000 FXUS62 KRAH 041847 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 247 PM EDT FRI JUL 4 2008 .SYNOPSIS... HIGH PRESSURE CENTERED OVER THE ATLANTIC WILL ALLOW MOISTURE TO INCREASE ACROSS CENTRAL NORTH CAROLINA THIS WEEKEND. THE INCREASED MOISTURE COMBINED WITH AN UPPER LEVEL TROUGH TO THE WEST WILL RESULT IN AN INCREASED CHANCE OF SCATTERED SHOWERS AND THUNDERSTORMS THROUGH THE END WEEKEND AND INTO EARLY NEXT WEEK. .NEAR TERM /THROUGH SATURDAY/... AS OF 200 PM FRIDAY... THERE ARE MIXED SIGNALS REGARDING CONVECTIVE CHANCES FOR THE REST OF TODAY INTO TONIGHT. FIRST OFF... ISOLATED CONVECTION HAS DEVELOPED IN THE FOOTHILLS AND AS FAR EAST AS THE SW PIEDMONT AS OF 2 PM. WEAK LOW LEVEL CONVERGENCE ASSOCIATED WITH A LEE TROUGH AND MLCAPES OF 500-1000 J/KG APPEAR TO BE THE REASONS FOR THE CONVECTIVE INITIATION. IT IS DIFFICULT TO ASCERTAIN THE EVOLUTION OF CONVECTION THIS AFTERNOON AS DEWPOINTS BEGIN TO LOWER WITH DEEP MIXING ESTABLISHED. DEWPOINTS WILL DROP INTO THE UPPER 50S AND LOWER 60S THROUGH THE REST OF THE AFTERNOON...AND THIS WILL PREVENT CAPE VALUES FROM INCREASING ANY MORE. WILL SHOW A 20 POP ISOLATED COVERAGE FOR THE WESTERN PIEDMONT TO ACCOUNT FOR CURRENT ACTIVITY ON RADAR. FURTHER EAST...WILL LEAVE THE REST OF THE AFTERNOON DRY AS CAPPING EVIDENT THIS MORNING ON THE MHX SOUNDING SHOULD BE SUFFICIENT TO PREVENT DEVELOPMENT AS MODELS DO NOT ERODE THE CAP UNTIL LATER THIS EVENING. THERE APPEARS TO BE A BETTER CHANCE AT CONVECTION...ESPECIALLY OVER NORTHWEST PORTIONS OF THE CWA THIS EVENING. AS MIXING IS LOST...BOUNDARY LAYER MOISTURE WILL INCREASE AS SFC DEWPOINTS CLIMB BACK INTO THE UPPER 60S TO NEAR 70. IN ADDITION...A WEAK SHORT WAVE OVER THE TN VALLEY... NOTED WITH THE COOL POOL OVER NASHVILLE THIS MORNING...WILL SKIRT THE NW PIEDMONT THIS EVENING. THIS MAY PRODUCE ADDITIONAL CONVECTION IN THE FOOTHILLS THAT COULD THEN WORK ITS WAY INTO THE NW PIEDMONT. OUTFLOW BOUNDARIES WILL ALSO PLAY AN IMPORTANT ROLE IN DETERMINING CONVECTIVE EVOLUTION THIS EVENING...AND THAT IS VERY HARD TO DETAIL AT THIS JUNCTURE. WILL MAINTAIN THE THEME OF THE PREVIOUS FORECAST... WITH POPS INCREASING TO LOW END CHANCE IN AREAS NORTH AND WEST... ONLY SHOWING A SLIGHT CHANCE FURTHER SOUTHEAST WHERE THERE APPEARS TO BE NO APPRECIABLE UPPER LEVEL LIFT. AREAS IN THE SOUTHEAST WILL HAVE TO RELY ALMOST SOLELY ON OUTFLOW BOUNDARIES MOVING INTO THE AREA. MOST CONVECTION SHOULD DIMINISH AFTER 06Z WITH BOUNDARY LAYER STABILIZATION AND LACK OF SIGNIFICANT UPPER LEVEL SUPPORT. LOWS VERY MILD TONIGHT WITH AT LEAST PARTLY CLOUDY SKIES AND A PERSISTENT SW WIND. LOWS 69-73. AN INCREASE IN CONVECTIVE COVERAGE IS EXPECTED FOR SATURDAY. A BROAD MID AND UPPER LEVEL TROUGH OVER THE OHIO AND TN VALLEYS WILL KEEP A SOUTHWEST FLOW OVER OUR REGION. PRECIPITABLE WATERS RESPOND WITH VALUES CLIMBING TO NEAR 2 INCHES BY SATURDAY AFTERNOON. AT LEAST SOME MODEST UPPER LEVEL DIVERGENCE SETS UP OVER NORTHWESTER PORTIONS OF THE AREA SATURDAY AFTERNOON IN RESPONSE TO THE AREA BECOME POSITIONED IN THE RIGHT ENTRANCE REGION OF AN UPPER JET. THE JET POSITION IS MUCH MORE FAVORABLE ON THE NAM AS COMPARED TO THE GFS. AT THIS JUNCTURE IT IS HARD TO PINPOINT ANY LOCATIONS MORE FAVORED FOR CONVECTIVE COVERAGE. IF THE NAM IS CORRECT IN ITS JET PLACEMENT...THEN THE NW PIEDMONT WOULD SEE A GREATER COVERAGE. HOWEVER...THIS IS NOT CERTAIN AND WOULD PREFER TO SHOW A HIGH END CHANCE SCATTERED COVERAGE ACROSS THE ENTIRE AREA. DEEP LAYER SHEAR IS EXPECTED TO BE ONLY AROUND 20 KT... SO CONVECTIVE MODE SHOULD REMAIN PULSE IN NATURE. THEREFORE...OUTFLOW BOUNDARY INTERACTIONS WILL ONCE AGAIN GO A LONG WAY IN DETERMINING STORM COVERAGE AND LOCATION. WITH LIGHT WIND FIELDS ALOFT AND STORM MOTIONS OF ONLY AROUND 10 KT... THE STRONGER THUNDERSTORMS WILL BE EFFICIENT RAIN PRODUCERS GIVEN THE HIGH PRECIPITABLE WATER VALUES. AN ISOLATED SEVERE STORM CANNOT BE RULED OUT... BUT LACK OF SHEAR WILL PRECLUDE A WIDESPREAD EVENT. GREATER CLOUD COVERAGE AND RAIN CHANCES WILL HOLD TEMPS DOWN COMPARED TO TODAY. HIGHS 87-92. HAVE A HAPPY AND SAFE FOURTH OF JULY .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... AS OF 230 PM FRIDAY... SUMMARY SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS ARE EXPECTED THROUGHOUT THE SHORT TERM FORECAST PERIOD INCLUDING THE OVERNIGHT HOURS...ALTHOUGH ACTIVITY SHOULD BE MOST NUMEROUS DURING AFTERNOON PEAK HEATING ON SUN/MON. LOCALLY HEAVY RAINFALL WILL BE POSSIBLE WITH ANY THUNDERSTORMS. ISOLATED SEVERE THUNDERSTORMS WILL BE POSSIBLE PRIMARILY DURING THE AFTERNOON HOURS OF SUNDAY...ALTHOUGH A FEW STRONG TO SEVERE STORMS WILL BE POSSIBLE MONDAY AFTERNOON AS WELL. SATURDAY NIGHT THROUGH SUNDAY NIGHT STILL EXPECT SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS DURING THIS PERIOD WITH MID/UPPER LEVEL TROUGHING JUST TO OUR WEST OVER THE OH/TN VALLEYS...KEEPING A MOIST SOUTHERLY/SW FLOW THROUGHOUT THE COLUMN OVER THE CAROLINAS. FCST SOUNDINGS ACROSS CENTRAL NC SHOW FAIRLY IMPRESSIVE PWAT VALUES IN THE 1.75-2.00 RANGE THROUGHOUT THIS PERIOD. WITH PWAT VALUES THIS HIGH AND DEWPOINTS LIKELY IN THE UPPER 60S TO LOWER 70S...INSTABILITY WILL MOST DEFINITELY BE PRESENT AND ACCOUNTED FOR. AS FAR AS LIFT IS CONCERNED...BEING LOCATED JUST DOWNSTREAM OF THE MID/UPPER TROUGH TO THE WEST...WE WILL BE IN A FAVORABLE REGION FOR UPPER LEVEL DIVERGENCE...IN ADDITION TO SHORTWAVE IMPULSES ROUNDING THE BASE OF THE TROUGH AND LIFTING NE/ENE OVER THE CAROLINAS. TOUGH TO PICK OUT ANY AREA IN PARTICULAR FOR AN ENHANCED CHANCE OF SHOWERS/STORMS SINCE THIS MAY DEPEND ON THE EXACT TIMING/TRACK OF ANY SHORTWAVE IMPULSES AND/OR WHERE THE BETTER UPPER LEVEL DIVERGENCE IS LOCATED. THEREFORE...HAVE DECIDED TO ADVERTISE MID CHANCE POPS 40 ACROSS THE ENTIRE FORECAST AREA SAT NIGHT WHEN INSTABILITY WILL BE WEAKER...WITH 50 CHANCES DURING THE DAY SUNDAY WHEN DIURNAL HEATING WILL ALLOW FOR BETTER INSTABILITY...AND LOW CHANCE 30 POPS SUNDAY NIGHT AS THE MID/UPPER LEVEL TROUGH JUST TO OUR WEST BEGINS TO SHOW SIGNS OF WEAKENING/DEAMPLIFYING. LOW TEMPS SAT/SUN NIGHT SHOULD BE IN THE NORMAL TO SLIGHTLY ABOVE NORMAL RANGE IN THE UPPER 60S TO LOWER 70S. HIGH TEMPS ON SUNDAY SHOULD HAVE NO PROBLEM MAKING IT INTO THE MID/UPPER 80S...AND WHETHER OR NOT SOME LOCATIONS SEE LOWER 90S WILL DEPEND ON HOW MUCH CLOUD COVER AND CONVECTION IS PRESENT. GIVEN THE HIGH PWAT VALUES AND SCATTERED TO OCCASIONALLY NUMEROUS SHOWERS AND THUNDERSTORMS EXPECTED...LOCALLY HEAVY RAINFALL CAN BE EXPECTED...WITH A POTENTIAL FOR FLOODING...PARTICULARLY IN URBAN AREAS. AS FAR AS SEVERE WEATHER IS CONCERNED...LOW/MID LEVEL FLOW IS PROGGED TO GENERALLY BE AT OR BELOW 20 KNOTS THROUGH 700MB... INCREASING TO MAYBE 25-30 KNOTS IN THE MID-LEVELS SUNDAY AFTERNOON. THIS MAY MAKE IT DIFFICULT FOR AN ORGANIZED SEVERE WEATHER THREAT TO DEVELOP...AND EXPECT THAT ANY SEVERE STORMS WOULD BE OF THE PULSE/ISOLATED VARIETY...WITH A PRIMARY THREAT OF DAMAGING WINDS IN THE FORM OF WET MICROBURSTS AND HAIL UP TO THE SIZE OF QUARTERS. MONDAY AND MONDAY NIGHT THE MID/UPPER LEVEL TROUGH IS PROGGED TO CONTINUE TO WEAKEN AND DEAMPLIFY DURING THE DAY MONDAY AS IT LIFTS ENE/NE ACROSS THE LOWER MID-ATLANTIC. ALTHOUGH UPPER LEVEL LIFT WILL BE WEAKENING...FCST SOUNDINGS CONTINUE TO SHOW VERY MOIST PWAT VALUES IN THE 1.75 TO 2.00 RANGE...WITH PLENTY OF AVAILABLE INSTABILITY. HAVE THEREFORE DECIDED TO ADVERTISE MID-CHANCE 40 POPS ACROSS THE ENTIRE FORECAST AREA DURING THE DAYTIME PEAK-HEATING HOURS. A FEW STORMS MAY BRIEFLY BECOME STRONG TO SEVERE DURING THE AFTERNOON...WITH A PRIMARY THREAT OF DAMAGING WINDS AND LARGE HAIL. WILL KEEP A SLIGHT CHANCE 20 OF SHOWERS/STORMS MONDAY NIGHT GIVEN CONTINUED HIGH PWAT VALUES AND THE LIKELY PRESENCE OF ELEVATED INSTABILITY. THE UPPER LEVEL PATTERN BECOMES MORE UNIDIRECTIONAL BY THIS TIME...HOWEVER...ANY ONGOING ACTIVITY MAY KEEP GOING WELL PAST SUNSET WITH THE HELP OF MESOSCALE BOUNDARIES...AND THIS IS WHY THE SLIGHT CHANCE WILL BE LEFT IN FOR MONDAY NIGHT. HIGH TEMPS ON MONDAY SHOULD BE SIMILAR TO SUNDAY...GENERALLY IN THE MID/UPPER 80S WITH A FEW LOCATIONS MAKING IT INTO THE LOWER 90S IF GIVEN ENOUGH SUNSHINE. LOW TEMPS MONDAY NIGHT SIMILAR TO PREVIOUS NIGHTS...RANGING FROM THE UPPER 60S TO LOWER 70S. -VINCENT .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 245 PM FRIDAY... THE BERMUDA RIDGE ATTEMPTS TO RETROGRADE BACK TOWARD THE SOUTHEAST COAST AND FL THROUGH MID WEEK...WHILE SHORTWAVE ENERGY MOVING ACROSS THE US/CANADA BORDER ALLOWS THE WESTERLIES TO DIP A BIT SOUTHWARD INTO THE NRN GREAT LAKES/ST LAWRENCE VALLEY/NORTHEAST. VERY LITTLE CHANGES AT THE SURFACE...WITH THE ATLANTIC-CENTERED SURFACE HIGH HOLDING IN PLACE AND EXTENDING WSW INTO THE SOUTHEAST COASTAL SECTIONS...WITH A PERSISTENT PIEDMONT TROUGH OVER CENTRAL/WRN NC AND PWAT VALUES REMAINING IN THE 120-140 OF NORMAL RANGE. AS MUCH AS I WOULD LIKE TO BE ABLE TO DISCERN ONE DAY AS BEING BETTER THAN ANOTHER FOR SCATTERED MAINLY AFTERNOON/EVENING SHOWERS AND STORMS...AT THIS RANGE AND WITH MODEL VARIATION IN THE DETAILS...IT REMAINS NEARLY IMPOSSIBLE. WILL CONTINUE WITH LOW CHANCE 30 POPS...MAINLY AFTERNOON AND EVENING...TUESDAY THROUGH FRIDAY. GFS/ECMWF THICKNESSES REMAIN NEAR NORMAL AND TEMPERATURES SHOULD RUN CLOSE TO NORMAL THROUGH THE PERIOD AS WELL. -GIH/VINCENT .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... AS OF 2 PM FRIDAY... IN GENERAL... VFR CONDITIONS EXPECTED THROUGH THE TAF PERIOD...WITH THE EXCEPTION BEING THE POTENTIAL FOR ISOLATED TO SCATTERED CONVECTION. FOR THE REST OF THE DAY THROUGH TONIGHT... BEST POTENTIAL FOR CONVECTION WILL BE AT THE TRIAD TERMINALS. IN THIS REGION...THE MID LEVEL CAP IS WEAKER AND LOW LEVEL CONVERGENCE COMBINED WITH A WEAK UPPER LEVEL DISTURBANCE MOVING EAST FROM THE TN VALLEY WILL SUPPORT THE DEVELOPMENT OF CONVECTION THROUGH LATE THIS AFTERNOON AND INTO TONIGHT. RESULTANT OUTFLOW BOUNDARIES EMANATING FROM CONVECTION OVER THE FOOTHILLS MAY ALSO BECOME A TRIGGER FOR CONVECTIVE DEVELOPMENT. TOO MUCH UNCERTAINTY REMAINS REGARDING COVERAGE AND TIMING OF CONVECTION...SO WILL INCLUDE A CB AT GSO/INT AND AS FAR EAST AS RDU FOR THIS EVENING THROUGH LATE TONIGHT. ANY CONVECTION ACROSS THE AREA SHOULD WANE DURING THE PREDAWN HOURS. WINDS AT 2 KFT WILL INCREASE TO AROUND 25 KT OVERNIGHT. WHILE WE MAY FALL SHORT OF EXACT LOW LEVEL WIND SHEAR CRITERIA...AT LEAST 15-20 KT OF LLWS WILL BE PRESENT AFTER MIDNIGHT WHICH COULD AFFECT SMALLER AIRCRAFT AND GENERAL AVIATION INTERESTS. AREAL EXTENT OF CONVECTION WILL INCREASE ON SATURDAY AS THERE WILL BE NO MID LEVEL CAP AND DEEP LAYER MOISTURE AND INSTABILITY IS PLENTIFUL. EXPECT SCATTERED TO NUMEROUS THUNDERSTORMS TO AFFECT CENTRAL NC STARTING ROUGHLY AROUND 16Z TOMORROW AND THIS ACTIVITY WILL LIKELY PERSIST INTO SATURDAY NIGHT. WILL INTRODUCE CB AT 16Z AT ALL TERMINALS TO ACCOUNT FOR THE CONVECTIVE POTENTIAL. OTHERWISE... VFR CONDITIONS EXPECTED OUTSIDE CONVECTION. CHANCES FOR DIURNAL CONVECTION WILL PERSIST THROUGH AT LEAST TUESDAY OF NEXT WEEK. .RAH WATCHES/WARNINGS/ADVISORIES... NONE. SYNOPSIS...JFB NEAR TERM...JFB SHORT TERM...VINCENT LONG TERM...GIH/VINCENT AVIATION...JFB