Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 150733
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
332 AM EDT TUE APR 15 2014

.SYNOPSIS...WARM AND MOIST SOUTHERLY FLOW WILL PERSIST AHEAD OF A
COLD FRONT THAT WILL CROSS THE CAROLINAS THIS AFTERNOON AND EVENING.
UNSEASONABLY STRONG AND COOL HIGH PRESSURE WILL THEN BUILD EAST
ACROSS THE MIDDLE ATLANTIC REGION TONIGHT THROUGH THURSDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 330 AM TUESDAY...

SURFACE DEWPOINTS IN THE MIDDLE TO UPPER 60S OVER THE SOUTHEASTERN
US WILL CONTINUE TO ADVECT NORTHWARD IN ADVANCE OF A COLD FRONT THAT
STRETCHED AT 07Z FROM NW PA SOUTH SOUTHWESTWARD THROUGH THE EASTERN
TN VALLEY...TO CENTRAL AL...AND THE TRAILING PARENT POSITIVELY-
TILTED UPPER TROUGH AXIS FROM THE WESTERN GREAT LAKES TO THE
SOUTHERN PLAINS. A LARGE AREA OF PRE-FRONTAL CONVECTION HAD
DEVELOPED WELL DOWNSTREAM OF THE FRONT EARLIER MON...AND THE LEADING
EDGE OF THIS ACTIVITY WAS ALREADY LIFTING NORTH ACROSS THE SC BORDER
EARLY THIS MORNING. THIS LARGE AREA OF SHOWERS AND ISOLATED
TRANSIENT MINI-SUPERCELL STRUCTURES...DRIVEN ALONG A STRENGTHENING
LLJ AXIS AND BY A COUPLE OF MCV/S OVER GA...WILL CONTINUE TO SPREAD
NORTH ACROSS THE PIEDMONT THROUGH THE MORNING COMMUTE. THOUGH
INSTABILITY WILL REMAIN RELATIVELY WEAK/AROUND 250 J/KG UNTIL
DIURNAL HEATING AND CONTINUED MOISTURE TRANSPORT OF THE
AFOREMENTIONED MID-UPPER 60S TD/S RESULTS IN FURTHER DESTABILIZATION
BY MIDDAY...LOW AND DEEP SHEAR PROFILES ARE SUPPORTIVE OF CONTINUED
MINI-SUPERCELL STRUCTURES CAPABLE OF PRODUCING STRONG WIND GUSTS AND
PERHAPS EVEN AN ISOLATED TORNADO IN LOCALLY DEEPER CONVECTION.

THE MORE APPRECIABLE SEVERE THREAT - GENERALLY EAST OF US HWY 1 -
WILL EVOLVE DURING THE MIDDAY TO AFTERNOON HOURS AS THE WARMING AND
MOISTENING BL YIELDS 1000-1500 J/KG OF MLCAPE...AND AS THE
AFOREMENTIONED COLD FRONT AND OVERLYING LARGER SCALE FORCING FOR
VERTICAL MOTION ACCOMPANYING THE UPPER TROUGH SPREAD ACROSS CENTRAL
NC BETWEEN 18-22Z THIS AFTERNOON. 1) LINEAR FRONTAL FORCING...2)
FORECAST DEEP SHEAR VECTORS ORIENTED GENERALLY PARALLEL TO THE
FRONT...AND 3) FORECAST HODOGRAPHS THAT STRAIGHTEN WITH TIME (AFTER
DISPLAYING A CYCLONICALLY-CURVED CHARACTER THIS MORNING)... SUGGEST
THE CONVECTIVE MODE WILL TRANSITION TO A MORE LINEAR ONE SUPPORTIVE
OF LINE SEGMENTS AND EMBEDDED TRANSIENT CIRCULATIONS THIS AFTERNOON.
DAMAGING STRAIGHT LINE WINDS WILL CONSEQUENTLY BE THE PRIMARY
THREAT...THOUGH AN ISOLATED TORNADO OR TWO WOULD BE POSSIBLE IF THE
MESOLOW ABOUT 100 MILES SE OF MONTGOMERY AL HOLDS TOGETHER AND
TRACKS THROUGH THE NC PIEDMONT...AS THE 00Z NAM SUGGESTS...AROUND
18Z.

EVEN BEHIND THE PRE-FRONTAL AND FRONTAL CONVECTION...THE TRAILING
UPPER FORCING AND RESULT WESTWARD SLOPE OF THE SATURATED AXIS ACROSS
THE FRONTAL ZONE SUGGESTS SOME POST-FRONTAL LIGHT RAIN - SIMILAR TO
WHAT HAS DEVELOPED OVER THE CENTRAL TN VALLEY THIS MORNING - WILL
LINGER INTO THE EVENING HOURS.

FLASH FLOOD GUIDANCE VALUES BETWEEN 2 AND 3 INCHES ACROSS THE CWA
SUGGESTS FLOODING WILL NOT BE A WIDESPREAD THREAT ENOUGH TO WARRANT
A WATCH...THOUGH A COUPLE OF FLS/S...OR FFW/S MAINLY FOR URBAN
AREAS...MAY ULTIMATELY BE NEEDED.

TEMPERATURES TODAY - STARTING OFF WARM IN THE 65-70 DEGREE RANGE -
WILL BE TRICKY GIVEN THE MULTIPLE ROUNDS OF CONVECTION...FOLLOWED
QUICKLY BY THE FRONTAL PASSAGE. PREVIOUSLY FORECAST UPPER 60S WEST
TO AROUND 80 EAST LOOKS GOOD...WITH A STRONG SOUTHERLY BREEZE WITH
GUSTS TO NEAR 3O MPH...BECOMING A WEST TO NORTHWESTERLY ONE WITH
SIMILARLY STRONG GUSTS LATE THIS AFTERNOON AND EVENING.

MINIMAL ADJUSTMENT NEEDED FOR LOWS IN STRONG CAA TONIGHT...INTO THE
30 TO 37 DEGREE RANGE...COOLEST WEST. THE FREEZE WATCH WILL
CONSEQUENTLY BE UPGRADED TO A WARNING.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 235 AM TUESDAY...

WED AND WED NIGHT: RISING HEIGHTS ALOFT/DNVA AND ASSOCIATED STRONG
SUBSIDENCE WILL RESULT IN FURTHER DEEP LAYER DRYING (SUNSHINE)
WED...FOLLOWED BY GENERALLY NEUTRAL VERTICAL MOTION...BUT WITH A
STILL STRONGLY CAPPED AND RESIDUALLY DRY REGIME OVER OUR REGION
THROUGH WED NIGHT. BENEATH THE STRONG SUBSIDENCE ALOFT...SURFACE
HIGH PRESSURE WILL CONSEQUENTLY BECOME UNSEASONABLY STRONG INTO THE
1040-1045 MB RANGE AS IT BUILDS FROM THE OH VALLEY TO NEW ENGLAND.
COOL NORTHEASTERLY FLOW AND DRY ADIABATIC MIXING THROUGH 900
MB...WITH A COUPLE OF DEGREES ADDED TO ACCOUNT FOR A USUAL SLIGHT
COOL BIAS WITH THIS TECHNIQUE LIKELY IN PART OWING TO A SUPER-
ADIABATIC NEAR SURFACE LAYER...SUPPORTS HIGHS IN THE LOWER TO MIDDLE
50S.

PROJECTED LOW LEVEL THICKNESS VALUES IN THE 1300-1310 METER RANGE AT
12Z THU...WITH OPTIMAL RADIATIONAL COOLING...WOULD SUPPORT MIDDLE
20S. HOWEVER...A PROJECTED 4-6 MB RISE IN MSL PRESSURE WITH THE
STRENGTHENING HIGH WED NIGHT WILL LIKELY MAINTAIN A NORTHEASTERLY
STIRRING FOR MOST AREAS OVERNIGHT...THOUGH WITH TYPICALLY
COOLER/SHELTERED AREA LIKELY TO EXPERIENCE PERIODS OF CALM. IN
ADDITION...MOISTURE ADVECTION IN NORTHEASTERLY FLOW BENEATH THE
CAPPING INVERSION MAY RESULT IN SCT TO BKN LOW CLOUDS MAINLY IN THE
COASTAL PLAIN LATE. AS SUCH...TEMPERATURES ARE APT TO DISPLAY A
RELATIVELY LARGE RANGE...FROM 28-30 DEGREES IN RURAL WESTERN
PIEDMONT LOCATIONS (IN CLOSEST PROXIMITY TO THE RIDGE AXIS) TO
AROUND FREEZING IN URBAN AREAS FROM RDU WESTWARD TO THE TRIAD...TO
33-37 DEGREES IN THE COASTAL PLAIN AND EASTERN SANDHILLS. -MWS

THURSDAY THROUGH THURSDAY NIGHT: THIS PERIOD SHOULD REMAIN DRY WITH
HIGH PRESSURE RIDGING IN FROM THE NORTHEAST...ALTHOUGH EXPECT CLOUDS
TO INCREASE DURING THE EVE/OVERNIGHT...ESPECIALLY ACROSS THE SOUTH
AND EAST...AS A LOW DEVELOPS OFF THE COAST. WITH THE CONTINUED NE
FLOW AND CAA...STILL EXPECT TEMPS TO BE BELOW NORMAL. HOWEVER...
GIVEN LOW-LEVEL THICKNESSES INCREASING FROM THE PREVIOUS NIGHT BY A
GOOD 30-40 METERS...EXPECT TEMPS TO INCREASE BY 5-10 DEGREES...HIGHS
IN THE LOW TO MID 60S AND LOWS IN THE UPPER 30S TO LOW 40S. -KCP

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
AS OF 300 AM TUESDAY...

THERE IS STILL A SLIGHT CHANCE OF RAIN ACROSS THE SOUTHEAST FRIDAY
NIGHT/SATURDAY MORNING AS THE ELONGATED LOW OFF THE COAST MOVES AWAY
FROM THE AREA...OTHERWISE THE LATEST GFS AND ECMWF RUNS KEEP THE
FORECAST DRY THROUGH MONDAY. AN UPPER LEVEL LOW SKIRTS NORTH OF
CENTRAL NC SATURDAY NIGHT/SUNDAY. THE GFS IS A BIT MORE AMPLIFIED
WITH THE LOW...BRINGING IT CLOSER TO THE AREA. DESPITE THE STRONG
UPPER LEVEL FORCING AND MOISTURE IN THE UPPER LEVELS...THE DRY AIR
EXPECTED IN THE MID LEVELS MAY BE ENOUGH TO KEEP THINGS DRY. HIGHS
FRIDAY IN THE MID TO UPPER 60S WITH LOWS IN THE MID 40S TO AROUND 50
DEGREES. HIGH PRESSURE TO THE NORTH WILL RIDGE INTO THE AREA SUNDAY
AND MONDAY. ASIDE FROM SOME HIGH CLOUDS...EXPECT EASTER SUNDAY TO BE
DRY AND MOSTLY SUNNY. HIGHS MAINLY IN THE LOW TO MID 70S WITH LOWS
IN THE MID TO UPPER 40S THROUGH THE END OF THE PERIOD.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
AS OF 200 AM TUESDAY...

24 HOUR TAF PERIOD: MVFR/IFR CONDITIONS ACROSS THE AREA WILL LIKELY
DECREASE FURTHER INTO IFR/LIFR BY DAYBREAK TUESDAY. HEAVY SHOWERS
AND THUNDERSTORMS ARE APPROACHING FROM THE SOUTHWEST...ALREADY
IMPACTING KINT AND KGSO...AND LIKELY MOVING OVER KFAY AND KRDU OVER
THE NEXT COUPLE HOURS (AND KRWI THEREAFTER). THOUGH IT IS POSSIBLE
THE CIGS MAY IMPROVE SLIGHTLY WITH THESE HEAVY SHOWERS...VISBYS WILL
LIKELY DECREASE. AS ALREADY SEEN AT KINT AND KGSO...SOUTHWEST WINDS
WILL BECOME GUSTY (20-25 KTS) AS THE LOW LEVEL FLOW STRENGTHENS. IF
THERE IS A BREAK IN THE PRECIP TUESDAY MORNING...CONDITIONS MAY
IMPROVE BACK TO MVFR...BUT EXPECT MORE SHOWERS AND THUNDERSTORMS TO
MOVE ACROSS THE AREA AHEAD OF THE COLD FRONT...EXPECTED TO MOVE FROM
WEST TO EAST THROUGH CENTRAL NC DURING THE LATE AFTERNOON/EARLY
EVENING. ALTHOUGH WINDS WILL REMAIN STRONG AND GUSTY THROUGH THE TAF
PERIOD...EXPECT THEM TO VEER TO THE WEST THEN NORTHWEST BEHIND THE
FRONT. CIGS WILL LIFT AND VISBYS WILL IMPROVE BEHIND THE FRONT...
WITH VFR CONDITIONS EXPECTED BY THE END OF THE PERIOD. -KC

LOOKING AHEAD: MOSTLY VFR CONDITIONS WILL PERSIST THROUGH THE END OF
THE WORK WEEK. THERE COULD BE SOME MORNING STRATUS BOTH FRIDAY AND
SATURDAY MORNING AS MOISTURE ONCE AGAIN INCREASES AHEAD OF OUR NEXT
SYSTEM APPROACHING FROM THE SOUTH THIS WEEKEND. -KRD

&&

.CLIMATE...
THE FOLLOWING ARE THE RECORD LOW TEMPERATURES FOR WED AND THU MORNING...
AND THE RECORD LOW MAXIMUM TEMPERATURES FOR WED:

            WED 04/16                    THU 04/17
     LOW/YEAR   LOW MAX/YEAR             LOW/YEAR
FAY:  28/1943        56/1950             31/1953
GSO:  25/1943        48/1929             29/1953
RDU:  28/1950        46/1890             29/1962

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
FREEZE WATCH FROM LATE TUESDAY NIGHT THROUGH WEDNESDAY MORNING
FOR NCZ007>010-021>026-038>041-073>077-083-084.

&&

$$

SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...MWS/KCP
LONG TERM...KCP
AVIATION...KCP
CLIMATE...MWS



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