816 PM CDT
ONLY MINOR TWEAKS TO POP/WX GRIDS THIS EVENING...TO ACCOUNT FOR
LATEST TRENDS WITH PRECIP TO THE NORTH/NORTHWEST.
LATEST RADAR IMAGERY SHOWING MAIN AREA OF PRECIP CONTINUES TO
REMAIN FURTHER NORTHWEST FROM SOUTH CENTRAL WISCONSIN SOUTHWEST
TOWARDS NORTHEAST IOWA...WITH WEAKER RETURNS CURRENTLY MOVING
THROUGH FAR NORTHERN ILLINOIS. THESE WEAKER RETURNS ARE ASSOCIATED
WITH A DEPARTING MID LEVEL WAVE WITH THE THE MAIN PRECIP AXIS TIED
TO THE LARGE SCALE UPPER LEVEL TROUGH...ATTENDANT SURFACE FEATURE
AND ASSOCIATED WEAK COLD FRONTAL BOUNDARY. AS THESE FEATURES SHIFT
EAST ACROSS THE MIDWEST TONIGHT...PRECIP CHANCES WILL INCREASE
EAST/SOUTHEAST ACROSS THE ENTIRE CWA. LATEST RUC ANALYSIS
INDICATING A WEAK TO MODERATE INSTABILITY AXIS CURRENTLY PRESENT
ACROSS SOUTHWEST WISCONSIN INTO NORTHEAST IOWA. WITH COOLER TEMPS
ALOFT/STEEPER LAPSE RATES ALSO SHIFTING SOUTHEAST WITH TIME
TONIGHT...THIS INSTABILITY AXIS WILL LIKELY BE PRESENT WITH FROPA
CLOSER TO THE MIDNIGHT TIMEFRAME. SO HAVE MAINTAINED A CHANCE OF
SHOWERS WITH A SLIGHT CHANCE OF THUNDER...BEFORE CONDITIONS DRY
AND CLEAR BEHIND THE FRONT TOWARDS EARLY MONDAY MORNING.
RODRIGUEZ
//PREV DISCUSSION...
259 PM CDT
SHORT TERM...TODAY THROUGH WEDNESDAY
MAIN CONCERN IN THE NEAR TERM IS PRECIPITATION POTENTIAL AND TIMING
THROUGH TONIGHT...AS UPPER TROUGH PROPAGATES ACROSS THE WESTERN
GREAT LAKES REGION AND PULLS A RELATIVELY WEAK COLD FRONT THROUGH
THE REGION TONIGHT. THE MAIN UPPER LEVEL SHORT WAVE AND ASSOCIATED
SURFACE LOW WILL PASS WELL TO THE NORTH OF THE FORECAST AREA...WHILE
A SECOND SHORT WAVE WILL RIPPLE SOUTHEAST FROM THE EASTERN DAKOTAS
TO THE WESTERN GREAT LAKES IN ASSOCIATION WITH 140+ KNOT UPPER JET
CORE WHICH WILL TRANSIT THE NORTHERN PLAINS AND UPPER MIDWEST
THROUGH THE PERIOD. THIS WILL HELP FOCUS STRONGER HEIGHT FALLS
A BIT FARTHER SOUTH INTO THE WESTERN LAKES...WITH THE STRONGEST DEEP
ASCENT ACROSS THE CWA TONIGHT. MID LEVEL LAPSE RATES ALSO STEEPEN TO
7.0-7.5 DEG/KM THIS EVENING...WHICH COINCIDENT WITH MID LEVEL TROUGH
MAY EVEN SUPPORT THE POTENTIAL FOR SOME ISOLATED THUNDER ALTHOUGH
ACTUAL ELEVATED CAPE IS RATHER MINIMAL PER FORECAST SOUNDINGS. THUS
WHILE SCATTERED SHOWERS MAY DEVELOP INTO MAINLY THE WEST/NORTHWEST
PARTS OF THE ILLINOIS CWA THIS AFTERNOON...IT APPEARS THE GREATER
POTENTIAL FOR MORE WIDESPREAD SHOWERS AND ISOLATED THUNDER WOULD BE
THIS EVENING AND OVERNIGHT. PASSAGE OF MID LEVEL WAVE AND SURFACE
FRONT PUSHING SOUTHEAST ACROSS CWA OVERNIGHT SHOULD ALLOW PRECIP TO
BE ENDING IN THE FAR EAST/SOUTHEAST COUNTIES TOWARD SUNRISE MONDAY
MORNING.
SHORT WAVE...AND THE ENTIRE LARGER SCALE EASTERN NOAM UPPER TROUGH
WILL THEN BE MOVING OFF TO THE EAST ON MONDAY...WITH BROAD UPPER
RIDGE SPREADING EAST ACROSS THE CENTRAL CONUS. RELATIVELY STRONG
HEIGHT RISES OF 80-100 METERS AND DEEP SUBSIDENCE SHOULD ALLOW FOR
FAIRLY QUICK EROSION OF ANY LINGERING MORNING CLOUD COVER. SURFACE
HIGH PRESSURE RIDGE SPREADS EAST ACROSS THE AREA DURING THE
AFTERNOON AND EVENING HOURS...SIMILAR TO YESTERDAY. SUNSHINE...
LIGHT WINDS AND TEMPS ONLY A FEW DEGREES COOLER THAN TODAY SHOULD
SUPPLY PLEASANT CONDITIONS TO THE CWA TO BEGIN THE WEEK.
ATTENTION THEN TURNS QUICKLY TO LOW PRESSURE DEVELOPING ACROSS THE
CENTRAL PLAINS MONDAY NIGHT. STRONG UPPER JET AND PROGRESSIVE NATURE
OF SHORT WAVE PROPAGATING ACROSS THE NORTHERN PLAINS RESULTS IN
RAPID SURFACE PRESSURE FALLS ACROSS THE MID-MISSOURI VALLEY DURING
THE NIGHT...HELPING TO INDUCE STRONG LOW LEVEL WARM ADVECTION ACROSS
THE MIDWEST WITH SURFACE WARM FRONT EXTENDING FROM THE LOW OVER
EASTERN NEBRASKA TO JUST NORTH OF THE IL/WI BORDER BY 12Z TUESDAY.
GUIDANCE IN AGREEMENT IN DEVELOPING LOW LEVEL JET OF 40-50 KT
FOCUSING FROM MN INTO WI BY MORNING...WITH MOISTURE CONVERGENCE
ALONG ELEVATED WARM FRONT ALLOWING SATURATION TO DEVELOP NORTH OF
THE SURFACE WARM FRONT MAINLY NORTH OF THE CWA. THUS HIGHEST POPS
LATE MONDAY NIGHT INTO TUESDAY MORNING WILL BE NORTH OF IL/WI BORDER
AND WILL QUICKLY DIMINISH SOUTH INTO NORTHERN IL.
BEYOND 12Z TUESDAY...GUIDANCE CONTINUES TO SHOW SOME SPREAD WITH
RESPECT TO THE TRACK AND STRENGTH OF THE SURFACE LOW AS IT MOVES
ACROSS THE AREA. ECMWF...GEM AND UKMET RUNS CONTINUE TO DEPICT
SLIGHTLY STRONGER LOW PASSING NORTH INTO WI LATE TUESDAY...WHILE 12Z
WRF AND GFS INDICATE A WEAKER SOLUTION THAT COMES ACROSS THE CWA.
DIFFERENCES ARE NOT TOO GREAT DURING THE DAY TUESDAY...WHICH WOULD
APPEAR TO PROVIDE BREEZY SOUTH WINDS WITH MOST OF CWA IN THE WARM
SECTOR...AND THE GREATEST PRECIP POTENTIAL OCCURRING ALONG/AHEAD OF
COLD FRONT WHICH PUSHES ACROSS THE FORECAST AREA LATE AFTERNOON AND
EVENING. THE COMBINATION OF A NARROW RIBBON OF 50 DEGREE SFC
DEWPOINTS AND STEEP MID-LEVEL LAPSE RATES OF 7-8 DEG/KM SUPPORT AT
LEAST A LOW CHANCE MENTION OF THUNDER DESPITE LITTLE INDICATED SFC
BASED CAPE. WARM SECTOR CAPABLE OF PRODUCING TEMPS IN THE MID/UPPER
70S ESPECIALLY ACROSS CENTRAL/SOUTHERN PARTS OF THE CWA...THOUGH
WILL BE A BIT CONSERVATIVE GIVEN THAT MAXES WILL BE CLOUD
COVER/PRECIP TREND DEPENDENT.
ALTHOUGH A FORECAST MORE ALIGNED WITH THE EC/GEM/UK SOLUTIONS IS
INITIALLY PREFERRED...THE TREND TOWARD THE MORE SUPPRESSED/SOUTH
SOLUTION NOTED IN THE 12Z GEFS ENSEMBLE COMPLICATES THE PICTURE
PARTICULARLY POST-FROPA IN THE WEDNESDAY AND THURSDAY TIME RANGE AS
THE SOUTHEASTWARD PROGRESSION OF THE FRONT IS SLOWED AND PRECIP
CHANCES WOULD LINGER. GFS/WRF SOLUTIONS DEPICT ANOTHER WAVE RIPPLING
ALONG THE FRONT AS WELL...MAKING IT TOUGH TO ELIMINATE POPS
WEDNESDAY INTO THURSDAY WITH UPPER TROUGH AXIS COMING THROUGH AS
WELL. IN EITHER CASE...SURFACE COLD FRONT SHOULD CLEAR THE SOUTHEAST
PART OF THE CWA BY 12Z WEDNESDAY. 850 TEMPS FALL TO AROUND -1 C BY
00Z THURSDAY...SUGGESTING TEMPS MAY STRUGGLE TO RISE MUCH THROUGH
THE DAY AS COLD ADVECTION OFFSETS DIURNAL HEATING. HIGHS WEDNESDAY
EXPECTED TO RANGE FROM 50 TO THE UPPER 50S...SOME 20 DEGREES COOLER
THAN TUESDAY.
LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY
LARGE POSITIVE TILT UPPER TROUGH IS PROGGED TO PUSH SLOWLY EAST
ACROSS THE REGION THROUGH THURSDAY...MAINTAINING A SLIGHT CHANCE OF
SHOWERS BEFORE AN ELONGATED AREA OF SFC HIGH PRESSURE BUILDS FROM
THE CENTRAL AND SOUTHERN PLAINS TO THE GREAT LAKES REGION THURSDAY
NIGHT. THIS COULD MAKE FOR A FAIRLY CHILLY NIGHT...WITH THE BEST
RADIATIVE COOLING CONDITIONS IN A COLD AIR MASS. RIDGE SETTLES SOUTH
OF THE AREA FRIDAY HOWEVER AS PATTERN REMAINS PROGRESSIVE ALOFT.
LONGER RANGE GUIDANCE INDICATES ANOTHER UPPER TROUGH DEVELOPING
ACROSS THE REGION FRIDAY...THOUGH SPREAD INCREASES IN MODEL
SOLUTIONS WITH RESPECT TO HOW MUCH AMPLIFICATION OF THIS TROUGH
OCCURS AND DEGREE OF ANY PRECIP THREAT. GENERAL AGREEMENT IN TROUGH
MOVING OFF SATURDAY WITH SFC HIGH PRESSURE AND DRY WEATHER.
GFS/ECMWF BOTH IN GOOD AGREEMENT WITH RIDGE MOVING OFF SUNDAY AND A
RETURN TO SOUTH/SOUTHWEST LOW LEVEL FLOW HERALDING A MODERATION IN
TEMPS. BLENDED GUIDANCE GENERALLY ACCEPTED BY DAYS 6-7 WITH MAXES
AROUND 50 RISING TO NEAR 60 BY SUNDAY...AND LOWS MAINLY IN THE 30S.
RATZER
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 06Z...
* SHOWERS AT MDW FOR THE NEXT HR OR SO.
* WIND SHIFT TO THE NORTHWEST EARLY THIS MORNING...THEN WINDS
TURNING BACK WESTERLY BY AFTERNOON AND SOUTHERLY THIS EVENING.
CMS
//DISCUSSION...UPDATED 06Z...
BACK EDGE OF SHOWERS/SCATTERED TS CURRENTLY MOVING ACROSS THE
CHICAGO AREA TERMINALS AND SHOULD BE EAST OF GYY BY 07Z-08Z.
NARROW AREA OF SOUTHWESTERLY WINDS BETWEEN THE PRECIP AND THE
COLD FRONT...THUS THE WIND SHIFT TO THE NORTHWEST STILL AN HR OR
TWO AWAY. NORTHWEST WINDS WILL THEN GRADUALLY TURN BACK WESTERLY
DURING THE MORNING HRS AND PICK UP IN SPEED TO 10-12KTS BY MIDDAY
AS THE NORTHERN EDGE OF A RIDGE OF HIGH PRESSURE PASSES ACROSS
THE AREA MONDAY AFTERNOON. WINDS WILL TURN BACK SOUTHERLY INTO
THIS EVENING. CMS
//ORD AND MDW CONFIDENCE...UPDATED 06Z...
* MEDIUM CONFIDENCE REGARDING WIND SPEEDS/DIRECTION AND WIND
SHIFTS THROUGH THE PERIOD. CMS
//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...
TUESDAY...STRONG/GUSTY SOUTHERLY WINDS THROUGH AFTERNOON SHIFTING
NORTH IN THE EVENING. MVFR CIGS POSSIBLE LATE. CHANCE OF SHRA.
SLIGHT CHANCE OF TSRA.
WEDNESDAY...MVFR/IFR POSSIBLE EARLY. CHANCE OF SHRA.
THURSDAY...SLIGHT CHANCE OF SHRA.
FRIDAY...VFR.
SATURDAY...VFR.
&&
.MARINE...
217 AM CDT
LOW PRESSURE MOVING ACROSS SOUTHERN ONTARIO THIS MORNING HAS PUSHED
A COLD FRONT ACROSS LAKE MICHIGAN. WESTERLY WINDS IN THE WAKE OF
THIS FRONT WILL CONTINUE TODAY...BUT THEY ARE EXPECTED TO SLOWLY ABATE
THROUGHOUT THE AFTERNOON.
ANOTHER AREA OF LOW PRESSURE IS EXPECTED TO MOVE INTO NORTHERN
ILLINOIS LATER ON TUESDAY. AS THIS OCCURS...A WARM FRONT EXTENDING
TO THE EAST OF THIS LOW MAY LIFT ACROSS PORTIONS OF SOUTHERN LAKE
MICHIGAN. THIS WARM FRONT WILL LIKELY BE A MAJOR TRANSITION ZONE
BETWEEN GUSTY SOUTHERLY WINDS SOUTH OF THE FRONT...TO GUSTY
NORTHEASTERLY WINDS TO THE NORTH. GUSTY OFFSHORE SOUTHERLY WINDS
MAY BE STRONG ENOUGH TO RESULT IN SMALL CRAFT CONDITIONS FOR THE
INDIANA AND POSSIBLY THE ILLINOIS NEAR SHORE WATERS...DEPENDING ON
THE NORTHWARD EXTENT OF THE WARM FRONT. THERE CONTINUES TO BE
UNCERTAINTY ON THE EXACT NORTHWARD EXTENT OF THE WARM FRONT. BECAUSE
OF THIS...WE WILL HOLD OFF ON ANY HEADLINES AT THIS TIME.
THE LOW/COLD FRONT WILL PUSH SOUTH OF THE LAKE BY WEDNESDAY. THIS
WILL ALLOW GUSTY NORTHERLY WINDS TO DEVELOP ACROSS THE ENTIRE LAKE.
ALTHOUGH GALE FORCE WINDS ARE NOT ANTICIPATED BEHIND THE FRONT...THERE
COULD BE A PERIOD OF 25 TO 30 KT WINDS ON WEDNESDAY. ALSO DUE TO THE
LONG NORTH TO SOUTH FETCH...WAVES ALONG THE SOUTHERN HALF OF THE
LAKE MAY BE IN THE 4 TO 8 FT RANGE. THIS WILL LIKELY PRODUCE SMALL
CRAFT CONDITIONS AGAIN WEDNESDAY AND WEDNESDAY NIGHT.
KJB
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&
$$
