELLITE DERIVED WINDS SHOWS EAST WINDS OF 35-45 KNOTS OVER
MUCH OF THE CENTRAL AND EASTERN GULF...LOCAL GUSTS ARE HIGHER WITH
THE FEW BUOYS THAT ARE OUT OVER THE OPEN GULF REPORTING GUSTS
EXCEEDING 50 MPH ALREADY EARLIER TODAY.

TEMPERATURES OVER NEARLY ALL OF SOUTHERN ALASKA ARE WELL ABOVE
NORMAL ONCE AGAIN TODAY. 12Z SOUNDINGS THIS MORNING FROM
ANCHORAGE TO KODIAK TO KING SALMON ALL SHOW DEEP AND BROAD
SOUTH TO SOUTHEASTERLY FLOW THROUGHOUT NEARLY ALL OF THE
ATMOSPHERIC COLUMN. THESE WINDS CONTINUE TO PUMP ABNORMALLY WARM
AIR THROUGHOUT MAINLAND ALASKA...THOUGH THE CLOUD COVER SHOULD
TEMPER THE WARMING FROM THE STRENGTHENING LATE FEBRUARY SUN
SOMEWHAT.

RADAR SHOWS SCATTERED RAIN AND SNOW SHOWER ACTIVITY THROUGH
WESTERN PRINCE WILLIAM SOUND INTO THE EASTERN KENAI...ALONG WITH
A FEW MORE BEING DETECTED SOUTH OF CLAM GULCH. A FEW FLURRIES AND
SPRINKLES ARE ALL THAT HAVE BEEN REPORTED TODAY AROUND THE
ANCHORAGE BOWL AS THE CHUGACH MOUNTAINS HAVE LARGELY SHADOWED THE
PRECIPITATION TRYING TO CROSS THEM. FURTHER WEST...A WEAK WAVE IS
MOVING INTO THE WOOD RIVER MOUNTAINS AND DISSIPATING FLURRIES ARE MOVING
NORTH ALONG THE COAST WEST OF BETHEL.

UPPER LEVELS...
THERE ARE TWO UPPER LEVEL LOWS NEAR SOUTHERN ALASKA. THE
STRONGEST/COLDEST ONE IS CENTERED SOUTH OF THE CENTRAL ALEUTIANS.
WHILE NOT PRODUCING MUCH IN THE WAY OF SENSIBLE SURFACE
WEATHER...THIS LOW WILL ABSORB EACH OF THE OTHER LOWS EXPECTED TO
APPROACH IT IN THE SHORT-TERM. THE OTHER WEAKER LOW IS THE
VERTICALLY STACKED LOW TRACKING SOUTH OF KODIAK. WHILE THIS LOW
HAS A MUCH MORE IMPRESSIVE SIGNATURE ON SATELLITE...WEAKENING OF
THIS FEATURE WILL CONTINUE. AN UPPER LEVEL TROUGH IS MOVING
WESTWARD ACROSS THE EASTERN ALEUTIANS...BUT IT WILL BE THE FIRST
VICTIM OF THE STRONG UPPER LOW. THE STRONG SURFACE FRONT MOVING
NORTH THROUGH THE GULF STRETCHES INTO THE UPPER LEVELS NORTH OF
THE KODIAK LOW...BOTH OF WHICH ARE HELPING DRIVE THE FRONT TOWARDS
THE GULF COAST. FINALLY...THE NEXT UPPER LEVEL WAVE THAT WILL MOVE
INTO THE SOUTHWEST GULF IS TRACKING ALONG WITH THE VERY ACTIVE
SUBTROPICAL JET SOUTH OF THE UPPER LOW OVER THE OPEN NORTH
PACIFIC. MORE ON THIS FEATURE BELOW.

&&

.MODEL DISCUSSION...
MANY OF THE FORECAST MODELS HAVE BEEN HAVING TROUBLE INITIALIZING
THE KODIAK LOW...THE FRONT BARRELING TOWARDS THE COAST...AND
THEIR ASSOCIATED SMALLER FEATURES THIS AFTERNOON. THE CANADIAN/GEM
MODEL HAS BEEN HANDLING THE LOW THE BEST OF ALL OF THE OTHERS...SO
IT WAS THE CHOSEN SOLUTION FOR THIS FORECAST PACKAGE. THIS
SOLUTION WAS ALSO CHOSEN FOR ITS INITIAL HANDLING OF THE UPPER
TROUGH MOVING OVER THE EASTERN ALEUTIANS.

AFTER ABOUT 36 HOURS...THE GEM BECOMES AN OUTLIER...SO A BLEND TO
THE EC SOLUTION WAS TAKEN FROM THERE. THE DISAGREEMENT AT 36 HOURS
REGARDS THE NEXT DISTURBANCE IN THE WAVE TRAIN. THIS
DISTURBANCE... CURRENTLY TRACKING SOUTH OF THE UPPER LOW WITH THE
UPPER LEVEL JET...WILL ROUND THE EASTERN PERIPHERY OF THE LOW AND
HEAD TOWARDS THE ALASKA PENINSULA AND EASTERN ALEUTIANS. THE
OUTLIER GFS IS MUCH QUICKER THAN THE OTHER MODELS BRINGING THE LOW
THROUGH THAT AREA. THE EC WAS IN FAR BETTER AGREEMENT WITH THE
OTHER MODELS...AND HAS THE MOST REASONABLE TRACK OF THE
LOW...LARGELY KEEPING AS THE AVERAGE BETWEEN THE OTHER MODELS
CLUSTERED AROUND IT.

A FRONT AND A NEW ASSOCIATED LOW DEVELOPS EAST OF THIS
LOW...TRACKING NORTHWARD TOWARD THE GULF. JUST LIKE WITH THE
KODIAK LOW...THE GFS WAS TOO STRONG AND TOO FAST WITH ITS MOVEMENT.
THE EC FOLLOWED VERY CLOSELY WITH THE SREF AND WAS CLUSTERED IN
THE MIDDLE OF THE OTHER MODELS MOVING THE FRONT NORTHWARD TOWARDS
THE GULF. IN FACT...WITH THE EXCEPTION OF THE GFS...ALL OF THE
MODELS ARE CLUSTERED CLOSE TOGETHER WITH THE PLACEMENT OF THE
LARGE SCALE FRONT...BUT WHERE THE ASSOCIATED LOW DEVELOPS IS THE
SUBJECT OF SIGNIFICANT ENOUGH DISAGREEMENT THAT THE EC WAS CHOSEN
AS AN AVERAGE SOLUTION BETWEEN THE REMAINDER OF THE FORECAST
SOLUTIONS. FORECAST CONFIDENCE IS ABOUT AVERAGE...WITH GOOD
CONFIDENCE ON WHERE THE LARGER FEATURES TRACK...AND LOWER
CONFIDENCE ON THE SMALLER SCALE DISTURBANCES AND LOWS THAT DEVELOP
IN ASSOCIATION WITH THEM.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE STRONG FRONTAL SYSTEM STRETCHED ACROSS THE GULF OF ALASKA
WILL CONTINUE TO LIFT NORTH THIS EVENING TO THE NORTHERN GULF
COAST WHERE IT WILL STALL THROUGH SUNDAY. THE ASSOCIATED SURFACE
LOW IN THE SOUTHERN GULF IS CURRENTLY STRETCHING TO AN ELONGATED
AREA OF LOW PRESSURE AND DEVELOPING MULTIPLE CENTERS. THE WESTERN
MOST LOW WILL PULL BACK TO THE NORTHWEST AND CROSS THE ALASKA
PENINSULA JUST TO THE EAST OF COLD BAY LATE TONIGHT THROUGH EARLY
SUNDAY MORNING. THE NEXT LOW CENTER LIFTS NORTH AND OVER SOUTHERN
KODIAK ISLAND EARLY SUNDAY MORNING...WHILE A THIRD MORE OPEN WAVE
TROUGH ROTATES ACROSS THE BARREN ISLANDS MIDDAY SUNDAY. WIDESPREAD
PRECIPITATION...HEAVY AT TIMES...WILL CONTINUE ACROSS THE GULF
COAST REGION THROUGHOUT THIS PROGRESSION WITH ABUNDANT RAIN AT
LOWER ELEVATIONS AND HEAVY WET SNOW HIGHER UP.

THE NEXT FEATURE OF INTEREST IS AN UPPER LEVEL TROUGH LIFTING
NORTH OVER KODIAK ISLAND SUNDAY AFTERNOON...OVER THE KENAI
PENINSULA SUNDAY EVENING AND INTO SOUTH CENTRAL ALASKA SUNDAY
NIGHT. THIS TROUGH IS BRINGING ENOUGH COLD AIR AND INSTABILITY
WITH IT THAT THE PRECIPITATION TYPE SHOULD SWITCH OVER TO SNOW
SHOWERS FAIRLY QUICKLY AS IT PASSES WITH A FAST INCH OR TWO OF
SNOW POSSIBLE SUNDAY NIGHT. CURRENTLY 850 AND 700 MB FLOW
DIRECTION LOOKS MOST FAVORABLE FOR OROGRAPHIC ENHANCEMENT OF THESE
SNOW SHOWERS ALONG THE SUSITNA VALLEY AS WELL AS THE SOUTHERN
AND WESTERN TALKEETNA MOUNTAINS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE MAINLAND WILL REMAIN UNDER AN EASTERLY FLOW PATTERN ALOFT IN
THE SHORT TERM WITH A BRIEF BREAK TOMORROW EVENING AS A NORTH
PACIFIC SYSTEM SHIFTS THE FLOW TO THE SOUTH...SENDING A TROUGH
OVER THE MAINLAND. MOSTLY CLOUDY TO OVERCAST CONDITIONS WILL
PREVAIL WITH MODERATE NORTHERLY WINDS AT THE SURFACE AS THE NORTH
PACIFIC SYSTEM SENDS A COUPLE OF DISTURBANCES TOWARD THE MAINLAND.
EASTERLY DOWNSLOPE FLOW WILL KEEP EVERYWHERE MOSTLY DRY. A
SPRINKLE OR TWO CAN NOT BE RULED OUT. A BETTER CHANCE FOR
PRECIPITATION COMES TOMORROW EVENING AS TROUGH PUSHES FROM SOUTH
TO NORTH. MONDAY INTO TUESDAY THE STORM TRACK STAYS WELL TO THE
SOUTH KEEPING THE MAINLAND DRY WITH NORTHERLY SURFACE
WINDS...CLOUDS SHOULD BE DECREASING AS WELL...THROUGH AN UPPER
LEVEL TROUGH WILL KEEP SOME SHOWER ACTIVITY NEAR THE ALASKA RANGE.
TEMPERATURES WILL CONTINUE TO REMAIN ABOVE NORMAL.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A LOW PRESSURE SYSTEM WILL SHEAR OUT OVER THE SOUTHERN BERING SEA
TONIGHT WHICH WILL SEND A FRONT FROM THE ALASKA PENINSULA THROUGH
THE PRIBILOF ISLANDS. AREAS OF RAIN IN THAT VICINITY WILL
GRADUALLY PUSH NORTHWARD ON SUNDAY BRINGING A BRIEF DRIER PERIOD
TO MOST OF THE EASTERN CHAIN AND BERING. LATE SUNDAY INTO
MONDAY...A COMPACT SYSTEM WILL PUSH TOWARD THE EASTERN ALEUTIANS
AND THE ALASKA PENINSULA SENDING A GALE FORCE FRONT INTO THE
SOUTHERN BERING.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
AN ACTIVE WET PATTERN CONTINUES ACROSS THE GULF AND ALASKA
PENINSULA AS LOW PRESSURE REMAINS THE DOMINANT WEATHER PATTERN
SOUTH OF THE PENINSULA. DRIER CONDITIONS WILL PREVAIL INLAND DUE
TO DOWNSLOPING ALONG MOUNTAINS AND SURFACE RIDGING THAT REBUILDS
INTO CENTRAL ALASKA AT THE BEGINNING OF NEXT WEEK. MODELS ARE IN
FAIR AGREEMENT WITH THE OVERALL SYNOPTIC PATTERN. THE LONG RANGE
FORECAST WAS INFLUENCED WITH THE ECMWF AS IT PROVIDED BETTER
CONSISTENCY FOR UPDATES.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING 119 120 130 131 138.
 GALE WARNING 125 132 136 137 139 150 155 160 180 185.
 HEAVY FRZ SPRAY 185.

&&

SYNOPSIS AND MODEL DISCUSSION...JW
SOUTHCENTRAL ALASKA...JR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ML
LONG TERM...KH