Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS62 KRAH 230327 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1027 PM EST MON DEC 22 2014 .SYNOPSIS...A COLD AIR DAMMING RIDGE WILL REMAIN LOCKED IN PLACE EAST OF THE APPALACHIANS THROUGH TUESDAY. A WARM FRONT WILL LIFT NORTHWARD THROUGH THE REGION LATE TUESDAY NIGHT AND WEDNESDAY AS A DEVELOPING LOW PRESSURE SYSTEM STRENGTHENS WEST OF THE MOUNTAINS. && .NEAR TERM /THROUGH TUESDAY/... AS OF 1025 PM MONDAY... TONIGHT: WV SATELLITE AND UPPER AIR DATA THIS EVENING REVEAL A STRONGLY DIGGING/AMPLIFYING TROUGH OVER THE EASTERN ROCKIES...WITH PERTURBED SOUTHWESTERLY FLOW EAST OF THE TROUGH AXIS FROM THE EAST PACIFIC TO THE EASTERN US COAST. ONE SUCH PERTURBATION AND ASSOCIATED AREA OF SHOWERS FROM NE GA AND THE SC UPSTATE WILL TRACK NE ACROSS THE WESTERN PIEDMONT TONIGHT...AND IN CONJUNCTION WITH A STRONG 925 MB FRONTAL ZONE OVER THE PIEDMONT CHARACTERIZED BY A 13 C TEMP DIFFERENTIAL BETWEEN GSO AND MHX PER 00Z RAOB DATA...WILL SUPPORT PERIODS OF RAIN OVER THE WESTERN PIEDMONT. UPSTREAM HOURLY RAINFALL AMOUNTS SUPPORT THE LATEST RAP AND HRRR QPF OF AROUND A TENTH TO TWO TENTHS OF ADDITIONAL RAIN...VERSUS LIGHTER AMOUNTS NOTED BY THE EC/GFS/NAM. OTHERWISE AND ELSEWHERE...PERIODS OF NORTHERLY 5-10 MPH WIND-BLOWN DRIZZLE...AND A CHANCE OF MEASURABLE RAIN...WILL PREVAIL. A SATURATED AND NEAR-FULLY WET-BULBED LOWEST SEVERAL THOUSAND FT...OWING TO CAD FROM A PARENT 1032 MB SURFACE HIGH NEAR NOVA SCOTIA...WILL SUPPORT LITTLE VARIATION IN TEMPERATURES FROM THEIR 10 PM READINGS IN THE MIDDLE 30S TO AROUND 40 DEGREES. -MWS AS OF 300 PM MONDAY... TUESDAY...NO MECHANISM NOTED TO SCOUR OUT THE CAD AIR MASS SO EXPECT A CONTINUATION OF THE EXTENSIVE OVERCAST WITH PATCHES OF LIGHT RAIN/DRIZZLE. EXPECT TO SEE A NOTEWORTHY INCREASE IN RAIN COVERAGE AND INTENSITY LATE IN THE DAY AS S/W (NOW CROSSING CENTRAL TX) ADVANCES EAST TOWARD OUR REGION. THIS FEATURE WILL INCREASE DIVERGENCE ALOFT AS WELL AS INCREASE ISENTROPIC UPGLIDE IN THE LOWER LAYERS OF THE ATMOSPHERE. THESE FACTORS IN COMBINATION WITH PRECIP WATER VALUES WELL ABOVE NORMAL SHOULD RESULT IN AREAS OF MODERATE- BRIEFLY HEAVY RAINFALL LATE IN THE DAY OR EARLY EVENING ACROSS THE WESTERN PIEDMONT. DAYTIME TEMPS WILL REMAIN WELL BELOW NORMAL. USED THE HIGH RES WRF- ARW FOR HOURLY TEMPS AS GFS-BASED GUIDANCE APPEARS TO BE ERODING THE CAD (AND ITS LINGERING EFFECTS) TOO QUICKLY. TEMPS BY LATE AFTERNOON SHOULD VARY FROM THE UPPER 30S/LOWER 40S OVER THE PIEDMONT TO NEAR 50 OVER THE FAR SE. && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... AS OF 300 PM MONDAY... A POWERFUL 175KT PACIFIC JET DIGGING THROUGH THE WESTERN US WILL HELP TO CARVE OUT A HIGH AMPLITUDE TROUGH OVER THE CENTRAL US...WITH AN EMBEDDED SOUTHERN STREAM CLOSED LOW. AN ALMOST EQUALLY POWERFUL JET WILL EVOLVE OVER THE EASTERN US ON THE LEADING SIDE OF THE UPPER TROUGH WHICH WILL BE THE IMPETUS FOR A WET AND UNSETTLED PERIOD TUESDAY NIGHT THROUGH CHRISTMAS EVE AS THE UPPER TROUGH AND ATTENDANT COLD FRONT MOVES SLOWLY EAST-NORTHEASTWARD THROUGH THE REGION EARLY CHRISTMAS DAY. IN ADVANCE OF THE HIGH AMPLITUDE LONGWAVE TROUGH AND ATTENDANT SFC COLD FRONT...DEEP INFLUX OF PACIFIC MOISTURE...SUPPLEMENTED WITH A LOW-LEVEL CARIBBEAN FEED...WILL ADVECT ANOMALOUSLY HIGH PWATS OF 1.5- 1.7" INTO THE AREA TUESDAY NIGHT-WEDNESDAY(WITHIN THE 99TH PERCENTILE WITH THE HIGHEST OBSERVED DEC PWAT DATING BACK TO 1948 IS 1.59"-12/21/1991). THIS STRONG MOISTURE FLUX CONVERGENCE ALONG THE NORTHWARD RETREATING WARM FRONT...AND ENHANCED LOCALLY OVER THE MORE STEEPLY SLOPED PORTION OF THE LINGERING COLD DOME WILL RESULT IN A WIDESPREAD SOAKING RAIN OF 1-2"...HEAVY AT TIMES TUESDAY NIGHT AND INTO CHRISTMAS EVE MORNING. ONCE THE WARM FRONT LIFTS NORTHWARD INTO THE VIRGINIA...THERE WILL LIKELY BE A LULL IN PRECIP DURING THE DAY WITH BREEZY CONDITIONS DEVELOPING IN THE WARM SECTOR. THEN BY LATE AFTERNOON AND INTO THE EVENING(BETWEEN 00Z-06Z THURSDAY)....THE EAST-WEST PASSAGE OF THE COLD FRONT AND ACCOMPANYING BAND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS WILL BRING ONE LAST ROUND OF RAIN INTO THE AREA. SEVERE POTENTIAL: EVALUATING SEVERE POTENTIAL IN A LOW CAPE-HIGH SHEAR ENVIRONMENT IS ALWAYS A CHALLENGE...EVEN AT CLOSER TIME SCALES OF 6-12 HOURS. THE LULL IN PRECIP DURING MUCH OF THE DAYTIME HOURS...MAY ALLOW FOR SOME MODEST HEATING...ESPECIALLY FROM THE US 1 CORRIDOR EASTWARD...WHICH COULD LEAD TO BETTER DESTABILIZATION THAN WHAT MODELS CURRENTLY SHOW(100-200J/KG MUCAPE). GIVEN STRONG SHEAR ALONE...CANNOT RULE OUT AN ISOLATED SEVERE...BUT WEAK LAPSE RATES ALOFT OF 5.0-5.5 C/KM ALONG WITH THE MAIN DYNAMICS PASSING OVER THE GREAT LAKES WILL LIMIT A MORE ROBUST SEVERE THREAT. ADDITIONALLY... IF WE SEE WIDESPREAD RAINFALL AMOUNTS NEAR THE HIGHER SIDE OF THE EXPECTED QPF OF 2.0"...MINOR FLOODING WILL BE POSSIBLE ACROSS PORTIONS OF THE NEUSE AND TAR. SEE HYDROLOGICAL DISCUSSION BELOW FOR ADDITIONAL DETAILS. TEMPERATURES VERY CHALLENGING WITH HIGH BUST POTENTIAL...DEPENDENT ON EVOLUTION/TIMING/LOCATION OF THE RETREATING WEDGE FRONT INTO THE CLIMATOLOGICALLY FAVORED AREA ACROSS THE FAR NW PIEDMONT TUESDAY NIGHT AND INTO THE DAY ON WEDNESDAY. SUCH A STRONG CAD EVENT WOULD STRONGLY SUGGEST FAVORING THE COOLER NAM/MET GUIDANCE THROUGH EARLY WEDNESDAY WITH THE WELL KNOWN MODEL BIAS OF ERODING THE CAD TOO QUICKLY. LOWS TUESDAY NIGHT WILL LIKELY OCCUR EARLY IN THE NIGHT WITH RISING TEMPERATURES THEREAFTER IN ALL BUT THE FAR NW PIEDMONT THROUGH DAYBREAK. A LARGE RANGE IN TEMPERATURES ARE EXPECTED ON WEDNESDAY WITH THE POTENTIAL FOR THE SHALLOW WEDGE AIRMASS TO HOLD ON ACROSS THE EXTREME NW CORNER...KEEPING TEMPS IN THE 50S. THE REMAINDER OF THE FORECASTER AREA WILL BE IN THE WARM SECTOR WITH HIGHS IN THE UPPER 60S ACROSS THE CENTRAL PIEDMONT...AND LOWER 70S ACROSS THE SANDHILLS AND COASTAL PLAIN. CLEARING AND COOLING WEDNESDAY NIGHT IN THE WAKE OF THE COLD FRONT LOOKS A BIT DELAYED THAN WHAT MODELS WERE SHOWING A DAY OR TWO AGO. NOT AS COOL AS WE ORIGINALLY THOUGHT. LOWS IN THE MID TO UPPER 40S NW TO MID 50S SE. && .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 300 PM MONDAY... DEEPENING SURFACE LOW LIFTING NEWD INTO SE CANADA WILL RESULT IN BREEZY CONDITIONS ON CHRISTMAS DAY. OTHERWISE DRY WITH SEASONABLY MILD TEMPERATURES CONTINUING INTO FRIDAY AS HIGH PRESSURE BUILDS IN FROM THE NORTHERN GULF. MODEL SPREAD BEGINS TO INCREASE DRAMATICALLY LATE FRIDAY THROUGH THE WEEKEND...WITH THE EC MUCH DEEPER WITH THE NEXT MID/UPPER LEVEL TROUGH...RESULTING IN YET ANOTHER WET AND UNSETTLED PERIOD LATE AS IT TRACKS AN AREA OF LOW PRESSURE ACROSS THE SOUTHERN/CENTRAL APPALACHIANS LATE SATURDAY AND INTO SUNDAY. THE GFS REMAINS MUCH FLATTER WITH THE UPPER TROUGH...PRODUCING LITTLE TO NO PRECIP OVER THE CAROLINAS. WILL INDICATE SLIGHT CHANCE POPS UNTIL BETTER AGREEMENT IS REACHED. COOLER TO SLIGHTLY BELOW NORMAL TEMPERATURES ARE EXPECTED BEHIND THE FRONT EARLY NEXT WEEK. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... AS OF 715 PM MONDAY... AVIATION CONDITIONS WILL REMAIN POOR WELL ON THROUGH TONIGHT AND TUESDAY...WITH PERIODS OF RAIN/DRIZZLE AND A LIGHT NORTHEASTERLY WIND ALONG WITH THE ALREADY LOW CLOUDS AND LIMITED VSBYS. THERE IS HIGH CONFIDENCE OF LIFR CONDITIONS THROUGH THE NIGHT AND THERE MAY ALSO BE SOME VLIFR CONDITIONS RESULTING FROM FOG BETWEEN 06Z AND 12Z. THERE WILL BE NO CHANGE IN THE AIRMASS OVER NC ON TUESDAY...SO ONLY MINIMAL IMPROVEMENT IN CONDITIONS IS EXPECTED. CEILINGS MAY LIFT A LITTLE DURING THE AFTERNOON ALLOWING IFR CONDITIONS TO DEVELOP...BUT CONFIDENCE IN THIS IS LOW GIVEN HOW LITTLE CONDITIONS CHANGED EARLIER TODAY. PERIODS OF LIGHT RAIN AND DRIZZLE WILL CONTINUE. OUTLOOK... AN UPPER LEVEL TROUGH AND ASSOCIATED COLD FRONT WILL APPROACH THE REGION TUESDAY NIGHT AND WEDNESDAY...LEADING TO AN INCREASED CHANCE OF SHOWERS...ALONG WITH GUSTY WINDS AND A FEW ISOLATED THUNDERSTORMS (MAINLY OVER EASTERN NC). THUS...AVIATION CONDITIONS WILL REMAIN POOR THROUGH AT LEAST WEDNESDAY....BEFORE A COLD FRONT CROSSES THE AREA LATE WEDNESDAY NIGHT AND EARLY THURSDAY. BEHIND THE FRONT...BLUSTERY WESTERLY WINDS WILL OCCUR CHRISTMAS DAY WITH GUSTS 30-35KTS POSSIBLE. OTHERWISE VFR CONDITIONS EXPECTED TO RETURN CHRISTMAS DAY AND PERSIST THROUGH SATURDAY. && .HYDROLOGY... AS OF 230 PM MONDAY... ANTECEDENT RAINFALL OVER THE PAST 24 HOURS RANGED FROM A MINIMA OF ABOUT A TENTH OF AN INCH IN THE NORTHWEST PIEDMONT (THE UPPER YADKIN/PEE DEE AND UPPER HAW RIVER BASINS) TO A STRIPE OF 1 INCH PLUS ACROSS THE SOUTHEAST (THE CENTRAL NEUSE AND CENTRAL CAPE FEAR BASINS). WILL SEE ONLY MINOR RISES ON THE MAINSTEM RIVERS IN RESPONSE...BUT THIS IS THE 3RD FAIRLY SIGNIFICANT RAINFALL EVENT (>0.5 INCHES) OVER THE AREA SINCE 12/10. RELATIVE SOIL MOISTURE PERCENTAGES IN THE 0-200 CM COLUMN HAVE BEEN INCREASING...WITH HIGHER PERCENTILES NEARER THE SURFACE...SO QUICKER RUNOFF IS EXPECTED FROM OUR UPCOMING RAIN EVENT. CURRENT QUANTITATIVE PRECIP FORECASTS FROM THE GEFS AND NAEFS ENSEMBLES ARE IN LOCKSTEP AGREEMENT AT PRESENT...WITH HEAVIEST RAIN (~1.3-1.5 INCHES) FROM TOMORROW NIGHT THROUGH CHRISTMAS MORNING. RAINFALL AMOUNTS IN THIS RANGE COULD POTENTIALLY CAUSE SOME MINOR FLOODING ON THE NEUSE RIVER AND TAR RIVER LATE ON CHRISTMAS DAY...BUT IT WOULD BE LOW IMPACT WITH THOSE RIVERS BARELY REACHING MINOR FLOOD STAGE. THE UPSHOT...RIVER FLOODING WILL ONLY BE AN ISSUE IF RAINFALL FORECASTS BEGIN TRENDING HIGHER...INTO THE 2 INCH PLUS RANGE. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...MWS/WSS SHORT TERM...CBL LONG TERM...CBL AVIATION...BLS HYDROLOGY...MLM

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.