Area Forecast Discussion


726 
FXUS62 KRAH 130821
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
421 AM EDT TUE AUG 13 2013
.SYNOPSIS...
A COLD FRONT WILL TRACK SOUTHEAST THROUGH CENTRAL NORTH CAROLINA 
LATE THIS EVENING AND TONIGHT AND WILL BECOME STATIONARY ALONG THE 
COAST THROUGH LATE IN THE WEEK.  
&&
.NEAR TERM /THROUGH TUESDAY NIGHT/...
AS OF 420 AM TUESDAY
UPPER LEVEL LOW PRESSURE WILL SWING SE FROM SOUTH CENTRAL CANADA 
INTO THE EASTERN GREAT LAKES THROUGH TUESDAY NIGHT...WITH THE TROUGH 
EXTENDING SW INTO THE MIDWEST SWINGING EASTWARD TOWARD THE MID 
ATLANTIC...DAMPENING THE HIGH PRESSURE OVER THE SOUTHEAST U.S. THE 
SURFACE TROUGH WILL STRENGTHEN AS THE COLD FRONT APPROACHES FROM THE 
WEST. EXPECT THE FRONT TO BE ORIENTED SW-NE AND MOVE THROUGH NC BY 
12Z WEDNESDAY...WITH BEST CHANCES FOR CONVECTION AHEAD OF IT...18Z 
TUE IN THE NW THROUGH 12Z WED ACROSS THE SE. EXPECT PWAT VALUES 
AROUND 2 INCHES AHEAD OF THE FRONT...WITH THE BEST LOW LEVEL 
MOISTURE ACROSS THE SE. MLCAPE RANGING FROM AROUND 1500 J/KG IN THE 
NW TO AROUND 2500 J/KG IN THE SE. GIVEN MODERATE INSTABILITY...A 
GOOD FOCUS IN THE FORM OF SFC-H85 CONVERGENCE...AND A POTENTIAL FOR 
DPVA ASSOC/W SMALL AMPLITUDE DISTURBANCES PROGRESSING EAST INTO THE 
VIRGINIAS IN CYCLONIC FLOW ALOFT DURING THE AFT/EVE...EXPECT 
SCATTERED TO WIDESPREAD SHOWERS AND THUNDERSTORMS AT PEAK HEATING. 
EXPECT HIGH TEMPS IN THE UPPER 80S NW TO MID 90S SE. TIMING OF THE 
FROPA WILL HAVE AN IMPACT ON HOW MUCH THE LOWS FALL FROM THE 
PREVIOUS NIGHT...FOR NOW EXPECT LOWS IN THE MID 60S NW TO LOW 70S 
SE. 
SEVERE THREAT:
DEEP LAYER SHEAR OF 25-35 KTS...COMBINED WITH GOOD LOW-LEVEL 
MOISTURE AND MARGINAL INSTABILITY (DISCUSSED ABOVE) WILL SUPPORT THE 
THREAT FOR SOME STORMS TO PRODUCE DAMAGING WINDS...MOST LIKELY ALONG 
AND EAST OF HWY 1 BETWEEN 21Z TUESDAY AND 06Z WEDNESDAY.
&&
.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
AS OF 300 AM TUESDAY...
MODELS HAVE SPED UP THE TIMING OF THE COLD FRONT THROUGH THE AREA
WEDNESDAY MORNING...WITH CURRENT PROJECTIONS HAVING THE FRONT ALONG
THE COAST BY DAYBREAK WEDNESDAY...WHERE IT THEN BECOMES STATIONARY. 
WILL HOLD ONTO CHANCE POPS ACROSS THE FAR SE...OTHERWISE IT SHOULD 
BE DRY AND MUCH COOLER AND LOWERING HUMIDITY. HIGHS IN THE LOWER 
TO MID 80S. LOWS WEDNESDAY NIGHT IN THE LOWER TO MID 60S.    
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
AS OF 310 AM TUESDAY...
...MODERATE TO HEAVY RAINFALL STILL EXPECTED FOR THE 
SOUTHEAST THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK...  
SANDWICHED BETWEEN A RETROGRADING DEEP LAYER RIDGE OVER THE WESTERN 
ATLANTIC AND ANOTHER DEEP LAYER RIDGE OVER THE ROCKIES...A MID/UPPER 
LEVEL TROUGH THAT EXTENDS FROM THE GREAT LAKES SOUTHWARD INTO THE 
LOWER MS VALLEY WILL PERSIST THROUGH EARLY NEXT WEEK. AT THE 
SURFACE...SURFACE HIGH PRESSURE OVER THE OHIO VALLEY WILL BUILD INTO 
THE MID-ATLANTIC/SOUTHERN NEW ENGLAND REGION AS STATIONARY SURFACE 
FRONT EXTENDS FROM THE GULF COAST STATES NORTHEASTWARD UP THE 
SOUTHEAST COAST.   
RAIN CHANCES THURSDAY AND FRIDAY ARE EXPECTED TO REMAIN CONFINED 
INVOF THE STALLED FRONT NEAR THE COAST...LEAVING MUCH OF CENTRAL NC 
DRY AND UNDER THE INFLUENCE OF THE LOW-LEVEL NELY FLOW WITH 
TEMPERATURES A GOOD 7 TO 10 DEGREES BELOW NORMAL AND VERY 
COMFORTABLE RH LEVELS FOR MID AUGUST.   
 
BY FRIDAY NIGHT AND INTO THE WEEKEND...SHORTWAVE ENERGY DIGGING
SOUTHEASTWARD THROUGH THE BROAD CYCLONIC FLOW ALOFT WILL ALLOW 
SEVERAL WAVES TO DEVELOP ALONG THE COASTAL FRONT WITH OVERRUNNING 
PRECIP BEGINNING TO SPREAD BACK INLAND ATOP THE COOL AND DRY SURFACE 
HIGH PRESSURE RIDGE IN PLACE OVER CENTRAL NC AND TRIGGERING A 
STRONG WARM SEASON CAD EVENT. RESULTANT F-GEN RESPONSE ATOP THE CAD
ALONG...ALONG WITH THE POTENTIAL FOR SHORTWAVE DISTURBANCES IN THE 
SOUTHERLY FLOW ALOFT AND POTENTIALLY RETROGRESSION OF THE COASTAL/CAD
FRONT INTO THE EASTERN NC WILL BRING THE THE THREAT FOR MODERATE TO 
HEAVY RAINFALL. 
THE GFS AND CMC STILL TAKE AN AREA OF LOW PRESSURE/TROPICAL WAVE 
IN THE GULF OF MEXICO NORTHWARD TOWARD THE GULF COAST AND INTO THE 
SOUTHEAST TRACKING ALONG THE STALLED FRONTAL ZONE...WHILE THE 
ECMWF/UKMET RUNS DO NOT...KEEPING THE SYSTEM ON A MORE WESTWARD 
TRAJECTORY. PER NHC...WILL EMPHASIZE THE ECMWF/UKMET SOLUTION...
WITH NO TROPICAL INTERACTION EXPECTED AT THIS TIME. 
FLOODING APPEARS TO BE THE GREATEST SEVERE WEATHER THREAT AT THIS 
TIME WITH 7 DAY WPC RAINFALL PROJECTIONS OF WIDESPREAD 2 TO 5 INCHES
OF RAIN WITH HIGHEST RAINFALL AMOUNTS IN THE EAST. IT IS IMPORTANT 
TO NOT THAT IF THE COASTAL/CAD BOUNDARY RETREATS WELL INLAND...WARM 
SECTOR DESTABILIZATION AND ENHANCED LOW-LEVEL SHEAR/HELICITY ALONG 
THE FRONT WOULD SUPPORT THE THREAT FOR ROTATING SEVERE STORMS WITH 
AN ISOLATED TORNADO POSSIBLE SUNDAY OR MONDAY.   
TEMPERATURES WILL START OUT IN THE LOWER 80S THURSDAY AND FRIDAY...
WITH RAIN COOLED HIGHS IN THE MID TO UPPER 70S THROUGH THE WEEKEND. 
LOWS WILL GENERALLY BE LOW TO MID 60S EARLY IN THE PERIOD WITH MID 
TO UPPER 60S FORECAST BY EARLY NEXT WEEK.
 
&&
.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
AS OF 210 AM TUESDAY...
24 HOUR TAF PERIOD:
OVER THE PAST AND NEXT FEW HOURS ALL TAF SITES HAVE RECEIVED OR WILL 
RECEIVE SOME RAIN...AND THUNDERSTORMS WITH HEAVY RAIN ARE STILL 
POSSIBLE AT KRDU AND KRWI (AND POTENTIALLY KFAY) THROUGH THE REST OF 
THE NIGHT. ACCOMPANYING THE STORMS IS THE CHANCE FOR REDUCED VISBYS 
AND CIGS (IFR/LIFR) AND GUSTY WINDS. GIVEN THE RAINFALL...EXPECT 
FOG/LOW STRATUS TO DEVELOP WHERE THE RAIN HAS PASSED (ALREADY 
OCCURRING AT KINT). THE VISBY RESTRICTIONS SHOULD IMPROVE AFTER 
SUNRISE TUESDAY MORNING. ADDITIONAL SHOWERS AND THUNDERSTORMS ARE 
EXPECTED TO MOVE ACROSS THE AREA AHEAD OF A COLD FRONT EXPECTED TO 
MOVE THROUGH CENTRAL NC TUESDAY AFT/EVE. WILL CONTINUE TO CARRY VCTS 
AND CB AT ALL TAF SITES...WITH THE POTENTIAL FOR SOME GUSTY WINDS 
AND SUB-VFR CONDITIONS ACCOMPANYING STORMS THAT IMPACT ANY OF THE 
TERMINALS. -KC
LOOKING AHEAD:
VFR CONDITIONS ARE EXPECTED BY MID/LATE WEDNESDAY MORNING AS THE 
FRONT PUSHES TO THE SOUTH OF THE AREA. THE FRONT WILL STALL OUT JUST 
SOUTH OF CENTRAL NC AND IT IS POSSIBLE THAT THE KFAY COULD SEE A 
CONTINUED CHANCE OF SHOWERS/STORMS DURING THE AFTERNOON AND EVENING 
HOURS WED/THUR. -BSD
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...CBL
NEAR TERM...KC
SHORT TERM..CBL
LONG TERM...CBL
AVIATION...KC/BSD