WFO RAH Logo

WFO RAH Text Data

FXUS62 KRAH 081523
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1120 PM EDT TUE JUL 8 2008

.SYNOPSIS...
A WARM AND HUMID AIR MASS OVER THE REGION... COMBINED WITH AN UPPER 
LEVEL TROUGH IN THE AREA... WILL RESULT IN THE DEVELOPMENT OF 
SCATTERED MAINLY AFTERNOON AND EVENING THUNDERSTORMS AGAIN TODAY. 
THE TROUGH WILL SHIFT EAST OF THE AREA TONIGHT. A SURFACE BOUNDARY 
WILL APPROACH THE AREA FROM NORTHWEST LATE WEDNESDAY.

&&

.NEAR TERM /REST OF TODAY THROUGH TONIGHT/...
AS OF 1120 PM TUESDAY...

ATMOSPHERIC CONDITIONS ARE CERTAINLY RIPE FOR CONVECTION TODAY. 
MODIFICATION OF THE 12Z GSO SOUNDING FOR PROBABLE AFTERNOON TEMP AND 
DEW POINT SHOWS STRONG INSTABILITY... OVER 3700 J/KG OF MUCAPE... 
AND VERY HIGH CAPE VALUES NEAR 1000 J/KG IN THE HAIL GROWTH REGION 
OF -10C TO -30C ALOFT... AND THIS INSTABILITY IS ALSO REFLECTED IN 
THE COLD POOL ALOFT... -12C AT 12Z AT 500 MB. AVAILABLE MOISTURE IS 
MORE THAN SUFFICIENT WITH PRECIPITABLE WATER NEARLY 150% OF 
NORMAL... ALTHOUGH IT SHOULD BE BEST IN THE CENTRAL/EAST SECTIONS OF 
THE CWA... ALONG AND EAST OF THE MID LEVEL TROUGH AXIS. WE ALSO HAVE 
A POTENTIAL CONVECTIVE INSTIGATOR IN THE FORM OF A WEAK VORTICITY 
MAXIMUM... APPARENTLY SOURCED FROM AN EASTERN IOWA MCS YESTERDAY... 
THAT WILL CONTINUE ROUNDING THE TROUGH BASE PASSING THROUGH 
SOUTHERN/EASTERN NC. HOWEVER... THE LATEST MODELS... PARTICULARLY 
THE 06Z GFS AND 00Z WRF-ARW... ACTUALLY SHOW VERY LITTLE PRECIP OVER 
CENTRAL NC THROUGH TONIGHT... AND THIS MAY BE DUE IN PART TO ITS 
OVERBLOWING THE VORTICITY MAXIMUM AND HENCE OVERDOING THE NVA BEHIND 
IT. AND... DEEP LAYER SHEAR IS UNIMPRESSIVE AS WELL... ONLY 15 KTS 
AT MOST. NEVERTHELESS... WITH THE OBSERVED DATA SUPPORTING THIS MUCH 
INSTABILITY AND WITH PLENTY OF HEATING TAKING PLACE OVER MUCH OF THE 
CWA... WILL RAISE POPS TO LIKELY ACROSS MOST OF THE CWA... MAINLY 
SOUTHERN AND EASTERN SECTIONS THAT WILL BE INFLUENCED BY PVA. GIVEN 
THE DEGREE OF MID LEVEL INSTABILITY... HAIL AND NEARLY CONTINUOUS 
LIGHTNING WILL BE THE PRIMARY WEATHER THREATS THROUGH TONIGHT... 
ALTHOUGH WITH THE 30+ C VERTICAL THETA-E DIFFERENCE IN THE GSO 
SOUNDING... DAMAGING WINDS CANNOT BE RULED OUT EITHER. FINALLY... 
SEVERAL PARAMETERS INCLUDING THE HIGH CAPE (BOTH MUCAPE AND -10 TO 
-30C CAPE)... K-INDEX OF 33-36... AND NORMALIZED CAPE OF 0.25 ALL 
SUPPORT VERY VIGOROUS UPDRAFTS AND RAPID CHARGE SEPARATION... THUS 
THE MENTION OF FREQUENT LIGHTNING HAS BEEN ADDED TO THE FORECAST 
THROUGH TONIGHT. HAVE BUMPED HIGHS UP A FEW DEGREES IN THE EAST 
WHERE MORNING SUNSHINE AND HEATING HAVE BEEN ABUNDANT... AND HAVE 
LOWERED THEM A DEGREE OR TWO IN THE WEST BENEATH CONSIDERABLE MID 
CLOUDINESS AND SHOWERS.

THE COLUMN IS EXPECTED TO REMAIN AT LEAST MODERATELY UNSTABLE WELL 
INTO THE EVENING... AND THE RISK OF NUMEROUS STORMS WILL LIKELY 
EXTEND TO NEAR OR SHORTLY AFTER MIDNIGHT. THE MID LEVEL TROUGH AXIS 
AND ITS ATTENDANT COOL POOL ALOFT WILL SHIFT TO COASTAL NC TOWARD 
06Z TONIGHT. INCREASING TEMPERATURES AND ANTICYCLONIC FLOW IN THE 
MID LEVELS SHOULD FORCE A WEST-TO-EAST TAPERING OFF OF SHOWERS AND 
STORMS OVERNIGHT. HOWEVER PRECIPITABLE WATER STAYS QUITE HIGH OVER 
MUCH OF THE CWA... AND WE WILL NEED TO WATCH ANY MCS THAT DEVELOPS 
OVER MO/OHIO VALLEY... AS ANY RESULTANT MCV MAY INDUCE NEW 
CONVECTION LATE TONIGHT OVER CENTRAL/EASTERN NC. LOWS SHOULD BE VERY 
MILD... AROUND 70-74. -GIH

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 200 PM MONDAY...

WEDNESDAY:

MOISTURE ADVECTION WILL BE UNDERWAY IN LOW LEVEL SOUTHWEST FLOW
AS A LEE TROF DEVELOPS AHEAD OF AN APPROACHING FRONT. A HOT SOUPY
AIRMASS WILL RESULT...WITH PROGGED PRECIPITABLE WATERS APPROACHING
2 INCHES. FORCING WILL BE RATHER WEAK...HENCE NEAR CLIMATOLOGICAL
CHANCE POPS...WHICH WILL BE MAINLY INSTIGATED BY THE LOW LEVEL
TROF...THUS EXPECT A BIT MORE ACTIVITY IN THE WEST...WITH SOME
EASTWARD PROPAGATION IN WESTERLY FLOW. HIGHS WILL BE EDGING UP IN
WESTERLY FLOW...88 TO 92 DEGREES. 

WEDNESDAY NIGHT:

WEDNESDAYS DIURNAL CONVECTION WILL BE LARGELY A MEMORY BY
MIDNIGHT. HOWEVER...LINGERING OUTFLOW BOUNDARIES AND WEAK LOW
LEVEL CONVERGENCE RESULTING FROM AN APPROACHING SURFACE BOUNDARY
COULD INITIATE WIDELY SCATTERED CONVECTION OVERNIGHT.

THURSDAY AND THURSDAY NIGHT:

A SURFACE FRONT WILL MOVE ACROSS THE AREA ON THURSDAY AND STRONG
LOW LEVEL CONVERGENCE WILL HAVE SUFFICIENT INSTABILITY IN THE HOT
AND MOIST AIRMASS TO PRODUCE SCATTERED...MAINLY LATE DAY
THUNDERSTORMS ONCE AGAIN. UPPER SUPPORT IS RATHER WEAK...
HOWEVER...SO THE CONVECTION WILL DIE OFF QUICKLY AFTER SUNSET.
HIGHS THURSDAY WILL REACH NEAR 90. WE WILL START TO SEE SOME
CHANGE IN THE AIRMASS...AS SURFACE WINDS SHIFT TO A SLIGHTLY
COOLER AND DRIER NORTHWEST FLOW BEHIND THE FRONT LATE ON THURSDAY. 

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 240 AM TUESDAY...

DRIER AIR OVER THE REGION FRIDAY AND SATURDAY AS HIGH PRESSURE 
BUILDS INTO THE AREA FROM THE NORTHWEST... AND SETTLES OVER THE AREA 
SATURDAY. HIGHS IN THE 80S TO AROUND 90. LOWS IN THE UPPER 60S TO 
LOWER 70S.

MOISTURE RETURNS TO THE REGION SUNDAY INTO MONDAY AS HIGH PRESSURE 
MOVES OFFSHORE AND A COLD FRONT APPROACHES FROM THE WEST RESULTING 
SOUTHWEST FLOW OVER THE AREA. WITH THE FRONTAL SYSTEM AND INCREASED 
MOISTURE WILL COME A CHANCE FOR SHOWERS AND STORMS. HIGHS IN THE 
LOWER 90S. LOWS SUNDAY NIGHT IN THE UPPER 60S NORTHWEST TO LOWER 70S 
SOUTHEAST.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
AS OF 740 AM TUESDAY...

PATCHY STRATUS AND FOG MAINLY OVER THE CENTRAL AND EASTERN TAF AREA 
WILL LIFT BY LATE MORNING. OTHERWISE WE CAN EXPECT SCATTERED TO 
BROKEN CLOUDS AT 3 TO 5 THOUSAND FEET WITH HIGHER CLOUDS ABOVE. 

MID AND UPPER LEVEL TROUGHS OVER THE WESTERN PORTION OF THE CWA WILL 
COMBINE WITH WITH PRECIP WATER VALUES IN EXCESS OF 1.75 INCHES... 
K'S NEAR 30... AND CAPE 2500 TO 3000 J/KG.  THERE WILL BE A CHANCE 
OF SHOWERS OVER THE WEST THIS MORNING. SHOWERS AND STORMS WILL BE 
POSSIBLE DURING THE AFTERNOON INTO THE OVERNIGHT HOURS... SO HAVE 
ADDED CB TO TAFS. LATER FORECAST WILL BETTER DEFINE LOCATION OF 
STORMS ONCE THEY BEGIN TO DEVELOP. MVFR CONDITIONS WILL BE POSSIBLE 
IN SHOWERS WITH IFR CONDITIONS IN STRONGER STORMS. WINDS WILL 
INCREASE TO 10 KNOTS FROM THE SOUTHWEST. 

THE CHANCE FOR STORMS WILL CONTINUE THROUGH THURSDAY AS A FRONT 
MOVES ACROSS THE AREA WEDNESDAY AND LINGERS OVER EASTERN NORTH 
CAROLINA INTO THURSDAY. HIGH PRESSURE WILL BUILD INTO THE REGION 
FROM THE NORTHWEST FRIDAY AND SETTLE OVER THE AREA SATURDAY. 
RETURNING VFR CONDITIONS TO THE AREA FOR THE FIRST PART OF THE 
WEEKEND.

&&

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

&&

$$
SYNOPSIS...HARTFIELD
NEAR TERM...HARTFIELD
SHORT TERM...MLM
LONG TERM...RHJ
AVIATION...RHJ