Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 231431 AFDILN AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON OH 1031 AM EDT THU APR 23 2015 .SYNOPSIS... HIGH PRESSURE WILL MAINTAIN CONTROL OF THE WEATHER THROUGH THE END OF THE WEEK...WITH DRY AND COOL CONDITIONS...AND FROST DURING THE EARLY MORNING HOURS. AN AREA OF LOW PRESSURE WILL TRACK ACROSS THE REGION ON SATURDAY...BRINGING RAIN WITH A CHANCE OF THUNDERSTORMS. ANOTHER AREA OF HIGH PRESSURE WILL MOVE IN FOR SUNDAY AND MONDAY...WITH DRY WEATHER EXPECTED TO START THE WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... SHOULD BE ANOTHER DAY WITH GOOD MIXING UP TO BETWEEN 750 MB AND 800 MB. THIS WILL RESULT IN GUSTY NORTHWEST WINDS AND LOWER DEW POINTS. ALREADY SEEING SOME OF THAT OCCURRING IN SOUTHERN INDIANA. THESE LOWER DEW POINTS WILL RESULT IN LOW RELATIVE HUMIDITY. ALTHOUGH THE GROUND IS STILL WET THERE WILL BE SOME DRYING OF FUELS. SO THERE IS AN ENHANCED FIRE DANGER ACROSS SOUTHERN COUNTIES. STRATOCUMULUS WILL DEVELOP WITH GREATEST COVERAGE IN THE NORTHEAST COUNTIES. FORECAST TEMPERATURES STILL LOOK REASONABLE. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/... RADIATIONAL COOLING CONDITIONS EARLY FRIDAY MORNING WILL BE RATHER FAVORABLE...AS AN ELONGATED NNW-TO-SSE AREA OF HIGH PRESSURE MOVES INTO THE MIDDLE OHIO VALLEY BY 12Z. SOME SLIGHT WARM ADVECTION ALOFT (MAINLY ABOVE 850MB) WILL HELP KEEP CLOUDS AWAY...WHILE THE AIR CLOSER TO THE GROUND WILL REMAIN MOSTLY UNMODIFIED. THUS...TEMPERATURES ARE EXPECTED TO FALL EASILY INTO THE LOWER 30S FOR THE ENTIRE CWA. CONFIDENCE IS HIGH THAT THE NORTHERN HALF OF THE FORECAST AREA WILL DROP BELOW FREEZING...WITH OUTLYING LOCATIONS (ESPECIALLY SHELTERED PLACES WITH NO WIND) POSSIBLY DROPPING INTO THE 20S. FURTHER TO THE SOUTH...CONDITIONS MAY NOT BE QUITE COOL ENOUGH FOR WIDESPREAD FREEZING TO OCCUR...THOUGH ISOLATED READINGS NEAR 30 DEGREES WILL CERTAINLY BE POSSIBLE. BASED ON THESE LEVELS OF FORECAST CONFIDENCE...AND A WELL-COLLABORATED FORECAST WITH SURROUNDING OFFICES...FROST ADVISORIES AND FREEZE WARNINGS HAVE BEEN PUT IN PLACE. AFTER COMING OUT OF THE COLDEST MORNING THROUGH THE ENTIRE SEVEN-DAY FORECAST...CONDITIONS FRIDAY WILL BE FAIRLY TRANQUIL. WARM ADVECTION WILL STRENGTHEN ALOFT...WITH MOISTURE ALSO MOVING IN AND THICKENING UP THE CLOUDS IN THE HIGH AND MID LEVELS. HOWEVER...AS WINDS BEGIN TO INCREASE AT THE SURFACE (ONCE THE HIGH MOVES AWAY)...THEY WILL DO SO OUT OF THE EAST. THIS WILL NOT SUPPORT MUCH WARMING AT THE SURFACE...AND THUS THE GAINS ALOFT ALONE (THROUGH MIXING) WILL ONLY ALLOW FOR A TEMPERATURE RISE OF A FEW DEGREES FROM THURSDAY TO FRIDAY. THE WEATHER WILL GET MORE ACTIVE AGAIN FROM LATE FRIDAY NIGHT THROUGH SUNDAY MORNING. A 500MB SHORTWAVE WILL EJECT OFF THE HIGH PLAINS AND MOVE EAST...CROSSING THE OHIO VALLEY ON SATURDAY. AS IT DOES THIS...IT WILL WEAKEN...AS IT BECOMES ABSORBED IN THE FLOW AROUND THE LARGE UPPER LOW NEAR THE CANADIAN MARITIME PROVINCES. AN AREA OF SURFACE LOW PRESSURE IS FORECAST TO MOVE EAST OUT OF THE MIDDLE MISSISSIPPI VALLEY...PASSING THROUGH THE SOUTHERNMOST SECTIONS OF THE OHIO VALLEY BY SATURDAY NIGHT. HOWEVER...AT 850MB...THE LOW TRACK WILL BE FURTHER TO THE NORTH. THIS SETS UP A SCENARIO WHERE WARMER AIR (AND FRONTAL FORCING) WILL EXTEND ACROSS THE VAST MAJORITY OF THE ILN FORECAST AREA...DESPITE COOL AND STABLE BOUNDARY LAYER CONDITIONS. POPS WERE INCREASED TO CATEGORICAL FOR MOST OF THE FORECAST AREA ON SATURDAY MORNING...WITH LIKELY/CHANCE POPS IN CENTRAL OHIO. CONFIDENCE IN THE PRECIPITATION PATTERN IS HIGHEST AT THE ONSET OF THE EVENT. THERE ARE STILL SOME MODEL DISAGREEMENTS IN HOW THE PRECIPITATION WILL LAY OUT ON THE BACK SIDE OF THE SYSTEM GOING INTO SATURDAY NIGHT AND SUNDAY MORNING...IN PART DUE TO SLIGHTLY DIFFERING DEPICTIONS OF THE SURFACE/850MB LOW TRACKS. DEPENDING ON HOW FAR NORTH THE WARM FRONT MOVES...SOME ELEVATED INSTABILITY WILL LIKELY BUILD INTO THE SOUTHERN PORTIONS OF THE FORECAST AREA ON SATURDAY...LEADING TO A CHANCE OF THUNDERSTORMS. THE GFS IS THE MOST AGGRESSIVE WITH THE FRONT...WHILE THE NAM/ECMWF MOSTLY KEEP ANY INSTABILITY EVEN CLOSE TO SURFACE-BASED SOUTH OF THE CWA BORDERS. WITH RAIN OCCURRING (AND COOL EASTERLY FLOW AT THE SURFACE)...TEMPERATURES WILL STRUGGLE TO RISE MUCH ON SATURDAY...AND IF ANYTHING THE GOING FORECAST (HIGH 40S TO HIGH 50S) COULD BE GENEROUS. ANOTHER ELONGATED SURFACE HIGH WILL BEGIN TO MOVE INTO THE OHIO VALLEY BY SUNDAY...WITH COOL NNW FLOW ON THE WEST EDGE OF THE SEEMINGLY-PERPETUAL NORTHEASTERN-STATES UPPER LOW. THOUGH CONDITIONS SUNDAY WILL BE DRY...THIS PATTERN WILL KEEP TEMPERATURES ROUGHLY 5-10 DEGREES BELOW NORMAL TO END THE WEEKEND. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... A LARGE LOW SPINNING OFF THE NEW ENGLAND COAST AT H5 WILL KEEP A COOL AND GENERALLY CLOUDY /AT LEAST IN UPPER LEVELS/ FORECAST IN THE BEGINNING OF NEXT WEEK EVEN THOUGH A SURFACE HIGH NORTH OF THE GREAT LAKES PUSHES COOL AND SOMEWHAT DRIER AIR TO THE REGION OFF OF THE SURFACE. THE SURFACE HIGH AND ASSOCIATED INVERTED RIDGE IN OHIO VALLEY HOLDS SWAY THROUGH THE EARLY PART OF THE WEEK. THIS OCCURS AS A SURFACE LOW TAKES A WAY SOUTHERLY TRACK THROUGH THE GULF STATES FOR THE MIDDLE PART OF NEXT WEEK. THE PATTERN IN OHIO VALLEY AT THE END OF THE FORECAST SHOWS INCREASING MOISTURE FROM THE SOUTHERN SYSTEM TOPPED BY A GENERALLY MUDDLED YET TROUGH-Y PATTERN AT H5. REMOVED TUESDAY SHOWERS AND SAW SOME INDICATION OF SHOWER ACTIVITY LATER WED AND INTO THURS WITH A HIGHER PROBABILITY TO START WITH IN THE EAST. KEPT TEMPERATURES CLOSE TO GUIDANCE WHICH GRADUALLY WARMED UP HIGHS AND OPENED A LARGER DIURNAL WITH SOME DRIER AIR WORKING IN THE EARLY PART OF THE WEEK. IF CLOUD COVER BREAKS FOR A SIGNIFICANT PERIOD OF TIME DURING THE DAY TEMPS WILL BE MUCH TOO COOL...BUT IN THIS PATTERN THEY GENERALLY CU UP NICELY AND LIMIT SUCH WARMUPS TO THE EARLY PART OF THE DAY...FLATTENING THEM OUT IN THE AFTERNOON. && .AVIATION /15Z THURSDAY THROUGH MONDAY/... LARGE SCALE UPPER LEVEL LOW CENTER OVER SOUTHEAST CANADA THIS MORNING WILL ROTATE SOUTHEAST TO A POSITION NEAR THE MAIN/NEW BRUNSWICK MARITIMES BY 12Z FRIDAY. FOR TODAY...ONE MORE DAY OF CYCLONIC LOW LEVEL FLOW ACROSS THE GREAT LAKES WILL BRING SCT TO BKN DIURNALLY DRIVEN CUMULUS CLOUDS. WITH DEEP MIXING EXPECTED...WINDS WILL INCREASE FROM THE WEST/NORTHWEST BETWEEN 15 AND 20 KNOTS WITH GUSTS IN THE 20 TO 30 KNOT RANGE. FOR TONIGHT...AS THE UPPER LEVEL LOW MOVES EAST...A SURFACE RIDGE OF HIGH PRESSURE WILL BUILD INTO THE WESTERN GREAT LAKES AND MIDDLE OHIO VALLEY REGION. SKIES WILL CLEAR THIS EVENING...WINDS WILL DIMINISH...AND WILL LIKELY GO CALM AT MOST TAF SITES BETWEEN 06Z AND 12Z. OUTLOOK...MVFR CEILINGS AND VISIBILITIES LIKELY FRIDAY NIGHT THROUGH SATURDAY NIGHT. IFR CEILINGS POSSIBLE SATURDAY INTO SATURDAY NIGHT. THUNDERSTORMS POSSIBLE SATURDAY. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...FREEZE WARNING FROM 2 AM TO 9 AM EDT FRIDAY FOR OHZ026-034-035- 042>046-051>056-060>065-073-074. FROST ADVISORY FROM 2 AM TO 9 AM EDT FRIDAY FOR OHZ070>072- 077>082-088. KY...FROST ADVISORY FROM 2 AM TO 9 AM EDT FRIDAY FOR KYZ089>100. IN...FREEZE WARNING FROM 2 AM TO 9 AM EDT FRIDAY FOR INZ050-058-059. FROST ADVISORY FROM 2 AM TO 9 AM EDT FRIDAY FOR INZ066-073>075- 080. && $$ SYNOPSIS...HATZOS NEAR TERM... SHORT TERM...HATZOS LONG TERM...FRANKS AVIATION...HICKMAN

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