229 FXUS63 KLOT 151159 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 659 AM CDT FRI MAR 15 2013 .DISCUSSION... 256 AM CDT PLENTY OF FORECAST CHALLENGES THIS MORNING INCLUDING TEMPS TODAY...PRECIP CHANCES/TYPES TODAY/TONIGHT AND THEN POTENTIAL LATE WEEKEND SYSTEM AND ASSOCIATED PRECIP AMOUNTS/CHANCES/TYPES. SOUTHERLY WINDS...HIGHER DEWPOINTS...AND INCREASING HIGH CLOUDINESS HELPING HOLD TEMPS UP A BIT EARLY THIS MORNING. WEAK COLD FRONT OVER NORTHERN WISCONSIN IS DROPPING SOUTH TOWARD THE REGION WITH FRONT LIKELY TO ACCELERATE DOWN THE LAKE THIS MORNING AS IT GETS A THERMAL BOOST FROM THE CHILLY LAKE. AHEAD OF THE BACK DOOR FRONT COMING DOWN OFF THE LAKE EXPECT TEMPS TO WARM RATHER NICELY THIS MORNING GIVEN THE MILD START TO THE DAY AND SOME FILTERED SUNSHINE. TEMPS YESTERDAY IN THE WARM SECTOR OVER SOUTHERN IA/NORTHERN MO EXCEEDED GUIDANCE BY A GOOD 5-10F IN MANY AREAS AND ANTICIPATE THAT WE TOO WILL EXCEED GUIDANCE TODAY...THOUGH PROBABLY BY NOT AS MUCH. HAVE BUMPED TEMPS UP SOME AND STILL WONDER IF SOUTHERN CWA MAY NOT REACH 60F IN SPOTS. AS LAKE ENHANCED FRONT TURNS WINDS NE TODAY EXPECT A RATHER SHARP DROP IN TEMPS NEAR THE LAKE INITIALLY WITH COLDER AIR SPILLING INLAND DURING THE AFTERNOON. RUC GUIDANCE ANALYZED A SHORTWAVE OVER THE DAKOTAS WHICH CORRESPONDS NICELY TO BLOSSOMING AREA OF SNOW. THIS SHORTWAVE WILL RIDE THE NW FLOW TOWARD THE AREA THIS AFTERNOON WITH PRECIPITATION LIKELY TO SPREAD ESE TOWARD THE AREA...LIKELY FOCUSING NEAR SHARPENING 925/850MB FRONTAL BOUNDARY OVER SOUTHERN WI INTO FAR NORTHERN ILLINOIS. BEST CHANCES FOR PRECIP APPEAR TO BE MIDDAY INTO MID AFTERNOON BEFORE THAT SHORTWAVE MOVES AWAY WITH DECREASING PRECIP CHANCES AFTER 21Z. ANOTHER...SLIGHTLY MORE VIGOROUS SHORTWAVE GRAZES BY THE REGION TONIGHT WITH ANOTHER SHOT OF PRECIPITATION EXPECTED TONIGHT...AGAIN FOCUSED OVER NORTHERN CWA BUT BETTER PRECIP CHANCES WILL BE FARTHER SOUTH WITH THIS SECOND WAVE. PRECIP TYPE SHOULD BE PRIMARILY RAIN TODAY...BUT AS COLDER AIR MASS MOVES IN AND DEEPENS TONIGHT EXPECT PRECIP TO TRANSITION TOWARD SNOW WITH SOME MINOR ACCUMULATIONS EVEN POSSIBLE...MAINLY NORTHERN AREAS. PRECIP SHOULD END BY SAT MORNING BUT FORECAST SOUNDINGS SUGGEST THAT SHARP FRONTAL INVERSION DEVELOPS WHICH MAY WELL END UP TRAPPING MOISTURE IN THE LOW LEVELS AND KEEPING US CLOUDY SATURDAY. COULD POSSIBLY SEE PARTIAL CLEARING SATURDAY NIGHT...BUT THINK THE CHANCES ARENT GREAT AND HAVE KEPT TEMPS UP A BIT SAT NIGHT GIVEN THE EXPECTATION OF CLOUDINESS. IF WE SEE ANY CLEARING SATURDAY NIGHT IT IS LIKELY TO GIVE WAY TO MORE CLOUDS HEADING INTO SUNDAY NEXT SYSTEM APPROACHES THE REGION. GFS/ECMWF REMAIN IN PRETTY GOOD AGREEMENT THAT THE NEXT SYSTEM WILL FEATURE TWO DISTINCT WAVES WHICH ARE NOT PROGGED TO PHASE BEFORE MOVING ACROSS THE REGION. THE LEAD/SOUTHERN STREAM SYSTEM REMAINS PROGGED TO PASS TO OUR SOUTH SUNDAY NIGHT WITH SOME VARIABILITY IN THE MODELS WITH REPECT TO HOW FAR NORTH PRECIP GETS WITH THIS LEAD WAVE. GFS/FIM ARE FAIRLY FAR NORTH AND ROBUST WITH QPF AMOUNTS IN OUR CWA...ESPECIALLY SOUTHERN AREAS. LATEST ECMWF IS A BIT MORE SURPRESSED WITH THE AREA AND RESULT PRECIP. TEMPS COULD BE MARGINALLY COLD ENOUGH FOR WET SNOW WITH EVEN SOME ACCUM POSSIBLE IF GFS VERIFIES...BUT P-TYPE WILL BE CLOSE AND JUST WENT WITH RAIN/SNOW AT THIS POINT. GIVEN THE LEAD WAVE IS FAIRLY LOW AMPLITUDE MODELS MAY NOT BE RESOLVING IT PREFECTLY AND LATER RUNS MAY END UP SHIFTING THE TRACK NORTH OR SOUTH SO CONFIDENCE IN PRECIP NOT OVERLY HIGH SUNDAY NIGHT. MORE VIGOROUS/COLDER NORTHERN STREAM WAVE PROGGED TO AFFECT THE AREA MONDAY INTO MONDAY NIGHT. BY THIS TIME THE LEAD WAVE WILL LIKELY HAVE SHUNTED MUCH OF THE BETTER MOISTURE FARTHER EAST...BUT COLD AIR MASS AND STRONG FORCING LOOKS TO BE ENOUGH TO SQUEEZE OUT SOME PRECIP...PROBABLY IN THE FORM OF SNOW MONDAY AND POSSIBLY LINGERING INTO MONDAY NIGHT. NOT LOOKING FOR BIG PRECIP TOTALS BUT WIND...COLD AND SNOW WILL LEAVE IT FEELING MORE LIKE WINTER JANUARY THAN MID MARCH. DRY AND SEASONABLY COLD WEATHER LOOKS TO PERSIST THROUGH THE REMAINDER OF NEXT WEEK. IZZI && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 12Z... * LIGHT SOUTHWEST WINDS BECOMING LIGHT AND VARIABLE BY MID MORNING...BEFORE TURNING MORE NORTHEAST BY MID DAY. * VFR CEILINGS GRADUALLY LOWERING TODAY...AND WITH CONDITIONS BECOMING MVFR THIS AFTERNOON AS RAIN MOVES OVERHEAD. * MVFR CEILINGS LOWERING TONIGHT WITH IFR CEILINGS POSSIBLE...ALSO WITH ANOTHER CHANCE OF A RAIN/SNOW MIX AND A POSSIBILITY FOR MORE PREVAILING SNOW/SLEET. RODRIGUEZ //DISCUSSION...UPDATED 12Z... OUTSIDE OF SOME PATCHY FOG...RELATIVELY QUIET CONDITIONS ONGOING THIS MORNING WITH ONLY MID/HIGH LEVEL CLOUD COVER IN PLACE AS WELL AS A LIGHT WIND FIELD ACROSS THE TERMINALS. EXPECT THESE QUIET CONDITIONS TO PREVAIL THROUGH THIS MORNING BEFORE A LOWERING TREND IS EXPECTED BY THIS AFTERNOON AS A SYSTEM DROPPING OUT OF THE NORTHWEST WILL BRING A CHANCE FOR FOR LIGHT RAIN. IT DOES APPEAR AS IF MVFR CONDITIONS WILL BE POSSIBLE AS THIS RAIN ARRIVES WITH VIS LIKELY FALLING TO 3-5SM IN LIGHT RAIN/FOG. MVFR CEILINGS SHOULD REMAIN IN PLACE AS PRECIP EXITS TO THE SOUTHEAST WITH A LULL IN THE ACTIVITY EXPECTED BEFORE PRECIP ARRIVES ONCE AGAIN LATER THIS EVENING. ANOTHER SYSTEM WILL DROP SOUTHEAST ACROSS THE AREA BRINGING PRECIP ACROSS THE TERMINALS...BUT WITH CONDITIONS FAVORING MORE OF A RAIN/SNOW MIX. ALTHOUGH A RAIN/SNOW MIX IS FAVORED...THERE IS THE POSSIBILITY FOR THIS PRECIP TO BE MORE OF THE FROZEN TYPE WITH SNOW OR SLEET POSSIBLE. HAVE WENT PREVAILING WITH THE RAIN/SNOW BUT HAVE INCLUDED A PROB30 GROUP FOR A POSSIBILITY OF THIS MORE FROZEN PRECIP. ITS DURING THIS TIME THIS EVENING THAT CEILINGS SHOULD BE LOWERING...MORE TOWARDS LOW END MVFR. IFR CONDITIONS ARE STILL POSSIBLE TONIGHT...BUT HAVE NOT COMPLETELY INTRODUCED THESE LOWER CEILINGS AT THIS TIME. WINDS HAVE BECOME MORE LIGHT AND VARIABLE THIS MORNING...AND EXPECT THESE LIGHTER WINDS TO BE IN PLACE BEFORE WINDS TURN MORE OFF OF THE LAKE BY MID DAY. THIS NORTHEAST WIND WILL BE THE FAVORED DIRECTION THROUGH MOST OF THE FORECAST PERIOD. RODRIGUEZ //ORD AND MDW CONFIDENCE...UPDATED 12Z... * MEDIUM HIGH CONFIDENCE WITH WIND SPEED/DIRECTION TRENDS TODAY. * HIGH CONFIDENCE WITH CEILINGS THROUGH EARLY AFTERNOON...MEDIUM CONFIDENCE WITH CEILING TRENDS LATER THIS AFTERNOON INTO TONIGHT. * MEDIUM CONFIDENCE WITH MVFR CEILINGS AND RAIN/SNOW MIX TONIGHT...WITH LOW MEDIUM CONFIDENCE OF IFR CEILINGS AND THE POSSIBILITY FOR MORE PREVAILING SNOW/SLEET. RODRIGUEZ //OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z... SATURDAY NIGHT...VFR. SUNDAY...CHANCE FOR SNOW LATE...WITH POSSIBLE MVFR. MONDAY...CHANCE FOR SNOW...WITH POSSIBLE MVFR. TUESDAY...VFR. WEDNESDAY...VFR. THURSDAY...VFR. RODRIGUEZ && .MARINE... 358 AM CDT A RATHER DISTINCT DIFFERENCE IN OVERALL WIND SPEEDS IS BEING CURRENTLY OBSERVED ACROSS THE NORTH AND SOUTH HALVES OF LAKE MICHIGAN...WITH SOUTHWEST WINDS TO 30KT BEING REPORTED OVER THE NORTHERN HALF AND ONLY 10 TO 20 KT ACROSS THE SOUTH. DO EXPECT A DIMINISHING TREND ACROSS THE ENTIRE LAKE THROUGH MID DAY AS THE CURRENT TROUGH OF LOW PRESSURE OVER SOUTHERN ONTARIO CONTINUES TO EXIT OFF TO THE EAST/SOUTHEAST. ALTHOUGH DO EXPECT AN ATTENDANT COLD FRONT TO PUSH DOWN THE LAKE TODAY WITH WINDS BECOMING MORE NORTHERLY. AS HIGH PRESSURE APPROACHES FROM THE NORTHWEST AND ANOTHER AREA OF LOW PRESSURE MOVES SOUTHEAST JUST SOUTH OF THE LAKE TONIGHT INTO SATURDAY MORNING...DO EXPECT THE PRESSURE FIELD TO BE SUPPORTIVE OF PERSISTENT NORTHEAST WINDS OF 15 TO 25 KT WHICH WILL HELP BUILD WAVES ACROSS THE SOUTHERN HALF OF THE LAKE AND NEARSHORE WATERS. WINDS AND WAVES WILL DIMINISH ON SATURDAY...BUT WITH WINDS EXPECTED TO INCREASE ONCE AGAIN OUT OF THE NORTHWEST SATURDAY NIGHT. DO EXPECT THE STRONGEST WINDS OF 30 KT TO BE OBSERVED PRIMARILY ACROSS THE NORTHERN HALF OF THE LAKE. HIGH PRESSURE BUILDING ACROSS THE GREAT LAKES REGION ON SUNDAY WILL HELP WINDS DIMINISH...BUT WITH THIS PERIOD RATHER BRIEF AS YET ANOTHER TROUGH OF LOW PRESSURE WILL APPROACH FROM THE WEST AND HELP WINDS INCREASE SUNDAY NIGHT INTO MONDAY. ALTHOUGH THERE IS SOME UNCERTAINTY WITH THE EXACT TRACK OF THIS TROUGH OF LOW PRESSURE AS IT DEPARTS TO THE EAST LATE MONDAY NIGHT...MODEL GUIDANCE IS INDICATING THAT WEST/NORTHWEST GALES TO 35 KT COULD BE POSSIBLE BY MONDAY NIGHT AND LASTING INTO TUESDAY. RODRIGUEZ && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...1 AM SATURDAY TO 10 PM SATURDAY. && $$