805
FXUS63 KILX 291746
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1246 PM CDT THU JUL 29 2021
SYNOPSIS
ISSUED AT 156 AM CDT THU JUL 29 2021
OPPRESSIVE HEAT IS EXPECTED TODAY AS HEAT INDEX VALUES SURGE INTO
THE TRIPLE DIGITS. SHOWERS AND THUNDERSTORMS WILL LIKELY DEVELOP
LATER THIS AFTERNOON AND EXTEND INTO EARLY EVENING ALONG AND AHEAD
OF A COLD FRONT. A FEW OF THESE STORMS MAY BECOME SEVERE WITH
DAMAGING WINDS, LARGE HAIL, LOCALIZED FLASH FLOODING, AND EVEN A
TORNADO POSSIBLE. COOLER TEMPERATURES ARRIVE FRIDAY AND WILL
EXTEND INTO EARLY NEXT WEEK.
UPDATE
ISSUED AT 1043 AM CDT THU JUL 29 2021
STORMS STILL ONGOING IN THE NORTH AND SLOWLY MOVING SOUTH-
SOUTHEAST AND DISSIPATING WHILE MOVING SOUTHEAST. LOTS OF CIRRUS
OVER THE AREA AS WELL AND THIS COULD HOLD TEMPS DOWN A BIT.
HOWEVER, ANY BREAKS IN THE CLOUDS AND TEMPS SHOULD STILL QUICKLY
RISE WHERE THE HOLES ARE. SO ONLY DROPPED TEMPS BY 1-2 DEGREES.
WITH DWPTS STILL IN THE MID 70S OVER MOST OF THE AREA, HEAT INDEX
VALUES ARE STILL EXPECTED TO REACH 105 OR HIGHER OVER THE AREA AS
WELL...SO NOT CHANGE TO THE ADVISORY PLANNED. SO, OVERALL HAVE
MADE ADJUSTMENTS TO THE POP/WX GRIDS TO ACCOUNT FOR CURRENT
CONDITIONS AND FORECAST FOR THIS AFTERNOON...STILL EXPECTING MORE
CONVECTION, AND SMALL UPDATE TO TEMPS. UPDATE WILL BE SENT
SHORTLY.
SHORT TERM
(TODAY AND TONIGHT)
ISSUED AT 156 AM CDT THU JUL 29 2021
IMPACTFUL WEATHER IS EXPECTED TODAY ACROSS THE REGION AS A DUAL
THREAT BEARS DOWN ON THE MIDWEST. DANGEROUS HEAT HAS TRIGGERED A
HEAT ADVISORY FOR THIS AFTERNOON, WHILE A SEVERE WEATHER EPISODE
LOOMS BY EVENING.
DANGEROUS HEAT:
THE PERIPHERY OF A 594MB HEAT RIDGE CONTINUES TO BUILD EASTWARD
INTO PORTIONS OF THE MISSISSIPPI AND OHIO RIVER VALLEYS.
TEMPERATURES ARE EXPECTED TO WARM INTO THE LOWER 90S THIS
AFTERNOON JUXTAPOSED TO SURFACE DEWPOINTS CLIMBING INTO THE UPPER
70S. THIS COMBINATION OF HEAT AND HUMIDITY WILL PRODUCE HEAT INDEX
VALUES BETWEEN 105F - 110F, AND HAS PROMPTED A HEAT ADVISORY FOR
OUR ENTIRE OUTLOOK AREA UNTIL 8 PM CDT.
SEVERE WEATHER POTENTIAL:
ALL EYES REMAIN ON THE MCC PUSHING ACROSS WI/IA/IL EARLY THIS
MORNING. WHILE CONVECTION MAY LINGER INTO THE DAYLIGHT HOURS
ACROSS NORTHERN IL, THE EXPECTATION IS FOR THIS COMPLEX OF STORMS
TO WEAKEN AS THE LLJ BEGINS TO RECEDE AND THE MAIN MID- LEVEL
SHORTWAVE DEPARTS TOWARD THE EASTERN GREAT LAKES REGION. A QUICK
GLANCE AT LOT/DVN RADAR IMAGERY REVEALS A PAIR OF OUTFLOW
BOUNDARIES THAT ARE SAGGING SOUTHWARD ACROSS NORTHERN ILLINOIS
AHEAD OF A WEAKLY FORCED COLD FRONT. THIS CONVECTIVE DEBRIS WILL
PROVE CRITICAL FOR STORM RE- INITIATION LATER THIS AFTERNOON.
THE BOUNDARY LAYER WILL BECOME VERY UNSTABLE TODAY AHEAD OF THE
COLD FRONT, AND WILL BE AIDED BY AN ELEVATED MIXED-LAYER THAT
ADVECTS IN FROM THE NORTHWEST. UPPER 70S SURFACE DEWPOINTS AND
STEEP MID- LEVEL LAPSE RATES WILL YIELD HIGHLY BUOYANT PARCELS
(4000-5000 J/KG SBCAPE) AHEAD OF THE FRONT AS A CAPPING INVERSION
ERODES BY 18Z. AT THIS TIME, IT IS NOT CLEAR WHETHER CONVECTIVE
INITIATION WILL OCCUR ALONG A PRE-EXISTING OUTFLOW BOUNDARY, OR
THE FRONT, AS BOTH FEATURES FIGURE TO LIE IN FAIRLY CLOSE
PROXIMITY TO EACH OTHER EARLY THIS AFTERNOON.
AS WITH ANY SEVERE WEATHER SETUP, THERE ARE A FEW LIMITING
FACTORS. TODAY, THE MAIN ONE IS INSUFFICIENT DEEP LAYER SHEAR.
WITH THE UPPER- LEVEL JET CORE DISPLACED NORTHWARD ACROSS THE
GREAT LAKES REGION, CENTRAL ILLINOIS WILL ONLY HAVE 20-25 KTS OF
DEEP LAYER SHEAR TO WORK WITH. THIS FIGURES TO LIMIT THE AMOUNT OF
UPDRAFTS THAT CAN BECOME ORGANIZED/SEVERE THIS AFTERNOON. OTHER
LIMITING FACTORS INCLUDE WEAK SURFACE CONVERGENCE AND THE LACK OF
A DEFINABLE MID- LEVEL SHORTWAVE TROUGH TO HELP ENHANCE FORCING.
NEVERTHELESS, WE DO ANTICIPATE ISOLATED INSTANCES OF SEVERE
WEATHER TO DEVELOP LATER THIS AFTERNOON GIVEN THE SUPREME
INSTABILITY IN PLACE. STORM- RELATIVE HODOGRAPHS FAVOR MOSTLY
MULTI-CELL CLUSTERS, BUT A FEW DISCRETE CELLS CANNOT BE RULED OUT,
ESPECIALLY EAST OF I-57 WHERE SHEAR WILL BE HIGHEST. THUS, ALL
SEVERE WEATHER HAZARDS REMAIN POSSIBLE GOING INTO EARLY EVENING.
LOCALIZED FLASH FLOODING IS ALSO A CONCERN GIVEN THE VERY HUMID
AIR MASS. THE HREF IS SIGNALING SOME 1"+/HR RATES ACROSS THE
AREA.
THE FRONT WILL PUSH SOUTH OF OUR OUTLOOK AREA BY 03Z, AND SKIES
WILL BEGIN TO CLEAR FROM NORTH TO SOUTH IN ITS WAKE. OVERNIGHT
LOWS WILL COOL INTO THE MID-TO-UPPER 60S.
LONG TERM
(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 156 AM CDT THU JUL 29 2021
COOLER AND DRIER CONDITIONS WILL RETURN BY FRIDAY AS SURFACE HIGH
PRESSURE BEGINS TO BUILD IN FROM THE NORTH. THE NBM KNOCKS
TEMPERATURES DOWN INTO THE MID-TO-LOWER 80S HEADING INTO THIS
WEEKEND AS THE 594MB HEAT RIDGE GETS SQUEEZED WESTWARD BY A
STRONG UPPER- LEVEL LOW DEVELOPING OVER THE HUDSON BAY.
SHOWERS AND THUNDERSTORMS WILL REMAIN A POSSIBILITY LATE FRIDAY
EVENING INTO SATURDAY, MAINLY SOUTH OF A GALESBURG TO
LAWRENCEVILLE LINE, AS AN MCS SKIRTS THE MID-MISSISSIPPI VALLEY.
A STRETCH OF DRIER BUT CONTINUED COOL WEATHER THEN LOOKS LIKELY BY
SUNDAY AS ANOTHER COLD FRONT PUSHES ACROSS THE REGION. THESE
COOLER CONDITIONS WILL REMAIN IN PLACE THROUGH THE MIDDLE OF NEXT
WEEK WITH DAILY HIGHS IN THE LOW 80S AND OVERNIGHT LOWS NEAR 60.
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1246 PM CDT THU JUL 29 2021
MODELS NOT HANDLING THE CURRENT STORM SITUATION VERY WELL SO
LOCATION OF MESOSCALE FEATURES WILL BE THE KEY TO THE FORECAST.
SCATTERED STORMS STILL POPPING IN THE NORTH NEAR PIA AND MOVING
TOWARD BMI THIS AFTERNOON BUT REST OF THE AREA IS JUST SEEING
EITHER LIGHT RAIN OR HIGH BASED CLOUDS. ATMOSPHERE IS BECOMING
INCREASINGLY MORE UNSTABLE, BUT IT REMAINS CAPPED OVER MOST OF THE
AREA. THE OUTFLOW BOUNDARY IS DOWN NEAR I-72 WHILE THE FRONT IS
STILL IN NORTHERN IL. ONCE CAP ERODES AND FRONT ARRIVES, STORMS
WILL DEVELOP AGAIN...FIRST AT PIA, THEN BMI AND THEN MOVING SOUTH
TOWARD SPI/DEC/CMI. HAVE INCLUDED TEMPO GROUPS FOR ALL SITES AT
BEST GUESS OF 3HR PERIOD WHEN CONVECTION IS POSSIBLE AT EACH SITE.
OTHERWISE VCTS FOR 1-2HRS AFTER THE TEMPO GROUPS. AFTER PRECIP,
CLOUDS SHOULD SCATTER OUT AND FOG SHOULD DEVELOP GETTING AS LOW AS
4SM WITH 2SM TEMPO IN THE MORNING. WINDS WILL BE WEST TO
SOUTHWESTERLY AND THEN BECOMING NORTHWEST AFTER PRECIP AND THE
LIGHT AND VARIABLE OVERNIGHT THROUGH MORNING.
ILX WATCHES/WARNINGS/ADVISORIES
HEAT ADVISORY UNTIL 8 PM CDT THIS EVENING FOR ILZ027>031-036>038-
040>057-061>063-066>068-071>073.
UPDATE...AUTEN
SYNOPSIS...MJA
SHORT TERM...MJA
LONG TERM...MJA
AVIATION...AUTEN
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