RAH issues Area Forecast Discussion (AFD) 462 FXUS62 KRAH 141651 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1250 PM EDT MON JUL 14 2014 .SYNOPSIS...A COLD FRONT WILL MOVE EAST ACROSS THE STATE TUESDAY AND TUESDAY NIGHT...REACHING THE COAST BY WEDNESDAY MORNING. HIGH PRESSURE WILL BUILD IN FROM THE GREAT LAKES THURSDAY AND FRIDAY BRINGING COOLER AND DRIER CONDITIONS. && .NEAR TERM /TODAY AND TONIGHT/... AS OF 215 AM MONDAY... CYCLONIC FLOW ALOFT WILL STRENGTHEN OVER THE NORTHERN MS/OH RIVER VALLEY TODAY AS AN ANOMALOUSLY/UNSEASONABLY DEEP UPPER LEVEL LOW DIGS SOUTHEAST FROM CANADA INTO THE UPPER GREAT LAKES. PROGRESSIVE SMALL AMPLITUDE DISTURBANCES ROUNDING THE BASE OF THE AMPLIFYING TROUGH WILL EJECT ENE THROUGH THE TN/OH VALLEY AND MID-ATLANTIC (I.E. KY/WV/MD) THIS AFT/EVE...REMAINING WELL N/NW OF CENTRAL NC WHERE LITTLE IF ANY HEIGHT FALLS WILL OCCUR THROUGH 00Z. AS A RESULT...FORCING FOR ASCENT IN CENTRAL NC WILL BE CONFINED TO WEAK/SHALLOW CONVERGENCE IN VICINITY OF THE PIEDMONT TROUGH AND PERHAPS THE SEABREEZE IN THE FAR SE COASTAL PLAIN. DESPITE THE PRESENCE OF WEAK MID-LEVEL LAPSE RATES (5.5-6.0 C/KM)...STRONG DIURNAL HEATING AND RICH LOW-LEVEL MOISTURE ADVECTING INTO THE REGION FROM THE SW WILL RESULT IN MODERATE DIURNAL DESTABILIZATION WITH MLCAPE RANGING FROM 1000-2000 J/KG (STRONGEST EAST). GIVEN WEAK SYNOPTIC FORCING AND SEASONABLE MOISTURE/INSTABILITY... EXPECT NEAR CLIMATOLOGICAL CHANCES (~30%) FOR CONVECTION THIS AFT/EVE...WITH ABOVE NORMAL HIGH TEMPS SIMILAR TO OR SLIGHTLY WARMER THAN YESTERDAY...IN THE LOWER/MID 90S. WILL MAINTAIN A 20-30% CHANCE OF CONVECTION OVERNIGHT IN ASSOC/W 30-50 METER H5 HEIGHT FALLS AND AN INCREASING POTENTIAL FOR SMALL AMPLITUDE DISTURBANCES TRACKING INTO WESTERN PORTIONS OF THE CAROLINAS IN STRENGTHENING SW FLOW ALOFT. EXPECT LOWS IN THE LOWER/MID 70S WITH INCREASING MID/UPPER LEVEL CLOUD COVER LIKELY. SEVERE POTENTIAL: DEEP-LAYER SHEAR WILL RANGE FROM 10 KT (SE) TO 20 KT (NW) OVER CENTRAL NC THROUGH THIS EVENING...INCREASING TO 20-30 KT IN THE FAR NW PIEDMONT AFTER MIDNIGHT. WEAK 0-6 KM SHEAR...WEAK MID-LEVEL LAPSE RATES...WEAK SYNOPTIC FORCING...RICH LOW-LEVEL MOISTURE...MODERATE INSTABILITY AND MODERATE DCAPE TYPIFY THE SUMMER CONVECTIVE ENVIRONMENT IN CENTRAL NC. AS SUCH...ASIDE FROM A CONDITIONAL POTENTIAL FOR A BRIEF/LOCALIZED DOWNBURST...SEVERE WEATHER IS NOT EXPECTED THROUGH THIS EVENING. ALTHOUGH THE KINEMATIC ENVIRONMENT WILL GRADUALLY BECOME MORE FAVORABLE FOR CONVECTIVE ORGANIZATION IN THE NW PIEDMONT LATE TONIGHT...THIS FACTOR MAY LARGELY BE OFFSET BY POOR DIURNAL TIMING. -VINCENT && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... AS OF 300 AM MONDAY... UNSEASONABLY STRONG HEIGHT FALLS WILL OCCUR OVER THE CAROLINAS AND MID-ATLANTIC ON TUESDAY AS SHORTWAVE ENERGY DIVES SOUTHEAST THROUGH THE WESTERN FRINGE OF THE UPPER LEVEL TROUGH...ROUNDS THE BASE... AND EJECTS ENE/NE INTO THE MID-ATLANTIC AND CAROLINAS IN STRENGTHENING SW FLOW ALOFT. A COLD FRONT ATTENDANT THE AMPLIFYING UPPER LEVEL TROUGH WILL TRACK INTO THE AREA TUE AFT/EVE. A WEAK WAVE OF LOW PRESSURE WILL LIKELY DEVELOP ALONG THE FRONT IN THE MID- ATLANTIC...WITH ANOTHER WEAK WAVE POSSIBLE ALONG THE FRONT IN THE CAROLINAS. DESPITE WEAKER DESTABILIZATION DUE TO MORE PERVASIVE CLOUD COVER...THE COMBINATION OF UNSEASONABLY STRONG SYNOPTIC FORCING...DEEP MOISTURE (PWAT 1.75-2.00")...AND FAVORABLE DIURNAL TIMING SUGGEST WIDESPREAD SHOWERS AND THUNDERSTORMS WITH HIGHS RANGING FROM THE MID 80S TO LOWER 90S. CONVECTION WILL LIKELY PERSIST THROUGH THE OVERNIGHT HOURS...THOUGH GRADUALLY DECREASING IN COVERAGE AND ENDING FROM WEST-EAST AS THE LOW-LEVEL TROUGH /COLD FRONT/ PROGRESS TOWARD THE COAST AND A DRIER MID-LEVEL AIRMASS ADVECTS INTO THE REGION FROM THE WEST. SEVERE POTENTIAL: WIDESPREAD CLOUD COVER AND THE POSSIBLE PRESENCE OF SCATTERED CONVECTION DURING THE LATE MORNING AND EARLY AFTERNOON MAKE IT DIFFICULT TO ASSESS CONVECTIVE EVOLUTION ON TUE. DESPITE DEEP MOISTURE AND WEAK LAPSE RATES...FAVORABLE DIURNAL TIMING SHOULD ALLOW MARGINAL TO MODERATE DESTABILIZATION (500-1500 J/KG MLCAPE) IN THE PRESENCE OF UNSEASONABLY STRONG DPVA /LAYER LIFTING/ AND STRONG DEEP LAYER SHEAR (30-40 KT). AS A RESULT...EXPECT ORGANIZED CONVECTION COMPRISED OF MULTICELL CLUSTERS AND A FEW SUPERCELLS... THE LATTER OF WHICH MAY BE CONFINED ACROSS THE N/NW PIEDMONT (TRIANGLE NORTH AND WEST) WHERE DEEP-LAYER SHEAR WILL BE MORE FAVORABLE. THE PRIMARY CONVECTIVE THREAT WILL BE DAMAGING WINDS AND QUARTER SIZED HAIL...THOUGH LARGER HAIL (1.00-1.75") WOULD BE POSSIBLE IN ASSOCIATION WITH THE MOST ROBUST UPDRAFTS...PRIMARILY THOSE WITH MID-LEVEL MESOCYCLONES (I.E. SUPERCELLS). -VINCENT && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... AS OF 126 AM MONDAY... DUE TO THE STRENGTH AND DEPTH OF THE MID/UPPER TROUGH SEEN DIVING SOUTH ON THE CURRENT WV SATELLITE IMAGERY AND THE LATEST MODELS PROJECTIONS... THERE IS LITTLE DOUBT THAT MUCH COOLER AND DRIER AIR WILL REACH DEEP INTO THE SOUTHEASTERN STATES THURSDAY AND FRIDAY AS THIS TROUGH DIGS FROM THE GREAT LAKES DEEP INTO THE TENNESSEE VALLEY REGION. THE LEAD COLD FRONT IS WITH HIGH CONFIDENCE SLATED BY THE MODELS TO BE NEAR THE COAST AT 12Z/WED. THE FRONT THEN IS PROJECTED TO STALL TO OUR SOUTH (NEAR CHARLESTON SC) THURSDAY AND FRIDAY. THEREFORE... THE FOCUS OF CONVECTION WILL BE ENDING WEDNESDAY MORNING FOR OUR EASTERN (COASTAL PLAIN COUNTIES)... WITH CLEARING EXPECTED WEDNESDAY INTO WEDNESDAY EVENING FROM NW TO SE. THE MAIN HIGHLIGHT WEDNESDAY NIGHT THROUGH FRIDAY WILL BE THE MUCH COOLER TEMPERATURES. LOWS SHOULD DIP WELL DOWN INTO THE 60S... WITH SOME 50S LIKELY OVER THE NORTHERN AND CENTRAL PIEDMONT REGIONS THURSDAY AND FRIDAY. THESE READINGS WILL BE 10+ DEGREES BELOW NORMAL. HIGHS SHOULD STAY IN THE LOWER TO MID 80S (A GOOD 5-8 DEGREES BELOW NORMAL). THE NEXT CHANCE OF SHOWERS AND THUNDERSTORMS SHOULD ARRIVE BY FRIDAY NIGHT OR NEXT WEEKEND AS THE UPPER FLOW RETROGRADES ALLOWING FOR A SW FLOW ALOFT AIDED BY ANOTHER MID/UPPER LOW THAT MAY DEVELOP OVER THE GREAT LAKES. THIS WOULD BRING MORE SIGNIFICANT RAINFALL TO OUR REGION BY NEXT WEEKEND. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... AS OF 1250 PM MONDAY... ISOLATED CONVECTION WILL BE POSSIBLE LATE THIS AFTERNOON AND EVENING...OTHERWISE VFR CONDITIONS ARE EXPECTED THROUGH TUESDAY AFTERNOON. SHOWERS AND THUNDERSTORMS WILL SPREAD INTO THE WEST (GSO/INT) BY EARLY AFTERNOON AS A COLD FRONT MOVES SLOWLY EAST ACROSS CENTRAL AND EASTERN NC THROUGH TUESDAY NIGHT. WINDS WILL BE SOUTH TO SOUTHWEST AT LESS THAN 10 KNOTS THROUGH THE TAF PERIOD. TUESDAY...ACTIVITY WILL BEGIN TO BLOSSOM BY PEAK HEATING (18-03Z)... JUST BEYOND THE 24 HOUR TAF VALID PERIOD. CONVECTIVE ACTIVITY WILL PRODUCE SCATTERED TO FAIRLY WIDESPREAD MVFR CONDITIONS...OTHERWISE EXPECT SCATTERED TO BROKEN MODERATE VFR-BASED CUMULUS. VFR CONDITIONS ARE EXPECTED AFTER FRONTAL PASSAGE...BY 03Z IN THE WEST...AND BY 09Z IN THE EAST...ALTHOUGH SOME MVFR FOG WILL BE POSSIBLE IN AREAS WHICH RECEIVE HEAVY SHOWERS. WINDS WILL BE LIGHT SOUTH TO SOUTHWEST PRIOR TO THE COLD FRONT TUESDAY...SHIFTING TO NORTHERLY AFTER THE FRONT PASSES. IN THE LONGER RANGE...WEAK HIGH PRESSURE WILL PRODUCE VFR CONDITIONS THROUGH THURSDAY. AN UPPER TROF IN THE MIDWEST WILL BE TRANSLATING EAST...INCREASING THE CHANCE OF RAIN LATE FRIDAY AND SATURDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...MLM/32 NEAR TERM...VINCENT SHORT TERM...VINCENT LONG TERM...32 AVIATION..MLM
Posted on: Mon, 14 Jul 2014 16:52:03 +0000
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