Small Craft Advisory 212, NWS Anchorage, AK

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

.ANALYSIS AND UPPER LEVELS...

AN UPPER LEVEL TROUGH IS OVER MAINLAND AK THIS MORNING WITH AN
EMBEDDED CUTOFF LOW CENTERED OVER THE NORTHERN SUSITNA VALLEY. A
DEVELOPING TROUGH IS OVER THE CENTRAL ALEUTIANS...AND A RIDGE OF
HIGH PRESSURE IS BUILDING OVER WESTERN AK. A 110 KT ZONAL JET IS
OVER THE NORTHERN GULF OF AK. AT THE SURFACE...COLD AND DRY AIR
STREAMING ACROSS THE FORECAST AREA IS INDUCING SOME SNOW SHOWER
ACTIVITY EAST OF THE ALASKA AND ALEUTIAN RANGES....AND ACROSS THE
GULF AS THE COLD FRONT MOVES EAST. THIS COLD AIR IN CONJUNCTION
WITH THE JET IS IN THE PROCESS OF SPINNING UP A LOW OVER THE
NORTHERN GULF. IN THE WEST...HIGH PRESSURE CONTINUES TO BUILD OVER
THE BERING AND WESTERN AK...AND A LOW SOUTH OF ADAK IS BRINGING
SNOW WITH GALE AND STORM FORCE WINDS TO MUCH OF THE ALEUTIAN
CHAIN.

&&

.MODEL DISCUSSION...

MODELS ARE IN GOOD AGREEMENT THROUGH THE SHORT TERM. HIGH PRESSURE
WITH COLD AND DRY AIR WILL CONTINUE BUILDING ACROSS THE MAINLAND
ZONES THROUGH TUE NIGHT. LOW PRESSURE WILL DEVELOP TODAY OVER THE
NORTHERN GULF AND EXIT OVER SE AK TUE MORNING. THIS WILL SET UP A
SIGNIFICANT GRADIENT BETWEEN THE MAINLAND AND THE GULF WHICH
WILL CAUSE SIGNIFICANT OUTFLOW GAP WINDS. IN THE WEST...THE LOW
SOUTH OF THE ALEUTIANS WILL RAPIDLY MOVE WELL SOUTH OF THE AREA
TONIGHT...DRAGGING THE ASSOCIATED FRONT AWAY FROM THE
ALEUTIANS...AND A WEAK UPPER LEVEL DISTURBANCE ENTERS THE WESTERN
BERING TUE NIGHT. THE FORECASTS WERE GUIDED BY THE EC...WITH SOME
GEM REGIONAL INFLUENCE FOR OUTFLOW WINDS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (MONDAY AND TUESDAY)...

STRONG UPPER LOW CURRENTLY OVER THE SUSITNA VALLEY WILL CONTINUE
ITS RAPID PACE EASTWARD TODAY. AT THE SURFACE...SEVERAL WEAK LOWS
HAVE SPUN UP UNDERNEATH THE INCREASING CYCLONIC FLOW ALOFT AND
HAVE LOCALLY ENHANCED NORTH/NORTHWEST WINDS THIS MORNING. ONE OF
THESE LOWS IS NEAR EASTERN PRINCE WILLIAM SOUND WHILE ANOTHER IS
ONSHORE THE SOUTHERN KENAI PENINSULA AND HAS PRODUCED THE STRONG
WINDS AND SNOW SHOWERS AROUND KACHEMAK BAY. BOTH OF THESE FEATURES
WILL MOVE QUICKLY TO THE EAST/SOUTHEAST TODAY AS THE LARGE-SCALE
OFFSHORE MOVEMENT OF MASS IN THE ATMOSPHERE GETS UNDERWAY. THIS
WILL ACTIVATE ALL OF THE USUAL OUTFLOW GAP WINDS FROM THE BARREN
ISLANDS TO RESURRECTION BAY AND ON UP TO PRINCE WILLIAM SOUND.
AS THE COLD AIR BEGINS TO DUMP MORE SIGNIFICANTLY OFF THE ALASKAN
LANDMASS THIS MORNING A STRENGTHENING TROUGH OF LOW PRESSURE WILL
BE LEFT ALONG THE COAST AS A RESULT OF STRONG HEAT FLUX FROM THE
WATER. THIS WILL REINFORCE PRESSURE GRADIENTS...AND AS A RESULT
THE STRONGEST WINDS OF THIS MODERATE "OUTFLOW" EVENT WILL LIKELY
OCCUR OVERNIGHT TONIGHT AS COLD AIR ADVECTION INTO THE REGION
PEAKS.

BY TUESDAY...OVERALL FLOW BECOMES MORE ZONAL AND COLD
ADVECTION DIMINISHES...HELPING GAP WINDS TO RELAX. A CONTINUED DRY
AIRMASS AND WEAK TRANSIENT MIDLEVEL RIDGING WILL KEEP SKIES CLEAR
AND SUNNY FOR MOST AREAS THROUGH THE MIDDLE OF THE WEEK.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
WITH THE UPPER LEVEL TROUGH NOW SWINGING EAST OF SOUTHWEST
ALASKA...QUIET YET SOMEWHAT CHILLY WEATHER WILL PREVAIL FOR THE
NEXT COUPLE OF DAYS. SCATTERED SNOW SHOWERS LINGERING ALONG THE
WEST SLOPES OF THE ALASKA RANGE AND NORTH SIDE OF THE ALASKA
PENINSULA WILL TAPER OFF TODAY LEAVING ISOLATED INSTABILITY DRIVEN
SHOWERS BRUSHING THE BERING COAST THE ONLY PRECIPITATION EXPECTED.

TEMPERATURE WISE...EXPECTING ONLY LITTLE RECOVERY IN THE
HIGH TEMPERATURES TODAY THEN A MUCH COLDER NIGHT TONIGHT AND
TUESDAY NIGHT AS WINDS BECOMING SOMEWHAT WEAKER AND THE LOWER
ATMOSPHERE MORE STABLE.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE LOW PRESSURE SYSTEM SOUTH OF ADAK WILL MOVE SLOWLY EAST
TODAY AND TONIGHT BEFORE SLIDING SOUTH ON TUESDAY AND TUESDAY
NIGHT AS A SHARP UPPER LEVEL RIDGE BUILDS OVER THE WESTERN
ALEUTIANS. UPPER LEVEL TROUGHING AND A VERY COLD AIR MASS WILL
WILL PERSIST OVER THE BERING AND CONTINUE TO MAKE FREEZING AND
HEAVY FREEZING SPRAY A CONCERN OVER A GOOD PORTION OF THE
BERING...AS WELL AS SOUTH OF THE ALASKA PENINSULA WHERE GUSTY
OUTFLOW WINDS WILL CARRY THE COLDER AIR AS WELL.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
MOSTLY CLEAR SKIES...OFFSHORE FLOW...AND OUTFLOW WINDS WILL
CONTINUE OVER MUCH OF THE SOUTH MAINLAND THROUGH THURSDAY. OVER
THE BERING...A LOW SKIRTING THE CENTRAL ALEUTIANS WILL MOVE INTO
THE NORTH PACIFIC ON WEDNESDAY...DRAGGING COLD AIR AND SNOW
SHOWERS TO MUCH OF THE REGION THAT SHOULD PERSIST INTO THURSDAY.

ANOTHER SYSTEM LOOKS TO ENTER THE WESTERN ALEUTIANS ON THURSDAY
AS AN UPPER LEVEL TROUGH BECOMES NEARLY STATIONARY OVER THE
WESTERN BERING. THIS WILL BRING A PERIOD OF STORMY AND MORE ACTIVE
WEATHER TO THE BERING SEA REGION THAT WILL LIKELY CONTINUE INTO
NEXT WEEK.

OVER THE GULF THERE CONTINUES TO BE DISCREPANCIES IN THE MODELS
WITH THE STRENGTH OF AN ARCTIC TROUGH OVER THE MAINLAND AND
RESULTING LOW OVER THE GULF. THE GFS CONTINUES TO BE
EXTRAORDINARILY CONSISTENT WITH A MUCH DEEPER AND WARMER SYSTEM
APPROACHING THE NORTH GULF COAST ON FRIDAY...WHILE THE EC AND GEM
BRING A MUCH WEAKER AND (IMPORTANTLY) COOLER SYSTEM TOWARDS THE
NORTHERN PANHANDLE. AFTER COORDINATION WITH WPC AND WFO JUNEAU
THIS MORNING...IT WAS DECIDED TO CONTINUE TO TREAT THE GFS AS AN
OUTLIER AND INSTEAD THE EXTENDED FORECAST USED AN EC/GEM BLEND ON
FRIDAY. CONFIDENCE HOWEVER CONTINUES TO BE FAIRLY LOW...AND MODEL
TRENDS WILL NEED TO BE CLOSELY WATCHED OVER THE COMING DAYS.

BY LATE NEXT WEEKEND...THERE IS VERY GOOD AGREEMENT THAT A
FAMILIAR PATTERN WILL RETURN TO MAINLAND ALASKA AS A BUILDING
NORTHEAST PACIFIC RIDGE MAKES ITS RETURN. BECAUSE OF THIS IT NOW
APPEARS THAT THE MAINLAND WILL RETURN TO THE WARM AND STORMY
PATTERN SEEN FOR MOST OF THIS WINTER BY EARLY NEXT WEEK (IF NOT
BEFORE AS THE GFS HAS BEEN INDICATING).

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES...120 121 127 131 139 141 170 173-175 178
STORMS...130 177
HVY FRZG SPRY...121 126-131 138 139 150 160 165 179-181 185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...DS
SOUTHCENTRAL ALASKA...AD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...DEK/CC