Small Craft Advisory 530, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 PM AKDT SUN JUL 31 2011

CORRECTED TYPO

.MODEL DISCUSSION...
MODELS ARE IN EXCELLENT AGREEMENT WITH THE SYNOPTIC PATTERN FOR THE
SHORT TERM. GUIDANCE KEEPS A BROAD CYCLONIC FLOW OVER THE STATE WITH
TWO LARGER SYSTEMS ROTATING THROUGH THE TROUGH. THE FIRST WORKING
SOUTH OF THE ALEUTIANS AND ANOTHER DROPPING INTO BERING SEA FROM THE
CHUKCHI PENINSULA BY WEDNESDAY. THE LATTER LOOKS TO BECOME A CLOSED
UPPER LOW OVER THE YUKON DELTA BY LATE WEEK. THE NAM AND GFS ARE
SIMILAR BUT BELIEVE THE 12Z NAM/EC WILL HANDLE THE GULF FEATURES
BETTER.

.ANALYSIS AND UPPER LEVELS...
UPPER LEVEL PATTERN FEATURES A LARGE MEAN TROUGH EMANATING FROM THE
POLAR VORTEX. EMBEDDED DISTURBANCES PROPAGATING THROUGH THE FLOW WILL
CONTINUE TO AFFECT SOUTHERN ALASKA FOR THE COMING DAYS. THE LEADING
WAVE IS MOVING UP INTO THE COPPER RIVER BASIN TODAY BRINGING
SCATTERED TO NUMEROUS SHOWERS. THE NEXT SHORTWAVE TROUGH IS DROPPING
INTO KUSKOKWIM DELTA REGION THIS AFTERNOON BRINGING WIDESPREAD RAIN
WHICH WILL PROGRESS SOUTHEASTWARD THROUGH THE EVENING. OUT IN THE
PACIFIC...A MOIST WESTERLY FLOW ALOFT LIES BETWEEN A CLOSED UPPER LOW
OFF WEST OF THE ALEUTIANS AND A RIDGE IN THE NORTHWEST PACIFIC. THE
SYSTEM WILL PROGRESS SOUTH OF THE ALEUTIANS AND ENTER THE CIRCULATION
OF THE LARGE SCALE TROUGH OVER WESTERN ALASKA AND SWING INTO THE GULF
TUESDAY.

.SHORT TERM FORECAST...
SOUTH CENTRAL...
MANY SHORT WAVE TROUGHS ROTATING AROUND LARGE TROUGH IN THE BERING
WITH AN ANCHOR POLAR LOW. ONE MOVED THROUGH LAST NIGHT WITH ANOTHER
THIS AFTERNOON. YET ANOTHER...A BIT STRONGER WITH VERY GOOD UPPER
LEVEL SUPPORT...WILL MOVE THROUGH TOMORROW. ALL THIS MEANS FOR A VERY
UNSETTLED PATTERN. SHOWERS CAN BE EXPECTED OFF AND ON OVER MOST OF
THE AREA THE NEXT FEW DAYS. THE MORE WIDESPREAD PRECIP WILL BE
TOMORROW. COASTAL LOCATIONS WILL NOT ESCAPE PRECIP THROUGH MUCH OF
THE WEEK. THE WAVE TONIGHT INTO TOMORROW WILL BRING A STRONGER FLOW
ALOFT AS WELL. HIGH PRESSURE WILL BUILD IN THE EASTERN GULF WHILE THE
TROUGH DIGS IN THE BERING. AS A RESULT...SOUTHERLY FLOW WILL INCREASE
OVER THE AREA. WITH A SURFACE TROUGH DEEPENING OVER THE WESTERN GULF
INTO A 998 MB BY TUESDAY...FLOW WILL INCREASE AT THE SURFACE AS WELL.
AN ENHANCED AREA OF HIGH PRESSURE WILL BE OVER THE NORTHERN GULF
WHERE A BARRIER JET IS EXPECTED TO INCREASE OVER THE NEXT COUPLE DAYS
DUE TO THE FLOW AROUND THE LOW AND INCREASED UPPER LEVEL JET SUPPORT.

SOUTHWEST ALASKA...
SHORT WAVE TROUGH AND ASSOCIATED SURFACE LOW ROTATING THROUGH THE
AREA THIS AFTERNOON WITH WIDESPREAD RAIN. CONTINUED WESTERLY MOIST
FLOW WITH THE SURFACE LOW REMAINING OVER BRISTOL BAY. SOME DECENT MID
AND UPPER LEVEL SUPPORT WITH THE SURFACE LOW FOR WIDESPREAD RAIN TO
CONTINUE THROUGH MONDAY. SOME GOOD SURFACE WINDS ALSO THAT WILL
SPREAD INTO THE EASTERN BERING BEHIND THIS LOW. THE UPPER LEVEL
TROUGH AXIS TO MOVE INTO THE AREA TUESDAY MORNING WITH RAIN ENDING
FROM WEST TO EAST. COLDER AIR TO FILTER INTO THE AREA THOUGH.
HOWEVER...THE SURFACE LOW RE-DEVELOPS OVER KODIAK WITH RAIN AND
SHOWERS ALONG THE ALEUTIAN RANGE AND WEST TO DILLINGHAM TUESDAY.
ANOTHER UPPER LEVEL LOW WITH AN ASSOCIATED SURFACE LOW TO MOVE INTO
THE NUNIVAK ISLAND AREA LATE WEDNESDAY. A MODERATE WARM FRONT WITH
GOOD UPPER LEVEL SUPPORT TO PUSH INLAND WEDNESDAY NIGHT.

BERING AND ALEUTIAN...
AN UPPER CLOSED LOW IN THE WESTERN ALEUTIANS TO SWING INTO THE BIG
TROUGH IN THE CENTRAL ALEUTIANS. THIS UPPER LOW WILL INCREASE SHOWER
ACTIVITY OVER THE AREA TONIGHT AND TOMORROW. WINDS ON THE BACKSIDE OF
THE BRISTOL BAY LOW MONDAY NIGHT AND TUESDAY WILL BE MODERATE. THIS
WILL DROP OFF QUICKLY AS THE LOW DEVELOPS IN THE WESTERN GULF
TUESDAY. THE NEXT LOW DROPPING INTO THE BERING WEDNESDAY WILL
INCREASE THE WESTERLY FLOW AND PRECIPITATION ONCE AGAIN OVER THE
BERING. MEANWHILE...STRATUS AND SURFACE HIGH PRESSURE WILL DOMINATE
THE BERING AFTER THE KUSKOKWIM LOW MOVES OUT OF THE AREA MONDAY
NIGHT.

.LONG TERM FORECAST...
START TO SEE SOME MODEL DISCREPANCIES STARTING ON WEDNESDAY NIGHT
OVER THE STATE. THE LARGE POLAR SHORT WAVE TROUGH THAT IS SWINGING
INTO THE BERING STRAIT IS HANDLED WELL. HOWEVER...THE SHORT WAVE
TROUGH THAT PRECEDED IT THROUGH THE AKPEN AND GULF WAS WELL OUT OF
PHASE BETWEEN THE EC AND GFS. BELIEVE IN MORE OF THE GFS SOLUTION
SINCE RIDGE ALONG THE COAST WILL HAMPER ANY PROGRESSION OF THE WAVE
ACROSS THE GULF WEDNESDAY INTO THURSDAY. SOME DIFFERENCE ALSO ON HOW
THE POLAR LOW AND PRECEDING SHORT WAVE SETTLER INTO THE BERING. THE
GFS DIGS A BIT DEEPER THAN THE EC. THE RESULT IS THE FORECAST WILL
SPLIT THE DIFFERENCE SINCE THE EXACT SOLUTIONS HAVE BEEN SWAYING BACK
AND FORTH. ANY WAY YOU SLICE IT...THE WEATHER WILL BE COOLER THAN
NORMAL AND MOSTLY WET.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...NONE
FIRE WEATHER...NONE

JN JUL 11