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