-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 180717
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
317 AM EDT TUE JUN 18 2013

.SYNOPSIS...
A COLD FRONT WILL APPROACH FROM THE NORTHWEST LATE TODAY...AND MOVE
SLOWLY SOUTHEAST ACROSS THE REGION TONIGHT INTO WEDNESDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
AS OF 310 AM TUESDAY...

SURFACE ANALYSIS THIS MORNING REVEALED A LEESIDE TROUGH OVER THE NC
FOOTHILLS. IN ADDITION...A 1011 MB SURFACE WAVE WAS CENTERED OVER
THE MID SOUTH...ALONG A FRONTAL ZONE DRAPED FROM THE SOUTHERN PLAINS
NORTHEASTWARD THROUGH THE EASTERN TN VALLEY/CENTRAL APPALACHIANS TO
THE DELMARVA/NEW JERSEY COAST. A SEPARATE NORTHERN STREAM FRONT
ARCED FROM NEW ENGLAND SOUTHWESTWARD TO AN ELONGATED 1011 MB AREA OF
LOW PRESSURE FROM OH TO IL...THEN NORTHWESTWARD TO INTO THE UPPER
MIDWEST.

TODAY: WHILE A MOIST...WEAKLY INHIBITED...AND MARGINALLY UNSTABLE
AIRMASS OVER NC WILL NOT NEED MUCH IMPETUS TO FORCE CONVECTION...THE
COMBINATION OF SUBSIDENCE IN THE WAKE OF A LEAD MCV OVER
SOUTHEASTERN NC AT PRESENT...AND THE LOCATION OF THE SOUTHERNMOST
FRONTAL ZONE ACROSS THE TN VALLEY AND CENTRAL APPALACHIANS (IE. TO
OUR NW) SHOULD TEND TO LIMIT CONVECTIVE COVERAGE OVER CENTRAL NC
THROUGH EARLY TO MID AFTERNOON. HOWEVER...A SHORTWAVE TROUGH OVER
THE MO VALLEY THIS MORNING IS PROGGED TO LIFT ENE TO NE ALONG THE
SPINE OF THE APPALACHIAN CHAIN THIS AFTERNOON...AND THE ASSOCIATED
BRUNT OF THIS FORCING FROM THE NW NC PIEDMONT NORTHWARD THROUGH VA
SHOULD HELP FOCUS CONVECTIVE DEVELOPMENT ALONG A THE LEE TROUGH OVER
WESTERN NC/VA...WITH THIS ACTIVITY LIKELY TO SPREAD ENE ACROSS THE
WESTERN AND NORTHERN NC PIEDMONT AFTER 3 OR 4 PM. MEANWHILE...MORE
THAN A COUPLE OF THE HI-RES CAMS INDICATE AN AREA OF STORMS AND AN
ASSOCIATED MCV OVER MS/NORTHWESTERN AL THIS MORNING MAY PIVOT ENE
ACROSS THE SANDHILLS AND COASTAL PLAIN LATER THIS AFTERNOON AND
EVENING...POSSIBLY MERGING WITH THE ACTIVITY FROM THE PIEDMONT.

BOTH MARGINAL INSTABILITY OF 1000 J/KG OR LESS OWING TO WEAK LAPSE
RATES ALOFT...AS WELL AS MARGINAL EFFECTIVE BULK SHEAR IN THE 20-30
KT RANGE...STILL SUGGEST ANY SEVERE THREAT WILL BE LOW...WITH
PERHAPS A FEW STRONG PRECIPITATION-LOADED WIND GUSTS. A MORE LIKELY
SCENARIO REMAINS A THREAT OF DOWNPOURS AND LOCALIZED FLOODING...
THOUGH ANY SUCH FLOODING WILL NOT BE WIDESPREAD AND INSTEAD CONFINED
MOST LIKELY TO URBAN AREAS SINCE THE ANDREA-SOAKED SOIL HAS DRIED IN
THE PAST WEEK TO 10 DAYS...AND RESULTANT FLASH FLOOD GUIDANCE VALUES
HAVE INCREASED...INTO THE 2.5 TO 3 INCH RANGE FOR ONE HOUR FOR
EXAMPLE. HIGH TEMPERATURES TODAY ARE LIKELY TO REACH THE LOWER TO
MIDDLE 80S...WITH A FEW UPPER 80S POSSIBLE TOWARD KFAY AND KGSB.

TONIGHT: WHILE THERE MAY BE A LULL THIS EVENING AFTER THE AFTERNOON
AND EARLY EVENING CONVECTION...THE LEAD SURFACE BOUNDARY IS FORECAST
TO SETTLE SOUTHEASTWARD INTO CENTRAL NC ABOUT THE TIME THE SURFACE
WAVE OVER THE MID SOUTH TRACKS TOWARD INTO OUR REGION. THE PASSAGE
OF THE SURFACE WAVE - ONE SUPPORTED FROM ALOFT BY THE APPROACH OF A
NORTHERN STREAM SHORTWAVE TROUGH FROM THE UPPER MIDWEST THIS
MORNING - WILL ENCOURAGE RENEWED DEVELOPMENT OF AN AREA OF SHOWERS
AND ISOLATED STORMS OVER CENTRAL NC OVERNIGHT. LOWS...WITH MOSTLY
CLOUDY SKIES...IN THE MIDDLE 60S TO AROUND 70 DEGREES. TOTAL
RAINFALL AMOUNTS IN THE ONE TO TWO INCH RANGE WILL BE COMMON...
HIGHEST NORTH AND NORTHWEST...THOUGH AS WITH ANY CONVECTIVE
PRECIPITATION THERE WILL BE SOME AREAS THAT LIKELY RECEIVE
CONSIDERABLY LESS.
-- End Changed Discussion --

&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
-- Changed Discussion --
AS OF 240 PM MONDAY...

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.

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.
-- End Changed Discussion --

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
-- Changed Discussion --
AS OF 315 AM TUESDAY...

THURSDAY THROUGH FRIDAY NIGHT...HIGH PRESSURE BUILDS ACROSS SOUTHERN
NEW ENGLAND SHORE...EXTENDING DOWN THE MID ATLANTIC COAST WITH DRY
NORTHEAST TO EAST FLOW. THE PLEASANT ENSUING COOL DAMMING SCENARIO
WILL LINGER INTO THE WEEKEND...WITH THICKNESSES INDICATIVE OF TEMPS
A GOOD CATEGORY BELOW NORMAL...LOW-MID 80S. WILL MAKE SOME GRID
ADJUSTMENTS ON THURSDAY AND FRIDAY TO FAVOR COOLER TEMPS IN THE
NORTHEAST WHERE MARITIME FLOW WILL BE STRONGEST/COOLEST. MINS WILL
BE GENERALLY LOW AND MID 60S.

SATURDAY THROUGH MONDAY...THE COOL SURFACE HIGH WILL WEAKEN AND
DRIFT EAST WITH A GRADUAL RETURN OF MORE SOUTHERLY FLOW BY LATE
WEEKEND. MEANWHILE...UPPER RIDGING WILL BUILD EAST OUT OF THE
MIDWEST INTO THE EASTERN CONUS SATURDAY THROUGH MONDAY. SOUTHERLY
FLOW WILL RESULT IN INCREASING HUMIDITY SUNDAY INTO MONDAY. WITH THE
CAPPING MID LEVEL RIDGE OVERHEAD...CONVECTION WILL BE ISOLATED
OUTSIDE OF PERHAPS SOME DIFFERENTIAL HEATING ON THE EASTERN SLOPES
AND POTENTIAL FOR SOME SEA BREEZE CONVECTION TO MIGRATE INLAND INTO
THE COASTAL PLAIN. AT THIS POINT...THE CHANCES ARE TOO SMALL TO
MENTION IN THE FORECAST. THE AIRMASS WILL GRADUALLY WARM UP WITH THE
SOUTHERLY FLOW AND PERSISTENCE OF THE UPPER RIDGE INTO MONDAY...
HIGHS WILL WARM FROM THE MID 80S SATURDAY TO THE UPPER 80S...PERHAPS
LOWER 90S ON MONDAY. MINS WILL BE IN THE 60S.
-- End Changed Discussion --

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
AS OF 130 AM TUESDAY...

CONVECTION HAS WEAKENED WITH THE LOSS OF HEATING AND PATCHY LIGHT
RAIN LINGERS EARLY THIS MORNING. MVFR/IFR CEILINGS ARE LIKELY TO
COME AND GO JUST ABOUT ANYWHERE IN THE AREA FOR THE REMAINDER OF THE
NIGHT...WITH LIFR CEILINGS AND MVFR FOG POSSIBLE TOWARDS 12Z.

TODAY...MVFR CIGS AND VSBYS CAN BE EXPECTED IN SCATTERED TO NUMEROUS
SHOWERS AND THUNDERSTORMS...WITH ACTIVITY PEAKING IN THE AFTERNOON
AND EVENING HOURS. ADDITIONAL DISTURBANCES WILL BE CROSSING THE AREA
ACCOMPANYING THE WEAK COLD FRONT TONIGHT...AGAIN 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.

&&

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

&&

$$

SYNOPSIS...MLM
NEAR TERM...MWS
SHORT TERM...WSS
LONG TERM...MLM
AVIATION...MLM