756
FXUS63 KLOT 071954
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
254 PM CDT TUE JUL 7 2020
SHORT TERM
248 PM CDT
THROUGH WEDNESDAY NIGHT...
A GENERALLY UNCAPPED ENVIRONMENT HAS BEEN COMMON ACROSS MUCH OF
THE CWA EARLY THIS AFTERNOON, THOUGH SOURCES OF LIFT, LOW-LEVEL
MIXING AND MID-LEVEL DRY AIR ENTRAINMENT HAVE LIMITED CUMULUS
GROWTH FOR MOST AREA. A SUBTLE AND SMALL KINK IN THE MID-LEVELS
EVIDENT IN WV IMAGERY WAS THE APPARENT EXTRA TRIGGER FOR STRONG
CONVECTION OVER NORTHWEST INDIANA OVER THE PAST TWO HOURS. SINCE
SURFACE MOISTURE WAS A LITTLE HIGHER (DEW POINTS AROUND 70F)
COMPARED TO MOST OF THE ILLINOIS PORTION OF THE CWA (MID TO UPPER
60S DEW POINTS), DEEPER VERTICAL GROWTH WAS ACHIEVED THERE.
ADDITIONAL POCKETS OF TOWERING CUMULUS CONTINUE TO SHOW UP ON
SATELLITE ACROSS THE REMAINDER OF THE CWA, MOST NOTABLY ON THE
LAKE BREEZE IN COOK COUNTY. WITH A LACK OF DEEPER FORCING FOR THE
NEXT COUPLE HOURS, DEVELOPMENT SHOULD BE SOMEWHAT LIMITED AWAY
FROM THE LAKE BREEZE AND ANY REMNANT OUTFLOW BOUNDARIES FROM
STORMS OVER THE PAST COUPLE HOURS.
RAPID DEVELOPMENT OF CONVECTION AHEAD OF A PRONOUNCED MCV ACROSS
NORTHEAST IOWA HAS OCCURRED IN THE PAST HOUR ACROSS SOUTHEAST MN
AND SOUTHWEST WI. THIS ACTIVITY IS EXPECTED TO SLOWLY DRIFT EAST
THROUGH THE REMAINDER OF THE AFTERNOON AMIDST WEAK DEEP-LAYER
FLOW. WHILE SUBSTANTIAL COLD POOL DEVELOPMENT IS NOT EXPECTED,
OUTFLOW FROM THIS ACTIVITY COMBINED WITH A TRAILING TROUGH INTO
EASTERN IOWA WILL BECOME A RENEWED FOCUS FOR CONVECTION MOVING
INTO THE CWA EARLY THIS EVENING. WITH MID-LEVEL LAPSE RATES
BECOMING MORE UNFAVORABLE WITH EASTWARD EXTENT, OVERALL COVERAGE
AND INTENSITY OF THE ACTIVITY SHOULD DIMINISH WITH TIME.
ULTIMATELY, RESIDUAL THUNDERSTORMS MAY REACH NORTH-CENTRAL IL
PRIOR TO SUNSET, WITH POSSIBLY SOME REMNANT SHOWERS SURVIVING INTO
THE CHICAGO METRO CLOSE TO MIDNIGHT.
A MID-LEVEL RIDGE AXIS DRIFTING OVER THE CWA WEDNESDAY MORNING
WILL SHIFT FAR ENOUGH EAST BY THE AFTERNOON TO ALLOW CAPPING FROM
THE SUBSIDENCE INVERSION TO WEAKEN. WHILE SLIGHT CAPPING SHOULD
REMAIN, ISOLATED CONVECTION COULD DEVELOP WHERE FOCUSED
CONVERGENCE EXISTS. PRIMARILY THIS WOULD BE ALONG THE LAKE
MICHIGAN LAKE BREEZE AND ANY POTENTIAL REMNANT OUTFLOW BOUNDARIES
FROM CONVECTION THIS EVENING.
LITTLE CHANGE WAS MADE TO THE TEMPERATURE FORECAST FOR WEDNESDAY
AS THE WARM STRETCH CONTINUES. WITH WEAKER CAPPING IN PLACE,
DAYTIME MIXING SHOULD AT LEAST LOWER AFTERNOON DEW POINTS A COUPLE
DEGREES FROM THE MORNING HOURS AS HAS BEEN THE CASE FOR SEVERAL
DAYS NOW. MAX TEMPS IN THE 92-94 RANGE INLAND COMBINED WITH
AFTERNOON DEW POINTS IN THE UPPER 60S WILL PRODUCE HEAT INDEX
VALUES IN THE 95- 100F RANGE.
KLUBER
LONG TERM
254 PM CDT
THURSDAY THROUGH TUESDAY...
THURSDAY WILL BE SIMILAR TO WEDNESDAY WITH HOT AND HUMID CONDITIONS
REMAINING, WITH HIGH TEMPS PERHAPS A SMIDGE LOWER THAN BEFORE DUE TO
INCREASING CLOUD COVER. THURSDAY EVENING INTO FRIDAY, SHOWER AND
THUNDERSTORM CHANCES WILL INCREASE AS AN UPPER-LEVEL WAVE AND
PERHAPS A CONVECTIVELY-GENERATED MCV APPROACHES FROM THE WEST.
DEPENDING ON THE TIMING OF THE WAVE, A FEW "PULSEY" STRONG TO SEVERE
STORMS LOOK POSSIBLE WITH FREQUENT LIGHTNING, TORRENTIAL DOWNPOURS,
SMALL HAIL, AND WIND GUSTS STRONG ENOUGH TO DOWN TREE LIMBS AS THE
MAIN RISKS.
THIS WEEKEND, THE GREAT LAKES WILL BE POSITIONED BENEATH WEAK UPPER-
LEVEL TROUGHING LEADING TO A BREAK IN THE HOT AND HUMID
CONDITIONS. SUNDAY APPEARS TO BE THE COOLEST DAY WITH HIGHS
TOPPING OFF IN THE MID TO UPPER 80S AS A SECONDARY COLD FRONT
SNEAKS IN FROM THE NORTH. HAZARDOUS SWIMMING CONDITIONS MAY
DEVELOP IN THE WAKE OF THE FRONT FOR LAKE MICHIGAN BEACHES SUNDAY
AFTERNOON AND EVENING.
BORCHARDT
AVIATION
FOR THE 18Z TAFS...
DEEP CONVECTION IS ATTEMPTING TO DEVELOP ON VARIOUS SURFACE
BOUNDARIES ACROSS NORTHERN ILLINOIS AND NORTHWEST INDIANA AT TAF
ISSUANCE, PRIMARILY ON A LAKE BREEZE IN NORTHWEST INDIANA AND A
WEAK SURFACE TROUGH FROM NORTH-CENTRAL TO WEST-CENTRAL ILLINOIS.
ISOLATED TO WIDELY SCATTERED ACTIVITY IS EXPECTED TO CONTINUE TO
DEVELOP THROUGH THE AFTERNOON ON THESE FEATURES. CONFIDENCE IN TS
DIRECTLY AFFECTING A GIVEN TERMINAL REMAINS LOW ENOUGH TO PRECLUDE
A TEMPO TS GROUP IN THE TAF, BUT COVERAGE SHOULD BE HIGH ENOUGH
THAT AIRSPACES AROUND THE TERMINALS MINIMALLY SEE SOME IMPACTS.
WHILE MID-LEVEL DRY AIR ENTRAINMENT WILL LIMIT INTENSITY OF MOST
CELLS, A FEW COULD BECOME DEEP ENOUGH TO PRODUCE GUSTY DOWNDRAFTS
OF 20-30 KNOTS IMMEDIATELY UNDER AND NEAR THE CELL.
A LOW TO MID-LEVEL WAVE MOVING SOUTHEAST ACROSS SOUTHEAST MN AND
NORTH-CENTRAL IA IS EXPECTED TO FORCE SCATTERED CONVECTION THROUGH
THIS AFTERNOON. IF COVERAGE BECOME HIGH ENOUGH TO FORM LARGER
CLUSTERS OF STORMS OR ANY EXISTING STORMS ARE MAINTAINED INTO THE
EVENING, RESIDUAL SHOWERS AND OUTFLOW WINDS MAY AFFECT THE
CHICAGO- AREA TERMINALS MID TO LATE EVENING.
OTHERWISE, CONDITIONS SHOULD BE RELATIVELY QUIET THROUGH THE
MORNING HOURS ON WEDNESDAY, WITH VRB WINDS 5 KNOTS OR LESS
(FAVORING THE SE QUADRANT THIS EVENING AND SW QUADRANT OVERNIGHT
INTO WEDNESDAY MORNING.) ENOUGH CAPPING SHOULD EXIST FOR ORD/MDW
ON WEDNESDAY AFTERNOON TO LIMIT CONVECTIVE POTENTIAL ON A LAKE
BREEZE, BUT A WIDELY ISOLATED THUNDERSTORM CANNOT BE RULED OUT.
KLUBER
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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