Small Craft Advisory 452, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1248 PM AKDT FRI JUN 6 2014

.ANALYSIS AND UPPER LEVELS...THE LAST IN A SERIES OF SUNNY AND WARM
DAYS ACROSS SOUTHCENTRAL AND SOUTHWEST ALASKA WILL SOON BE COMING
TO AN END AS TWO LARGE UPPER LEVEL LOWS IMPINGE ON THE LAST VESTIGES
OF UPPER LEVEL RIDGING. ONE UPPER LOW IS OVER THE NORTHWEST ALASKA
COAST WITH A TROUGH DIGGING SOUTHWARD ACROSS THE NORTHERN BERING
AND WESTERN ALASKA. ANOTHER LOW/TROUGH SOUTH OF THE KODIAK ISLAND
IS LIFTING NORTHEASTWARD INTO THE GULF WITH CLOUDS AND SHOWERS
GRADUALLY SPREADING NORTH AND WESTWARD ALONG THE GULF COAST AND
OVER THE ALASKA PENINSULA INTO BRISTOL BAY. YET ANOTHER LOW JUST
UPSTREAM TO THE SOUTH OF THE ALEUTIANS IS BEGINNING TO CATCH UP TO
THE FIRST LOW...WITH MERGING OF THE TWO EXPECTED TONIGHT. A SURFACE
LOW AND FRONTAL SYSTEM ARE ALSO GRADUALLY LIFTING NORTHWARD WITH
STEADY RAIN OVER MUCH OF THE GULF AND KODIAK ISLAND. RIDGING OUT
AHEAD OF THE FRONT IS ONCE AGAIN PRODUCING GUSTY WINDS THROUGH THE
USUAL GAPS IN SOUTHCENTRAL.

THE POSITION OF THE THERMAL TROUGH IS SIMILAR TO YESTERDAY...EXTENDING
FROM THE KUSKOKWIM DELTA NORTHEASTWARD TO INTERIOR ALASKA. THE 12Z
BETHEL SOUNDING IS ONCE AGAIN PRIMED FOR AFTERNOON/EVENING CONVECTION
AS THE SURFACE HEATS UP.

LASTLY...UPPER LEVEL RIDGING PERSISTS OVER THE WESTERN TO CENTRAL
BERING SEA WITH REMARKABLY CLEAR SKIES OVER MUCH OF THIS REGION.
THIS PRODUCED A RECORD HIGH TEMPERATURE ON SAINT PAUL ISLAND ON
THURSDAY.

&&

.MODEL DISCUSSION...THIS IS A CHALLENGING FORECAST DUE TO THE
COMPLEX INTERACTION OF THE TWO UPPER LEVEL TROUGHS AND WAVES
EMBEDDED WITH THE FLOW AROUND THEM. THIS IS REFLECTED IN THE MODEL
FORECASTS...WHICH SHOW THE SAME GENERAL SYNOPTIC SOLUTION BUT
DIFFER ON THE EXACT TRACK OF THE UPPER LOW CENTERS AND MORE
SIGNIFICANTLY ON THE PLACEMENT AND STRENGTH OF INDIVIDUAL WAVES.
THE NAM IS THE BIGGEST OUTLIER ON THE 12Z MODEL CYCLE...AGGRESSIVELY
TRACKING AN UPPER WAVE FROM THE GULF OF ALASKA NORTHWESTWARD
ACROSS SOUTHCENTRAL AND SOUTHWEST ALASKA AND SETTING UP A
DEFORMATION ZONE BETWEEN THE TWO TROUGHS OVER SOUTHWEST ALASKA 12
HOURS OR MORE EARLIER THAN ANY OTHER SOLUTION. A LOOK AT WATER
VAPOR IMAGERY SHOWS A ROBUST SHORT-WAVE OVER THE CENTRAL GULF.
OTHER MODELS MAY BE UNDERPLAYING THIS BUT NOT QUITE READY TO JUMP
ON THE NAM SOLUTION. WILL WATCH SATELLITE AND RADAR TRENDS AND
MAY END UP GOING SOMEWHERE IN BETWEEN THE NAM AND OTHER SOLUTIONS.

THE FORECAST DOESN'T GET ANY EASIER THIS WEEKEND AS THE SOUTHERN
LOW MOVES INTO THE CENTRAL GULF AND WAVES ROTATE AROUND THE NORTH
SIDE OF THE LOW INTO SOUTHCENTRAL. IT IS REALLY HARD TO PLACE
THESE WAVES...SO WILL HAVE TO CONTINUE TO USE A FAIRLY BROADBRUSH
APPROACH TO THE PRECIP FORECAST. WILL USE A SIMILAR APPROACH ALL
THE WAY THROUGH EARLY NEXT WEEK AS THE GULF LOW EXITS TO THE EAST
AND FOCUS SHIFTS TO THE NORTHERN LOW...SETTING UP SHOP SOMEWHERE
ALONG THE WEST COAST.

EARLY AFTERNOON UPDATE TO THIS MODEL DISCUSSION...THE 18Z NAM HAS
COME IN MUCH CLOSER TO THE OTHER SOLUTIONS OVER THE NEXT 24 HOURS.
WILL ADJUST FORECAST ACCORDINGLY BASED ON BETTER AGREEMENT.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...MODELS HAVE TRENDED A LITTLE STRONGER WITH
WINDS OUT AHEAD OF THE FRONTAL SYSTEM OVER THE GULF. PLUS AS THE
FRONT GETS CLOSER TO THE COAST WILL SEE A BARRIER JET SET UP.
THEREFORE WILL INCREASE THE AREA OF GALE FORCE WINDS TO COVER THE
NORTH GULF COAST. AFTER FRONT DISSIPATE SATURDAY MORNING A SURFACE
RIDGE WILL BUILD BACK IN ALONG THE NORTH GULF COAST...SO NOW
EXPECT ONE MORE DAY OF GUSTY WINDS THROUGH TURNAGAIN
ARM/ANCHORAGE...KNIK RIVER VALLEY/PALMER...AND ALONG THE COPPER
RIVER.

OTHER THAN THE WIND THE BIG STORY FOR THE WEEKEND WILL BE CLOUDIER
AND COOLER CONDITIONS WITH RAIN ALONG THE COAST. PRECIP CHANCES
INLAND ARE UNCERTAIN AT THIS POINT DUE TO THE CHALLENGE OF TRACKING
THE MANY UPPER LEVEL DISTURBANCES MOVING AROUND THE LOW CENTER.
HOWEVER CHANCES ARE THERE WILL BE PERIODS OF SHOWERS OR RAIN FOR
MOST PLACES OVER THE NEXT FEW DAYS. THE MOST WIDESPREAD RAIN WILL
LIKELY BE SUNDAY DUE TO THE CLOSE PROXIMITY TO THE LOW CENTER AT
THAT POINT IN TIME.

SOUTHWEST ALASKA...A LINE OF THUNDERSTORMS FORMED ALONG THE
THERMAL TROUGH ON THURSDAY AFTERNOON AND EVENING...AFFECTING
PRIMARILY AREAS SOUTH AND EAST OF BETHEL. UPPER LEVEL TEMPERATURES
HAVE WARMED A BIT TODAY AND DON'T EXPECT THE SAME FORCED LIFT FROM
A SHORT-WAVE THAT PASSED JUST NORTH OF THE AREA ON THURSDAY.
THE AIR MASS IS STILL QUITE UNSTABLE...SO MAY SEE A FEW ISOLATED
THUNDERSTORMS...JUST LESS WIDESPREAD THAN THURSDAY. OVER THE NEXT
24 HOURS THE BERING TROUGH WILL CONTINUE TO DIG SOUTH AND
EASTWARD WHILE SHORT-WAVES MOVING OVER TOP OF THE GULF LOW TRACK
WESTWARD. THIS WILL SET UP A DEFORMATION ZONE OVER SOUTHWEST
ALASKA DURING THE DAY SATURDAY WITH STABLE RAIN DEVELOPING ACROSS
MUCH OF THE REGION BY LATE SATURDAY AFTERNOON. THE TROUGH WILL
SWING EASTWARD AS THE GULF LOW EXITS TOWARD SOUTHEAST ALASKA
SATURDAY NIGHT AND SUNDAY...SO THE RAIN WILL HOLD ON LONGEST FROM
BRISTOL BAY TO THE KUSKOKWIM VALLEY WITH SHOWERS PERSISTING ALONG
THE KUSKOKWIM DELTA. THE POSITION OF THE UPPER LOW OVER THE BERING
AND EMBEDDED SHORT-WAVES BECOMES MUCH MORE UNCERTAIN ON
MONDAY...BUT THE PATTERN WILL REMAIN FAVORABLE FOR CLOUDS AND
SHOWERS.

BERING SEA/ALEUTIANS...THE ONLY FEATURE OF NOTE IS AN UPPER LEVEL
LOW DROPPING QUICKLY SOUTHWARD ACROSS THE WESTERN BERING AND
ALEUTIANS SATURDAY AND SATURDAY NIGHT. OTHERWISE WEAK RIDGING WILL
HOLD IN ALOFT AND CONTINUE TO PROVIDE QUIET CONDITIONS ACROSS MOST
OF THE REGION.

&&

.LONG TERM FORECAST...MEDIUM RANGE MODELS AGREE ON THE GENERAL
LARGE SCALE PATTERN IN THE DAY 4 THROUGH 7 PERIOD WITH A TROUGH
OVER THE BERING/WESTERN ALASKA AND RIDGING OVER WESTERN CANADA
INTO MAINLAND ALASKA. HOWEVER THERE CONTINUE TO BE LARGE DIFFERENCES
IN EVOLUTION OF INDIVIDUAL FEATURES AS WELL AS POOR RUN-TO-RUN
CONSISTENCY. MOST NOTABLY...THE ULTIMATE DESTINATION OF THE UPPER
LOW ALONG THE WEST COAST. AT A MINIMUM...THIS PATTERN SUPPORTS
DIURNAL CONVECTION OVER MAINLAND ALASKA WITH A MIX OF SUN AND
CLOUDS. THERE IS A HIGHER PROBABILITY OF STABLE PRECIP OVER
WESTERN ALASKA...ESPECIALLY IF THE UPPER LOW HANGS AROUND A FEW
MORE DAYS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 120 131 138.
FIRE WEATHER...NONE.

&&

SEB JUN 14