FXUS63 KLOT 230556 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 1256 AM CDT THU MAY 23 2013 .DISCUSSION... 307 PM CDT SYNOPSIS...TODAY AND TOMORROW MORNING LOOK LIKE THE LAST OF THE ACTIVE WEATHER THROUGH AT LEAST LATE THIS WEEK AS A BLOCKING PATTERN SETS UP ALOFT. BELOW NORMAL TEMPS ARE EXPECTED TOMORROW AS THE UPPER LEVEL TROUGH PASSES OVERHEAD...BUT TEMPS RETURN TO NEAR NORMAL FOR MEMORIAL DAY. TODAY THROUGH THURSDAY... THE SURFACE LOW STRETCHES FROM NE IOWA THROUGH MICHIGAN THIS AFTERNOON WHILE ITS COLD FRONT LIES IN WESTERN MO AND EASTERN KS. THE LOW AND THE UPPER LEVEL TROUGH WILL CONTINUE TO WEAKEN WITH THE LOW PASSING THROUGH NORTHERN IL TONIGHT. FOG IS EXPECTED ACROSS THE LAKE AND MAY MOVE ONSHORE TONIGHT AS WINDS TURN NORTHEAST. NOT EXPECTING THE FOG TO MOVE TOO FAR INLAND...MAYBE AN MILE OR TWO. FOR PRECIP...THE MAJORITY OF CONVECTION HAS MOVED OUT OF THE CWA...BUT ANOTHER ROUND OF SHOWERS AND POSSIBLY SOME THUNDER IS POSSIBLE THIS AFTERNOON AND OVERNIGHT. A BREAK IN THE CLOUD COVER HAS ALLOWED SOME ISOLATED CONVECTIVE SHOWERS TO FORM MENDOTA SOUTH THROUGH SOUTHERN IL. LOW LEVEL LAPSE RATES HAVE INCREASED TO 7 DEGREES C PER KM OR GREATER IN THE AREAS THAT HAVE SEEN THE SUN. THEREFORE EXPECTING SCATTERED SHOWERS AND A FEW THUNDERSTORMS TO MOVE INTO AREAS ALONG AND SOUTHEAST OF I-55 THIS AFTERNOON. DEWPOINTS ALONG THIS LINE ARE IN THE MID TO UPPER 50S...BUT THINKING THESE SHOWERS WILL ALSO PRODUCE BRIEF HEAVY DOWNPOURS LIKE THE SHOWERS AND STORMS WE EXPERIENCED THIS MORNING. ANOTHER AXIS OF RAIN WILL STRETCH FROM NORTHERN MICHIGAN THROUGH SOUTHERN WI AND NORTHEAST IA ON THE BACKSIDE OF THE LOW. THE LINE OF SHOWERS WILL GRADUALLY SINK SOUTH...BUT THINKING THE RAIN WILL NOT INFILTRATE NORTHERN IL UNTIL AFTER MIDNIGHT TONIGHT. THE RAIN WILL LIKELY LINGER INTO THURSDAY MORNING AND GRADUALLY EXIT TO THE SOUTHEAST AS THE LOW MOVES OUT OF THE REGION. CLOUDS WILL QUICKLY ERODE WITH IT LEADING TO A MOSTLY SUNNY LATE AFTERNOON/EVENING THURSDAY. FOR TEMPS...MUCH COLDER AIR FUNNELS IN TONIGHT AND TOMORROW AS THE UPPER LEVEL TROUGH PASSES OVERHEAD. HIGH TEMPS TOMORROW WILL BE MUCH COOLER IN THE 50S AND 60S...AND COOLER BY THE LAKE DUE TO ONSHORE FLOW. TEMPS THURSDAY NIGHT ARE ANOTHER CONCERN GIVEN THE LIGHT WINDS AND CLEAR SKIES. WENT A DEGREE OR TWO COOLER...WITH ONSHORE FLOW KEEPING DOWNTOWN AND AREAS ALONG THE LAKE A BIT WARMER. PATCHY FROST IS CERTAINLY POSSIBLE LATE THURSDAY NIGHT INTO FRIDAY MORNING...ESPECIALLY NORTH OF I-80...BUT THINKING TEMPS WILL REMAIN ABOVE FREEZING ACROSS THE CWA. FRIDAY AND SATURDAY... THE BLOCKING PATTERN BEGINS TO TAKE SHAPE FRIDAY WITH A TROUGH OVER THE NORTHWEST COAST...THE RIDGE GROWS ACROSS THE GREAT PLAINS...AND THE TROUGH REMAINS OVER THE EAST COAST. THE UPPER LEVEL JET IS ALSO INCREDIBLY WEAK DURING THIS TIME FRAME...WHICH HELPS THE BLOCKING PATTERN REMAIN IN PLACE. AT THE SURFACE...A HIGH PRESSURE RIDGE SINKS SOUTH OVER THE WESTERN GREAT LAKES. THE RIDGE HELPS PUSH SOME OF THE COOLER CANADIAN AIR OUT OF THE REGION...BUT TEMPS LOOK TO REMAIN BELOW NORMAL THROUGH THE END OF THIS WEEK. GUIDANCE SUGGESTS A WEAK UPPER LEVEL DISTURBANCE MAY TRAVEL AROUND THE UPPER LEVEL RIDGE AND LEAD TO A CHANCE OF SHOWERS AND THUNDERSTORMS SATURDAY AND SUNDAY. EXTENDED...SUNDAY THROUGH TUESDAY... THE BLOCKING PATTERN BEGINS TO BREAK UP SUNDAY NIGHT INTO MONDAY AS THE EAST COAST TROUGH FINALLY BEGINS TO SHIFT NORTHEAST. THIS ALLOWS THE RIDGE TO OPEN WITH SHORT WAVE TROUGHS PASSING THROUGH OUR AREA. GUIDANCE DIFFERS ON WHERE AND WHEN THESE DISTURBANCES WILL PASS...THEREFORE WENT WITH A CHANCE OF SHOWERS AND THUNDERSTORMS THROUGHOUT THE EXTENDED. THE BEST DAY FOR PRECIP APPEARS TO BE TUESDAY OR WEDNESDAY AS AN UPPER LEVEL PASSES THROUGH SOUTHERN WI. NEXT WEEK BEGINS WITH A WARMING TREND. NEAR NORMAL TEMPS ARE EXPECTED FOR MEMORIAL DAY AND BACK INTO THE UPPER 70S OR LOW 80S BY MID WEEK. JEE && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 06Z... * IFR/LIFR CIGS THROUGH AROUND 12Z. * A PERIOD OF SHOWERS 12Z-16Z WITH CIGS LIFTING TO MVFR. * CLEARING EARLY AFTERNOON. * NORTHEAST WINDS LESS THAN 10KT THRU 12Z...THEN N TO NNE WINDS INCREASING TO 20-30KT BY MID MORNING-AFTN. ALLSOPP //DISCUSSION...UPDATED 06Z... AT 05Z COLD FRONT EXTENDED FROM JUST NORTH OF RFD TO MDW. AHEAD OF FRONT WINDS WERE WEST 5-10 KT WITH MVFR CIGS 2-3K FT. BEHIND THE FRONT WINDS WERE NORTHEAST 5-10 KT WITH CIGS DROPPING TO 3-5 HUNDRED FEET AND VSBY 3-5 MILES. LOW CIG ALREADY INTO ORD AND SHOULD SPREAD INTO RFD...DPA...AND MDW SHORTLY. THESE CONDITIONS SHOULD THEN PREVAIL THROUGH 12Z. THERE HAVE BEEN REPORTS OF PATCHY DENSE FOG OVER LAKE MI BUT VSBYS OVER LAND HAVE BEEN HOLDING IN THE 3-5 SM RANGE FOR THE MOST PART. THERE ARE A FEW SPOTTY LIGHT SHOWERS OR SPRINKLES OVER NORTHERN IL BUT THE MAIN AREA OF RAIN WAS STILL ALONG AND N OF AN AXIS FROM DBQ TO MKE. THIS WILL SHIFT SOUTH AND SOUTHEAST INTO THE CHICAGO AREA TAFS AROUND DAYBREAK. THIS AREA OF SHOWERS COMES ALONG WITH THE PUSH OF STRONGER WINDS AND COLDER DRIER AIR. THEREFORE EXPECTING CIGS AND VSBYS TO IMPROVE SLIGHTLY AFTER AROUND 12Z. COULD SEE SOME BRIEF LOCAL VSBY REDUCTION IN SHOWERS DURING THE MORNING BUT OVERALL EXPECT IMPROVING TREND THROUGH THE MORNING HOURS. SHOWERS WILL END AND WINDS WILL RAMP UP MID TO LATE MORNING. MVFR CIGS WILL LIFT AND SCATTER OUT QUICKLY BY EARLY AFTERNOON. WINDS WILL PICK UP TO 20KT WITH GUSTS OF 30 KT OR MORE THROUGH AFTERNOON. WIND DIRECTION WILL BE 360-020. WINDS WILL DROP OFF QUICKLY AROUND SUNSET. ALLSOPP //ORD AND MDW CONFIDENCE...UPDATED 06Z... * MEDIUM CONFIDENCE IN CIG FCST. * MEDIUM CONFIDENCE IN VISIBILITY FORECAST. COULD SEE VSBY DROP TO AROUND 3SM AT TIMES IN FOG OVERNIGHT AND AGAIN IN SHOWERS DURING THE MORNING. * MEDIUM CONFIDENCE IN TIMING OF RAIN. COULD BE SOME SPOTTY SPRINKLES THROUGH THE OVERNIGHT BUT MAIN AREA OF RAIN IS EXPECTED AFTER 12Z. * MEDIUM CONFIDENCE IN TIMING OF IFR CIG LIFTING TO MVFR THIS MORNING AND IN TIMING OF CLEARING THIS AFTERNOON. * HIGH CONFIDENCE IN WIND FORECAST. ALLSOPP //OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z... * FRIDAY...DRY. VFR. * SATURDAY...SLIGHT CHANCE OF TSRA AFTERNOON/EVENING. * SUNDAY THROUGH TUESDAY...CHANCE OF SHRA/SLIGHT CHANCE OF TSRA. && .MARINE... 1250 PM CDT SURFACE LOW WILL MOVE EAST OF THE LAKE TONIGHT WITH STRONG HIGH PRESSURE BUILDING INTO THE REGION. TIGHT PRESSURE GRADIENT WITH FAIRLY STRONG LATE SEASON HIGH PRESSURE WILL COMBINE WITH A HEALTHY SURGE OF COLD AIR LOOKS LIKELY TO RESULT IN A PERIOD OF GALE FORCE WINDS LATE TONIGHT INTO THURSDAY...PARTICULARLY ACROSS SOUTHERN PORTIONS OF THE LAKE. WILL BE UPGRADING GALE WATCH TO A WARNING WITH THE AFTERNOON FORECAST AND INCLUDE THE NSH IN A WARNING...WITH EXPECTATION THAT A SMALL CRAFT ADV WILL BE NEEDED TOMORROW NIGHT INTO FRIDAY FOR LINGERING WAVES. BEYOND THIS WIND EVENT AN EXTENDED PERIOD OF FAIRLY BENIGN CONDITIONS EXPECTED ON THE LAKE THROUGH THE WEEKEND WITH HIGH PRESSURE OVER THE AREA. IZZI && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...DENSE FOG ADVISORY...LMZ080-LMZ366-LMZ565-LMZ567-LMZ669-LMZ671- LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-LMZ874- LMZ876-LMZ878 UNTIL 3 AM THURSDAY. GALE WARNING...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742- LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876- LMZ878...7 AM THURSDAY TO 9 PM THURSDAY. GALE WARNING...LMZ366-LMZ565-LMZ567-LMZ669-LMZ868-LMZ870...4 AM THURSDAY TO 3 PM THURSDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO