Area Forecast Discussion
Issued by NWS Chicago, IL

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000 FXUS63 KLOT 192211 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 411 PM CST FRI DEC 19 2014 .SHORT TERM... 237 PM CST THROUGH SATURDAY... UNFORTUNATELY IT LOOKS LIKE WE WILL REMAIN LOCKED IN THE CLOUDS YET AGAIN TONIGHT...DESPITE A CLEARING WEDGE THAT EXTENDS FROM WESTCENTRAL IL TO SOUTHERN IN. WITH HIGH PRESSURE OVERHEAD THE ABILITY TO MIX TO THE SFC DRIER AIR HAS BEEN NONEXISTENT. WITH THE CONSIDERABLE SOLAR SHIELDING THIS AFTERNOON...SFC TEMPS HAVE BEEN UNABLE TO WARM MUCH. TEMPS IN MOST LOCATIONS HAVE REMAINED ARND 30 TO A FEW LOW 30S ACROSS THE FAR SOUTHERN CWFA. OVERNIGHT THE SFC RIDGE WILL DRIFT EAST...ALLOWING LGT/VRB WINDS TO SLOWLY TURN SOUTHWESTERLY BY DAYBREAK SAT. OVERNIGHT LOWS WILL GENERALLY BE IN THE LOW/MID 20S...BUT IF CLOUDS REMAIN THICK ENOUGH IT IS PLAUSIBLE THAT TEMPS COULD HOLD IN THE MID/UPR 20S. GUIDANCE HAS INDICATED A WEAK LOBE OF VORTICITY ALONG THE NORTHERN STREAM PUSHING EAST ACROSS THE NORTHERN PLAINS OVERNIGHT...ARRIVING ACROSS THE GREAT LAKES REGION AROUND SAT MORNING. WHILE IT APPEARS MOST OF THE NEAR SFC WILL REMAIN DRY...THERE IS SOME WEAK FORCING IN THE MID-LVLS ALONG WITH MARGINAL SATURATION THAT SOME FLURRIES COULD OCCUR DURING THE MORNING HOURS. WITH YET ANOTHER DAY OF CONTINUED CLOUDINESS SAT...IT APPEARS LESS FAVORABLE FOR ANY BUMP TO THE TEMPS. SO HAVE NUDGED TEMPS DOWN A DEGREE TO THE MID 30S ACROSS THE CWFA. SATURDAY NIGHT WILL GENERALLY REMAIN DRY...HOWEVER THERE IS ANOTHER WEAK VORT TRYING TO LIFT NORTHEAST ACROSS IOWA LATE SAT NGT/EARLY SUN. WITH A SLIGHT WARM LAYER TRYING TO LIFT ACROSS THE REGION...HOWEVER HAVE HELD ONTO MAINLY LGT SNOW. THERE IS SOME CONCERN THAT TEMPS ALOFT COULD BE WARM ENOUGH TO FULLY MELT ANY DENDRITES. THE OTHER CONCERN WORTH MENTIONING IS THAT THE LIFT/OMEGA IS LACKING LATE SAT NGT...SO DROPLET SIZE COULD BE SMALL AND INSTEAD OF ANY DENDRITES THERE COULD END UP BEING PATCHY FREEZING DRIZZLE...MAINLY AFTER MIDNIGHT. BEACHLER && .LONG TERM... 237 PM CST SUNDAY THROUGH SATURDAY... 500MB TROUGH WILL BEGIN TO DIG SOUTH ACROSS THE CENTRAL CONUS SUN INTO MON...WITH A SERIES OF MID-LVL VORTS PROGGED TO SLIDE SOUTHEAST ACROSS THE CANADIAN ROCKIES INTO THE NORTHERN PLAINS. THE MAIN FOCUS WILL BE ON A STRONGER SHORTWAVE DEVELOPING SUN NGT/EARLY MON ACROSS THE DAKOTAS...EXPECTED TO SLIDE SOUTHEAST ACROSS NORTHERN IL. ALTHOUGH CONFIDENCE IN THE TIMING/PLACEMENT OF THIS PATH IS LOW GIVEN CONTINUED CORRECTIONS BASED ON THE LATEST GUIDANCE CYCLES. MOISTURE WILL BE ADVECTING NORTH OF THIS LOW MON...WITH PRECIP ARRIVING MON MORNING LIKELY AS MAINLY RAIN OR PERHAPS A RAIN/SNOW MIX ACROSS THE NORTHERN CWFA. THEN A QUICK PUSH OF MUCH WARMER AIR WILL BRING TEMPS INTO THE UPR 30S/NEAR 40 MON AFTN AND SHOULD TURN ANY PRECIP TO PLAIN RAIN. AS MON NGT PROGRESSES...THE LOW IS PROGGED TO STEADILY DEEPEN AND LIFT NORTHEAST ACROSS NORTHERN IL EARLY TUE. FROPA CURRENTLY PROGGED FOR TUE EVE...BRINGING COLDER AIR BACK INTO THE FORECAST AREA AND TURNING RAIN OVER TO LGT SNOW. MON NGT WITH THE WARM AIR STEADILY ADVECTING NORTH...TEMPS WILL REMAIN IN THE MID/UPR 30S. TUE TEMPS COULD PUSH EVEN WARMER...DEPENDING ON THE PLACEMENT/TIMING OF FROPA. CURRENT INDICATIONS ARE THAT TEMPS WILL PUSH INTO THE LOW/MID 40S TUE AFTN. CHRISTMAS EVE THROUGH CHRISTMAS DAY... ENSEMBLES ALONG WITH OPERATIONAL SOLUTIONS HAVE BEEN TARGETING THE SYSTEM BECOMING WRAPPED UP OVER THE GREAT LAKES REGION AND POSSIBLY TRANSITIONING INTO ANOTHER LOW OVER SOUTHERN ONTARIO/SOUTHWEST QUEBEC CHRISTMAS DAY. A TIGHT GRADIENT WILL REMAIN OVER THE REGION BOTH CHRISTMAS EVE/CHRISTMAS DAY...WITH TEMPS RETURNING TO MORE SEASONAL CONDITIONS IN THE LOW/MID 30S. BEACHLER && .AVIATION...
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//ORD AND MDW CONCERNS...UPDATED 22Z... * MVFR CIGS. ED F //DISCUSSION...UPDATED 18Z... RELATIVELY UNCHANGING CONDITIONS ARE EXPECTED TO CONTINUE THROUGH THE TAF PERIOD WITH PRIMARILY MVFR CIGS AND LIGHT WINDS. WINDS THIS AFTERNOON ARE GENERALLY 5 KT OR LESS AND OUT OF THE NORTH OR NORTHWEST...BUT WILL LIKELY BECOME MORE VARIABLE AND POSSIBLY CALM FOR A PERIOD THIS EVENING AND OVERNIGHT...BEFORE SOUTHERLY WINDS START TO CREEP IN BEHIND THE HIGH TOMORROW. WHILE A FEW BREAKS IN THE CLOUDS MAY DEVELOP...EXPECT MVFR CIGS TO GENERALLY REMAIN LOCKED IN UNDER A STRONG INVERSION WITH SOME LOWERING OVERNIGHT. BMD //ORD AND MDW CONFIDENCE...UPDATED 22Z... * MEDIUM TO HIGH IN CIGS. * HIGH IN REMAINING FORECAST ELEMENTS. ED F //OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z... SATURDAY NIGHT...MVFR LIKELY. LIGHT SOUTH WINDS. SUNDAY...SLGT CHANCE FLURRIES/FREEZING DRIZZLE EARLY. MVFR LIKELY. SOUTH-SOUTHEAST WINDS. MONDAY AND TUESDAY...CHANCE OF RAIN...ESPECIALLY MONDAY NIGHT. MVFR LIKELY. SOUTHEAST WINDS MONDAY BECOMING SOUTHWEST TUESDAY. WEDNESDAY...CHANCE OF SNOW. MVFR POSSIBLE. GUSTY WEST WINDS. THURSDAY...DRY. VFR. RATZER
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&& .MARINE... 200 PM CST HIGH PRESSURE IS OVER THE REGION AND IT WILL SLOWLY SHIFT EAST THROUGH SUNDAY NIGHT. LIGHT WINDS BECOME SOUTHWEST OVERNIGHT. THE NEXT LOW MOVES OVER THE DAKOTAS SUNDAY NIGHT WITH SOUTH WINDS INCREASING TO 30 KT. MODELS DISAGREE WITH EXACT PATH OF THIS LOW. ONE HAS THE LOW DEEPENING OVER LAKE SUPERIOR WEDNESDAY WHILE ANOTHER HAS THE LOW DEEPENING OVER LAKE ERIE. SOUTHEAST WINDS AROUND 25 KT ARE EXPECTED THROUGH MONDAY NIGHT AHEAD OF THE LOW...THEN WINDS BECOME WEST BEHIND IT. FOR SPEEDS WENT MIDDLE OF THE ROAD GIVEN THE VARIABILITY. COULD DEFINITELY SEE HIGHER GUSTS IF THE LOW DEEPENS CLOSER TO THE LAKE. MODELS AGREE ON VERY STRONG WINDS BEHIND THE LOW WEDNESDAY NIGHT THROUGH THURSDAY. HAVE HIGH END GALES IN THE FORECAST AND SOME GUIDANCE MEMBERS SUGGEST LOW END STORM FORCE GUSTS MAY BE POSSIBLE. DO NOT HAVE THE CONFIDENCE TO GO THAT HIGH JUST YET...BUT HAVE HIGH CONFIDENCE IN AT LEAST GALES. THE LOW SHIFTS NORTHEAST WITH WINDS DIMINISHING THURSDAY NIGHT. THE NEXT LOW HOWEVER MOVES OVER THE SOUTHERN PLAINS THURSDAY EVENING. JEE && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ 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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