Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 150703 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 303 AM EDT TUE APR 15 2014 .SYNOPSIS...WARM AND MOIST SOUTHERLY FLOW WILL PERSIST AHEAD OF A COLD FRONT THAT WILL CROSS THE CAROLINAS THIS AFTERNOON AND EVENING. UNSEASONABLY STRONG AND COOL HIGH PRESSURE WILL THEN BUILD EAST ACROSS THE MIDDLE ATLANTIC REGION TONIGHT THROUGH THURSDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1015 PM MONDAY... WARM MOIST AIR CONTINUES TO FILTER INTO CENTRAL NC THIS EVENING WITH DEWPOINTS INCREASING INTO THE LOWER TO MID 60S AS SOUTH TO SOUTHEASTERLY FLOW IS INCREASING IN ADVANCE OF A STRONG COLD FRONT... CURRENTLY EXTENDING FROM THE EASTERN GREAT LAKES REGION SOUTH-SOUTHWESTWARD TO THE AROUND NEW ORLEANS. THIS FRONT WILL CONTINUE PUSHING EASTWARD OVERNIGHT... APPROACHING THE CENTRAL TO SOUTHERN APPALACHIANS BY 12Z TUESDAY. THE WEAK PRE-FRONTAL BAND OF CONVECTION THAT MOVED ACROSS TN/GA/SC AND WESTERN NC EARLIER TODAY WEAKENED FURTHER THIS EVENING AND HAS LEFT AN OUTFLOW BOUNDARY ACROSS PORTIONS OF THE WESTERN PIEDMONT. NEW SHOWERS AND STORMS ARE NOW FORMING ON THE BOUNDARY. INSTABILITY IS INCREASE ACROSS THE AREA IN GENERAL... WITH A NOSE OF MLCAPE (SMALL AMOUNT 100-250 J/KG) EXTENDING UP TOWARDS THE DAVIDSON/ROWAN COUNTY LINE. THIS COUPLE WITH STRONG DEEP LAYER SHEAR (0-6 KM SHEAR OF AROUND 40-50 KTS) AND A FAVORABLE LOW LEVEL WIND PROFILE (0-1KM SRH OF 150-200 M2/S2) HAS YIELDED SOME WEAK ROTATION WITH THESE VERY SHALLOW SHOWERS/STORMS FROM TIME TO TIME. AT THIS TIME DO NOT THINK ANY WEAK ROTATION WILL RESULT IN ANY ISOLATED BRIEF TORNADOES AS THE UPDRAFTS DO NO APPEAR STRONG ENOUGH. THAT SAID... WE WILL NEED TO KEEP AN EYE ON THE RADAR FOR ANY QUICK SPIKE IN INTENSITY WITH THESE SHOWERS/STORMS SINCE THEY ARE INVOF THE REMNANT OUTFLOW BOUNDARY FROM EARLIER. GIVEN THE ABOVE MENTIONED DEEP SHEAR AND FAVORABLE ATLANTIC LOW LEVEL SOUTHEASTERLY INFLOW WE WILL NEED TO WATCH ANY CONVECTION THAT FORMS OVER THE AREA OVERNIGHT... ESPECIALLY WITH THE LATEST RAP SHOWING AS MUCH AS 500 J/KG OF MLCAPE MOVING INTO OUR SOUTH/SOUTHEASTERN HALF OF CENTRAL NC OVERNIGHT. LATEST HRRR AND RAP SHOW AN INCREASE IN ACTIVITY AFTER 06Z TONIGHT. THUS... WILL MAINTAIN HIGH POPS AFTER 06Z TONIGHT AND MAINTAIN MENTION OF SOME STRONG WIND GUSTS. EXPECT OVERNIGHT LOWS WILL BE WARM GIVEN THE INCREASING MOISTURE/CLOUD COVER. THUS... EXPECT LOW TEMPS WILL BE IN THE LOWER TO MID 60S. TUE-TUE NIGHT: WEAKENING LIFT BUT WITH INCREASING 0-3KM SHEAR MOVES EAST ACROSS CENTRAL NORTH CAROLINA EARLY TUESDAY...THEN THERE IS FORECAST A BRIEF RESPITE IN THE CHANCES FOR SHOWERS AROUND MID- MORNING WITH A SLIGHT DECREASE IN 850MB THETA-E VALUES AND INSTABILITY. AS THE AFTERNOON APPROACHES...850MB WINDS SHOULD INCREASE TO 50 TO 55KT AS A 120KT 300MB JET MOVES THROUGH THE AREA...COINCIDENT WITH THE RIGHT ENTRANCE REGION OF A 90KT 500MB JET. WHILE 1000-500MB LAPSE RATES ARE ONLY FORECAST AROUND 6C/KM...AND THOSE MAINLY EAST OF U.S. 1... MUCAPE THAT INCREASES OVERNIGHT TO NEARLY 1000J/KG ON THE NAM OVER THE FAR SOUTHWEST PIEDMONT CONTINUES TO PUSH ACROSS CENTRAL NORTH CAROLINA WITH VALUES FROM 1000-1500J/KG DURING TUESDAY. 0-3KM SHEAR IS ON THE ORDER OF 40- 50KT TUESDAY AFTERNOON...INCREASING FURTHER TOWARD THE INTERSTATE 95 CORRIDOR LATE. MODEST LAPSE RATES IN A BROADLY MOIST AIR MASS SHOULD HELP TO LIMIT AVAILABLE INSTABILITY... BUT SYSTEM DYNAMICS ALONG AND AHEAD OF THE FRONT COULD COMPENSATE FOR THIS AND MAKE FOR THE POTENTIAL FOR ISOLATED SEVERE STORMS TUESDAY. IF A LOCATION SEEMED TO HAVE A BETTER CHANCE OF ISOLATED SEVERE STORMS...IT WOULD SEEM TO BE ALONG AND EAST OF U.S. 1 WHERE THE OVERALL INSTABILITY AND SHEAR WILL BE BETTER TUESDAY AFTERNOON...AS LIFTED INDICES THERE SHOULD BE -2C TO -4C...WITH BETTER HEATING EXPECTED. THE PRIMARY SEVERE THREAT IS ANTICIPATED TO BE WIND...BUT WITH 0-3KM HELICITY VALUES FROM 100- 300 M2/S2...AN ISOLATED TORNADO CANNOT BE RULED OUT. HIGHS WERE LEANED TOWARD THE WARMER MAV GUIDANCE ANTICIPATING A BREAK IN PRECIPITATION DURING THE MORNING...UPPER 60S NORTHWEST TO AROUND 80 SOUTHEAST. STRONG COLD AIR ADVECTION TAKES PLACE TUESDAY NIGHT AS HIGH PRESSURE MOVES IN. ONCE THE STRONG MID-LEVEL TROUGH MOVES THROUGH THE THREAT OF PRECIPITATION SHOULD END...THEN IMPACTS TURN TOWARD THE POTENTIAL FOR FREEZING CONDITIONS. THE GUIDANCE HAS BEEN CONSISTENT FORECASTING LOWS AT OR BELOW FREEZING FOR A COUPLE OF RUNS MAINLY ALONG AND WEST OF INTERSTATE 95...AND WHILE WINDS IN MANY LOCATIONS SHOULD STAY UP THROUGH A LARGE PART OF THE NIGHT IN A TIGHT GRADIENT BEHIND THE COLD FRONT AS THE HIGH BUILDS IN...LATE AT NIGHT THERE SHOULD BE JUST ENOUGH WIND REDUCTION IN COMBINATION WITH SIMPLE ADVECTION TO RESULT IN SEVERAL AREAS WITH TEMPERATURES BELOW FREEZING. WILL ISSUE A FREEZE WATCH FOR A LARGE PART OF CENTRAL NORTH CAROLINA FOR TUESDAY NIGHT INTO EARLY WEDNESDAY MORNING... KEEPING OUT THE IMMEDIATE INTERSTATE 95 CORRIDOR FOR NOW DUE TO GREATER WIND AND MIXING EXPECTED THERE. LOWS TUESDAY NIGHT 29 TO 32 MOSTLY FROM U.S. 1 WEST...33 TO 37 IN THE INTERSTATE 95 CORRIDOR. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 235 AM TUESDAY... WED AND WED NIGHT: RISING HEIGHTS ALOFT/DNVA AND ASSOCIATED STRONG SUBSIDENCE WILL RESULT IN FURTHER DEEP LAYER DRYING (SUNSHINE) WED...FOLLOWED BY GENERALLY NEUTRAL VERTICAL MOTION...BUT WITH A STILL STRONGLY CAPPED AND RESIDUALLY DRY REGIME OVER OUR REGION THROUGH WED NIGHT. BENEATH THE STRONG SUBSIDENCE ALOFT...SURFACE HIGH PRESSURE WILL CONSEQUENTLY BECOME UNSEASONABLY STRONG INTO THE 1040-1045 MB RANGE AS IT BUILDS FROM THE OH VALLEY TO NEW ENGLAND. COOL NORTHEASTERLY FLOW AND DRY ADIABATIC MIXING THROUGH 900 MB...WITH A COUPLE OF DEGREES ADDED TO ACCOUNT FOR A USUAL SLIGHT COOL BIAS WITH THIS TECHNIQUE LIKELY IN PART OWING TO A SUPER- ADIABATIC NEAR SURFACE LAYER...SUPPORTS HIGHS IN THE LOWER TO MIDDLE 50S. PROJECTED LOW LEVEL THICKNESS VALUES IN THE 1300-1310 METER RANGE AT 12Z THU...WITH OPTIMAL RADIATIONAL COOLING...WOULD SUPPORT MIDDLE 20S. HOWEVER...A PROJECTED 4-6 MB RISE IN MSL PRESSURE WITH THE STRENGTHENING HIGH WED NIGHT WILL LIKELY MAINTAIN A NORTHEASTERLY STIRRING FOR MOST AREAS OVERNIGHT...THOUGH WITH TYPICALLY COOLER/SHELTERED AREA LIKELY TO EXPERIENCE PERIODS OF CALM. IN ADDITION...MOISTURE ADVECTION IN NORTHEASTERLY FLOW BENEATH THE CAPPING INVERSION MAY RESULT IN SCT TO BKN LOW CLOUDS MAINLY IN THE COASTAL PLAIN LATE. AS SUCH...TEMPERATURES ARE APT TO DISPLAY A RELATIVELY LARGE RANGE...FROM 28-30 DEGREES IN RURAL WESTERN PIEDMONT LOCATIONS (IN CLOSEST PROXIMITY TO THE RIDGE AXIS) TO AROUND FREEZING IN URBAN AREAS FROM RDU WESTWARD TO THE TRIAD...TO 33-37 DEGREES IN THE COASTAL PLAIN AND EASTERN SANDHILLS. -MWS THURSDAY THROUGH THURSDAY NIGHT: THIS PERIOD SHOULD REMAIN DRY WITH HIGH PRESSURE RIDGING IN FROM THE NORTHEAST...ALTHOUGH EXPECT CLOUDS TO INCREASE DURING THE EVE/OVERNIGHT...ESPECIALLY ACROSS THE SOUTH AND EAST...AS A LOW DEVELOPS OFF THE COAST. WITH THE CONTINUED NE FLOW AND CAA...STILL EXPECT TEMPS TO BE BELOW NORMAL. HOWEVER... GIVEN LOW-LEVEL THICKNESSES INCREASING FROM THE PREVIOUS NIGHT BY A GOOD 30-40 METERS...EXPECT TEMPS TO INCREASE BY 5-10 DEGREES...HIGHS IN THE LOW TO MID 60S AND LOWS IN THE UPPER 30S TO LOW 40S. -KCP && .LONG TERM /FRIDAY THROUGH TUESDAY/...
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AS OF 300 AM TUESDAY... THERE IS STILL A SLIGHT CHANCE OF RAIN ACROSS THE SOUTHEAST FRIDAY NIGHT/SATURDAY MORNING AS THE ELONGATED LOW OFF THE COAST MOVES AWAY FROM THE AREA...OTHERWISE THE LATEST GFS AND ECMWF RUNS KEEP THE FORECAST DRY THROUGH MONDAY. AN UPPER LEVEL LOW SKIRTS NORTH OF CENTRAL NC SATURDAY NIGHT/SUNDAY. THE GFS IS A BIT MORE AMPLIFIED WITH THE LOW...BRINGING IT CLOSER TO THE AREA. DESPITE THE STRONG UPPER LEVEL FORCING AND MOISTURE IN THE UPPER LEVELS...THE DRY AIR EXPECTED IN THE MID LEVELS MAY BE ENOUGH TO KEEP THINGS DRY. HIGHS FRIDAY IN THE MID TO UPPER 60S WITH LOWS IN THE MID 40S TO AROUND 50 DEGREES. HIGH PRESSURE TO THE NORTH WILL RIDGE INTO THE AREA SUNDAY AND MONDAY. ASIDE FROM SOME HIGH CLOUDS...EXPECT EASTER SUNDAY TO BE DRY AND MOSTLY SUNNY. HIGHS MAINLY IN THE LOW TO MID 70S WITH LOWS IN THE MID TO UPPER 40S THROUGH THE END OF THE PERIOD.
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&& .AVIATION /06Z TUESDAY THROUGH SATURDAY/... AS OF 200 AM TUESDAY... 24 HOUR TAF PERIOD: MVFR/IFR CONDITIONS ACROSS THE AREA WILL LIKELY DECREASE FURTHER INTO IFR/LIFR BY DAYBREAK TUESDAY. HEAVY SHOWERS AND THUNDERSTORMS ARE APPROACHING FROM THE SOUTHWEST...ALREADY IMPACTING KINT AND KGSO...AND LIKELY MOVING OVER KFAY AND KRDU OVER THE NEXT COUPLE HOURS (AND KRWI THEREAFTER). THOUGH IT IS POSSIBLE THE CIGS MAY IMPROVE SLIGHTLY WITH THESE HEAVY SHOWERS...VISBYS WILL LIKELY DECREASE. AS ALREADY SEEN AT KINT AND KGSO...SOUTHWEST WINDS WILL BECOME GUSTY (20-25 KTS) AS THE LOW LEVEL FLOW STRENGTHENS. IF THERE IS A BREAK IN THE PRECIP TUESDAY MORNING...CONDITIONS MAY IMPROVE BACK TO MVFR...BUT EXPECT MORE SHOWERS AND THUNDERSTORMS TO MOVE ACROSS THE AREA AHEAD OF THE COLD FRONT...EXPECTED TO MOVE FROM WEST TO EAST THROUGH CENTRAL NC DURING THE LATE AFTERNOON/EARLY EVENING. ALTHOUGH WINDS WILL REMAIN STRONG AND GUSTY THROUGH THE TAF PERIOD...EXPECT THEM TO VEER TO THE WEST THEN NORTHWEST BEHIND THE FRONT. CIGS WILL LIFT AND VISBYS WILL IMPROVE BEHIND THE FRONT... WITH VFR CONDITIONS EXPECTED BY THE END OF THE PERIOD. -KC LOOKING AHEAD: MOSTLY VFR CONDITIONS WILL PERSIST THROUGH THE END OF THE WORK WEEK. THERE COULD BE SOME MORNING STRATUS BOTH FRIDAY AND SATURDAY MORNING AS MOISTURE ONCE AGAIN INCREASES AHEAD OF OUR NEXT SYSTEM APPROACHING FROM THE SOUTH THIS WEEKEND. -KRD && .CLIMATE... THE FOLLOWING ARE THE RECORD LOW TEMPERATURES FOR WED AND THU MORNING... AND THE RECORD LOW MAXIMUM TEMPERATURES FOR WED: WED 04/16 THU 04/17 LOW/YEAR LOW MAX/YEAR LOW/YEAR FAY: 28/1943 56/1950 31/1953 GSO: 25/1943 48/1929 29/1953 RDU: 28/1950 46/1890 29/1962 && .RAH WATCHES/WARNINGS/ADVISORIES... FREEZE WATCH FROM LATE TUESDAY NIGHT THROUGH WEDNESDAY MORNING FOR NCZ007>010-021>026-038>041-073>077-083-084. && $$ SYNOPSIS...MWS NEAR TERM...BSD/DJF SHORT TERM...MWS/KCP LONG TERM...KCP AVIATION...KCP/KRD CLIMATE...MWS

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