Area Forecast Discussion
Issued by NWS Wilmington, OH

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553 FXUS61 KILN 141533 AFDILN AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON OH 1033 AM EST SUN FEB 14 2016 .SYNOPSIS... SNOW WILL OCCUR NORTH OF A WARM FRONT THAT WILL APPROACH FROM THE SOUTHWEST TODAY AND LIFT THROUGH THE AREA TONIGHT. AN AREA OF LOW PRESSURE WILL PASS JUST SOUTHEAST OF THE REGION MONDAY AFTERNOON AND NIGHT. ANOTHER LOW PRESSURE SYSTEM WILL CROSS THE AREA TUESDAY AFTERNOON AND EVENING. && .NEAR TERM /THROUGH TONIGHT/... ADJUSTMENTS FOR THE NEAR TERM OF THE FORECAST WERE FOCUSED ON THE SNOW POTENTIAL THIS AFTERNOON...WITH SOME SLIGHT ADJUSTMENTS TO FORECAST NUMBERS REQUIRED. SOME MINOR CHANGES WERE ALSO MADE OVERNIGHT AND GOING INTO MONDAY...BUT THE FORECAST THINKING FOR THE SETUP FROM OVERNIGHT INTO TOMORROW HAS NOT CHANGED MUCH. WATER VAPOR SATELLITE IMAGERY SHOWS A WELL-DEFINED SPIN IN IOWA...ASSOCIATED WITH THE SHORTWAVE THAT IS MOVING TOWARD THE REGION TODAY. AS THIS SHORTWAVE MOVES EAST...FORCING IS BEGINNING TO INCREASE IN THE LOWER OHIO VALLEY...DRIVEN JUST AS MUCH BY FORCING A LITTLE LOWER IN THE ATMOSPHERE. WITH HIGH PRESSURE MOVING EAST OF THE OHIO VALLEY...A SWITCH TO SOUTHERLY FLOW HAS OCCURRED...AND WARM FRONTAL PROCESSES ARE UNDERWAY. CONVERGENCE AND ISENTROPIC ASCENT IS GRADUALLY INCREASING IN STRENGTH AHEAD OF THE INCREASED SOUTHERLY FLOW...AND PRECIPITATION IN ILLINOIS / WESTERN KENTUCKY / EASTERN MISSOURI HAS BECOME WIDESPREAD. ALTHOUGH MODELS ARE IN STRONG AGREEMENT ON THIS OVERALL SETUP...THERE ARE STILL SOME CONFLICTING FACTORS PREVENTING A HIGH-CONFIDENCE FORECAST FOR THE EVENTUAL SNOWFALL NUMBERS. RECENT HIGH-RESOLUTION MODEL RUNS AND SOME OF THE 06Z OPERATIONAL RUNS HAVE DEFINITELY INDICATED A LITTLE STRONGER FORCING THAN PERHAPS PREVIOUSLY INDICATED. CONSEQUENTLY...QPF AMOUNTS (ESPECIALLY OVER THE FAR SOUTHWESTERN CWA) HAVE INCREASED AS WELL. OF COURSE...QPF SHOULD ONLY BE USED AS ONE FACTOR IN THE FORECAST PROCESS...AND NEEDS TO BE SCRUTINIZED. THE LOCATION AND STRENGTH OF THE FORCING AND MOISTURE ARE OF GREATER CONCERN TO LOOK INTO. FOR EXAMPLE...BOTH THE RECENT HRRR AND RAP RUNS HAVE AROUND A TENTH OF AN INCH OF LIQUID EQUIVALENT IN THE SOUTHWESTERN ILN COUNTIES BEFORE 18Z...VALUES THAT ARE SIMPLY NOT OCCURRING RIGHT NOW (WITH JUST ONE OR TWO REPORTS OF SOME LIGHT SNOW FROM THE MOSTLY-VIRGA ECHOES CURRENTLY MOVING THROUGH CENTRAL AND EASTERN KENTUCKY). FURTHERMORE...SNOW RATIOS MUST BE CONSIDERED THROUGH THE DEPTH OF THE THERMAL PROFILE...AND CANNOT BE BASED SOLELY ON SURFACE TEMPERATURES. IN FACT...IT IS THE STRENGTH OF THE WARMING ALOFT (LEADING TO THE ISENTROPIC ASCENT) THAT WILL HELP LIMIT SNOW RATIOS...BY DEVELOPING A DEEP ISOTHERMAL LAYER OF ROUGHLY -8C TO -10C FROM THE SURFACE THROUGH 700MB. THIS IS NOT ESPECIALLY FAVORABLE FOR EFFICIENT SNOW PRODUCTION...AND WILL LIKELY KEEP RATIOS AT OR BELOW 15:1. HOWEVER...THERE WILL BE A PERIOD WHERE THE CONTRIBUTION OF FORCING FROM THE SHORTWAVE ALLOWS FOR ASCENT THROUGH AN EVEN DEEPER LAYER...PERHAPS ALLOWING FOR A PERIOD OF AN HOUR OR TWO WITH SOME HEAVIER SNOW RATES. WITH ALL THE FACTORS CONSIDERED TOGETHER...SNOW NUMBERS WERE INCREASED BY ABOUT A HALF INCH THROUGH THE CENTER OF THE ILN FORECAST AREA...AND BY ALMOST AN INCH IN THE FAR SOUTH AND SOUTHWEST. THE WSW PRODUCT WAS BROKEN OUT INTO TWO GROUPS TO ALLOW FOR A 2-3 INCH FORECAST AND A 3-4 INCH FORECAST. THE FORECAST THINKING DID NOT CHANGE MUCH WITH REGARDS TO THE POTENTIAL FOR FREEZING DRIZZLE EARLY MONDAY MORNING. ONCE THE DEEP-LAYER MOISTURE HAS DEPARTED...AND SATURATION IS LIMITED TO BELOW -10C...ICE CRYSTALS ARE UNLIKELY TO BE INTRODUCED INTO THE ATMOSPHERE. THOUGH STRONG FORCING WILL ALSO BE DEPARTED...WEAK ISENTROPIC ASCENT WILL CONTINUE IN THE LOW-LEVELS...ALLOWING FOR THE POTENTIAL FOR FREEZING DRIZZLE. THOUGH TEMPERATURES WILL BE RISING GOING INTO MONDAY MORNING...THE COLD GROUND CONDITIONS WILL BE VERY SLUGGISH IN THEIR RESPONSE...WITH SOME POTENTIAL FOR LIGHT DEPOSITION OF ICE IF DRIZZLE IS ABLE TO DEVELOP. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... SHORT WAVE TRACKING OUT OF THE SOUTHERN PLAINS WILL HEAD INTO THE CENTRAL APPALACHIANS MONDAY INTO MONDAY NIGHT. GUIDANCE IS COMING INTO PRETTY GOOD AGREEMENT THAT THE ASSOCIATED SURFACE LOW WILL MOVE FROM MIDDLE TENNESSEE INTO EASTERN KENTUCKY AND THEN WEST VIRGINIA. SHIELD OF PRECIPITATION NORTH OF THE LOW WILL SPREAD INTO THE SOUTHERN AND EASTERN ZONES MONDAY AFTERNOON THROUGH MONDAY NIGHT. WARMER TEMPERATURES SHOULD RESULT IN MUCH OF THE PRECIPITATION WILL BE IN THE FORM OF RAIN EXCEPT PERHAPS ON THE NORTHWEST EDGE. A NARROW SURFACE RIDGE WILL MOVE ACROSS THE REGION TUESDAY MORNING PROVIDING A BRIEF RESPITE FROM PRECIPITATION. BUT THEN A WELL DEVELOPED CLIPPER WILL MOVE ACROSS THE AREA TUESDAY AFTERNOON AND NIGHT. 00Z NAM AND GFS ARE IN EXCELLENT AGREEMENT BUT WITH THE ECMWF BEING A BIT SLOWER THERE IS SOME TIMING UNCERTAINTY. CURRENTLY APPEARS THAT THIS WILL BRING SNOW IN THE NORTHERN PART OF THE FORECAST AREA WITH RAIN OR SNOW IN THE SOUTH DEPENDING ON THE LOW LEVEL TEMPERATURES. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... ON WEDNESDAY...WILL GO WITH A DRY FORECAST...ALTHOUGH CONSIDERABLE CAA STRATOCUMULUS IS EXPECTED. FOR WEDNESDAY NIGHT INTO THURSDAY...HIGH PRESSURE WILL BUILD SOUTH INTO THE OHIO VALLEY. SKIES ARE EXPECTED TO BECOME PARTLY CLOUDY. MODELS DIFFERENT ON THE EXTENT OF COLD AIR FILTERING IN THE REGION...SO HAVE SIDED WITH A WPC BLENDED APPROACH. AS THE HIGH MOVES EAST THURSDAY NIGHT...A WARM FRONT IS FORECAST TO APPROACH FROM THE WEST. WE SHOULD SEE AN INCREASE IN WAA INDUCED CLOUDS. AS OF NOW...ANY PCPN GENERATED WITH THE WARM FRONT IS EXPECTED TO STAY NORTHWEST OF THE AREA. OVERNIGHT LOWS WILL BE EARLY FOLLOWED BY SLOWLY RISING TEMPERATURES AS WINDS INCREASE FROM THE SOUTH. FOR FRIDAY INTO FRIDAY NIGHT...LOW PRESSURE WILL TRAVERSE THE GREAT LAKES AS A COLD FRONT PUSHES IN FROM THE NORTHWEST. MODELS VARY ON HOW MUCH MOISTURE WILL BE PULLED NORTHWARD ALONG AND AHEAD OF THE FRONT SYSTEM...ALONG WITH THE TIMING...SO HAVE GONE WITH A CHANCE OF RAIN. FRIDAY CERTAINLY LOOKS TO BE THE WARMEST DAY OF THE EXTENDED WITH TEMPERATURES RISING INTO THE 50S AREA WIDE. ON SATURDAY...FRONT EXITS TO THE EAST...BUT CAA STRATOCUMULUS MOVES INTO THE REGION. PCPN WILL MOVE EAST AS WELL. TEMPERATURES WILL COOL INTO THE MID 40S TO LOWER 50S FOR HIGHS. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/... VFR AND DRY CONDITIONS WILL START OUT THE TAF PERIOD. ALTHOUGH A FEW FLURRIES CANNOT BE RULED OUT AT KCVG THIS MORNING MOST OF THE SNOW WILL MOVE INTO THE TAF SITES THIS AFTERNOON INTO TONIGHT. CIGS WILL LOWER AND VSBYS WILL BE REDUCED WITH THE SNOWFALL. THE DEEPER MOISTURE WILL MOVE OUT TONIGHT. THERE IS SOME QUESTION AS TO WHETHER ICE WILL BE IN THE CLOUDS OVERNIGHT TONIGHT INTO EARLY MONDAY MORNING. WHETHER OR NOT THERE IS OR NOT WILL DETERMINE WHETHER OR NOT LIGHT SNOW WILL CONTINUE OVERNIGHT TONIGHT OR WHETHER FREEZING DRIZZLE WILL BE PRESENT. THERE ARE ENOUGH INDICATIONS TO SUGGEST THAT SNOW WILL TRANSITION TO FREEZING DRIZZLE AND THEREFORE HAVE FREEZING DRIZZLE IN TOWARDS THE END OF THE TAF PERIOD. CIGS WILL BE LOWER IN THE IFR CATEGORY DURING THIS TIME AND POTENTIALLY EVEN LIFR. OUTLOOK...MVFR/IFR CONDITIONS ARE POSSIBLE WITH PRECIPITATION FROM MONDAY THROUGH TUESDAY NIGHT. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...WINTER WEATHER ADVISORY UNTIL 10 AM EST MONDAY FOR OHZ063>065- 070>074-077>082-088. KY...WINTER WEATHER ADVISORY UNTIL 10 AM EST MONDAY FOR KYZ089>100. IN...WINTER WEATHER ADVISORY UNTIL 10 AM EST MONDAY FOR INZ066- 073>075-080. && $$ SYNOPSIS... NEAR TERM...HATZOS SHORT TERM... LONG TERM...HICKMAN AVIATION...NOVAK

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