Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 051803 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 203 PM EDT THU MAY 5 2016 .SYNOPSIS... DEEP LOW PRESSURE WILL WOBBLE SLOWLY EASTWARD OVER THE MIDATLANTIC REGION AND CAROLINAS THROUGH FRIDAY NIGHT... BRINGING UNSETTLED WEATHER. THIS LOW PRESSURE WILL MOVE NORTHEAST AWAY FROM THE AREA EARLY SATURDAY... BRINGING IMPROVING WEATHER FOR SATURDAY INTO SUNDAY. A COLD FRONT APPROACHING FROM THE NORTHWEST WILL STALL OUT NEAR THE VIRGINIA NORTH CAROLINA BORDER LATE SUNDAY INTO MONDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 245 AM THURSDAY... 1206 PM... QUICK UPDATE THIS MORNING TO HANDLE EVOLVING SYSTEM ACROSS NC AND VA. AS OF LATE MORNING THE UPPER LOW WAS LOCATED ACROSS FAR EASTERN TN AND SOUTHEAST KY PLACING CENTRAL IN A FAVORABLE REGION FOR PRIMARILY SHALLOW CONVECTION WITH A GOOD DEAL PRIMARILY SUB-SEVERE HAIL AND LOCALLY HEAVY RAIN. LATEST SPC SURFACE ANALYSIS SHOWS WEAK SURFACE BASED INSTABILITY IN AN AXIS STRETCHING FROM ROXBORO SOUTHEAST ACROSS THE TRIANGLE REGION INTO THE SOUTHERN PIEDMONT WITH SBCAPE VALUES RANGING ABOVE 500 J/KG IN THE SANDHILLS AND SOUTHERN PIEDMONT. DEEP LAYER SHEAR IS IMPRESSIVE AHEAD OF THE UPPER LOW RANGING FROM 40 TO 50 KTS FROM US 1 EAST. HAVE ADJUSTED POPS A BIT MORE FOR TODAY AND EXPANDED THE COVERAGE AND INCLUSION OF THUNDER. TEMPERATURES WILL BE COMPLICATED BUT HAVE GENERALLY ADJUSTED THEM DOWNWARD GIVEN PRECIPITATION AMOUNTS AND A SLIGHT DECREASE IN DEW POINTS. -BLAES PREVIOUS DISCUSSION... QUITE AN UNSETTLED PATTERN IS EXPECTED FOR THE NEXT 24-30 HRS... WITH A GREATER CHANCE OF PRECIP ESPECIALLY IN THE TRIANGLE AND TO THE NORTH AND EAST. THE LATEST SURFACE MAP SHOWS ONE FRONT AND LOW HEADING OFFSHORE WHILE ANOTHER FRONT AND LOW APPROACH FROM THE NW. THE MID-UPPER LEVEL VORTEX THAT WILL DRIVE OUR WEATHER FOR THE NEXT COUPLE OF DAYS IS CLEARLY NOTED ON WATER VAPOR IMAGERY OVER THE OH VALLEY AND IS POISED TO DRIFT SLOWLY SOUTHEAST TO A POSITION CENTERED OVER THE CAROLINAS TODAY... WITH MULTIPLE LOBES OF VORTICITY ROTATING ABOUT ITS CENTER. ONE SUCH WAVE IS NOW SWINGING THROUGH THE WRN PIEDMONT BRINGING A BROAD BUT BROKEN BAND OF SHOWERS INTO OUR WRN COUNTIES... FUELED IN PART BY STEEP MID LEVEL LAPSE RATES OF 6.8-7.0 C/KM ACTING ON ELEVATED PW AROUND 0.75 IN. MODELS INCLUDING CONVECTION-ALLOWING AND TRADITIONAL MODELS ALL SHOW UPSCALE GROWTH OF THIS PRECIP AS IT SHIFTS SLOWLY EASTWARD THROUGH CENTRAL NC... CULMINATING IN A BAND OF MODERATE TO HEAVY PRECIP PIVOTING OVER THE CENTRAL THEN NE CWA... SUPPORTED BY FOCUSED UPPER DIVERGENCE ATOP LOW LEVEL MASS CONVERGENCE ALONG A SURFACE TROUGH EXTENDING FROM THE JUST- OFFSHORE LOW BACK ACROSS ERN/NRN NC AND THROUGH CENTRAL VA... AS WELL AS WEAK INSTABILITY WITH DAYTIME HEATING... EXACERBATED BY MID LEVEL LAPSE RATES OF 6.5-7.5 C/KM AS THE LOW TRACKS OVER THE REGION. WITH PLENTIFUL LIFT AND MOISTURE... HAVE RAISED POPS ACROSS THE BOARD... STARTING WITH CHANCE POPS MAINLY IN THE WRN HALF EARLY THIS MORNING SPREADING EASTWARD AND TRENDING UP TO CATEGORICAL NE TAPERING TO GOOD CHANCE SOUTH AND WEST (FARTHER FROM THE BEST STACKED FORCING FOR ASCENT) FOR THE AFTERNOON INTO THE NIGHT. DESPITE THE MODEST INSTABILITY... THE STEEP LAPSE RATES STILL PRESENT A THREAT FOR A FEW STORMS... ALONG WITH SMALL HAIL... PARTICULARLY IN AND NEAR AREAS THAT SEE SOME HEATING THIS AFTERNOON. WHILE ANY INSTABILITY IS APT TO DECREASE AFTER NIGHTFALL... OTHER LIFT MECHANISMS PERSIST... INCLUDING MID LEVEL DPVA AS WAVES ROTATE AROUND THE LOW AND LOW LEVEL CONFLUENT FLOW ALONG THE PERSISTENT TROUGH... AND WILL MAINTAIN HIGH POPS THROUGH THE NIGHT... ESPECIALLY NE. SUCH AN EXTENDED PERIOD OF A FOCUSED MODERATE TO HEAVY RAIN OVER THE NE CWA WOULD BRING ABOUT CONCERN FOR FLOODING... HOWEVER FLASH FLOOD GUIDANCE IS RATHER HIGH HERE (2.5- 3.5" IN 3 HRS)... SUGGESTING MORE OF AN URBAN AND SMALL STREAM FLOOD THREAT. AS SUCH... WILL NOT ISSUE A FLASH FLOOD WATCH... BUT WILL KEEP A CLOSE EYE ON THIS POTENTIAL THROUGH TODAY. THICKNESSES WILL BE HELD DOWN BY CONSIDERABLE CLOUD COVER THROUGH MUCH OF THE DAY AND COLD AIR ADVECTION WITH PERIODS OF SHOWERS... SO EXPECT CHILLY WELL- BELOW- NORMAL HIGHS IN THE UPPER 50S TO LOWER 60S ALONG/NORTH OF HIGHWAY 64 WITH MID 60S SOUTH WHERE PRECIP WILL BE MORE PATCHY AND LIGHTER. LOWS TONIGHT IN THE MID 40S TO AROUND 50. -GIH && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... AS OF 310 AM THURSDAY... THE STACKED LOW PRESSURE WILL HOLD OVER ERN VA AND THE DELMARVA THROUGH FRI BEFORE THE SURFACE LOW WEAKENS AND THE LOW ALOFT WOBBLES NORTHWARD. WHILE LIFT-INDUCING FEATURES SUCH AS THE LOW LEVEL CONFLUENT FLOW AND UPPER DIVERGENCE ARE LIKELY TO BE WEAKER FRI WITH VERY MARGINAL INSTABILITY PREDICTED... THE SWATHS OF DPVA WILL CONTINUE AS WAVES SWING AROUND THE LOW CENTER... AND ONE VORTICITY MAX IN PARTICULAR DROPPING SE FROM THE OH VALLEY FRI WILL ONCE AGAIN LEAD TO STEEP MID LEVEL LAPSE RATES IN THE AFTERNOON OVER THE CAROLINAS... AS PW REMAINS QUITE HIGH AT 0.80-1.0". SEE NO REASON WHY WE WON`T SEE ANOTHER ROUND OF SCATTERED TO NUMEROUS SHOWERS AND PERHAPS A STORM OR TWO MAINLY IN THE AFTERNOON WITH HEATING... AND ESPECIALLY OVER THE NRN AND ERN CWA... WHERE LIFT AND MOISTURE WILL BE BEST. THIS ACTIVITY WILL DWINDLE AFTER NIGHTFALL WITH NOCTURNAL COOLING AND THE DEPARTURE OF THE MID LEVEL LOW WITH SUBSEQUENT RISING HEIGHTS AND DECREASING MOISTURE THROUGH THE COLUMN. WILL TREND POPS DOWN TO SLIGHTLY CHANCE NORTH AND EAST IN THE EVENING WITH NO POPS OVERNIGHT AND DECREASING CLOUDS. EXPECT HIGHS FRI FROM THE LOW 60S NORTH TO UPPER 60S SOUTH... AND LOWS FRI NIGHT IN THE UPPER 40S TO LOWER 50S. -GIH && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... AS OF 300 AM THURSDAY... SATURDAY AND SUNDAY: INTERESTING FORECAST FOR THE WEEKEND AS THE UPPER LEVEL LOW WILL BE WELL NORTH OF THE AREA WITH THE ASSOCIATED UPPER TROUGH MOVING OFF OF THE ATLANTIC COAST. BOTH OF THESE FEATURES ARE BEING USHERED ON BY A NEWLY DEVELOPING UPPER TROUGH OVER THE GREAT LAKES ON SATURDAY WHICH WILL QUICKLY DIG INTO NY AND NEW ENGLAND BY SUNDAY. THIS WILL PUSH A WEAK COLD FRONT THROUGH THE AREA EARLY SUNDAY MORNING ASSOCIATED WITH A SURFACE LOW OVER SOUTHERN QUEBEC. THIS WONT HOLD LONG HOWEVER AS THE UPPER TROUGH BECOMES NEGATIVELY TILTED...ALMOST PULLING THE SURFACE FRONT OFFSHORE AND THEN SURFACE HIGH PRESSURE OVER FLORIDA BUILDS NORTHWARD OVER CENTRAL NC. THE SENSIBLE WEATHER UPSHOT OF ALL OF THIS IS THAT DESPITE THE COLD FRONT MOVING THROUGH EARLY SUNDAY...TEMPERATURES ON SUNDAY AFTERNOON WILL ACTUALLY BE WARMER THEN ON SATURDAY. EXPECT MID 70S ON SATURDAY AFTERNOON BUT RISING TO AT LEAST THE LOW IF NOT MID 80S BY LATER IN THE AFTERNOON ON SUNDAY. ANY PRECIP CHANCES LOOK TO BE ACROSS THE NORTH ON SUNDAY MORNING WITH THE FRONT BUT ONLY SLIGHT CHANCES AT THIS TIME. CERTAINLY NOTHING TO DETER OUTDOOR PLANS AT THIS TIME. NIGHTTIME LOWS DURING THIS PERIOD IN THE UPPER 50S TO LOWER 60S. MONDAY THROUGH WEDNESDAY: A FAIRLY STRAIGHT FORWARD FORECAST FOR THE BEGINNING OF NEXT WEEK AS HIGH PRESSURE OVER THE WESTERN ATLANTIC WILL CONTROL THE WEATHER ON MONDAY...KEEPING CONDITIONS DRY AND WITH SOUTHERLY RETURN FLOW...FAIRLY WARM. ON TUESDAY...A RAGGED LOW PRESSURE SYSTEM OVER THE MISSISSIPPI VALLEY WILL GRADUALLY WORK EASTWARD. WHILE DETAILS REGARDING TIMING AND LOCATION HAVE YET TO BE RESOLVED...THE TREND IS THE SAME. PRECIPITATION CHANCES WILL INCREASE ON TUESDAY...WITH BEST CHANCES FOR ANY SHOWERS OR POTENTIALLY A THUNDERSTORM IN THE NORTHWEST PIEDMONT. BY WEDNESDAY...THE LOW IS EVEN MORE DISORGANIZED BUT WILL BE POSITIONED OVER NY AND THE MID ATLANTIC STATES...FURTHER INCREASING PRECIPITATION CHANCES WEDNESDAY AFTERNOON. THIS WOULD ALSO BE THE BEST CHANCE FOR THUNDER IN THE FORECAST BUT TOO FAR OUT TO TELL WHAT SEVERE CHANCES WOULD BE. RIGHT NOW...SEVERE PARAMETERS ARE NOT ALL THAT FAVORABLE FOR SEVERE WX...ESPECIALLY GIVEN THE LACK OF DYNAMICS AS THE UPPER JET BASICALLY DISSOLVES. HIGHS DURING THIS TIME IN THE LOW TO MID 80S WITH LOWS IN THE LOW TO MID 60S. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... AS OF 200 PM THURSDAY... WIDESPREAD ADVERSE AVIATION CONDITIONS ARE EXPECTED THIS AFTERNOON THROUGH EARLY FRIDAY MORNING. MVFR TO IFR CONDITIONS WILL DOMINATE ACROSS MUCH OF CENTRAL NC THROUGH TONIGHT. A STRONG UPPER LEVEL LOW PRESSURE SYSTEM WILL MOVE EAST ACROSS THE CAROLINAS THIS AFTERNOON AND TONIGHT AND THEN LIFT NORTH TO NEAR DELAWARE BY FRIDAY AFTERNOON. SEVERAL AREAS OR CLUSTERS OF SHOWERS AND EVEN FEW THUNDERSTORMS THIS AFTERNOON WILL ROTATE AROUND THE UPPER LOW THROUGH THE PERIOD. AN AREA OF WIDESPREAD RAIN ACROSS THE EASTERN PIEDMONT AND THE COASTAL PLAIN EARLY THIS AFTERNOON WILL PIVOT NORTH TOWARD EARLY EVENING WITH A LULL OVER MUCH OF THE AREA BEFORE ANOTHER AREA OF WIDESPREAD SHOWERS DROP SOUTH FROM SOUTHERN VA TONIGHT AND SPREADS EAST ACROSS THE AREA. SCATTERED THUNDERSTORMS ARE EXPECTED THROUGH EARLY THIS EVENING...MAINLY ACROSS THE EASTERN PIEDMONT...COASTAL PLAIN AND SANDHILLS INCLUDING KRDU/KRWI/KFAY. EVEN WITH THE LULL OR BREAKS IN THE RAIN TONIGHT...WIDESPREAD IFR CIGS AND MVFR/IFR VSBYS ARE EXPECTED. CIGS AND VSBYS WILL BEGIN TO IMPROVE DURING THE LATE MORNING FRIDAY WITH VFR CONDITIONS BECOMING MORE PROMINENT DURING THE AFTERNOON. LOOKING FURTHER AHEAD BEYOND 18Z FRIDAY... AVIATION CONDITIONS WILL CONTINUE TO IMPROVE ON FRIDAY AND FRIDAY NIGHT WITH JUST A SMALL CHANCE OF A SHOWER. OTHERWISE...MAINLY VFR CIGS AND VSBYS ARE EXPECTED. DESPITE PERIODS OF CLOUDINESS AND A SMALL THREAT OF A SHOWER...VFR CONDITIONS SHOULD PREVAIL OVER THE WEEKEND INTO MONDAY BEFORE THE NEXT STORM SYSTEM APPROACHES ON TUESDAY. -BLAES && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...BLAES/HARTFIELD SHORT TERM...HARTFIELD LONG TERM...RE AVIATION...BLAES

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