Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 010915 AFDJKL AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE JACKSON KY 515 AM EDT WED JUL 1 2015 .SHORT TERM...(TODAY THROUGH THURSDAY) ISSUED AT 417 AM EDT WED JUL 1 2015 A WET PERIOD WILL BE IN STORE. WE WILL START OFF THIS MORNING WITH A LARGE LONGWAVE TROUGH CONTINUING ACROSS THE REGION. THE SHORTWAVE WHICH SPARKED RAIN AND STORMS YESTERDAY WILL BEGIN SHIFTING NORTHEAST AND OUT OF THE REGION WHILE ANOTHER SMALLER SHORTWAVE BEGINS TO TAKE FORM UPSTREAM OF EASTERN KY. THE GFS...NAM...AND ECMWF ARE ALL IN GOOD AGREEMENT THAT AN MCS WILL FROM AS A RESULT OF THIS SHORTWAVE...SETTLING ACROSS MISSOURI BY 12Z THIS MORNING. WITH NW FLOW STILL IN PLACE...EXPECT SOME OF THE MOISTURE FROM THIS SYSTEM TO ADVECT INTO KY...IN CONJUNCTION WITH ANY LEFT OVER MOISTURE FROM YESTERDAY/S SYSTEM. AS WE BEGIN HEATING THROUGH THE DAY...THIS MOISTURE WILL BEGIN RISING AND SCT SHOWERS AND THUNDERSTORMS TO START DEVELOPING ACROSS THE REGION. WHILE A WEAK FRONTAL BOUNDARY WILL BE POSITIONED ALONG THE OHIO RIVER VALLEY...IT SEEMS AS THOUGH THE WARMEST AND MOST UNSTABLE AIR WILL PROVOKE THE BEST STORM POTENTIAL ACROSS THE SOUTHERN CWA...CLOSER TO THE TN BORDER. ACCORDING TO SOUNDINGS IN THIS AREA...THE LAST TWO RUNS OF THE NAM12 MODEL HAVE BEEN IN GOOD AGREEMENT WITH SHOWING CAPE VALUES TOPPING OUT NEAR 4000 J/KG BETWEEN 18 AND 21Z...A STRONG FAT CAPE...AND DRYING ALOFT WHICH MAY PROMOTE SOME DECENT HAIL POTENTIAL. LI/S WILL EVEN BE TOPPING OUT AROUND -9 AT KSME AND KLOZ...SUPPORTING THE IDEA FOR UNSTABLE CONDITIONS CONDUCIVE TO STRONG THUNDERSTORM DEVELOPMENT. THAT BEING SAID...AS YOU HEAD FARTHER NORTH...INSTABILITY AND WIND SHEAR DROPS SIGNIFICANTLY AS YOU LOSE INFLUENCE FROM THE UPSTREAM MCS. THIS CORRELATES WELL TO THE MRG AND SLIGHT RISK AREAS OF THE SPC DAY 1 CONVECTIVE OUTLOOK. BY THIS EVENING...IT ALMOST APPEARS AS THOUGH THE MODELS ARE TRYING TO PULL SOME OF THE OUTFLOW MOISTURE FROM THE DIMINISHING MCS EASTWARD ACROSS CENTRAL AND EASTERN KY...SPAWNING ADDITIONAL SHOWERS AND THUNDERSTORMS ACROSS THE REGION AS IT MOVES EASTWARD. HOWEVER...THIS IS ALSO WHERE WE START TO GET INTO SOME DIFFERENCES BETWEEN THE MODELS AS WELL. THE ECMWF SOLUTION IS ALMOST CREATING TWO MCS/S. THE FIRST OF WHICH WAS MENTIONED ABOVE...QUICKLY WASHING OUT AS IT SHIFTS EASTWARD ACROSS KY...THEN A SECONDARY MCS DEVELOPING IN IT/S PLACE LATE TONIGHT. THIS SOLUTION SEEMS UNLIKELY...AS THE EXITING SHORTWAVE SEEMS TO TAKE AN UNREALISTIC STRAIGHT EASTERLY PATH...AND THE NEW MCS REDEVELOPS TOO FAST. WOULD LEAN MORE TOWARDS THE GFS AND NAM FOR THE OVERNIGHT PERIOD...WHICH SHOW A GRADUAL INTENSIFICATION OF THE MCS OVER MISSOURI...AND ALSO PEG SLIGHTLY LOWER QPF COMPARED TO THAT OF THE ECMWF ACROSS THE JKL CWA. BY THURSDAY...THE MCS WILL FOLLOW THE SHORTWAVE AND ROUND THE LONGWAVE TROUGH AXIS. IN THIS SCENARIO...WOULD TEND THE LEAN TOWARDS THE ECMWF AND THE NAM 12...SINCE THE GFS SEEMS TO BE PULLING THE TROUGH AXIS MUCH FURTHER SOUTHWARD...AND THEREBY PRODUCING A STRONGER SYSTEM...COMPLETE WITH A DEVELOPING SURFACE LOW TRACKING UP THE OHIO RIVER. THIS PEGS THE HIGHEST QPF ACROSS THE NORTHERN CWA AND ALONG AND NORTH OF THE OHIO RIVER VALLEY...WHICH IS OUT OF AGREEMENT WITH EVERY OTHER MODEL...AND WAS HIGHLIGHTED BY THE WPC MODEL DIAGNOSTIC DISCUSSION AS BEING UNREALISTIC. INSTEAD...EXPECT THE BEST MOISTURE TO RIDE ALONG THE TROUGH AXIS WITH BEST INSTABILITY AND QPF THEREFORE LOCATED ACROSS OUR SOUTHERN CWA AND IN THE TN VALLEY. CONCERNING THE AMOUNT OF MOISTURE...PWATS IN THE 1.75 TO 2.00 INCH RANGE ARE POSSIBLE THROUGH THE DAY THURSDAY...WITH WPC PEGGING AROUND AN INCH OF PRECIP OVER A 6 HOUR PERIOD DURING THE DAY NEAR THE TN BORDER. SOME OF THE HEAVIER STORMS/SHOWERS MAY PRODUCE LOCALLY HIGHER AMOUNTS AS WELL. THIS MAY CREATE SOME PROBLEMS AS WE HEAD INTO THURSDAY NIGHT AND THE HEART OF THE MCS TRAVELS ACROSS EASTERN KY AND BRINGS WIDESPREAD HEAVY RAINFALL. EXPECT FLASH FLOODING TO BE A CONCERN...ESPECIALLY HEADING INTO THE BEGINNING OF THE EXTENDED PERIOD WHEN PWATS ARE EXPECTED TO TOP OUT BETWEEN 2.1 AND 2.25 INCHES ACROSS THE SOUTHERN CWA. AFTER SOME DISCUSSION WITH MRX ABOUT WHETHER OR NOT TO GO AHEAD AND ISSUE A FLASH FLOOD WATCH...ULTIMATELY DECIDED TO HOLD OFF UNTIL DURING THE DAY TOMORROW. THE PRIMARY REASON BEING THAT THE MODELS ARE STILL SHOWING SOME DISAGREEMENT AND EACH ONE HAS SOME UNREALISTIC SCENARIOS...NOT TO MENTION THIS LATEST RUNS OF THE ECMWF SHOWED SOME INCONSISTENCIES COMPARED TO THE PREVIOUS RUN. WOULD HOPE THAT IN THE NEXT ONE TO TWO RUNS...AS THE MCS GETS GOING TODAY...THE MODELS WILL START TO GET A BETTER HANDLE ON THE UPCOMING SITUATION...AS WELL AS HOW FAR NORTH INTO OUR CWA FLASH FLOODING MIGHT BE OF CONCERN. .LONG TERM...(THURSDAY NIGHT THROUGH TUESDAY) ISSUED AT 515 AM EDT WED JUL 1 2015 SEEING MORE SIGNIFICANT DIFFERENCES IN THE DETERMINISTIC ECMWF AND GFS THROUGH THE EXTENDED. OVERALL UPPER LEVEL PATTERN BECOMES LESS AMPLIFIED THROUGH THE PERIOD. GFS IS MORE AMPLIFIED... STRONGER WITH SHORT WAVE ENERGY DROPPING INTO THE MID-MISSISSIPPI AND OHIO VALLEY AT THE START OF THE EXTENDED...FRI INTO SAT. NATIONAL GUIDANCE SUGGEST THE OPERATIONAL GFS IS TOO STRONG WITH THIS SYSTEM CONSIDERING UPSTREAM ENERGY AND ITS INFLUENCE ON EVOLUTION OF THE WAVE THROUGH THE OHIO VALLEY. A BLEND OF SOLUTIONS/GUIDANCE APPEARS TO BE THE BEST APPROACH FOR THE EXTENDED PORTION OF THE FORECAST...PERHAPS WITH A NUDGE TOWARDS THE DETERMINISTIC ECMWF. SENSIBLE WEATHER STILL LOOKS UNSETTLED WITH AT LEAST A CHANCE OF RAIN EACH DAY. BAROCLINC...OR FRONTAL ZONE APPEARS TO STALL OUT ACROSS THE REGION. MODELS ARE SHOWING SUBTLE DIFFERENCES IN THE EXACT LOCATION OF THIS ZONE OF UNSETTLED WEATHER. MOST LIKELY LOCATION APPEARS TO BE SOUTH OF THE OHIO RIVER BUT NORTH OF THE TENN VALLEY. THE WEATHER WILL BE QUITE ACTIVE WITHIN THIS SECTOR WHICH INCLUDES THE COMMONWEALTH. CONSIDERING THE RECENT RAINFALL WE HAVE EXPERIENCED OVER THE LAST FEW DAYS...HYDRO ISSUES COULD BECOME A CONCERN AS MULTIPLE DISTURBANCES TRACK THROUGH THE AREA. TEMPERATURES WILL PROBABLY TREND A BIT CLOSER TO NORMAL THROUGH THE PERIOD...ESPECIALLY TOWARDS THE END OF THE FORECAST WINDOW. && .AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT) ISSUED AT 200 AM EDT WED JUL 1 2015 SHOWERS CONTINUE TO DIMINISH ACROSS THE REGION OVERNIGHT WITH LOSS OF HEAT INDUCED INSTABILITY. HOWEVER...A LARGE AMOUNT OF MOISTURE HAS BEEN LEFT OVER ACROSS MUCH OF EASTERN KY...ESPECIALLY IN AREAS THAT RECEIVED RAINFALL THIS EVENING. AS TEMPERATURES CONTINUE TO COOL OVERNIGHT...FOG WILL CONTINUE TO FORM AND THICKEN. SEVERAL TAF SITES ARE ALREADY REPORTING FOG...AND IF THEY CONTINUE TO DROP IN VISIBILITY SOME MAY ACTUALLY GO BELOW AIRPORT MINS FOR A PERIOD BY LATE TONIGHT/EARLY MORNING. THAT BEING SAID...SOME TAF SITES MAY CONTINUE TO FLUCTUATE BETWEEN CATEGORIES DEPENDING ON THE VARYING DEGREE OF THE FOG OVERNIGHT. AS THE FOG BURNS OFF IN THE MORNING...IT WILL BE REPLACED BY A RENEWED CHANCE OF SHOWERS AND THUNDERSTORMS...ESPECIALLY IN THE AFTERNOON AND EVENING. TRIED TO GEAR TAFS TOWARD THIS IDEA...BUT ACTUAL VIS AND CIGS WILL VARY THROUGHOUT THE DAY AS STORMS DEVELOP AND PASS NEARBY...OR EVEN OVER THE TAF SITE. A HEAVIER AREA OF RAIN WILL MOVE IN LATE IN THE EVENING...WITH ALL TAF SITES EXPECTED TO BE AFFECTED. THE EXACT IMPACTS ARE STILL UNCERTAIN...BUT TRENDED TOWARDS MVFR CIGS AND MVFR/HIGH END IFR VIS AT THIS TIME. && .JKL WATCHES/WARNINGS/ADVISORIES...NONE. && $$ SHORT TERM...JMW LONG TERM...RAY AVIATION...JMW

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