Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 012217 AFDILN AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON OH 517 PM EST SUN MAR 1 2015 .SYNOPSIS... SNOW WILL END ACROSS THE MIDDLE OHIO VALLEY THIS EVENING...AS HIGH PRESSURE BUILDS IN FROM THE WEST...PROVIDING DRY CONDITIONS FOR MONDAY. A STRONG AREA OF LOW PRESSURE WILL MOVE NORTH OF THE REGION ON TUESDAY THROUGH TUESDAY NIGHT. THIS WILL BRING A MIX OF SNOW AND FREEZING RAIN...TURNING TO RAIN DURING THE AFTERNOON. ADDITIONAL RAIN AND SNOW MAY PERSIST THROUGH WEDNESDAY NIGHT. DRY HIGH PRESSURE WILL MOVE INTO THE REGION FOR THE END OF THE WEEK. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... WITH THE EASTWARD-PROGRESSING BAND OF SNOW NOW MOVING OUT OF THE AREA...ALL HEADLINES HAVE BEEN CANCELLED. ANOTHER BATCH OF SNOW OVER SOUTHERN INDIANA WILL LIKELY WORK ITS WAY INTO THE SOUTHERN THIRD OF THE ILN FORECAST AREA IN THE NEXT FEW HOURS...PRODUCING LIGHT ACCUMULATIONS AS TEMPERATURES SLOWLY BEGIN TO FALL. PREVIOUS DISCUSSION > SNOW IS NOT QUITE DONE ACROSS THE REGION THIS AFTERNOON...WITH ANOTHER FAIRLY HEALTHY BAND MOVING INTO WEST CENTRAL OHIO AS OF 245 PM. ALTHOUGH THE SOUTHERN TIER OF ADVISORIES WAS SET TO EXPIRE AT 300 PM...THIS WAS EXTENDED FOR A FEW HOURS...JUST TO KEEP IT UP WHILE SNOW FOR THE EVENT HAS NOT YET ENDED. ADDITIONAL ACCUMULATIONS ARE GOING TO BE UNDER AN INCH (PROBABLY WELL UNDER AN INCH IN MOST LOCATIONS). ONE OR TWO MORE WEAK BANDS OF SNOW MAY FORM THIS EVENING...AS INDICATED BY HIGH-RESOLUTION MODELS (AND SEEMING TO BE RIDING ON THE ELEVATED THETA-E GRADIENT ON THE LEADING EDGE OF THE COLDER AIR). SOME CATEGORICAL POPS WERE MAINTAINED THROUGH 8PM...WITH A GRADUAL NW-TO-SE TAPERING OFF OF LIGHT SNOW CHANCES AFTER THAT. COLD ADVECTION BEHIND THE SURFACE FRONT IS ALREADY BEGINNING IN THE NORTHWESTERN CWA...AND AS THIS FRONT SHIFTS SOUTHEAST THROUGH THE REGION TONIGHT...SUB-FREEZING TEMPS WILL QUICKLY SPREAD ACROSS THE ENTIRE FORECAST AREA. WITH FRESH SNOW AND SOME CLEARING EXPECTED IN THE NORTHWEST CWA...MIN TEMPS WERE LOWERED INTO THE MIDDLE TEENS...AND VALUES A LITTLE BELOW THESE APPEAR TO BE A POSSIBILITY. MIN TEMPERATURES RANGE FROM THERE INTO THE UPPER 20S FOR THE SOUTHEASTERN CORNER OF THE FORECAST AREA. && .SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/... RELATIVELY QUIET CONDITIONS ARE EXPECTED ON MONDAY...AS AN AREA OF HIGH PRESSURE MOVES IN FROM THE WEST. THIS HIGH WILL NOT BE IN PLACE FOR LONG...WITH ITS CENTER FORECAST TO BE OVER OHIO ON MONDAY EVENING...AND CLEAR OF THE AREA QUICKLY THEREAFTER. THIS SHOULD ALLOW FOR MORE SUN THAN CLOUDS ON MONDAY...THOUGH SOME LOW-LEVEL CLOUDS WILL STILL BE SCOURING OUT IN THE EASTERN CWA DURING THE MORNING...AND SOME HIGH CLOUDS IN ADVANCE OF THE NEXT SYSTEM WILL ALREADY BE MOVING IN BY AFTERNOON. TEMPERATURES WILL GET TO NEAR OR JUST ABOVE THE FREEZING MARK IN THE SOUTHERN THIRD OF THE CWA...WITH COOLER VALUES FURTHER NORTH (WITH FRESH SNOW ON THE GROUND). GFS RAW MODEL TEMPS (ESPECIALLY AT 00Z) APPEAR TO BE SIGNIFICANTLY TOO COOL...AND WERE NOT USED. AS HIGH PRESSURE MOVES AWAY ON MONDAY EVENING...ATTENTION WILL TURN TO A MULTI-FACETED INCOMING WEATHER SYSTEM...WHICH WILL AFFECT THE REGION THROUGH MUCH OF TUESDAY AND INTO WEDNESDAY. FLOW ON THE BACK SIDE OF THE HIGH WILL SWITCH TO SOUTHEASTERLY AT THE SURFACE...AND SOUTHWESTERLY ALOFT. WEAK RIDGING OVER THE OHIO VALLEY AND SOUTHEASTERN STATES WILL GIVE WAY TO A DEVELOPING TROUGH IN THE PLAINS...SETTING UP A FAVORABLE AND DEEP PATH FOR MOISTURE TRANSPORT OUT OF THE GULF OF MEXICO. THERE IS HIGH CONFIDENCE IN A SIGNIFICANT WARMING OCCURRING ALOFT BETWEEN 00Z TUESDAY (MONDAY EVENING) AND 18Z TUESDAY (TUESDAY AFTERNOON). HOWEVER...A SHALLOW LAYER OF ARCTIC AIR (INFLUENCED BY SNOW COVER) WILL BE SLOW TO RETREAT...LEADING TO A SURFACE TEMPERATURE FORECAST THAT INCREASES ONLY SLOWLY EARLY TUESDAY MORNING. ISENTROPICALLY-DRIVEN PRECIPITATION WILL DEVELOP AND MOVE INTO THE ILN CWA AS EARLY AS 06Z...THOUGH CONVERGENCE AHEAD OF THE STRENGTHENING LOW-LEVEL JET WILL BE MAXIMIZED BETWEEN 12Z AND 21Z. THE STRENGTH OF THE WARM LAYER WILL BE SUCH THAT...OUTSIDE OF A VERY BRIEF PERIOD OF POSSIBLE SLEET NEAR THE ONSET OF PRECIPITATION...FREEZING RAIN WILL BE THE FAVORED PRECIPITATION TYPE FOR A PERIOD OF SEVERAL HOURS. AS AN EXAMPLE...A GFS BUFKIT SOUNDING FOR KDAY AT 15Z TUESDAY HAS A SURFACE TEMPERATURE OF -2...WITH A SATURATED WARM LAYER 5000 FEET THICK (AND MAXING OUT AT +5). THUS...THE USE OF FREEZING RAIN IN THE WEATHER GRIDS WAS SIGNIFICANTLY INCREASED...WITH HIGH-END POPS (70 TO 100 PERCENT) TO MATCH THE CONFIDENCE. WHILE THIS PRECIPITATION MAY BE MORE SHOWERY IN NATURE THAN PURELY STRATIFORM...LIQUID AMOUNTS ARE LIKELY TO BE ONE TO TWO TENTHS OF AN INCH THROUGH 18Z. THE END RESULT FOR AN ICE FORECAST IS THAT THE ENTIRE CWA WILL BE LIKELY TO GET A LIGHT GLAZE OF A FEW HUNDREDTHS...WHILE THE NORTHWESTERN HALF OF THE CWA WILL HAVE THE GREATEST POTENTIAL FOR HIGHER ACCUMULATIONS...PERHAPS A TENTH OR SLIGHTLY HIGHER. HOWEVER...WARNING CRITERIA ICE LOOKS VERY UNLIKELY. FURTHER COMPLICATING MATTERS...THE FAR NORTHERN SECTIONS OF THE CWA MAY GET INTO THE PRECIPITATION BEFORE THE WARM LAYER ARRIVES...ALLOWING FOR A FEW HOURS OF LIGHT SNOW. ACCUMULATIONS DO NOT APPEAR LIKELY TO EXCEED AN INCH. THE FREEZING RAIN THREAT WILL END FROM SOUTH TO NORTH AS SURFACE TEMPERATURES EVENTUALLY BEGIN A QUICK RISE...AS THE WARM FRONT MOVES NORTH THROUGH THE FORECAST AREA. AS THIS OCCURS...THE AXIS OF HEAVIEST PRECIPITATION WILL SET UP ACROSS THE CWA ON A SW-TO-NE ORIENTATION. THIS AXIS WILL SHIFT SOUTHEAST WITH TIME...AS A COLD FRONT ADVANCES FROM THE NORTHWEST...AND PUSHING THE HEAVIEST PRECIPITATION SOUTHEAST OF THE CWA BY EARLY WEDNESDAY MORNING. AS THIS OCCURS...TEMPERATURES MAY BECOME COLD ENOUGH FOR A MIX WITH SNOW AT THE SAME TIME. HOWEVER...THERE IS A LOT MORE SPREAD IN THE MODELS AT THE END OF THE EVOLUTION OF THIS WEATHER SYSTEM THAN AT THE BEGINNING...SO THE TIMING OF THIS TRANSITION IS UNCLEAR. IF THERE IS GOING TO BE ANY POTENTIAL FOR CONVECTIVE SHOWERS WITH THIS SYSTEM...IT APPEARS TO BE IN THE SOUTHEASTERN CWA ON TUESDAY EVENING. ELEVATED THUNDERSTORMS APPEAR TO BE A FAIRLY LOW PROBABILITY...THOUGH NOT IMPOSSIBLE TO OCCUR. NEAR-SURFACE THERMODYNAMICS LOOK RATHER UNFAVORABLE FOR ANY WIND POTENTIAL DURING THE SAME TIME PERIOD...BUT A STRONGER SOUTHERLY PUSH OF WARM AIR COULD CHANGE THAT. SOME PERIODS OF HEAVY RAIN MAY BE POSSIBLE...AS PRECIPITABLE WATER VALUES EASILY CLIMB OVER AN INCH. AS HAS BEEN COVERED IN PREVIOUS DISCUSSIONS...THE COMBINATION OF WARMING TEMPERATURES / SNOW MELT / RAINFALL WILL LEAD TO A POTENTIAL FOR FLOODING DURING THE MIDDLE OF THE WEEK. RAINFALL FORECAST AMOUNTS BY THEMSELVES ARE NOT OVERLY CONCERNING RIGHT NOW (AN INCH OR TWO OVER A PERIOD OF 24 HOURS)...BUT THE SNOW COMPLICATES MATTERS IN THIS CASE. THE HEAVIEST RAIN IS EXPECTED TO FALL OVER THE SOUTHERN AND SOUTHEASTERN SECTIONS OF THE CWA. TEMPS WILL HIT THEIR HIGHEST VALUES FOR THE ENTIRE WEEK ON TUESDAY EVENING...BEFORE COLD AIR BEGINS MOVING IN AHEAD OF THE FRONT. CONFIDENCE IN THE EXACT TEMPERATURE VALUES IS NOT VERY HIGH...SINCE THIS IS A NON-DIURNAL SCENARIO DRIVEN BY STRONG ADVECTION...AND A STRONG GRADIENT WILL EXIST ACROSS THE CWA. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... MODELS CONTINUE TO STRUGGLE AS TO HOW FAST PCPN WILL EXIT OUR AREA ON WEDNESDAY...OR WHETHER IT WILL REDEVELOP WELL NORTH OF SOUTHEASTWARD MOVING COLD FRONTAL BOUNDARY. THE GFS IS THE OUTLIER IN THAT IT PUSHES PCPN THROUGH THE REMAINDER OF THE REGION DURING THE MORNING. THIS SEEMS TO BE DRIVEN BY ITS SOLUTION OF PUSHING A BROAD MID LEVEL TROUGH THROUGH THE REGION QUICKER. THIS SOLUTION ALSO RESULTS IN FASTER CAA INTO THE REGION. THE OTHER OPERATIONAL MODELS...NAM...CMC AND ECMWF INDICATE A SLOWER MID LEVEL TROUGH PROPAGATION. THE NAM LOOKS STRANGE AT THE SFC...SO HAVE TAKEN A BLEND OF THE CMC/ECMWF SOLUTION. THIS SOLUTION ALLOWS FOR REDEVELOPMENT OF PCPN NORTH OF THE FRONTAL BOUNDARY INTO OUR REGION. THE REDEVELOPMENT SEEMS TO BE MAINLY DRIVEN BY UPPER LEVEL JET DYNAMICS RESULTING IN AN ANAFRONT CONFIGURATION. WILL KEEP POPS GOING ON WEDNESDAY WITH LIKELY OR HIGHER FCST FOR POINTS MAINLY SOUTH OF I-70. PCPN SHOULD TRANSITION TO SNOW THROUGH THE DAY AS CAA CONTINUES. HOWEVER...THERE COULD BE SOME MIXED PCPN EARLY ON IF CAA IS FASTER AT THE SFC THAN WARMER AIR ALOFT. PCPN SHOULD GRADUALLY EXIT THE REGION WEDNESDAY NIGHT AS MORE ARCTIC AIR FILTERS IN FROM THE NORTHWEST. THE REMAINDER OF THE EXTENDED SHOULD BE RELATIVELY QUIET CONSIDERING THE RECENT ACTIVE WEATHER. ARCTIC HIGH PRESSURE WILL BUILD INTO THE REGION ON THURSDAY...MOVING EAST OF THE AREA THURSDAY NIGHT. WELL BELOW NORMAL TEMPERATURES ARE FORECAST WITH HIGHS IN THE TEENS AND 20S ON THURSDAY...FOLLOWED BY SINGLE DIGIT LOWS THURSDAY NIGHT. NORMAL HIGHS ARE IN THE MID AND UPPER 40S AND NORMAL LOWS ARE IN THE UPPER 20S TO THE LOWER 30S. FOR FRIDAY INTO SUNDAY...AN UPPER LEVEL SPLIT FLOW PATTERN WILL DEVELOP OVER THE CONUS AND SRN CANADA WITH NORTHWESTERLY FLOW PERSISTING INTO THE GREAT LAKES. THE GOOD NEWS IS THAT ANY FRONTAL SYSTEMS WILL BE WEAK WITH A MODIFICATION OF THE AIRMASS EXPECTED. A WEAK FRONT IS FORECAST TO SHEAR OUT ACROSS THE GREAT LAKES FRIDAY NIGHT INTO SATURDAY...FOLLOWED BY MORE HIGH PRESSURE ON SUNDAY. && .AVIATION /22Z SUNDAY THROUGH FRIDAY/... TRIED TO BE OPTIMISTIC WITH THE SNOW AND SLEET/ZR MIX THIS AFTERNOON AND EARLY EVENING...ENDING MOST TAF SITES BY 23Z AND KEEPING MVFR CIGS THROUGH DAYBREAK. H8 DRY PUNCH MAY BE ENOUGH TO ERODE THE CLOUD DECK UNDERNEATH IT TOMORROW BUT I KEPT A CIG AT CMH/LCK WHERE THE COLD POOL OF AIR AT THIS LEVEL WILL REMAIN IN A GENERAL CAA PATTERN. REMAINING TAF SITES WILL SEE SOME GENTLE INCREASE IN H8 TEMPS AS A RIDGE BUILDS OVER THE MIDWEST AND NOSES INTO THE OHIO VALLEY IN THE AFTERNOON. AM NOT OVERLY CONVINCED THAT THE CIG AT CMH WILL REMAIN A MVFR CIG BUT ON THE FLIP SIDE OF THE COIN AM CONCERNED THAT THE CLOUD DECK AT REMAINING SITES MAY BE MORE PREVALENT THAN IS IN THE FCST. MADE THE CIG TOMORROW A TEMPO GROUP VERSUS PREVAILING ATTM. OUTLOOK...MVFR/IFR CEILINGS AND VISIBILITIES ARE POSSIBLE TUESDAY INTO WEDNESDAY WITH RAIN AND SNOW. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...NONE. KY...NONE. IN...NONE. && $$ SYNOPSIS...HATZOS NEAR TERM...HATZOS SHORT TERM...HATZOS LONG TERM...HICKMAN AVIATION...FRANKS

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