249 FXUS63 KLOT 160006 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 706 PM CDT FRI MAR 15 2013 .DISCUSSION... 343 PM CDT A VERY SLOPPY PATTERN SETTING UP FOR THE NEXT SEVERAL DAYS. FOR THE LARGE SCALE PATTERN...WEAK RIDGING OVER THE WRN CONUS AND WEAK TROUGHING OVER THE ERN CONUS WITH A PERSISTENT POLAR VORTEX INVOF HUDSON BAY WILL KEEP THE LOCAL AREA UNDER GENERALLY NWLY FLOW ALOFT. WITH THE MODELS INDICATING A SERIES OF MID LEVEL IMPULSES DROPPING OUT OF SOUTH-CENTRAL CANADA OVER THE NEXT SEVERAL DAYS... SOME STRONGER THAN OTHERS. THIS WILL BRING PERIODS OF RAIN AND/OR SNOW...INTERMINGLED WITH PERIODS OF DRY WEATHER AND GENERALLY BELOW NORMAL TEMPERATURES. FOR THE REMAINDER OF THE AFTERNOON AND THOUGH THE EVENING...A SHORTWAVE DROPPING SEWD THROUGH THE REGION IS BRINGING PCPN TO THE AREA...GENERALLY NORTH OF A LINE FROM FREEPORT...TO JOLIET... RENSSELAER. WITH TEMPERATURES ACROSS THE CWA RANGING FROM AROUND 50F IN THE PONTIAC AREA TO THE LOWER 30S OVER FAR NERN IL/NERN WI...THERE IS A CHANCE FOR SOME SNOW TO MIX WITH THE RAIN THROUGH EARLY THIS EVENING...ESPECIALLY OVER LAKE AND MCHENRY COUNTIES. OVERNIGHT TONIGHT. COOLER AIR WILL OOZE SEWD ACROSS THE CWA AS A WEAK LAKE-ENHANCED COLD FRONT SAGS SWD. GENERALLY FEEL THAT ANY PCPN OVERNIGHT TONIGHT WILL BE RATHER LIGHT AS THE BETTER FORCING SHOULD BE OVER WISCONSIN AND SRN LAKE MICHIGAN...SO ONLY SOME LIGHT SNOW ACCUMULATION IS LIKELY GENERALLY UP TO AROUND 1 INCH. SOUTH OF THE WEAK FRONTAL BOUNDARY...TEMPERATURES SHOULD REMAIN HIGH ENOUGH THAT THE PCPN WILL REMAIN ALL LIQUID. AS THE MAIN FORCING SHIFTS OFF TO THE EAST AND COOL...NORTHERLY FLOW SETS UP ACROSS THE REGION TOMORROW...THERE MAY BE PERIODS OF FLURRIES OR FREEZING DRIZZLE THROUGH TOMORROW MORNING. AS HIGH PRESSURE BUILDS OUT OF CANADA AND ACROSS THE MIDDLE AND UPPER MISSISSIPPI VALLEY TOMORROW...THE FIRST BREAK IN THE PCPN WILL OCCUR,. HOWEVER...HIGH TEMPERATURES SATURDAY AFTERNOON ONLY IN THE LOWER 30S TO LOWER 40S AND NELY FLOW OFF OF LAKE MICHIGAN WILL ONLY LEAD TO A RAW DAY. THE NEXT CONCERN WILL BE A NORTHERN STREAM SHORTWAVE DROPPING INTO THE NRN PLAINS BY SUNDAY AFTERNOON AND A SRN STREAM SHORT WAVE LIFTING OUT OF THE SOUTH HIGH PLAINS AT THE SAME TIME. AT THIS POINT...THE MODELS DO NOT INDICATE ANY PHASING OF THE TWO SYSTEMS...WITH SRN STREAM SYSTEM IMPACTING THE CWA FIRST...BRINGING SOME PCPN INTO THE SRN COUNTIES BY LATE SUNDAY AFTERNOON. THE PCPN SHOULD SPREAD NWD THROUGH THE EVENING AS THE ASSOCIATED SFC LOW MOVES INTO THE BOOTHEEL REGION OF MISSOURI. HIGH PRESSURE OVER THE ERN GREAT LAKES WILL HELP SUPPRESS THE PCPN...AT LEAST INITIALLY...BUT THE HIGH SHOULD MOVE TO SRN QUEBEC AND NEW ENGLAND...ALLOWING THE PCPN TO POSSIBLY SPREAD ACROSS THE ENTIRE CWA BY EARLY MONDAY MORNING. WHILE THE PCPN WILL INITIALLY START OUT AS RAIN...COOLER AIR FILTERING IN OVERNIGHT WILL ALLOW THE PCPN TO TRANSITION OVER TO LIGHT SNOW BY MONDAY MORNING. AS ALL OF THIS IS GOING ON...THE NRN STREAM SHORTWAVE WILL TRACK ACROSS THE NRN PLAINS AND INTO MINNESOTA. THIS SYSTEM IS EXPECTED TO TRACK EWD THROUGH NRN WISCONSIN MONDAY EVENING TO SRN ONTARIO BY TUESDAY AFTERNOON. AGAIN...WITH THE STRONGEST FORCING REMAINING WELL NORTH OF THE LOCALLY AREA...ONLY EXPECT GENERALLY LIGHT PCPN AMOUNTS...BUT EXTENSIVE CLOUD COVER AND STRENGTHENING WEST WINDS AS AN ASSOCIATED COLD FRONT SWEEPS THROUGH THE REGION...MONDAY AND TUESDAY WILL BE RATHER UNPLEASANT. HIGHS ON MONDAY WILL RANGE FROM THE UPPER 30S TO AROUND 40F...AND TUESDAY WILL BE EVEN COOLER FOLLOWING THE FRONTAL PASSAGE...WITH HIGHS RANGING FROM THE LOW 30S OVER NRN IL TO THE MIDDLE TO UPPER 30S OVER NWRN INDIANA AND EAST-CENTRAL IL. THIS WILL CERTAINLY BE A POOR LEAD-IN TO ASTRONOMICAL SPRING...WHICH WILL BE WEDNESDAY MARCH 20 AT 602 AM CDT. WITH ANOTHER AREA OF ARCTIC HIGH PRESSURE BUILDING OUT OF CANADA AND ACROSS THE UPPER MIDWEST...THE FIRST DAY OF SPRING WILL SEE INCREASING SUNSHINE...BUT LITTLE IN THE WAY OF WARMING AS PERSISTENT WEAK COLD ADVECTION ALLOWS FOR LITTLE OR NO MODERATION OF TEMPERATURES...WITH THE FIRST DAY OF SPRING STARTING OUT IN THE MIDDLE TO UPPER TEENS OVER PORTIONS OF THE CWA GENERALLY NORTH OF I-80...INCLUDING THE ROCKFORD METRO AREA. THE REMAINDER OF THE CWA...INCLUDING THE CHICAGO METRO AREA SHOULD START OUT THE DAY IN THE LOWER 20S. HIGHS ON WEDNESDAY WILL NOT SIGNIFICANTLY VARY FROM THE PREVIOUS COUPLE DAYS...RANGING FROM THE LOWER 30S ALONG THE WISCONSIN BORDER TO THE UPPER 30S TO THE SOUTH. THE REMAINDER OF THE FORECAST PERIOD...THURSDAY AND FRIDAY SHOULD SEE AT LEAST A LITTLE MODERATION TO TEMPERATURES AS THE HIGH PRESSURE BUILDS TO THE EAST. HOWEVER...THE LONGER RANGE MODEL GUIDANCE IS INDICATING A STRONG SOUTHERN STREAM SYSTEM PUSHING OUT INTO THE PLAINS...AND WHICH COULD BEGIN TO IMPACT THE WEATHER FOR THE LOCAL AREA BY THURSDAY NIGHT. KREIN && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 00Z... * IFR CIG/VIS CONDITIONS LIKELY OVERNIGHT. * EAST-NORTHEAST WINDS 10-15 KT OVERNIGHT...BECOMING NORTH- NORTHEAST EARLY SATURDAY AND EVENTUALLY DECREASING LATE. * RAIN ENDING CURRENTLY...BUT A PERIOD OF DRIZZLE/SNOW AND POSSIBLY FREEZING DRIZZLE LIKELY AFTER MIDNIGHT INTO EARLY SATURDAY MORNING. * CIGS IMPROVING TO MVFR BY MID/LATE MORNING SATURDAY. RATZER //DISCUSSION...UPDATED 00Z... SLOW-MOVING COLD FRONT SAGGED ACROSS FAR NORTH/NORTHEAST IL THIS AFTERNOON...AND WILL CONTINUE TO SETTLE SOUTH OF THE TERMINALS THIS EVENING AS AN AREA OF LOW PRESSURE MOVES EAST ALONG THE FRONT ACROSS CENTRAL IL. RAIN...ASSOCIATED WITH AN UPPER DISTURBANCE TRACKING ALONG THE THERMAL DISCONTINUITY NORTH OF THE SURFACE FRONT...HAS SATURATED LOW LEVELS AND HAS PRODUCED IFR CIG/VIS CONDITIONS WHICH WILL LIKELY CONTINUE TO PERSIST OVERNIGHT AS EAST-NORTHEAST LOW LEVEL WINDS SLOWLY COOL THE BOUNDARY LAYER. COULD BE A BRIEF PERIOD OF IMPROVEMENT IN CIG HEIGHTS THIS EVENING WITH RAIN ENDING...THOUGH COOL NORTHEAST FLOW AND SUNSET ARGUE AGAINST MUCH IN THE WAY OF SIGNIFICANT IMPROVEMENT. ANOTHER UPPER LEVEL DISTURBANCE CURRENTLY OVER MINNESOTA WILL TRACK SOUTHEAST ACROSS WI LATER TONIGHT...AND WILL GRAZE NORTHERN IL AND NORTHWEST INDIANA TERMINALS WITH THE POTENTIAL FOR ADDITIONAL LIGHT PRECIPITATION. MOST RECENT MODEL RUNS MAINTAIN RELATIVELY WARM THERMAL PROFILES BELOW 5000 FT AGL...WHICH SUGGESTS THAT ANY LIGHT PRECIP WHICH DEVELOPS WOULD INITIALLY BE IN LIQUID FORM. FORECAST SOUNDINGS THEN SLOWLY COOL THE COLUMN BELOW FREEZING DURING THE PRE-DAWN HOURS...THOUGH LACK OF SOLID SATURATION ABOVE THE VERY MOIST BOUNDARY LAYER INDICATES THAT DRIZZLE/FREEZING DRIZZLE PERHAPS AT TIMES MIXED WITH SOME WET LIGHT SNOW IS MOST LIKELY. NOT EXPECTED TO BE A SIGNIFICANT ISSUE AS SURFACE TEMPS ONLY SLOWLY LOWER THROUGH THE 30 DEGREE RANGE OR SO BY MORNING...THOUGH THE POTENTIAL FOR SOME MIXED LIGHT PRECIP DOES EXIST. PASSAGE OF THIS SECOND UPPER DISTURBANCE SHOULD SHUT OFF THREAT OF ANY ORGANIZED PRECIP EARLY SATURDAY MORNING...WITH MORE NORTH-NORTHEASTERLY LOW LEVEL WINDS BRINGING SOMEWHAT DRIER AIR AND ALLOWING CIGS TO LIFT INTO MVFR RANGE. WINDS...HAVE SHIFTED EAST-NORTHEAST BEHIND THE COLD FRONT EARLY THIS EVENING. SPEEDS SHOULD GRADUALLY COME UP A LITTLE INTO THE 10-15 KT RANGE OVERNIGHT AS SURFACE LOW PASSES SOUTH OF THE TERMINALS AND GRADIENT TIGHTENS A BIT...AND COLDER LOW LEVEL AIR STEEPENS BOUNDARY LAYER LAPSE RATES. WINDS SHOULD SLOWLY DECREASE SATURDAY AFTERNOON AS LOW PULLS AWAY. RATZER //ORD AND MDW CONFIDENCE...UPDATED 00Z... * HIGH CONFIDENCE IN PREDOMINANTLY IFR CIGS TONIGHT WITH 2-5SM FOG. LOW CONFIDENCE THAT THERE COULD BE A BRIEF PERIOD OF CIGS IMPROVING TO LOW MVFR THIS EVENING. * MEDIUM CONFIDENCE IN TIMING AND TYPE OF PRECIPITATION AFTER MIDNIGHT INTO EARLY SATURDAY. * HIGH CONFIDENCE IN WIND TRENDS. * HIGH CONFIDENCE IN IMPROVING VIS AND CIGS SATURDAY. RATZER //OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z... SUNDAY...VFR. SLIGHT CHANCE OF SNOW LATE SUNDAY NIGHT. MONDAY...SNOW/RAIN LIKELY. IFR POSSIBLE. TUESDAY THROUGH THURSDAY...VFR. RATZER && .MARINE... 225 PM CDT SEVERAL SYSTEMS WILL AFFECT THE REGION THROUGH THE NEXT WEEK WHICH WILL RESULT IN UPS AND DOWNS IN WIND SPEEDS THROUGH THE PERIOD...WITH GALES POSSIBLE LATER MONDAY/TUESDAY. LOW PRESSURE CONTINUES TO WORK EASTWARD INTO THE ST. LAWRENCE VALLEY THIS AFTERNOON WITH A TRAILING COLD FRONT HAVING DROPPED SOUTH ACROSS LAKE MICHIGAN EARLIER THIS AFTERNOON. WEAK LOW PRESSURE ACROSS THE CENTRAL PLAINS WILL MOVE EASTWARD AND PASS SOUTH OF THE LAKE TONIGHT. THIS WILL HELP INTENSIFY NORTHEASTERLY WINDS ACROSS MUCH OF THE LAKE AS HIGH PRESSURE PASSES NORTH OF THE LAKE. THE FETCH WILL BE LONG ENOUGH AND PERSISTENT ENOUGH TO KICK WAVES UP INTO SMALL CRAFT ADVISORY RANGE ACROSS THE ILLINOIS NEARSHORE WATERS EARLY SATURDAY MORNING. THE INDIANA NEARSHORE WATERS WILL BE MORE MARGINAL WHILE WINDS ARE STILL NORTHEAST EARLY SATURDAY MORNING BUT A SHIFT TO A NORTH WIND BY MIDDAY SHOULD SUPPORT SMALL CRAFT CONDITIONS THERE AS WELL SO WILL EXPAND THE SMALL CRAFT ADVISORY TO MICHIGAN CITY. WINDS WILL EASE INTO SUNDAY AS HIGH PRESSURE MOVES OVER THE LAKE. LOW PRESSURE WILL TAKE SHAPE ACROSS THE NORTHERN PLAINS LATER SUNDAY AND LIFT NORTHEASTWARD TOWARD THE U.P. OF MICHIGAN MONDAY EVENING. THE PRESSURE GRADIENT WILL TIGHTEN RESULTING IN STRENGTHENING SOUTHEAST WINDS EARLY MONDAY WHICH THEN FLIP WEST OR SOUTHWEST...THEN TO NORTHWEST AS THE LOW PASSES MONDAY EVENING/NIGHT. THE LOW WILL DEEPEN SLIGHTLY WHILE PASSING NORTH OF THE LAKE MONDAY NIGHT WHILE STRONG HIGH PRESSURE BUILDS INTO THE SOUTHERN PLAINS/LOWER MISSISSIPPI VALLEY. WITH COLDER AIR SPREADING IN COMBINING WITH THE TIGHT PRESSURE GRADIENT LOW TO EVEN MID RANGE GALES ARE A GOOD POSSIBILITY. THE GRADIENT WILL REMAIN STRONG SO WINDS WILL BE SLOW TO EASE TUESDAY NIGHT BUT SPEEDS SHOULD FALL JUST BELOW GALE FORCE SOMETIME TUESDAY NIGHT. SUB-GALE FORCE NORTHWEST WINDS WILL THEN CONTINUE INTO LATE THURSDAY. HIGH PRESSURE THEN SPREADS IN WEST OF THE LAKE WHILE LOW PRESSURE ACROSS EASTERN CANADA ACTUALLY PUSHES WESTWARD. THIS WILL KEEP BREEZY NORTHERLY WINDS GOING ACROSS THE LAKE INTO NEXT WEEKEND. MDB && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...1 AM SATURDAY TO 10 PM SATURDAY. SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...7 AM SATURDAY TO 10 PM SATURDAY. && $$