Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 211047 AFDILN AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON OH 647 AM EDT SUN SEP 21 2014 .SYNOPSIS... A COLD FRONT WILL MOVE SOUTHEAST THROUGH THE OHIO VALLEY TODAY...AS AN AREA OF UPPER LEVEL LOW PRESSURE CROSSES THE GREAT LAKES. BEHIND THE FRONT...COOLER AND DRIER CONDITIONS WILL BUILD INTO THE REGION FOR MONDAY. AN AREA OF HIGH PRESSURE WILL PERSIST OVER THE OHIO VALLEY THROUGH THE WEEK...WITH DRY CONDITIONS EXPECTED THROUGH THE WEEKEND...AND A GRADUAL WARMING TREND. && .NEAR TERM /THROUGH TONIGHT/... AMPLIFIED FLOW IN THE MID-LEVELS REMAINS IN PLACE OVER THE EASTERN HALF OF THE COUNTRY...WITH A LARGE TROUGH EXTENDING INTO THE GREAT LAKES AND OHIO VALLEY REGION. THE PRIMARY SHORTWAVE ENERGY ASSOCIATED WITH THE TROUGH REMAINS UPSTREAM...BUT WILL HAVE A ROLE IN CONDITIONS TONIGHT (DISCUSSED IN THE SHORT TERM SECTION OF THE AFD). FOR NOW...THE AREA REMAINS IN A REGIME OF SOUTHWESTERLY FLOW (SURFACE) TO WESTERLY FLOW (ALOFT) AHEAD OF THE TROUGH...IN A GENERALLY FAVORABLE AREA FOR ASCENT. AT THE SURFACE..A SLOW-MOVING COLD FRONT CURRENTLY EXTENDS FROM LAKE MICHIGAN THROUGH NORTHERN MISSOURI. THE OHIO VALLEY REMAINS IN THE WARM SECTOR...IN AN AIR MASS THAT HAS YET TO BE WORKED OVER...DESPITE DIURNAL SURFACE STABILIZATION. AN AREA OF ELEVATED INSTABILITY EXISTS AHEAD OF THE PRECIPITATION AXIS...AND MODEL SOUNDINGS IN THE WESTERN HALF OF THE ILN CWA SUGGEST AT LEAST 500 J/KG (MAYBE AS HIGH AS 1000 J/KG) OF INSTABILITY WHEN LIFTING A PARCEL FROM AROUND 925MB. WITH AROUND 40 KNOTS OF DEEP LAYER SHEAR TO SUPPORT STORM ORGANIZATION...THERE WAS SOME CONCERN OF A POSSIBLE MARGINAL HAIL THREAT OVER INDIANA AND INTO WESTERN OHIO. ULTIMATELY...WITH WEAK LOW-LEVEL FORCING...THE CONVECTION HAS REMAINED GENERALLY UNFOCUSED. RADAR TRENDS FOR THE PAST SEVERAL HOURS SUGGEST NOTHING MORE THAN A THREAT FOR SOME HEAVY RAIN...AND PEA SIZE HAIL AT MOST. THE ELEVATED NATURE OF THE CONVECTION WILL MAKE ANY GUSTY WINDS VERY UNLIKELY. THE AXIS OF PRECIPITATION HAS BEEN MOVING VERY SLOWLY...BUT RECENT HRRR RUNS SEEM TO TIME THE PRECIPITATION FAIRLY WELL...ALLOWING IT TO EXIT THE EASTERN CWA BY 15Z. WITH A GRADUAL DOWNWARD TREND EXPECTED IN STORM COVERAGE...POPS BEGIN AS HIGH AS 80 PERCENT IN THE NW CWA BEFORE DIMINISHING TO 40 PERCENT IN THE SE. BASED ON THETA-E DEPICTIONS...IT APPEARS THAT THE ACTUAL COLD FRONT WILL NOT GET INTO THE CWA UNTIL THE AFTERNOON. REDEVELOPMENT ALONG THE FRONT CURRENTLY APPEARS UNLIKELY FOR MOST OF THE CWA...WITH A SLIGHT CHANCE OF A SHOWER MAINLY NEAR AND EAST OF US-23. TEMPERATURES TODAY WILL BE INFLUENCED BY THE EVENTUAL POSITIONING OF THE FRONT...AS WELL AS SKY COVER. BEHIND THE MORNING CONVECTION...CLOUDS ARE EXPECTED TO BREAK...ESPECIALLY IN THE SOUTHWESTERN HALF OF THE CWA. TO THE NORTH...ADDITIONAL CLOUDS WILL LIKELY DEVELOP...AS A RESULT OF THE APPROACHING MID-LEVEL SHORTWAVE AND COLD ADVECTION BEHIND THE FRONT. BECAUSE OF THESE FACTORS...A GRADIENT WAS USED IN THE MAX TEMP GRIDS. FORECAST VALUES ARE AS HIGH AS 80 DEGREES IN THE SOUTHEAST...WITH TEMPERATURES MUCH CLOSER TO 70 DEGREES IN THE NORTHWEST. && .SHORT TERM /MONDAY THROUGH WEDNESDAY/... BY EVENING...THE SURFACE COLD FRONT IS EXPECTED TO BE THROUGH THE ILN CWA. HOWEVER...THE AXIS OF THE 500MB TROUGH WILL BE ROTATING THROUGH THE GREAT LAKES. THERE IS A SIGNIFICANT INCREASE IN MODEL RH IN THE LOW LEVELS TONIGHT...AND IT IS LIKELY THAT A STRATOCUMULUS DECK WILL ENVELOP THE ILN CWA FROM NORTH TO SOUTH. THE WRF-NMM / WRF-ARW MODELS ARE IN AGREEMENT WITH CMC/GFS GUIDANCE IN ALLOWING FOR SOME LIGHT SHOWERS TO DEVELOP IN THE NORTHERN HALF OF THE CWA THIS EVENING. SLIGHT CHANCE POPS HAVE BEEN MAINTAINED IN THE FORECAST FOR THIS...THOUGH THERE WAS SOME CONSIDERATION TO INCREASE POPS (KEEPING QPF LIGHT) IN THE FAR NORTH. THOUGH COLD ADVECTION TONIGHT WILL BE NOTABLE...THE CLOUDS MAY ACTUALLY KEEP TEMPERATURES FROM PLUMMETING TOO FAR. AFTER THE CLOUDS DISSIPATE (PERHAPS NOT ALL THAT QUICKLY) ON MONDAY MORNING...A VERY TRANQUIL WEATHER PATTERN WILL BEGIN TO SET UP FOR THE REST OF THE WEEK. A SPRAWLING AREA OF VERY DRY HIGH PRESSURE WILL GET CAUGHT UNDER A MID-LEVEL RIDGE...BETWEEN THE QUICK UPPER FLOW IN CANADA AND THE VERY STAGNANT TROPICAL CONDITIONS WELL TO THE SOUTH. THE AIR MASS WILL ALSO START OUT RATHER COOL...WITH 850MB TEMPS OF BELOW 5 DEGREES CELSIUS ON MONDAY MORNING. ALTHOUGH THE TREND THROUGH THE WEEK SHOULD BE FOR A GRADUAL WARMING TREND...AS THE CENTER OF THE HIGH VERY SLOWLY MOVES EAST OF THE OHIO VALLEY...IT APPEARS THAT MONDAY NIGHT / TUESDAY MORNING WILL LIKELY BE THE COOLEST. UNDER CLEAR SKIES AND LIGHT WINDS...MIN TEMPS LOOK TO BE IN THE LOWER 40S...ABOUT 10-15 DEGREES BELOW NORMAL. RECORD LOWS AT THE CLIMATE SITES ARE WELL INTO THE 30S AND SHOULD BE EASILY SAFE...BUT OUTLYING LOCATIONS MAY DROP INTO THE UPPER 30S. WITH NO CHANGE TO THE PATTERN HEADING INTO TUESDAY AND WEDNESDAY...THE FORECAST IS FAIRLY STRAIGHTFORWARD...WITH SLIGHT INCREASES IN TEMPERATURES EACH DAY AND SUNNY SKIES EXPECTED. && .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... MID/UPPER LEVEL RIDGE WILL REMAIN IN PLACE ACROSS THE REGION THROUGH THE END OF THE WEEK. THIS WILL RESULT IN DRY CONDITIONS AND FAIRLY SEASONABLE TEMPERATURES THROUGH THE LONG TERM PERIOD. AS THE AIRMASS SLOWLY MODIFIES...HIGH TEMPERATURES WILL GRADUALLY WARM EACH DAY...FROM THE LOW TO MID 70S MID WEEK INTO THE UPPER 70S TO AROUND 80 DEGREES BY THE WEEKEND. && .AVIATION /10Z SUNDAY THROUGH THURSDAY/... COLD FRONT WILL MOVE SOUTHEAST THROUGH THE FORECAST AREA LATE THIS MORNING AND EARLY THIS AFTERNOON. RADAR SHOWS A BAND OF WIDELY SCATTERED SHOWERS AHEAD OF THE FRONT EXTENDING ACROSS SOUTHERN INDIANA NORTHEASTWARD TOWARDS CMH. THE BAND IS MOVING TO THE EAST AND WEAKENING. THESE SHOWERS ARE EXPECTED TO MOVE THROUGH THE TERMINALS BY 12Z THUS WILL NOT BE INCLUDED IN THE 12Z TAFS. BEHIND THESE SHOWERS LEADING BACK TO THE FRONT WILL BE BAND OF LOW LEVEL MOISTURE GENERATING CIGS BTWN FL015 AND FL025. AHEAD OF THE FRONT SURFACE WINDS WILL BE SW 10 TO 15 WITH A FEW GUST TO 20KT. AFTER FROPA WINDS WILL TURN TO THE WEST AND GRADUALLY NW AT 15 TO 20KT WITH GUST 25 TO 30KT. MVFR CLOUDS ASSOCIATED WITH THE FRONT ARE EXPECTED TO CLEAR THE AREA BY NOON LEAVING SCT SC BTWN 040-050. LOW LEVEL MOISTURE ASSOCIATED WITH AN UPR LEVEL TROF WILL MOVE INTO THE FORECAST AREA LATE AFTN AND PRODUCE CIGS BTWN FL040 AND 050. THESE CLOUDS COULD PRODUCE A FEW SPRINKLES N OF I-70 AND HAVE NOT BEEN INCLUDED IN THE FCST. AS THE UPR LVL TROF MOVES TO THE EAST OF THE AREA LATE TONIGHT AND EARLY MON MORNING SKIES SHOULD CLEAR. DURING THE NIGHT WINDS WILL BE NW AND LOSE THEIR GUSTINESS. OUTLOOK...FOR MONDAY THROUGH THURSDAY...VFR. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...NONE. KY...NONE. IN...NONE. && $$ SYNOPSIS...HATZOS NEAR TERM...HATZOS SHORT TERM...HATZOS LONG TERM...JGL AVIATION...HAYDU

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