Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 301311 AFDILN AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON OH 911 AM EDT TUE JUN 30 2015 .SYNOPSIS...
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A SURFACE LOW WILL TRACK TO THE LOWER GREAT LAKES FROM THE WESTERN GREAT LAKES REGION TODAY. AT THE SAME TIME...THE AXIS OF AN UPPER LOW WILL SLIDE EAST THROUGH THE GREAT LAKES AND OHIO VALLEY THIS AFTERNOON AND EVENING. WEAK SURFACE HIGH PRESSURE WILL THEN SETTLE OVER THE REGION WEDNESDAY INTO THURSDAY...WITH A LOW CUTTING EAST THROUGH THE SOUTHERN OHIO AND TENNESSEE VALLEYS ON THURSDAY AND THURSDAY NIGHT.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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MORNING UPDATE GENERALLY ATTEMPTED TO TIME THE SHOWERS IN CENTRAL OHIO OUT OF THE CWA AND TO NOSE THE AREA OF SHOWERS IN WEST CENTRAL OHIO INTO THE CWA. UPSTREAM CONVECTIVE COMPLEX HAS LOST THE DEEP CONVECTION AND SUBSEQUENT ELECTRICAL ACTIVITY BUT HAS SPARKED SHOWERS OVER A BROADER AREA TO THE WEST OF I-75 AND N OF I-70. THESE SHOWERS LOOK TO BE TRACKING JUST SOUTH OF EAST AND MODELS ARE SLOW IN THE INITIATION OF STORMS TODAY BUT INDICATE A RAPID EXPANSION ACROSS THE REGION AS SUN HELPS DESTABILIZE THE BOUNDARY LAYER. BLENDED THE EARLIER ONSET OF SHOWERS TO THE CURRENT FORECAST WHICH IS STILL ON TRACK. PREV DISC BELOW... THE FORECAST FOCUS GOING INTO THE AFTERNOON WILL BE ON THE POTENTIAL FOR THUNDERSTORM DEVELOPMENT. POPS WERE LARGELY BASED ON SPC-WRF AND NCAR ENSEMBLE SIMULATED REFLECTIVITY PROJECTIONS...SPREADING LIKELY POPS ACROSS THE CWA FROM NORTHWEST TO SOUTHEAST BETWEEN 18Z AND 00Z. THIS REGION WILL BE AHEAD OF THE UPPER TROUGH AXIS...IN A FAVORABLE AREA OF LIFT. ALTHOUGH THE SURFACE PRESSURE PATTERN IS KIND OF A MESS...THERE DOES SEEM TO BE A WEAK BOUNDARY MOVING SOUTHEAST INTO THE ILN FORECAST AREA...WITH CONVERGENT FLOW ALSO HELPING TO PROVIDE FORCING FOR STORM DEVELOPMENT. WITH COOLER AIR MOVING IN ALOFT...THANKS TO THE UPPER TROUGH...MID-LEVEL LAPSE RATES WILL BE STEEPING SLIGHTLY. EVEN THOUGH NEAR-SURFACE CONDITIONS WILL NOT BE ESPECIALLY MOIST OR WARM...INSTABILITY SHOULD BE ABLE TO BUILD FAIRLY WELL...UP TO AROUND 1500 J/KG OF SBCAPE. LOOKING UPSTREAM EARLY THIS MORNING...SOME THUNDERSTORM CELLS MOVING INTO INDIANA ARE AN INDICATION OF ELEVATED INSTABILITY...WHICH FURTHER SUGGESTS THAT DIURNAL HEATING WILL BE ABLE TO GENERATE SOME ENERGY OUT OF THIS AIRMASS. WIND SHEAR IS FORECAST TO BE MARGINAL...PRIMARILY UNIDIRECTIONAL FROM THE WEST...AND PERHAPS AROUND 15-25 KNOTS THROUGH A 6KM LAYER. THUS...THE INGREDIENTS ARE EXPECTED TO BE IN PLACE FOR A LOW-END SEVERE EVENT ACROSS THE FORECAST AREA. TIMING SHOULD BE MAINLY DIURNAL...WITH A THREAT FOR WIND AND HAIL. HOWEVER...THE EXPECTED INSTABILITY AND SHEAR ARE SIMPLY NOT EXPECTED TO BE APPRECIABLE ENOUGH FOR A SIGNIFICANT OR WIDESPREAD EVENT. SINCE THE OVERALL FOCUS IS NOT PARTICULARLY WELL-DEFINED...AND ENVIRONMENTAL CONDITIONS WILL BE SIMILAR ACROSS THE REGION...CHANCES FOR STRONG STORMS DO NOT APPEAR SIGNIFICANTLY DIFFERENT FROM ONE SECTION OF THE CWA TO ANOTHER. HOWEVER...IF RECENT HRRR RUNS ARE CORRECT (AND STORMS MOVE THROUGH A LITTLE FASTER THAN CURRENTLY FORECAST)...THE CHANCES FOR STRONGER STORMS MAY SHIFT SLIGHTLY SOUTH AND EAST. CLOUDS SHOULD BREAK ENOUGH TO ALLOW SOME INSOLATION FOR MOST LOCATIONS IN THE CWA TODAY...THOUGH CENTRAL OHIO MAY STAY IN THE CLOUDS A LITTLE LONGER THAN ELSEWHERE. THUS...A NNE-TO-SSW TEMPERATURE GRADIENT WAS EMPLOYED IN THE GRIDS...WITH MID TO UPPER 70S IN THE NORTHERN/NORTHEASTERN CWA...AND LOWER 80S IN THE FAR SOUTH.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY/... WITH THE AXIS OF THE UPPER LEVEL TROUGH CROSSING THE MIDDLE OHIO VALLEY ON FRIDAY EVENING...FAVORABLE CONDITIONS FOR ASCENT WILL QUICKLY COME TO AN END...AND PRECIPITATION SHOULD DIMINISH FROM NORTHWEST TO SOUTHEAST ACROSS THE FORECAST AREA. UPPER FLOW WILL REMAIN GENERALLY NORTHWESTERLY OVER THE REGION THROUGH THE REST OF THE WEEK...AND THOUGH THERE IS GENERAL AGREEMENT IN THE ARRANGEMENT OF THE SURFACE PATTERN THROUGH FRIDAY...THE EXACT LATITUDINAL ALIGNMENT WILL HAVE A BIG ROLE IN THUNDERSTORM CHANCES (ESPECIALLY ON THURSDAY). DRY CONDITIONS ARE EXPECTED TONIGHT AND THROUGH THE DAY ON WEDNESDAY...AS SURFACE HIGH PRESSURE BEGINS TO BUILD IN OVER THE GREAT LAKES REGION. 925MB/850MB TEMPERATURES WILL COOL BY ONE OR TWO DEGREES CELSIUS FROM TUESDAY TO WEDNESDAY...BUT WITH CLOUD COVER EXPECTED TO BE FAIRLY LIMITED...TEMPERATURES SHOULD STILL RISE TO SIMILAR VALUES AS ON TUESDAY. WITH FORECAST HIGHS IN THE MIDDLE 70S TO AROUND 80...CONDITIONS WILL REMAIN ABOUT FIVE DEGREES BELOW CLIMATOLOGICAL NORMALS. AS THE GREAT LAKES SURFACE HIGH GROWS IN SIZE HEADED INTO THURSDAY...ITS EVENTUAL MOVEMENT WILL DETERMINE HOW FAR SOUTH A FRONTAL BOUNDARY AND CONVERGENT ZONE WILL SET UP FROM WEDNESDAY NIGHT THROUGH FRIDAY. THIS WILL BE AN IMPORTANT QUESTION...AS MODELS HAVE CONSISTENTLY SHOWN THAT CONVECTION WILL BE LIKELY ALONG THIS BOUNDARY...PERHAPS WITH ONE OR MORE CONVECTIVE SYSTEMS MOVING IN THE QUICK WESTERLY FLOW ALOFT. IN GENERAL...THE LAST 12 HOURS OF MODEL RUNS HAVE FAVORED A SLIGHT SHIFT TO A SOUTHWARD SOLUTION...SETTLING STORMS ACROSS THE SOUTHERN HALF OF THE OHIO VALLEY. SOME CHANGES WERE NECESSARY TO THE POP GRIDS THROUGH THIS TIME FRAME...SIGNIFICANTLY LIMITING CONVECTIVE CHANCES IN THE NORTHERN HALF OF THE CWA...WHILE STILL ALLOWING A CHANCE FOR CONVECTION (ESPECIALLY IN THE SOUTHERN HALF) ON THURSDAY. WITH THIS BOUNDARY SETTING UP SOUTH OF THE CWA...TEMPERATURES SHOULD REMAIN SLIGHTLY BELOW NORMAL THROUGH THE FORECAST PERIOD. && .LONG TERM /FRIDAY NIGHT THROUGH MONDAY/... MID/UPPER LEVEL TROUGH WILL PERSIST ACROSS THE EASTERN UNITED STATES INTO EARLY NEXT WEEK AS THE WEST COAST RIDGE AXIS SHIFTS VERY SLOWLY EASTWARD. THERE ARE SOME MODEL DISCREPANCIES WITH THE NORTHWARD EXTENT OF THE SHORT WAVE ENERGY MOVING THROUGH THE TROUGH ON THURSDAY. AS A RESULT...HAVE STUCK CLOSE TO THE MODEL BLEND/CURRENT FORECAST WITH THIS...RANGING POPS FROM LOW CHANCE NORTH TO LIKELY IN THE FAR SOUTH. ON THE BACK SIDE OF THIS SHORT WAVE...WE SHOULD GET INTO A PCPN MINIMUM FOR THURSDAY NIGHT INTO FRIDAY MORNING. HEADING INTO THE WEEKEND AND EARLY NEXT WEEK...IT BECOMES MORE DIFFICULT TO TIME/PLACE SHORT WAVE ENERGY IN THE TROUGHY PATTERN. WILL THEREFORE MAINTAIN SOME LOWER CHANCE POPS THROUGH THE REMAINDER OF THE LONG TERM PERIOD. WITH THE TROUGH IN PLACE ACROSS THE REGION...TEMPERATURES WILL REMAIN AT OR SLIGHTLY BELOW SEASONABLE NORMALS. EXPECT AFTERNOON HIGHS IN THE UPPER 70S TO LOWER 80S. && .AVIATION /11Z TUESDAY THROUGH SATURDAY/... THE COMBINATION OF RECENT RAINFALL...LIGHT WINDS...AND SATURATED LOW LEVELS HAVE RESULTED IN VARYING AMOUNTS OF CEILING AND VISIBILITY REDUCTIONS ACROSS THE TAF FORECAST AREA THIS MORNING. IT APPEARS THE WORST CONDITIONS WILL CONTINUE FOR KILN...KDAY...KCMH...AND KLCK THROUGH AT LEAST 14Z...WITH PREVAILING CEILINGS AND VISIBILITIES IMPROVING TO VFR BY 16Z. FOR LATER TODAY...REGION WILL REMAIN UNDER A NORTHWEST FLOW PATTERN ALOFT. ANOTHER IN A SERIES OF EMBEDDED DISTURBANCES IS EXPECTED TO WORK ITS WAY EAST ACROSS THE REGION BY THE AFTERNOON HOURS. THIS FEATURE WILL TEAM UP WITH A LOW LEVEL CONVERGENT BOUNDARY...ALONG WITH A QUICKLY DESTABILIZING AIRMASS...TO PRODUCE SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS. ATTM...BELIEVE ALL TERMINALS WARRANT A TEMPO THUNDERSTORM GROUP WITH MVFR CONDITIONS DURING THE 18Z AND 22Z TIME FRAME...OR PEAK HEATING. AS TYPICAL...LOCAL VISIBILITIES CAN DROP BELOW INTO THE IFR OR LOWER CATEGORY WHERE THE MORE ROBUST CELLS OCCUR. WINDS BY AFTERNOON WILL BE GENERALLY FROM A 240 TO 250 DIRECTION WITH SYNOPTIC SCALE GUSTS IN THE LOWER 20 KNOTS. BY THIS EVENING...DISTURBANCE PIVOTS AWAY AS WELL AS THE CONVERGENT BOUNDARY. WITH THE LOSS OF DAYTIME HEATING...CONVECTION SHOULD WANE FAIRLY QUICKLY DURING THE EVENING. A WEAK COLD FRONT WILL APPROACH THE REGION FROM THE NORTHWEST OVERNIGHT. WITH THE LACK OF FORCING...NOT MUCH IS EXPECTED WITH THIS BOUNDARY ATTM. SKIES SHOULD BECOME PARTLY CLOUDY WITH PERHAPS SOME MVFR VISIBILITIES DEVELOPING. OUTLOOK...THUNDERSTORMS POSSIBLE WEDNESDAY NIGHT INTO THURSDAY AND AGAIN FRIDAY NIGHT INTO SATURDAY. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...NONE. KY...NONE. IN...NONE. && $$ SYNOPSIS...FRANKS NEAR TERM...FRANKS SHORT TERM...HATZOS LONG TERM...JGL AVIATION...HICKMAN

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