Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 261453 AFDJKL AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE JACKSON KY 1053 AM EDT SAT JUL 26 2014 .UPDATE...
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ISSUED AT 1053 AM EDT SAT JUL 26 2014 THUNDERSTORMS WHICH BLEW UP EARLY THIS MORNING OVER INDIANA CONTINUE TO RACE SOUTHEASTWARD TOWARD OUR NORTHWEST COUNTIES BUT ARE WEAKENING AS THEY ENCOUNTER A MUCH MORE STABLE AIRMASS OVER NORTHERN KENTUCKY. WILL INCREASE POPS A BIT AS FAR SOUTH AS THE MOUNTAIN PARKWAY AS A SHOWER OR TWO MAY MAKE IT INTO THESE AREAS BUT SPRINKLES ARE THE MORE LIKELY OUTCOME IF ANYTHING FALLS AT ALL. THE BIGGER ISSUE WILL BE THE DEBRIS CLOUDS FROM THESE STORMS WHICH WILL LIKELY KEEP OUR TEMPS SUBDUED FOR THE NEXT FEW HOURS. THESE CLOUDS SHOULD PROGRESS THROUGH AND OUT OF OUR AREA BY MID AFTERNOON THOUGH SO STILL EXPECT MOST LOCATIONS TO WARM NICELY LATE INTO THE MID TO UPPER 80S. THE ONLY OTHER CHANGE WAS TO BEEF UP THE SEVERE WORDING LATE TONIGHT INTO SUNDAY EVENING IN THE GRIDS AS ALL SIGNS ARE A GO FOR A SIGNIFICANT SEVERE WEATHER OUTBREAK ACROSS OUR REGION. UPDATE ISSUED AT 734 AM EDT SAT JUL 26 2014 LOADED IN THE LATEST OBSERVATIONAL GUIDANCE FOR TEMPS...WINDS...AND DEW POINTS ACROSS THE REGION TO MAKE SURE THE DIURNAL TREND AND ONGOING CONDITIONS WERE REFLECTED IN THE FORECAST. OVERALL...IT LOOKS AS THOUGH THE FORECAST IS WELL ON TRACK THROUGH THE MORNING HOURS.
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&& .SHORT TERM...(TODAY THROUGH SUNDAY) ISSUED AT 502 AM EDT SAT JUL 26 2014 A STRONG SHORTWAVE CURRENTLY SITTING OVER SOUTHERN SASKATCHEWAN IS STILL ON TRACK TO BRING SOME VERY UNSETTLED WEATHER TO KY DURING THE SHORT TERM PERIOD. A SURGE OF SOUTHERLY WINDS AND WARM AIR ADVECTION WILL BE THE MAIN FOCUS FOR TODAY...AS A WARM FRONT PUSHES THROUGH THE REGION DURING THE AFTERNOON. THIS WILL DRIVE TEMPERATURES TO NEAR THE 90 DEGREE MARK...WITH HUMIDITY VALUES MAKING A RISE AS WELL. MEANWHILE...THE ASSOCIATED COLD FRONT...SPANNING FROM THE UPPER GREAT LAKES REGION TO KANSAS THIS AFTERNOON...WILL PUSH EASTWARD BY THE EVENING AS THE SHORTWAVE AND SURFACE LOW MOVE INTO SOUTHERN MANITOBA. AS IT NEARS THE OHIO RIVER VALLEY REGION...EXPECT CLOUDS TO INCREASE FROM NORTH TO SOUTH...AND SHOWERS AND THUNDERSTORMS TO BEGIN AFFECTING THE REGION FROM THE SAME DIRECTION DURING THE OVERNIGHT HOURS. DESPITE A NEAR-SURFACE INVERSION...LOW LEVEL WIND SHEAR IS QUITE GOOD...THERE IS GOOD SPEED SHEER IN THE MID AND UPPER LEVELS...LAPSE RATES RISE INTO THE 6.0 TO 6.5 C/KM RANGE...AND PWAT VALUES EXCEED 1.8 TO 2.0 INCHES FOR A 6 HOUR PERIOD IN SOME LOCATIONS. BASED ON THIS...STILL SUPPORTING THE IDEA THAT ANY STORMS THAT DEVELOP OVERNIGHT WILL HOLD A THREAT FOR HEAVY RAINFALL AS WELL AS DAMAGING WINDS AS THE STORMS COLLAPSE. BY 15Z...THINGS START TO GET A LITTLE MORE INTERESTING. LOW LEVEL WIND SHEAR IS QUITE IMPRESSIVE...WITH WIND SPEEDS REACHING IN EXCESS OF 50 KNOTS BY 12K FEET. DAYTIME HEATING WILL BREAK THE LOW LEVEL INVERSION EARLY ON...WITH TEMPS EXPECTED TO SURGE BACK INTO THE MID AND UPPER 80S BY AFTERNOON. A STRONG LOW LEVEL JET...AS WELL AS THE UPPER LEVEL JET POSITION THEMSELVES FROM WEST TO EAST ACROSS THE OHIO RIVER VALLEY REGION...WITH THE BEST ACTIVITY EXPECTED TO FORM ALONG THIS AXIS. A FEW THINGS TO NOTE...BETWEEN 12 AND 18Z SUNDAY...THE LATEST ECMWF IS POINTING AT THE BEST QVECTOR CONVERGENCE SETTING UP CLOSER TO THE ACTUAL LOW PRESSURE CENTER...OVER THE UPPER GREAT LAKES AND EXPANDING INTO NORTHERN INDIANA AND OHIO. THE UPPER LEVEL JET/S HORIZONTAL POSITION ALSO SUPPORTS THAT STORMS WILL SET UP AND MOVE IN THE SAME DIRECTION...FROM WEST TO EAST...RATHER THAN FROM NORTH TO SOUTH. THE 6Z NAM12 STORM RELATIVE MOTION IS ALSO FROM THE WNW. WHILE FORECAST SOUNDINGS SHOW A PRIME ENVIRONMENT FOR MCS/S TO FORM...THE OVERALL BEST FORCING STILL SEEMS TO BE TO OUR NORTH CLOSER TO THE LOW PRESSURE SYSTEM AND ALONG THE NORTHERN HALF OF THE JET MAXIMAS. AGREE WITH SPC/S THINKING THAT THE BEST MCS/S WILL DEVELOP HERE...WITH STRONG OUTFLOWS PUSHING OUTWARDS...INCLUDING SOUTHWARD INTO THE OHIO RIVER VALLEY AND EASTERN KY REGION. ALONG THESE OUTFLOWS IS WHERE WE CAN EXPECT THE BEST SEVERE POTENTIAL IN THE AFTERNOON FOR EASTERN KY. BY 18Z...AND CONTINUING INTO SUNDAY EVENING...FORECAST SOUNDINGS SHOW AN IMPRESSIVE SIGNATURE FOR SEVERE POTENTIAL...WITH CONTINUED STRONG WINDS IN THE MID LEVELS AND RESULTING GOOD SPEED SHEER...MOIST LOW LEVELS...BUT VERY DRY MID AND UPPER LEVELS. ALL OF THIS IS INDICATIVE OF GOOD DAMAGING DOWNDRAFT POTENTIAL...AS WELL AS A LARGE HAIL THREAT. THE CONCERN HOWEVER IS THE LOSS OF LOW LEVEL DIRECTIONAL SHEER...ESPECIALLY IN THE LOWEST 2K FEET...AND THEREFORE THE LACK OF HIGH HELICITY VALUES IN THIS LEVEL. AS NOTED ABOVE...THINK THE BEST SEVERE MCS STORMS AT THIS POINT WILL BE DRIVEN BY THE LLVL WIND SHEER CREATED BY THE OUTFLOW BOUNDARIES FROM LARGER MCS/S TO OUR NORTH...AND FADING MCS/S OVER OUR AREA. GIVEN THE FAST MOTION OF THESE STORMS...WOULD NOT BE OPPOSED TO THE IDEA OF A LINE OF STORMS DEVELOPING ALONG AN OUTFLOW BOUNDARY...WITH EMBEDDED SUPER CELLS AND A FEW ISOLATED SPIN UP TORNADOES POSSIBLE WITHIN THE ORGANIZED LINE. BUT THAT IS NOT TO SAY THAT SOME ISOLATED TO SCATTERED INDIVIDUAL CELLS COULD NOT DEVELOP AS WELL IN ADDITION...WITH THE MAIN THREAT BEING DAMAGING WINDS AND LARGE HAIL. THE STORM SYSTEM SHEAR...MOISTURE PROFILE...AND LI/S WOULD DEFINITELY SUPPORT THIS POTENTIAL AS WELL. PERHAPS THE BIGGEST THING TO QUESTION IS WHERE THE BOUNDARY WILL SET UP. GIVEN THE PARAMETERS AND UNCERTAINTY...ALL STORM MODES...INCLUDING QLCS/S...SUPERCELLS...AND BOW ECHOS ARE POSSIBLE. WILL CONTINUE TO MONITOR THE SITUATION AS THINGS PROGRESS...AND FINE TUNE THE FORECAST AS MORE INFORMATION IS MADE AVAILABLE. .LONG TERM...(SUNDAY NIGHT THROUGH FRIDAY) ISSUED AT 415 AM EDT SAT JUL 26 2014 THE MODELS ARE IN GOOD AGREEMENT WITH AN AMPLIFIED PATTERN TO CONTINUE THROUGH THE PERIOD. TROUGHING WILL DOMINATE ACROSS THE EASTERN HALF OF THE CONUS...WITH RIDGING OUT WEST. A STRONG SHORT WAVE TROUGH AND SURFACE COLD FRONT WILL CROSS THE OHIO VALLEY SUNDAY NIGHT...WITH STRONG TO SEVERE CONVECTION LIKELY ONGOING ACROSS EASTERN KENTUCKY IN THE EVENING. ONCE THIS HAS CLEARED OUT...MUCH COOLER AIR WILL INVADE FROM THE NORTHWEST...WITH HIGHS RETREATING TO THE 70S. THE CYCLONIC FLOW LINGERING ACROSS THE AREA WILL ALLOW FOR AT LEAST A SMALL CHANCE OF CONVECTION DURING PEAK HEATING ON MONDAY AND TUESDAY. DRY WEATHER WILL ENSUE FOR WEDNESDAY AND FOR MOST LOCATIONS THURSDAY...BESIDES A STRAY SHOWER OR STORM POPPING UP ALONG THE SOUTHEAST TERRAIN. AN UPPER LEVEL LOW THEN LOOKS TO EVOLVE ACROSS THE MISSISSIPPI VALLEY THROUGH NEXT WEEKEND...WITH DIURNALLY DRIVEN CONVECTION BECOMING MORE OF A THREAT ONCE AGAIN. TEMPERATURES WILL MODIFY SOMEWHAT...BUT WILL STILL AVERAGE BELOW NORMAL. && .AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING) ISSUED AT 725 AM EDT SAT JUL 26 2014 WARM MOIST AIR FLOWING IN FROM THE SOUTH...AND A COLD FRONT CURRENTLY POISED TO OUR NW...WITH BRING UNSETTLED CONDITIONS BY THE SECOND HALF OF THE TAF PERIOD. FOR TODAY...EXPECT LITTLE CONCERNS OTHER THAN SOME SCT TO AT TIMES BKN MID AND UPPER LEVEL CLOUDS. THEN...AS THE FRONT NEARS CLOSER TO THE OHIO RIVER OVERNIGHT...CLOUDS WILL THICKEN FROM NORTH TO SOUTH ACROSS THE REGION...WITH CHANCES FOR SHOWERS AND THUNDERSTORMS QUICKLY FOLLOWING BETWEEN 6 AND 12Z. EXPECT CIGS TO REMAIN ABOVE VFR FOR THE MOST PART OVERNIGHT...THOUGH IF ANY SHOWERS OR THUNDERSTORMS DEVELOP AND MOVE OVER A TAF SITE...VISIBILITIES COULD BE REDUCED DURING THE DURATION OF THE STORM. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...ABE SHORT TERM...JMW LONG TERM...GEOGERIAN AVIATION...JMW

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