880
FXUS63 KLOT 222354
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
654 PM CDT TUE JUN 22 2021
SHORT TERM
317 PM CDT
THROUGH WEDNESDAY NIGHT...
IT WAS ANOTHER PLEASANT - COOLER THAN NORMAL - SUMMER DAY TODAY
WITH HIGHS IN THE LOWER TO MID 70S WITH THE LOCAL AREA UNDER THE
SURFACE RIDGE AXIS.
OFF AND ON WARM ADVECTIVE SHOWERS ARE EXPECTED TO PUSH INTO THE
AREA OVERNIGHT ALONG THE NOSE OF THE LOW-LEVEL JET, POTENTIALLY
AIDED BY A WEAK MID-LEVEL DISTURBANCE. THESE SHOWERS ARE EXPECTED
TO EXPAND IN COVERAGE OVERNIGHT INTO WEDNESDAY MORNING BUT SHOULD
BE RATHER INTERMITTENT, RATHER THAN RAINING ALL NIGHT AND THROUGH
THE MORNING. THERE IS A PERIOD WHERE GUIDANCE SHOWS A WEAK AXIS
OF MUCAPE MOVES OVERHEAD WHICH WOULD SUPPORT AT LEAST MENTION OF
EMBEDDED THUNDER POSSIBLE.
THE UPPER TROUGH AXIS SHIFTS OFF TO THE EAST ON WEDNESDAY WITH
WARMER AIR LIFTING BACK INTO THE AREA BEHIND THE SHOWERS. THIS
WILL ALLOW TEMPERATURES TO WARM BACK INTO THE LOWER 80S FOR MOST
AREAS. THIS WILL ALSO BE AIDED BY MIXING DOWN OF GUSTY WINDS
THROUGH THE AFTERNOON WITH GUSTS UP TO 25-30 MPH POSSIBLE. THERE
COULD BE A FEW ISOLATED SHOWERS THAT LINGER INTO THE AFTERNOON
PERIOD, BUT FOR NOW WILL MAINTAIN A DRY FORECAST FOR THAT PERIOD.
THE STRONG LOW LEVEL JET REMAINS OVERHEAD INTO WEDNESDAY NIGHT
WHICH COULD ALLOW FOR SPORADIC STRONGER GUSTS TO PERSIST INTO THE
EVENING AND OVERNIGHT HOURS.
PETR
LONG TERM
333 PM CDT
THURSDAY THROUGH TUESDAY...
MAIN LONG TERM FORECAST FOCUS CONTINUES TO BE ON THUNDERSTORM
CHANCES AND COVERAGE THURSDAY INTO SATURDAY ALONG WITH THE POTENTIAL
FOR LOCALLY HEAVY RAINFALL AND SEVERE WEATHER.
AREAS OF CONVECTION ARE LIKELY WEST AND NORTHWEST OF THE CWA LATER
WEDNESDAY NIGHT INTO EARLY THURSDAY MORNING. GUIDANCE CONTINUES TO
INDICATE A MINOR AMPLITUDE SHORT WAVE TROUGH WILL RIPPLE THROUGH
WESTERLY MID-LEVEL FLOW, WHILE THE NOSE OF A SOUTHWESTERLY LOW LEVEL
JET ORIENTS WARM/MOIST ADVECTION INTO FAR NORTHERN IL/SOUTHERN WI
THURSDAY MORNING. THIS SUGGESTS AT LEAST SOME POTENTIAL FOR UPSTREAM
CONVECTION TO WORK INTO ESPECIALLY NORTH CENTRAL IL AND THE IL/WI
STATE LINE AFTER SUNRISE THURSDAY, THOUGH PERHAPS IN A DECAYING MODE
BY THAT TIME. CONFIDENCE REMAINS FAIRLY LOW ON EVOLUTION INTO THE
CWA, BUT CHANCE POPS CONTINUE TO APPEAR WARRANTED FOR THE NORTHWEST
CWA THURSDAY. ITS POSSIBLE THAT PRECIP CHANCES WILL REMAIN
ISOLATED/SCATTERED THURSDAY AFTERNOON/EVENING.
MEDIUM-RANGE GUIDANCE IS IN REASONABLY GOOD AGREEMENT IN BRINGING
ANOTHER SOMEWHAT MORE AMPLIFIED MID-LEVEL TROUGH ACROSS THE AREA
LATE THURSDAY NIGHT INTO FRIDAY, BEFORE A LARGE UPPER TROUGH DIGS
ACROSS THE UPPER MIDWEST AND GREAT LAKES REGION INTO THE WEEKEND. A
PAIR OF SURFACE LOWS ACCOMPANY THESE UPPER FEATURES, WHICH SLOWLY
TRAIL A SURFACE COLD FRONT INTO THE AREA FRIDAY NIGHT THROUGH
SUNDAY. SOME TIMING/LOCATIONS DIFFERENCES REMAIN, WHICH ALONG WITH
ANY MODULATION OF MCS OUTFLOW BOUNDARIES AND EFFECTS ON INSTABILITY
DURING THE THE PERIOD, BUT STRONG, POSSIBLY SEVERE THUNDERSTORMS ARE
CERTAINLY POSSIBLE. IN ADDITION, PRECIPITABLE WATER VALUES APPROACH
2 INCHES ON THURSDAY BUT ON FRIDAY WITH LOWER 70S DEWPOINTS,
POSSIBLE MID 70S DEWPOINTS POOLING ALONG THE FRONTAL BOUNDARY,
PRECIPITABLE WATER VALUES PUSH INTO THE 2 TO 2.30 INCH RANGE. THUS,
TORRENTIAL RAIN AND LOCALIZED FLOODING WOULD BE POSSIBLE. MODEL QPF
AMOUNTS VARY QUITE A BIT REGARDING THE PLACEMENT OF THE HEAVIEST
AXIS, BUT IN GENERAL, THE MODELS ARE SHOWING THE POTENTIAL FOR
SEVERAL INCHES OF RAIN NEARBY. HIGH POPS FROM THE BLENDED GUIDANCE
STILL LOOK FINE FOR THIS TIME PERIOD.
WITH THE UPPER TROUGH EXPECTED TO BE OVER THE REGION THROUGH AT
LEAST EARLY NEXT WEEK, POSSIBLY CLOSING OFF AS AN UPPER LOW FOR A
TIME AS THE ECMWF AND GEM ARE INDICATING, AT LEAST CHANCE POPS ARE
NEEDED FOR THE REST OF THE EXTENDED PERIOD. ITS LIKELY THAT AS THESE
TIME PERIODS APPROACH, POPS CAN BE TRIMMED AT NIGHT WITH MAINLY
DIURNALLY DRIVEN ACTIVITY BUT TOO EARLY FOR THAT DETAIL YET. AND THE
FRONT MAY BE STRONG ENOUGH TO CLEAR PRECIP FROM THE AREA FOR PART OF
THE TIME THIS WEEKEND.
BETTER MOISTURE AND FRONTAL FOCUS MOVES EAST/SOUTHEAST OF THE AREA
INTO EARLY NEXT WEEK, THOUGH UPPER LOW WOBBLING IN THE VICINITY AS
INDICATED IN EC/GEM SOLUTIONS MAY WARRANT AT LEAST SOME CHANCE
POPS INTO MONDAY/TUESDAY.
CMS/RATZER
RATZER
AVIATION
FOR THE 00Z TAFS...
AVIATION FORECAST CONCERNS:
* SHOWERS AND PERHAPS AN ISOLATED THUNDERSTORM OR TWO DEVELOPING
LATE TONIGHT AND PERSISTING INTO WEDNESDAY MORNING.
* SOUTH-SOUTHWEST WINDS BECOME SOMEWHAT GUSTY LATE TONIGHT AND
MORE SO WEDNESDAY, WITH GUSTS NEAR 30 KTS POSSIBLE WEDNESDAY
AFTERNOON.
* BREEZY CONDITIONS PERSIST WEDNESDAY EVENING, MAINTAINING SOME
DEGREE OF SURFACE GUSTS. 40-45 KT LOW LEVEL JET WILL RESULT IN
LLWS POTENTIAL ESPECIALLY IF SURFACE GUSTS REMAIN ON THE LOWER
SIDE.
A MID-LEVEL DISTURBANCE DIGGING SOUTHEAST FROM THE UPPER MISSOURI
VALLEY WAS INDUCING SOUTH-SOUTHWESTERLY RETURN FLOW WEST OF THE
MISSISSIPPI RIVER LATE THIS AFTERNOON. THE RESULTING LOW LEVEL JET
WAS PRODUCING ELEVATED SHOWERS AND THUNDERSTORMS WITHIN THE REGION
OF MOIST ASCENT FOCUSED ACROSS IA EARLY THIS EVENING. THIS
ACTIVITY IS EXPECTED TO DEVELOP EAST-SOUTHEAST INTO PARTS OF
NORTHERN IL LATER THIS EVENING, WITH SHOWERS AND A FEW ISOLATED
THUNDERSTORMS PERSISTING THROUGH WEDNESDAY MORNING AS THE LOW
LEVEL AXIS SHIFTS EAST. THE BEST CHANCE OF THUNDERSTORMS IS EXPECTED
TO REMAIN MAINLY TO THE WEST AND SOUTHWEST OF THE TERMINALS DURING
THIS PERIOD, THOUGH AN ISOLATED THUNDERSTORM CAN'T BE RULED OUT
ESPECIALLY EARLY WEDNESDAY MORNING. KRFD MAY HAVE THE BEST
POTENTIAL FOR ISOLATED THUNDER, AND HAVE INCLUDED A TEMPO MENTION
THERE LATER TONIGHT. IT DOES APPEAR THAT A PERIOD OF SCATTERED
SHOWERS WILL AFFECT THE TERMINALS HOWEVER. CLOUD BASES AND
PREVAILING VISIBILITIES ARE EXPECTED TO REMAIN VFR.
LIGHT WINDS WILL BACK SOUTH-SOUTHWEST THIS EVENING, AND WILL
INCREASE A BIT OVERNIGHT AS WARM ADVECTION STRENGTHENS. SOME GUSTS
AROUND 20 KTS ARE POSSIBLE LATE DESPITE THE NOCTURNALLY STABILIZED
BOUNDARY LAYER AS FLOW INCREASES ALOFT. SOUTHWEST WINDS WILL
INCREASE WEDNESDAY, WITH GUSTS AROUND 30 KT POSSIBLE BY AFTERNOON
AS THE SURFACE PRESSURE GRADIENT TIGHTENS AND 850 MB FLOW
INCREASES INTO THE 30-35 KT RANGE. WINDS WILL LIKELY REMAIN
SOMEWHAT GUSTY EVEN AFTER SUNSET WEDNESDAY NIGHT, THOUGH SOME
POTENTIAL FOR LLWS WILL EXIST AS THE LOW LEVEL JET INCREASES TO
40-45 KTS.
RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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