Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 260218 AFDILN AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON OH 1018 PM EDT MON APR 25 2016 .SYNOPSIS... LOW PRESSURE WILL MOVE EAST ACROSS THE SOUTHERN GREAT LAKES TONIGHT...AS A COLD FRONT GRADUALLY MOVES INTO THE NORTHERN OHIO VALLEY AREA ON TUESDAY. CHANCES FOR SHOWERS AND THUNDERSTORMS WILL INCREASE LATE TONIGHT AND INTO THE DAY ON TUESDAY...AS THE COLD FRONT STALLS OUT OVER THE REGION. CHANCES FOR PRECIPITATION WILL CONTINUE INTO WEDNESDAY AND THURSDAY...WITH SLIGHTLY COOLER TEMPERATURES THAN EARLY IN THE WEEK. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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A SMALL AREA OF MID CLOUDS ARE AFFECTING SOME OF THE NRN COUNTIES ATTM...BUT OVER THE LAST HOUR THEY HAVE BEEN DISSIPATING AS THEY DRIFT TO THE EAST. CONVECTION OUT OVER IL/LAKE MICHIGAN WILL SLOWLY WORK TOWARDS THE FA OVERNIGHT. EXPECT IT TO BE UNDER A WEAKENING TREND BY THE TIME IT GETS HERE AFT 06Z. KEPT THE BEST POPS IN THE NORTH FOR TONIGHT. WITH THE REGION IN THE WARM SECTOR OVERNIGHT MIN TEMPS WILL BE ON THE WARM SIDE...GENERALLY 60-65 DEGREES.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... BY 12Z TUESDAY MORNING...THE SURFACE COLD FRONT WILL BE ORIENTED IN A WSW-TO-ENE ORIENTATION...MOVING SOUTH NEAR THE SOUTHERN MICHIGAN BORDER. THIS FRONT WILL CONTINUE TO MOVE SOUTH INTO THE ILN FORECAST AREA DURING THE DAY...BUT ITS PROGRESS WILL NOT BE FAST...AND IT IS EVENTUALLY EXPECTED TO BECOME NEARLY STATIONARY ACROSS THE FAR SOUTHERN SECTIONS OF THE CWA BY TUESDAY NIGHT. THERE IS A MARKED WIND SHIFT ALONG THE FRONT...WITH WARM SOUTHWESTERLY FLOW TO ITS SOUTH...AND COOLER/DRIER NNE FLOW BEHIND IT. THIS WILL HAVE AN IMPACT ON TEMPERATURES...WITH AN 8-10 DEGREE GRADIENT IN MAX TEMPS EXPECTED FROM NORTH TO SOUTH. THE FRONT WILL ALSO HAVE AN IMPACT ON PRECIPITATION PLACEMENT...AS WILL BE DESCRIBED IN FURTHER DETAIL BELOW. IN SHORT...CHANCES FOR RAIN (AND CERTAINLY CHANCES FOR STORMS) WILL BE VERY LIMITED NORTH OF THE BOUNDARY. THERE MAY STILL BE SOME ONGOING SHOWERS / WEAK CONVECTION ACROSS THE FORECAST AREA ON TUESDAY MORNING...BUT THIS ACTIVITY SHOULD CONTINUE TO REMAIN RELATIVELY LOW IN INTENSITY AS IT MOVES EAST OF THE CWA. THIS SHOULD SET UP MOST OF THE REST OF THE MORNING AND EARLY AFTERNOON AS A DOWN PERIOD FOR CONVECTIVE ACTIVITY...AND PERHAPS ALSO A PERIOD THAT MAY ALLOW SOME BREAKS IN THE CLOUD COVER ALONG AND AHEAD OF THE COLD FRONT. WITH HEATING AND INCREASING DEWPOINTS EXPECTED SOUTH OF THE FRONT...ALIGNED WITH COOLING TEMPERATURES ALOFT...INSTABILITY IS EXPECTED TO GROW DURING THE MORNING AND AFTERNOON. AHEAD OF A WEAK SHORTWAVE...STORM INITIATION IS EXPECTED TO OCCUR DURING THE AFTERNOON. THE EXACT TIMING AND PLACEMENT OF INITIATION REMAINS SOMEWHAT UNCERTAIN...AS IT WILL DEPEND ON HOW FAR SOUTH THE SURFACE FRONT GETS...AND THE EXACT TIMING OF THE SHORTWAVE. SINCE THE SURFACE FRONT WILL BE MOVING VERY SLOWLY...IT WILL ACT AS A FOCUS FOR CONVECTION...BUT NOT NECESSARILY A FEATURE TO BE USED FOR TIMING PURPOSES. WHAT APPEARS MOST LIKELY IS THAT CONVECTION DEVELOPS AND MOVES EAST-SOUTHEAST ACROSS THE SOUTHERN HALF OF THE CWA...MAINLY FROM LATE AFTERNOON INTO THE MID-EVENING. THE POTENTIAL FOR SEVERE WEATHER EXISTS IN THIS SCENARIO...WITH A FEW FACTORS TO CONSIDER REGARDING THE MAGNITUDE OF THE THREAT. INSTABILITY WILL BE SIGNIFICANTLY DEPENDENT ON THE CLOUD SITUATION DURING THE HOURS OF PEAK HEATING...WHICH IS SOMEWHAT UNCERTAIN. LOOKING ACROSS A SUITE OF DETERMINISTIC MODELS AS WELL AS SREF GUIDANCE FOR THE SOUTHERN SECTION OF THE ILN FORECAST AREA...SURFACE BASED CAPE IS EXPECTED TO BE AS HIGH AS 2000 J/KG...WITH 1KM MIXED-LAYER CAPE AROUND 1500 J/KG. SOME RAW MODEL OUTPUT ACTUALLY INDICATED SBCAPE AS HIGH AS 2500 J/KG...BUT THAT WOULD SEEM TO BE A HIGHER-END SCENARIO...AND WAS NOT SUPPORTED AS A MOST LIKELY OUTCOME BASED ON SREF GUIDANCE. SHOULD THESE VALUES BECOME REALIZED (IF LEFTOVER CLOUDS AND RAIN ARE NOT PROHIBITIVE)...THIS IS CERTAINLY SUFFICIENT INSTABILITY TO SUPPORT STRONG/DEEP CONVECTION. STORM ORGANIZATION...BY WAY OF SHEAR...IS LESS CERTAIN. THOUGH THERE IS SOME MODEST DIRECTIONAL NORTHWESTERLY SHEAR...THE OVERALL QUALITY OF DEEP-LAYER BULK SHEAR IS NOT IMPRESSIVE...WITH ONLY AROUND 20-25 KNOTS OF 0-6KM SHEAR IN THE AREA WHERE STORMS ARE EXPECTED TO BE THE MOST ROBUST. SHEAR IS STRONGER FURTHER NORTH...WHERE THE SURFACE FRONTAL POSITION WILL MAKE STORMS MUCH LESS LIKELY TO DEVELOP. THE END RESULT IS THAT CONVECTION MOVING THROUGH THE SOUTHERN HALF (AND ESPECIALLY SOUTHERN THIRD) OF THE ILN FORECAST AREA ON TUESDAY AFTERNOON/EVENING WILL HAVE THE POTENTIAL TO BECOME SEVERE. WEAK SHEAR WILL INHIBIT OVERALL STORM ORGANIZATION...BUT SOME DAMAGING WINDS AND LARGE HAIL APPEAR TO BE POSSIBLE...GIVEN THE POSITIONING OF THE FRONT AND THE EXPECTED INSTABILITY. CERTAINLY NOT A HIGHER-END RISK...BUT ONE WORTH A CONTINUED MENTION IN THE HAZARDOUS WEATHER OUTLOOK. CONVECTION IS FORECAST TO MOVE SOUTHEAST OF THE ILN FORECAST AREA LATER ON TUESDAY NIGHT...AND POPS WILL BE SIGNIFICANTLY LIMITED AFTER 06Z. THE PRESENCE OF THE COLD FRONT WILL LEAD TO A BIG GRADIENT IN MIN TEMPS EARLY WEDNESDAY MORNING...AND 12Z MODEL RUNS HAVE COME IN SLIGHTLY COLDER (OR PERHAPS JUST SLIGHTLY FURTHER SOUTH WITH THE FRONTAL POSITION). LOWER TO MID 40S NOW APPEAR POSSIBLE IN THE FAR NORTHEASTERN ILN FORECAST AREA...WHILE THE FAR SOUTH MAY REMAIN IN THE MIDDLE TO UPPER 50S. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... FRONTAL BOUNDARY NEAR OUR SOUTHERN/WESTERN CWFA BORDER ON WEDNESDAY WILL REMAIN QUASI-STATIONARY. SOME LIFT WILL OCCUR UP AND OVER THE BOUNDARY THROUGH THE DAY WHICH WILL KEEP A CHANCE OF SHOWERS AND THUNDERSTORMS IN THE FORECAST. FOR WEDNESDAY NIGHT...A LEAD S/WV IS STILL FORECAST TO MOVE WEST TO EAST ACROSS THE REGION. THIS WILL IMPINGE A LOW LEVEL JET ALONG THE FRONTAL BOUNDARY AS IT TRIES TO LIFT A LITTLE TO THE NORTH. THIS DYNAMIC SETUP SHOULD SPREAD SHOWERS AND EMBEDDED THUNDERSTORMS FROM WEST TO EAST OVERNIGHT. FOR THURSDAY INTO THURSDAY NIGHT...DISCREPANCIES CONTINUE AMONGST THE OPERATIONAL MODELS WITH THE NEXT S/WV AND HOW IT RIPPLES A SURFACE LOW ALONG THE FRONTAL BOUNDARY THROUGH OUR REGION. HAVE TAKEN A MORE SOUTHERLY APPROACH WITH THE LOW WHICH WILL KEEP THE THREAT FOR SHOWERS AND THUNDERSTORMS ON THURSDAY. CHANCES WILL DECREASE THURSDAY EVENING AS THE LOW BEGINS TO PULL AWAY. WEAK RIDGING WILL RETURN FOR FRIDAY INTO FRIDAY NIGHT ALONG WITH DRY AND SEASONAL TEMPERATURES. 12Z GUIDANCE IS STILL SHOWING TIMING DISCREPANCIES WITH THE APPROACH OF THE NEXT WEATHER SYSTEM OVER THE WEEKEND. HAVE TAKEN MORE OF A BLEND OF THE ECMWF AND WPC GUIDANCE TO TRY AND PINPOINT THE HIGHEST THREAT FOR PCPN. THIS SHOULD OCCUR ON SUNDAY WITH DECREASING CHANCES ON MONDAY AS THE SYSTEM SLOWLY MOVES ACROSS THE REGION. NEAR OR SLIGHTLY ABOVE TEMPERATURES EARLY IN THE PERIOD WILL TREND TO SLIGHTLY BELOW NORMAL VALUES BY EARLY NEXT WEEK DUE TO THE LIKELIHOOD OF PCPN AND CLOUDY SKIES. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/... DIURNAL CU IS QUICKLY DISSIPATING THIS EVENING AND CLEAR TO SCATTERED CLOUDS ARE EXPECTED FOR THE FIRST PART OF THE FA PERIOD. CDFNT WILL APPRAOCH THE AREA AFTER 06Z. MODELS ARE DIFFERING ON TIMING AND PLACEMENT OF FRONT AND QPF FOR LATER TONIGHT. THE CONSENSUS IS LEANING TOWARDS SOME SCATTERED PCPN WORKING INTO KDAY AROUND 09Z. WENT WITH VCSH AT THIS TIME DUE TO THE UNCERTAINTY OF PLACEMENT AND THUNDER POSSIBILITY. GUIDANCE IS SUGGESTING THAT MVFR CIGS WILL BE POSSIBLE WITH THIS FIRST SHOT OF PCPN. AS FRONT SAGS DOWN INTO SRN OHIO/INDIANA TOMORROW THE FIRST SHOT OF PCPN WEAKENS. THEN AS DAYTIME HEATING GETS GOING THE ATMOSPHERE BECOMES UNSTABLE AND EXPECT SCATTERED TSTM TO DEVELOP AND AFFECT THE SRN TAFS. KEPT A PERIOD OF TEMPO TSRA FOR THE AFTN HOURS IN THE S. WITH THE FRONT PUSHING THROUGH THE NRN TAFS DURING THE MORNING EXPECT THE ATMOSPHERE TO BE A LITTLE MORE STABLE AROUND I-70...SO ONLY WENT WITH VCSH IN THE AFTN UP THERE. CONVECTION SHOULD BECOME MUCH FOR SCATTERED TOWARDS 00Z. WINDS WILL TURN FROM SOUTHWEST AHEAD OF THE FRONT TO NORTHWEST POST FRONTAL. OUTLOOK...MVFR CIGS AND VSBYS WITH SOME THUNDERSTORMS POSSIBLE WEDNESDAY INTO THURSDAY. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...NONE. KY...NONE. IN...NONE. && $$ SYNOPSIS...HATZOS NEAR TERM...SITES SHORT TERM...HATZOS LONG TERM...HICKMAN AVIATION...SITES

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