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 18Z...
* STRONG GUSTY NORTHEAST WINDS DIMINISHING LATE THIS AFTERNOON
INTO THIS EVENING.
* MVFR CEILINGS IMPROVING THROUGH THIS EVENING.
* A FEW PERIODS OF -RA POSSIBLE UNTIL MID AFTERNOON.
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 18Z...
* HIGH CONFIDENCE IN WIND DIRECTION AND SPEED.
* MEDIUM CONFIDENCE IN CEILING TREND.
* MEDIUM CONFIDENCE IN PRECIPITATION TREND.
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...
828 AM CDT...UPDATED...
AS THE SURFACE LOW HAS WORKED EAST INTO SOUTHERN IL...THE
NORTHEAST WINDS ACROSS SOUTHERN LAKE MI HAVE FURTHER INCREASED.
CHICAGO AREA RADAR WIND PROFILES INDICATE 35 TO 40 KT WINDS WITHIN
3000 FT OF THE GROUND...AND SUCH GUST SPEEDS HAVE BEEN SEEN NEAR
THE SURFACE FROM KENOSHA SOUTH TO THE CHICAGO CRIB. THE PRESSURE
GRADIENT DRIVING THE WINDS REMAINS AT A SIMILAR STRENGTH ACROSS
SOUTHERN LAKE MI AND THE NEARSHORE AREAS OF IL AND IN THROUGH
EARLY THIS AFTERNOON. THUS HAVE EXTENDED THE GALE WARNING INTO
MID-AFTERNOON. NEAR SHORE AREAS ARE BECOMING MORE FAVORED TO SEE
SMALL CRAFT ADVISORY CONDITIONS THROUGH THIS EVENING.
MTF
PREV DISCUSSION...
SURFACE LOW ACROSS SOUTHERN MISSOURI WILL CONTINUE TO DEEPEN THIS
MORNING AND SHIFT TO THE EAST...ACROSS SOUTHERN ILLINOIS. THE
OCCASIONAL GALE FORCE WINDS ACROSS THE SOUTHERN LAKE WILL CONTINUE
THROUGH THE EARLY MORNING HOURS...OR POTENTIALLY INTO THE LATE
MORNING. WINDS WILL THEN BEGIN TO ABATE...BUT STILL REMAIN IN THE
15 TO 25 KT RANGE THROUGH THE OVERNIGHT HOURS AS THE SURFACE LOW
WEAKENS AND MOVES SOUTHEAST BEFORE HIGH PRESSURE BUILDS IN THROUGH
THE END OF THE WEEK. BY THE WEEKEND...THE HIGH PRESSURE WILL MOVE
EAST AND A DEVELOPING LOW ACROSS THE CENTRAL PLAINS WILL TIGHTEN
THE GRADIENT AS IT LIFTS NORTH INTO CANADA. THIS WILL BRING THE
CHANCES FOR SOUTHERLY GALES SATURDAY NIGHT AND INTO SUNDAY.
SHEA
&&
.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.
&&
$$
