Area Forecast Discussion
Issued by NWS Chicago, IL

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000 FXUS63 KLOT 301604 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 1104 AM CDT THU OCT 30 2014 .UPDATE... 1059 AM CDT GOING FORECAST FOR THE REST OF TODAY LOOKS FAIRLY ON TRACK WITH ONLY SMALL ADJUSTMENTS. THE EMPHASIS ON THE FORECAST CONTINUES TO BE ON THE STRONG AUTUMN SYSTEM FRIDAY. THE AREA FINDS ITSELF BETWEEN TWO SHORT WAVE DISTURBANCES LATE THIS MORNING AND AS A RESULT A THINNING IN CLOUD COVER HAS BEEN SEEN ACROSS NORTHEAST IL AND NORTHWEST IN. EXPECTING VARIABILITY IN SKY TO OCCUR THE REST OF THE DAY THAT WILL PROBABLY AVERAGE OUT TO MOSTLY CLOUDY. THIS BREAK HAS ALLOWED TEMPERATURES IN SOME PLACES TO OUTPACE PREVIOUS FORECAST AND HAVE ADJUSTED HIGHS UP A DEGREE TO TWO IN EASTERN AREAS. WEAKER LESS ORGANIZED FORCING BETWEEN THE TWO WAVES SHOULD CONTINUE TO KEEP ANY RAIN LIGHT OR EVEN JUST SPRINKLES...WITH THE BETTER CHANCE FOR A FEW HUNDREDTHS OF AN INCH BEING SOUTH OF I-80 WITH THE SOUTHERN DISTURBANCE THIS AFTERNOON. LOOKING AHEAD TO FRIDAY...THE WINDY DAY AND EVENING CONTINUES ON TRACK WITH THE HIGHEST WIND SPEEDS AND IMPACTS BEING NEAR THE LAKE SHORE. THE SETUP FOR LAKE EFFECT SNOW IS CONTINUING TO BE WEIGHED AND MODEL DIFFERENCES DO EXIST IN THE LOWEST THERMAL PROFILES. WITH LIKELY MODEST TO TEMPORARY HEAVY PRECIPITATION RATES GIVEN THE HIGH LAKE-INDUCED INSTABILITY...COULD CERTAINLY REALIZE PRETTY LOW VISIBILITY IN PARTS OF NORTHWEST INDIANA AND POSSIBLY ALONG THE COOK COUNTY SHORE AT TIMES FRIDAY IF SNOW CAN BE THE DOMINANT PRECIPITATION TYPE. MTF && .SHORT TERM... 343 AM CDT FOR THE REMAINDER OF THE NIGHT AND INTO THURSDAY MORNING...WEATHER CONDITIONS WILL REMAIN QUIET ACROSS THE REGION UNTIL A STRONG COLD FRONT SWEEPS THROUGH THE AREA LATE TONIGHT. UNDER CLEAR SKIES AND WITH DEWPOINTS IN THE MIDDLE 20S TO LOWER 30S...TEMPERATURES ACROSS THE REGION HAVE BEEN DROPPING FAST OVERNIGHT UNDER FAVORABLE RADIATIVE COOLING. HOWEVER...A WEAK SHORTWAVE DROPPING SEWD THROUGH THE NRN PLAINS AND ACROSS THE MIDDLE AND UPPER MISSISSIPPI VALLEY WILL BRING INCREASING MID AND HIGH LEVEL CLOUDINESS...THROUGH THE EARLY MORNING HOURS...TEMPERING THE TEMPERATURE DROP OFF. HOWEVER...OVERNIGHT LOW TEMPERATURES WILL STILL DROP INTO THE UPPER 20S TO LOWER 30S ACROSS THE AREA AWAY FROM THE CHICAGO METRO AREA URBAN HEAT ISLAND...WHERE TEMPERATURES WILL ONLY DROP INTO THE UPPER 30S TO LOWER 40S. AT THE SURFACE...HIGH PRESSURE IS SLIDING SEWD ACROSS THE REGION...KEEPING WINDS NEAR CALM. AS THE HIGH SLIDES INTO THE OHIO VALLEY LATER TODAY...WINDS WILL BECOME MORE WLY...BUT WITH A WEAK GRADIENT IN PLACE...WINDS SHOULD REMAIN LIGHT THROUGH THE DAY AND INTO THE EARLY EVENING. WITH HEIGHT FALLS ASSOCIATED WITH THE PASSAGE OF THE SHORTWAVE AND A GENERAL COLD ADVECTIVE PATTERN IN PLACE ALOFT...ANTICIPATE ANOTHER CHILLY DAY WITH HIGHS ONLY IN THE LOWER TO MIDDLE 50S. A STRONG COLD FRONT IS EXPECTED TO DROP OUT OF THE NRN PLAINS AND PUSH INTO NWRN IL BY AROUND MIDNIGHT AND THE QUICKLY PUSH SEWD ACROSS THE REGION...BRINGING A QUICK WIND SHIFT TO NWLY. STRONG COLD ADVECTION AND STRONG PRESSURE RISES OF 6MB/6HR WILL BRING STRONG...GUSTY WINDS. LATEST FORECAST SOUNDING SHOW WINDS ARND 30 MPH AT THE TOP OF THE MIXED LAYER OVER LAND...WHICH WOULD SUPPORT GUSTS NEAR 30 MPH AT THE SFC BY ARND DAYBREAK FRIDAY MORNING. KREIN && .LONG TERM... 308 AM CDT STRONG UPPER TROUGH/CLOSED LOW WILL CONTINUE TO DIG SOUTH THROUGH THE WESTERN LAKES REGION FRIDAY. STRONG COLD AIR ADVECTION AND TIGHTENING PRESSURE GRADIENT BETWEEN DEVELOPING SFC LOW TO OUR EAST AND STRENGTHENING SFC HIGH APPROACHING FROM THE NORTHWEST WILL RESULT IN STRONG NORTHERLY WINDS FRIDAY...ESPECIALLY NEAR THE LAKE. FORECAST SOUNDINGS SUPPORT GUSTS TO AROUND 40 MPH MOST AREAS FRIDAY...THOUGH THE LESSER FRICTION AND STRONGER INSTABILITY AND RESULTANT MIXING NEAR THE LAKE SHOULD SUPPORT WIND GUSTS OF 50+ MPH NEAR THE LAKE...ESPECIALLY COOK COUNTY AND NW INDIANA SHORE. COULD BE A MARGINAL HIGH WIND WARNING FOR LAKE SHORE AREAS WITH A SOLID WIND ADVISORY EVENT LIKELY. GIVEN THE UNCERTAINTY OPTED TO HOLD OFF ON HEADLINES FOR NOW AND WILL LET LATER SHIFTS DECIDE. THE FULL FETCH STORM FORCE WINDS WILL RESULT IN 20FT+ WAVES...PARTICULARLY FOR COOK COUNTY INTO NW INDIANA GIVEN THE 350-360 WIND DIRECTION. LAKE LEVELS ARE NEARLY 2 FEET HIGHER THAN LAST YEAR AND PREVIOUS YEARS...SO EVEN THOUGH WAVES WILL NOT BE QUITE AS HIGH AS SANDY A FEW YEARS AGO...THE LAKE SHORE FLOODING IMPACT COULD BE SIMILAR. HAVE GONE AHEAD AND ISSUED A LAKESHORE FLOOD ADVISORY TO HIGHLIGHT THE LIKELY COASTAL INUNDATION IMPACT FROM THE LARGE AND BATTERING WAVES. COULD SEE SOME SHOWERS ALONG THE COLD FRONT TONIGHT...BUT FRONT SHOULD CLEAR THE AREA BY FRIDAY MORNING WITH SYNOPTIC PRECIP THREAT LARGELY ENDING. HOWEVER...VERY IMPRESSIVE LAKE EFFECT SET-UP LOOKS TO DEVELOP FRIDAY INTO FRIDAY EVENING WITH VERY HIGH LAKE INDUCED EQUILIBRIUM LEVELS UP TO AROUND 20KFT AND UP TO NEARLY -30C. GIVEN THE LIKELY PRESENCE OF SUPER COOLED LIQUID IN THE CLOUDS AND HIGH EQUILIBRIUM LEVELS IT SEEMS QUITE LIKELY THAT ISOLATED THUNDERSTORMS WILL OCCUR IN ADDITION TO FAIRLY WIDESPREAD SHOWERS FRIDAY. THESE EARLY SEASON LAKE EFFECT EVENTS ARE ALWAYS TRICKY WITH P-TYPE AS THE VERY COLD AIR ALOFT...AROUND -8 TO -10C AT 850MB WOULD SOLIDLY SUPPORT SNOW DESPITE WARM WATER TEMPS IN THE 50S STILL. HAVE GONE WITH RAIN OR SNOW SHOWERS FOR NOW...BUT THINK THE FARTHER INLAND AWAY FROM THE LAKE YOU GET THE BETTER CHANCE WILL BE FOR ALL SNOW SHOWERS FRIDAY AFTERNOON AND EVENING INTO NW INDIANA. GIVEN THE POTENTIAL FOR THUNDERSTORMS AND ADDED DYNAMIC COOLING AM CONCERNED THAT SOME PORTIONS OF NW INDIANA...ESPECIALLY A BIT INLAND FROM THE LAKE...COULD END UP WITH A SLUSHY COUPLE INCHES OF SNOW ACCUMULATION ON GRASSY SURFACES BY FRIDAY EVENING...THOUGH CONFIDENCE IS TOO LOW TO HIT THAT TOO HARD AT THIS TIME. LOW LEVEL FLOW SHOULD SLOWLY VEER SO THAT THE FOCUS FOR LAKE EFFECT PRECIP SHOULD START IN PORTER COUNTY EARLY FRIDAY AND GRADUALLY SHIFT WEST INTO LAKE COUNTY INDIANA FRIDAY AFTERNOON AND POTENTIALLY INTO SOUTHEAST COOK COUNTY FRIDAY EVENING BEFORE INVERSION HEIGHTS CRASH AND LAKE EFFECT WINDS DOWN LATE FRIDAY NIGHT. THE COMBINATION OF STRONG WINDS AND UNSEASONABLY COLD TEMPS WILL SEND WIND CHILLS DROPPING INTO THE 20S DURING TRICK OR TREATING HOURS FRIDAY EVENING...WITH EVEN LESS FAVORABLE TRICK OR TREATING WEATHER IN NW INDIANA UNDER THE LAKE EFFECT RAIN/SNOW SHOWERS. AFTER THE UNSEASONABLY COLD TEMPERATURES AND WIND CHILLS FRIDAY INTO FRIDAY NIGHT...LOOK FOR QUIET CONDITIONS OVER THE WEEKEND WITH VERY SLOWLY MODERATING TEMPERATURES. PROGRESSIVE PATTERN SHOULD RESULT IN TRANSIENT RIDGE MOVING EAST OF THE AREA EARLY NEXT WEEK WITH NEXT SYSTEM BRINGING THE POTENTIAL FOR SHOWERS MONDAY NIGHT INTO TUESDAY. TEMPERATURES SHOULD BE CLOSER TO SEASONAL NORMAL NEXT WEEK RETURNING TO WHAT WILL FEEL LIKE THE RATHER PLEASANT 50S FOLLOWING FRIDAY`S FLIRTATION WITH WINTER-LIKE TEMPERATURES. IZZI && .AVIATION...
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//ORD AND MDW CONCERNS...UPDATED 16Z... * TIMING OF COLD FRONT PASSAGE WITH WIND SHIFT TO NWLY...GUSTS TO 30KT AND CIGS LOWERING TO MVFR AND CHANCE SHRA. * CHANCE SHRA WITH THE PASSAGE OF THE COLD FRONT. KREIN/RODRIGUEZ //DISCUSSION...UPDATED 12Z... CONDITIONS WILL BE QUIET AT THE TERMINALS THROUGH MUCH OF THE PERIOD...BUT A STRONG COLD FRONT MOVING THROUGH THE REGION LATE TONIGHT WILL BRING STRONG NORTH WINDS. HOWEVER...THIS MORNING...A MID LEVEL IMPULSE CROSSING THE MIDDLE MISSISSIPPI VALLEY IS BRINGING INCREASING MID AND HIGH CLOUDINESS. LATEST RADAR IMAGERY SHOWS SOME SCT SHRA OVER IOWA AND MISSOURI ASSOCIATED WITH THIS SYSTEM...BUT WITH A VERY DRY AIRMASS IN PLACE...DO NOT EXPECT ANY PCPN AT THE TERMINALS. WITH SFC HIGH PRESSURE CENTERED OVER SRN IL/IN...WINDS WILL BE LIGHT AND VARIABLE INITIALLY...BUT AS THE HIGH SLIDES OFF TO THE SOUTHEAST...WINDS SHOULD BECOME MORE SWLY-WLY THROUGH THE DAY AND INTO THE EVENING...WITH SPEEDS REMAINING LESS THAN 10KT. AN ABRUPT CHANGE IS EXPECTED LATE TONIGHT AS A STRONG COLD FRONT PUSHES SOUTH ACROSS THE AREA. THE LATEST GUIDANCE SUGGESTS THAT THE FRONT WILL PUSH THROUGH RFD BY EARLY EVENING...AND THEN QUICKLY PUSHING SOUTH THROUGH THE CHICAGO AREA TERMINALS SHORTLY THEREAFTER. THIS WILL BE A VERY SHARP BOUNDARY AND WINDS SHOULD QUICKLY SHIFT TO NWLY. AS COLD ADVECTION AND STRONG PRESSURE RISES DEVELOP BEHIND THE FROM...WINDS WILL STRENGTHEN WITH GUSTS UP TO 35-40 KT FOLLOWING THE FROPA. THERE WILL ALSO BE A SHALLOW BAND OF MOISTURE WITH THE FRONT...AND EXPECT THAT CIGS SHOULD QUICKLY DROP TO LOWER END MVFR LEVELS. THERE IS A CHANCE FOR SOME SHRA FOLLOWING THE FROPA FOR A BRIEF PERIOD. KREIN //ORD AND MDW CONFIDENCE...UPDATED 16Z... * HIGH CONFIDENCE IN ALL FORECAST ELEMENTS UP TO THE TIMING OF THE COLD FRONT PASSAGE THURSDAY NIGHT. * HIGH CONFIDENCE IN THE IMPACTS OF THE FROPA ON TERMINAL CONDITIONS...BUT MEDIUM CONFIDENCE ON THE EXACT TIMING. * LOW CONFIDENCE IN TIMING AND COVERAGE OF PCPN WITH THE FROPA. KREIN/RODRIGUEZ //OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z... * FRIDAY NIGHT...STRONG NORTH WINDS GUSTING TO 30 KT. CHANCE OF SHRA OR SHSN. * SATURDAY...VFR. WX NIL. NORTHEAST WINDS 10-15KT. * SUNDAY...VFR. WX NIL. SOUTH WINDS. * MONDAY...CHANCE OF SHRA. GUSTY SOUTHERLY WINDS. * TUESDAY...CHANCE OF SHRA. WESTERLY WINDS. * WEDNESDAY...VFR. WX NIL. SOUTHWEST WINDS.
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&& .MARINE... 319 AM CDT SHARP UPPER TROUGH WILL DIG INTO THE WESTERN GREAT LAKES REGION TONIGHT AND RESULT IN SURFACE LOW DEVELOPING AND SLOWLY INTENSIFYING TONIGHT INTO FRIDAY OVER THE EASTERN LAKES. MEANWHILE...UPSTREAM HIGH PRESSURE OVER THE CANADIAN PRAIRIES WILL STRENGTHEN AS IT MOVES SOUTHEAST INTO THE NORTHERN PLAINS TONIGHT INTO FRIDAY. THE RESULT WILL BE A VERY TIGHT PRESSURE GRADIENT DEVELOPING OVER THE AREA LATER TONIGHT INTO FRIDAY AND WHEN COMBINED WITH THE EXTREME INSTABILITY LIKELY TO DEVELOP AS A RESULT OF THE VERY COLD AIR ALOFT MOVING IN...AM EXPECTING A PERIOD OF HIGH END GALES TO LOW END STORM FORCE WINDS OVER THE LAKE LATE TONIGHT THROUGH FRIDAY NIGHT. CURRENT INDICATIONS ARE THAT THE LONGEST DURATION AND HIGHEST PROBABILITY OF STORM FORCE WINDS WILL EXIST OVER SOUTHERN LAKE MICHIGAN AND HAVE OPTED TO UPGRADE TO A STORM WARNING THERE FOR FRIDAY...INCLUDING THE NORTHWEST INDIANA NEARSHORE WATERS UP TO NORTHERLY ISLAND IN THE ILLINOIS NEARSHORE. THE NORTHERN PORTIONS OF THE ILLINOIS NEARSHORE MAY END UP WITH A MORE OFFSHORE FETCH IN THE 350-360 RANGE LESSENING THE THREAT OF STORM FORCE WINDS A BIT. NORTHERN PORTIONS OF THE LAKE COULD SEE STORM FORCE GUSTS FOR A TIME FRIDAY MORNING BUT DURATION LOOKS TO BE LESS AND CONFIDENCE LOWER...SO JUST HINTED AT THIS THREAT IN THE GLF. FULL FETCH NORTH STORM FORCE WINDS SHOULD HAVE NO PROBLEM KICKING WAVES UP TO AROUND OR JUST ABOVE 20 FT OVER SOUTHERN PORTIONS OF THE LAKE FRIDAY AFTERNOON AND EVENING. WINDS SHOULD SUBSIDE RATHER QUICKLY FRIDAY NIGHT INTO SATURDAY AS THE PATTERN REMAINS PROGRESSIVE AND THE HIGH PRESSURE RESPONSIBLE FOR THE STORM EVENT MOVES INTO THE WESTERN LAKES REGION ALLOWING WINDS AND EVENTUALLY WAVES TO SUBSIDE SATURDAY. LATER SUNDAY INTO EARLY NEXT WEEK 25-30KT SOUTHERLY WINDS COULD DEVELOP AS HIGH PUSHES OFF TO THE EAST AND NEW LOW PRESSURE DEVELOPS OVER THE NORTHERN PLAINS. IZZI && .LOT WATCHES/WARNINGS/ADVISORIES... IL...LAKESHORE FLOOD ADVISORY...ILZ014...11 AM FRIDAY TO 4 AM SATURDAY. IN...LAKESHORE FLOOD ADVISORY...INZ001-INZ002...11 AM FRIDAY TO 4 AM SATURDAY. LM...GALE WARNING...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ741-LMZ742- LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ870-LMZ872-LMZ874- LMZ876-LMZ878...7 PM FRIDAY TO 4 AM SATURDAY. STORM WARNING...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ741-LMZ742- LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ870-LMZ872-LMZ874- LMZ876-LMZ878...6 AM FRIDAY TO 7 PM FRIDAY. GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567- LMZ868...1 AM FRIDAY TO 10 PM FRIDAY. GALE WARNING...LMZ740...6 AM FRIDAY TO 4 AM SATURDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO

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