Area Forecast Discussion
Issued by NWS Charleston, WV

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000 FXUS61 KRLX 040707 AFDRLX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON WV 307 AM EDT WED MAY 4 2016 .SYNOPSIS... COLD FRONT CROSSES WEDNESDAY NIGHT. LARGE UPPER LEVEL LOW BRINGS COOL AND UNSETTLED WEATHER FOR THURSDAY THROUGH FRIDAY. WARM FRONT SATURDAY. ANOTHER COLD FRONT SUNDAY. && .NEAR TERM /THROUGH TONIGHT/... WEAK SURFACE HIGH SHIFTS EAST THIS AFTERNOON AND FOR THE MOST PART WINDS WILL BE LIGHT THROUGH THE DAY WITH SOUTHWEST WINDS PICKING UP SLIGHTLY AHEAD OF AN APPROACHING COLD FRONT LATER IN THE AFTERNOON AND EARLY EVENING. DECIDED TO KEEP POP CLOSE TO PREVIOUS FORECAST WITH BULK OF SHOWERS ARRIVING LATE AFTERNOON TO EARLY EVENING WITH THE COLD FRONT AS NAM/GEM/AND MESO MODELS ARE ADVERTISING. UPPER LEVEL LOW DIVING SOUTHWARD WILL BRING COLD TEMPS ALOFT WITH T700 -2 STANDARD DEVIATIONS BELOW NORMAL. INSTABILITY WILL BE WEAK BUT WITH SUCH LOW FREEZING LEVELS...ANY STORMS THAT DEVELOP WILL LIKELY BRING SMALL HAIL OR GRAUPEL THIS AFTERNOON AND EVENING. THIS SYSTEM DOES NOT ADVERTISE HIGH PWATS WITH IT...SO NOT EXPECTING TORRENTIAL RAIN. HOWEVER...WE HAVE TO STILL KEEP A CLOSE EYE ON THE FLASH FLOOD THREAT DUE TO WEAK FLOW ALOFT WITH UPPER A LEVEL SYSTEM. CORFIDI VECTORS...GENERALLY LESS THAN 10KTS COULD MAKE FOR NEARLY STATIONARY SHOWERS/STORMS AND TRAINING WILL BE A REAL POSSIBILITY. OVERALL QPF SHOULD BE FAIRLY LIGHT...BUT LOCALIZED HEAVY RAINFALL WILL BE POSSIBLE WITH SLOW MOVING SHOWERS/STORMS AND THIS COMBINED WITH SATURATED SOILS ALREADY WILL ELEVATE THE THREAT FOR LOCALIZED FLOODING. AT THIS TIME THOUGH CONFIDENCE IS TOO LOW TO ISSUE A FLASH FLOOD WATCH AT ANY ONE LOCATION...BUT THE THREAT IS HIGH ENOUGH THAT IT WARRANTED A SLIGHT RISK IN WPC EXCESSIVE RAINFALL OUTLOOK. TEMPERATURES WILL ALSO CONTINUE ON THE COOL SIDE WITH THE CHILLY PATTERN AS UPPER LOW MOVES OVERHEAD LATE TONIGHT INTO THURSDAY MORNING. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... REALLY DIFFICULT TRYING TO TRACK THE FORCING AS A LATE SEASON CLOSED UPPER LEVEL LOW PINWHEELS TOWARDS THE CAROLINA COAST. COLD FRONT PASSES AT THE NEAR TERM/SHORT TERM BREAK...AND THEN IT APPEARS A NEW AXIS OF DEFORMATION SHOULD FORM ALONG OR NEAR THE MOUNTAINS THURSDAY AND THURSDAY NIGHT. WITH THE UPPER LOW ROTATING BACK TO THE NORTH INTO NEW ENGLAND...POPS WILL BE SLOW TO ERODE OVER THE EASTERN HALF OF THE CWA INTO THE FRIDAY TIME FRAME. FROM A FORECAST STANDPOINT...THE MAIN CHANGE IS THE INCREASE IN THE POPS TO THE LIKELY RANGE. LEANED ON THE NON CONVECTIVE MODELS FOR THIS SET UP...THAT IS...THE GFS AND ECMWF...AND LEAVE THE NAM OUT GIVEN A SOUTHWARD BIAS TO THE UPPER LOW. HAVE THUNDER IN THE FORECAST...AND GIVEN THE COLD POOL ALOFT WITH 500MB TEMPERATURES WELL BELOW -20C...SMALL HAIL COULD OCCUR IN ANY OF THE THUNDERSTORMS...EVEN IF LOW TOPPED ON THURSDAY. THUNDER POTENTIAL SHOULD BE SOMEWHAT DIURNALLY DRIVEN. PRECIPITABLE WATER VALUES SHOULD BE LOWER THAN 0.80 INCHES...SO THAT SHOULD LIMIT THE QPF A BIT. GOING BELOW GUIDANCE NUMBERS FOR MAX TEMPERATURES THURSDAY AS IT SEEMS THE COLD POOL IS BEING UNDERESTIMATED. && .LONG TERM /SATURDAY THROUGH TUESDAY/... USED AN BLEND OF THE OPERATIONAL MODELS AND ENSEMBLE MEANS FOR FRIDAY NIGHT INTO SATURDAY. THIS HAS THE UPPER LOW MOVING OFF TO THE EAST FRIDAY NIGHT. A WARM FRONT THEN PUSHES NORTHWARD THROUGH THE AREA ON SATURDAY...FOLLOWED BY ANOTHER COLD FRONT ON SUNDAY. FOR THE BEGINNING OF THE WORK WEEK...TRANSITIONED TO A BLEND OF THE ECMWF...CANADIAN...AND ECMWF ENSEMBLE MEAN. && .AVIATION /07Z WEDNESDAY THROUGH SUNDAY/... CEILINGS ARE STARTING TO FALL TO MVFR AND IN THE AREAS THAT WERE CLEAR WE ARE STARTING TO SEE SOME FOG DEVELOP. EKN HAS CLEARED OUT AND WITHIN AN HOUR THE VISIBILITY STARTED TO DROP...BELIEVE THAT THIS TREND WILL CONTINUE AND THEY WILL END UP WITH LIFR CONDITIONS THERE WITH FOG. MOST OTHER AREAS MAY SEE VSBY DROP TO MVFR OVERNIGHT ALONG WITH THE MVFR CIGS. IF A SOLID OVERCAST PERSISTS...THIS MAY NOT HAPPEN...BUT THE TREND THUS FAR HAS BEEN SIGHTS WAVERING BETWEEN BROKEN TO OVERCAST SKIES. ANY FOG WILL BURN OFF THIS MORNING AFTER SUNRISE...HOWEVER MVFR MORNING CIGS MAY PERSIST UNTIL LATER THIS AFTERNOON...BUT STILL NOT CERTAIN THAT WILL BE THE CASE AS FRONT APPROACHES LATER TODAY. A COLD FRONT WILL BRING SHOWERS AND THUNDERSTORMS BY LATE AFTERNOON AND EARLY THIS EVENING. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 06Z THURSDAY... FORECAST CONFIDENCE: LOW TO MEDIUM. ALTERNATE SCENARIOS: CIGS WILL TEND TO VARY THROUGH THE MORNING HOURS WITH HOLES IN THE STRATOCU LAYER. MVFR FOG MAY NOT FORM AND ON THE OTHER HAND...HOLES IN THE OVERCAST MAY ALLOW IFR FOG TO FORM. FINALLY...HOW LONG MVFR CEILING LAST INTO THE DAYTIME HOURS IS STILL UNCERTAIN AT THIS TIME. THE TIMING OF SHOWERS AND THUNDERSTORMS ARRIVING FROM THE WEST ON THIS AFTERNOON MAY VARY AS MODELS STILL DIFFER. THUNDERSTORMS MAY BRING IFR CONDITIONS AND CONTAIN SMALL HAIL OR GRAUPEL WEDNESDAY AFTERNOON. EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY OF WFO FORECAST TO AVAILABLE MODEL INFORMATION: H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS. L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. DATE WED 05/04/16 UTC 1HRLY 06 07 08 09 10 11 12 13 14 15 16 17 EDT 1HRLY 02 03 04 05 06 07 08 09 10 11 12 13 CRW CONSISTENCY M M M M M M M M M M M H HTS CONSISTENCY H M M M M M M M H H H H BKW CONSISTENCY L L L L L L L L M M M M EKN CONSISTENCY L L L L L L L M M M M H PKB CONSISTENCY M M M M M M M M M M H H CKB CONSISTENCY M M M M M L L M M M M H AFTER 06Z THURSDAY... IFR POSSIBLE IN THUNDERSTORMS INTO WEDNESDAY EVENING AND AGAIN THURSDAY AFTERNOON. && .RLX WATCHES/WARNINGS/ADVISORIES... WV...NONE. OH...NONE. KY...NONE. VA...NONE. && $$ SYNOPSIS...ARJ/MPK NEAR TERM...MPK SHORT TERM...ARJ LONG TERM...RPY AVIATION...MPK

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