129 FXUS63 KLOT 272005 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 305 PM CDT THU AUG 27 2015 .SHORT TERM... 246 PM CDT THROUGH FRIDAY NIGHT... TONIGHT... VISIBLE IMAGERY THIS AFTERNOON SHOWS SOME FAIR WEATHER CUMULUS CLOUDS ACROSS NORTHERN IL/NORTHWEST IN...WITH A CIRRUS SHIELD ARRIVING OVERHEAD. THIS CIRRUS SHIELD WAS FROM THE AREA OF SHOWERS/THUNDERSTORMS OVER THE CENTRAL PLAINS. WITH HIGH PRESSURE CENTERED OVER THE REGION...THE EASTERN PROGRESSION OF PRECIP AND THE LOW OVER THE CENTRAL PLAINS WILL BE SLOW TO MOVE. THIS WILL ALLOW QUIET CONDITIONS TO LINGER TONIGHT...SO HAVE MAINTAIN A DRY FORECAST. SKIES WILL STEADILY THICKEN OVERNIGHT AS THE LOW DRIFTS EAST. EXPECT OVERNIGHT LOWS TO FALL INTO THE MID/UPR 50S ACROSS THE BULK OF THE FORECAST AREA...WITH SOME AREAS CLOSER TO LAKE MICHIGAN SEEING A LIGHT ONSHORE FLOW AND KEEPING TEMPS IN THE LOW 60S. FRIDAY THROUGH FRIDAY NIGHT... DIFFERENCES AMONGST OPERATIONAL SOLUTIONS LINGERS INTO FRI MORNING...WITH SOME OF THE HI-RES SIMULATIONS ANTICIPATING AN AREA OF STORMS/RAIN TO PUSH EAST INTO EASTERN IOWA THEN QUICKLY DECAY SHORTLY AFTER DAYBREAK FRI. GIVEN A RATHER STABLE ENVIRONMENT OVER NORTHERN IL/NORTHWEST IN WITH CONSIDERABLE CLOUD COVER...THIS APPEARS FAVORABLE TO OCCUR. INSTABILITY DOES NOT LOOK TO EXPAND MUCH DURING THE LATE MORNING/AFTERNOON HOURS...HOWEVER WITH SOME BETTER FORCING ARRIVING IN THE MID-LVLS LATE MORNING/AFTERNOON...THIS MAY ALLOW FOR SOME EMBEDDED THUNDER TO DEVELOP WITH THE SHORTWAVE AS IT APPROACHES THE REGION. HAVE ONLY MADE MINOR ADJUSTMENTS TO THE PRECIP COVERAGE AND TIMING. ONE ITEM THAT MAY NEED FURTHER ADJUSTMENTS WILL BE HIGH TEMPS FOR FRI...GIVEN THE THICKENING SOLAR SHIELDING. HAVE NUDGED TEMPS DOWN A DEGREES INTO THE LOW/MID 70S FOR CENTRAL/NORTH AND UPR 70S ACROSS THE FAR SOUTH. THERE MAY BE ENOUGH CLOUD COVER TO LIMIT HEATING...AND KEEP TEMPS SEVERAL DEGREES COOLER IN THE UPR 60S TO LOWER 70S. PRECIP CHANCES WILL CONTINUE THRU FRI NIGHT...BUT WITH THE SHORTWAVE LIFTING NORTHEAST ACROSS WISC...THE BEST PROBS FOR PRECIP WILL BE FOCUSED TO OUR NORTH. HAVE REFLECTED THIS WITHIN THE CURRENT PRECIP FORECAST WITH LOWER POPS FURTHER SOUTH. TEMPS FRI NIGHT WILL LIKELY REMAIN MILD GIVEN THE THICK CLOUD COVER...WITH LOWS IN THE MID 60S. BEACHLER && .LONG TERM... 256 PM CDT SATURDAY NIGHT THROUGH THURSDAY... FOCUS ON THE EXTENDED IS FOR WEEKEND PRECIPITATION CHANCES/LINGERING CLOUD COVER AND IMPACT ON TEMPERATURES...THEN SHIFTING TO AN EXTENDED PERIOD OF WARM AND DRY CONDITIONS. AT THE START OF THE PERIOD...THE LEADING UPPER DISTURBANCE...EMANATING FROM COLORADO...WILL HAVE LIFTED NORTH AND EAST OF THE AREA. TRAILING ENERGY FROM WYOMING WILL STILL CREATE SOME LIFT IN THE MORNING...IN ADDITION TO A NORTHERN STREAM PACIFIC SHORTWAVE ENERGY MOVING INTO THE BACK SIDE OF THE SLOW MOVING UPPER LOW WHICH WILL KEEP PRECIPITATION CHANCES IN THE FORECAST FOR SATURDAY AFTERNOON. CONFIDENCE ON THE DETAILS IS A BIT LIMITED AT THIS POINT AS THERE IS STILL QUITE A BIT OF MODEL UNCERTAINTY AS TO WHAT DEGREE THESE DISTURBANCES INTERACT AND THEIR TIMING. THE INTERACTION OF THESE DISTUBBANCES ARE ALSO PLAYING HAVOC ON HOW QUICKLY THE ASSOCIATED SURFACE LOW MOVES THROUGH...AND MORE SPECIFICALLY PRECIPITATION CHANCES DURING THE AFTERNOON SATURDAY...AS IF THE SURFACE BOUNDARY LINGERS...LOW LEVEL CONVERGENCE AND MOIST UNSTABLE ENVIRONMENT MAY PROMOTE THE REDEVELOPMENT OF THUNDERSTORMS SATURDAY AFTERNOON AFTER THE MAIN UPPER FORCING DEPARTS. EITHER WAY...MOST GUIDANCE SUGGEST SOME DEGREE OF UPPER LEVEL TROUGHING SATURDAY NIGHT INTO SUNDAY..THOUGH MUCH WEAKER THEN ON SATURDAY. STURDAY NIGHT INTO SUNDAY MORNING LOOKS TO BE A QUIET PERIOD. THERE COULD BE SOME LINGERING CLOUDINESS OR MAY SOME LIGHT RAIN SHOWERS...ESPECIALLY CLOSER TO LAKE MICHIGAN. WE WILL STILL HAVE A FAIRLY MOIST ENVIORNMENT IN THE WARM SECTOR AHEAD OF THE SURFACE LOW WHERE SOME SHOWERS AND THUNDERSTORMS REMAIN POSSIBLE...ESPEICALLY GIVEN THE WPC PREFERENCE FOR A SOLUTION PROGRESSION OF THE LOW. LOW CONFIDENCE EXISTS NONETHELESS...WITH AREAS SOUTH AND EAST FAVORED FOR ANY ADDITIONAL PRECIPITATION. MODELS ARE IN VERY GOOD AGREEMENT WITH REGARDS TO THE EXPANSION OF THE UPPER RIDGE IN THE WEST OVER MUCH OF THE EASTERN TWO THIRDS OF THE COUNTY. THIS WILL BE ESPECIALLY TRUE FOR MUCH OF THE NATIONS HEARTLAND...WHILE THE SOUTH AND THE EAST COAST MAY FEEL SOME IMPACTS FROM TROPICAL STORM ERIKA AND AN ADDITIONAL CUT OFF LOW IN THE GULF OF MEXICO. THE ECMWF REMAINS THE MORE AGREESIVE MODEL WITH REGARDS TO THE LOWER LEVEL WARMING...BUT BOTH MODELS IN VERY GOOD AGREEMENT FOR AN EXTENDED PERIOD OF HIGH TEMPERATURES IN THE UPPER 80S TO LOW 90S ...AND IF THE WARMER ECMWF VERIFIES...BEGINNING TUESDAY...AFTER A TRANSITION DAY OF MID 80S ON MONDAY. ENSEMBLE TEMPERATURE ANOMALIES ARE STILL ONLY IN THE 2 STANDARD DEVIATION ABOVE NORMAL CATEGORY...BASED ON THE MORE TEMPERED GFS...AND FORTUNATELY DEWPOINTS LOOK TO PEAK IN THE MID 60S...RESULTING IN HEAT INDICES IN THE UPPER 80S TO LOW 90S. WITH A WEAK LOW LEVEL WIND COMPONENT AND THE SURFACE HIGH FOCUSED TO OUR EAST...ONSHORE FLOW AT TIMES WILL KEEP AFTERNOON CONDITIONS COOLER AT THE LAKEFRONT. KMD && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 20Z... * SOUTHEAST WINDS JUST UNDER 10KTS THIS AFTERNOON. * POSSIBLE LAKE BREEZE AND EASTERLY WINDS FRIDAY AFTERNOON. CMS //DISCUSSION...UPDATED 18Z... MAIN FORECAST CONCERN AND CHALLENGE WILL BE WIND DIRECTIONS THRU THE PERIOD. WINDS ARE GENERALLY LIGHT SOUTHEASTERLY ACROSS THE AREA EARLY THIS AFTERNOON WITH SPEEDS UNDER 10KTS THOUGH THERE IS SOME VARIABILITY TO THE WIND DIRECTIONS. A LAKE BREEZE HAS FORMED ACROSS FAR NORTHEAST IL. THIS LAKE BREEZE MAY TURN WINDS A BIT MORE EASTERLY...IF IT MAKES IT TO ORD/MDW...BUT SPEEDS SHOULD REMAIN UNDER 10KTS. SPEEDS WILL DIMINISH A BIT THIS EVENING WITH SOUTHERLY WINDS EXPECTED FRIDAY MORNING. LOW PRESSURE OVER THE PLAINS WILL MOVE TO NORTHEAST IA BY FRIDAY EVENING. THE GRADIENT WILL TIGHTEN FRIDAY AFTERNOON WITH SOUTH/SOUTHEASTERLY WINDS AROUND 10KTS FRIDAY AFTERNOON. ITS POSSIBLE A LAKE BREEZE WILL REACH ORD/MDW MID/LATE FRIDAY AFTERNOON TURNING WINDS MORE TO THE EAST/SOUTHEAST WITH THE POTENTIAL FOR 10KTS WITH THIS LAKE BREEZE. ANY PRECIPITATION FROM THE APPROACHING LOW PRESSURE SHOULD BE AFTER THE 30 HR ORD TAF AND PERHAPS EVEN AFTER 00Z AT RFD. SOME LIGHT/SHALLOW GROUND FOG IS POSSIBLE OVERNIGHT INTO FRIDAY MORNING. NOT EXPECTING ANYTHING TOO WIDESPREAD AND CONFIDENCE IS LOW SO NO MENTION WITH THIS FORECAST. CU/STRATOCU MAY BE SLOW TO SCATTER OUT ACROSS FAR NORTHEAST IL AND NORTHWEST INDIANA THIS AFTERNOON BUT CIGS SHOULD REMAIN AT OR JUST ABOVE 3KFT. CMS. //ORD AND MDW CONFIDENCE...UPDATED 20Z... * MEDIUM FOR WINDS THRU THE PERIOD. CMS //OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z... FRIDAY NIGHT...SHRA AND CHC TSRA. MAINLY VFR. SOUTHEAST WINDS. SATURDAY...SHRA AND SCHC TSRA. MVFR OR LOWER PSBL. SOUTH WINDS BCMG NORTHWEST OVERNIGHT. SUNDAY...VFR. NORTH WINDS BCMG SOUTH OVERNIGHT. MONDAY AND TUESDAY...VFR. SOUTH WINDS. WEDNESDAY...VFR. SOUTHEAST WINDS. JEE && .MARINE... 256 PM CDT HIGH PRESSURE EAST OF LAKE MICHIGAN WILL CONTINUE EAST TONIGHT...AS LOW PRESSURE OVER THE CNETRAL PLAINS DEEPENS AND MOVES INTO IOWA FRIDAY AFTERNOON. THE LOW WILL SLOW ITS EASTWARD PROGRESS AS THE RIDGE AXIS ASSOCAITED WITH THE DEPARTING HIGH EXTENDS BACK NORTHWESTWARD TO THE NORTHERN LAKES. AS THE LOW APPROACHES FRIDAY NIGHT...A PERIOD OF GUSTY EAST THEN SOUTHEAST WINDS WILL SETUP ACROSS THE SOUTHERN HALF OF THE LAKE...POSSIBLY APPROACHING 25 KT. THE LOW WILL PASS OVER THE SOUTHERN TIP OF LAKE MICHIGAN LATER SATURDAY INTO EARLY SUNDAY AND WEAKEN. HIGH PRESSURE WILL THEN TAKE CONTROL OF THE EASTERN THIRD OF THE COUNTRY FOR MOST OF THE UPCOMING WEEK...WITH LOW PRESSURE REMAINING IN THE CENTRAL HIGH PLAINS. KMD && .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