Severe Thunderstorm Warning 314, NWS Raleigh, NC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
320 PM EDT SAT AUG 22 2009

.SYNOPSIS...
A VERY MOIST AIR MASS COUPLED WITH THE APPROACH OF AN UNSEASONABLY
STRONG UPPER LEVEL TROUGH WILL RESULT IN SCATTERED SHOWERS AND
THUNDERSTORMS ACROSS THE AREA TODAY AND TONIGHT. DRIER AIR ALOFT
WILL OVERSPREAD THE REGION SUNDAY...LIMITING THE DEVELOPMENT OF
SHOWERS AND STORMS. WEAK HIGH PRESSURE WILL BUILD INTO THE AREA FROM
THE NORTHWEST MONDAY INTO TUESDAY.

&&

.NEAR TERM /THROUGH SUNDAY/...
AS OF 300 PM SATURDAY...

SHOWERS AND THUNDERSTORMS EAST OF HIGHWAY ONE SUPPORTED BY GOOD
UPPER LEVEL DIVERGENCE WHICH SHOULD ALLOW THEM TO PERSIST TO NEAR
MIDNIGHT OVER THE COASTAL PLAIN. ISOLATED TO WIDELY SCATTERED
SHOWERS AND THUNDERSTORMS TO THE WEST OF THAT AREA WILL HAVE SUPPORT
FROM THE LOW LEVEL TROUGH AND MAY BE ABLE TO PERSIST PAST MIDNIGHT
ALONG AND JUST WEST OF THE HIGHWAY ONE CORRIDOR. SHOULD BECOME DRY
WELL BEFORE DAWN. SEVERE THREAT MINIMAL BUT NOT ZERO FOR DAMAGING
DOWNBURST WINDS ANYWHERE IN CENTRAL NORTH CAROLINA BUT PREFERRED
NEAR THE SURFACE TROUGH.

STRATUS SHOULD DEVELOP LATE TONIGHT AND BE MORE WIDESPREAD AND
PERSISTENT THAN THIS MORNING. COOLER AIR FILTERING IN FROM THE
NORTHWEST WILL STILL ALLOW TEMPERATURES TO DIP INTO THE UPPER 60S
IN THE NORTHWEST AND NORTH CENTRAL. 70 TO 73 EXTREME EAST PARTS.

SURFACE TROUGH PERSISTS OVER THE AREA SUNDAY BUT IT APPEARS THE
TRIGGER FOR ANY SIGNIFICANT CONVECTION WILL BE THE CONTINUED SLOW
APPROACH OF THE MID LEVEL TROUGH. BEST RAIN CHANCES WILL BE ACROSS
THE NORTH IN THE LATE AFTERNOON...BUT STILL ONLY IN THE CHANCE
RANGE. ONLY MILDLY UNSTABLE SUNDAY AND COVERAGE OF STORMS SHOULD BE
LIMITED COMPARED TO TODAY. AFTERNOON HIGH TEMPERATURES 85 TO 90.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
AS OF 319 PM SATURDAY...

THE WEAKENING L/W TROUGH AND ASSOCIATED COOL POOL ALOFT WILL
LINGER INVOF THE CENTRAL APPALACHIANS THROUGH THE PERIOD... WHICH
COULD SUPPORT ISOLATED AFTERNOON CONVECTION... ESPECIALLY MONDAY INVOF
THE SURFACE BOUNDARY EXPECTED TO DIFFUSE OVER THE COASTAL PLAIN
AND SANDHILLS. BY TUESDAY... 1) INCREASINGLY DRY AND CAPPED MID
LEVELS... 2) INCREASINGLY ANTICYCLONIC/DIVERGENT LOW LEVEL FLOW IN
THE WAKE OF THE SURFACE FRONT/TROUGH.. AND 3) THE MIXING OUT OF
LOW LEVEL MOISTURE INTO 60 TO 65 DEGREE RANGE... ARGUE FOR LIMITED IF
ANY CONVECTION OVER CENTRAL NC ON TUESDAY. HIGH TEMPERATURES IN
THE UPPER 80S TO AROUND 90 EXPECTED... WITH A RANGE OF 63 TO 70
DEGREES FOR LOWS.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 245 PM SATURDAY...

OVERVIEW: MEDIUM RANGE NWP MODELS IN GENERAL AGREEMENT THAT THE
INITIAL SHEAR AXIS/DEFORMATION ZONE ALOFT OVER CENTRAL NC WILL
DRIFT OFFSHORE AND WEAKEN AS A MORE VIGOROUS NORTHERN STREAM
TROUGH SWEEPS EASTWARD ACROSS SE CANADA WEDNESDAY THROUGH
THURSDAY. THE ASSOCIATED HEIGHT FALLS ALOFT SHOULD PROPEL A
(BACK DOOR) COLD FRONT SOUTHWARD INTO THE VICINITY OF CENTRAL NC
BY LATE WEEK... THOUGH TIMING AND SOUTHWARD PROGRESS REMAIN
QUESTIONABLE GIVEN THE PRESENCE OF A SUBTROPICAL RIDGE OVER THE
SOUTHEASTERN US AND AMPLITUDE DIFFERENCES WITH THE TROUGH IN THE
MEDIUM RANGE GUIDANCE. IF THE FRONT EVEN MAKES IT INTO CENTRAL NC
-- FAVORED AT THIS TIME IN THE LATE THURSDAY INTO FRIDAY TIME
FRAME -- THEN IT MAY ULTIMATELY RETREAT NORTHWARD AND DIFFUSE AS
SHORTWAVE RIDGING BUILDS ACROSS THE NE QUARTER OF THE NATION
FRIDAY-SATURDAY BEHIND THE SE CANADA TROUGH (AND AHEAD OF ANOTHER
UPSTREAM TROUGH APPROACHING BY THAT TIME FROM CENTRAL CANADA AND
THE GREAT LAKES).

THE ATMOSPHERE SHOULD BE RELATIVELY DRY AND CAPPED ALOFT EARLY IN
THE PERIOD... WHICH ARGUES FOR NO MORE THAN AN ISOLATED STORM OR
TWO OVER THE SOUTHERN SANDHILLS AND COASTAL PLAIN... WHERE
CLIMATOLOGICALLY RICHER LOW LEVEL MOISTURE MAY ALLOW PARCELS TO
OVERCOME THE CAP INVOF THE SEA BREEZE. LOW LEVEL THICKNESSES
SUPPORT HIGH TEMPERATURES GENERALLY 89 TO 93 DEGREES... PERHAPS A
FEW MID 90S BY THURSDAY. 66 TO 71 DEGREES.

PRECIPITATION CHANCES MAY INCREASE (20-30 POP) AS THE AFOREMENTIONED
SURFACE FRONT NEARS THE REGION BY LATE WEEK... BUT BACK DOOR FRONTS
CLIMATOLOGICALLY PROVIDE RELATIVELY WEAK AND SHALLOW LIFT THAT
OFTEN FAIL TO SUPPORT MUCH CONVECTION... PARTICULARLY SO IN THIS
INSTANCE WITH THE RESIDUALLY DRY AND CAPPED MID LEVELS. TEMPERATURES
FRIDAY AND SATURDAY WILL BE DEPENDENT ON THE LOCATION OF THE
FRONT... BUT WILL MAINTAIN THE CURRENTLY ADVERTISED COOLER 85 TO
AROUND 90 DEGREES FROM NORTH TO SOUTH EACH DAY... WARMEST
SATURDAY. CLIMO OVERNIGHT LOWS AGAIN GENERALLY UPPER 60S TO AROUND
70 DEGREES.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
AS OF 145 PM...

WIDESPREAD STORMS MAINLY EAST OF HIGHWAY ONE AT THIS TIME. ISOLATED
STORMS TO THE WEST EXPECTED TO BECOME MORE WIDESPREAD LATER THIS
AFTERNOON. CONVECTION IN THE SOUTH IS EXPECTED TO END IN THE
EVENING. TOWARD THE VIRGINIA BORDER STORMS MAY PERSIST INTO THE
EARLY HOURS AFTER MIDNIGHT. SOME MVFR FOG AND IFR STRATUS EXPECTED
BEFORE SUNRISE SUNDAY.

THE FRONT IS EXPECTED STALL ACROSS THE REGION ON SUNDAY AFTERNOON
PROVIDING THE NORTH AND EAST PORTIONS OF THE AREA WITH ISOLATED TO
POSSIBLY SCATTERED SHOWERS AND THUNDERSTORMS. THE FRONT SHOULD PUSH
EAST OF THE AREA BY SUNDAY NIGHT. VFR SKIES/VISIBILITIES SHOULD
RETURN TO ALL AREAS MONDAY AFTERNOON THROUGH WEDNESDAY.

&&

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

&&

SYNOPSIS...
NEAR TERM...
SHORT TERM...MWS
LONG TERM...MWS
AVIATION...

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RALEIGH NC
1125 AM EDT SAT AUG 22 2009

NCZ007>011-021>028-038>043-073>078-083>086-088-089-230930-
PERSON-GRANVILLE-VANCE-WARREN-HALIFAX-FORSYTH-GUILFORD-ALAMANCE-
ORANGE-DURHAM-FRANKLIN-NASH-EDGECOMBE-DAVIDSON-RANDOLPH-CHATHAM-WAKE-
JOHNSTON-WILSON-STANLY-MONTGOMERY-MOORE-LEE-HARNETT-WAYNE-ANSON-
RICHMOND-SCOTLAND-HOKE-CUMBERLAND-SAMPSON-
1125 AM EDT SAT AUG 22 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL NORTH CAROLINA.

.DAY ONE...TODAY AND TONIGHT.

A FEW SEVERE THUNDERSTORMS ARE EXPECTED THIS AFTERNOON... MAINLY
NORTH AND EAST OF A GREENSBORO TO FAYETTEVILLE LINE. THE PRIMARY
THREAT IS EXPECTED TO BE DAMAGING DOWNBURST WINDS.

SCATTERED SHOWERS AND THUNDERSTORMS WILL PRODUCE LOCALLY HEAVY
RAINFALL. IF THE SHOWERS AND STORMS MOVE REPEATEDLY OVER THE SAME
LOCATION...FLASH FLOODING MAY OCCUR.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY.

ISOLATED STRONG TO SEVERE THUNDERSTORMS MAY OCCUR SUNDAY
AFTERNOON. THE MAIN SEVERE WEATHER THREAT WILL LOCALIZED DAMAGING
DOWNBURSTS WINDS AND HAIL UP TO THE SIZE OF PENNIES. THE THREAT
FOR SEVERE STORMS APPEARS GREATEST ALONG AND EAST OF HIGHWAY ONE.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTERS ARE ENCOURAGED TO REPORT ANY SEVERE OR
SIGNIFICANT WEATHER ASSOCIATED WITH THE STORMS TODAY AND SUNDAY.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RALEIGH NC
406 PM EDT SAT AUG 22 2009

NCZ022-222100-
GUILFORD-
406 PM EDT SAT AUG 22 2009

...A STRONG THUNDERSTORM WILL MOVE ACROSS GUILFORD COUNTY THROUGH 500
PM EDT...

AT 403 PM EDT...DOPPLER RADAR INDICATED A STRONG THUNDERSTORM 5 MILES
SOUTH OF COLFAX...OR NEAR THE PIEDMONT TRIAD AIRPORT...MOVING EAST
AT 10 MPH. WINDS OF 40 MPH WERE REPORTED BY A SPOTTER AT THE
PIEDMONT TRIAD FARMERS MARKET. THIS WIND WILL BLOW AROUND
TENTS...GARBAGE CANS AND OTHER LIGHT OBJECTS.

SOME LOCATIONS AFFECTED BY THIS STORM INCLUDE...JAMESTOWN...HIGH
POINT AND GREENSBORO.

GUSTY WINDS OF 40 MPH AND VERY HEAVY RAIN CAN BE EXPECTED WITH THIS
BAND OF STORMS.

VERY HEAVY RAIN WITH RAINFALL CAN BE EXPECTED ALONG AND NORTH OF
INTERSTATE 40. MOTORISTS SHOULD DRIVE WITH CAUTION TO AVOID
HYDROPLANING.

JO

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RALEIGH NC
412 PM EDT SAT AUG 22 2009

NCZ038-222115-
DAVIDSON-
412 PM EDT SAT AUG 22 2009

...A STRONG THUNDERSTORM WILL MOVE ACROSS SOUTHERN DAVIDSON COUNTY
THROUGH 515 PM EDT...

AT 409 PM EDT...DOPPLER RADAR INDICATED STRONG THUNDERSTORMS
EXTENDING FROM SALISBURY TO GRANITE QUARRY AND KANNAPOLIS...MOVING
EAST AT 20 MPH. THESE STORMS ARE LIKELY PRODUCING WIND GUSTS UP TO
40 TO 45 MPH.

SOME LOCATIONS AFFECTED BY THIS STORM INCLUDE...HIGH ROCK AROUND 435
PM...NEWSOM AROUND 440 PM AND DENTON AROUND 445 PM.

GUSTY WINDS OF 40 TO 50 MPH ALONG WITH VERY HEAVY RAIN CAN BE
EXPECTED WITH THESE STORMS.

IF ON OR NEAR HIGH ROCK LAKE MOVE TO A SAFE HARBOR OF SHELTER. MOVE
TO SAFE SHELTER NOW. DONT BE CAUGHT ON THE WATER IN A THUNDERSTORM

JO

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