Small Craft Advisory 497, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
323 PM AKDT WED SEP 5 2012

.SHORT TERM...RIDGE AXIS EXTENDS FROM PAWG-PAKT AND CONTINUES TO
SLOWLY MOVE OFF TO THE SOUTHEAST AND WILL BE OUT OF OUR AREA BY
THIS EVENING. A MODERATE OCCLUDED FRONT EXTENDING SSW FROM YAKUTAT
IS FORECAST TO WEAKEN AS IT PUSHES SOUTHEAST ACROSS SOUTHEAST
ALASKA TONIGHT. A FLAT RIDGE WILL BUILD INTO THE GULF ON THURSDAY.

 OCCLUDED FRONT EXTENDING FROM PAYA SOUTHWEST UNDER 140 KT SW JET
HAS DEEP MOISTURE AND IS CURRENTLY PRODUCING HEAVY RAIN ACROSS THE
NORTHEAST GULF. THIS WILL TAPER OFF QUICKLY AS FRONT MOVES THROUGH
BUT WILL KEEP RAIN IN FORECAST AS OFFSHORE FLOW CONTINUES IN POST
FRONTAL ENVIRONMENT. THIS COULD LEAD TO LOW CIGS AND VISIBILITIES
WITH LOW LEVEL STABILIZING AS RIDGE BUILDS IN.

 IT APPEARS THAT THE GALES ASSOCIATED WITH LOW LEVEL BARRIER JET
ARE DIMINISHING WITH EVEN SATELLITE SHOWING THIS FEATURE
DISSIPATING. HAVE SOLID SMCR WINDS FOR LYNN CANAL AND STRONG WIND
HEADLINE FOR PAGY INTO EARLY EVENING WITH 10 MB CYXY-PAJN
GRADIENT. ONCE FRONT MOVES THROUGH WINDS WILL EASE QUICKLY. WINDS
INCREASE AGAIN THURSDAY AFTERNOON WITH THERMAL GRADIENT ACROSS THE
COAST MOUNTAINS. IN THE GULF WILL START OFF NEAR SHORE WINDS SE
AROUND 20KT THAT SHIFT TO THE SOUTHWEST IN EVENING. OFFSHORE SW
WINDS REACH 25 KT. A BUILDING WEST SWELL WILL PUSH SEAS UPWARDS OF
10 FEET ON THURSDAY.

 FRONT WILL MOVE THROUGH NORTHERN PANHANDLE THIS EVENING AND THINK
WILL SEE SOME MODERATE RAIN HERE. FRONT IS WEAKENING AS IT DROPS
SOUTH WITH DILUENT FLOW IN THE UPPER LEVELS. WHATS LEFT OF THE
FRONT WILL BE ACROSS SOUTHERN AREAS LATE TONIGHT AND POSSIBLY
EARLY THURSDAY. ALL AREAS WILL BE IN WESTERLY FLO PARTLY CLOUDY IN
THE AFTERNOON FOR SE CORNER. WILL KEEP POPS IN CHANCE CATEGORY
NORTH AND LIKELY FOR PAYA ON THURSDAY.

 MODELS WERE SIMILAR TODAY. GFS PRESSURE GRADIENT MATCHED UP BEST
WITH OBS AND WAS USED TO GENERATE PRESSURE.

 &&

 .LONG TERM...AT MID LEVELS: HIGH PRESSURE RIDGE ORIENTATED FROM
SOUTHWEST TO NORTHEAST FROM THE NORTH PACIFIC INTO NORTHERN
BRITISH COLUMBIA WILL TRACK TO THE EAST. FIRST IN A SERIES OF
WAVES EXTENDING FROM PARENT LOW OVER THE NORTHERN AK INTERIOR WILL
MOVE OVER THE NORTHERN AK GULF THEN MOVING OVER THE NORTHERN
PANHANDLE THROUGH THURSDAY. A HIGH PRESSURE RIDGE WILL BUILD OVER
THE PANHANDLE FRIDAY WHILE A LOW DROPS OVER THE BERING SEA OVER
THE ALEUTIANS AND INTO THE WESTERN GULF SATURDAY. BY THE WEEKEND
THIS MID LEVEL LOW WILL BECOME THE DOMINANT FEATURES IN THE AK
GULF. THE THE LOW CENTER DROPS TO THE SOUTH AND MOVES OVER THE
SOUTHERN PANHANDLE THE TROUGH WILL BECOME NEGATIVELY TILTED. FROM
THE START OF THE WEEK ANOTHER MID LEVEL HIGH PRESSURE RIDGE WILL
MOVE ACROSS THE GULF AND THEN OVER THE PANHANDLE TUESDAY WHILE
ANOTHER MID LEVEL LOW MOVES INTO THE WESTERN GULF.

AT SURFACE: WITH THE RIDGE OF HIGH PRESSURE OVER THE PANHANDLE
WILL SEE A DRY PERIOD THURSDAY NIGHT INTO THURSDAY MORNING BUT AT
THIS TIME NOT EXPECTING AS MUCH CLEARING MAINLY DUE TO CURRENT
CONDITIONS BEHIND THE FRONT IN THE WESTERN GULF. ON THE BACKSIDE
OF THE RIDGE A LOW IN THE RIGHT ENTRANCE REGION OF 300 MB JET WILL
MOVE UP FROM THE NORTH PACIFIC TRACKING NORTHEASTWARD INTO THE AK
GULF. EXACT TRACK AND STRENGTH OF THIS FEATURE IS UNCERTAIN BUT
THERE IS CONSENSUS THAT THE LOW WILL PICK UP WINDS TO NEAR GALES
WITH RAIN DEVELOPING OVER THE PANHANDLE FROM NORTH TO SOUTH. THE
POSITION OF THE LOW WILL BE A SIGNIFICANT DETERMINATION IN THE
STRENGTH OF THE WINDS AND LOCATION OF THE HIGHEST WINDS. AS THIS
FEATURE WEAKENS A SECOND LOW ASSOCIATED WITH THE MID LEVEL TROUGH
DROPPING IN FROM THE BERING SEA AND IN THE LEFT JET EXIT REGION
WILL MOVE WESTWARD ACROSS THE AK GULF WITH THE CENTER NEARING CAPE
DECISION. RAIN WILL AGAIN DEVELOP ACROSS THE PANHANDLE FOR THE
WEEKEND. NOT EXPECTING MUCH OF A BREAK IN PRECIPITATION BETWEEN
THE TWO SYSTEMS HOWEVER BY THE START OF NEXT WEEK WITH THE
DEVELOPING RIDGE WILL HAVE A BREAK IN THE STEADY RAINFALL FOR A
DAY...IN TIME FOR THE NEXT SYSTEM TUESDAY TO BRING RAIN TO THE
PANHANDLE.

 THERE IS A SPLIT BETWEEN THE EUROPEAN MODELS AND NORTH AMERICAN
MODELS WITH THE LOW FOR FRIDAY. THE ECMWF/UKMET SHOWED A DEEPER
LOW POSITIONED MORE TO THE NORTHWEST WHILE THE NAM/GFS HAD A
WEAKER CENTER LOCATED MORE TO THE SOUTHEAST. THE 12Z ECMWF DID
POSITION THE LOW CENTER A BIT CLOSER TO THE NORTH AMERICAN MODEL
SOLUTIONS BUT STILL NOT A STRAIGHT CONSENSUS. WHILE BOTH SOLUTIONS
INDICATE RAIN FOR THE PANHANDLE WITH GFS SOLUTION BRINGS HIGHER
RAINFALL AMOUNTS. THE ECMWF/UKMET INDICATE STRONGER WINDS DUE TO
THE DEEPER CENTER. AT THIS TIME DID NOT PUSH WINDS QUITE TO GALES
DUE TO THE UNCERTAINTY OF THE LOW TRACK. DECIDED TO USE THE 12Z
ECMWF TO UPDATE GRIDS TO DAY 4. FOR THE WEEKEND SYSTEM MODELS WERE
IN BETTER AGREEMENT WITH TH POSITION OF THE LOW HOWEVER THE ECMWF
WAS STILL STRONGER THAN THE GFS. USED NEW HPC FOR AN ENSEMBLE
SOLUTION FOR THE REMAINDER OF THE LONG RANGE. DO EXPECT THE FALL
PATTERN TO CONTINUE TO EMERGE SO EXPECT HIGHER SEAS...STRONGER
WINDS AND MORE RAIN TO BE THE NORM.

 FORECAST CONFIDENCE IS BELOW AVERAGE. WHILE THERE IS FAIR
AGREEMENT WITH THE SYNOPTIC PATTERN MESOSCALE DETAILS AMONG THE
MODELS AND BETWEEN RUNS ID RATHER POOR. EXPECT THAT THE
FORECAST...ESPECIALLY WINDS...WILL CHANGE AS THE SYSTEMS DEVELOP.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND UNTIL 10 PM AKDT THIS EVENING FOR AKZ018.
MARINE...SMALL CRAFT ADVISORY FOR PKZ011>013-022-036-042-043-051-052.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041.

&&

MM/PRB