Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 280537 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 1237 AM EST SAT FEB 28 2015 .SYNOPSIS... HIGH PRESSURE WILL WEDGE DOWN THE COAST THIS WEEKEND. DRY BUT CHILLY WEATHER IS EXPECTED ON SATURDAY. RAIN CHANCES WILL INCREASE SUNDAY AS TEMPERATURES MODERATE. A COLD FRONT WILL CROSS THE AREA MONDAY ACCOMPANIED BY SHOWERS. SEASONABLE WEATHER IS EXPECTED TUESDAY BEFORE THIS FRONT LIFTS NORTH AS A WARM FRONT WEDNESDAY...BRINGING ONE DAY OF WELL ABOVE NORMAL TEMPERATURES. ANOTHER COLD FRONT WILL APPROACH WEDNESDAY NIGHT OR THURSDAY. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... AS OF 945 PM FRIDAY...SUBTROPICAL JET STREAM MOISTURE CONTINUES OVER THE COASTAL CAROLINAS...WITH UPSTREAM SATELLITE TRENDS INDICATING THE WESTERN EDGE OF THIS CLOUD DECK MAY NOT DRIFT OFFSHORE AFTER ALL. NORTHEAST WINDS ARE FIRMLY ESTABLISHED AT THE SURFACE... ALTHOUGH WIND SPEEDS HAVE YET TO RAMP UP WITH THE COLD AIR SURGE EXPECTED TO BEGIN AROUND MIDNIGHT. RECENT RUC AND HRRR MODEL TRENDS HAVE BEEN UPWARD WITH LOW TEMPERATURES TONIGHT AND I HAVE MADE UPWARD TWEAKS AT MOST LOCATIONS: 27-31 ACROSS SE NORTH CAROLINA AND 29-32 OVER NE SOUTH CAROLINA...WARMEST AT THE COAST. DISCUSSION FROM 630 PM FOLLOWS... ONLY MINOR CHANGES MADE TO THE NEAR TERM FORECAST THIS EVENING. THE LEADING EDGE OF A NE SURGE CURRENTLY DROPPING SOUTH ACROSS THE CHESAPEAKE BAY WILL REACH OUR AREA AFTER MIDNIGHT. THE BIGGEST QUESTION REMAINS HOW MUCH (IF ANY) LOW CLOUDINESS DEVELOPS IN THE NORTHEASTERLY LOW-LEVEL FLOW BEHIND THE SURGE? 18Z NAM AND GFS MODEL OUTPUT SHOW ENOUGH MOISTURE IN THE LOWEST 1000 FEET OF THE ATMOSPHERE DEVELOPING OVERHEAD BETWEEN 09-12Z (4-7 AM) TO PRODUCE LOW CLOUDS. A LOCAL RULE OF THUMB IS TO LOOK AT CONVERGENCE/DIVERGENCE WITHIN THE MOISTURE-BEARING LAYER TO HELP DIAGNOSE THE POTENTIAL FOR LOW CLOUDINESS -- AND ALL MODELS SHOW DIVERGENCE ON THE 1000 MB SURFACE TONIGHT. FOR THIS REASON I HAVE REDUCED THE AMOUNT OF FORECAST CLOUDINESS LATE TONIGHT... ANTICIPATING MAINLY 300 MB CIRRUS MOISTURE. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/... AS OF 3 PM FRIDAY...DEVELOPING COLD WEDGE THIS WEEKEND WILL KEEP SKIES CLOUDY AND HOLD HIGHS 10 TO 20 DEGREES BELOW CLIMO. WEAKLY AMPLIFIED MID LEVEL PATTERN WILL CONTINUE TO PUMP MOISTURE INTO THE SOUTHEAST. SOUTHWEST FLOW ALOFT COMBINED WITH LOW LEVEL NORTHEAST FLOW WILL MAINTAIN WEAK ISENTROPIC LIFT FOR MUCH OF THE PERIOD BUT LOW LEVEL DRY AIR HOLDING ON SAT AND MOST OF SAT NIGHT WILL KEEP THE REGION DRY FOR THE FIRST HALF OF THE WEEKEND. LOW LEVELS MOISTEN UP SUN MORNING WITH LIGHT RAIN SPREADING OVER THE AREA AS COASTAL TROUGH DEVELOPS OFFSHORE. LATER SUN MID LEVEL RIDGE EXPANDING NORTH FROM THE GULF OF MEXICO STARTS TO WEAKEN THE WEDGE...LESSENING ISENTROPIC LIFT. WEDGE COMPLETELY BREAKS DOWN SUN NIGHT WITH LIGHT WESTERLY FLOW DEVELOPING AFTER MIDNIGHT. ALTHOUGH NORTHERLY FLOW CONTINUES AT THE SURFACE DURING SUN THERE WILL BE SOME MODEST WARM ADVECTION JUST ABOVE THE BOUNDARY LAYER. THIS WILL HELP PUSH HIGHS ON SUN CLOSER TO CLIMO...THOUGH TEMPS WILL ULTIMATELY FALL 5 TO 10 DEGREES SHORT. CLOUD COVER WILL HELP KEEP LOWS NEAR FREEZING SAT NIGHT. WARM ADVECTION ALONG WITH CLOUDS WILL KEEP LOWS NEAR CLIMO SUN NIGHT. && .LONG TERM /MONDAY THROUGH FRIDAY/... AS OF 330 PM FRIDAY...COLD FRONT WILL MAKE ITS WAY OFF SHORE MONDAY AS HIGH PRESSURE BUILDS DOWN FROM THE NORTHWEST TO NORTH. DEEPER WESTERLY FLOW EARLY MONDAY WILL BECOME NW AS SHORTWAVE MOVES OFF TO THE E-NE THROUGH LATE MONDAY. THEREFORE...INITIALLY THE DOWNSLOPE FLOW AND SOME BREAKS OF SUNSHINE SHOULD PUSH TEMP UP AROUND 60 ON MONDAY. BY LATER ON MONDAY A DEEPER NW FLOW WILL INCREASE CAA BRINGING 850 TEMPS FROM CLOSE TO 10C EARLY MON DOWN TO 4 C BY TUES MORNING. THE WINDS WILL SHIFT AROUND BECOMING MORE NORTHERLY OVERNIGHT AND MORE ON SHORE BY TUES AFTN. INCREASING CLOUD COVER AND WINDS MON NIGHT SHOULD KEEP TEMPS ABOVE NORMAL. A RIDGE IN THE MID TO UPPER LEVELS WILL PUSH UP FROM THE GULF MON NIGHT INTO TUES AND WILL SHARPEN AS TROUGH DIGS DOWN THROUGH THE MID WEST BY WED. AT THE SAME TIME THE SFC HIGH TO THE NORTH WILL MOVE OFF SHORE THROUGH TUES AND RIDGE TO THE SOUTH WILL HELP PUSH COLD FRONT BACK NORTH AS WARM FRONT. A BRIEF WEDGE WILL DEVELOP WITH INCREASING ISENTROPIC LIFT AS WARM FRONT MOVES NORTH INTO SHALLOW RELATIVELY COOLER AIR IN PLACE ON TUES. EXPECT CLOUDS AND CHC OF PCP ON TUES AS WARM FRONT LIFTS NORTH. WILL KEEP A LARGER TEMP RANGE IN TIGHTENED GRADIENT BETWEEN COOL TEMPS TO THE NORTH AND WARMER TEMPS TO THE SOUTH ON TUES BEFORE WARM FRONT LIFTS BY END OF DAY. TUES NIGHT WILL HAVE NEAR STEADY OR RISING TEMPS IN WAA BEHIND FRONT. COASTAL CAROLINAS WILL BE IN WARM AND MOIST AIR MASS ON WED AHEAD OF APPROACHING COLD FRONT. TEMPS SHOULD SOAR INTO THE 70S MOST PLACES EXCEPT CLOSER TO THE COAST WHERE COOLER OCEAN TEMPS WILL KEEP THE AIR COOLER. ALTHOUGH CLOUDS WILL LIMIT WARMING...SOME BREAKS MAY PUSH TEMPS HIGHER IN A FEW PLACES. ECMWF IS MUCH SLOWER WITH COLD FRONT WHILE GFS BRINGS IT THROUGH BY MIDNIGHT WED NIGHT. FOR NOW WILL HEDGE TOWARD SLOWER FROPA AND KEEP TEMPS WARMER WED NIGHT AND WILL BRING FRONT THROUGH EARLIER ON THURS WITH TEMPS COOLING IN CAA THROUGH THURS INTO FRI. IF FRONT COMES EARLIER THAN SHOWERS WILL BE MORE WIDESPREAD ON WED AFTN AND EVENING. OVERALL EXPECT INCREASING SHOWERS AHEAD OF FRONT. EXPECT TEMPS BELOW NORMAL AGAIN LATE THURS INTO FRI AS COLD AND DRY HIGH PRESSURE BUILDS IN. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... AS OF 06Z...VFR EXPECTED THROUGH THE VALID TAF PERIOD AS HIGH PRESSURE CONTINUES TO BUILD IN...WITH POSSIBLE MVFR ALONG THE COAST TOWARDS THE END OF THE PERIOD. LATEST SATELLITE IMAGERY DEPICTS A SWATH OF SCT HIGH CLOUDS ACROSS THE AREA. THIS WILL PERSIST THROUGH THE OVERNIGHT HOURS AND ALLOW FOR VFR TO PREVAIL WITH LIGHT NORTHEAST WINDS. AFTER DAYBREAK...EXPECT A GRADUAL TIGHTENING OF THE PRESSURE GRADIENT WHICH WILL BRING AN INCREASE IN NORTHEAST WINDS...SUSTAINED AOB 15 KTS AND GUSTS UP TO AROUND 20 KTS. MOISTURE WITHIN THE ATMOSPHERIC COLUMN IS FORECAST TO INCREASE AS WELL YIELDING INCREASING MID TO HIGH CLOUDS DURING THE DAYLIGHT HOURS TODAY. INTO THE EVENING HOURS...THERE IS THE POSSIBILITY OF LOWERING CIGS ALONG THE COAST WHICH COULD CREATE MVFR. EXTENDED OUTLOOK...MVFR/IFR POSSIBLE LATE SUNDAY THROUGH TUESDAY AS A WEDGE SETS UP. WINDY WEDNESDAY WITH POSSIBLE SHOWERS WEDNESDAY NIGHT. OTHERWISE EXPECT VFR. && .MARINE... .NEAR TERM /THROUGH TONIGHT/... AS OF 945 PM FRIDAY...WINDS AND SEAS ARE RAMPING UP MORE SLOWLY THAN ANTICIPATED...DELAYING THE ONSET OF SMALL CRAFT ADVISORY CONDITIONS. UPSTREAM OBSERVATIONS ACROSS THE OUTER BANKS AND NORTHEASTERN NORTH CAROLINA CONTINUE TO SUPPORT THE IDEA OF STRONGER WINDS MOVING INTO THE AREA OVER THE NEXT FEW HOURS. THERE IS LITTLE SPREAD IN MODEL GUIDANCE LENDING HIGH CONFIDENCE THAT WE WILL EVENTUALLY SEE THESE DETERIORATING CONDITIONS DEVELOP. DISCUSSION FROM 630 PM FOLLOWS... NO SIGNIFICANT CHANGES ARE NEEDED TO THE FORECAST WITH THIS EARLY-EVENING UPDATE. FORECAST WIND SPEEDS HAVE BEEN REDUCED BY 3-5 KNOTS BASED ON OBSERVATIONS THROUGH THE EVENING...WITH INCREASING SPEEDS EXPECTED OVERNIGHT AS THE PRESSURE GRADIENT TIGHTENS UP ON THE SOUTH EDGE OF HIGH PRESSURE. SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... AS OF 3 PM FRIDAY...SURFACE HIGH WEDGING DOWN THE EAST COAST WILL MAINTAIN A PINCHED GRADIENT OVER THE WATERS SAT AND SAT NIGHT. NORTHEAST FLOW WILL BE SOLIDLY IN THE 20 TO 25 KT RANGE WITH SEAS 4 TO 8 FT SAT. ONLY EXCEPTION WILL BE LOCATIONS WHERE NORTHEAST FLOW IS OFFSHORE. IN THESE LOCATIONS NEAR SHORE SEAS WILL RUN 1 TO 3 FT. GRADIENT STARTS TO RELAX LATE SAT NIGHT AS COASTAL TROUGH TAKES SHAPE AND HIGH STARTS TO WEAKEN. WINDS DROP UNDER 20 KT EARLY SUN MORNING AND BY AFTERNOON WILL BE 10 KT OR LESS. REDUCTION IN NORTHEAST FLOW WILL ALLOW SEAS TO DROP AND BY DAYBREAK SUN SEAS SHOULD BE 3 TO 5 FT AND 2 TO 4 FT BY THE END OF THE PERIOD. LONG TERM /MONDAY THROUGH TUESDAY/... AS OF 300 AM FRIDAY...A COLD FRONT WILL DROP TOWARDS...AND THEN ACROSS...THE WATERS DURING MONDAY PRODUCING VARIABLE WINDS THAT WILL VEER FROM SW EARLY MONDAY...TO NE BY TUESDAY MORNING. THE GRADIENT REMAINS RATHER WEAK DURING THIS TIME HOWEVER...SO SPEEDS WILL BE LESS THAN 15 KTS THROUGH THE DAY. THIS FRONT WILL STALL SOUTH OF THE WATERS THE FIRST HALF OF TUESDAY...MAINTAINING THE NE WINDS...BEFORE LIFTING RAPIDLY BACK NORTH AS A WARM FRONT LATE TUESDAY. WINDS WILL AGAIN VEER THROUGH HALF THE COMPASS...BECOMING SW AND RISING TO 15-20 KTS LATE. SEAS OF 2-4 FT WILL BE COMMON MONDAY AND THE FIRST HALF OF TUESDAY...ALTHOUGH COMPRISED BY A VARIETY OF WIND WAVES WHICH WILL FOLLOW THE PRIMARY WIND DIRECTION. THIS WILL LIKELY CREATE PERIODS OF CONFUSED WAVE STATES DURING MONDAY AND TUESDAY. LATE TUESDAY SEAS BUILD TOWARDS 6 FT...AND AN SCA MAY BE REQUIRED AT THE END OF THE PERIOD. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 5 AM EST SUNDAY FOR AMZ250-252-254-256. && $$ NEAR TERM...TRA SHORT TERM...III LONG TERM...RGZ AVIATION...SGL/31

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