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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 171920
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
320 PM EDT MON JUN 17 2013

.SYNOPSIS...
A COLD FRONT WILL APPROACH FROM THE NORTHWEST TUESDAY MOVE ACROSS
OUR REGION TUESDAY NIGHT INTO WEDNESDAY.

&&

.NEAR TERM /THROUGH TUESDAY/...
AS OF 3 PM MONDAY...

REST OF TODAY AND TONIGHT:
A SERIES OF MID LEVEL DISTURBANCE ARE EXPECTED TO MOVE ACROSS
CENTRAL NC THIS AFTERNOON INTO THE EVENING. THE LEAD DISTURBANCE IS
CURRENTLY HELPING TO FUEL SHOWER AND THUNDERSTORM ACTIVITY ACROSS
THE COASTAL PLAIN AND EASTERN SANDHILLS.... WITH THE SECOND AND
LIKELY MORE PROBLEMATIC DISTURBANCE MOVING EASTWARD OUT OF THE
HIGHER TERRAIN NOW AND HELPING TO DEVELOP SHOWERS AND STORMS ACROSS
THE HIGHER TERRAIN (ALONG WITH DIFFERENTIAL HEATING) AND WESTERN
PIEDMONT. EXPECT THIS ACTIVITY SHOULD MOVE EASTWARD ACROSS THE
AREA... AS THE MEAN 850-300MB FLOW IS WESTERLY AT AROUND 20 KTS. WRT
A SEVERE THREAT... THE SPC MESOPAGE IS SHOWING MLCAPES ARE GENERALLY
AROUND 500 TO 1000 J/KG... WITH NOW UPWARDS OF 25 TO 30 KTS OF
EFFECTIVE DEEP LAYER SHEAR. EXPECT MLCAPE VALUES WILL TOP OUT IN THE
1000-1200 J/KG RANGE THIS AFTERNOON. THUS... WITH A LITTLE BETTER
INSTABILITY AND SHEAR THAN FIRST THOUGH... THINK WE MIGHT SEE A
LITTLE ORGANIZATION ASSOCIATED WITH THE CONVECTION AS THE SECOND
DISTURBANCE CROSS THE AREA THIS AFTERNOON INTO THE EVENING. GIVEN
MID LEVEL LAPSE RATES REMAIN POOR WITH PW`S IN THE 1.7 TO 2.0 INCH
RANGE... THINK THE SEVERE THREAT WILL STILL REMAIN LOW... WITH THE
DAMAGING WINDS THE MAIN THREAT AND LOCALIZED FLOODING IN URBAN AREAS.

EXPECT ANY SHOWER AND THUNDERSTORM ACTIVITY SHOULD END/DECREASE IN
COVERAGE FROM A WEST TO EAST FASHION THIS EVENING AS THE WEAK MID
LEVEL DISTURBANCE PUSHES EASTWARD AND EVENTUALLY THROUGH OUR
AREA/COUPLED WITH NOCTURNAL COOLING. HOWEVER... WILL MAINTAIN AT
LEAST A SLIGHT CHANCE POP THROUGHOUT THE NIGHT AS WE WILL CONTINUE
TO BE WARM AND MOIST (PW`S 1.75 TO 2.0) WITH POSSIBLE WEAK/SUBTLE
PERTURBATIONS ALOFT APT TO CROSS THE AREA IN THE WESTERLY FLOW
OVERNIGHT... GIVEN AT LEAST ISOLATED TO SCATTERED CONVECTION EXTENDS
WESTWARD SOUTHEASTERN KS AND SOUTHERN MO. EXPECT LOW TEMPS TONIGHT
WILL BE AROUND 70/LOWER 70S.

TUESDAY:
MAIN S/W TROUGH AND ASSOCIATED WEAK COLD FRONT ARE EXPECTED TO
APPROACH THE REGION ON TUESDAY... WITH MOST MODELS NOW SHOWING THE
FEATURES CROSSING THE REGION BEYOND THE NEAR TERM FORECAST TIME
FRAME. HAVE TRENDED THE FORECAST TOWARDS A BLEND OF THE 12Z/17TH
NAM AND 00Z/17TH ECMWF FOR TIMING AND STRENGTH OF THE NEXT SYSTEM
(WHICH HOLDS THE SYSTEM TO THE WEST OF THE AREA THROUGH 00Z/19TH)...
WHICH IS IN LINE WITH THE ABOVE THINKING. THUS... HAVE LOWERED POPS
A BIT FOR TUESDAY. HOWEVER... STILL HAVE LIKELY POPS... AND EXPECT
AT LEAST SCATTERED SHOWERS AND STORMS ASSOCIATED WITH CONTINUED WEAK
DISTURBANCES CROSSING THE AREA IN THE INCREASINGLY CYCLONIC FLOW
ALOFT (WEST-SOUTHWESTERLY MID LEVEL FLOW) AND MOIST ATMO. THIS WILL
HELP TO SHARPEN UP A PRE-FRONTAL TROUGH TUESDAY AFTERNOON. EXPECT WE
WILL AGAIN HAVE A MARGINAL SVR THREAT... WITH STRONG TO DAMAGING
WINDS THE MAIN THREAT. DEEP LAYER SHEAR IS EXPECTED TO BE IN THE 20
TO 30 KT RANGE... WITH MLCAPE VALUES AGAIN AROUND 1000 J/KG. WITH
THE EXPECTED INCREASE IN CONVECTIVE COVERAGE... WE WILL NEED TO KEEP
AN EYE ON URBAN AREAS THAT RECEIVE ANY HEAVY RAIN FROM THE SHOWERS
AND STORMS (FLASH FLOODING THREAT). EXPECT HIGH TEMPS WILL AGAIN BE
HAMPERED BY CLOUD COVER. THUS... WILL GO WITH HIGHS RANGING FROM THE
LOWER TO MID 80S... WITH PERHAPS SOME UPPER 80S ACROSS OUR FAR EAST
AND SOUTH.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
AS OF 240 PM MONDAY...

TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...
MODEL GUIDANCE CONTINUES TO OFFER VARYING TIMING SCENARIOS
CONCERNING THE MID LEVEL S/W AND ATTENDANT SFC FRONT WHICH IS
EXPECTED TO EFFECT OUR REGION TUESDAY NIGHT INTO WEDNESDAY. THE
12Z/17TH GFS HAS TRENDED SLIGHTLY SHARPER AND FASTER WITH THE
TROUGH. THE 12Z CANADIAN/12Z NAM AND 00Z ECMWF FAVOR A SLOWER (6-12
HOURS SLOWER) SOLUTION. FAVORING MODEL CONSENSUS WOULD SUGGEST
PAINTING THE HIGHEST POPS OVERNIGHT TUESDAY NIGHT THROUGH WEDNESDAY
MORNING WITH RAIN CHANCES DECREASING FROM THE WEST-NW WEDNESDAY
AFTERNOON. THE SHORT TERM MODEL GUIDANCE DEPICT A SFC WAVE CROSSING
CENTRAL NC LATE TUESDAY NIGHT INTO WEDNESDAY MORNING. THIS FEATURE
SHOULD ENHANCE LOW LEVEL HELICITY WHICH IS DEPICTED NICELY (BUT ONLY
FOR AN HOUR OR TWO) BY BUFKIT HODOGRAPHS DISPLAY WITH AN ARCHING
HODOGRAPH IN THE SFC-3KM RANGE. WOULD PREFER A SLIGHTLY STRONGER
WIND PROFILE PLUS AIR MASS MORE THAN MARGINALLY UNSTABLE BEFORE
HIGHLIGHTING SEVERE STORM THREAT IN THE HWO.

FOR NOW WILL INTRODUCE A TREND OF INCREASING POPS LATE TUESDAY NIGHT
THROUGH EARLY AFTERNOON WEDNESDAY THEN DECREASING POPS MID AFTERNOON
WEDNESDAY THROUGH EARLY WEDNESDAY EVENING.

HIGH TEMPS WEDNESDAY WILL BE HELD BACK BY EXTENSIVE CLOUDINESS AND
SCATTERED-NUMEROUS SHOWERS AND THUNDERSTORMS. PLAN TO MAINTAIN MAX
TEMPS NEAR 80-LOWER 80S. MIN TEMPS TUESDAY NIGHT WILL BE WARM IN THE
HUMID AIR MASS (UPPER 60S TO LOWER 70S) WHILE TEMPS OVERNIGHT
WEDNESDAY NIGHT SHOULD BE 3-5 DEGREES COOLER (LOW-MID 60S) BEHIND
THE SFC FRONT.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
AS OF 3 PM MONDAY...

THURSDAY THROUGH FRIDAY NIGHT...SFC HIGH PRESSURE WILL EXTEND ACROSS
CENTRAL NC THU-FRI BEHIND THE EXITING MID LEVEL S/W. LOW LEVEL NE
FLOW WILL SPREAD AND MAINTAIN A DRY STABLE AIR MASS OVER CENTRAL NC.
THIS WILL LIMIT/INHIBIT CONVECTIVE DEVELOPMENT. LOW LEVEL
THICKNESSES AVERAGE 10M BELOW NORMAL. THIS TRANSLATES TO HIGH TEMPS
IN THE LOW-MID 80S. OVERNIGHT TEMPS GENERALLY IN THE LOW-MID 60S.

SATURDAY THROUGH MONDAY...A NARROW UPPER RIDGE WILL STRETCH FROM THE
SOUTHERN PLAINS INTO THE CENTRAL APPALACHIANS AND MID ATLANTIC
SATURDAY THROUGH MONDAY. ATTENDANT SFC RIDGE WILL GRADUALLY WEAKEN
THROUGH THE WEEKEND. THIS WILL CAUSE THE LOW LEVEL FLOW TO GRADUALLY
VEER FROM E-NE ON SATURDAY TO A S-SE FLOW LATE SUNDAY INTO MONDAY.
THIS SLY FLOW REGIME WILL RESULT IN AN UPTICK IN HUMIDITY LEVELS
SUNDAY INTO MONDAY. AT THIS TIME...CHANCES FOR AFTERNOON-EVENING
CONVECTION APPEAR TOO SMALL TO MENTION IN FORECAST.

PRESENCE OF UPPER LEVEL RIDGE WILL CAUSE AIR MASS TO MODIFY AS
WELL...YIELDING LOW LEVEL THICKNESSES ABOUT 10M ABOVE NORMAL BY
EARLY NEXT WEEK. THUS EXPECT HIGH TEMPS IN THE MID-UPPER 80S
SATURDAY...WARMING INTO THE UPPER 80S TO LOWER 90S ON MONDAY.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
-- Changed Discussion --
AS OF 310 PM MONDAY...

ISOLATED TO SCATTERED SHOWERS AND STORMS ARE EXPECTED ACROSS
CENTRAL NC THIS AFTERNOON AND THIS EVENING.... WITH MVFR/IFR
CONDITIONS POSSIBLE ALONG WITH GUSTY WINDS WITH THE STRONGEST
SHOWERS AND STORMS. EXPECT A LULL OVERNIGHT ACROSS AT LEAST THE
NORTHERN TIER IN SUBSIDENCE BEHIND A WEAK UPPER SHORTWAVE. VERY
MOIST AIRMASS WILL BE FAVORABLE FOR FOG AND PERHAPS SOME IFR/LIFR
CEILINGS IF WE GET SOME BREAKS TO ALLOW RADIATIONAL COOLING AND
WINDS CALM IN THE PREDAWN. ANY SUB VFR CONDITIONS ARE EXPECTED TO
LIFT AFTER DAYBREAK TOMORROW... ALTHOUGH WE MAY SEE CIGS SLOWLY
RISE. AT THIS TIME WILL SHOW SUB VFR CIGS SCATTERING OUT BY 12Z...
ALTHOUGH CONFIDENCE REMAINS LOW... AND WE MAY SEE A BRIEF PERIOD OF
MVFR CIGS AS DIURNAL MIXING DEEPENS THROUGH THE MORNING.

ADDITIONAL DISTURBANCES WILL BE CROSSING THE AREA ALONG WITH A WEAK
COLD FRONT TUESDAY NIGHT INTO WEDNESDAY...WITH PERIODS OF SHOWERS
AND STORMS PRODUCING SUB-VFR CONDITIONS. VFR CONDITIONS ARE
GENERALLY EXPECTED FROM THURSDAY ONWARD... OUTSIDE OF POSSIBLY SOME
EARLY MORNING STRATUS AND OR FOG DURING THE PRE-DAWN HOURS OF EACH
MORNING.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...BSD
NEAR TERM...BSD
SHORT TERM...WSS
LONG TERM...WSS
AVIATION...BSD/MLM