HAMweather.com Area Forecast Discussion for County Warning Area RAH

Thu, 16 Feb 2012 07:51:44 GMT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
100 AM EST THU FEB 16 2012

.SYNOPSIS...
HIGH PRESSURE WILL SHIFT EAST AND OFFSHORE THIS MORNING. A WEAK 
PRESSURE SYSTEM AND ASSOCIATED COLD FRONT WILL MOVE ACROSS THE 
REGION THURSDAY AFTERNOON AND EVENING. 

.NEAR TERM /TONIGHT/...
AS OF 910 PM WEDNESDAY...

A DRY AIRMASS IS IN PLACE THIS EVENING ACROSS CENTRAL NC
AS A 1026 MB SURFACE HIGH WAS CENTERED OVER THE REGION. 
THICKENING WAA MID/UPPER LEVEL CLOUD CANOPY ASSOCIATED WITH 
A DAMPENING WAVE OVER MISSOURI HAS ALREADY ADVANCED EASTWARD
ACROSS WESTERN HALF OF THE STATE....AND WILL CONTINUE TO SPREAD EAST 
OVERNIGHT AS THE WAVE REACHES THE OHIO VALLEY/LOWER GREAT LAKES BY 
THURSDAY MORNING. HOWEVER ANY MEASURABLE RAIN SHOULD HOLD OFF UNTIL 
AFTER DAYBREAK AS THE ANTECEDENT DRY LOW-LEVEL AIRMASS(CHARACTERIZED 
BY SFC DEWPOINTS IN THE 25 TO 35F RANGE)WILL UNDERGO ONLY SLIGHT 
MODERATION AS SURFACE HIGH SHIFTS OFFSHORE LATE.  

BASED ON LATEST SATELLITE AND OBSERVATIONS TRENDS...RADIATIONAL 
COOLING HAS ALREADY CEASED ACROSS THE WESTERN PIEDMONT...WITH 
ANOTHER 2 TO 3 HOURS OF COOLING IN THE EAST BEFORE IT IS MET WITH
THE SAME FATE. FORECAST MINS TONIGHT LOOK A GOOD 4 TO 7 DEGREES TOO 
COOL IN THE WEST...2 TO 4 DEGREES TOO WARM ACROSS CENTRAL AREAS.
NORTHERN COASTAL PLAIN COUNTIES COULD STILL POTENTIALLY REACH 
PROJECTED LOWS OF UPPER 30S IN THE NEXT COUPLE OF HOUR. 
OVERNIGHT LOWS FROM NEAR 50 WEST TO UPPER 30S NORTHEAST. 
 

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
AS OF 215 PM WEDNESDAY...

HIGH CONFIDENCE IN RAIN ON THURSDAY...LOW CONFIDENCE IN AMOUNT.

MODELS ARE IN GOOD OVERALL AGREEMENT IN THE FORECAST OF THE CURRENT 
MID-UPPER TROUGH CURRENTLY MOVING OUT OF TEXAS AND OKLAHOMA. 
CONVECTION HAS BEEN BLOSSOMING OVER SE TEXAS THIS AFTERNOON. THIS 
HAS BEEN HANDLED WELL THUS FAR BY THE 12Z GFS. ALL MODELS GENERALLY 
SHOW THE MID-UPPER TROUGH PROGRESSING QUICKLY ENE TOWARD OUR REGION 
TONIGHT AND THURSDAY. THE AFOREMENTIONED 12Z/GFS HAS PICKED UP ON 
THE CONVECTION FLARING UP ALREADY OVER SE TEXAS... AND HAS THIS 
CONVECTION SPREADING ENE ACROSS MS/AL AND GA OVERNIGHT THROUGH 
12Z/THU. FROM THERE... MODELS DIVERGE ON POP/QPF OVER NC THURSDAY. 

THE LATEST GFS AND NOW THE LATEST EUROPEAN MODELS DEPICT ALMOST 
DOUBLE THE QPF OR RAINFALL AMOUNTS ACROSS MUCH OF OUR REGION THAN 
THE 12Z/NAM WITH THE EVENT. YET... THE HIGH RESOLUTION MODELS IN 
PARTICULAR THE SPC WRF AND THE HRRR DEPICT MINIMAL QPF OVER CENTRAL 
NC. THIS LACK OF QPF MAY BE THE WAY TO GO GIVEN THE NCEP MODELS 
TYPICAL FAILURE IN CAPTURING GULF COAST CONVECTION AND ITS ROLE IN 
DISRUPTING MOISTURE TRANSPORT INTO THE CAROLINAS UPSTREAM.

HOWEVER... THE LATEST EURO SUPPORTS HEAVIER QPF ACROSS CENTRAL NC 
WITH THE CONVECTION FALLING APART AS IT SWEEPS ACROSS THE DEEP SOUTH 
LATE TONIGHT AND THURSDAY. WITH THIS IN MIND... WE WILL KEEP CURRENT 
CATEGORICAL POP IN PLACE... AND CONTINUE TO FORECAST RAINFALL 
AMOUNTS OF AROUND 0.25. IF CONVECTION DOES NOT SPREAD EAST ACROSS 
GA... AND THE DEEP MOISTURE TRANSPORT (35-45KT SSW FLOW 925-850MB) 
IN THE MODELS IS NOT DISRUPTED... THEN QPF OF UP TO A HALF INCH 
WOULD BE LIKELY. HIGHS SHOULD SHOW QUITE A RANGE WITH SOME LIGHT 
RAIN IN THE WEST EARLY... KEEPING HIGHS IN THE 50-55 RANGE. HIGHS 
SHOULD REACH THE LOWER 60S AROUND FAY TO GSB. 

THURSDAY NIGHT... SHOWERS WILL QUICKLY MOVE EAST WITH THE TROUGH... 
BUT LOW LEVEL MOISTURE WILL LAG PER THE LATEST MODELS. DEPENDING ON 
IF THE GROUND GETS WET OR NOT... FOG WILL/WILL NOT BE AN ISSUE. IF 
WE SQUEEZE OUT 0.10 OR SO... THEN FOG WILL BE LIKELY. OTHERWISE... 
PARTLY CLOUDY WITH LOWS 35-40. 

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
AS OF 300 PM WEDNESDAY...

FRIDAY AND FRIDAY NIGHT:
A DEAMPLIFYING SHORTWAVE PROGRESSING EAST THROUGH THE MID-ATLANTIC 
ON THU (AND ITS ATTENDANT SFC LOW DEVELOPING OVER THE CAROLINAS) 
WILL MOVE OFFSHORE THU NIGHT. EXPECT CLEAR SKIES EVERYWHERE BY 12Z 
FRI MORNING AS DRY HIGH PRESSURE BUILDS INTO THE AREA FROM THE W/NW. 
HIGH PRESSURE WILL CONTINUE TO BUILD INTO THE MID-ATLANTIC/CAROLINAS 
FROM DURING THE DAY FRI...AND IS PROGGED TO BE CENTERED NEAR THE 
MID-ATLANTIC COAST BY 12Z SAT. UNIFORM/FLAT FLOW ALOFT IS EXPECTED 
OVER THE CAROLINAS FRI THROUGH FRI NIGHT. WITH THE ABOVE IN MIND... 
EXPECT SUNNY SKIES DURING THE DAY FRI. 1000-850 MB THICKNESSES ARE 
PROGGED TO RANGE FROM 1335-1345 METERS N-S ON FRIDAY...SUGGESTING 
HIGHS RANGING FROM 59-65F OR SO...WARMEST NEAR THE SC BORDER. A LOW 
PRESSURE SYSTEM IS EXPECTED TO BEGIN DEVELOPING IN VICINITY OF THE 
TX GULF COAST LATE FRI NIGHT AS SHORTWAVE ENERGY CURRENTLY 
PROGRESSING SOUTH THROUGH CA/NV AMPLIFIES INTO A CLOSED UPPER LOW 
AND STARTS TRACKING EAST TOWARD WESTERN TX. IT IS POSSIBLE THAT SOME 
UPPER LEVEL CLOUD COVER COULD MOVE INTO THE CAROLINAS DOWNSTREAM OF 
PRECIPITATION EXPECTED ALONG THE GULF COAST STATES LATE FRI NIGHT... 
HOWEVER...THE LATEST MODEL GUIDANCE INDICATES THAT MOST OF THE 
INCREASE IN MID/UPPER LEVEL CLOUD COVER SHOULD HOLD OFF UNTIL AFTER 
SUNRISE SAT (WHEN PRECIP IS EXPECTED TO BLOSSOM OVER THE DEEP 
SOUTH)...WITH MINIMAL IMPACT ON LOW TEMPS. WILL FCST LOWS RANGING 
FROM THE LOWER/MID 30S TO UPPER 30S SAT MORNING...COLDEST IN THE 
TYPICAL SHELTERED/LOW-LYING AREAS...PARTICULARLY IN EAST/NE PORTIONS 
OF THE AREA.

SATURDAY THROUGH SUNDAY NIGHT:
SIGNIFICANT UNCERTAINTY PERSISTS W/REGARD TO THE EVOLUTION OF THE 
AFOREMENTIONED STORM SYSTEM AS IT TRACKS FROM THE TX GULF COAST 
THROUGH THE DEEP SOUTH AND INTO THE CAROLINAS/MID-ATLANTIC THIS 
WEEKEND. THE OPERATIONAL MODELS ARE HAVING A VERY DIFFICULT TIME 
DETERMINING HOW MUCH (IF ANY) PHASING WILL OCCUR BETWEEN THE 
SHORTWAVE ENERGY EJECTING EASTWARD FROM TX INTO THE DEEP SOUTH 
SAT/SAT NIGHT AND NORTHERN STREAM SHORTWAVE ENERGY DIVING SOUTHEAST 
FROM WESTERN CANADA THROUGH THE UPPER MIDWEST/GREAT LAKES INTO THE 
TN/OH VALLEYS. EXACTLY HOW THE NORTHERN/SOUTHERN STREAM SHORTWAVE 
ENERGY INTERACTS WILL IN LARGE PART DETERMINE THE SUBSEQUENT 
EVOLUTION OF THE LOW PRESSURE SYSTEM OVER AND OFFSHORE THE CAROLINAS 
THIS WEEKEND. AT THIS TIME...THE ECMWF IS STILL THE PREFERRED MODEL 
OF CHOICE GIVEN ITS CONSISTENCY AND BETTER TRACK RECORD...ALTHOUGH 
CONSIDERABLE UNCERTAINTY PERSISTS EVEN WITH THE ECMWF DUE TO THE 
COMPLEX NATURE OF THE UPPER LEVEL PATTERN AND THAT SOME OF THE KEY 
FEATURES WILL NOT BE SAMPLED WELL BY THE RAOB NETWORK UNTIL LATER 
THIS WEEK. WITH THE ABOVE IN MIND...ASIDE FROM INTRODUCING PRECIP 
CHANCES FROM SW-NE SATURDAY AFTERNOON (A BIT EARLIER THAN PREVIOUSLY 
INDICATED)...WILL MAKE FEW CHANGES TO THE CURRENT FORECAST FOR 
SATURDAY THROUGH SUNDAY NIGHT.

MONDAY THROUGH WEDNESDAY:
THERE IS REASONABLE AGREEMENT AMONG THE LONG TERM MODELS THAT DRY 
HIGH PRESSURE WILL BUILD INTO THE CAROLINAS IN THE WAKE OF THE LOW 
PRESSURE SYSTEM DEPARTING THE CAROLINA COAST SUN/SUN NIGHT...AND AT 
THIS TIME EXPECT DRY CONDITIONS WITH SUNNY SKIES AND HIGHS NEAR 
NORMAL IN THE LOWER/MID 50S...WITH LOWS MON NIGHT IN THE LOWER 30S. 
UNCERTAINTY GROWS AGAIN BY MID-WEEK IN ADVANCE OF THE NEXT SYSTEM 
EXPECTED TO APPROACH THE AREA FROM THE WEST LATE TUE NIGHT INTO WED. 
AT THIS TIME...WILL KEEP THE FCST DRY ON TUE WITH HIGH PRESSURE 
SLOWLY SHIFTING OFFSHORE THE CAROLINAS. A WARM/MOIST SOUTHERLY 
RETURN FLOW IS PROGGED TO DEVELOP BY TUE NIGHT/WED AS HIGH PRESSURE 
MOVES OFFSHORE IN ADVANCE OF THE NEXT SYSTEM PROGGED TO APPROACH THE 
AREA BY MID-WEEK...AND WILL INTRODUCE A 30% CHANCE FOR SHOWERS ON 
WED. -VINCENT 

.AVIATION /06Z THURSDAY THROUGH SUNDAY/...
AS OF 100 AM THURSDAY...

CURRENT VFR CONDITIONS ACROSS CENTRAL NC WILL DETERIORATE FROM WEST 
TO EAST BY MIDDAY AS RAIN SPREADS EAST ACROSS THE AREA.  THE 
RAIN...AND ASSOCIATED LOW CEILINGS...APPEAR TO BE APPROACHING AS 
MUCH AS 2 TO 3 HOURS FASTER THAN IN PREVIOUS FORECASTS.  THERE 
REMAINS SOME UNCERTAINTY AS TO HOW HEAVY THE RAIN WILL BE EAST OF 
THE MOUNTAINS...BUT THERE IS STILL GOOD CONFIDENCE THAT CEILINGS 
WILL FALL TO IFR BY 15Z AT KGSO/KINT...AND BY 18Z TO 20Z AT 
KRDU/KFAY/KRWI.  WHERE RAIN IS HEAVIER...LIFR CEILINGS AND IFR VSBYS 
WILL BE POSSIBLE.  SOUTHEASTERLY SURFACE WINDS ARE NOT EXPECTED TO 
BE VERY STRONG OR GUSTY...BUT IF ANY GUSTS DO DEVELOP IT WOULD BE 
MORE LIKELY AT KFAY AS A WARM FRONT LIFTS INTO EASTERN.  WINDS WILL 
THEN TURN TO WEST-NORTHWESTERLY AFTER 00Z AS DRIER AIR FILTERS INTO 
THE AREA AND SKIES BEGIN TO CLEAR.  SOME FOG MAY BE POSSIBLE AFTER 
06Z FRIDAY.

OUTLOOK...
THE FOG IS EXPECTED TO LIFT EARLY FRIDAY...WITH VFR 
CONDITIONS RETURNING BY 15Z FRIDAY MORNING. THERE IS AN INCREASING 
CHANCE OF WIDESPREAD RAIN WITH IFR CIGS/VSBYS AS ANOTHER SYSTEM 
APPROACHES OUR REGION THIS WEEKEND.

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