Small Craft Advisory 492, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT SAT JUL 14 2012

.ANALYSIS AND UPPER LEVELS...
BIG PICTURE IS TROUGH OVER THE BERING TO BREAK DOWN WITH THE FLOW
BECOMING MORE ZONAL OVER ALASKA EARLY THIS WEEK. THE MEAN TROUGH
ESTABLISHES OVER THE MAINLAND BY THE END OF THE WEEK WITH A RIDGE
OVER THE BERING.

A COUPLE OF UPPER LEVEL LOWS ARE SITUATED OVER THE EASTERN ALEUTIANS
AND EASTERN BERING IS BRINGING THE BULK OF THE WEATHER TO OUR
FORECAST AREA. THE UPPER LEVEL SUPPORT FOR THE LOWS IS GOOD WITH A
100 KT JET EXTENDING FROM THE BASE OF THE TROUGH INTO SOUTH CENTRAL
ALASKA. THE SOUTHWEST FLOW OVER SOUTHWEST AND SOUTH CENTRAL ALASKA
PROVIDING PLENTY OF MOISTURE TO THE AREA AS WELL. SINCE THE AIR MASS
IS NOT STABLE...SEEING SOME ISOLATED SHOWERS OVER SOUTH CENTRAL. AN
UPPER LEVEL DISTURBANCE AHEAD OF THE MAIN SURFACE LOW IS PROVIDING
GOOD LIFT IN COMBINATION WITH THE UPPER LOW NEAR NUNIVAK ISLAND. THE
BULK OF THE PRECIPITATION IS OCCURRING OVER THE KUSKOKWIM VALLEY. THE
FRONT ASSOCIATED WITH THE SURFACE LOW SOUTH OF COLD BAY IS STARTING
TO PUSH PRECIPITATION TO THE AKPEN AND TOWARD KODIAK ISLAND THIS
AFTERNOON. THE RIDGE IN THE GULF HAS SHIFTED EAST TODAY WITH SOME
BREAKS IN THE CLOUD COVER OVER SOUTH CENTRAL ALASKA.

.MODEL DISCUSSION...
MODELS ARE IN GOOD AGREEMENT THROUGH THE ENTIRE NEXT WEEK. THE ONLY
DIFFERENCES ARE IN STRENGTH OF THE LOWS AS THEY MOVE THROUGH THE
AREA. THE DIFFERENCES ARE MINOR.

THE TWO UPPER LEVEL LOWS WILL MERGE OVER SOUTHWEST ALASKA TONIGHT
WITH A SHORT WAVE TROUGH MOVING OUT OF THE NORTH PACIFIC TO KODIAK
ISLAND SUNDAY MORNING. THIS WAVE WILL MOVE ALONG THE JET CORE WHICH
WILL BE SITUATED FROM THE NORTH PACIFIC POINTED AT THE COPPER RIVER
DELTA BY SUNDAY MORNING. THE WAVE WILL PUNCH THROUGH SOUTH CENTRAL
ALASKA SUNDAY AS THE JET CORE WEAKENS AND CONTINUES TO SLIDE
EASTWARD. THE UPPER LOW REMAINS OVER SOUTHWEST ALASKA DURING THIS
TIME WITH A PORTION OF THE UPPER LOW ESTABLISHING A BASE NEAR ADAK
MONDAY. THIS ORIENTATION OF THE UPPER LEVEL LOWS KEEPS SOUTHWEST AND
SOUTH CENTRAL ALASKA IN MOIST AND CONDITIONALLY UNSTABLE SOUTHWEST
FLOW. THE UPPER LOW OVER ADAK SWINGS EAST MID WEEK AS A TROUGH OF LOW
PRESSURE MOVES THROUGH THE ARCTIC INTO NORTHWEST ALASKA. THIS BREAKS
DOWN THE RIDGE IN THE GULF AND ESTABLISHES THE LONG WAVE TROUGH OVER
THE MAINLAND THROUGH NEXT WEEKEND.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
SURFACE HIGH PRESSURE AND A TRANSITIONAL UPPER LEVEL RIDGE HAS
ALLOWED FOR SOME BREAKS IN CLOUD COVER OVER SOUTH CENTRAL ALASKA
TODAY. HOWEVER...ENOUGH MOISTURE AND INSTABILITY FOR ISOLATED
SHOWERS. IN ADDITION...AN UPPER LEVEL DISTURBANCE IS QUICKLY MOVING
THROUGH THE AREA THIS AFTERNOON. THE UPPER LOW WITH AN ASSOCIATED JET
IN THE EASTERN BERING KEEPING A GOOD MOIST SOUTHWEST FLOW OVER THE
AREA. AN ASSOCIATED FRONT WITH THE LOW MOVING INTO BRISTOL BAY
TONIGHT WILL MOVE THROUGH KODIAK ISLAND THIS AFTERNOON AND TO THE
NORTHERN GULF COAST TONIGHT. AHEAD OF THE FRONT...RIDGING ALONG THE
COAST AND GOOD UPPER LEVEL WINDS WILL COMBINE TO CREATE A MODERATE TO
STRONG BARRIER JET WITH STRONG TURNAGAIN ARM WINDS. THIS WILL
CONTINUE UNTIL THE FRONT PASSES SOMETIME TOMORROW AFTERNOON. RAIN
WILL SPREAD FROM KODIAK TONIGHT TO PRINCE WILLIAM SOUND AREA. THE
WESTERN KENAI...MAT VALLEY...ANCHORAGE AND COPPER RIVER BASIN WILL BE
THE LAST TO RECEIVE PRECIPITATION AS THE WIND PATTERN WILL CREATE A
RAIN SHADOW FOR THESE AREAS. PRECIPITATION WILL WANE QUICKLY SUNDAY
NIGHT INTO MONDAY AS SURFACE AND UPPER LEVEL HIGH PRESSURE MOVES INTO
THE REGION. A SURFACE LOW TROUGH WILL REMAIN ALONG THE NORTHERN GULF
COAST MONDAY AND CREATE SOME WESTERLY GAP WINDS IN WHITTIER INTO THE
SOUND. THERE MAY ALSO BE SOME NORTHERLY GAP WINDS NEAR SEWARD.
ANOTHER LOW SOUTH OF COLD BAY TUESDAY WILL PUSH SOME PRECIPITATION TO
KODIAK ISLAND. AS THIS LOW AND THE UPPER LOW OVER THE EASTERN BERING
SWING EAST TUESDAY...PRECIPITATION WILL SPREAD TO THE KENAI PENINSULA
TUESDAY NIGHT.

SOUTHWEST ALASKA...
RAIN HAS SPREAD OVER SOUTHWEST ALASKA WITH AN UPPER LOW OVER NUNIVAK
ISLAND AND A STACKED LOW OVER THE EASTERN ALEUTIANS. STRONG WINDS AND
MODERATE TO LOCALLY HEAVY PRECIPITATION WILL REMAIN OVER THE KUSKO
DELTA AND BRISTOL BAY THROUGH TOMORROW AS THE SURFACE LOW MOVES INTO
THE KUSKO DELTA. PRECIPITATION WILL FLOW INTO THE KUSKO VALLEY...BUT
THE HEAVIEST IS EXPECTED ALONG THE COAST AND THE ADJACENT MOUNTAINS.
SOME AREAS ALONG THE ALEUTIAN RANGE WILL EXPERIENCE STRONG GAP WINDS
AND SOME DRY PATCHES TONIGHT DUE TO RAIN SHADOWS DOWNSTREAM OF THE
ALEUTIAN MOUNTAINS. THE FLOW SWITCHES TO SOUTHERLY IN THE AREA AS THE
LOW MOVES INLAND BY TOMORROW MORNING SPREADING PRECIPITATION OVER THE
ENTIRE AREA. THE SURFACE LOW LEAVES THE AREA MONDAY WITH RESIDUAL
MOISTURE IN PLACE. WITH THE MOISTURE AND UPPER LOW STILL IN
PLACE...ISOLATED TO SCATTERED SHOWERS TO REMAIN INTO MONDAY. HIGH
PRESSURE MOVES THROUGH QUICKLY MONDAY NIGHT/TUESDAY. THE NEXT LOW IN
THE ALEUTIANS PUSHES SOME PRECIPITATION INTO BRISTOL BAY/KUSKO VALLEY
TUESDAY.

BERING SEA/ALEUTIANS
RAIN AND STRONG WINDS ARE ASSOCIATED WITH THE LOW JUST SOUTH OF COLD
BAY. THE LOW WILL LIFT INTO SOUTHWEST ALASKA SUNDAY. WINDS ON THE
BACKSIDE OF THE LOW WILL BE SMALL CRAFT WITH SOME LOCALIZED GUSTS TO
40 OR 50 MPH. HIGH PRESSURE WITH STRATUS AND FOG WILL BE THE RULE
OVER THE REMAINDER OF THE BERING AND ALEUTIANS. ANOTHER LOW TO
APPROACH THE CENTRAL/EASTER ALEUTIANS MONDAY. THIS LOW IS MUCH WEAKER
THAN THE CURRENT LOW. CURRENTLY...THE FORECAST LOOKS FOR SMALL CRAFT
WINDS AND MODERATE PRECIPITATION. THIS LOW WILL CROSS INTO THE BERING
TUESDAY AND DISSIPATE BY WEDNESDAY.

.LONG TERM FORECAST...
WITH THE TRANSITION FROM THE TROUGH IN THE BERING TO OVER THE
MAINLAND...THERE WILL BE SHOWER ACTIVITY EARLY IN THE MID TERM OVER
THE EASTERN ALEUTIANS AND SOUTHWEST ALASKA. BY MID WEEK...THE
PRECIPITATION PROBLEMS WILL SHIFT OVER JUST THE MAINLAND. THE AIR
MASS WILL BEGIN TO DRY OUT SOME IN THE NORTHWEST/WESTERLY FLOW BUT
WITH THE COLDER AIR ALOFT SOME CONVECTIVE ELEMENTS WILL BE POSSIBLE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 130 132 150 160
FIRE WEATHER...NONE

JN