507
FXUS63 KLOT 182021
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
321 PM CDT THU JUL 18 2019
SHORT TERM
313 PM CDT
THROUGH SUNDAY...
THE ONLY ADDITIONAL CHANGE MADE TO THE GOING HEADLINES WAS TO PUSH
OFF THE START TIME OF LAKE AND PORTER IN UNTIL 15Z FRIDAY TO MATCH
THE TIMING WE MADE EARLIER IN NORTHEAST IL.
OVERALL, THE MORNING MCS PRODUCED A WAKE LOW WHICH SIGNIFICANTLY
DISRUPTED THE LARGER SCALE SURFACE PRESSURE PATTERN OVER THE AREA.
AS A RESULT, WE HAVE CONTINUED TO EXPERIENCE GUSTY EAST-
SOUTHEASTERLY WINDS OVER MUCH OF NORTHEASTERN IL. THE REMNANT
OUTFLOW BOUNDARY CURRENTLY RESIDES OVER FAR SOUTHERN BENTON AND
IROQUOIS COUNTIES IN MY SOUTHEAST. TO THE NORTH OF THIS, WINDS
ARE GENERALLY SOUTH-SOUTHEASTERLY. CLEARING SKIES HAS ALLOWED FOR
SOME DECENT RECOVERY, WITH TEMPERATURES WARMING INTO THE LOWER TO
MID 80S AT THE TIME OF THIS WRITING. IT STILL APPEARS THAT THIS
TREND OF MODIFICATION WILL CONTINUE THROUGH LATE THIS AFTERNOON AS
THE WINDS GRADUALLY VEER MORE SOUTH-SOUTHWESTERLY. BECAUSE OF
THIS IT IS EXPECTED THAT OUR HIGH TEMPERATURES FOR THE DAY WILL
HIT VERY LATE THIS AFTERNOON, OR EARLY THIS EVENING OVER NORTHERN
IL.
HEAT INDICES OVER FAR NORTHEASTERN IL AND NORTHWESTERN IN COULD
CLIMB INTO THE 90S, TO POSSIBLY NEAR 100 IN A FEW AREAS BEFORE
SUNSET AS TEMPERATURES RECOVER INTO THE MID TO UPPER 80S. HOWEVER,
THE MORE EXTREME HEAT INDICES ARE LIKELY TO REMAIN SOUTH AND WEST
OF THE CHICAGO AREA. FOR THIS REASON THE GOING START TIME OF 21Z
SEEMS GOOD FOR AREAS OUTSIDE THE CHICAGO METRO AREA.
THERE IS ANOTHER THREAT FOR SOME THUNDERSTORMS TONIGHT, BUT THIS
THREAT WILL MAINLY RESIDE TO OUR NORTH IN WI AS THE LOW-LEVEL JET
RAMPS UP AGAIN. THESE STORMS COULD AGAIN TREND TO THE EAST-
SOUTHEAST, POSSIBLY REACHING FAR NORTHERN IL OVERNIGHT. IT DOES
APPEAR THAT CAPPING WILL BE STRONGER TONIGHT OVER MUCH OF OUR
AREA, SO IT APPEARS UNLIKELY THAT THESE STORMS WOULD SURVIVE TO
FAR SOUTH INTO IL.
OTHERWISE, THE HEAT WILL BE ON FOR THE ENTIRE AREA FOR BOTH FRIDAY
AND SATURDAY. NOT MUCH HAS CHANGED WITH THE FORECAST FOR THESE TWO
DAYS. OVERALL, WE ARE EXPECTING SIMILAR CONDITIONS EACH DAY, WITH
HIGH TEMPERATURES IN THE MID TO POSSIBLY UPPER 90S, AND HEAT
INDICES AROUND 110 TO POSSIBLY AS HIGH AS 115 IN SOME AREAS.
OVERNIGHT LOWS BOTH TONIGHT AND FRIDAY NIGHT WILL REMAIN VERY WARM
AND HUMID, SO LITTLE TO NO RELIEF IS EXPECTED AT NIGHT.
A COLD FRONT IS EXPECTED TO DROP SOUTHWARD OVER NORTHERN IL LATER
SATURDAY AFTERNOON AND EVENING. THIS FRONTAL PASSAGE WILL MARK
THE END OF THE DANGEROUS HEAT ACROSS THE AREA, THOUGH IT WILL COME
AT THE PRICE OF MORE STORMS. THUNDERSTORMS LOOK LIKE A GOOD BET
OVER FAR NORTHERN IL AS EARLY AS LATE AFTERNOON SATURDAY, BUT
MOST LIKELY OVER THE AREA SATURDAY NIGHT INTO SUNDAY EVENING.
THESE STORMS ARE LIKELY TO BE VERY HEAVY RAIN PRODUCERS, AND SOME
FLASH FLOOD RISK COULD DEVELOP AS THE EASTERLY STORM MOTION COULD
RESULT IN TRAINING CELLS. THIS POSSIBILITY WILL NEED TO BE
MONITORED. SOME OF THESE STORMS COULD ALSO BE ON THE STRONG SIDE,
WITH STRONG WIND GUSTS.
OTHERWISE, EXPECT MUCH COOLER CONDITIONS OVER THE AREA FOR SUNDAY
WITH THE STORMS AND THE SHIFT TO NORTHERLY WINDS.
KJB
LONG TERM
320 PM CDT
SUNDAY NIGHT THROUGH THURSDAY...
A PERIOD OF MUCH QUIETER AND PLEASANT WEATHER IS EXPECTED FOR
MUCH OF NEXT WEEK FOLLOWING THE SATURDAY NIGHT COLD FRONT PASSAGE.
NORTHWEST FLOW ALOFT WILL SET UP OVER THE REGION FOR MUCH OF THE
WEEK AS A LARGE UPPER RIDGE BUILDS IN THE WEST AND A TROUGH SETS
UP OVER THE EAST. A LARGE AREA OF SURFACE HIGH PRESSURE IS LIKELY
TO DROP SOUTHWARD OVER THE REGION EARLY NEXT WEEK AND THIS SHOULD
RESULT IN MAINLY DRY AND COOL CONDITIONS OVER THE AREA.
TEMPERATURES IN THIS PATTERN ARE LIKELY TO ONLY BE IN THE LOW TO
MID 80S INLAND AND POSSIBLY INTO THE UPPER 70S ALONG THE LAKE
SHORES. TEMPERATURES SHOULD BEGIN TO MODERATE BACK INTO THE MID TO
UPPER 80S LATER IN THE WEEK.
KJB
AVIATION
FOR THE 18Z TAFS...
LAST OF THE SHRA/TSRA ACTIVITY EXITING TO THE EAST AT THIS TIME.
CEILINGS WILL QUICKLY IMPROVE OVER THE NEXT 1-2 HOURS AS WELL.
SOUTHEAST WINDS TRAIL THE PRECIPITATION WITH SOME 20-25 KT GUSTS
SHOWING UP IN THE CHICAGO METRO BUT THESE SHOULD BE SHORT LIVED.
WINDS WILL TURN MORE SOUTH-SOUTHEAST AND EVENTUALLY SOUTH THROUGH
MID TO LATE AFTERNOON. THERE MAY BE A LULL IN THE GUSTS PRIOR TO
20Z BUT WITH INCREASING SUNSHINE DO EXPECT GUSTS INTO THE 20 TO
PERHAPS 25 KT RANGE TO DEVELOP ACROSS THE TERMINALS. GUSTS WILL
EASE THIS EVENING WITH A LIGHT SOUTH-SOUTHWEST BREEZE OVERNIGHT.
GUSTS WILL INCREASE TO AROUND 20 KT LATER FRIDAY MORNING.
ONE OTHER CONCERN IS FOR ANOTHER ROUND OF THUNDERSTORMS TO
DEVELOP OVERNIGHT. AT THIS POINT, THEY ARE FAVORED TO REMAIN NORTH
OF THE TERMINALS, BUT WILL INCLUDE A PROB30 FOR THUNDER AT RFD
TOWARD DAYBREAK. WILL ALSO NEED TO WATCH FOR A WIND SHIFT TO
SPREAD IN FROM THE NORTH IN CONJUNCTION WITH THE STORMS TO THE
NORTH AND THEIR OUTFLOW BUT THIS IS A LOW PROBABILITY SCENARIO SO
WILL NOT INCLUDE ANY MENTION IN THE TAFS.
MDB
LOT WATCHES/WARNINGS/ADVISORIES
IL...EXCESSIVE HEAT WARNING...ILZ008-ILZ010-ILZ011-ILZ019-ILZ020-
ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-ILZ039 UNTIL 7 PM
SATURDAY.
EXCESSIVE HEAT WARNING...ILZ012-ILZ013-ILZ014...10 AM FRIDAY TO
7 PM SATURDAY.
HEAT ADVISORY...ILZ003 UNTIL 11 PM FRIDAY.
HEAT ADVISORY...ILZ004-ILZ005-ILZ006...10 AM FRIDAY TO 11 PM
FRIDAY.
IN...EXCESSIVE HEAT WARNING...INZ001-INZ002...10 AM FRIDAY TO 7 PM
SATURDAY.
EXCESSIVE HEAT WARNING...INZ010-INZ011-INZ019 UNTIL 7 PM
SATURDAY.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
UNTIL 7 PM THURSDAY.
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