Special Weather Statement, NWS Raleigh, NC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
319 PM EDT FRI MAY 27 2011

.SYNOPSIS...
AN UPPER LEVEL LOW PRESSURE SYSTEM WILL EDGE SLOWLY EAST ACROSS
OUR REGION THROUGH SATURDAY. HIGH PRESSURE WILL THEN EXPAND ACROSS
THE MIDDLE ATLANTIC AND SOUTHEAST STATES SUNDAY THROUGH EARLY NEXT
WEEK.

&&

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

NARROW REGION OF LOW LEVEL CONFLUENCE...STRENGTHEN LIKELY BY THE
APPROACH OF A MID LEVEL VORTICITY MAXIMUM APPROACHING FROM UPSTATE
SC...ENHANCING/MAINTAINING A LINE OF CONVECTION ACROSS THE HEART OF
CENTRAL NC. 850MB TRANSPORT BEST THIS AFTERNOON IN VICINITY OF
HIGHWAY 1 BUT MODELS SHIFT THIS TRANSPORT TOWARD THE WESTERN
PIEDMONT THIS EVENING....LIKELY DUE TO MID LEVEL TROUGH LIFTING OVER
GA/SC AND SOME UPPER DIVERGENCE CAUSED BY 300MB JET LIFTING NWD
ACROSS SOUTHERN NEW ENGLAND.

WHILE SOME OF THE CONVECTION WILL LIKELY DISSIPATE WITH LOSS OF
HEATING...PRESENCE OF MID LEVEL TROUGH AND PROBABILITY OF ANOTHER
VORT MAX ROUND BASE OF TROUGH WILL MAINTAIN SOME ORGANIZED
CONVECTION OVER CENTRAL NC THROUGH THE NIGHT. HIGHEST THREAT WILL BE
OVER THE WESTERN TWO-THIRDS OF THE CWA. IN ADDITION...SATELLITE
BASED PRECIPITABLE WATER IMAGERY SUGGEST A PLUME OF 1.5-1.6 INCHES
LIFTING INTO CENTRAL NC FROM COASTAL GA-SC. DUE TO PROXIMITY OF THIS
PLUME AND POTENTIAL FOR SCATTERED-NUMEROUS CONVECTION TO OCCUR
THROUGH MOST OF THE NIGHT...A FLASH FLOOD WATCH HAS BEEN ISSUED FOR
AREAS WEST OF A HENDERSON-RALEIGH-FAYETTEVILLE LINE THROUGH 6 AM
SATURDAY.

SATURDAY...EXPECT LOW CLOUDS EARLY...LIFTING INTO A BROKEN CU FIELD
BY MIDDAY-EARLY AFTERNOON. WITH MID LEVEL TROUGH IN VICINITY...MAY
SEE A FEW SHOWERS/STORMS IN THE MORNING. WITH HEATING...EXPECT
SCATTERED CONVECTION TO BLOSSOM IN THE AFTERNOON...THOUGH NOT AS
EXTENSIVE AS CURRENT EVENT. GREATEST THREAT OF CONVECTION WILL BE
OVER THE COASTAL PLAIN AND SANDHILLS WHERE LOW LEVEL INSTABILITY
WILL BE GREATEST. WHILE COULD SEE A STORM OR TWO IN THE
WEST...BUILDING MID-UPPER LEVEL HEIGHTS IN WAKE OF DEPARTING TROUGH
MAY LIMIT CONVECTIVE POTENTIAL.

MAX TEMPS SATURDAY DEPENDENT UPON INSOLATION. RH CROSS SECTIONS
SUGGEST APPRECIABLE DRYING IN THE MID-UPPER LAYERS. IF THIS
OCCURS...THIS SHOULD ALLOW FOR SOME PARTIAL SUN. LEANED TOWARD THE
WARM SIDE OF MOS GUIDANCE WITH LOW-MID 80S EXPECTED IN THE
AFTERNOON.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
AS OF 250 PM FRIDAY...

EXPECT DECREASING RAIN CHANCES AND INCREASING HEAT OVER THE LATTER
HALF OF THE HOLIDAY WEEKEND.

FOR SATURDAY NIGHT: SATURDAY AFTERNOON'S CONVECTION SHOULD BE
QUICKLY WEAKENING BY EARLY TO MID EVENING WITH THE LOSS OF HEATING.
THE WEAK UPPER LEVEL SHEAR AXIS SITTING OVER ERN NC SLIPS OFF THE
COAST AND WEAKENS FURTHER SATURDAY NIGHT IN THE FACE OF STRONG
RIDGING BUILDING OVERHEAD FROM THE SW... WITH HEIGHTS ALOFT RISING
30-50 METERS OVERNIGHT AND MID LEVEL LAPSE RATES DECREASING. LIGHT
LOW LEVEL FLOW FROM THE SSE -- AROUND THE PERIPHERY OF THE SURFACE
HIGH CENTERED WELL TO OUR NE -- AND THE RESULTING UPSLOPE COMPONENT
MAY HELP SUPPORT SCATTERED SHALLOW SHOWERS INTO THE EVENING IN THE
FAR WRN CWA. MOIST LOW LEVELS... LIGHT SURFACE WINDS... AND THE LACK
OF HIGHER CLOUD COVER WILL CONTRIBUTE TO SURFACE COOLING AND
FOG/STRATUS DEVELOPMENT TOWARD SUNDAY MORNING... ESPECIALLY OVER THE
WRN CWA. LOWS 64-67.

FOR SUNDAY/SUNDAY NIGHT: THE SURFACE HIGH WILL CONTINUE TO NOSE INTO
CENTRAL NC FROM THE NE AS RIDGING ALOFT BUILDS STEADILY IN FROM THE
WSW. MID LEVEL LAPSE ARE PROJECTED TO REMAIN RATHER WEAK OVER ALL
BUT WESTERN NC... AND WHILE PRECIPITABLE WATER VALUES SHOULD BE
SLIGHTLY ABOVE NORMAL WITH MLCAPE VALUES APPROACHING MODERATE
LEVELS... ANY CONVECTION WILL HAVE WEAK VERTICAL ACCELERATIONS WITH
POOR ORGANIZATION DUE TO THE LOW DEEP LAYER SHEAR. WOULD EXPECT TO
SEE ISOLATED TO SCATTERED CONVECTION JUST TO OUR WEST AND
PARTICULARLY OVER THE HIGHER TERRAIN... BUT GIVEN THE WEAK STEERING
WITH LIGHT WINDS FROM THE SURFACE ON UP THROUGH THE MID LEVELS...
THIS ACTIVITY SHOULD HOLD TO OUR WEST. WILL LEAVE POPS OUT OF THE
FORECAST FOR NOW... ALTHOUGH I WOULDN'T BE SURPRISED TO SEE ONE OR
TWO ISOLATED AFTERNOON STORMS. HIGHS 87-90. THE MID LEVEL
ANTICYCLONE REMAINS CENTERED OVER ERN KY ELONGATED SW TO NE THROUGH
SUNDAY NIGHT WITH SURFACE-850 MB RIDGING EXTENDING IN FROM THE ENE.
THE NEAR-SURFACE MOISTURE IS LIKELY TO BE A LITTLE LOWER THAN ON
SATURDAY WITH A DAY OF STRONG HEATING... SO WE SHOULD SEE JUST
PATCHES OF FOG. LOWS IN THE MID-UPPER 60S.

FOR MONDAY: THE CENTER OF THE CLOSED MID LEVEL ANTICYCLONE DRIFTS
OVER THE OH/KY BORDER AND CONTINUES TO STRENGTHEN TO NEAR 5950
METERS. LOW LEVEL MOISTURE DECREASES FURTHER WITH CONTINUED VERY
WEAK WINDS FROM THE SURFACE UP THROUGH THE MID LEVELS. WHILE MODELS
PROJECT PRECIPITABLE WATER HOLDING NEAR 150 PERCENT OF NORMAL
(HIGHEST OVER NE CWA) WITH 850-700 MB WINDS STRENGTHENING A BIT TO
AROUND 25 KTS OUT OF THE NE... HIGH SURFACE DEW POINT DEPRESSIONS...
WARM MID LEVELS... AND THE LACK OF ANY CONVECTIVE FOCUS SHOULD HOLD
PRECIP CHANCES DOWN. WILL KEEP THE FORECAST DRY... BUT AGAIN... ONE
OR TWO ISOLATED CELLS MAY STILL OCCUR. LOW LEVEL THICKNESSES OF
1415-1425 METERS SUPPORT HIGHS OF 89-93. -GIH

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AS OF 255 PM FRIDAY...

THE HOT AND DRY WEATHER IS LIKELY TO HOLD THROUGH MID WEEK... BEFORE
THE ANOMALOUSLY WARM AIR MASS FINALLY GIVES WAY TO A BIT MORE
SEASONABLE AIR AS A BACKDOOR FRONT MOVES INTO THE AREA. THE STRONG
MID LEVEL RIDGE SLOWLY RETROGRADES BACK TO THE WSW AND EXPANDS OVER
THE MID MISS VALLEY INTO TX BY LATE WEEK... AND THIS BUBBLE OF HIGH
PRESSURE WILL DEFLECT ANY PERTURBATIONS TO THE NORTH AND EAST OF NC
THROUGH WEDNESDAY. BY THURSDAY AND FRIDAY... THE CENTER OF THE MID
LEVEL RIDGE SETTLES OVER WRN TX AND OK AS A VORTEX OVER SOUTH
CENTRAL CANADA DROPS TO THE EAST THEN SOUTHEAST AND DIGS OVER THE
NORTHEAST STATES AND SE CANADA. THIS IS EXPECTED TO HELP PUSH A
BACKDOOR FRONT SOUTHWARD THROUGH NC LATE IN THE WORK WEEK. WHILE
MODELS DIFFER ON TIMING WITH THE GFS FAVORING A LATE WEDNESDAY NIGHT
FRONTAL PASSAGE WHILE THE ECMWF FAVORS A LATER THURSDAY NIGHT
PASSAGE... CONFIDENCE IS ABOVE NORMAL AT THIS TIME RANGE THAT WE'LL
SEE A TRANSITION FROM THE EXCESSIVE HEAT TOWARD A BIT MORE
SEASONABLE TEMPERATURES. EXPECT HIGHS TO TREND FROM THE LOW-MID 90S
TUESDAY/WEDNESDAY TO THE MID 80S ON FRIDAY... WITH INCREASING CLOUD
COVER AND A CHANCE OF SHOWERS/STORMS THURSDAY/FRIDAY. -GIH

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
AS OF 240 PM FRIDAY...

ADVERSE AVIATION WEATHER CONDITIONS THIS AFTERNOON AS A LINE OF
SLOW MOVING THUNDERSTORMS DRIFT NORTHWARD ACROSS THE REGION. THIS
WILL CAUSE WIDESPREAD MVFR/IFR CONDITIONS. EXPECT CONVECTION TO
SLOWLY DIMINISH THIS EVENING WITH LOSS OF HEATING BUT A SLOW
MOVING MID-UPPER LEVEL TROUGH WILL LIKELY MAINTAIN SOME ORGANIZED
CONVECTION OVER THE WESTERN TWO-THIRDS OF CENTRAL NC THROUGH THE
NIGHT.

EXPECT EARLY MORNING STRATUS AND AREAS OF FOG SATURDAY. STRATUS
AND FOG WILL LIFT INTO A BROKEN CU FIELD BY MID MORNING. ISOLATED
TO SCATTERED SHOWERS AND THUNDERSTORMS WILL BECOME MORE PROMINENT
OVER THE COASTAL PLAIN AND SANDHILLS AND POSSIBLY THE PIEDMONT BY
EARLY SATURDAY AFTERNOON WITH MVFR CONDITIONS IN VICINITY OF THE
SHOWERS AND STORMS.

IMPROVING WEATHER CONDITIONS EXPECTED SATURDAY NIGHT INTO SUNDAY
WITH A 2-4 HOUR PERIOD OF MVFR/IFR FOG PROBABLE SUNDAY MORNING.

VFR CONDITIONS EXPECTED SUNDAY THROUGH WEDNESDAY AS HIGH
PRESSURE TO OUR W-NW WILL INFLUENCE OUR WEATHER.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR NCZ007>009-021>025-
038>041-073>077-083>086-088.

&&

SYNOPSIS...WSS
NEAR TERM...WSS
SHORT TERM...HARTFIELD
LONG TERM...HARTFIELD/WSS
AVIATION...WSS

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE RALEIGH NC
237 PM EDT FRI MAY 27 2011

NCZ010-011-026>028-042-043-078-089-281000-
WARREN-HALIFAX-FRANKLIN-NASH-EDGECOMBE-JOHNSTON-WILSON-WAYNE-SAMPSON-
237 PM EDT FRI MAY 27 2011

...SEVERE THUNDERSTORM WATCH 387 IN EFFECT UNTIL 7 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.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY.

HAZARDOUS WEATHER IS NOT EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTERS SHOULD REPORT SEVERE WEATHER AS SOON AS IT IS
SAFE TO DO SO. PLEASE STAY TUNED FOR LATER WATCHES AND WARNINGS.

NCZ007>009-021>025-038>041-073>077-083>086-088-281000-
PERSON-GRANVILLE-VANCE-FORSYTH-GUILFORD-ALAMANCE-ORANGE-DURHAM-
DAVIDSON-RANDOLPH-CHATHAM-WAKE-STANLY-MONTGOMERY-MOORE-LEE-HARNETT-
ANSON-RICHMOND-SCOTLAND-HOKE-CUMBERLAND-
237 PM EDT FRI MAY 27 2011

...SEVERE THUNDERSTORM WATCH 387 IN EFFECT UNTIL 7 PM EDT THIS
EVENING...
...FLASH FLOOD WATCH IN EFFECT THROUGH LATE TONIGHT...

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.
   FLASH FLOOD WATCH.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY.

HAZARDOUS WEATHER IS NOT EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTERS SHOULD REPORT SEVERE WEATHER AS SOON AS IT IS
SAFE TO DO SO. PLEASE STAY TUNED FOR LATER WATCHES AND WARNINGS.

GIH