558 FXUS62 KRAH 151905 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 305 PM EDT FRI APR 15 2011 .SYNOPSIS... HIGH PRESSURE WILL DRIFT OFFSHORE TONIGHT. A POWERFUL STORM SYSTEM WILL CROSS OUR REGION ON SATURDAY...FOLLOWED BY HIGH PRESSURE FOR SATURDAY NIGHT AND SUNDAY. && .NEAR TERM /THROUGH SATURDAY NIGHT/... AS OF 200 PM FRIDAY... ...SEVERE WEATHER OUTBREAK WITH A MODERATE RISK FOR SEVERE STORMS SATURDAY... 1730Z SPC DAY 2 OUTLOOK INCREASED SEVERE WEATHER THREAT TO MODERATE FOR SATURDAY. FROM THE SPC DISCUSSION...WIDESPREAD DAMAGING WINDS AND A FEW STRONG TORNADOES WILL BE POSSIBLE ACROSS THE CENTRAL AND ERN CAROLINAS ON SATURDAY. SATURDAY IS SETTING UP TO BE A TEXT BOOK LARGE SCALE SEVERE WEATHER OUTBREAK WITH THE POTENTIAL FOR WIDESPREAD DAMAGE. TONIGHT: CURRENT BAND OF SHOWERS AND STORMS OVER ERN TENN SHOULD SLOW ITS FORWARD PROGRESSION AND HANG UP ALONG THE MOUNTAINS SINCE IT HAS RACED OUT AHEAD OF THE PRIMARY FORCING AND UPPER LOW. FOR TONIGHT INCREASING SLW FLOW WITH THE DEVELOP OF THE LOW LEVEL JET OVERNIGHT WILL START TO SURGE MOISTURE NORTH INTO THE REGION AFTER MIDNIGHT. WITH THE INCREASE IN MOISTURE AND LOW LEVEL CONFLUENCE SOME RAPIDLY MOVING SHOWERS MOVING SOUTH TO NORTH COULD DEVELOP FROM 09-15Z AND THIS IS SUPPORTING ON A NUMBER OF THE WRF RUNS. A CHANCE FOR SHOWERS AFTER MIDNIGHT WEST OF HIGHWAY ONE...WITH PERHAPS A TENTH INCH WEST OF HIGHWAY 220 BEFORE SUNRISE...AND CHANCES FOR MEASURABLE RAIN SPREADING EAST BEFORE SUNRISE. WITH INCREASING SLY FLOW...CLOUD COVER AND LOW LEVEL WINDS TEMPS OVERNIGHT WILL BE UNIFORM AND RATHER MILD IN THE MIDDLE 50S. SKIES WILL BECOME OVERCAST AFTER MIDNIGHT. SATURDAY...MAIN ITEM TO NOTE IS THE MODELS HAVE INCREASED INSTABILITY FROM 11 AM THROUGH 5 PM WITH MLCAPE 1600 J/KG ACROSS CENTRAL NC. THIS COMPARED TO MODELS YESTERDAY PREDICTING WEAKER MLCAPE FROM 500-1000 J/KG. SHEAR WILL SUPPORT DISCRETE CELLS DEVELOPING AHEAD OF A DANGEROUS SQUALL LINE. 0-3 KM SHEAR IS FORECAST AROUND 40 M/S WITH HELICITY IN EXCESS OF 450 M2/S2. IN FACT 0-1 KM SHEAR WILL BE IN EXCESS OF 20 M/S WITH HELICITY OVER 300 M2/S2 SUPPORTIVE OF TORNADOES. ALONG WITH THE INSTABILITY AND SHEAR LCL VALUES FALL TO LESS THAN 1500 FEET. THE DANGEROUS COMBINATION OF HIGH SHEAR...MODERATE CAPE AND LOW LCLS WILL BE SUPPORTIVE OF DISCRETE SUPERCELLS CAPABLE OF PRODUCING TORNADOES AHEAD OF A MAIN SQUALL LINE CAPABLE OF WIDESPREAD DAMAGING WIND AND ADDITIONAL TORNADOES. A FEW INTENSELY ROTATING SUPERCELLS WITH A THREAT OF TORNADOES WILL LIKELY EXIST. TIMING: THE NAM IS A LITTLE SLOWER WITH THE SYSTEM THAN THE GFS BY ABOUT 2-3 HOURS. WILL TREND TOWARDS THE FASTER WRF SOLUTIONS WHICH BRING THE LINE OF STORMS TO THE TRIAD AROUND NOON...TO THE TRIANGLE AROUND 2 PM AND EAST OF I-95 AROUND 3 PM. THE EXACT TIMING OF THE SQUALL LINE IS DIFFICULT AND IT COULD COME IN A LITTLE LATER IF THE NAM IS CORRECT. THAT SAID EXPECT DISCRETE STORMS SOME OF WHICH COULD BE SEVERE OR TORNADIC WELL AHEAD OF THE MAIN LINE ESPECIALLY AS WE MOVE INTO THE AFTERNOON AND INSTABILITY INCREASES. HIGHS SATURDAY IN THE MID 70S WITH DEW POINTS IN THE LOWER 60S. WITH THE TIGHT PRESSURE GRADIENT EXPECT GUSTY WINDS OF 30 TO 40 MPH WITH THE STRONG SLY FLOW OUTSIDE OF THE STORMS. IF THIS INCREASES A WIND ADVISORY MAY BE NEEDED FOR SATURDAY AFTERNOON. SATURDAY NIGHT, A SMALL BAND OF SHOWERS MAY BE POSSIBLE WITH THE UPPER LOW SATURDAY EVENING DUE TO THE LARGE SCALE ASCENT AND SURFACE FRONT. AS OF NOW MOISTURE LOOKS TOO LIMITED TO PRODUCE SHOWERS, BUT WILL HAVE TO KEEP AN EYE ON THIS WITH LATER FORECASTS. LOWS SATURDAY NIGHT IN THE MID 40S. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 230 PM FRIDAY... SURFACE HIGH PRESSURE WILL BE IN CONTROL OF THE WEATHER ACROSS CENTRAL NC AS IT PROGRESSES FAIRLY QUICKLY EASTWARD ACROSS THE SOUTHEASTERN US. THIS WILL RESULT IN FAIR WEATHER AND THEN AS RETURN FLOW SETS BY SUNDAY AFTERNOON...A WARMING TREND THROUGH THE PERIOD. THICKNESS VALUES WILL REBOUND TO NEAR 1380M BY MONDAY AFTERNOON WHICH SHOULD TRANSLATE TO HIGH TEMPS IN THE MID TO UPPER 70S (A GOOD FIVE DEGREES WARMER THAN WHAT IS EXPECTED ON SUNDAY). OVERNIGHT LOWS WILL ALSO BE ON A MODERATING TREND...WITH UPPER 40S TO NEAR 50 DEGREES EXPECTED SUNDAY NIGHT AND MID 50S EXPECTED BY MONDAY NIGHT. && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 255 PM FRIDAY... DURING THE BEGINNING OF THE LONG TERM PERIOD...THE SUBTROPICAL RIDGE IS PROGGED TO STRENGTHEN OVER THE SOUTHWESTERN ATLANTIC AND THE SOUTHEASTERN US. THIS FEATURE IS EXPECTED TO PUSH THE NEXT STORM SYSTEM MOVING OUT OF THE PLAINS NEXT WEEK NORTH OF THE FORECAST AREA AS IT TRACKS INTO THE UPPER GREAT LAKES REGION. THEREFORE THE TRAILING FRONTAL ZONE AND ASSOCIATED PRECIP IS EXPECTED TO ALSO REMAIN NORTH OF THE REGION THROUGH AT LEAST THURSDAY...RESULTING IN DRY CONDITIONS AND A CONTINUED WARMING TREND. HIGH TEMPS ARE EXPECTED TO RISE FROM THE LOW 80S ON TUESDAY TO THE MID TO UPPER 80S BY THURSDAY. THE AFOREMENTIONED SUBTROPICAL RIDGE IS THEN PROGGED TO BECOME SUPPRESSED TO THE SOUTH WHICH SHOULD ALLOW THE FRONTAL ZONE TO DRIFT SOUTHWARD INTO THE REGION LATE THURSDAY INTO FRIDAY. THEREFORE WILL SHOW LOW END CHANCE POPS FOR THE THURSDAY NIGHT INTO FRIDAY...WITH SLIGHTLY COOLER TEMPS ON FRIDAY. && .AVIATION /17Z FRIDAY THROUGH TUESDAY/... AS OF 200 PM FRIDAY... VFR CONDITIONS WILL PERSIST THIS AFTERNOON AND EVENING...BUT CLOUD COVER WILL INCREASE WITH A STRENGTHENING AND INCREASINGLY MOIST SOUTHEASTERLY FLOW AND ASSOCIATED. EXPECT IFR-MVFR CONDITIONS BETWEEN 04-08Z SATURDAY. INCREASING SOUTHERLY WINDS (TO AROUND 40 KTS) AND ASSOCIATED SHEAR JUST ABOVE THE SURFACE WILL ALSO PRODUCE MECHANICAL TURBULENCE OVERNIGHT. A SOUTHEASTERLY SURFACE WIND WILL INCREASE TO 15 KT RANGE WITH OCCASIONAL GUSTINESS TO AROUND 25 KTS BY SATURDAY MORNING. A PERIOD OF SCATTERED SHOWERS ARE POSSIBLE EARLY SATURDAY FROM 09-14Z WITH THE STRONG SLY LOW LEVEL FLOW. CONDITIONS MAY BRIEFLY IMPROVE BY A CATEGORY MID TO LATE SATURDAY MORNING...TO LOW MVFR (PARTICULARLY AT EASTERN TERMINALS (KRWI/KFAY)...BEFORE LOWERING AGAIN IN WIDESPREAD SHOWERS AND THUNDERSTORMS. EXPECT WINDY CONDITIONS IN SOUTH SOUTHEASTERLY SURFACE FLOW...MIDDAY THROUGH SATURDAY AFTERNOON WITH GUSTS TO 35 KT. A DANGEROUS SQUALL LINE IS FORECAST TO MOVE FROM WEST TO EAST ACROSS ALL TERMINAL FROM 17Z-22Z WITH A THREAT OF WINDS IN EXCESS OF 52KTS AND ISOLATED TORNADOES. VFR CONDITIONS ARE EXPECTED TO RETURN AS HIGH PRESSURE BUILDS IN SATURDAY NIGHT THROUGH EARLY NEXT WEEK. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...JO NEAR TERM...JO SHORT TERM...KRR LONG TERM...KRR AVIATION...JO