Small Craft Advisory 816, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKDT FRI OCT 18 2013

.ANALYSIS AND UPPER LEVELS...THE MAJOR DIFFERENCE IN THE PATTERN OVER
THE LAST 24 HRS IS THAT THE ELONGATED TROUGH THAT WAS OVER THE
WESTERN GULF HAS DUG ALL THE WAY DOWN TO NEAR 35N. IT HAS BEEN IN
LARGE PART REPLACED BY THE MASSIVE LOW TRACKING JUST NORTH OF THE
ALEUTIANS. THIS LOW SHOWS SOME VERY INTERESTING EXTRA-TROPICAL
CHARACTERISTICS ON SATELLITE IN THE MID AND UPPER LEVELS. THERE IS A
BROAD SWATH OF UNUSUALLY DRY AIR JUST TO THE EAST AND SOUTH OF THE
CENTER. THIS IS LIKELY THE REMNANTS OF THE UPPER LEVEL RIDGE FROM ITS
PREVIOUS TYPHOON STAGE. IT ALSO SHOWS A DEVELOPING LOW CENTER ALOFT
EVEN AS THE SURFACE LOW BEGINS TO WEAKEN. THIS IS THE SYSTEM
REPLACING THE FORMER WARM CORE ANTICYCLONE WITH A COLD COLD CYCLONE.
IT CONTINUES TO SPREAD STORM FORCE WINDS EASTWARD THROUGH THE
ALEUTIANS. IT IS ALSO TAPPING INTO SOME OF THE DEEPER SUB-TROPICAL
MOISTURE COURTESY OF THE PREVIOUSLY MENTIONED TROUGH AND SPREADING
MUCH OF THAT AS RAIN INTO THE SOUTHERN HALF OF THE STATE.

.MODEL DISCUSSION...IN THE BIG PICTURE...MODELS REMAIN IN VERY GOOD
AGREEMENT FOR THE FIRST 36 HRS OR SO. THERE REMAIN SOME DIFFERENCES
IN THE FINER DETAILS WHICH WILL PLAY A ROLE IN THE SENSIBLE
WEATHER...ESPECIALLY HERE IN ANCHORAGE. AS THE STRONG LOW OVER THE
ALEUTIANS TRACKS EASTWARD IT WILL HELP TO DEVELOP A TRIPLE POINT NEAR
KODIAK ISLAND LATE TONIGHT. THE GFS AND EC ARE ABOUT 6 HRS SLOWER
WITH THIS FEATURE THAN THE NAM. THE NAM BRINGS IT IN THE GULF COAST
JUST AFTER MIDNIGHT TONIGHT WITH JUST SLIGHTLY MORE INTENSITY THAN
THE OTHER MODELS. THIS FORECAST PACKAGE WAS WEIGHTED TOWARD THE
GFS/EC SOLUTION AS THE NAM HAS BEEN TRENDING WEAKER OVER TIME. THAT
SAID...IT DOES LOOK LIKE THERE WILL BE ENOUGH OF A "BREAK" BETWEEN
THIS MORNING'S SYSTEM AND TONIGHT'S SYSTEM FOR ANCHORAGE WINDS TO
TURN BACK DOWN INLET FOR MUCH OF THE EVENING.

WITH THE LARGE ALEUTIAN LOW...ALL MODELS REMAIN IN GOOD AGREEMENT
TRACKING THE LOW RIGHT TOWARDS NUNIVAK ISLAND BY SATURDAY AFTERNOON.
ALL MODELS AGREE THAT IT WILL SLOWLY WEAKEN IN THIS AREA THROUGH
SUNDAY. THE BIGGEST DIFFERENCE APPEARS TO BE HOW FAR TO THE WEST IT
RETROGRADES BEFORE IT FALLS APART. THIS DIFFERENCE WILL AFFECT HOW
FAR INLAND THE HEAVIEST RAIN AND STRONGEST WINDS REMAIN THROUGH THE
WEEKEND.

.SHORT TERM FORECAST...SOUTH CENTRAL...IT SEEMS AS IF WE ARE IN A
RINSE AND REPEAT PATTERN FOR THE TIME BEING. ONE FRONT HAS MOVED
ONSHORE THIS MORNING AND BROUGHT PLENTY OF RAIN TO MOST AREAS. IN THE
PAST 24 HRS...PORTAGE HAS RECEIVED OVER 2 INCHES AND VALDEZ REPORTED
JUST UNDER AN INCH. MEANWHILE...THE SOUTHEAST FLOW HAS DOWNSLOPED
MUCH OF ANCHORAGE AND LESS THAN A TENTH OF INCH OF RAIN HAS REACHED
THE GROUND. AS THE FRONT SWEEPS THROUGH THIS MORNING...IT SHOULD BE
ONLY A MATTER OF TIME BEFORE THE WINDS MIX DOWN INTO TOWN AND
PRECIPITATION ACCUMULATES A BIT MORE.

THE NEXT FRONT WILL ARRIVE LATE TONIGHT. IT WILL BE A VERY SIMILAR
SITUATION WITH STRONG WINDS THROUGH THE TURNAGAIN AND OVER THE HIGHER
ELEVATIONS FIRST. WIND SPEEDS WITH THIS SYSTEM WILL BE ON PAR WITH
THE OTHER WIND EVENTS THIS WEEK. IT LOOKS AS IF ALL LOCATIONS WILL
REMAIN UNDER WARNING CRITERIA ONCE AGAIN.

SOUTHWEST AK...AN UPPER LEVEL LOW WILL MOVE QUICKLY TO THE EAST THIS
MORNING. THIS SHOULD BRING A VERY QUICK BREAK IN THE GUSTY WINDS AND
RAIN. THE LEADING PORTION OF THE PRECIPITATION SHIELD FROM THE
ALEUTIAN LOW WILL MOVE INTO THE COAST BY EARLY AFTERNOON. THEN THE
MAIN PIECE OF ENERGY ASSOCIATED WITH THE LOW WILL BRING ANOTHER OF
HEAVY RAIN AND STRONG WINDS TONIGHT INTO SATURDAY. AS THE LOW PARKS
ITSELF OFF THE COAST THROUGH THE WEEKEND...CONDITIONS WILL BE SLOW TO
IMPROVE.

ALEUTIANS...STORM FORCE WINDS AND BOUTS OF HEAVY RAIN WILL DOMINATE
THE AREA AS THE LOW MOVES EAST TODAY AND SATURDAY. THE STRONGEST
WINDS WILL REMAIN ON THE SOUTHERN SIDE OF THE CHAIN. COLDER AIR WILL
WRAP AROUND THE BACKSIDE OF THE LOW AND TRIGGER NUMEROUS RAIN AND
SNOW SHOWERS FOR MOST LOCATIONS THROUGH THE WEEKEND.

.LONG TERM FORECAST...THE MODELS ARE CONVERGING ON A SOLUTION OF A
MID 990 MB LOW MOVING ALONG THE ALEUTIAN CHAIN BY THE EARLY PART OF
NEXT WEEK. AS THIS SYSTEM DEVELOP...THERE LOOKS TO BE A RELATIVE LULL
IN THE ACTION FOR MUCH OF SOUTH CENTRAL. CLOUDS AND MOUNTAIN SHOWERS
WILL STILL PERSIST UNDER BROAD SOUTHWEST FLOW...BUT WINDS SHOULD
DIMINISH. BY THE MIDDLE OF THE WEEK THE MODELS ARE HINTING AT A
SECONDARY LOW DEVELOPING IN THE SOUTHERN GULF.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...STORM WARNING...172 173 174 175 176 177
         GALE WARNING...414 411 412 413 150 155 160 165 170 171 178
         180 181 185 119 130 131 132
FIRE WEATHER...NONE

OTTENWELLER OCT 13