Small Craft Advisory 163, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
417 PM AKST FRI FEB 20 2015

.ANALYSIS AND UPPER LEVELS...
A HIGH AMPLITUDE PATTERN CONTINUES TO SET UP OVER THE MAINLAND.
THE ANCHOR UPPER LEVEL LOW PRESSURE HAS NOT CHANGED POSITION WHILE
THE EASTERN PACIFIC/WESTERN NORTH AMERICA RIDGE CONTINUES TO
BECOME MORE ESTABLISHED. BETWEEN THESE TWO FEATURES THE UPPER
LEVEL JET STREAMS FROM STRAIGHT SOUTH TO NORTH WITH A CONNECTION
TO THE SUB-TROPICS BRINGING A WARM/MOIST AIR MASS WITH OVER 200
PERCENT OF NORMAL PRECIPITABLE WATER. RIDING THE LEFT FRONT EXIT
REGION OF THE 140KT JET STREAK IS A STRONG SHORTWAVE TROUGH
PULLING A WARM/OCCLUDED FRONT NORTHWARD OVER THE WESTERN GULF.

CONSIDERABLE MID-LEVEL AND HIGH CLOUDS HAVE SPREAD OVER THE
MAINLAND AHEAD OF THE SYSTEM AND ARE HAMPERING TEMPERATURES FROM
RISING IN PARTS OF THE SUSITNA VALLEY AND ANCHORAGE BOWL WHILE
WINDS IN THE MATANUSKA VALLEY ARE MIXING THE LOWER ATMOSPHERE UP
QUITE NICELY BRINGING TEMPERATURES INTO THE MID 30S. THE FOCUS ON
TEMPERATURES CONCERNS PRECIPITATION TYPE AS THE FRONT MOVES OVER
THE MAINLAND THIS EVENING AND TOMORROW. AN ABOVE FREEZING WARM
NOSE IS ALREADY PRESENT ON THE 20/12Z SOUNDING OVER ANCHORAGE WITH
TEMPERATURES ON THE HILLSIDE ALREADY INTO THE MID TO UPPER 30S
WHILE THE REMAINDER OF THE BOWL IS BELOW FREEZING. THE FOCUS OF
THE FORECAST TODAY WILL REVOLVE AROUND FREEZING RAIN CHANCES IN
THE NEAR TERM AS WELL AS COPIOUS AMOUNTS OF PRECIPITATION ALONG
THE NORTH GULF COAST WITH HIGH FREEZING LEVELS.

&&

.MODEL DISCUSSION...
GUIDANCE IS IN REALLY GOOD AGREEMENT WITH THE TIMING/STRENGTH AND
TRACK OF THE APPROACHING SHORTWAVE TROUGH AND FRONT CONSIDERING
THE LOWER LATITUDE WHERE THEY ORIGINATED FROM. THE MAIN
DIFFERENCES IN GUIDANCE ARE THE USUAL...VARYING AMOUNTS OF
PRECIPITATION COMING OVER THE LEE OF THE CHUGACH/KENAI MOUNTAINS
IN A DOWNSLOPE REGIME. ALL GUIDANCE IS IN AGREEMENT WITH BRINGING
PRECIPITATION OVER THE COOK INLET REGION WITH FRONT/TROUGH PASSAGE
TOMORROW AFTERNOON.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A WEATHER FRONT WILL PUSH INTO THE AREA TONIGHT. THIS SYSTEM WILL
HAVE HAVE SOME INITIAL STORM FORCE WINDS THROUGH THE BARREN
ISLANDS AND SHELIKOF STRAIT. PRECIPITATION HAS ALREADY BEGUN
ACROSS SOUTHERN AND EASTERN PARTS OF THE KENAI PENINSULA...AND
WILL MOVE INLAND TONIGHT THROUGH THE WEEKEND. MOST OF THIS
PRECIPITATION WILL FALL AS RAIN AT LOWER ELEVATIONS DUE TO THE
RATHER WARM AIR ASSOCIATED WITH THE SOUTHERLY FLOW. SOME POCKETS
OF FREEZING RAIN ARE POSSIBLE INLAND ESPECIALLY IN SHELTERED
LOCATIONS.

FOR ANCHORAGE...WITH STRONGEST WINDS ALOFT REMAINING NEAR
MOUNTAINTOP LEVEL...AND WITH LARGELY GEOSTROPHIC FLOW ACROSS
TURNAGAIN ARM AS WELL AS A STRONG SOUTHERLY UPPER LEVEL
JET...EXPECT LIGHT BUT GENERALLY STEADY PRECIPITATION THROUGH MUCH
OF THE WEEKEND. TOTAL QPF THROUGH THE WEEKEND WILL LIKELY BE
AROUND ONE-QUARTER TO ONE-HALF INCH.

FOR PRINCE WILLIAM SOUND...WITH PRECIPITATION EXPECTED TO FALL AS
RAIN THROUGH THE WEEKEND AND REACH UPWARDS OF 2 TO 4
INCHES...URBAN AND SMALL STREAM FLOODING IS POSSIBLE ESPECIALLY
NEAR VALDEZ AS RAIN COMBINES WITH SNOWMELT TO CREATE PONDING OF
WATER ON ROADWAYS WHERE THERE IS POOR OR NO DRAINAGE.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 THROUGH 3)...
UNSEASONABLY WARM AND WET WEATHER CONTINUES TO PUSH INTO THE
SOUTHWEST MAINLAND FROM THE NORTH PACIFIC...AND WILL PERSIST
THROUGH THE END OF THE WEEKEND. THE INITIAL FRONT CONTINUES TO
WEAKEN AND EXIT OUR AREA TO THE NORTH...DIMINISHING SHOWERS OVER
THE KUSKOKWIM DELTA THIS EVENING. HOWEVER...A STRENGTHENING LOW
SOUTH OF THE ALASKA PENINSULA WILL TRACK NORTH INTO THE EASTERN
BERING BY MORNING...BRINGING WITH IT A SECONDARY FRONT THAT WILL
PUSH THROUGH THE BRISTOL BAY ZONE OVERNIGHT TONIGHT AND THROUGH
THE KUSKOKWIM DELTA BY TOMORROW AFTERNOON. THIS SECONDARY SYSTEM
IS EXPECTED TO BE SLIGHTLY STRONGER THAN THE PREVIOUS SYSTEM AS IT
WILL HAVE SLIGHTLY BETTER UPPER LEVEL SUPPORT...THUS HAVING
SLIGHTLY STRONGER WINDS THAN THE PREVIOUS SYSTEM. ALONG WITH
SLIGHTLY STRONGER WINDS AROUND THE BRISTOL BAY AND KUSKOKWIM DELTA
AREAS...THIS SYSTEM WILL CONTINUE TO FILTER IN UNSEASONABLY WARM
TEMPERATURES AND WET CONDITIONS OVER MUCH OF THE AREA INTO THE
WEEKEND AS IT PROGRESSES NORTHWARD. THE TYPICAL "COLD SPOTS" OVER
THE LOWER KUSKOKWIM VALLEY (SLEETMUTE AND STONY RIVER) HAVE
STARTED TO CLIMB ABOVE FREEZING...AS WARMER AIR CONTINUES TO
ADVECT OVER THE AREA. WHILE A LITTLE SNOW MAY STILL MIX IN WITH
THE RAIN...THE DOMINANT PRECIPITATION TYPE OVER THE AREA WILL
REMAIN RAIN. THE TYPICAL DOWNSLOPED LOCATIONS...KING SALMON AND
BETHEL...WILL SEE SOME RAIN-SHADOWING TO START THE EVENT. BUT AS
THE UPPER LEVEL TROUGH PUSHES THROUGH SATURDAY...RAIN SHOULD
OVERSPREAD MOST LOCATIONS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 THROUGH 3)...
ONE SMALL WEAK LOW CONTINUES TO SPIN AND FALL APART OVER THE
WESTERN BERING. THE BIGGER STORY IS THE EASTERN BERING WHERE WAVE
AFTER WAVE WILL CONTINUE TO TRACK FROM THE NORTH PACIFIC UP ALONG
THE WEST COAST INTO THE BERING STRAIT. THIS PATTERN IS KEEPING
THINGS WARM AND WET FOR THE EXTREME EASTERN ALEUTIANS INTO THE
ALASKA PENINSULA. BUT IT IS ALSO SETTING UP A NICE DEFORMATION
ZONE THROUGH THE CENTRAL ALEUTIANS WITH COLD AIR TO THE WEST. THIS
SHOULD MAKE FOR SOME GALE FORCE NORTHERLY WINDS AND BE ABLE TO
SQUEEZE OUT A FEW INCHES OF SNOW FOR PLACES LIKE ATKA AND ADAK. A
SERIES OF WEAK WAVES ASSOCIATED WITH A STATIONARY UPPER LEVEL LOW
OVER THE KAMCHATKA PENINSULA WILL DEVELOP A WEAK SURFACE
REFLECTION OVER THE WESTERN BERING SUNDAY AFTERNOON...KEEPING WET
AND GUSTY CONDITIONS OVER THE AREA THROUGH THE BEGINNING OF NEXT
WEEK.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE NORTH PACIFIC LOW WILL CONTINUE TO IMPACT THE MAINLAND WITH
PERIODS OF RAIN AND CLOUDY SKIES FROM LATE SUNDAY INTO MONDAY. BY
MONDAY EVENING...THE FRONT ALONG THE GULF COAST WILL DISSIPATE
AND AN UPPER LEVEL TROUGH OVER THE BERING WILL LIFT NORTHWARD.
THIS WILL BRING A SHORT LIVED REPRIEVE FROM THE CLOUDY AND WET
CONDITIONS AS ANOTHER WARM NORTH PACIFIC LOW WILL APPROACH THE
AKPENN ON TUESDAY. THE MODELS BEGIN TO BREAK DOWN WITH THE LOW
TRACK OF THIS SYSTEM ON WEDNESDAY...SO IT IS DIFFICULT TO
DETERMINE IF THIS SYSTEM WILL BRING SIMILAR IMPACTS TO THE
MAINLAND AS THE SYSTEM THIS WEEKEND. THE EC IS MUCH WEAKER WITH
THIS SYSTEM...ALLOWING FOR RIDGING OVER THE MAINLAND TO KEEP A
BULK OF THE PRECIPITATION CONFINED TO THE GULF COAST AND BRISTOL
BAY...AND IS PROBABLY THE BEST CASE SCENARIO BY KEEPING THE
MAINLAND STILL WARM WITH MORE SHOWERY PRECIPITATION. THE GFS ON
THE OTHER HAND IS MORE AGGRESSIVE WITH THIS SYSTEM...PUSHING WARM
AIR AND PRECIPITATION THROUGHOUT THE SOUTHERN MAINLAND INTO
THURSDAY. BY LATE NEXT WEEK...THERE IS FAIRLY GOOD AGREEMENT THAT
RIDGING WILL DEVELOP FROM THE EASTERN BERING INTO THE BERING WITH
OFFSHORE FLOW...WHICH SHOULD BRING AN END (AT LEAST FOR NOW) TO
THE WARM AND MOIST NORTH PACIFIC LOWS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM 130 131 138
         GALE 119 120 132 136 137 139 150 160 175 176 180
         HEAVY FREEZING SPRAY 185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ML
SOUTHCENTRAL ALASKA...CC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...DEK