-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 270229
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1030 PM EDT SAT JUL 26 2014

.SYNOPSIS...A SURFACE TROUGH WILL DEVELOP OVER THE WESTERN PIEDMONT
THIS WEEKEND...RESULTING IN A VERY WARM SOUTHWEST FLOW. A STRONG
COLD FRONT WILL CROSS THE AREA ON MONDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1030 PM SATURDAY...

MAIN ADJUSTMENT TO THE FORECAST OVERNIGHT WAS TO BEEF UP CLOUD
COVERAGE OVER MOST OF THE PIEDMONT. THIS ALSO REQUIRED A SLIGHT
ADJUSTMENT UPWARD IN OVERNIGHT TEMPS. ALSO...INDICATIONS THAT MOSTLY
CLOUDY SKIES SUNDAY MORNING MAY INHIBIT INSOLATION UNTIL EARLY
AFTERNOON. THIS MAY RESULT IN MAX TEMPS A COUPLE OF DEGREES COOLER
THAN PREVIOUS FORECAST.

INITIAL S/W RESPONSIBLE FOR CONVECTION ACROSS THE MID OH VALLEY THIS
AFTERNOON TRACKING EAST INTO THE NORTHERN MID ATLANTIC. W-NW FLOW
ALOFT HAS SPREAD CONVECTIVE DEBRIS CLOUDINESS INTO THE PIEDMONT THIS
EVENING...THICKEST OVER THE NW PIEDMONT. WHILE EXPECT HIGH LEVEL
CLOUDS TO THIN WITH TIME...OPAQUENESS MAY BE ENOUGH ACROSS THE
PIEDMONT TO RESULT IN MIN TEMPS A COUPLE OF DEGREES WARMER THAN
PREVIOUS FORECAST...ESPECIALLY IN THE TRIAD VICINITY. ALSO...ARRIVAL
OF HIGH LEVEL CLOUDS WILL INHIBIT FOG FORMATION SO NOT EXPECTING
MUCH IN FOG OVERNIGHT.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AS OF 1030 PM SATURDAY...

SUNDAY...BAND OF CONVECTION OCCURRING AT 02Z ACROSS THE LOWER OH
VALLEY PROJECTED TO MOVE EAST-SE AND CROSS THE SW VA/NORTHERN NC
MOUNTAINS SHORTLY AFTER DAYBREAK. BULK OF CONVECTION EXPECTED TO
FIZZLE AS IT ADVANCES EAST PAST THE MOUNTAINS BUT ENOUGH RESIDUAL
CLOUDINESS WILL OCCUR TO LIMIT INSOLATION FOR A GOOD PART OF THE
MORNING...ESPECIALLY IN THE TRIAD...WITH PARTLY-MOSTLY CLOUDY SKIES
PROBABLE IN THE TRIANGLE AREA FROM MID-LATE MORNING UNTIL MID
AFTERNOON. IF THIS CLOUDINESS MATERIALIZES...THIS WILL HAVE AN
EFFECT TEMPS. HAVE SHADED MAX TEMPS DOWN OF COUPLE OF DEGREES IN THE
PIEDMONT AND NORTHERN COASTAL PLAIN. NOT AS CONFIDENT ABOUT THE
SOUTHERN COUNTIES WHERE MORE SUN THAN CLOUDS EXPECTED. THUS MAX
TEMPS IN THE UPPER 90S STILL APPEAR ON TRACK WITH HEAT INDICES 102-
104 DEGREES LIKELY.

MAY SEE A STRAY THUNDERSTORM OR TWO SUNDAY MORNING OCCUR ALONG THE
VA BORDER COUNTIES IN ASSOCIATION WITH THE WEAKENING THUNDERSTORM
COMPLEX. SUBSIDENCE IN THE WAKE OF THE EXITING MCV MAY INHIBIT
CONVECTIVE DEVELOPMENT IN THE AFTERNOON ACROSS THE REGION. -WSS

SUNDAY NIGHT...THE PREFRONTAL SFC TROUGH IS PROGGED BY THE GFS AND
NAM TO CROSS THE MOUNTAINS AROUND 06Z MONDAY THEN MOVE INTO OUR
WESTERN ZONES BY 12Z MON. DESPITE THIS LOW LEVEL FORCING...THE
MODELS HAVE LITTLE IF ANY QPF ACROSS MOST OF OUR CWA DURING THE
OVERNIGHT HOURS...PERHAPS DUE IN PART TO A DRY WESTERLY FLOW
PRECEDING IT AND LOW LEVEL NIGHT-TIME STABILITY.  ANY CONVECTION
THAT CAN GET GOING OVERNIGHT WOULD LIKELY BE ELEVATED...BUT STILL
WORTH CLOSE WATCHING. FOR NOW WILL CONTINUE SLIGHT CHANCE POPS
ACROSS THE ENTIRE CWA SUNDAY NIGHT.

THE OTHER MAIN CONCERN FOR SUNDAY IS TEMPS AND HIGH HEAT INDICES.
GUIDANCE CURRENTLY HAS TEMPS RANGING FROM AROUND 94 NW TO AROUND 98
SE. WITH DWPTS RANGING FROM THE MID 60S NW TO AROUND 70 SE...HEAT
INDICES WILL LIKELY RANGE FROM 100-103 ACROSS OUR SOUTHERN COASTAL
PLAIN ZONES. WHILE THIS IS BELOW HEAT ADVISORY CRITERIA...WE HAVE
HAVE THIS HIGHLIGHTED IN OUR CURRENT HWO. LOWS SUNDAY NIGHT IN THE
LOWER TO MID 70S. -NP

MONDAY AND MONDAY NIGHT: THE UNSEASONABLY STRONG SHORTWAVE
TROUGH/LOW TRAVERSING THE GREAT LAKES THIS WEEKEND WILL MOVE NE
THROUGH NY AND ALONG THE U.S./CANADA BORDER THROUGH MONDAY NIGHT.
ITS ASSOCIATED COLD FRONT WILL MOVE THROUGH THE AREA MONDAY
AFT/EVE...RESULTING IN INCREASED CHANCES FOR SEVERE WEATHER. THE GFS
AND ECMWF HAVE COME INTO BETTER AGREEMENT WITH THE TIMING AND
LOCATION OF THE FRONT...HOWEVER THE CHANCES FOR CONVECTION HAVE
DECREASED SOMEWHAT. THE BEST CHANCES ARE STILL MAINLY ALONG AND EAST
OF I-95 FROM 18Z MONDAY THROUGH 06Z TUESDAY. IN THIS FAVORED
REGION...MODELS ARE FORECASTING MUCAPE IN THE 1500-2500 J/KG
RANGE...0-6 KM BULK SHEAR OF 40-50 KTS...LOW LEVEL LAPSE RATES OF 8-
8.5 DEG/KM...AND MID LEVEL LAPSE RATES OF 6.5-7 DEG/KM. LOW LEVEL
SHEAR REMAINS WEAK. GIVEN THAT ENVIRONMENT...EXPECT CONVECTION...
WHERE IT DEVELOPS...TO BE STRONG TO SEVERE...WITH THE MAIN THREATS
BEING LARGE HAIL AND DAMAGING WINDS. THERE CONTINUES TO BE
UNCERTAINTIES WITH RESPECT TO COVERAGE OF CONVECTION AND WHETHER
THERE WILL BE MUCH OVER CENTRAL NC. SOME OF THE MODELS INDICATE THAT
THE CONVECTION WILL FALL APART AS IT CROSSES THE APPALACHIANS...
WITH SOME REDEVELOPMENT ALONG THE COAST LATE MONDAY AND/OR REMAIN
NORTH OF THE NC/VA BORDER. THE GFS CONTINUES TO FORECAST THE BEST
UPPER LEVEL FORCING WELL TO THE NORTH OF THE AREA. THUS...ALTHOUGH
THE CHANCE FOR CONVECTION DEFINITELY EXISTS AND SHOULD IT DEVELOP
ITS LIKELY THAT STORMS WILL BE STRONG/SEVERE...CONFIDENCE IS
DECREASING WITH REGARD TO WHETHER STORMS WILL DEVELOP OVER THE AREA.
ALSO...RESIDUAL CLOUDINESS AND OUTFLOW BOUNDARIES FROM CONVECTION
SUNDAY/SUNDAY NIGHT (SHOULD IT OCCUR) MAY ALSO PLAY A ROLE IN
LIMITING CONVECTION. HIGHS WILL BE MAINLY IN THE UPPER 80S NW TO MID
90S SE WITH OVERNIGHT LOWS...DEPENDING ON THE PROGRESSION OF THE
FRONT...MAINLY IN THE LOW 60S NW TO UPPER 60S SE. -KC

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
AS OF 235 PM SATURDAY...

THE UPPER LEVEL TROUGH WILL REMAIN OVER...TO JUST WEST OF THE REGION
THROUGH THE PERIOD. AT THE SURFACE...HIGH PRESSURE WILL BUILD INTO
THE AREA BEHIND THE FRONT...BRINGING COOLER AND DRIER AIR INTO
CENTRAL NC THROUGH THE END OF THE WEEK. THIS WILL RESULT IN BELOW
NORMAL TEMPERATURES...WITH HIGHS IN THE LOW TO MID 80S THROUGH THE
WEEK AND LOWS FROM THE UPPER 50S TO MID 60S TUE/WED NIGHTS AND LOW
TO MID 60S THU/FRI NIGHTS. WITH THE SUBSIDENCE IN THE WEST/NORTHWEST
FLOW ALOFT AND SIGNIFICANTLY DRIER AIR ADVECTING INTO THE MID/UPPER
LEVELS...EXPECT MUCH OF THE WEEK TO REMAIN DRY...WITH SOME SLIGHT
CHANCES IN THE NW FRI/SAT AS THE UPPER LEVEL TROUGH SHIFTS WEST AND
THE PIEDMONT TROUGH TRIES TO DEVELOP OVER THE AREA ONCE AGAIN.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
AS OF 740 PM SATURDAY...

MAINLY VFR CONDITIONS ARE EXPECTED TO CONTINUE FOR THE 24 HOUR TAF
PERIOD. UPSTREAM CONVECTION CURRENTLY OVER THE OHIO VALLEY MOVING
INTO THE CENTRAL APPALACHIANS AND CONVECTION FURTHER UPSTREAM/WEST
ACROSS THE MIDWEST WILL HELP TO SPREAD SOME MID AND HIGH CLOUD COVER
INTO THE AREA OVERNIGHT (NO CONVECTION OUTSIDE OF A POSSIBLY ROUGE
SHOWER ACROSS THE NORTH/NORTHWEST NEAR DAYBREAK). THIS COMBINED WITH
A WEST TO SOUTHWESTERLY LOW LEVEL FLOW SHOULD LEAD TO LESS OF A
CHANCE FOR SOME SUB-VFR CONDITIONS TONIGHT. LOCATIONS ACROSS THE
EASTERN HALF OF THE AREA MAY STILL SEE SOME MVFR VISBYS NEAR
DAYBREAK THOUGH... WITH FOG PRONE KRWI POSSIBLY SEE VISBYS RANGE
FROM LIFR TO VFR OVERNIGHT. CONFIDENCE IN SUB-VFR CONDITIONS IS LOW
THOUGH... SO WILL JUST INCLUDED A TEMPO MENTION OF SUB-VFR
CONDITIONS AT THE EASTERN TAF SITES FOR THE PRE-DAWN HOURS OF SUNDAY.

DURING THE DAY SUNDAY...LOOK FOR MOSTLY VFR CONDITIONS TO CONTINUE.
LATER IN THE DAY (MID MORNING ONWARD)...A BRIEF SHOWER OR TSTM WITH
LOCAL IFR CONDITIONS WILL BE POSSIBLE MAINLY ACROSS THE NORTHERN
HALF OF CENTRAL NC...AHEAD OF AN APPROACHING PREFRONTAL TROUGH.
GIVEN THE TIME FRAME AND LOW CONFIDENCE WILL LEAVE OUT ANY MENTION
OF CONVECTION AND SUB-VFR CONDITIONS DURING THE DAY SUNDAY.
HOWEVER... WE EXPECTED SOUTHWESTERLY WINDS TO STRENGTHEN DURING THE
AFTERNOON ON SUNDAY... WITH POSSIBLY SOME GUSTS TO 20 MPH....
POSSIBLY EVEN 25 MPH.

BEYOND THE 24 HOUR TAF PERIOD...A COLD FRONT WILL MOVE ACROSS
CENTRAL NC ON MONDAY...BRINGING THE CHANCE FOR SHOWERS AND TSTMS AND
ASSOC REDUCED FLIGHT CONDITIONS MONDAY MORNING/MONDAY AFTERNOON
...ESP ALONG AND EAST OF A LINE FROM KRDU TO KFAY. VFR CONDITIONS
ARE EXPECTED TO RETURN BEHIND THE FRONT FOR THE MIDWEEK PERIOD.

&&

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

&&

$$

SYNOPSIS...WSS
NEAR TERM...WSS
SHORT TERM...WSS/NP/KC
LONG TERM...KC
AVIATION...BSD/NP