343 AM CDT
MAIN FORECAST CONCERN THIS MORNING IS WITH EVOLUTION OF
PRECIPITATION ACROSS THE FORECAST AREA TODAY...AND ITS GRADUAL
DISSIPATION FROM THE NORTHWEST.
CLOSED UPPER LOW WAS LOCATED OVER SOUTHERN MISSOURI EARLY THIS
MORNING...WITH ITS OCCLUDED SURFACE LOW POISED TO CROSS THE
MISSISSIPPI JUST SOUTH OF KSTL. NEARLY STATIONARY COLD FRONT WHICH
SLIPPED INTO THE FORECAST AREA ON WEDNESDAY WAS ALONG THE SOUTHERN
BORDER OF THE CWA. FAIRLY IMPRESSIVE BAND OF PRECIP EXISTS WITHIN
ELEVATED FRONTAL ZONE ON THE COOL SIDE OF THE SURFACE BOUNDARY...
EXTENDING FROM WESTERN ILLINOIS NORTHEAST ACROSS SOUTHEAST WISCONSIN
AND INTO LOWER MICHIGAN AT 08Z. OVERALL RADAR TREND INDICATES
NARROWING AND SLIGHT WEAKENING OF THE REFLECTIVITY RETURNS OVER THE
PAST FEW HOURS...AND THIS TREND IS EXPECTED TO CONTINUE AS COUPLED
UPPER JET STRUCTURE BREAKS DOWN AND LOW LEVEL FRONTOGENESIS BEGINS
WEAKENS AS SYSTEM TO THE SOUTH BEGINS TO FILL. STRONGEST DEEP LAYER
ASCENT...NOTED IN LAYER Q-VECTOR CONVERGENCE AND OMEGA FIELDS...WILL
BE ACROSS THE FORECAST AREA THIS MORNING THEN WILL PASS OFF TO THE
EAST/SOUTHEAST OF THE CWA WITH THE UPPER TROUGH AXIS THROUGH EARLY
EVENING. GUIDANCE IN GENERALLY GOOD AGREEMENT WITH THESE TRENDS
TODAY...AND INDICATE RAIN SHOULD END ACROSS THE NORTHERN PARTS OF
THE CWA BY MIDDAY...AND ACROSS THE SOUTH/SOUTHEAST COUNTIES OF THE
CWA BY EARLY EVENING. RAINFALL...WHICH HAS EXCEEDED 0.75 INCHES OVER
PARTS OF NORTH CENTRAL ILLINOIS...SHOULD BECOME MORE FOCUSED ACROSS
THE SOUTHERN COUNTIES THIS MORNING...WITH SOME AREAS THERE PICKING
UP PERHAPS 0.25 TO 0.50 INCHES BEFORE RAIN ENDS. BLUSTERY NORTHEAST
WINDS GUSTING TO 35 MPH AT TIMES THROUGH MIDDAY WILL MAKE FOR A
RATHER RAW-FEELING DAY...WITH TEMPS STRUGGLING TO BREAK THE 50
DEGREE MARK IN MANY AREAS AND PREFER COOLER MAV GUIDANCE.
CLOSED LOW SLOWLY FILLS AND TRACKS OFF TO THE SOUTHEAST INTO THE
SOUTHERN APPALACHIANS TONIGHT...ALLOWING AMPLIFIED UPPER RIDGE TO
SPREAD ACROSS THE AREA AND SURFACE HIGH PRESSURE RIDGE TO MOVE INTO
NORTHWEST IL BY FRIDAY MORNING. CLEARING SKIES...DECREASING WINDS
AND COOL/LOW DEW POINT AIR SHOULD LEAD TO FAIRLY STRONG RADIATIONAL
COOLING CONDITIONS...ESPECIALLY ACROSS FAR NORTH CENTRAL IL WHICH
WILL BE CLOSER TO THE RIDGE AXIS COME MORNING. HAVE INCLUDED SOME
PATCHY FOG LATE TONIGHT THERE...WITH KRFD HAVING REPORTING 0.80
INCHES OF RAIN. FOR THE SAME REASONS HAVE GONE A LITTLE CLOSER TO
THE MUCH COLDER MAV GUIDANCE FOR NORTH CENTRAL IL TONIGHT.
SURFACE RIDGE DRIFTS ACROSS THE FORECAST AREA FRIDAY AND FRIDAY
EVENING. PLENTY OF SUNSHINE AND SLIGHT MODERATION OF TEMPS ALOFT
SHOULD HELP TO OFFSET OTHERWISE COOL EASTERLY LOW LEVEL FLOW...
WITH GUIDANCE TEMPS IN THE LOW-MID 50S LOOKING REASONABLE WITH
SHALLOW MIXING. WINDS THE SHIFT MORE SOUTHERLY FRIDAY NIGHT WITH
WARM ADVECTION RAMPING UP ABOVE THE BOUNDARY LAYER IN RESPONSE TO
LARGE SCALE TROUGH MOVING ACROSS THE WESTERN CONUS. AS HAS BEEN THE
CASE FOR MANY RUNS NOW...GUIDANCE CONTINUES TO LIFT A NEGATIVELY
TILTED MID LEVEL SHORT WAVE TROUGH OUT OF THE LARGE SCALE TROUGH AND
ACROSS THE PLAINS AND UPPER MIDWEST THROUGH THE WEEKEND. WHILE SOME
DIFFERENCES DO REMAIN AMONGST VARIOUS GUIDANCE WITH THE
SPEED/POSITION OF THE SURFACE LOW THROUGH EARLY SUNDAY...IT PASSES
WELL NORTHWEST OF THE WFO CHICAGO FORECAST AREA AND PRESENTS MAINLY
INCREASINGLY WINDY AND MILDER WEATHER. LOW LEVEL FLOW INITIALLY FROM
THE SOUTH-SOUTHEAST IS RATHER DRY PER TIME SECTIONS AND SOUNDINGS
FROM VARIOUS MODELS...AND ALL GUIDANCE IS DRY FOR THE CWA THROUGH
ABOUT 12Z SUNDAY. LONGER RANGE GFS/ECMWF RUNS WRAP OCCLUDED COLD
FRONT THROUGH THE AREA SUNDAY NIGHT...WITH THE POTENTIAL FOR SPOTTY
LIGHT PRECIP EVENTUALLY DEVELOPING IN THE NARROW LOW LEVEL MOISTURE
AXIS ALONG THE FRONT SUNDAY NIGHT ACROSS THE SOUTHEAST HALF OF THE
CWA.
STILL APPEARS THAT THE LOW LEVEL THERMAL RIDGE AXIS PASSES THROUGH
SATURDAY NIGHT...WITH THE WARM SECTOR OCCLUDING SUNDAY WITH THE
APPROACH OF THE SFC FRONT. HAVE MAINTAINED FORECAST TEMPS IN THE
GUIDANCE TEMPS IN THE UPPER 50S TO LOWER 60S LOOK OK FOR NOW GIVEN
THE LOW LEVEL THERMAL PROGS. SOUTH WINDS LOOK TO BECOME FAIRLY GUSTY
SUNDAY WITH DEEPER MIXING AHEAD OF THE SURFACE FRONT. GFS BUFFER
SOUNDINGS INDICATE 35-40 MPH GUSTS POSSIBLE.
FRONT THEN BECOMES NEARLY STATIONARY ACROSS OR JUST SOUTHEAST OF
THE CWA ON MONDAY AS IT BECOMES ALIGNED WITH THE MID/UPPER FLOW.
THIS WILL CONTINUE TO FOCUS A LOW CHANCE POP ACROSS THE SOUTHEAST
CWA MONDAY...BEFORE INCREASING AND SPREADING ACROSS THE ENTIRE
FORECAST AREA LATER MONDAY NIGHT INTO WEDNESDAY AS GUIDANCE BRINGS
ANOTHER UPPER TROUGH AND ITS ASSOCIATED SURFACE LOW ALONG THE FRONT
EARLY NEXT WEEK.
RATZER
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 20Z...
* GUSTY NORTHEAST WINDS DIMINISHING AROUND 00Z.
* MVFR CEILINGS IMPROVING THROUGH THE EVENING.
* LIGHT RAIN IN THE AREA UNTIL ABOUT 22Z. OCCASIONAL MVFR VIS AT
MDW. VFR VIS AT ORD.
PAW
//DISCUSSION...UPDATED 18Z...
LOW PRESSURE SYSTEM CENTERED OVER SOUTHERN IL WILL CONTINUE MOVING
TO THE EAST. THE TERMINALS HAVE BEEN ON THE NORTHERN FRINGE OF A
LARGE AREA OF PRECIPITATION ASSOCIATED WITH THE LOW...WHICH WILL
ALSO MOVE AWAY TO THE EAST. HIGH PRESSURE WILL BE BUILDING INTO
THE AREA FROM THE WEST TONIGHT. THIS WILL ALLOW WINDS TO DIMINISH
RAPIDLY THIS EVENING AND CEILINGS TO CLEAR OUT. A CLASSIC SET UP
FOR FOG TO DEVELOP TOWARDS DAYBREAK ON FRIDAY...ESPECIALLY AT RFD
AND DPA.
PAW
//ORD AND MDW CONFIDENCE...UPDATED 20Z...
* HIGH CONFIDENCE IN WIND...CEILING AND PRECIPITATION TREND.
MEDIUM CONFIDENCE IN TIMING FOR EACH ELEMENT.
PAW
//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...
FRIDAY NIGHT...VFR.
SATURDAY...VFR.
SUNDAY...SLIGHT CHANCE OF SHRA LATE...OTHERWISE VFR.
MONDAY...SLIGHT CHANCE OF SHRA...OTHERWISE VFR.
TUESDAY...SHRA LIKELY...OTHERWISE VFR.
WEDNESDAY...CHANCE OF SHRA...OTHERWISE VFR.
RODRIGUEZ
&&
.MARINE...
225 PM CDT
AS THE LOW PRESSURE OVER SOUTHERN IL MIGRATES EAST...THE PRESSURE
GRADIENT WILL GRADUALLY RELAX OVER SOUTHERN LAKE MI TONIGHT. THIS
WILL ALLOW FOR NORTHEAST WINDS TO FALL SLOWLY AWAY FROM GALE
CRITERIA. WIND SPEED OBSERVATIONS NEAR THE SURFACE ARE ALSO
TRENDING DOWN...MANY JUST BELOW 30 KTS AS OF 215 PM. GUSTS
OF 25 TO 30 KTS WILL REMAIN POSSIBLE THROUGH THE EVENING HOURS.
WAVE HEIGHTS WILL ACCORDINGLY FALL TONIGHT...WITH THE HIGHEST
HEIGHTS SEEN BETWEEN THE SOUTH BUOY AND CHICAGO GIVEN THE LONG
DURATION NORTHEAST WIND DIRECTION. GIVEN THE HIGHER WINDS IN THE
IL AND IN NEAR SHORE AREAS...HAVE ISSUED A SMALL CRAFT ADVISORY TO
FOLLOW THE GALE WARNING. THIS WILL BE IN EFFECT INTO FRIDAY
MORNING WITH THE SLOWLY SUBSIDING WAVES. THE HIGH PRESSURE RIDGE
WILL MOVE OVER THE AREA QUICKLY DURING FRIDAY OFFERING A BRIEF
RESPITE...BEFORE SOUTHERLY FLOW AND A TIGHTENED PRESSURE GRADIENT
ONCE AGAIN BUILDS OVER LAKE MI. THIS LOOKS TO SUPPORT GALE
CONDITIONS...POTENTIALLY AS EARLY AS SATURDAY AFTERNOON...BUT MOST
FAVORED SATURDAY NIGHT INTO SUNDAY.
MTF
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
LMZ878 UNTIL 3 PM THURSDAY.
SMALL CRAFT ADVISORY...NEARSHORE WATERS
UNTIL 10 AM FRIDAY.
&&
$$
