Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 010707 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 305 AM EDT MON SEP 1 2014 .SYNOPSIS...THE REGION WILL REMAIN UNDER THE INFLUENCE OF HIGH PRESSURE THROUGH MIDWEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 305 AM MONDAY... BERMUDA HIGH PRESSURE WILL CONTINUE TO SUPPLY A WARM AND HUMID SOUTHERLY FLOW TODAY...WITH WEAK SOUTHWESTERLY FLOW ALOFT. THE H85 THERMAL RIDGE...WITH TEMPS AROUND 20C...SHIFTS OVER THE PIEDMONT...AND LOW-LEVEL THICKNESSES ARE FORECAST TO START OUT AROUND 1420M...ABOUT 10M HIGHER THAN SUNDAY MORNING. STATISTICAL AGREEMENT IS IN PRETTY GOOD AGREEMENT WITH MID 90S AROUND ALL OF CENTRAL NC. THE LEE/THERMAL TROUGH SHOULD SHARPEN AND DEWPOINTS SHOULD MIX OUT MORE IN THE WEST WITH A LITTLE MORE WESTERLY WIND...BUT TO THE EAST DEWPOINTS WILL BE IN THE UPPER 60S AND LOWER 70S...WHICH WILL PUSH HEAT INDICES UP AROUND 100 DEGREES. A WEAK WAVE OVER WEST VIRGINIA..NOTED IN WATER VAPOR IMAGERY THIS MORNING...SHOULD PASS OFF TO THE NORTH OF THE AREA TODAY...LEAVING THE SEABREEZE AND/OR DIFFERENTIAL HEATING AS THE MAIN TRIGGERS FOR CONVECTION THIS AFTERNOON. WILL INCLUDE A CHANCE POP ACROSS THE SANDHILLS AND SOUTHERN COASTAL PLAIN WHERE MODEST MLCAPE OF 1500 J/KG IS FORECAST TO DEVELOP. OTHERWISE JUST A SLIGHT CHANCE ACROSS THE WEST. CONVECTION WILL BE DIURNALLY DRIVEN AND WILL COME TO AN END EARLY THIS EVENING. STRATUS WILL BE POSSIBLE AGAIN..WITH GUIDANCE AGAIN POINTING TO THE COASTAL PLAIN. LOWS IN THE UPPER 60S AND LOWER 70S. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... AS OF 303 PM SUNDAY... A WEAK SHEAR AXIS...AN EXTENSION OF THE LOW AMPLITUDE SHORTWAVE TROUGH MOVING THROUGH THE NORTHERN MID-ATLANTIC STATES/NORTHEAST US...IS FORECAST TO CROSS EASTERN PORTIONS OF THE FORECAST AREA DURING PEAK AFTERNOON HEATING. THIS WEAK SUPPORT ALOFT COUPLED WITH MESOSCALE FORCING ALONG THE INLAND RETREATING SEA BREEZE MAY RESULT IN SLIGHTLY BETTER COVERAGE/POPS ACROSS THE COASTAL PLAIN AND SANDHILLS REGION WITH ISOLATED POPS ELSEWHERE AS UPPER RIDGE ALOFT LOOMS CLOSE BY. ANY CONVECTION SHOULD DIMINISH AFTER SUNSET. THE BIGGER STORY WILL BE THE HEAT AS LOW-LEVEL THICKNESSES CLIMB ANOTHER 10 METERS TO AROUND 1435M AND H8 TEMPS WARMING TO 21C...WHICH SHOULD EQUATE TO AT LEAST ANOTHER 2 TO 3 DEGREE INCREASE FROM SUNDAY`S HIGH TEMPS. HIGHS 93 TO 97 WITH HEAT INDICES OF 100 TO 103 ACROSS THE SANDHILLS AND COASTAL PLAIN. WILL HIGHLIGHT THESE +100 F HEAT INDICES IN THE HAZARDS WEATHER OUTLOOK(HWO). LOWS MONDAY NIGHT 70 TO 75. FOR TUE/TUE NIGHT: A PROMINENT MID LEVEL TROUGH CROSSES QUEBEC/ST LAWRENCE VALLEY AND THE NORTHEAST STATES DURING THIS PERIOD... ACCOMPANIED BY A SURFACE COLD FRONT. THE SOUTHERN PORTION OF THIS TROUGH MERELY BRUSHES ACROSS VA/NC... AND WHILE A SHARPENING OF THE LEE SURFACE TROUGH IS ANTICIPATED... THE FRONT ITSELF IS LIKELY TO HOLD TO OUR NORTH... STRETCHING WEST-EAST... ALTHOUGH THE 850 MB TROUGH IS EXPECTED TO SHIFT EAST ACROSS CENTRAL NC. SOUTHWESTERLY JETTING UP TO 20 KTS AHEAD OF THIS 850 MB TROUGH (AND ASSOCIATED LOW LEVEL MOISTURE POOLING) AND MINOR MID LEVEL HEIGHT FALLS (JUST 10-20 M) SHOULD HELP FUEL SCATTERED LATE AFTERNOON & EVENING STORMS. THE MOST WIDESPREAD AND STRONGEST STORMS SHOULD BE TO OUR NORTH BENEATH THE RIGHT ENTRANCE REGION OF THE UPPER JET CORE... AND WHERE MID LEVEL FLOW IS FASTER. BUT PW WILL BE WELL ABOVE NORMAL... PROJECTED TO BE IN THE 1.7-1.9" RANGE PLACING IT ABOVE THE 75TH PERCENTILE... AND STEERING FLOW WILL BE WEAK... SO ANY SHOWERS/STORMS MAY BE SLOW- MOVING WITH HEAVY RAIN. AND WITH THE GFS MUCAPE REACHING 1500-2500 J/KG OVER MUCH OF CENTRAL NC... A STRONG TO SEVERE PULSE STORM OR TWO CAN`T BE RULED OUT. THICKNESSES OF MORE THAN 20 M ABOVE NORMAL WILL EQUATE TO STEAMY HIGHS IN THE MID 90S... WITH LOWS IN THE LOW TO MID 70S. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... AS OF 250 AM MONDAY... A HOT SUB-TROPICAL RIDGE OVER THE SOUTHEAST WILL WAX AND WANE THROUGHOUT THE FORECAST PERIOD. AFTER PEAKING OVER THE SE EARLY THIS WEEK...THE RIDGE WILL BRIEFLY RETREAT WEST AND YIELD TO A GENERALLY E-W ORIENTED MID LEVEL SHEAR AXIS FORECAST TO DRIFT SOUTH INTO THE CAROLINAS WED-THU...BEFORE EXPANDING NORTHWARD ONCE AGAIN...INTO THE OH VALLEY AND MIDDLE ATLANTIC...FRI-SAT. MEDIUM RANGE ENSEMBLE GUIDANCE SUGGESTS THIS TREND WILL CONTINUE INTO NEXT WEEK...WITH BRIEF WEAKENING OF THE SUB-TROPICAL RIDGE SUN-MON...AT THE BASE OF A PROGRESSIVE NORTHERN STREAM TROUGH FORECAST TO CROSS SE CANADA... ONLY TO RE-EXPAND THROUGH MID WEEK. THE EBB AND FLOW OF THE PATTERN ALOFT...AND ASSOCIATED PERIODIC RELAXATION OF THE SUB-TROPICAL RIDGE...WILL ALLOW A PAIR OF COLD FRONTS TO SETTLE INTO NC - ONE WED INTO THU AND THE OTHER SAT NIGHT- SUN. BOTH MODEST COOLING AND ABOVE AVG PRECIPITATION CHANCES WILL OCCUR DURING THESE TIMES...IN CONTRAST TO OTHERWISE HOT CONDITIONS IN THE LOWER TO MIDDLE 90S...WITH DIURNALLY; PIEDMONT, AND SEA- BREEZE-DRIVEN CONVECTION. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... AS OF 130 AM MONDAY... SOUTHERLY FLOW CONTINUES AROUND THE BERMUDA HIGH...WHICH WILL LIKELY LEAD TO THE DEVELOPMENT OF STRATUS AGAIN LATE TONIGHT. THE NC COASTAL PLAIN IS THE FAVORED AREA FOR MVFR TO POSSIBLY IFR CEILINGS...ESPECIALLY FROM KFAY NORTH TO KRWI AFTER 08Z. VFR CONDITIONS ARE EXPECTED TO RETURN AFTER SUNRISE...WITH ISOLATED SHOWERS/STORMS POSSIBLE THIS AFTERNOON...WITH THE BEST CHANCE AT KFAY AFTER 18Z. OUTLOOK... BRIEF RESTRICTIONS IN DIURNAL CONVECTION ARE POSSIBLE EACH AFTERNOON...WITH RESTRICTIONS IN LOW CLOUDS AND FOG DURING THE PRE-DAWN MORNING HOURS. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...SEC NEAR TERM...BLS SHORT TERM...CBL LONG TERM...MWS AVIATION...SEC/BLS

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