Area Forecast Discussion
Issued by NWS Northern Indiana

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000 FXUS63 KIWX 011755 AFDIWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NORTHERN INDIANA 1255 PM EST SUN MAR 1 2015 .SYNOPSIS... ISSUED AT 1254 PM EST SUN MAR 1 2015 SNOW WILL TAPER OFF THIS AFTERNOON ACROSS THE AREA WITH CLEARING SKIES ARRIVING TONIGHT AS HIGH PRESSURE MOVES INTO THE REGION. HIGHS TODAY AND MONDAY WILL BE IN THE UPPER 20S. LOWS TONIGHT WILL BE AROUND 15 DEGREES. && .UPDATE... ISSUED AT 1241 PM EST SUN MAR 1 2015 FORECAST STILL ON TRACK WITH NO ADDITIONAL HEADLINES PLANNED AS RADAR TRENDS SUGGEST SNOW FALL MAY BE STARTING TO WIND DOWN OVER THE NEXT SEVERAL HOURS FROM WEST TO EAST. RADAR TRENDS SHOWING A FEW BANDS OF MODERATE SNOWFALL ACROSS NORTHERN INDIANA INTO NW OHIO. THUS FAR...HEAVIEST SNOW HAS REMAINED NORTH OF AREAS IMPACTED EARLIER TODAY WITH AN ADDITIONAL INCH OR SO SINCE THE LAST UPDATE. ONE OF THE BANDS SITTING OVER THE OFFICE HAS PRODUCED SOME NICE DENDRITES AND DROPS VSBYS TO AROUND A HALF MILE AT TIMES. OUTSIDE OF THE HEAVIER SNOW SHOWERS...SOME THIN SPOTS IN THE CLOUDS HAVE ALLOWED THE SUN TO PEAK OUT...INDICATING THAT MOISTURE WAS BEGINNING TO WANE SOMEWHAT (TEMP NOW 25). TRENDS IN GRIDS REFLECT THIS ALREADY SO SHOULD BE IN GOOD SHAPE. COORDINATED WITH KCLE ON ADVISORIES BEING EXPANDED NORTH. WITH TRENDS SHOWING THE RAPID DECREASE AND TEMPERATURES WARMING...WILL HOLD OFF ON ANY HEADLINES AND ISSUE GENERIC SPS FOR THE AREA TO COVER THE HEAVIER SNOW SHOWERS. && .SHORT TERM...(TODAY AND TONIGHT) ISSUED AT 443 AM EST SUN MAR 1 2015 SEVERAL FACTORS COMING TOGETHER FOR ACCUMULATING SNOW WITH THE POTENTIAL FOR EVENT SNOWFALL TOTALS TO EXCEED 6 INCHES BY THIS EVENING. FAVOR THE GFS WHICH HAS BEEN CONSISTENT WITH THIS SYSTEM AND APPEARS TO HAVE A BETTER HANDLE THAN THE NAM WITH THE MID AND UPPER LEVEL MOISTURE FIELDS ASSOCIATED WITH THIS SYSTEM AND ALSO THE DRY SLOT MOVING INTO THE AREA. AN UPPER LEVEL TROF WILL MOVE EAST AND WILL BE ABLE TO TAP SOME MID LEVEL MOISTURE AS ISENTROPIC LIFT PERSISTS ON THE 290K SURFACE. ALSO... MESO BANDING IS POSSIBLE GIVEN FAVORABLE EQUIVALENT POTENTIAL VORTICITY OVER AN AREA OF FRONTOGENESIS...MAINLY SOUTH OF HIGHWAY 30. IN ADDITION TO THIS...THE DENDRITIC GROWTH ZONE IS IN THE CLOUD LAYER. OVERNIGHT SNOW RATIOS TO LIQUID HAVE BEEN AROUND 14 TO 1. EXPECT THE HEAVIEST SNOW WHERE THE ABOVE FACTORS COME TOGETHER BEST ON THE SOUTHEAST FRINGE OF THE FORECAST AREA FROM MARION TO PORTLAND TO LIMA. ANTICIPATE EVENT TOTAL SNOWFALL IN THIS AREA AROUND 7 INCHES... WITH LESSER AMOUNTS FARTHER NORTH. GIVEN THE RELATIVELY LONG DURATION OF THIS EVENT WITH MAINLY LIGHT SNOW WITHOUT BLOWING AND DRIFTING SNOW...HAVE DECIDED NOT TO UPGRADE TO A WINTER STORM WARNING. && .LONG TERM...(MONDAY THROUGH SATURDAY) ISSUED AT 443 AM EST SUN MAR 1 2015 INTENSE FOCUS CONTINUES ON STRONG STORM SYSTEM MONDAY NIGHT THROUGH TUE NIGHT WITH PRECIPITATION TYPE REMAINING THE BIGGEST CONCERN AND QUESTION. OVERALL MODELS IN AGREEMENT SYNOPTICALLY BUT AS IS ALWAYS THE CASE...IMPORTANT THERMODYNAMIC DETAILS VARY SIGNIFICANTLY AMONG THE MODELS AND THERE REMAINS NO CLEAR ANSWER. WATER VAPOR SHOWS UPPER LEVEL LOW DROPPING SOUTH ALONG CA COAST THIS MORNING AS EXPECTED. WEST SOUTHWEST FLOW ALOFT CONTINUES FROM SOUTHWEST CONUS INTO THE MIDWEST. LEADING NOSE OF SUBTROPICAL MOISTURE PLUME ORIGINATING OVER SOUTH CENTRAL PACIFIC ALREADY RACING NORTHEAST INTO WEST TEXAS THIS MORNING. THIS DEEP MOISTURE PLUME STILL EXPECTED TO BE TAPPED BY EJECTING LOW MONDAY AND WILL SPREAD INTO OUR AREA BY TUESDAY. THE CHALLENGE WITH THIS FORECAST CONTINUES TO BE FOCUSED ON PCPN TYPE TUESDAY MORNING. MODELS HAVE TRENDED COOLER...ESPECIALLY LATE MONDAY NIGHT WHERE THERMAL PROFILES SUGGEST ALL SNOW INITIALLY. LATEST RUNS HAVE ALSO BROUGHT LIGHT QPF BACK INTO WESTERN AREAS AFTER 09Z. EXPECT ANY PCPN THAT DOES FALL PRIOR TO 12Z TO BE LIGHT SNOW. OF REAL CONCERN IS THE TREND IN LATEST ECMWF AND NAM12 WITH COOLER SFC TEMPS TUESDAY. BOTH MODELS MASS 2M TEMP FIELDS NOW BARELY BRING THE 32F ISOTHERM INTO THE SOUTHWEST THIRD OF AREA BY 18Z BUT THEN QUICKLY WARM TEMPS INTO MID TO UPPER 30S BETWEEN 18 AND 00Z. GFS REMAINS MUCH FASTER WITH WARMING AS IT HAS ALL AREAS GENERALLY ABOVE 32F BY 18Z. AS WE HAVE BEEN DISCUSSING...THE DEEP SNOWPACK AND RETREATING HIGH PRESSURE SHOULD HELP KEEP A COLD WEDGE NEAR THE SURFACE TUE MORNING UNTIL THE STRONGER WARMER AIR ADVECTION ALOFT OVERWHELMS LOWER LEVELS IN AFTERNOON. ECMWF HAS SHOWN GOOD VERIFICATION SCORES RECENTLY WITH RESPECT TO MAX AND MIN TEMPS AND NAM12 SHOULD HAVE A BETTER HANDLE ON THE LOWER LEVELS COMPARED TO GFS DESPITE ITS RECENT UPGRADES. HAVE USED OUR POWT PROCEDURES TO GENERATE PCPN TYPE WEATHER GRIDS FOR TUE. UNFORTUNATELY WE ARE NOT ABLE TO INGEST MAXT ALOFT FROM ECMWF SO HAD TO USE NAM12 FOR THIS WITH MANUAL ADJUSTMENT TOWARD EXPECTED ECMWF TEMPS. RESULT IS AS EXPECTED WITH MOST AREAS SEEING SNOW INITIALLY TUE MORNING BUT QUICKLY TRANSITIONING TO A FEW HOURS OF FREEZING RAIN AND SLEET BEFORE FINALLY CHANGING TO ALL RAIN IN AFTERNOON. THIS RESULTS IN A FEW INCHES OF SNOW CENTRAL AND NORTH FOLLOWED BY FREEZING RAIN WITH ICE ACCUMULATIONS BETWEEN ONE AND TWO TENTHS DEPENDING ON AMOUNT OF TIME BELOW FREEZING. A REAL MESSY SITUATION CERTAINLY APPEARS ON TRACK FOR MOST AREAS WITH SNOW...ICE THEN RAIN...TRANSITIONING FROM SOUTH TO NORTH. MORE THAN LIKELY WE ARE LOOKING AT AN ADVISORY LEVEL SITUATION AT THIS TIME. HOWEVER...IF SFC TEMPS DO NOT WARM ABOVE FREEZING UNTIL LATER IN DAY...MORE ICE WOULD BE POSSIBLE AND COULD SEE SOME AREAS FLIRT WITH ICE STORM WARNING CRITERIA OF A QUARTER INCH. HOPEFULLY MODEL THERMAL FIELDS WILL COME INTO BETTER ALIGNMENT OVER NEXT 24 TO 36 HOURS. THE HEAVY RAIN POTENTIAL IS QUICKLY DIMINISHING AS MODEL QPF HAS DECREASED SUBSTANTIALLY LAST SEVERAL RUNS. HOWEVER...STILL LOOKS LIKE A HALF INCH TO POSSIBLY THREE QUARTERS OF AN INCH OF PCPN COULD FALL. DEEPER SNOWPACK MAY ACTUALLY ABSORB A LOT OF THIS AND DELAY RUNOFF. THIS VERY DIFFICULT TO DETERMINE AND WILL STILL MENTION LOCAL FLOODING POSSIBILITY IN HWO WITH ICE JAM POTENTIAL AND SNOW PACKED STORM DRAINS POSSIBLY INHIBITING PROPER DRAINAGE. REMAINDER OF FORECAST GENERALLY FOLLOWS SUPERBLEND AS LOADED. TURNING VERY COLD AGAIN BEHIND THIS SYSTEM MID WEEK WITH HIGHS IN TEENS AND LOWS AROUND ZERO. && .AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON) ISSUED AT 1241 PM EST SUN MAR 1 2015 VSBYS AT BOTH SITES HAVE BEEN HOVERING IN THE 1 TO 2 SM RANGE WITH KSBN AS LOW AS 3/4SM. CIGS HAVE GENERALLY BEEN AROUND 2000 FT. RADAR TRENDS SHOW OVERALL SPEED OF SNOW SHOWERS IS MOVING AT A DECENT CLIP WITH SIGNS OF SNOW BEGINNING TO TAPER OFF IN EASTERN ILLINOIS. HAVE ENDED SNOW A TOUCH FASTER AT BOTH SITES WITH MVFR CIGS TO PERSIST INTO EARLY EVENING BEFORE CLEARING RAPIDLY ARRIVES WITH VFR CONDITIONS THE REST OF THE PERIOD. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR INZ022>027-032>034. MI...NONE. OH...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR OHZ016- 024-025. LM...NONE. && $$ UPDATE...FISHER SYNOPSIS...SKIPPER SHORT TERM...SKIPPER LONG TERM...LASHLEY AVIATION...FISHER VISIT US AT WWW.WEATHER.GOV/IWX (ALL LOWER CASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSNORTHERNINDIANA WWW.TWITTER.COM/NWSIWX WWW.YOUTUBE.COM/NWSNORTHERNINDIANA

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