Small Craft Advisory 429, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
406 PM AKDT MON MAY 18 2015

.ANALYSIS AND UPPER LEVELS...
THE STRONG UPPER LEVEL RIDGE PERSISTS OVER THE EASTERN HALF OF THE
STATE WHILE THE SOUTHWEST MAINLAND REMAINS UNDER STRONG DUE
SOUTHERLY FLOW IN THE UPPER LEVELS. THE BERING SEA IS UNDER AN
UPPER LEVEL TROUGH WITH A CUT OFF LOW THAT IS SOUTH OF AMCHITKA
THIS AFTERNOON. THE JET STREAM IS RUNNING SOUTH OF THIS LOW BUT
WILL AMPLIFY OVER THE NEXT TWO DAYS AS THE SYSTEM MOVES EASTWARD.
THIS WILL MOVE THE JET STREAM OVER SOUTHWEST MAINLAND
ALASKA...KEEPING THE RAIN IN THE REGION. THE FRONT IS REMAINING IN
THIS REGION DUE TO THE STRONG RIDGE THAT IS NOT MOVING MUCH. AN
INTERESTING FEATURE THAT CAN BE SEEN ON THE VISIBLE SATELLITE THIS
AFTERNOON IS THE SEA BREEZE FRONT OVER THE WESTERN KENAI
PENINSULA. THIS CAN BE SEE JUST INLAND FROM COOK INLET IN THE
CUMULUS CLOUDS THAT HAVE DEVELOPED ALONG THE BOUNDARY.

&&

.MODEL DISCUSSION...
MODELS ARE STILL DOING WELL TODAY AND ARE IN OVERALL BETTER
AGREEMENT WITH THE WAY THE LOW WHICH IS CURRENTLY SOUTH OF THE
WESTERN ALEUTIANS WILL ELONGATE AND THEN DEVELOP A SECOND LOW IN
THE EASTERN BERING SEA TUESDAY NIGHT. BY THURSDAY THE MODELS ALL
HAVE THE UPPER LEVEL HIGH OVER THE ALCAN BORDER WITH THE FRONTAL
AREA REMAINING OVER THE SOUTHWEST MAINLAND AND WESTERN ALASKA. THE
GFS IS JUST A LITTLE FARTHER WEST WITH THE POSITIONING OF THE
RIDGE AXIS THAN THE ECMWF. THIS MAY HAVE IMPACT ON THE CLOUDINESS
OVER SOUTHCENTRAL ALASKA AS THERE WILL BE A SHARP EDGE BETWEEN
CLOUDS AND CLEAR SKIES. THEREFORE THE ECMWF SOLUTION WOULD BRING
MORE CLOUDS INTO SOUTHCENTRAL ALASKA THAN THE GFS SOLUTION. EITHER
SOLUTION WILL KEEP THE COPPER RIVER BASIN SUNNY AND PERSISTENT
RAIN IN SOUTHWEST MAINLAND ALASKA.

&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA...
HIGH PRESSURE WILL DOMINATE MUCH OF THE SOUTHCENTRAL FOR THE NEXT
COUPLE DAYS WHICH WILL RESULT IN CONTINUED CLEAR SKIES AND WARM
TEMPERATURES FOR THE MAJORITY OF THE SOUTHCENTRAL. HOWEVER...THE
REMNANTS OF THE FRONT NEAR KODIAK ARE PUSHING MORE CLOUD COVER
OVER COOK INLET AND ARE STILL BRINGING RAIN TO KODIAK ISLAND. THE
MARINE LAYER IS ALSO PUSHING INTO PRINCE WILLIAM SOUND BRINGING
STRATUS AND FOG TO AREAS NEAR THE NORTH GULF COAST. ANOTHER FRONT
WILL MAKE IT TO KODIAK ISLAND BY LATE WEDNESDAY AND SIMILARLY TO
THE PREVIOUS FRONT THIS ONE IS EXPECTED TO STALL OUT OVER THE
ISLAND. WINDS UNDERNEATH THE HIGH SHOULD BE LIGHT BUT THERE WILL
BE SEA BREEZES IN THE NORMAL LOCATIONS AROUND COOK INLET AND
PRINCE WILLIAM SOUND.

&&

.FIRE WEATHER...
WITH THE DRY CONDITIONS AND CLEAR SKIES RH VALUES WILL BE A
CONCERN AS AFTERNOON TEMPERATURES REACH THEIR MAX. SEVERAL PLACES
AROUND THE SOUTHCENTRAL WILL DROP BELOW 30 PERCENT BUT THE COPPER
RIVER BASIN WILL MAKE IT DOWN BELOW 15 PERCENT IN THE AFTERNOON
AND EVENING HOURS THROUGH TUESDAY. WITH THE LIGHT WINDS AROUND
THE SOUTHCENTRAL MOST AREAS WILL NOT APPROACH RED FLAG CRITERIA
WITH THE EXCEPTION OF THE COPPER RIVER BASIN BASED SOLELY ON THEIR
LOW HUMIDITIES.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TONIGHT THROUGH WED)...

RAIN SHOWER ACTIVITY ACROSS SOUTHWEST ALASKA LOOKS TO BECOME MORE
STEADY STATE LATE TONIGHT AND ON TUESDAY AS AN UPPER LEVEL TROUGH
IS EXPECTED TO PUSH THROUGH THE AREA. A FRONT ASSOCIATED WITH AN
AREA OF LOW PRESSURE OVER THE CENTRAL AND EASTERN ALEUTIANS IS
EXPECTED TO MOVE ONSHORE LATE TUESDAY INTO WEDNESDAY MORNING. THE
FRONTAL ORIENTATION APPEARS TO BE FAVORABLE FOR DOWNSLOPING TO
DEVELOP ACROSS INTERIOR PORTIONS OF THE BRISTOL BAY AREA AS WELL
AS GUSTY WINDS PUSHING THROUGH KAMISHAK GAP/LAKE CLARK PASS. THE
MAJORITY OF THE RAINFALL APPEARS TO BE CONFINED TO COASTAL
LOCATIONS TUESDAY AND WEDNESDAY AS THE FRONT IS EXPECTED TO STALL
AND MAKE LITTLE PROGRESS INLAND. ALONG THE PACIFIC SIDE OF THE
ALASKA PENINSULA...RAINFALL WILL BE HEAVY AT TIMES AS CLOUDS AND
MOISTURE UPSLOPE ALONG THE HIGHER ELEVATIONS (ALEUTIAN RANGE). A
LARGE PRECIPITABLE WATER PLUME HAS BEGUN TO DEVELOP ACROSS THE
NORTH PACIFIC ASSOCIATED WITH THE LOW OVER THE ALEUTIANS ISLANDS
WHICH WILL SPREAD EASTWARD IN THE COMING DAYS AND AID IN THE
DEVELOPMENT OF THE HEAVY RAINFALL ALONG THE ALASKA PENINSULA.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TONIGHT THROUGH WED)...

THE PERIOD OF UNSETTLED WEATHER LOOKS TO CONTINUE ACROSS THE
BERING SEA WITH A LITTLE BIT OF A LIGHT AT THE END OF THE TUNNEL.
AN AREA OF LOW PRESSURE IS CURRENTLY LOCATED SOUTHWEST OF ADAK
AND ATKA AND IS DRIVING A FRONT ALONG THE CENTRAL ALEUTIANS...WITH
DECENT RAINFALL RATES. THIS LOW IS EXPECTED TO WEAKEN AS IT DROPS
SOUTH INTO THE NORTH PACIFIC TUESDAY AFTERNOON AND EVENTUALLY
SPLIT INTO TWO SEPARATE LOWS ON WEDNESDAY. ONE LOW WILL DEVELOP
NEAR SAINT PAUL ISLAND WHILE THE PARENT LOW REMAINS SOUTH OF THE
ALEUTIAN CHAIN. THE LOW SOUTH OF THE ALEUTIANS WILL ALLOW FOR AN INFLUX
OF MOISTURE FROM THE NORTH PACIFIC...WHICH WILL AID IN INCREASED
RAINFALL RATES AND RAIN TOTALS ACROSS THE PACIFIC COASTLINES. A
RIDGE BEGINS TO BUILD ACROSS THE FAR WESTERN BERING SEA ON TUESDAY
AND WILL SPREAD EASTWARD THROUGH THE WEEK. HOWEVER...AS IS ALL TOO
COMMON IN THE SUMMER MONTHS...HIGH PRESSURE BRINGS THE POSSIBILITY
FOR LOW STRATUS AND FOG.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE CURRENT PATTERN WILL PERSIST INTO THE END OF THE WORK WEEK AS
HIGH PRESSURE CONTINUES TO DOMINATE THE EASTERN HALF OF THE
MAINLAND AND A LONGWAVE TROUGH REMAINS OVER THE CENTRAL AND
EASTERN BERING. THIS WILL SUPPORT CONTINUED DRY WEATHER AND ABOVE
NORMAL TEMPERATURES ACROSS SOUTHCENTRAL ALASKA...WITH ANOTHER IN A
SERIES OF SURFACE FRONTS AND A NORTH TO SOUTH ORIENTED JET STREAM
KEEPING ABUNDANT MOISTURE AND PRECIPITATION OVER THE SOUTHWEST
MAINLAND AND EASTERN BERING. THE PATTERN WILL BEGIN TO SHIFT
TOWARDS THE WEEKEND AS THE REMNANTS OF TYPHOON DOLPHIN MOVE INTO
THE WESTERN BERING AND INTERACT WITH AN UPPER WAVE MOVING OFF OF
THE KAMCHATKA PENINSULA. THE BERING TROUGH WILL BEGIN TO BE
DISPLACED TO THE EAST AS THIS LOW MOVES EASTWARD INTO THE
BERING...EVENTUALLY CAUSING AN EASTWARD SHIFT IN THE DOWNSTREAM
RIDGE AXIS. THIS WILL LEAD TO INCREASING CHANCES OF PRECIPITATION
AND SLOWLY MODERATING TEMPERATURES OVER SOUTHCENTRAL ALASKA
THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...RED FLAG WARNING 141.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...CB