544
FXUS63 KLOT 162034
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
334 PM CDT TUE JUL 16 2019
SHORT TERM
225 PM CDT
THROUGH WEDNESDAY...
WIDELY SCATTERED SHOWERS CONTINUE ACROSS MUCH OF THE AREA,
ESPECIALLY SOUTH OF I-88. WHILE A FEW THUNDERSTORMS STILL REMAIN
POSSIBLE OVER THE NEXT FEW HOURS BEFORE THE ACTIVITY BEGINS TO
WANE, THE MAIN STORY WITH THESE SHOWERS WILL BE THE ISOLATED HEAVY
RAIN RATES. THE AIRMASS IN PLACE OVER THE AREA IS OF TROPICAL
ORIGIN AND FEATURES IN EXCESS OF 2 INCH PRECIPITABLE WATER VALUES.
THEREFORE, EXPECT VERY EFFICIENT WARM RAIN PROCESSES WITH 2+ INCH
PER HOUR RATES FROM THESE STORMS. LUCKILY IT APPEARS THE
RESIDENCE TIME OF THESE HEAVY RAIN RATES OVER A GIVEN AREA WILL
BE LIMITED AS THE CELLS MOVE NORTHEAST AROUND 15 MPH. HOWEVER, IF
ANY CELL TRAINING OCCURS, THERE IS AT LEAST SOME SMALL RISK FOR
SOME LOCALIZED AREAS OF EXCESSIVE RAINFALL. THIS WILL NEED TO BE
MONITORED OVER THE NEXT FEW HOURS.
OTHERWISE, EXPECT MUCH OF THIS ACTIVITY TO BEGIN TO WANE THIS
EVENING. THERE REMAINS A SMALL CHANCE THAT A FEW STORMS DEVELOPING
WEST OF THE AREA THIS AFTERNOON COULD MAKE IT INTO NORTH CENTRAL
IL LATER THIS EVENING BEFORE WEAKENING, BUT CONFIDENCE ON THIS
REMAINS LOW. AT THIS TIME WE CONTINUE TO MENTION A SLIGHT CHANCE
FOR A FEW STORMS OVER NORTH CENTRAL IL LATER THIS EVENING.
IT APPEARS THAT MOST, IF NOT ALL OF WEDNESDAY WILL REMAIN DRY
ACROSS THE AREA. THE ONLY EXCEPTION TO THIS IS IF A FEW ISOLATED
SHOWERS AND THUNDERSTORMS DEVELOP ALONG AN AFTERNOON LAKE BREEZE.
DUE TO THE LOW PROBABILITIES FOR ANY STORMS TO DEVELOP ALONG THIS
FEATURE, I HAVE CONTINUED WILL A DRY FORECAST WITH SUB 15% POPS
WEDNESDAY AFTERNOON. OTHERWISE, EXPECT PARTLY SUNNY SKIES AND WARM
CONDITIONS WEDNESDAY, WITH HIGHS IN THE UPPER 80S INLAND (HEAT
INDICES INTO THE MID TO UPPER 90S). HOWEVER, AREAS NEAR THE LAKE
WILL REMAIN A BIT COOLER DUE TO AN ONSHORE WIND WITH THE INLAND
MOVING LAKE BREEZE.
KJB
LONG TERM
322 PM CDT
WEDNESDAY NIGHT THROUGH TUESDAY...
ATTENTION IN THIS PERIOD CERTAINLY IS THE HEAT. AN EXCESSIVE HEAT
WATCH HAS BEEN ISSUED THURSDAY P.M. THROUGH SATURDAY P.M. FOR
COOK COUNTY, INCLUDING CHICAGO, AS THAT IS THE MOST CONCERNING
LOCATION BECAUSE OF THE URBAN HEAT ISLAND CORE OF CHICAGO WHERE
LITTLE RELIEF AT NIGHTS WILL OCCUR. NO HEADLINE YET FOR ELSEWHERE,
BECAUSE IN PART OF CONCERNS FOR MCS EFFECTS INTO THURSDAY MORNING
WHICH ARE ALSO A CONCERN FOR CHICAGO. AT LEAST AN ADVISORY LOOKS
VERY LIKELY, AND DO HAVE TIME FOR THAT WITH STILL 48 HOURS OUT.
DO THINK EXCESSIVE HEAT HEADLINES ARE POSSIBLE FOR OTHER OUTLYING
PARTS OF ILLINOIS, MAINLY NORTH CENTRAL ILLINOIS, FOR 110 HEAT
INDEX CONCERNS ON THURSDAY AFTERNOON AND/OR FRIDAY AFTERNOON.
CONFIDENCE WAS JUST A LITTLE BELOW ISSUANCE RIGHT NOW.
THE FIRST ITEM OF INTEREST CONTINUES TO BE THE MCS POTENTIAL LATER
WEDNESDAY NIGHT INTO THURSDAY MORNING AND ITS EFFECTS ON
TEMPERATURES POTENTIALLY INTO THURSDAY. ORGANIZED CONVECTION
CONTINUES TO LOOK LIKELY TO DEVELOP LATER WEDNESDAY AFTERNOON INTO
THE EVENING ACROSS OR NEAR SOUTHERN MINNESOTA. THE PRECISE
LATITUDE THIS OCCURS IS IMPORTANT AND THAT REMAINS UNCERTAIN, BUT
THERE MAY BE SOME MODULATION OF EFFECTIVE AIR UPSTREAM DUE TO THE
LATE TONIGHT INTO WEDNESDAY MORNING MCS. IN GENERAL THE TREND HAS
CONTINUED TO BE TO LEAN TOWARD THE HIGHER-RESOLUTION GUIDANCE FOR
HANDLING OF COLD POOL DEVELOPMENT AND PROROGATION FOR WEDNESDAY
NIGHT, GIVEN THAT CONFIDENCE IS HIGH IN THE OTHER SYNOPTIC
INGREDIENTS NEEDED FOR MCS DEVELOPMENT AND SUSTAINABILITY. THE
DRIVING SHORT WAVE AND MID-LEVEL SPEED MAXIMUM LOOK TO PROGRESS
EASTWARD ACROSS WISCONSIN LATE WEDNESDAY NIGHT INTO EARLY THURSDAY
MORNING, BUT THE ROBUST LOW-LEVEL JET PROVIDES CORFIDI VECTOR
MOTIONS TO THE SOUTH. WHILE THE BEST LOW-LEVEL SHEAR IS NORTH OVER
WISCONSIN, IF THE MCS IS FULLY MATURE (WHICH IS LIKELY), WITH
AMPLE REPLENISHING MOISTURE SOME ACTIVITY IS LIKELY TO GET INTO
NORTHERN ILLINOIS. WHILE IT MAY NOT BE SEVERE, THOUGH THERE IS
THAT CHANCE, IT STILL SHOULD BE PROPOGATING WITH SOME
REDEVELOPMENT/FESTERING LIKELY THURSDAY MORNING OF ACTIVITY. THE
BIG UNCERTAINTY IS HOW FAR SOUTH INTO THE CWA, AND FOR NOW HAVE
COLLABORATED AN INCREASE IN STORM CHANCES ACROSS THE CWA, BUT
PRIMARILY ALONG/NORTH OF I-88.
OUTFLOW EFFECTS AND CLOUDS WILL BE FACTORS THAT COULD OFFSET HOW
RAPIDLY WARMING OCCURS ON THURSDAY, BUT THE SYNOPTIC PATTERN OF
STRONG SOUTHWESTERLY FLOW INTO THE REGION IS FAVORABLE FOR IT TO
OCCUR QUICKLY. SO MESOSCALE FACTORS WILL BE KEY AND JUST TOO FAR
OUT IN TIME TO SAY HOW MUCH. HAVE EASED TEMPERATURES SOME IN THE
NORTHERN CWA, MAINLY THE RATE AT WHICH THEY WARM THROUGH THE
MORNING. THE ELEVATED MIXED LAYER (EML) IS FORECAST TO ADVECT OVER
THE AREA, WHICH WILL LIKELY PREVENT SHARP MIXING OF DEW POINTS
FROM A MOIST LOWER ATMOSPHERE AS NOTED IN REGIONAL SOUNDINGS
ALREADY. CERTAINLY THERE IS POTENTIAL TO SHOOT INTO THE MID 90S
AREA WIDE, AND 110 HEAT INDEX MAY BE REACHED IN NORTH CENTRAL
ILLINOIS IF THAT WERE TO OCCUR. THURSDAY STILL LOOKS BREEZY IN THE
AFTERNOON, WHICH DOES KEEP THE WET BULB GLOBE TEMPERATURE (WBGT -
INDEX FOR HEAT RELATED STRESS) DOWN SOME. FOR THURSDAY NIGHT,
CONFIDENCE IS HIGH IN A WARM AND MUGGY NIGHT TO SET THE STAGE FOR
A HOT FRIDAY.
FRIDAY HAS PERSISTENTLY BEEN A DAY FORECAST TO HAVE THE THERMAL
RIDGE POISED OVER THE AREA AND REPLENISHING SOUTHWEST FLOW UNDER
NEAR FULL SUN. THE 850 MB TEMPERATURES OF 23-25C HISTORICALLY THIS
TIME OF YEAR HAVE PROVIDED HIGHS ALL WITHIN MID 90S-LOW 100S.
HAVE UPPER 90S FORECAST FOR ALMOST THE ENTIRE AREA. DEW POINTS
WILL PROBABLY MIX OUT SOME IN THIS PATTERN, BUT HOW MUCH AND HOW
GUIDANCE IS HANDLING THAT IS DIFFICULT TO SAY FOR CERTAIN,
INCLUDING FOR SATURDAY. HEAT INDICES LOOK TO DEFINITELY WARRANT AT
LEAST HEAT ADVISORIES, AND AGAIN THE DURATION OF THE HEAT IS A
KEY FACTOR FOR AN EXCESSIVE HEAT HEADLINE.
BY SATURDAY, THE SYNOPTIC FRONT WILL BE INCHING SOUTHWARD, AND THE
TREND HAS BEEN BACK TO FURTHER SOUTH FOR SATURDAY. BUT THERE DOES
NOT LOOK TO BE MUCH ACTIVITY ALONG IT INTO SATURDAY GIVEN A FAIRLY
LAMINAR MID-LEVEL FLOW INTO THE DAY, WHICH IS WHY STILL LEANING
UNIMPEDED HEAT ON SATURDAY, AND IT COULD HAVE TEMPERATURES THAT
EQUAL FRIDAY'S. DEW POINTS AGAIN SHOULD MIX OUT AT LEAST
SOMEWHAT. THE CHANCES FOR THUNDERSTORMS START TO INCREASE LATER
SATURDAY NIGHT INTO SUNDAY AS GUIDANCE CREEPS THE BOUNDARY
SOUTHWARD WITHIN A DAMPENING UPPER RIDGE PATTERN.
MTF
AVIATION
FOR THE 18Z TAFS...
SCATTERED SHOWERS HAVE BEEN RAPIDLY DEVELOPING ACROSS THE AREA
LATE THIS MORNING. EXPECT THIS TO CONTINUE TO BE THE CASE ACROSS
MUCH OF EASTERN IL AND NORTHWEST IN AS THE REMNANTS OF BARRY MOVE
ACROSS THE AREA. DIURNAL DESTABILIZATION MAY ALSO RESULT IN SOME
THUNDERSTORMS, ESPECIALLY OVER THE SOUTHERN CHICAGO AREA
TERMINALS. THE MAIN THREAT FROM THESE SHOWERS AND STORMS WILL BE
VERY HEAVY RAINFALL. IN FACT, VISIBILITIES MAY BRIEFLY DROP UNDER
2 MILES WITH THESE SHOWERS.
THIS ACTIVITY WILL LIKELY WANE ACROSS THE AREA LATER THIS
AFTERNOON, WITH THE EVENING AND OVERNIGHT PERIOD LIKELY REMAINING
DRY. DRY WEATHER IS ALSO FORECAST FOR WEDNESDAY, THOUGH AN
AFTERNOON LAKE BREEZE COULD SPARK OFF A FEW WIDELY SCATTERED
SHOWERS OR STORMS.
WINDS MAY BACK MORE SOUTH-SOUTHEASTERLY LATER THIS AFTERNOON AND
EVENING, BUT SPEEDS WILL REMAIN LIGHT. LIGHT AND VARIABLE WINDS
ARE EXPECTED ACROSS THE AREA TONIGHT INTO WEDNESDAY MORNING.
THEREAFTER, A LAKE BREEZE WILL LIKELY SHIFT INLAND, RESULTING IN
AN AFTERNOON EASTERLY WIND SHIFT AT THE CHICAGO AREA TERMINALS.
KJB
LOT WATCHES/WARNINGS/ADVISORIES
IL...EXCESSIVE HEAT WATCH...ILZ014...NOON THURSDAY TO 7 PM SATURDAY.
IN...NONE.
LM...NONE.
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