Area Forecast Discussion
Issued by NWS Chicago, IL

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000 FXUS63 KLOT 280312 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 912 PM CST TUE JAN 27 2015 .UPDATE... 905 PM CST LOW CLOUD COVER CONTINUES TO SLOWLY MOVE WESTWARD AND HAS CLEARED ALL BUT THE WESTERN FRINGES OF THE FORECAST AREA THIS EVENING. SATELLITE SHOWS SOME HIGHER CLOUD STREAKS APPROACHING FROM THE NORTHWEST AS UPPER RIDGING SHIFTS EASTWARD BUT COVERAGE LOOKS LOOKS TO BE SPORADIC THROUGH THE NIGHT AND MAY BE AT A MINIMUM DURING THE EARLY OVERNIGHT. TEMPERATURES HAVE BEGUN TO DROP OFF WHERE THANKS TO THE MAINLY CLEAR SKIES WITH SEVERAL SITES IN NORTH-CENTRAL ILLINOIS NOW IN THE TEENS. GIVEN THAT HIGHER CLOUD COVER LOOKS INTERMITTENT AND WINDS WILL DROP OFF WITH HIGH PRESSURE MOVING OVERHEAD HAVE GONE AHEAD AND LOWERED MINS OVERNIGHT FOR MOST AREAS...THOUGH WESTERN FRINGES MAY SEE LOWER LEVEL CLOUD COVER LINGER THROUGH THE NIGHT. WILL GO WITH LOWER TEENS FOR MUCH OF THE WESTERN/CENTRAL CWA AND SOME OF THE TRADITIONALLY COLDER SPOTS FROM LEE/OGLE COUNTIES TO DEKALB AND KANE COUNTIES COULD SEE VALUES A LITTLE BIT LOWER IF HIGH CLOUD COVER REMAINS VERY MINIMAL. WITH THE LOWER TEMPS AND SPORADIC HIGHER CLOUD COVER...FREEZING FOG WILL BE A CONCERN. THE COLDEST AREAS WILL LIKELY SEE A QUICK DROP OFF IN THE NEXT FEW HOURS WHICH MAY LEAD TO MORE FROST DEPOSITION RATHER THAN FOG FORMATION. WITH LIMITED CONFIDENCE IN THIS HAPPENING AND REASONABLE SUPPORT FOR SOME FOG DEVELOPMENT...WILL GO AHEAD AND ADD PATCHY FOG TO MUCH OF THE CENTRAL AND WESTERN CWA OR FROM THE FAR WESTERN CHICAGO METRO WEST AND SOUTHWEST FOR NOW. THIS MAY CAUSE SOME SLICK SPOTS ON ROADS OVERNIGHT. MDB && .SHORT TERM... 304 PM CST THROUGH THURSDAY... PRIMARY CONCERN IN THE NEAR TERM REVOLVES AROUND THE STRATUS DECK CURRENTLY OVER THE SOUTHWESTERN 2/3RDS OF THE CWA. WOULD ANTICIPATE A CONTINUED VERY SLOW CLEARING FROM THE EAST FOR A COUPLE MORE HOURS BEFORE LOW LEVEL FLOW DIMINISHES THIS EVENING BEFORE BACKING TO SOUTHERLY OVERNIGHT...WHICH MAY WELL SEND STRATUS SLOSHING BACK NORTH INTO AREAS THAT HAD PREVIOUSLY CLEARED OUT. TRIED TO REFLECT A TREND LIKE THIS IN THE HOURLY SKY GRIDS AND RESULTANT TEMPERATURE GRIDS...BUT GIVEN THE POOR MODEL HANDLING OF THIS CLOUDINESS IT PRETTY MUCH GUARANTEED THAT OUR CURRENT SKY GRIDS WILL BE WRONG SOMEWHERE AND NEED UPDATING WITH ACCOMPANYING CHANGES NEEDED IN TEMPS TONIGHT. WHERE SKIES BECOME/STAY CLEAR TONIGHT COULD SEE FREEZING GROUND FOG DEVELOP GIVEN THE LIGHT WINDS...BUT WILL LET EVENING SHIFT WATCH TRENDS AND ADD FREEZING FOG AS NEEDED. FOR WEDNESDAY HAVE OPTED TO BE OPTIMISTIC IN PUSHING STRATUS NORTH AND BREAKING IT UP IN THE MORNING BUT THIS VERY WELL MAY END UP BEING TOO OPTIMISTIC. ASSUMING THERE IS SOME SUNSHINE TOMORROW PRIOR TO THE ARRIVAL OF EXTENSIVE MID AND HIGH LEVEL CLOUDINESS THEN HIGHS COULD PUSH WELL INTO THE 30S...PARTICULARLY IN THE LESS SNOW COVERED AND MORE URBANIZED AREAS. DEVELOPING LOW PRESSURE TO OUR WEST SHOULD RESULT IN TIGHTENING PRESSURE GRADIENT AND STRENGTHENING SOUTHERLY WINDS WEDNESDAY. IZZI && .LONG TERM... 304 PM CST THURSDAY NIGHT THROUGH TUESDAY... BRISK SOUTH WINDS...WARM AIR ADVECTION...AND CLOUD COVER IN ADVANCE OF THE SYSTEM WEDNESDAY NIGHT SHOULD RESULT IN NEARLY STEADY TEMPS IN THE EVENING AND PROBABLY RISING A BIT OVERNIGHT. COULD SEE A BIT OF LIGHT RAIN OR DRIZZLE IN THE WARM SECTOR WEDNESDAY NIGHT FOLLOWED BY SOME POTENTIAL FOR A BIT OF WRAP AROUND RAIN OR SNOW SHOWERS THURSDAY ON THE BACK SIDE OF THE SYSTEM. STILL LOOKS LIKE PRETTY LIMITED MOISTURE WITH THE SYSTEM AND HIGHEST QPF FOCUSED TO OUR NORTH WITH LIGHT AMOUNTS IN OUR CWA AND ONLY MINIMAL THREAT OF ANY ACCUMULATED FROZEN/FREEZING PRECIP GIVEN THE FORECAST TRACK AND TEMPS. SHOT OF SEASONABLY COLD AIR WILL KNOCK TEMPS TO JUST A HAIR BELOW AVERAGE FRIDAY. VIGOROUS ALBERTA CLIPPER IS FORECAST TO RESULT IN AN AMPLIFYING LONG WAVE TROUGH OVER THE CENTRAL CONUS THIS WEEKEND. STILL SOME LARGE SPREAD BETWEEN MODELS WITH RESPECT TO THE DETAILS THIS WEEKEND...BUT THERE HAS BEEN SOME AGREEMENT THE PAST COUPLE DAYS ON THE GENERAL IDEA OF A LARGE SWATH OF ACCUMULATING SNOW POTENTIALLY AFFECTING THE REGION SAT NIGHT INTO SUNDAY. ARCTIC AIR IS FORECAST TO SURGE SOUTH INTO THE AREA IN THE WAKE OF THIS SYSTEM EARLY NEXT WEEK...BUT THE DURATION AND MAGNITUDE OF THIS ARCTIC INTRUSION ARE DEPENDENT ON WHICH MODEL YOU LOOK AT MEANING FAIRLY LOW FORECAST CONFIDENCE AT THIS POINT. IZZI && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 03Z... * GUSTY SSELY WINDS TOMORROW. * CHANCE FOR MVFR CIGS OR VIS LATE TONIGHT. KREIN //DISCUSSION...UPDATED 00Z... THE DECK OF MVFR STRATOCU CONTINUES TO ERODE FROM EAST TO WEST PER LATEST SATELLITE IMAGERY. RFD REMAINS THE ONLY TAF SITE STILL WITH MVFR CIGS AND IS JUST WEST OF THE EDGE OF THE CLEARING SKIES. THE EDGE OF THE CLEARING APPEARS TO HAVE SLOWED WITH THE SETTING SUN...SO HAVE DELAYED IMPROVEMENT OF CIGS THERE UNTIL 04Z...BUT THE CONFIDENCE IN THE EXACT TIMING IS LOW. AS HIGH PRESSURE SETTLES OVER THE AREA TONIGHT...WINDS WILL DROP OFF TO LGT/VRBL...AND WITH THE DECREASING CLOUD COVER...THERE SHOULD BE ENOUGH RADIATIVE COOLING FOR TEMPERATURES TO DROP LOW ENOUGH OVER RURAL AREAS TO ALLOW FOR SOME AREA OF BR DEVELOPMENT WITH VIS DROPPING INTO THE 3-5SM RANGE. ORD/MDW/GYY WILL LIKELY REMAIN VFR DUE TO URBAN HEAT ISLAND EFFECTS PREVENTING TEMPERATURES FROM DROPPING OFF AS MUCH. THE MAIN CONCERN FOR TOMORROW WILL BE WINDS. AS THE HIGH SETTLES TO THE SOUTH AND LOW PRESSURE TRACKS EWD ACROSS THE CNTRL PLAINS...A STRENGTHENING SOUTHERLY GRADIENT WILL SET UP...WITH WINDS INCREASING BY LATE MORNING. THERE SHOULD BE ADEQUATE SUNSHINE TO ALLOW FOR STRONGER WINDS ABOVE THE SFC TO MIX DOWN...WITH GUSTS IN THE 20-25KT RANGE LIKELY THROUGH THE AFTERNOON. THE LOW PRESSURE SYSTEM TRACKING ACROSS THE PLAINS SHOULD BRING THE NEXT CHANCE FOR PCPN AND REDUCED CIGS/VIS...BUT THIS WILL LIKELY NOT BE UNTIL AFTER MIDNIGHT TOMORROW NIGHT. KREIN //ORD AND MDW CONFIDENCE...UPDATED 03Z... * MEDIUM CONFIDENCE IN CIGS/VIS TRENDS. * HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS. KREIN //OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z... THURSDAY...CHANCE OF RAIN/SNOW. MVFR LIKELY/IFR POSSIBLE. FRIDAY...VFR. WX NIL. SATURDAY...CHANCE OF SNOW IN THE AFTERNOON AND OVERNIGHT. VFR EARLY THEN MVFR LIKELY/IFR POSSIBLE. SUNDAY...CHANCE OF SNOW. IFR POSSIBLE. MONDAY...VFR. WX NIL. KREIN && .MARINE... 318 PM CST LIGHTER NORTHERLY WINDS IN PLACE THIS AFTERNOON AS HIGH PRESSURE SPANS THE REGION...WILL FURTHER DIMINISH THIS EVENING AS THIS HIGH MOVES OVERHEAD. THIS HIGH WILL THEN CONTINUE SOUTHEAST TOWARDS THE OHIO VALLEY TONIGHT AS A TROUGH OF LOW PRESSURE MOVES EAST ACROSS THE CENTRAL PLAINS. THIS WILL HELP THE WINDS TO TURN BACK MORE SOUTHERLY AND THEN BEGIN TO SLOWLY INCREASE LATER TONIGHT INTO WEDNESDAY. THIS INCREASING TREND WILL CONTINUE THROUGHOUT THE DAY WEDNESDAY...WITH SOUTHERLY WINDS REALLY INCREASING DURING THE AFTERNOON TIME FRAME. THIS WILL LIKELY CREATE WINDS HAZARDOUS FOR SMALL CRAFT...AND SO HAVE ISSUED A SMALL CRAFT ADVISORY FOR WEDNESDAY AFTERNOON THROUGH LATE WEDNESDAY NIGHT WHEN WINDS WILL DIMINISH WITH THE APPROACHING LOW PRESSURE. THIS WILL LIKELY BE BRIEF AS WINDS WILL QUICKLY INCREASE ONCE AGAIN ON THE BACKSIDE OF THIS SYSTEM THURSDAY. ALSO...SOUTHERLY WINDS ACROSS THE SOUTHERN HALF OF THE LAKE COULD HOVER AROUND 30 KT A FOR A BRIEF WINDOW WEDNESDAY NIGHT. WILL NEED TO MONITOR TRENDS DURING THIS PERIOD...BUT WILL MAKE MENTION OF OCCASIONAL GALE FORCE GUSTS DURING THIS TIME. EXPECT STRONG WINDS TO BE IN PLACE ON THURSDAY...REALLY INCREASING INTO THE AFTERNOON AND EVENING HOURS. GALES ARE APPEARING LIKELY FOR THE ENTIRE LAKE DURING THIS TIME...EVEN FOR THE NEARSHORE WATERS...BUT WITH SPEEDS DIMINISHING ONCE AGAIN LATE THURSDAY NIGHT INTO FRIDAY. RODRIGUEZ && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744- LMZ745...NOON WEDNESDAY TO 4 AM THURSDAY. && $$ 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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