Severe Thunderstorm Warning 25, NWS Raleigh, NC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
359 PM EDT MON APR 20 2009

.SYNOPSIS...
A STORM SYSTEM WILL CONTINUE TO MOVE NORTHEAST THROUGH THE EASTERN
GREAT LAKES THIS AFTERNOON. MEANWHILE...THE TRAILING COLD FRONT WILL
PUSH EAST ACROSS NORTH CAROLINA THIS AFTERNOON AND EVENING.
SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS WILL ACCOMPANY THE
FRONTAL PASSAGE...WITH SOME STORMS POSSIBLY BECOMING SEVERE.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 345 PM MONDAY...

SEVERE PARAMETERS FOR TORNADOES WILL REMAIN MARGINAL ACROSS NC...
RELATIVE TO SOUTHERN AND CENTRAL VA... BUT A TORNADO WATCH -- #178
-- HAS BEEN ISSUED FOR THE NORTHERN PIEDMONT AND COASTAL PLAIN OF
NC UNTIL 02Z... BOUNDED BY ALAMANCE AND CHATHAM COUNTIES TO THE
WEST... AND WAKE... FRANKLIN... NASH AND EDGECOMBE COUNTIES TO THE
SOUTH. DMGG WINDS AND LARGE HAIL INSTEAD APPEAR TO BE THE PRIMARY
THREATS IN NC... AND INDEED A SEVERE THUNDERSTORM WATCH -- #179 -- HAS
ALSO BEEN ISSUED FOR THE THE REMAINDER OF CENTRAL NC FROM SCOTLAND
AND MOORE COUNTIES EASTWARD. SEE PREVIOUS MORNING DISCUSSION
BELOW FOR SEVERE DETAILS.

THE FRONT AND ASSOCIATED CHANCE OF SHOWERS AND THUNDERSTORMS --
THOUGH DECREASING IN INTENSITY OWING TO NOCTURNAL COOLING AND
EXPECTED/ONGOING PRE-FRONTAL CONVECTIVE OVERTURNING/DIABATIC COOLING
-- WILL LINGER IN THE COASTAL PLAIN THROUGH ABOUT MIDNIGHT... WITH
DRY CONDITIONS ELSEWHERE. LOW TEMPERATURES IN THE UPPER 40S TO
MIDDLE 50S EXPECTED.  -MWS

AS OF 1145 AM MONDAY...

MAIN FORECAST CONCERN REMAINS THE THREAT OF STRONG TO SEVERE
THUNDERSTORMS ACROSS CENTRAL NC... PARTICULARLY THE EASTERN HALF...
THIS AFTERNOON AND EVENING. OTHERWISE... IT SHOULD BE A RATHER WARM
AND BREEZY DAY... WITH TEMPERATURES RANGING FROM THE LOWER 70S TO
NEAR 80 DEGREES.

THE MID LEVEL DRY SLOT -- EVIDENT IN MOISTURE CHANNEL IMAGERY AND
UPSTREAM AT H5 AND H7 12Z RAOB ANALYSES -- WILL CONTINUE TO PUNCH
ACROSS NC FROM THE SW BEHIND THIS MORNINGS CONVECTION. THE MID LEVEL
DRYING WILL CONTINUE TO PROMOTE A SCATTERING OF THE BKN TO OVC CLOUD
COVER AND RESULTANT INCREASING INSOLATION THIS AFTERNOON. WHILE THE
PRIMARY NEGATIVELY-TILTED S/W TROUGH ALOFT HAS ALSO SHIFT WELL TO
OUR NW INTO THE OH VALLEY... A COUPLE OF TRAILING IMPULSES WITHIN
A SHEAR AXIS ALOFT -- THE MOST NOTABLE OF WHICH WAS LOCATED
BETWEEN BHM AND ATL AT 15Z -- WILL SWING NORTHEASTWARD ACROSS THE
CAROLINAS AND VA TODAY.

MEANWHILE... AT THE SURFACE... THE LATEST ANALYSES DEPICT A 998 SFC
LOW OVER MI... WITH A LEADING WARM FRONT EXTENDING SEWRD THROUGH
SOUTHERN VA TO THE SE VA COAST. THE WARM FRONT HAD BEEN DIABATICALLY
REINFORCED BY EARLIER CONVECTION... WITH RESULTANT T/TDS IN THE 50S
OVER CENTRAL VA TO LOW 70S OVER MID 60S SOUTH OF THE BOUNDARY IN THE
NC COASTAL PLAIN. THE COLD FRONT TRAILING THE LOW WAS SOMEWHAT
DISJOINTED... WITH ONE SEGMENT SEPARATING GENERALLY WRLY FLOW AND
CONTINENTAL AIR FROM MARITIME TROPICAL AIR SURGING FROM THE NE
GULF THROUGH EASTERN GA AND THE EASTERN CAROLINAS. ANOTHER MORE
WESTERN FRONTAL SEGMENT AND PRECEDING CONFLUENCE AXIS TRAILED FROM
THE MI LOW SOUTHWARD THROUGH THE EASTERN TN VALLEY.

WE ACCORDINGLY EXPECT PERHAPS A COUPLE OF BROKEN BANDS OF SHOWERS
AND THUNDERSTORMS TO DEVELOP ALONG THE AFOREMENTIONED LOW LEVEL FOCI
AS THE AIRMASS WARMS AND DESTABILIZES TODAY... WITHIN A REGION OF
INCREASING HT FALLS (20-40 M/12HR) AHEAD OF THE SHEAR AXIS AND
EMBEDDED IMPULSES ALOFT... AND INVOF AN ATTENDING MID/UPPER JET EXIT
REGION (ANALYZED FROM THE CENTRAL GULF COAST TO THE CENTRAL
CAROLINAS THIS MORNING). REGARDING THE SEVERE THREAT... DEEP LAYER
BULK SHEAR ON THE ORDER OF 40-50 KTS ATTENDANT THE OVERHEAD JETS
WILL PROMOTE STORM ORGANIZATION AREA-WIDE... THOUGH THE HIGHER
THETA-E AIR -- CHARACTERIZED BY FORECAST T/TDS IN THE UPPER
70S/LOW-MID 60S IN THE COASTAL PLAIN -- WILL RESULT IN THE GREATEST
MLCAPE (800-1200 J/KG) AND THREAT OF SEVERE ROUGHLY FROM RALEIGH
EASTWARD. GIVEN THE STORM ORGANIZING DEEP LAYER SHEAR... THE MAIN
WEATHER HAZARDS ARE EXPECTED TO BE DMGG WINDS OWING TO PROJECTED
STEEP LOW LEVEL LAPSE RATES/INVERTED-V PROFILES (AOA 7 C/KM) AND
LARGE THETA-E DIFFERENCES AND DCAPE (AOA 20 C AND 1000 J/KG...
RESPECTIVELY) DUE TO THE MID LEVEL DRY AIR... AND LARGE HAIL WITH
EXPECTED LOW FZ/WBZ LEVELS AND LARGE CAPE IN THE -10 TO -30 HAIL
GROWTH ZONE. THE TORNADO THREAT WILL REMAIN JUST NE OF OUR WARNING
AREA... WHERE LOW LEVEL SHEAR AND LOW LCL HTS WILL BE MAXIMIZED AND
MINIMIZED... RESPECTIVELY... INVOF THE WARM FRONT AND CORRIDOR OF
POSSIBLE TRIPLE PT LOW DEVELOPMENT OVER SOUTHERN VA TO THE
DELMARVA.  -MWS

&&

.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
AS OF 345 PM MONDAY...

A POTENT S/W TROUGH ALOFT -- WHICH TRAILED FROM AN UPPER LOW JUST
WEST OF LAFAYETTE, IN NWWRD THROUGH IA AND SOUTHERN MN -- WILL
PIVOT AROUND THE UPPER LOW AND SWEEP EAST OF THE CENTRAL
APPALACHIANS TUESDAY AFTERNOON. THE APPROACH/PASSAGE OF THE FORCING
FOR ASCENT AND MID LEVEL MOIST LAYER ATTENDANT THE S/W... AND
ACCOMPANYING RE-ENFORCING SURFACE COLD FRONT BELOW... SHOULD
PROMOTE THE DEVELOPMENT OF WIDELY SCATTERED HIGH-BASED SHOWERS AND
ISOLATED THUNDERSTORMS. SUBLIMATIONAL/EVAPORATIVE COOLING IN A DRY
SUB-CLOUD LAYER BELOW THE HIGH-BASED CONVECTION -- CHARACTERIZED
BY NEARLY DRY ADIABATIC 0-3 KM LAPSE RATES -- MAY FURTHER AUGMENT
WIND GUSTS TO NEAR 45 MPH IN THE HEAVIEST CORES... GIVEN PROJECTED
DRY MICROBURST THERMAL/MOISTURE PROFILES. PEA- SIZED HAIL MAY
ALSO ACCOMPANY ANY STORMS... GIVEN EXPECTED COOLING TEMPERATURES
ALOFT AND LOWERING FREEZING LEVELS ATTENDANT THE APPROACHING S/W
TROUGH. HIGH TEMPERATURES IN THE UPPER 60S NW TO MIDDLE 70S SE.

CLEARING AND COOLER TUESDAY NIGHT... WITH LOWS 41 TO 48 NW TO SE. -MWS

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
AS OF 305 AM MONDAY...

UPPER TROUGH OVER REGION WEDNESDAY WILL RESULT IN DRY BUT RELATIVELY
COOL WEATHER FOR CENTRAL NC. UPPER TROUGH LIFTS NE BY THU. WITH
HEIGHTS RISING IN RESPONSE TO EXITING TROUGH AND SURFACE HIGH
BUILDING INTO THE REGION FROM WEST...EXPECT TEMPS CLOSER TO NORMAL
THU.

LONG TERM MODEL GUIDANCE IN FAIRLY GOOD AGREEMENT ADVERTISING UPPER
LEVEL RIDGING OVER THE REGION WITH A LEE SIDE TROUGH DEVELOPING
SATURDAY INTO SUNDAY. MODELS DO VARY ON THE STRENGTH/ORIENTATION OF
RIDGE WITH 12Z/SUNDAY ECMWF WEAKENING RIDGE IN RESPONSE TO A S/W
CROSSING THE GREAT LAKES SAT INTO SUNDAY. THIS FEATURE SENDS A COLD
FRONT SOUTHWARD THROUGH THE AREA SUNDAY. 00Z GFS AND CANADIAN
MAINTAIN UPPER RIDGE OVER THE REGION WITH THE MAIN STORM TRACK
FARTHER NW (UPPER MS VALLEY INTO THE WESTERN LAKES). IF THE
GFS/CANADIAN VERIFY...MAX TEMPS DURING THE WEEKEND MAY END UP BEING
3-5 DEGREES WARMER THAN FORECAST (MID/UPPER 80S). PLENTY OF TIME TO
FINE TUNE.

FOR THIS FORECAST PACKAGE...DID DECREASE MIN TEMPS THU MORNING A
COUPLE OF DEGREES FROM PREVIOUS FORECAST AS MODEL THICKNESSES
PROJECTED FOR THU MORNING (1325-1329M) HISTORICALLY SUPPORT MIN
TEMPS IN THE MID 30S. ALSO...ADJUSTED MAX TEMPS UP A FEW DEGREES
SATURDAY AS LOW LEVEL SW FLOW INDUCED BY LEE SIDE TROUGH DEVELOPMENT
SHOULD AID IN BOOSTING TEMPS UNDER SUNNY SKIES. IF SATURDAY
THICKNESSES VERIFY (1405-1408M)...MID/UPPER 80S WOULD BE WIDESPREAD
ACROSS THE AREA.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
AS OF 310 PM MONDAY...

TORNADO AND SEVERE THUNDERSTORM WATCHES HAVE BEEN ISSUED FOR ALL
BUT THE TRIAD TERMINALS THROUGH 02Z.

SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS IN MULTIPLE BROKEN
BANDS WILL CONTINUE TO OVERSPREAD CENTRAL NC THIS EVENING...
AHEAD OF AN APPROACHING COLD FRONT AND IMPULSE ALOFT. ASIDE FROM
THE USUAL SUB-VFR CIGS AND VISBYS... DAMAGING WIND IN EXCESS OF 58
MPH AND LARGE HAIL UP TO 2 INCHES IN DIAMETER WILL BE POSSIBLE IN
THE STRONGEST STORMS. AN ISOLATED TORNADO IS ALSO POSSIBLE NEAR
AND ESPECIALLY NORTH OF THE VA STATE LINE... IN CLOSER TO
PROXIMITY TO A CENTRAL VA WARM FRONT. CONDITIONS EXPECTED TO
BECOME VFR FROM WEST TO EAST LATER THIS EVENING... AND THEN
PERSIST THROUGH 18Z TUESDAY. HOWEVER... A BREEZY SW WIND -- 13-17
KTS WITH GUSTS 23-29 KTS -- WILL DEVELOP ONCE DAYTIME HEATING
COMMENCES BY LATE MORNING TUESDAY. THEREAFTER... THE APPROACH OF
A POTENT UPPER LEVEL DISTURBANCE WILL PROMOTE THE DEVELOPMENT OF
SCT TO BKN CIGS BETWEEN 6-10 THSD FT AS WELL AS HIGH-BASED SHOWERS
AND ISOLATED THUNDERSTORMS. PRECIPITATION FALLING FROM THE BASE OF
THE CONVECTION AND INTO A DRY SUB-CLOUD LAYER BELOW MAY AUGMENT
WIND GUSTS TO NEAR 40S KTS IN THE HEAVIEST CORES. PEA-SIZED HAIL
MAY ALSO OCCUR... GIVEN EXPECTED COOLING TEMPERATURES ALOFT AND
LOWERING FREEZING LEVELS ATTENDANT THE APPROACHING UPPER LEVEL
DISTURBANCE.

GENERALLY VFR CONDITIONS ARE EXPECTED TUE NIGHT THROUGH THE
WEEKEND... THOUGH ISOLATED AFTERNOON CONVECTION WILL BE POSSIBLE
FRIDAY AND SATURDAY AFTERNOONS.

&&

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

&&

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RALEIGH NC
336 PM EDT MON APR 20 2009

NCZ007>011-023>028-040-041-211945-
PERSON-GRANVILLE-VANCE-WARREN-HALIFAX-ALAMANCE-ORANGE-DURHAM-
FRANKLIN-NASH-EDGECOMBE-CHATHAM-WAKE-
336 PM EDT MON APR 20 2009

...TORNADO WATCH 178 IN EFFECT UNTIL 10 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.

   TORNADO WATCH.

SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS HAVE DEVELOPED THIS
AFTERNOON AHEAD OF AN EASTWARD MOVING COLD FRONT. SOME OF THESE
STORMS MAY BECOME SEVERE...WITH THE PRIMARY THREATS BEING LARGE
HAIL...DAMAGING WINDS...AND FREQUENT CLOUD TO GROUND LIGHTNING.
THERE IS ALSO A SMALL POTENTIAL OF AN ISOLATED TORNADO ACROSS THE
NORTHERN PIEDMONT AND NORTHEAST COASTAL PLAIN. THE BEST TIMING FOR
SEVERE WEATHER WILL OCCUR UNTIL 10 PM.

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

HAZARDOUS WEATHER IS NOT EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTERS ARE ENCOURAGED TO REPORT ANY SEVERE OR
SIGNIFICANT WEATHER ASSOCIATED WITH THESE STORMS.

NCZ042-043-075>078-085-086-088-089-211945-
JOHNSTON-WILSON-MOORE-LEE-HARNETT-WAYNE-SCOTLAND-HOKE-CUMBERLAND-
SAMPSON-
336 PM EDT MON APR 20 2009

...SEVERE THUNDERSTORM WATCH 179 IN EFFECT UNTIL 10 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.

SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS HAVE DEVELOPED THIS
AFTERNOON AHEAD OF AN EASTWARD MOVING COLD FRONT. SOME OF THESE
STORMS MAY BECOME SEVERE...WITH THE PRIMARY THREATS BEING LARGE
HAIL...DAMAGING WINDS...AND FREQUENT CLOUD TO GROUND LIGHTNING.
THE BEST TIMING FOR SEVERE WEATHER WILL OCCUR UNTIL 10 PM.

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

HAZARDOUS WEATHER IS NOT EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTERS ARE ENCOURAGED TO REPORT ANY SEVERE OR
SIGNIFICANT WEATHER ASSOCIATED WITH THESE STORMS.

NCZ021-022-038-039-073-074-083-084-211945-
FORSYTH-GUILFORD-DAVIDSON-RANDOLPH-STANLY-MONTGOMERY-ANSON-RICHMOND-
336 PM EDT MON APR 20 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL NORTH CAROLINA.

.DAY ONE...THIS AFTERNOON AND TONIGHT.

SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS HAVE DEVELOPED THIS
AFTERNOON AHEAD OF AN EASTWARD MOVING COLD FRONT. A STORM OR TWO MAY
BECOME SEVERE...WITH THE PRIMARY THREATS BEING LARGE HAIL AND
DAMAGING WINDS.

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

HAZARDOUS WEATHER IS NOT EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTERS ARE ENCOURAGED TO REPORT ANY SEVERE OR
SIGNIFICANT WEATHER ASSOCIATED WITH THESE STORMS.

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