Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 140705 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 305 AM EDT MON APR 14 2014 .SYNOPSIS...
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WARM AND DRY HIGH PRESSURE CENTERED OVER THE WESTERN ATLANTIC WILL EXTEND WESTWARD OVER OUR REGION THIS MORNING. A COLD FRONT WILL SLOWLY APPROACH THE REGION FROM THE WEST ON TODAY...THEN MOVE EAST ACROSS NORTH CAROLINA AND VIRGINIA LATE TONIGHT THROUGH TUESDAY. COOL HIGH PRESSURE WILL EXTEND INTO THE AREA FROM THE NORTH WEDNESDAY THROUGH THURSDAY.
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&& .NEAR TERM /THROUGH TUESDAY NIGHT/...
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AS OF 150 PM SUNDAY... THERE WILL LIKELY BE SOME PREFRONTAL WARM ADVECTION SHOWERS DURING THE DAY ON MONDAY (ESPECIALLY ACROSS THE WESTERN HALF OF THE FORECAST AREA)...LIKELY AIDED BY ANY WEAK PERTURBATIONS IN THE SOUTHWESTERLY FLOW ALOFT. IN ADDITION...SOME WEAK INSTABILITY (UP TO 500 J/KG) MAY BE ENOUGH TO TRIGGER AN ISOLATED THUNDERSTORM OR TWO MONDAY AFTERNOON. GIVEN THE CLOUD COVER AND POSSIBLE PRECIP...TEMPS ON MONDAY SHOULD BE SLIGHTLY LOWER THAN PREVIOUS DAYS. THEREFORE... AM EXPECTING HIGHS TO RISE INTO THE MID/UPPER 70S ACROSS THE WEST TO AROUND 80 DEGREES FURTHER EAST. A POWERFUL STORM SYSTEM IS ON TRACK TO AFFECT CENTRAL NC TUE WITH THREATS OF HEAVY RAIN AND STRONG STORMS. AFTER THE INITIAL BOUT OF PREFRONTAL SHOWERS EARLY MON NIGHT... THE BULK OF THE RAINFALL WITH THIS SYSTEM IS EXPECTED TO OCCUR LATE MON NIGHT THROUGH EARLY EVENING TUE... WITH CLEARING LATE TUE NIGHT. OVERVIEW FOR MON NIGHT: THE MID LEVEL RIDGE OVER THE SOUTHEAST COAST WILL STRENGTHEN BUT SHIFT OFFSHORE THROUGH MON. THIS MORNING`S UPPER AIR ANALYSES REVEAL TWO TROUGHS OF NOTE -- ONE ENTERING KS/OK/NRN TX AND A STRONGER/DEEPER TROUGH FROM S-CENTRAL CANADA THROUGH MT/ID/WY/UT. THIS REARWARD TROUGH WILL DIG AS IT SHIFTS EASTWARD... KICKING THE SLOWLY DEAMPLIFYING LEAD TROUGH EASTWARD. PASSAGE OF THIS WEAKENING LEAD TROUGH THROUGH THE MIDATLANTIC REGION IN ADDITION TO STEADILY INCREASING MOISTURE ADVECTION SHOULD FACILITATE FORMATION OF SCATTERED TO NUMEROUS SHOWERS HEADING INTO MON NIGHT... WITH THE BEST COVERAGE IN THE WRN CWA WHERE LOW LEVEL FLOW WILL BE ORTHOGONAL TO THE HIGHER TERRAIN THUS INTRODUCING ENHANCED FORCED UPGLIDE THERE... AND IT`S FARTHEST FROM THE INFLUENCES OF THE OFFSHORE-CENTERED RIDGE WITH BETTER LOW LEVEL CONFLUENCE. EXPECT POPS TO RANGE FROM GOOD CHANCE NE TO LIKELY WEST MON NIGHT... WITH STRENGTHENING SURFACE WINDS FROM THE SE AND SOUTH OVERNIGHT. OVERVIEW FOR TUE/TUE NIGHT: THE DEEP TROUGH FROM HUDSON BAY DOWN THROUGH THE GULF COAST WILL SHIFT EASTWARD OVER ERN NOAM THROUGH TUE NIGHT... TRANSITIONING FROM A SLIGHT POSITIVE TILT TO A NEUTRAL OR SLIGHT NEGATIVE TILT BUT DAMPENING IN THE PROCESS DUE TO TROUGHING DEVELOPING OVER CANADA AND THE WRN US. MODELS GENERALLY AGREE ON THE CORRESPONDING SURFACE FRONT REACHING THE FAR NW CWA (TRIAD AREA) BY 17Z-18Z... THEN CROSSING THE CWA BEFORE EXITING THE COASTAL PLAIN JUST PRIOR TO 00Z. A SOUTHERLY 850 MB JET OF 40-50 KTS SHIFTS EAST ACROSS NC TUE MORNING THROUGH AFTERNOON... LEADING TO INCREASING MASS CONVERGENCE OVER CENTRAL/ERN NC. FARTHER ALOFT... THE STRENGTHENING UPPER JET ON THE EAST SIDE OF THE TROUGH RESULTS IN INCREASING UPPER DIVERGENCE OVER NC LATE MON NIGHT THROUGHOUT TUE. GIVEN THIS DEEP LAYER FORCING FOR ASCENT... CATEGORICAL POPS ARE JUSTIFIED AREAWIDE FOR TUE. REGARDING THE HEAVY RAIN CHANCES... POCKETS OF HEAVIER RAIN ARE CERTAINLY POSSIBLE MON NIGHT GIVEN EXPECTATIONS OF INCREASING PW VALUES TO NEAR 200% OF NORMAL... BUT THE GREATEST PW SHOULD ARRIVE TUE WITH MODEL-PROJECTED VALUES WELL OVER 1.5"... WHICH WOULD BE AROUND 250% OF NORMAL. LOW LEVEL MOISTURE TRANSPORT INCREASES OVER THE EAST TUE... MOST MARKEDLY OVER GA/COASTAL SC AND FROM RICHMOND VA UP THROUGH NYC... BUT IS STILL PRONOUNCED OVER CENTRAL AND ESPECIALLY ERN NC IN THE AFTERNOON/EARLY EVENING WITH AN OPEN LONG FETCH FROM THE GULF AND BAHAMAS. WARM RAIN PROCESSES MAY ALSO COME INTO PLAY WITH A SOMEWHAT FAVORABLE WARM LAYER DEPTH OVER 3 KM... AND ANTICIPATED CELL MOVEMENT TOWARD THE NORTH OR NNE MAY LEAD TO TRAINING ECHOES MOVING REPEATEDLY OVER THE SAME AREA. ALL OF THIS SUPPORTS A HEAVY RAIN THREAT... AND WILL CONTINUE TO HIGHLIGHT THIS IN THE HAZARDOUS WEATHER OUTLOOK... WITH A FOCUS ON THE FAR NW AND EASTERN SECTIONS. EXPECT STORM TOTAL AMOUNTS OF JUST OVER AN INCH TO AS MUCH AS TWO INCHES IN ISOLATED SPOTS. AS OF NOW... IT LOOKS LIKE THE ONLY FACTOR THAT MIGHT CURB THIS THREAT WOULD BE IF SUBSTANTIAL CONVECTION TO OUR SOUTH INTERRUPTS MOISTURE TRANSPORT INTO CENTRAL NC. REGARDING THE STRONG/SEVERE STORM THREAT... MODELS INDICATE A COUPLE HUNDRED J/KG OF SBCAPE MON NIGHT... INCREASING TO 500-1000 J/KG FOR TUE... ALTHOUGH FORECAST SOUNDINGS INDICATE THE TUE CAPE IS TALL AND SKINNY WITH MLLR OF 5.5-6.0 C/KM... NOT GREAT FOR INDUCING VERY RAPID UPDRAFTS. 0-6 KM BULK SHEAR STARTS OUT DECENT MON NIGHT AT CLOSE TO 40 KTS AND GETS EVEN BETTER -- 80-90KTS -- TUE AFTERNOON/EARLY EVENING. LATEST SREF PROBABILITIES OF A COMBINATION OF CAPE AOA 500 J/KG AND DEEP LAYER SHEAR AOA 30 KTS WITH PRECIP REMAIN LOW MON NIGHT BUT INCREASE TO NEAR 40% BY EARLY AFTERNOON. THIS ALL SUPPORTS A GOOD CHANCE OF FAST-MOVING BOWING SEGMENTS WITH LOCALLY ENHANCED WIND GUSTS... ESPECIALLY ALONG/EAST OF HIGHWAY 1 TUE FROM VERY LATE MORNING THROUGH THE AFTERNOON HOURS. THIS RISK TOO WILL BE RETAINED IN THE HWO. REGARDING TEMPS: CLOUDS AND STRONG PREFRONTAL WARM AIR ADVECTION WILL LEAD TO VERY MILD LOWS MON NIGHT... AND HAVE WARMED THEM JUST A BIT TO 60-66. TEMPS TUE ARE LIKELY TO FOLLOW AN ATYPICAL TREND... WITH THE FRONTAL PASSAGE CAUSING HIGHS TO OCCUR IN THE EARLY AFTERNOON IN THE WRN CWA WITH A RAPID DROP THEREAFTER... WHILE THE COASTAL PLAIN SHOULD SEE A MORE TYPICAL MAX TEMP TIME IN THE MID- LATE AFTERNOON. EXPECT HIGHS TUE FROM THE MID 60S NW TO THE MID- UPPER 70S IN THE EAST. HAVE KEPT TUE NIGHT LOWS A BIT ON THE WARM SIDE OF GUIDANCE... BUT MODELS HAVE BEEN TRENDING COOLER ESPECIALLY IN THE WRN CWA. IF THIS TREND PERSISTS THROUGH LATER FORECASTS... COULD SEE SOME OUTLYING AREAS OF THE WRN PIEDMONT APPROACHING THE FREEZING MARK TUE NIGHT DESPITE CONTINUED MIXING. LOWS 34-41. -GIH
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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AS OF 245 AM MONDAY... RISING HEIGHTS ALOFT/DNVA AND ASSOCIATED STRONG SUBSIDENCE WILL RESULT IN FURTHER DEEP LAYER DRYING WED...FOLLOWED BY GENERALLY NEUTRAL VERTICAL MOTION BUT WITH STILL A RESIDUALLY DRY AND STRONGLY CAPPED REGIME OVER OUR REGION. SURFACE HIGH PRESSURE WILL CONSEQUENTLY BECOME UNSEASONABLY STRONG - INTO THE 1040-1045 MB RANGE AS IT BUILDS FROM THE OH VALLEY TO NEW ENGLAND. UNSEASONABLY COOL NORTHEASTERLY FLOW...WITH TEMPERATURES 10 TO 20 DEGREES BELOW AVERAGE...WILL RESULT OVER CENTRAL NC. INITIALLY CLEAR SKIES WED WILL BECOME PARTLY CLOUDY...TO PERHAPS MOSTLY SO IN THE COASTAL PLAIN...BY THU AFTERNOON...AS MOISTURE FLAT STRATOCUMULUS IS ADVECTED INLAND BENEATH THE CAP. PROJECTED LOW LEVEL THICKNESS VALUES IN THE 1300-1310 METER RANGE AT 12Z THU AND CLEAR SKIES WOULD SUPPORT SUB-FREEZING TEMPERATURES THU MORNING...BUT CONFIDENCE IS LOW REGARDING THE DEGREE OF CALM GIVEN A PROJECTED 4-6 MB RISE IN MSL PRESSURE WITH THE STRENGTHENING HIGH WED NIGHT. WILL ADJUST LOWS TO REFLECT MOSTLY LOWER TO MIDDLE 30S...COOLEST WEST...BUT THESE MAY NEED FURTHER DOWNWARD ADJUSTMENT (OR AT LEAST OPEN THE RANGE) TO INCLUDE SOME UPPER 20S IF IT INDEED APPEARS ANY PERIOD OF APPRECIABLE CALM WILL BE ATTAINED. SIMILARLY COOL IN THE MIDDLE 50S WED...WHICH MAY THREATEN THE RECORD LOW MAX OF 56 DEGREES AT KFAY FOR THE DATE. SEE CLIMATE SECTION BELOW. SLOW MODERATION TO AROUND 60 AND 40 DEGREES FOR HIGHS AND LOWS... RESPECTIVELY...THU AND THU NIGHT.
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&& .LONG TERM /FRIDAY THROUGH SUNDAY/...
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AS OF 300 AM MONDAY... THOUGH MODEL SOLUTION SPREAD REMAINS ABOVE AVERAGE DURING THE LONG TERM...THE EMERGING SIGNAL FROM THE MAJORITY OF BOTH THE ENSEMBLE AND SOLUTIONS OS FOR A DOMINANT NORTHERN STREAM ACROSS THE NORTHERN THIRD OF THE US...ONE THAT WILL INCLUDE AT LEAST ONE PRIMARY SHORTWAVE TROUGH AND ACCOMPANYING SURFACE CYCLONE FORECAST TO CROSS THE UPPER MIDWEST AND LOWER GREAT LAKES FRI-SAT - A STORM TRACK THAT WOULD RESULT IN A MOSTLY DRY COLD FRONTAL PASSAGE SAT-SAT NIGHT AS DEPICTED BY AT LEAST THE LAST SEVERAL RUNS OF THE GFS. ON THE OTHER HAND...THE LAST COUPLE OF RUNS OF THE OPERATIONAL ECMWF...WHICH HAVE MINIMAL SUPPORT FROM THE EC ENSEMBLE MEAN...SUGGEST MORE IN THE WAY OF SOUTHERN STREAM TROUGHING/ INTERACTION THAT WOULD RESULT IN SOME DEGREE OF COASTAL CYCLOGENESIS AND A WETTER PATTERN FOR AT LEAST THE EASTERN HALF OF NC DURING THE SAME TIME FRAME. IN EITHER SCENARIO...THE BEST CHANCES OF RAIN WOULD BE SAT-SAT NIGHT...SO MENTIONABLE POP WILL BE CONFINED TO THAT TIME UNTIL A CLEARER PICTURE EMERGES.
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&& .AVIATION /00Z MONDAY THROUGH SATURDAY/... AS OF 750 PM SUNDAY... VFR CONDITIONS WILL CONTINUE THIS EVENING INTO PORTIONS OF THE EARLY MORNING HOURS. HOWEVER... LOW LEVEL SOUTHERLY RETURN FLOW ACROSS THE AREA WILL CONTINUE TO MOISTEN THE LOW LEVEL AIRMASS EARLY MONDAY MORNING. WE MAY SEE SOME IFR AND/OR LIFR CIGS DEVELOP AROUND DAYBREAK MONDAY... WITH THE GREATLY PROBABILITY OF OCCURRENCE ACROSS THE WESTERN NORTHWESTERN PIEDMONT (KGSO/KINT). EXPECT ANY LOW STATUS THAT FORMS WILL LIFT BY MID MORNING WITH PERHAPS A BRIEF PERIOD OF SUB-VFR STRATOCUMULUS. VFR CONDITIONS ARE EXPECTED BY LATE MORNING/EARLY AFTERNOON. HOWEVER... A STRONG COLD FRONT WILL APPROACH THE AREA FROM THE WEST ON MONDAY... YIELDING INCREASING CLOUD COVER AND THE THREAT OF SOME AFTERNOON SHOWERS AND ISOLATED STORMS. THE GREATEST THREAT WILL BE ACROSS THE WESTERN PIEDMONT. THUS... HAVE ELECTED TO ADD A PROB 30 GROUP FOR SHOWERS THERE. ANY SHOWERS OR STORMS THAT DEVELOP LATE IN THE DAY WILL HAVE THE POTENTIAL TO PRODUCE SUB-VFR CONDITIONS. IN ADDITION... EXPECT SUSTAINED WINDS WILL INCREASE MONDAY MORNING INTO THE AFTERNOON INTO THE 10 TO 15 MPH RANGE... WITH SOME GUSTS OF UP TO 20 TO 25 MPH POSSIBLE. OUTLOOK...A PROLONGED PERIOD OF WIDESPREAD ADVERSE AVIATION CONDITIONS IS EXPECTED LATE MONDAY THROUGH TUESDAY AS A STRONG COLD FRONT APPROACHES AND CROSSES THE REGION. SHOWERS AND ISOLATED THUNDERSTORMS WILL INCREASE IN COVERAGE MONDAY NIGHT INTO TUESDAY MORNING...WITH THE HIGHEST PRECIP CHANCES (AND ESPECIALLY ISOLATED THUNDERSTORMS) OCCURRING TUESDAY/TUESDAY AFTERNOON. CONDITIONS WILL THEN IMPROVE AGAIN BY MIDWEEK. THEN ANOTHER SYSTEM WILL IMPACT THE AREA LATE FRIDAY INTO SATURDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...MWS NEAR TERM...KRD/GIH SHORT TERM...MWS LONG TERM...MWS AVIATION...BSD/KRD

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