Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 221045 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 645 AM EDT MON SEP 22 2014 .SYNOPSIS... A COLD FRONT WILL CROSS THE AREA THIS MORNING BEFORE STALLING OFFSHORE. AN UPPER LEVEL LOW WILL BRING A CHANCE FOR SOME SHOWERS AND ISOLATED THUNDERSTORMS THIS AFTERNOON AND TONIGHT. COOLER AND DRIER WEATHER IS EXPECTED ON TUESDAY. THE STALLED COLD FRONT OFFSHORE WILL WAVER BACK TOWARDS THE COAST DURING THE MIDDLE AND LATTER PART OF THE UPCOMING WEEK...BRINGING GOOD CHANCES FOR RAIN AND BELOW NORMAL TEMPERATURES. A WARMING AND DRYING TREND IS EXPECTED DURING THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 640 AM MONDAY...UPDATES THIS MORNING FOCUS ON THE CLUSTER OF SHOWERS FALLING OUT OF A MID-LEVEL CLOUD DECK ACROSS THE PEE DEE REGION OF SOUTH CAROLINA. 07Z HRRR BRINGS IT STEADILY EASTWARD OVER THE NEXT FEW HOURS WITH VERY LIGHT RAINFALL AMOUNTS EXPECTED. A NEW CLUSTER OF CONVECTION IS INDICATED TO DEVELOP IN THE SANTEE RIVER/CHARLESTON VICINITY BETWEEN 3-5 PM THIS AFTERNOON AHEAD OF THE UPPER LEVEL DISTURBANCE. THIS WILL PROBABLY BE UPRIGHT CONVECTION DEVELOPING ALONG AND JUST NORTH OF THE SURFACE FRONT...WITH UPPER LEVEL WINDS POTENTIALLY BLOWING LIGHT RAIN ANOTHER 30-50 MILES NORTH OF THE STORMS. NO SIGNIFICANT CHANGES HAVE BEEN MADE TO TEMPS OR WINDS. PREVIOUS DISCUSSION FROM 300 AM FOLLOWS... A POTENTIALLY INTERESTING FORECAST IS IN STORE FOR THE EASTERN CAROLINAS OVER THE NEXT 24 HOURS. A COLD FRONT CURRENTLY EXTENDING ALONG THE EASTERN EDGE OF THE NC PIEDMONT INTO CENTRAL SOUTH CAROLINA SHOULD PUSH OFF THE COAST BY MID MORNING WITH NORTH-NORTHEAST SURFACE WINDS ALLOWING A DRY CANADIAN AIRMASS TO BUILD SOUTHWARD. THIS IS A SHALLOW AIRMASS CHANGE...WITH WIND DIRECTIONS REMAINING WEST OR WEST-SOUTHWESTERLY AT AND ABOVE THE 850 MB LEVEL. THE FRONT WILL PUSH OUT JUST BEYOND THE GULF STREAM TONIGHT WITH STRENGTHENING LOW-LEVEL NORTHEAST FLOW DEVELOPING AS SURFACE PRESSURES RISE ACROSS THE MID-ATLANTIC REGION WITH HIGH PRESSURE BUILDING EASTWARD FROM THE MIDWEST. UP AT 500 MB AN UPPER DISTURBANCE DESCENDING INTO THE SOUTHERN APPALACHIANS THIS AFTERNOON IS EXPECTED TO CUT OFF TONIGHT OVER WESTERN SOUTH CAROLINA. THERE ARE A COUPLE CONCERNS WITH THE FORECAST WITHOUT A CLEAR ANSWER AT THIS EARLY HOUR. THE FIRST IS HOW MUCH MID-LEVEL CLOUD COVER HANGS AROUND TODAY AND WHAT IMPACT DOES IT HAVE ON TEMPERATURES? SATELLITE IMAGERY REVEALS A NARROW BAND OF THICK CLOUDS OVER CENTRAL AL/GA...MATCHING UP QUITE WELL WITH ANALYZED 700 MB RH MODEL FIELDS. BOTH THE 00Z NAM AND GFS ADVECT THIS MOISTURE ACROSS EASTERN SOUTH CAROLINA TODAY...LEADING ME TO BELIEVE THERE WILL BE TOO MUCH CLOUD COVER TO LET TEMPERATURES RISE ABOVE THE LOWER 80S. IN FACT MORE SUNSHINE UP IN THE LUMBERTON/ELIZABETHTOWN AREA WILL PROBABLY BALANCE OUT THE OVERALL COOLER AIRMASS TO PRODUCE LOWER 80S ACROSS THE ENTIRE FORECAST AREA TODAY. THE SECOND CONCERN IS WITH THE UPPER LOW CUTTING OFF TO OUR WEST TONIGHT HOW MUCH OVERRUNNING RAIN DEVELOPS? ISENTROPIC LIFT IS ANTICIPATED TO REMAIN WELL ABOVE THE FRONTAL INVERSION...PROBABLY NOT BEGINNING IN EARNEST UNTIL THE 310K THETA SURFACE WHICH WILL BE UP NEAR 600 MB. THE 00Z GFS IS THE MOST AGGRESSIVE WITH BRINGING RAIN ACROSS EASTERN SC LATE THIS AFTERNOON INTO TONIGHT. GIVEN THE RELATIVELY WEAK WIND FIELDS PROGGED TO EXIST BELOW 600 MB IT IS HARD TO BELIEVE THERE WILL BE SIGNIFICANT ADVECTION OF CONVECTIVE SHOWERS ONSHORE EITHER. MY HIGHEST POP FORECASTS ARE LIMITED TO COASTAL SOUTH CAROLINA IN THE 40-50 PERCENT RANGE...WITH 15-30 PERCENT CHANCES ELSEWHERE. CLOUDS WILL INHIBIT RADIATIONAL COOLING TONIGHT...HOWEVER INCREASING NORTHEAST WINDS WILL ADVECT IN SIGNIFICANTLY COOLER AIR LEADING TO LOWS FALLING INTO THE UPPER 50S FROM ELIZABETHTOWN THROUGH DILLON AND DARLINGTON. LOWER 60S ARE EXPECTED ALONG THE COAST...EXCEPT FOR SOME MID 60S ALONG THE COAST NEAR SOUTHPORT AND GEORGETOWN.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... AS OF 300 AM MONDAY...THE FIRST FULL OF DAY OF FALL ON TUESDAY BEGINS WITH COLD FRONT POSITIONED JUST OFFSHORE...AS LARGE CANADIAN HIGH PRESSURE CENTERED OVER THE OH VLY RIDGES DOWN INTO THE CAROLINAS. ALTHOUGH THIS FRONT WILL BE OFFSHORE...THERE IS SOME UNCERTAINTY INTO JUST HOW FAR FROM THE COAST IT WILL GET BEFORE STALLING. THE UPPER ENERGY DRIVING THIS FRONT WILL WEAKEN AND BECOME BROAD OVERHEAD...STALLING AS A GREAT LAKES AREA RIDGE BLOSSOMS FROM THE SOUTHWEST. THIS CREATES A DIFFICULT FORECAST BECAUSE...ALTHOUGH MOST OF THE AREA WILL BE DRY TUESDAY...THE BROAD LOW OVERHEAD WILL INTERACT WITH THE SURFACE BOUNDARY TO CAUSE WIDESPREAD RAIN SHOWERS LURKING JUST OFF THE COAST...POSSIBLY ALONG THE COAST. WINDS THROUGH THE LOWEST 600MB OF THE COLUMN WILL VEER TO THE E/NE...LIKELY DRIVING THE BOUNDARY /COASTAL TROUGH/ BACK TOWARDS SHORE. THIS CREATES INCREASING SHOWER CHANCES ON WEDNESDAY...HIGHEST POP NEAR THE COAST. ATTM IT LOOKS LIKE THE HEAVIEST RAIN WILL REMAIN JUST OFFSHORE WITH ONLY LIGHT RAIN ANTICIPATED WITHIN THE CWA. HOWEVER...THIS WILL NEED TO BE MONITORED CLOSELY AS A VERY SHARP GRADIENT WILL EXIST BETWEEN HEAVY RAIN AND JUST LIGHT SHOWERS. TEMPS BOTH TUESDAY AND WEDNESDAY WILL BE BELOW NORMAL FOR LATE SEPTEMBER...WITH HIGHS IN THE MID/UPR 70S BOTH DAYS. HOWEVER...TUESDAY WILL HAVE NOTICEABLY MORE SUNSHINE THAN WEDNESDAY. LOWS TUESDAY NIGHT WILL FEATURE WIDESPREAD 50S...WITH SOME LOW 50S POSSIBLE WEST OF I-95. MINS WEDNESDAY NIGHT WILL BE SEVERAL DEGREES WARMER THANKS TO INCREASING ONSHORE FLOW. && .LONG TERM /THURSDAY THROUGH SUNDAY/... AS OF 300 AM MONDAY...VERY UNSETTLED THE FIRST HALF OF THE PERIOD AS THE PATTERN TAKES ON MORE OF A WINTER-LIKE FEEL...BUT IMPROVEMENTS ARE EXPECTED FOR THE WEEKEND. DIFFUSE UPPER LOW OVERHEAD THURSDAY WILL WORK IN TANDEM WITH A COASTAL TROUGH JUST OFFSHORE TO PRODUCE WIDESPREAD CLOUDS AND RAIN THURSDAY/FRIDAY. STILL UNCERTAINTY EXISTING IN EXACTLY HOW THE PATTERN WILL EVOLVE LATE-WEEK...AS THERE WILL BE A VERY SHARP GRADIENT BETWEEN EXTREMELY HIGH PWATS LURKING JUST OFFSHORE...AND MUCH MORE TYPICAL PWATS TOWARDS I-95. THE DIFFERENCE IS DUE TO THE COASTAL TROUGH WHICH WILL BE SLOWLY ADVECTING WESTWARD ON DEEP EASTERLY FLOW...PUSHING THE BETTER RAIN CHANCES TOWARDS THE COAST. WPC GRAPHICS SHOW THIS GRADIENT WELL...WITH ABOUT 4 INCHES OF QPF CENTERED JUST OFF THE CAPE FEAR COAST...BUT LESS THAN ONE-QUARTER INCH IN THE WESTERN ZONES. THE ECMWF IS ONE OF THE MORE PESSIMISTIC MODELS...BUT IS FAVORED BY WPC...AND THE TREND HAS BEEN FOR A MORE UNSETTLED THU/FRI PERIOD. WILL BUMP POP TO MDT CHC FOR LATE WEEK AND CONTINUE WITH HIGHS BELOW CLIMO BUT LOWS SLIGHTLY ABOVE. THE COASTAL TROUGH WILL BEGIN TO ERODE SATURDAY AS RIDGING FINALLY DISPLACES THE UPPER TROUGH...BECOMING MORE PRONOUNCED AT THE END OF THE PERIOD. THIS SUGGESTS DRYING FOR THE WEEKEND...ESPECIALLY AT THE MID-LEVELS...AND RAIN CHANCES WILL TAKE A DECIDEDLY DOWNWARD TURN DURING THE WKND...ALTHOUGH IT MAY BE SLOW. IMPROVING CONDITIONS WILL ALSO ALLOW TEMPS TO RECOVER TO SEASONABLE NORMS. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... AS OF 06Z...HIGH CONFIDENCE OF VFR EARLY THIS MORNING AS WINDS REMAIN ELEVATED AS A COLD FRONT MOVES THROUGH. WINDS WILL SHIFT TO THE NW 06-07Z AT KFLO/KLBT AND 09-10Z AT THE COASTAL TERMINALS. CIGS SHOULD REMAIN AT OR ABOVE 4K. ISOLATED LIGHT SHOWERS POSSIBLE WITH FROPA THUS WILL CONTINUE TO MENTION VCSH. SHOWERS SHOULD DISSIPATE AFTER SUNRISE AS VFR CONTINUES. THICKNESS PATTERNS SUGGEST ACTUAL COLD AIR WILL LAG QUITE AWAYS BEHIND THE FRONT. A SLUGGISH PRESSURE PATTERN MAY CAUSE WIND DIRECTIONS TO BECOME VARIABLE AT THE COASTAL TERMINALS BY LATE MORNING OR IN THE AFTERNOON. WEAK LOW LEVEL CONVERGENCE AT THE COASTAL TERMINALS ALONG WITH INCREASING PVA MAY CAUSE MORE SIGNIFICANT SHOWER DEVELOPMENT IN THE AFTERNOON. STILL APPEARS VFR WILL CONTINUE AT THE COASTAL TERMINALS IN THE AFTERNOON. DURING THE EVENING WINDS WILL BECOME N-NE TERMINAL-WIDE AS HIGH PRESSURE BUILDS IN. EXTENDED OUTLOOK...VFR THROUGH WEDNESDAY. RAIN DEVELOPING THURSDAY AFTERNOON INTO FRIDAY WITH POSSIBLE MVFR/IFR CONDITIONS. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... AS OF 640 AM MONDAY...THE FRONT IS RUNNING ABOUT TWO HOURS SLOWER THAN EARLIER MODELS INDICATED. IT HAS CROSSED INTERSTATE 95 AND SHOULD BE AT THE BEACHES AROUND 9 AM. PREVIOUS DISCUSSION FROM 300 AM FOLLOWS... A COLD FRONT CURRENTLY EXTENDING ACROSS THE INTERIOR CAROLINAS WILL MOVE EAST AND OFF THE COAST LATER THIS MORNING. WESTERLY WINDS WILL TURN NORTH-NORTHEASTERLY BEHIND THE FRONT...WITH A SUBSTANTIAL INCREASE IN WIND SPEEDS EXPECTED TONIGHT AS HIGH PRESSURE OVER THE MIDWEST MOVES INTO THE MID- ATLANTIC STATES. SEAS CURRENTLY RANGING FROM 3-5 FEET WILL DIMINISH THIS AFTERNOON IN THE LIGHTER WINDS BEHIND THE FRONT...BUT SHOULD BUILD AGAIN OVERNIGHT IN RESPONSE TO THE INCREASING NE WIND. WE COULD BE NEAR SMALL CRAFT ADVISORY THRESHOLDS BY DAYBREAK TUESDAY. SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... AS OF 300 AM MONDAY...COLD FRONT STALLED JUST OFFSHORE TUESDAY MORNING WILL REMAIN NEARLY STATIONARY THROUGH MID-WEEK AS HIGH PRESSURE RIDGES DOWN THE COAST. THIS PRODUCES A PINCHED GRADIENT OVER THE WATERS...AND PERSISTENT NE WINDS OF 15-25 KTS...WITH LITTLE FLUCTUATION...BOTH TUESDAY AND WEDNESDAY. THESE GUSTY NE WINDS WILL DRIVE WAVE HEIGHTS UP TO 4-6 FT FT TUESDAY...AND REMAIN THERE ON WEDNESDAY...WITH A NE WIND WAVE THE DOMINANT GROUP. A SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED DURING MUCH OF THE PERIOD...BUT HOISTING THE HEADLINE WILL WAIT UNTIL MORE CERTAINTY ABOUT THE TIMING CAN BE DETERMINED. ONCE THE SCA IS ISSUED...IT WILL LIKELY REMAIN IN EFFECT FOR QUITE SOME TIME. LONG TERM /THURSDAY THROUGH FRIDAY/... AS OF 300 AM MONDAY...THE EXTENDED WILL BE MUCH LIKE THE SHORT TERM...AS A STAGNANT PATTERN KEEPS A COASTAL TROUGH JUST OFFSHORE AND A HIGH PRESSURE WEDGE INLAND. THIS PRODUCES A PROLONGED PERIOD OF NE WINDS DUE TO A PINCHED GRADIENT...AND WINDS OF 15-25 KTS WILL BE COMMON LATE WEEK. THIS EXTENDED PERIOD OF GUSTY NE WINDS WILL KEEP WAVE HEIGHTS AT 4-6 FT PRETTY MUCH THE ENTIRE FORECAST PERIOD...AND A SMALL CRAFT ADVISORY WHICH WILL LIKELY BE HOISTED EARLIER IN THE WEEK...WILL BE NEEDED FOR MOST...IF NOT ALL...OF THE LONG TERM.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...NONE. && $$ SYNOPSIS...JDW NEAR TERM...TRA SHORT TERM...JDW LONG TERM...JDW AVIATION...TRA MARINE...TRA/JDW

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