Special Weather Statement, NWS Raleigh, NC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
308 AM EDT TUE MAR 20 2012

.SYNOPSIS...
A LARGE AREA OF HIGH PRESSURE WILL HOLD OVER THE EASTERN UNITED
STATES THROUGH THE REST OF THE WEEK...BRINGING EARLY SUMMER-LIKE
CONDITIONS TO THE REGION. AN UPPER LEVEL LOW PRESSURE WILL APPROACH
FROM THE WEST BY THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 308 AM TUESDAY...

IN VERY NEAR TERM...NOT ANTICIPATING A DENSE FOG ADVISORY AT THIS
TIME AS FOG NOT NEARLY AS WIDESPREAD THIS MORNING COMPARED TO MONDAY
MORNING. HOWEVER...STILL EXPECT TO SEE POCKETS OF DENSE FOG
ESPECIALLY IN LOCALES THAT RECEIVED HEAVY RAINFALL MONDAY. PLAN TO
HANDLE THESE POCKETS OF DENSE FOG WITH SPECIAL WEATHER STATEMENTS
(UNLESS DENSE FOG BECOMES WIDESPREAD THEN WILL ISSUE AN ADVISORY).

TODAY AND TONIGHT...EARLY SUMMER-LIKE WEATHER PATTERN CONTINUES
TODAY AND TONIGHT WITH A SLOWLY AMPLIFYING NARROW UPPER LEVEL RIDGE
IMMEDIATELY TO OUR WEST AND A PAIR OF RELATIVELY WEAK BUT
RECOGNIZABLE UPPER LEVEL LOWS...ONE OFF THE VA CAPE AND THE OTHER
OVER EASTERN PA. THE CIRCULATION AROUND THESE WEATHER SYSTEMS WILL
MAINTAIN NNW FLOW OVER CENTRAL NC THROUGH TONIGHT. AIR MASS QUITE
MOIST FOR THIS TIME OF YEAR WITH BLENDED TOTAL PRECIP WATER VALUES
BETWEEN 1-1.2 INCHES (OR AOA 200 PERCENT OF NORMAL). WEAK
PERTURBATIONS IN THE NNW FLOW COUPLED WITH THE MOIST AIR MASS AND
MARGINAL INSTABILITY SUPPLIED BY STEEP MID LEVEL LAPSE RATES AND
INSOLATION WILL TRIGGER ISOLATED TO SCATTERED CONVECTION ACROSS
CENTRAL NC. MODEL GUIDANCE HAVING SOME DIFFICULTY PINPOINTING WHERE
CONVECTIVE THREAT IS GREATEST. CONSIDERING BEST MID LEVEL CONFLUENCE
IS OVER THE NORTHERN PIEDMONT (WHICH APPEARS TO BE AIDING ISOLATED
CONVECTION NOW OCCURRING IN VICINITY OF KERR LAKE) AND MAJORITY OF
MODEL GUIDANCE  EMPHASIZING THE NORTHERN AND WESTERN PIEDMONT FOR
DEEPER MOISTURE AND LIFT...WILL SHIFT EMPHASIS FOR BETTER POPS OVER
THE PIEDMONT VERSUS THE NORTHERN COASTAL PLAIN. A QUICK LOOK AT THE
AVAILABLE WRF MODEL GUIDANCE SUGGEST VAST MAJORITY OF CONVECTION
WILL NOT FIRE UNTIL MID-LATE AFTERNOON WHICH SEEMS FEASIBLE AT THIS
TIME AS PERTURBATION NOW SUSTAINING ISOLATED CONVECTION NEAR VA
BORDER IS PROJECTED TO BE ESE OF OUR REGION AFTER DAYBREAK WITH WEAK
SUBSIDENCE IN ITS WAKE. THUS HAVE DELAYED BEST POPS UNTIL 20-21Z.
SINCE ANTICIPATE A FEW MORE HOURS OF HEATING...HAVE RAISED MAX TEMPS
UP A COUPLE OF DEGREES FROM THE PREVIOUS FORECAST (UPPER 70S TO
AROUND 80).

DECENT MID LEVEL LAPSE RATES WILL AID IN GROWTH OF A FEW STORMS
TODAY. HOWEVER A MOIST COLUMN AND WEAK WIND FIELD SUGGEST THAT
SEVERE THREAT VERY LIMITED WITH MAIN T-STORM HAZARDS BEING FREQUENT
LIGHTNING...HEAVY DOWNPOURS AND HAIL UP TO THE SIZE OF DIME OR
NICKELS. DUE TO WEAK WINDS ALOFT...THE STORMS THAT OCCUR WILL DRIFT
SOUTHWARD AT LESS THAN 20 MPH.

EXPECT MAJORITY OF CONVECTION TO DISSIPATE BY MID EVENING THOUGH 00Z
NAM SUGGEST A RESURGENCE IN ISOLATED-SCATTERED CONVECTION OVER THE
WESTERN PIEDMONT AFTER 06Z (NAM WAS DEPICTING THIS SCENARIO LAST
NIGHT AS WELL). LITTLE EVIDENCE OF ANY SUPPORT ALOFT AT THIS TIME SO
WILL HAVE POPS NO HIGHER THAN SLIGHT CHANCE THROUGH THE OVERNIGHT
HOURS.OTHERWISE AREAS OF FOG PROBABLE WHERE SKIES CLEAR OFF.
CONTINUED MILD WITH OVERNIGHT TEMPS IN THE UPPER 50S TO AROUND 60.

&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
AS OF 308 AM TUESDAY...

WEDNESDAY INTO WEDNESDAY NIGHT...MAJORITY OF MODEL GUIDANCE DEPICT A
WEAK MID LEVEL TROUGH RETROGRADING ACROSS THE FORECAST AREA...A
REFLECTION OF THE PA LOW AND THE OFFSHORE UPPER LEVEL LOW MERGING IN
VICINITY OF SE VA/NE NC. AIR MASS PROJECTED TO REMAIN QUITE MOIST
AND WITH SLIGHTLY BETTER SYNOPTIC LIFT THROUGH THE COLUMN...EXPECT
A FEW MORE SHOWERS AND T-STORMS COMPARED TO THE PAST FEW DAYS. NOT
EXPECTING ANY SEVERE STORMS THAT THIS TIME AS WIND FIELD REMAINS
WEAK THOUGH THE STRONGER CELLS WILL PRODUCE FREQUENT LIGHTNING AND
SMALL HAIL. DUE TO ANTICIPATED CLOUD/CONVECTION COVERAGE...MAX TEMPS
SHOULD BE A CATEGORY OR TWO COOLER THAN TODAY. MID-UPPER 70S LOOK ON
TARGET THOUGH IF SHOWERS COMMENCE BY LATE MORNING...COULD SEE MAX
TEMPS 3-5 DEGREES COOLER THAN FORECAST.

EXPECT MAJORITY OF SHOWERS/ISOLATED T-STORMS TO DIMINISH WITH LOSS
OF INSOLATION THOUGH PRESENCE OF MID-UPPER LEVEL SHEAR AXIS SHOULD
MAINTAIN A SMALL THREAT FOR SHOWERS THROUGH THE NIGHT. CONTINUED
MILD WITH MIN TEMPS IN THE 50S TO NEAR 60.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
AS OF 300 AM TUESDAY...

DESPITE THE WESTERN END OF SURFACE RIDGING IN PLACE THURSDAY INTO
THURSDAY NIGHT...A MOIST AIR MASS REMAINS IN PLACE WITH PRECIPITABLE
WATER VALUES AROUND 1.25 INCHES...AND A 300MB JETLET OF 45-50KT
MOVES ACROSS SOUTHERN VIRGINIA DURING THE AFTERNOON AS FORECAST BY
THE GFS. LIFT IS MODEST AS A RESULT...UNDER A WEAKNESS IN RIDGING
ALOFT...ENOUGH GIVEN THE MOISTURE AND INSTABILITY...WITH LIFTED
INDICES TO -2C ON THE GFS...TO RESULT IN SCATTERED SHOWERS AND
THUNDERSTORMS THURSDAY...DIMINISHING THURSDAY NIGHT AS GFS BUFR
SOUNDINGS SHOW THE MOISTURE CONTENT FALLING TO PRECIPITABLE WATER
VALUES NEAR AN INCH IN A MORE STABLE AIR MASS. WINDS SURFACE AND
ALOFT ARE FAIRLY LIGHT...AROUND 10KT AT BEST THROUGH ABOUT 600MB...
WHICH SHOULD RESULT IN ANY SHOWER OR THUNDERSTORM BEING SOMEWHAT
SLOW MOVING. GFS BUFR SOUNDINGS SHOW THE AIR MASS IS SLIGHTLY MORE
STABLE FRIDAY...FORECASTING A VERY MODEST CAP AROUND 850MB...BUT THE
AIR MASS SHOULD MOISTEN AND WITH A SURFACE TROUGH MOVING INTO THE
WESTERN PIEDMONT DURING THE DAY...ISOLATED TO SCATTERED SHOWERS OR
THUNDERSTORMS COULD STILL OCCUR FRIDAY...THOUGH THE CHANCES AND/OR
COVERAGE SHOULD BE LESS THAN ON THURSDAY AS CONVERGENCE ALOFT
THURSDAY NIGHT CONTINUES SOMEWHAT INTO FRIDAY CLOSER TO THE NARROW
RIDGE AXIS ALOFT.

DIFFLUENCE ALOFT INCREASES SATURDAY...IN ADVANCE OF THE UPPER LOW
MOVING TOWARD THE MID-ATLANTIC AND THE CAROLINAS. OVERALL MOISTURE
INCREASES LATE FRIDAY INTO SATURDAY...AS PRECIPITABLE WATER VALUES
ARE FORECAST TO RISE TO AROUND 1.5 INCHES FOR SATURDAY. GFSX MOS
ENSEMBLE GUIDANCE CHANCES FOR PRECIPITATION ARE HIGHEST SATURDAY
INTO SUNDAY...AHEAD OF THE UPPER LOW IN GOOD DIFFLUENCE ALOFT
SATURDAY AND VERY NEAR OR UNDERNEATH THE UPPER LOW SUNDAY. DURING
THIS LONG-TERM PERIOD...THE HIGHEST FORECAST MIXED-LAYER CAPE OVER
THE LOWEST 1KM IS SATURDAY AND SUNDAY...NEARLY 1000J/KG BOTH
AFTERNOONS WITH LIFTED INDICES NEAR -4C. -10C TO -30C CAPE IS
FORECAST BETWEEN 400 AND 800J/KG...AND LAPSE RATES FROM 1000-500MB
STEEPEN ESPECIALLY NEAR OR UNDER THE UPPER LOW SUNDAY TO GREATER
THAN 7C/KM. DIFFICULT TO ASCERTAIN WHETHER MORE OF A BROAD SURFACE
OCCLUSION OR COLD FRONT MOVES THROUGH SATURDAY LIKE THE 12Z ECMWF...
OR THERE WILL BE A FRONT WITH A BETTER POTENTIAL FOR A SURFACE WAVE
AS THE GFS HAS FORECAST AT LEAST OVER ITS LAST TWO RUNS. THE LATTER
IS A LITTLE MORE CONCERNING REGARDING THE POTENTIAL FOR ISOLATED
SEVERE WEATHER SATURDAY GIVEN THE AVAILABLE MOISTURE...LIFT...AND
INSTABILITY...HOWEVER...WINDS THROUGH 850MB AGAIN ARE NOT TOO HIGH
AND THE GFS BUFR SOUNDINGS DO SHOW A WEAK CAP AROUND 850MB. MAY NOTE
AN ISOLATED SEVERE THUNDERSTORM POSSIBLE IN THE HWO SATURDAY DUE TO
THE EXPECTED LIFT SURFACE AND ALOFT WITH 0-6KM SHEAR INCREASING FROM
THE WEST DURING THE DAY...AND AGAIN ON SUNDAY COURTESY OF STEEPER
LAPSE RATES AND A WEAK INVERTED-V TYPE BUFR SOUNDING PROFILE WITH
SLIGHTLY STRONGER WINDS ALOFT. CURRENTLY...EVEN ON THE GFS WITH ITS
SURFACE WAVE SATURDAY...0-3KM HELICITY IS BELOW 100M2/S2. DRIER AIR
MOVING INTO CENTRAL NORTH CAROLINA ON THE CURRENT EXPECTED TRACK AND
TIMING OF THE UPPER LOW...FAIRLY SIMILAR ON THE GFS AND ECMWF...
SHOULD RESULT IN DIMINISHING CHANCES FOR SHOWERS OVERNIGHT SUNDAY
INTO EARLY MONDAY.

TEMPERATURES WILL REMAIN WELL ABOVE NORMAL IN THIS PART OF THE
FORECAST. 1000-850MB THICKNESSES SUGGEST HIGHS OF 70 OR BETTER EACH
DAY...EVEN WHEN READINGS SHOULD COOL WITH THE APPROACH AND PASSAGE
OF THE UPPER LOW. WARMEST TEMPERATURES ARE LIKELY FRIDAY IN A
SLIGHTLY DRIER AND MORE STABLE AIR MASS UNDER A SOUTHWEST SURFACE
FLOW. WITH DRYING BEHIND LOW PRESSURE MONDAY INTO MONDAY NIGHT...AS
SURFACE RIDGING BUILDS SOUTH...BY MONDAY NIGHT...IT IS POSSIBLE THAT
OVERNIGHT LOWS WILL RETURN TO THE 40S...THOUGH STILL AT LEAST A
CATEGORY OR TWO ABOVE NORMAL.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
AS OF 140 AM TUESDAY...

EXPECT AREAS OF MVFR/IFR VISIBILITY IN FOG TO DEVELOP ACROSS CENTRAL
NC THROUGH 6 AM...THEN PERSIST UNTIL 8-9 AM AS MAINLY CLEAR SKIES
ALOFT AND ADEQUATE LOW LEVEL MOISTURE PROVIDE CONDITIONS FAVORABLE
FOR THE FORMATION OF FOG. MAY SEE A FEW ISOLATED SHOWERS NORTH OF
KRDU AND KRWI THROUGH DAYBREAK BUT THESE SHOWERS TOO ISOLATED TO
MENTION IN THE TAF FORECAST FOR EITHER SITE.

LATER TODAY...EXPECT ISOLATED TO SCATTERED CONVECTION TO DEVELOP
LATE IN THE AFTERNOON AND PERSIST INTO THE EARLY EVENING HOURS. THE
BEST LOW-MID LEVEL CONFLUENCE SEEM TO FAVOR THE PIEDMONT COUNTIES
SUGGESTING A PERIOD OF SCATTERED CONVECTION LATE IN THE DAY AT
KRDU...KGSO AND KINT. HAVE INCLUDED A TEMPO GROUP AT THESE SITES AS
CONFIDENCE IS NOT HIGH ENOUGH TO MENTION A PREDOMINATE GROUP. IN
VICINITY OF THE SHOWERS AND T-STORMS...EXPECT MVFR
CEILING/VISIBILITY.

THE WEATHER PATTERN WILL CHANGE LITTLE ACROSS CENTRAL NC THROUGH
THU. EXPECT ANOTHER ROUND OF MVFR/IFR CEILINGS/VISIBILITY WEDNESDAY
MORNING AND THURSDAY MORNING. ALSO...ISOLATED SHOWERS/T-STORMS ARE
PROBABLE DURING THE OVERNIGHT HOURS..MAINLY ACROSS THE PIEDMONT
COUNTIES. SLIGHTLY HIGHER COVERAGE OF SCATTERED CONVECTION IS
ANTICIPATED WEDNESDAY AS A WEAK MID/UPPER LEVEL TROUGH DRIFTS ACROSS
THE REGION.

CONVECTIVE COVERAGE EXPECTED TO BE LESS THU INTO FRI AS MID/UPPER
LEVEL RIDGE EXTENDS OVERHEAD. THE APPROACH OF A LOW PRESSURE SYSTEM
WILL BRING A RENEWED THREAT FOR SCATTERED CONVECTION AND ASSOCIATED
MVFR CONDITIONS SATURDAY INTO SUNDAY.

&&

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

&&

SYNOPSIS...WSS
NEAR TERM...WSS
SHORT TERM...WSS
LONG TERM...DJF
AVIATION...WSS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RALEIGH NC
414 AM EDT TUE MAR 20 2012

NCZ007>011-021>028-038>043-073>078-083>086-088-089-210930-
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-
414 AM EDT TUE MAR 20 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL NORTH CAROLINA.

.DAY ONE...TODAY AND TONIGHT.

POCKETS OF DENSE FOG ARE POSSIBLE EARLY THIS MORNING ACROSS
CENTRAL NORTH CAROLINA. THE FOG WILL LIFT AND DISSIPATE PRIOR TO 9 AM.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY.

ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE SATURDAY AND SUNDAY.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RALEIGH NC
559 AM EDT TUE MAR 20 2012

NCZ040>042-077-201100-
CHATHAM-HARNETT-JOHNSTON-WAKE-
559 AM EDT TUE MAR 20 2012

...A STRONG THUNDERSTORM WILL MOVE ACROSS PARTS OF NORTHERN
HARNETT...WESTERN JOHNSTON...WESTERN AND SOUTHERN WAKE AND FAR
EASTERN CHATHAM COUNTIES THROUGH 700 AM EDT...

AT 557 AM EDT...DOPPLER RADAR INDICATED A STRONG THUNDERSTORM OVER
CARPENTER...OR ABOUT 7 MILES NORTHWEST OF CARY...MOVING SOUTH AT 20
MPH.

SOME LOCATIONS AFFECTED BY THIS STORM INCLUDE...CARPENTER...CARY...
APEX...NEW HILL...HOLLY SPRINGS...FUQUAY-VARINA.

HAZARDS INCLUDE...
HALF INCH DIAMETER SIZE HAIL.
GUSTY WINDS OF 30 TO 40 MPH.

FREQUENT LIGHTNING WAS ALSO OBSERVED WITH THE THUNDERSTORM...AS MUCH
AS ONE LIGHTNING STRIKE EVERY SIX SECONDS.

IF YOU SEE LIGHTNING OR HEAR THUNDER...YOU ARE AT RISK. TAKE SHELTER
INDOORS IMMEDIATELY. IF YOU CANNOT FIND SHELTER IN A BUILDING...A
VEHICLE PROVIDES SAFETY FROM LIGHTNING. PERSONS DRIVING DURING THE
MORNING COMMUTE SHOULD ALSO BE PREPARED FOR PONDING OF WATER ON
ROADS AND BRIEFLY POOR VISIBILITY DUE TO HEAVY RAINFALL. STAY TUNED
TO THIS STATION FOR THE LATEST WEATHER INFORMATION.

&&

LAT...LON 3551 7845 3548 7896 3551 7899 3552 7897
      3555 7902 3557 7904 3586 7901 3587 7871
TIME...MOT...LOC 0957Z 347DEG 15KT 3584 7889

DJF

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