Severe Thunderstorm Warning 221, NWS Raleigh, NC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
211 PM EDT MON JUL 27 2009

.SYNOPSIS...

AN UPPER DISTURBANCE WILL MOVE ACROSS NORTH CAROLINA THROUGH
TONIGHT. THE AREA WILL THEN LANGUISH UNDER DEEP SOUTHWEST FLOW
THROUGH LATE WEEK...PINNED BETWEEN A TROF OVER THE CENTRAL UNITED
STATES AND A STRONG BERMUDA HIGH OVER THE WESTERN ATLANTIC. THIS
WILL PRODUCE TYPICAL SUMMER...WARM AND HUMID...CONDITIONS WITH
UNSETTLED WEATHER THROUGH THE PERIOD.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 115 PM MONDAY...

INSTABILITY WILL BE REMAIN HIGH THIS EVENING WITH PRECIPITABLE
WATER VALUES OF AROUND 2 INCHES EAST OF THE SURFACE TROF. MIXED
LAYER CAPES WILL APPROACH 2K JOULES AND 0-6KM SHEAR ON THE ORDER
OF 30-35 M/S...SUPPORTIVE OF BETTER STORM ORGANIZATION THAN
SUNDAY. UPPER DYNAMIC SUPPORT FOR CONVECTION IS BETTER ALIGNED AS
WELL...TAKING THE FORM OF UPPER SPEED DIFFLUENCE AND AN
APPROACHING MID/UPPER LEVEL VORT MAXIMA LIFTING NORTHEAST TOWARDS
THE CENTRAL AND EASTERN CWFA. AS SUCH...WILL CONTINUE POPS IN THE
LIKELY CATEGORY...GRADUATED TOWARDS HIGHER VALUES IN THE EAST.

OVERNIGHT: CONVECTIVE COVERAGE AND INTENSITY SHOULD DIMINISH BY
MIDNIGHT OR SHORTLY THEREAFTER. WILL... HOWEVER RETAIN A SLIGHT
CHANCE POP FOR THE OVERNIGHT GIVEN THE EXPECTED PASSAGE OF A MORE
SOUTHERN DISTURBANCE ALOFT...LOWS 68 TO 73 DEGREES.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
AS OF 205 PM MONDAY...

THE PERSISTENT WARM (UPPER 80S TO LOWER 90S) AND MOIST AIRMASS IN
PLACE WILL SUPPORT AT LEAST A FEW THUNDERSTORMS AGAIN TUESDAY
AFTERNOON AND EVENING. UPPER SUPPORT WILL BE MUCH REDUCED AS
SUBSIDENCE IN THE WAKE OF THE SHORT WAVE MOVING THROUGH TONIGHT
WILL BE MORE SUPPRESSIVE THAN SUPPORTIVE. WILL KEEP POPS IN THE
LOW CHANCE CATEGORY WITH SLIGHTLY HIGHER NUMBERS IN THE EAST.

A MUCH STRONGER SHORT WAVE WILL BE APPROACHING FROM THE WEST ON
TUESDAY NIGHT. THIS WAVE WILL BE REACHING THE MOUNTAINS LATE...AND
AT THIS POINT WILL ONLY KEEP A SLIGHT CHANCE POP IN THE
OVERNIGHT. MINS WILL BE SIMILAR TO PAST DAYS...70-74. -MLM

AFTER A POSSIBLE REPRIEVE IN CONVECTION FOR TUESDAY...DEEPER MOISTURE
AND SUPPORT ALOFT IS FORECAST TO RETURN TO THE REGION AS THE UPPER
WAVE CURRENTLY OVER THE NORTHERN ROCKIES WILL PUSH EAST INTO THROUGH
THE MID-ATLANTIC STATES WEDNESDAY AFTERNOON/EVENING. THE MOIST
ADIABATIC PROFILES DEPICTED BY THE BUFR MODEL SOUNDINGS ARE QUITE
IMPRESSIVE...FEATURING PWATS OF 2.0 TO 2.1 ACROSS THE AREA.
THE LATEST 12Z/27 GFS IS OF LITTLE HELP RIGHT NOW...TAINTED BY
CONVECTIVE FEEDBACK ISSUES...AND A RESULTANT ERRONEOUS CLOSED SURFACE LOW
TRACKING EAST ACROSS EASTERN TN AND NORTHERN VIRGINIA...WHILE THE
WEAKER AND MORE REALISTIC NAM IMPLIES MORE AN OPEN TROUGH OVER THE
VIRGINIAS AND CAROLINAS...WITH THE CLOSED LOW OVER PENNSYLVANIA.
SURPRISINGLY...PROBABILISTIC FORECASTS FROM THE GLOBAL ENSEMBLE
MODEL ARE VERY CONSERVATIVE ON WEDNESDAY...KEEPING THE LIKELIHOOD
OF A ONE-QUARTER OF AN INCH OR MORE OF PRECIP OVER CENTRAL AT 20
PERCENT OR LESS. THUS WILL KEEP POPS IN THE GOOD CHANCE
RANGES...AROUND 50 PERCENT. HIGHS IN THE MID TO UPPER 80 ON
WEDNESDAY WITH LOWS WEDNESDAY NIGHT 69 TO 74. -CBL

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
AS OF 210 PM MONDAY...

...TYPICAL SUMMERTIME PATTERN FOR CENTRAL NC...

A BROAD MEAN TROUGH WILL REMAIN CENTERED OVER THE CENTRAL US/MS
VALLEY... AS THE STRONG SUBTROPICAL/BERMUDA RIDGE RETROGRADES OVER
THE SERN US. THE RESULTANT DEEP SWLY FLOW WILL KEEP A HUMID
AND MOIST AIRMASS IN PLACE OVER CENTRAL NC. SHORTWAVE ENERGY
TRAVERSING EAST/NORTHEAST THROUGH THE BASE OF THE LONGWAVE TROUGH
ALONG WITH WEAK LOW-LEVEL CONFLUENCE ALONG THE LEE SIDE SURFACE
TROUGH WILL SUPPORT SCATTERED AFTERNOON AND EVENING THUNDERSTORMS
EACH DAY. NEAR NORMAL HIGH TEMPERATURES OF 87 TO 93...WITH MILD
OVERNIGHT LOWS OF 69 TO 74.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
AS OF 200 PM...

STRONG INSTABILITY COMBINED WITH UPPER SUPPORT FROM A SHORT WAVE
AND ASSOCIATED SHEAR AXIS TRANSLATING ACROSS THE AREA WILL PRODUCE
SCATTERED STRONG THUNDERSTORMS FROM TAF INITIAL ISSUANCE INTO THE
EVENING...TAPERING OFF 02-04Z. THERE WILL BE NUMEROUS OUTFLOW
BOUNDARIES FROM THE VARIOUS STORMS PRODUCING GUSTY WINDS...WHICH
COULD EXCEED 30 KNOTS IN PROXIMITY TO STORMS. VISIBLITIES COULD BE
BRIEFLY IFR IN HEAVY RAIN...BUT CEILINGS WILL REMAIN LARGELY
VFR...PERHAPS VERY BRIEFLY MIFR DIRECTLY UNDER CONVECTION. SKIES
WILL SCATTER OUT AFTER LOSS OF INSOLATION...WITH WIDELY SCATTERED
CONVECTION POSSIBLE IN THE EAST (RDU/RWI/FAY) OVERNIGHT. IFR FOG
WILL BE POSSIBLE IN THE PREDAWN (09-12Z) AT TAF SITES WHICH
RECEIVE RAINFALL.

CONVECTION WILL BE MUCH LESS FOCUSED AND WIDELY SCATTERED
TOMORROW. VFR CONDITIONS EXPECTED THROUGH THE DAY AFTER ANY
LINGERING MORNING FOG BURNS OFF. WINDS WILL REMAIN FROM THE
SOUTHWEST AT 10 KNOTS OR LESS.

A NORMAL SUMMERTIME PATTERN WILL CONTINUE WEDNESDAY THROUGH
SATURDAY AS THE AREA REMAINS UNDER SOUTHWEST FLOW = WARM AND MOIST.
CONDITIONS WILL BE VFR...EXCEPT FOR WIDELY SCATTERED LATE DAY
CONVECTION AND PATCHY MVFR EARLY MORNING FOG EACH DAY.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

SYNOPSIS...MLM
NEAR TERM...MLM
SHORT TERM...MLM/CBL
LONG TERM...CBL
AVIATION...MLM

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RALEIGH NC
1257 PM EDT MON JUL 27 2009

NCZ007>011-024>028-040>043-075>078-084>086-088-089-281700-
PERSON-GRANVILLE-VANCE-WARREN-HALIFAX-ORANGE-DURHAM-FRANKLIN-NASH-
EDGECOMBE-CHATHAM-WAKE-JOHNSTON-WILSON-MOORE-LEE-HARNETT-WAYNE-
RICHMOND-SCOTLAND-HOKE-CUMBERLAND-SAMPSON-
1257 PM EDT MON JUL 27 2009

...SEVERE THUNDERSTORM WATCH 627 IN EFFECT UNTIL 8 PM EDT THIS
EVENING...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL NORTH CAROLINA.

.DAY ONE...THIS AFTERNOON AND TONIGHT.

PLEASE LISTEN TO NOAA WEATHER RADIO OR GO TO WEATHER.GOV ON THE
INTERNET FOR MORE INFORMATION ABOUT THE FOLLOWING HAZARDS.

   SEVERE THUNDERSTORM WATCH.

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND
EVENING ACROSS CENTRAL NORTH CAROLINA. AN UPPER DISTURBANCE WILL BE
SLOWLY PASSING OVER THE AREA TODAY...WHICH WILL RESULT IN THE
DEVELOPMENT OF SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS. A
FEW OF THESE THUNDERSTORMS COULD BECOME SEVERE AND PRODUCE DAMAGING
DOWNBURST WINDS IN EXCESS OF 60 MPH AND HAIL UP TO THE SIZE OF
NICKELS.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY.

THE PRESENCE OF BERMUDA HIGH PRESSURE WILL RESULT IN WARM AND
HUMID CONDITIONS... WITH AFTERNOON AND EVENING SHOWERS AND
THUNDERSTORMS EACH DAY THIS WEEK. WHILE THIS WEATHER PATTERN MAY
FUEL ISOLATED SEVERE THUNDERSTORMS... NO ORGANIZED SEVERE AND
HAZARDOUS WEATHER IS EXPECTED.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTER ACTIVATION WILL LIKELY BE NEEDED BETWEEN 200 PM
AND 800 PM TODAY. SPOTTERS SHOULD REPORT SEVERE WEATHER AS SOON AS
IT IS SAFE TO DO SO. PLEASE STAY TUNED FOR LATER WATCHES AND
WARNINGS.

NCZ021>023-038-039-073-074-083-281700-
FORSYTH-GUILFORD-ALAMANCE-DAVIDSON-RANDOLPH-STANLY-MONTGOMERY-ANSON-
1257 PM EDT MON JUL 27 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL NORTH CAROLINA.

.DAY ONE...THIS AFTERNOON AND TONIGHT.

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND
EVENING ACROSS CENTRAL NORTH CAROLINA. AN UPPER DISTURBANCE WILL BE
SLOWLY PASSING OVER THE AREA TODAY...WHICH WILL RESULT IN THE
DEVELOPMENT OF SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS.
ISOLATED STORMS COULD BECOME SEVERE AND PRODUCE DAMAGING
DOWNBURST WINDS IN EXCESS OF 60 MPH AND HAIL UP TO THE SIZE OF
NICKELS.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY.

THE PRESENCE OF BERMUDA HIGH PRESSURE WILL RESULT IN WARM AND
HUMID CONDITIONS... WITH AFTERNOON AND EVENING SHOWERS AND
THUNDERSTORMS EACH DAY THIS WEEK. WHILE THIS WEATHER PATTERN MAY
FUEL ISOLATED SEVERE THUNDERSTORMS... NO ORGANIZED SEVERE AND
HAZARDOUS WEATHER IS EXPECTED.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTER ACTIVATION IS NOT EXPECTED...HOWEVER...SPOTTERS
ARE ENCOURAGED TO REPORT ANY SEVERE WEATHER.

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