National Weather Service Raw Text Product

558 
FXUS62 KRAH 151905
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
305 PM EDT FRI APR 15 2011

.SYNOPSIS...
HIGH PRESSURE WILL DRIFT OFFSHORE TONIGHT. A POWERFUL STORM SYSTEM 
WILL CROSS OUR REGION ON SATURDAY...FOLLOWED BY HIGH PRESSURE FOR 
SATURDAY NIGHT AND SUNDAY.

&&

.NEAR TERM /THROUGH SATURDAY NIGHT/...
AS OF 200 PM FRIDAY...

...SEVERE WEATHER OUTBREAK WITH A MODERATE RISK FOR SEVERE STORMS
SATURDAY...

1730Z SPC DAY 2 OUTLOOK INCREASED SEVERE WEATHER THREAT TO MODERATE
FOR SATURDAY. FROM THE SPC DISCUSSION...WIDESPREAD DAMAGING WINDS AND
A FEW STRONG TORNADOES WILL BE POSSIBLE ACROSS THE CENTRAL AND ERN
CAROLINAS ON SATURDAY. SATURDAY IS SETTING UP TO BE A TEXT BOOK
LARGE SCALE SEVERE WEATHER OUTBREAK WITH THE POTENTIAL FOR
WIDESPREAD DAMAGE.

TONIGHT: CURRENT BAND OF SHOWERS AND STORMS OVER ERN TENN SHOULD
SLOW ITS FORWARD PROGRESSION AND HANG UP ALONG THE MOUNTAINS
SINCE IT HAS RACED OUT AHEAD OF THE PRIMARY FORCING AND UPPER LOW.
FOR TONIGHT INCREASING SLW FLOW WITH THE DEVELOP OF THE LOW LEVEL
JET OVERNIGHT WILL START TO SURGE MOISTURE NORTH INTO THE REGION
AFTER MIDNIGHT. WITH THE INCREASE IN MOISTURE AND LOW LEVEL
CONFLUENCE SOME RAPIDLY MOVING SHOWERS MOVING SOUTH TO NORTH COULD
DEVELOP FROM 09-15Z AND THIS IS SUPPORTING ON A NUMBER OF THE WRF
RUNS. A CHANCE FOR SHOWERS AFTER MIDNIGHT WEST OF HIGHWAY
ONE...WITH PERHAPS A TENTH INCH WEST OF HIGHWAY 220 BEFORE
SUNRISE...AND CHANCES FOR MEASURABLE RAIN SPREADING EAST BEFORE
SUNRISE. WITH INCREASING SLY FLOW...CLOUD COVER AND LOW LEVEL
WINDS TEMPS OVERNIGHT WILL BE UNIFORM AND RATHER MILD IN THE
MIDDLE 50S. SKIES WILL BECOME OVERCAST AFTER MIDNIGHT.

SATURDAY...MAIN ITEM TO NOTE IS THE MODELS HAVE INCREASED
INSTABILITY FROM 11 AM THROUGH 5 PM WITH MLCAPE 1600 J/KG ACROSS
CENTRAL NC. THIS COMPARED TO MODELS YESTERDAY PREDICTING WEAKER
MLCAPE FROM 500-1000 J/KG. SHEAR WILL SUPPORT DISCRETE CELLS
DEVELOPING AHEAD OF A DANGEROUS SQUALL LINE. 0-3 KM SHEAR IS
FORECAST AROUND 40 M/S WITH HELICITY IN EXCESS OF 450 M2/S2. IN
FACT 0-1 KM SHEAR WILL BE IN EXCESS OF 20 M/S WITH HELICITY OVER
300 M2/S2 SUPPORTIVE OF TORNADOES. ALONG WITH THE INSTABILITY AND
SHEAR LCL VALUES FALL TO LESS THAN 1500 FEET. THE DANGEROUS
COMBINATION OF HIGH SHEAR...MODERATE CAPE AND LOW LCLS WILL BE
SUPPORTIVE OF DISCRETE SUPERCELLS CAPABLE OF PRODUCING TORNADOES
AHEAD OF A MAIN SQUALL LINE CAPABLE OF WIDESPREAD DAMAGING WIND
AND ADDITIONAL TORNADOES. A FEW INTENSELY ROTATING SUPERCELLS
WITH A THREAT OF TORNADOES WILL LIKELY EXIST.

TIMING: THE NAM IS A LITTLE SLOWER WITH THE SYSTEM THAN THE GFS BY
ABOUT 2-3 HOURS. WILL TREND TOWARDS THE FASTER WRF SOLUTIONS
WHICH BRING THE LINE OF STORMS TO THE TRIAD AROUND NOON...TO THE
TRIANGLE AROUND 2 PM AND EAST OF I-95 AROUND 3 PM. THE EXACT
TIMING OF THE SQUALL LINE IS DIFFICULT AND IT COULD COME IN A
LITTLE LATER IF THE NAM IS CORRECT. THAT SAID EXPECT DISCRETE
STORMS SOME OF WHICH COULD BE SEVERE OR TORNADIC WELL AHEAD OF THE
MAIN LINE ESPECIALLY AS WE MOVE INTO THE AFTERNOON AND INSTABILITY
INCREASES.

HIGHS SATURDAY IN THE MID 70S WITH DEW POINTS IN THE LOWER 60S. 
WITH THE TIGHT PRESSURE GRADIENT EXPECT GUSTY WINDS OF 30 TO 40
MPH WITH THE STRONG SLY FLOW OUTSIDE OF THE STORMS. IF THIS
INCREASES A WIND ADVISORY MAY BE NEEDED FOR SATURDAY AFTERNOON. 

SATURDAY NIGHT, A SMALL BAND OF SHOWERS MAY BE POSSIBLE WITH THE 
UPPER LOW SATURDAY EVENING DUE TO THE LARGE SCALE ASCENT AND SURFACE 
FRONT. AS OF NOW MOISTURE LOOKS TOO LIMITED TO PRODUCE SHOWERS, BUT 
WILL HAVE TO KEEP AN EYE ON THIS WITH LATER FORECASTS. LOWS SATURDAY 
NIGHT IN THE MID 40S. 

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... 
AS OF 230 PM FRIDAY...

SURFACE HIGH PRESSURE WILL BE IN CONTROL OF THE WEATHER ACROSS 
CENTRAL NC AS IT PROGRESSES FAIRLY QUICKLY EASTWARD ACROSS THE 
SOUTHEASTERN US. THIS WILL RESULT IN FAIR WEATHER AND THEN AS RETURN 
FLOW SETS BY SUNDAY AFTERNOON...A WARMING TREND THROUGH THE PERIOD. 
THICKNESS VALUES WILL REBOUND TO NEAR 1380M BY MONDAY AFTERNOON 
WHICH SHOULD TRANSLATE TO HIGH TEMPS IN THE MID TO UPPER 70S (A GOOD 
FIVE DEGREES WARMER THAN WHAT IS EXPECTED ON SUNDAY). OVERNIGHT LOWS 
WILL ALSO BE ON A MODERATING TREND...WITH UPPER 40S TO NEAR 50 
DEGREES EXPECTED SUNDAY NIGHT AND MID 50S EXPECTED BY MONDAY 
NIGHT.      

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/... 
AS OF 255 PM FRIDAY...

DURING THE BEGINNING OF THE LONG TERM PERIOD...THE SUBTROPICAL RIDGE 
IS PROGGED TO STRENGTHEN OVER THE SOUTHWESTERN ATLANTIC AND THE 
SOUTHEASTERN US. THIS FEATURE IS EXPECTED TO PUSH THE NEXT STORM 
SYSTEM MOVING OUT OF THE PLAINS NEXT WEEK NORTH OF THE FORECAST AREA 
AS IT TRACKS INTO THE UPPER GREAT LAKES REGION. THEREFORE THE 
TRAILING FRONTAL ZONE AND ASSOCIATED PRECIP IS EXPECTED TO ALSO 
REMAIN NORTH OF THE REGION THROUGH AT LEAST THURSDAY...RESULTING IN 
DRY CONDITIONS AND A CONTINUED WARMING TREND. HIGH TEMPS ARE 
EXPECTED TO RISE FROM THE LOW 80S ON TUESDAY TO THE MID TO UPPER 80S 
BY THURSDAY. THE AFOREMENTIONED SUBTROPICAL RIDGE IS THEN PROGGED TO 
BECOME SUPPRESSED TO THE SOUTH WHICH SHOULD ALLOW THE FRONTAL ZONE 
TO DRIFT SOUTHWARD INTO THE REGION LATE THURSDAY INTO FRIDAY. 
THEREFORE WILL SHOW LOW END CHANCE POPS FOR THE THURSDAY NIGHT INTO 
FRIDAY...WITH SLIGHTLY COOLER TEMPS ON FRIDAY. 

&&

.AVIATION /17Z FRIDAY THROUGH TUESDAY/...
AS OF 200 PM FRIDAY...

VFR CONDITIONS WILL PERSIST THIS AFTERNOON AND EVENING...BUT CLOUD
COVER WILL INCREASE WITH A STRENGTHENING AND INCREASINGLY MOIST
SOUTHEASTERLY FLOW AND ASSOCIATED. EXPECT IFR-MVFR CONDITIONS
BETWEEN 04-08Z SATURDAY. INCREASING SOUTHERLY WINDS (TO
AROUND 40 KTS) AND ASSOCIATED SHEAR JUST ABOVE THE SURFACE WILL
ALSO PRODUCE MECHANICAL TURBULENCE OVERNIGHT. A SOUTHEASTERLY
SURFACE WIND WILL INCREASE TO 15 KT RANGE WITH OCCASIONAL
GUSTINESS TO AROUND 25 KTS BY SATURDAY MORNING. A PERIOD OF
SCATTERED SHOWERS ARE POSSIBLE EARLY SATURDAY FROM 09-14Z WITH THE
STRONG SLY LOW LEVEL FLOW.

CONDITIONS MAY BRIEFLY IMPROVE BY A CATEGORY MID TO LATE SATURDAY 
MORNING...TO LOW MVFR (PARTICULARLY AT EASTERN TERMINALS 
(KRWI/KFAY)...BEFORE LOWERING AGAIN IN WIDESPREAD SHOWERS AND 
THUNDERSTORMS. EXPECT WINDY CONDITIONS IN SOUTH SOUTHEASTERLY 
SURFACE FLOW...MIDDAY THROUGH SATURDAY AFTERNOON WITH GUSTS TO 35 
KT. 

A DANGEROUS SQUALL LINE IS FORECAST TO MOVE FROM WEST TO EAST
ACROSS ALL TERMINAL FROM 17Z-22Z WITH A THREAT OF WINDS IN EXCESS
OF 52KTS AND ISOLATED TORNADOES. 

VFR CONDITIONS ARE EXPECTED TO RETURN AS HIGH PRESSURE BUILDS IN 
SATURDAY NIGHT THROUGH EARLY NEXT WEEK.

&&

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

&&

$$
SYNOPSIS...JO
NEAR TERM...JO
SHORT TERM...KRR
LONG TERM...KRR
AVIATION...JO