Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 271808 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 208 PM EDT SUN JUL 27 2014 .SYNOPSIS...A SURFACE TROUGH WILL PERSIST OVER THE CAROLINAS TODAY. A STRONG COLD FRONT WILL CROSS THE AREA ON MONDAY...BRINGING NOTICEABLY COOLER AND LESS HUMID AIR INTO THE AREA. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1230 PM SUNDAY... MCV AND OUTFLOW-RELATED ASCENT...AND ASSOCIATED MAINTENANCE OF STRONG STORMS (WITH 40-45 KTS SAMPLED NEAR THE JOHNSTON/WAYNE CO BORDER BY KRAX RECENTLY)...HAVE MOVED QUICKLY ACROSS AND EAST OF THE RAH CWFA DURING THE PAST SEVERAL HOURS...AND WILL MOVE TO THE COAST THROUGH AROUND 20Z PER NEAR TERM NWP GUIDANCE. ANOTHER NW TO SE ORIENTED ARC OF SHOWERS AND STORMS HAS DEVELOPED IN THE WAKE OF THE MCV-RELATED STORMS...IN A ZONE OF QG FORCING FOR ASCENT...FORCED BY BOTH LOW LEVEL WAA AS WELL AS HEIGHT FALLS DOWNSTREAM OF AN UNSEASONABLY DEEP UPPER LOW APPROACHING FROM THE UPPER MIDWEST. SOME OF THIS TRAILING...WEAKER CONVECTION WILL BRUSH THE NORTHERN PIEDMONT AND NORTHERN COASTAL PLAIN THROUGH EARLY AFTERNOON. OTHERWISE...SATELLITE IMAGERY SUGGESTS THAT INITIALLY CONSIDERABLE MID-HIGH CLOUD WILL THIN AND PROVIDE FOR A FEW HOUR PERIOD OF STRONG HEATING TO DEVELOP FROM THE WESTERN CAROLINAS...COINCIDENT WITH THE ARRIVAL OF THE LEADING EDGE OF HOT/22C 12Z-OBSERVED H85 TEMPS AT KBNA. TEMPERATURES SHOULD CONSEQUENTLY HAVE AN OPPORTUNITY TO REBOUND INTO THE LOWER TO MIDDLE 90S OVER AT LEAST THE SOUTHWEST HALF OF THE FORECAST AREA. TO THE NORTHEAST/OVER THE NE PIEDMONT AND NORTHERN COASTAL PLAIN...TEMPERATURES ARE APT TO NOT CLIMB AS READILY/TO AROUND 90 DEGREES OR SO...OWING TO BOTH THE LATER ARRIVAL OF THE AFOREMENTIONED PLUME OF H85 HEAT (AFTER PEAK DIURNAL HEATING) AND LINGERING DIABATIC EFFECTS FROM EARLIER CONVECTION. IN FACT...THE CONFIGURATION OF THE WAA REGIME DEVELOPING FROM THE WEST AND EARLIER RAIN-COOLED AIR WILL FAVOR THE DEVELOPMENT OF A NW TO SE-ORIENTED OUTFLOW BOUNDARY/EFFECTIVE FRONT FROM THE TN VALLEY SOUTHEASTWARD ACROSS SOUTHERN VA/NORTHERN NC. IF SUCH A BOUNDARY DEVELOPS IT WILL SERVE TO ENHANCE WHAT NEAR TERM GUIDANCE SUGGESTS WILL BE ALREADY STRONG LOW LEVEL SHEAR IN THE 250-400 MS/S2 RANGE CENTERED OVER SOUTHSIDE VA AND NORTH-CENTRAL NC...FROM JUST PRIOR TO SUNSET THROUGH MIDNIGHT. MID-LEVEL/DEEP LAYER WINDS WILL BE EQUALLY IMPRESSIVE...AS THE EXIT REGION OF AN UPSTREAM MID LEVEL JET AT THE BASE OF THE UPPER MID WEST UPPER LOW EMERGES EAST OF THE CENTRAL APPALACHIANS AND STRENGTHENS KGSO AND KRNK 12Z-OBSERVED MID LEVEL FLOW OF ALREADY RESPECTABLE 35-40 KTS...INTO THE 45-55 KT RANGE THIS EVENING. THE STRONGLY SHEARED ENVIRONMENT WILL SUPPORT A CONDITIONAL PROBABILITY OF SEVERE THUNDERSTORMS OVER CENTRAL NC...PARTICULARLY FROM LATE THIS AFTERNOON THROUGH MIDNIGHT. WHETHER OR NOT STORMS INDEED DEVELOP AND INTERACT WITH THE FAVORABLE SHEAR PROFILES DURING THAT TIME REMAINS HIGHLY UNCERTAIN GIVEN THE UNCERTAINTIES ASSOCIATED WITH HOW CONVECTION EVOLVES UPSTREAM. IT IS POSSIBLE THAT SOME SCATTERED STORMS DEVELOP IN-SITU OVER CENTRAL NC INVOF THE OUTFLOW BOUNDARY/EFFECTIVE FRONT...AMIDST INCREASING LARGE SCALE LIFT AHEAD OF THE UPPER LOW...THOUGH ANY SUCH DEVELOPMENT IS LARGELY ABSENT IN NWP SOLUTIONS THROUGH THIS EVENING. GUIDANCE INSTEAD SUGGESTS THAT INCIPIENT STORMS OVER THE TN VALLEY EARLY THIS AFTERNOON WILL DEVELOP SOUTHEASTWARD AND SPREAD ACROSS THE CENTRAL APPALACHIANS LATE THIS EVENING...AND INTO CENTRAL NC AFTER LOW LEVEL SHEAR DIMINISHES - AND WHEN CINH SHOULD BE MAXIMIZED - DURING THE OVERNIGHT HOURS. WITH THE ABOVE AVERAGE UNCERTAINTIES IN MIND...WILL ADVERTISE A CHANCE OF STORMS MAINLY OVER THE NORTHERN HALF OF THE FORECAST AREA (INVOF THE BOUNDARY) THROUGH THIS EVENING - WITH AN ASSOCIATED CONDITIONAL PROBABILITY OF A MULTI-FACETED SVR RISK OF DAMAGING WINDS...LARGE HAIL...AND EVEN AN ISOLATED TORNADO GIVEN THE EXPECTED STRONG LOW LEVEL SHEAR CENTERED AROUND 00Z. ANY OVERNIGHT CONVECTION WOULD THEN POSE PRIMARILY A THREAT OF DAMAGING WIND...AND LARGE HAIL GIVEN STEEP MID LEVEL LAPSE RATES IN EXCESS OF 7C/KM EXPECTED TO RESIDE OVER CENTRAL NC. THIS SVR RISK TOO WILL BE A CONDITIONAL ONE WITH ABOVE AVERAGE UNCERTAINTY...GIVEN OPPOSING SIGNALS FOR STORM DEVELOPMENT/MAINTENANCE (IE. STRONG AND INCREASING FORCING FOR ASCENT DOWNSTREAM OF THE DEEP UPPER LOW VERSUS STRONG CINH (NEAR 200 J/KG) THAT MAY PROVE TOO GREAT TO OVERCOME). REGARDLESS...IT WILL BE MUGGY AND QUITE MILD OVERNIGHT...WITH LOWS GENERALLY IN THE MIDDLE 70S. && .SHORT TERM /MONDAY AND MONDAY NIGHT/... AS OF 315 AM SUNDAY... FOR THE LAST COUPLE OF RUNS MODELS HAVE PERSISTENT IN SHIFTING THE MOIST UNSTABLE AIRMASS SOUTHEASTWARD OVER THE NC COASTAL PLAIN MONDAY AFTERNOON WITH THE SURFACE COLD FRONT JUMPING EASTWARD...MERGING WITH THE PRE-FRONTAL SFC TROUGH AS MID-LEVEL DRY AIR SPREADS IN RAPIDLY FROM THE WEST. IN FACT IF THESE RECENT TRENDS CONTINUE OF SHIFTING THE CONVECTION EAST AND SOUTH OF THE AREA...MUCH OF THE FORECAST AREA COULD END UP BEING DRY ON MONDAY. WILL CONTINUE TO MONITOR THIS TREND ANOTHER MODEL ITERATION OR TWO BEFORE DECREASING POPS. SEVERE THREAT: STRONG 40-50KT MID-LEVEL FLOW COUPLED WITH STRONG DESTABILIZATION WITH ML CAPE VALUES OF 2000-3000 J/KG WILL RESULT IN A THREAT OF SUPERCELLS ACROSS EASTERN NC...ALONG AND EAST OF INTERSTATE 95. VERY LARGE HAIL ON THE ORDER OF 1.50 - 2.00 INCH DIAMETER AND DAMAGING WINDS IS POSSIBLE. HIGH TEMPERATURES MONDAY IN THE MID/UPPER 80S NW TO LOWER/MID 90S SE. THE COOL AIR BEGINS TO FILTER INTO THE AREA MONDAY NIGHT WITH LOWS RANGING FROM LOWER 60W NW TO MID/UPPER 60 SE. && .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 300 AM SUNDAY... UPPER LEVEL TROUGHING WILL STAY IN PLACE OVER THE EAST COAST THROUGHOUT THE ENTIRE LONG TERM PERIOD...WHILE AT THE SURFACE COOL...CANADIAN HIGH PRESSURE WILL GRADUALLY SETTLE EAST OVER THE EAST COAST...KEEPING THE FRONT OFFSHORE. ALL OF THIS WILL LEAD TO BELOW NORMAL TEMPS...WITH HIGHS GENERALLY IN THE LOW/MID 80S AND OVERNIGHT LOWS IN THE LOW/MID 60S...POSSIBLY EVEN SOME UPPER 50S IN THE NORMAL COOLER SPOTS. IN ADDITION...MOSTLY DRY CONDITIONS ARE EXPECTED THROUGH AT LEAST THURSDAY AS NORTHWESTERLY FLOW ALOFT MAINTAINS A DRY COLUMN...WITH PWAT VALUES PROGGED TO HOVER JUST ABOVE 1 INCH. BY LATE IN THE WEEK AND ESPECIALLY INTO THE WEEKEND...THE HIGHLY AMPLIFIED RIDGE OVER THE ATLANTIC WILL SHIFT WESTWARD...NUDGING THE UPPER LEVEL TROUGH BACK TOWARDS THE OHIO/MS RIVER VALLEYS. AS A RESULT...THE FRONT WILL WILL ALSO MOVE CLOSER TO THE COAST AND MODELS INDICATE A WAVE(S) A LOW PRESSURE TRACKING ALONG IT BY THE WEEKEND. ALSO...MOISTURE WILL GRADUALLY INCREASE (PWATS RISING BACK OVER 1.5 INCHES) AS FLOW ALOFT BECOMES MORE SOUTHWESTERLY. AS A RESULT OF ALL OF THIS...WILL SHOW PRECIP CHANCES INCREASING INTO THE LOW END CHANCE RANGE BY SATURDAY. HIGH TEMPS WILL STILL BE IN THE LOW/MID 80S...WITH OVERNIGHT LOWS IN THE LOW/MID 60S. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... AS OF 205 PM SUNDAY... SCATTERED SHOWERS AND STORMS...WHOSE PROBABILITY OF OCCURRENCE AT ANY PARTICULAR TERMINAL IS ONLY AROUND 20 PERCENT...MAY FORM IN-SITU OVER CENTRAL NC THIS AFTERNOON...IN ASSOCIATION WITH LIFT AHEAD OF A MID LEVEL DISTURBANCE MOVING INTO SOUTH-CENTRAL VA...AND IN THE VICINITY OF AN OUTFLOW BOUNDARY FROM NEAR KMTV TO KRDU TO KCTZ. IN ADDITION...A BRIEF PERIOD OF MVFR CEILINGS WILL BE POSSIBLE ON THE COOL SIDE OF THE OUTFLOW BOUNDARY (AT KRWI) THROUGH 20Z. ANOTHER CLUSTER OF SHOWERS AND STORMS...THE ONE CURRENTLY DEVELOPING OVER EASTERN KY...IS FORECAST TO SPREAD SOUTHEASTWARD AND INTO CENTRAL NC...LIKELY IN A GRADUALLY WEAKENING STATE...BETWEEN 02-08Z. THE RELATIVE BEST CHANCE OF STORMS WILL BE AT TRIAD TERMINALS...WITH PROGRESSIVELY LOWER PROBABILITIES TOWARD KRDU/KRWI AND ESPECIALLY KFAY. DESPITE THE PROBABLE WEAKENING OF THE STORMS AS THEY MOVE INTO CENTRAL NC...A WELL-ORGANIZED OUTFLOW BOUNDARY AND ASSOCIATED NORTHWESTERLY WIND GUSTS OF 25-35 KTS (STRONGEST AT KRDU/KRWI) MAY SURGE ALL THE WAY SOUTH THROUGH CENTRAL NC OVERNIGHT. A BREEZY WSW WIND EARLY MONDAY WILL VEER TO WEST OR WNW WITH THE PASSAGE OF A PRONOUNCED COLD FRONT MONDAY AFTERNOON. THE FRONT IS FORECAST TO BE A DRY ONE FOR MOST OF CENTRAL NC...WITH AROUND A 30 PERCENT CHANCE OF A STORM AT KRWI AND KFAY...AND HIGHER PROBABILITIES TOWARD COASTAL AREAS. PREDOMINATELY VFR CONDITIONS ARE OTHERWISE EXPECTED THROUGHOUT THE FORECAST PERIOD...AS CANADIAN HIGH PRESSURE BECOMES CENTERED OVER THE TN VALLEY AND CENTRAL APPALACHIANS THROUGH MID-WEEK. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...MWS SHORT TERM...CBL LONG TERM...KRD AVIATION...MWS

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