Small Craft Advisory 213, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
331 PM AKDT MON MAR 9 2015

.ANALYSIS AND UPPER LEVELS...
A COLD UPPER LEVEL LOW IS CROSSING SOUTHCENTRAL TODAY WITH A
100KT+ WESTERLY JET STREAM JUST TO THE SOUTH OVER THE GULF. WATER
VAPOR IMAGERY SHOWS A VORTICITY ANOMALY MOVING SOUTHERN COOK INLET
TO THE NORTHERN GULF. THIS ANOMALY REPRESENTS AND AREA OF STRONG
LARGE SCALE SINKING AIR WHICH HELPS MIX STRONGER WINDS FROM ALOFT
DOWN TO THE SURFACE. THERE WAS ACTUALLY A WEAK LOW LEVEL ROTATION
THIS MORNING OVER THE WESTERN KENAI PRODUCING SOME MODERATE TO
HEAVY SNOW SHOWERS. THAT HAS SINCE DISSIPATED...BUT EXPECT A WEAK
SURFACE LOW TO DEVELOP AS THIS ANOMALY CROSSES THE GULF. THUS FAR
THE MEAN FLOW HAS BEEN WESTERLY WITH THE STRONGEST WINDS THROUGH
EAST-WEST ORIENTED GAPS. NORTHERLY FLOW IS DEVELOPING BEHIND THE
UPPER LEVEL LOW WHICH WILL LEAD TO INCREASING WINDS THROUGH
NORTH-SOUTH GAPS...MOST NOTABLY IN THE THOMPSON PASS AND VALDEZ
AREA.

STRONG HIGH PRESSURE IS BUILDING IN BEHIND THE UPPER LOW FROM
SOUTHWEST ALASKA TO THE NORTHERN BERING SEA. ALTHOUGH CLOUDS
REMAIN OVER THE MARINE AREA...MOST OF SOUTHWEST ALASKA HAS CLEARED
OUT ALLOWING TEMPERATURES TO DROP BELOW ZERO IN SOME AREAS.

MEANWHILE A MATURE LOW JUST IS NEARLY STATIONARY JUST TO THE SOUTH
OF THE CENTRAL ALEUTIANS. THE CENTRAL PRESSURE OF THIS LOW IS ONLY
AROUND 1005 MB...WHICH IS USUALLY NOT A BIG DEAL. HOWEVER...THE
HIGH CENTERED OVER THE FAR NORTHWEST PACIFIC/SOUTHWEST BERING SEA
IS NEARLY 1045 MB. THUS...WIDESPREAD GALES WITH AN AREA OF EMBEDDED
STORM FORCE WINDS ARE BEING OBSERVED ALONG THE WESTERN AND CENTRAL
ALEUTIANS. PRECIP IS MAINLY IN THE FORM OF RAIN...ALTHOUGH THERE
COLDER AIR ON THE PERIPHERY OF THE STORM IS PRODUCING AREAS OF
WET SNOW. ONE LAST FEATURE OF NOTE IS A SHORT-WAVE TROUGH OVER THE
WESTERN BERING WHICH IS POISED TO DIG DOWN THE BACK SIDE OF THE
ALEUTIAN LOW/TROUGH...HELPING TO INCREASE BAROCLINICITY AND
STRENGTHEN WINDS EVEN MORE.

&&

.MODEL DISCUSSION...
MODELS REMAIN IN EXCELLENT AGREEMENT WITH LARGE SCALE FEATURES AND
FORECAST CONFIDENCE IS GENERALLY HIGH OVER THE NEXT COUPLE DAYS.
CHANGES TO EXISTING FORECASTS WILL BE MINIMAL.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (MONDAY AND TUESDAY)...
AN UPPER LEVEL LOW POSITIONED OVER THE COPPER RIVER BASIN WITH AN
ASSOCIATED TROUGH EXTENDS THROUGH THE KENAI PENINSULA INTO THE
ALASKA PENINSULA. THIS SYNOPTIC FEATURE WILL PUSH THROUGH THE
SOUTHCENTRAL ALASKA REGION TONIGHT AND BRING MORE COLDER AIR
UPSTREAM INTO THE AREA. THIS WILL REINFORCE THE ONGOING OUTFLOW
GAP WINDS THROUGH THE CHUGACH AND KENAI MOUNTAINS EXTENDING
INTO THE BARREN ISLANDS THROUGH MIDDAY TUESDAY. THE PRESSURE
GRADIENT WILL GRADUALLY WEAKEN BY TUESDAY AFTERNOON RESULTING IN
THE DIMINISHING OF THE OUTFLOW WINDS AS THE FLOW BECOMES MORE
ZONAL. THIS WILL CONTINUE TO BRING DRY AND COLDER CONDITIONS WITH
SUNNY SKIES GOING INTO THE MIDWEEK.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
WITH THE EXCEPTION OF SOME LOW CLOUDS MOVING THROUGH THE SOUTHWEST
MAINLAND TONIGHT...MOSTLY CLEAR SKIES ARE EXPECTED WITH BELOW NORMAL
TEMPERATURES CONTINUING DURING THIS PERIOD.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
LOW PRESSURE NEAR THE CENTRAL ALEUTIANS WILL MOVE OFF TO THE
SOUTHEAST TONIGHT AND TUESDAY. STRONG WINDS WILL CONTINUE
TONIGHT...THEN WEAKEN ACROSS THE ALEUTIANS AND SOUTHERN BERING
SEA. FREEZING SPRAY WILL CONTINUE TO BE A CONCERN WITH A NORTHERLY
COMPONENT TO THE WIND DURING THIS PERIOD...ESPECIALLY ACROSS THE
CENTRAL AND EASTERN BERING SEA.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
CONSENSUS IS FINALLY BEGINNING TO SHOW IN THE MODELS WITH THE LOW
APPROACHING THE GULF ON THURSDAY AFTER TODAYS RUNS. THEY ALL ARE
NOW IN MUCH BETTER AGREEMENT WITH THE PLACING OF A SLIGHTLY
WEAKER ARCTIC TROUGH OVER THE MAINLAND ON THURSDAY-FRIDAY...AND
NOW WITH THE 18Z GFS HAVE COME INTO MUCH BETTER AGREEMENT WITH A
SURFACE LOW TRACK NEAR YAKUTAT ON THURSDAY EVENING. THE GFS HAS
ALSO BECOME CONSISTENTLY WEAKER WITH THIS LOW INITIALLY WITH A
TRACK FURTHER TO THE EAST...WHICH WILL RESULT IN LESS WARM AIR
ADVECTION THAT IS NOW EXPECTED TO BE DIRECTED TOWARDS THE
PANHANDLE RATHER THAN THE SOUTH MAINLAND. THERE REMAINS SOME
DISAGREEMENT AS TO THE STRENGTH OF A WEAK TROUGH OR WAVE THAT WILL
FORM ALONG THE NORTH GULF COAST INTO PRINCE WILLIAM SOUND AS THIS
LOW APPROACHES THE COAST...BUT THIS SHOULD HAVE LITTLE IMPACT IN
THE OVERALL FORECAST OF SNOW SHOWERS DEVELOPING AND OUTFLOW WINDS
INCREASING ON FRIDAY. SNOWFALL FROM THIS SYSTEM AT THIS POINT
APPEARS MOST LIKELY ALONG THE NORTH GULF COAST AND COPPER RIVER
BASIN ON FRIDAY AND SATURDAY...WITH JUST A CHANCE OF SNOW SHOWERS
OVER INTERIOR LOCATIONS FURTHER TO THE WEST.

OVER THE BERING...A GALE FORCE FRONT ENTERING THE WESTERN
ALEUTIANS WEDNESDAY NIGHT WILL GET CAUGHT UP IN THE BROAD ARCTIC
TROUGH DESCENDING THROUGH THE MAINLAND DURING THE SAME
TIME...CAUSING THIS SYSTEM TO QUICKLY SHEER APART AND WEAKEN BY
FRIDAY MORNING. THIS WILL KEEP RAIN AND SNOW SHOWERS WITH NOTABLY
WEAKER WINDS IN THE FORECAST AS IT SPREADS INTO THE CENTRAL BERING
BY EARLY THIS WEEKEND.

BY SUNDAY...THERE CONTINUES TO BE VERY GOOD AGREEMENT THROUGHOUT
THE MODELS THAT THE NORTHEAST PACIFIC RIDGE WILL BUILD THROUGH THE
PANHANDLE INTO THE EASTERN INTERIOR (A FAMILIAR PATTERN FROM THIS
WINTER). BECAUSE OF THIS...THERE IS GOOD CONFIDENCE THAT ABOVE
NORMAL TEMPERATURES WILL RETURN TO THE SOUTHERN MAINLAND BY MONDAY
AND LIKELY PERSIST INTO MID WEEK. THIS WILL ALSO USHER IN A RETURN
TO WARM AND MOIST NORTH PACIFIC LOWS ON A NORTHERLY TRACK TO THE
MAINLAND AND EASTERN BERING FOR THE FIRST HALF OF NEXT WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING 177.
 GALE WARNING 127 130 131 170 173 174 175 178.
 HEAVY FREEZING SPRAY 121 126 127 128 129 130 131 138 139 141 160
165 179 180.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...PD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MBS
LONG TERM...DEK