Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 271536
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1036 AM CDT MON JUL 27 2015

.UPDATE...
ISSUED AT 1029 AM CDT MON JUL 27 2015
A WEAK BOUNDARY IS DRAPED ACROSS THE STATE THIS MORNING WITH VERY
LITTLE IN THE WAY OF CONVERGENCE. RIDGING ALOFT AND THE GENERAL
LACK OF A TRIGGER IS KEEPING THE POPS LOW OVER THE CWA THIS
MORNING EVEN WITH GENERAL INSTABILITY IN THE HOT AND MUGGY
AIRMASS. FORECAST GOING WELL OVERALL WITH TEMPS CLIMBING
CONSIDERABLY QUICKER IN THE GAPS IN THE CLOUD COVER THIS MORNING.
SOME CU DEVELOPMENT EARLY WILL ONLY CONTINUE TO FILL IN THE CLEAR
SPOTS IN THIS MORNINGS SKY AND KEEP A MOSTLY CLOUDY AFTERNOON IN
PLACE. NO SIGNIFICANT UPDATES ANTICIPATED AT THIS TIME TO THE
FORECAST OVERALL BUT WILL SEND OUT A QUICK UPDATE TO REMOVE
MORNING WORDING.

&&

.SHORT TERM...(TODAY)
ISSUED AT 247 AM CDT MON JUL 27 2015

MAIN FORECAST CONCERNS TODAY, MUCH LIKE THE PAST TWO DAYS, REVOLVE
AROUND THUNDERSTORM CHANCES AND HOW HIGH PEAK AFTERNOON HEAT INDEX
VALUES WILL CLIMB.

THUNDERSTORM COVERAGE THE PAST TWO DAYS HAS NOT BEEN BEEN VERY HIGH
DESPITE DECENT INSTABILITY AND LITTLE/NO CAPPING. FORECAST
INSTABILITY TODAY IS EXPECTED TO BE SIMILAR TO THE PAST COUPLE OF
DAYS, WITH PEAK VALUES IN THE 2500-3500 J/KB RANGE (HIGHEST IN THE
SOUTHERN HALF OF THE FORECAST AREA). SHEAR PROFILES OVER THE WEEKEND
WERE ALSO MODEST, AND SHOULD BE EVEN WEAKER TODAY WITH BULK SHEAR
VALUES ONLY FORECAST TO BE AROUND 20 KTS. THE MAIN FOCUS FOR STORMS
TODAY WILL BE THE WEAK STATIONARY FRONT THAT LIES ROUGHLY WEST-EAST
ACROSS CENTRAL ILLINOIS, AND POSSIBLY OUTFLOW BOUNDARIES FROM
CONVECTION THAT IS CURRENTLY OCCURRING JUST TO OUR SOUTH. BOTTOM
LINE, PLAN TO CARRY ONLY SLIGHT CHANCE/ISOLATED POPS TODAY, LIMITING
THEM MAINLY TO THE SOUTHERN HALF OF THE FORECAST AREA WHERE
INSTABILITY AND THE THREAT OF A FOCUSING BOUNDARY SHOULD BE HIGHEST.

TEMPERATURES TODAY SHOULD BE A LITTLE WARMER THAN YESTERDAY, MOSTLY
DUE TO LESS PRECIPITATION COVERAGE AND AN ASSOCIATED REDUCTION IN
CLOUD COVER. HOWEVER, WITH THE LINGERING STATIONARY BOUNDARY IN
PLACE, AND LIGHT LOW LEVEL WINDS IN ITS VICINITY, NO SIGNIFICANT
AIRMASS CHANGE IS ANTICIPATED. THIS SCENARIO RESULTS IN PEAK
AFTERNOON HEAT INDEX VALUES AROUND 100 OVER THE SOUTHERN PORTION OF
THE FORECAST AREA. SO, WHILE IT WILL BE QUITE WARM/HUMID ONCE AGAIN
TODAY, EXPECTED VALUES REMAIN BELOW ADVISORY CRITERIA.

.LONG TERM...(TONIGHT THROUGH SUNDAY)
ISSUED AT 247 AM CDT MON JUL 27 2015

DEEP UPPER TROUGH ALONG THE WEST COAST HELPING TO PUSH THE UPPER
RIDGE EASTWARD THE NEXT COUPLE DAYS...AS A STRONG LOW DEVELOPS
WITHIN THE TROUGH AND LIFTS NORTHEAST INTO WESTERN ONTARIO BY
WEDNESDAY MORNING. TUESDAY STILL LOOKING TO BE THE HOTTEST DAY OF
THE PERIOD WITH 925 MB TEMPERATURES REACHING 27-28C BY AFTERNOON.
MOST OF THE CWA SHOULD SEE TRIPLE DIGIT HEAT INDICES BY TUESDAY AND
BE NEAR 110 FROM ABOUT SPRINGFIELD-HAVANA WESTWARD. WE`RE STARTING
TO GET CLOSE TO THE TIME WE`LL NEED TO ISSUE A HEAT ADVISORY...BUT
WITH ADVISORY CONDITIONS STILL OVER 30 HOURS AWAY...WILL LIKELY WAIT
FOR THE AFTERNOON FORECAST PACKAGE BEFORE ISSUING IT.

COLD FRONT ASSOCIATED WITH THE LOW STILL EXPECTED TO CROSS THE
FORECAST AREA ON WEDNESDAY...WITH SOME 100-105 HEAT INDICES EAST OF
I-57 BEFORE THE FRONT BRINGS LOWER DEW POINTS BY MID AFTERNOON. MORE
COMFORTABLE CONDITIONS EXPECTED THE REMAINDER OF THE WEEK WITH A
GENERAL NORTHWEST FLOW...ALTHOUGH DEW POINTS ARE EXPECTED TO START
CREEPING UP AGAIN NEXT WEEKEND.

PRECIPITATION-WISE...ANY ISOLATED STORMS SHOULD FADE OFF EARLY THIS
EVENING. HAVE LARGELY REMOVED POP`S FOR TUESDAY AS THERE NOT BE MUCH
OF A FORCING MECHANISM IN MOST AREAS...ALTHOUGH THE NMM MODEL HINTS
AT SOME ISOLATED CONVECTION ACROSS WESTERN ILLINOIS DURING THE
AFTERNOON AS THE SOUTHERLY FLOW STARTS TO KICK IN. MAIN FOCUS FOR
RAIN WILL BE WITH THE PASSAGE OF THE FRONT...PRIMARILY LATE TUESDAY
NIGHT AND WEDNESDAY MORNING. DRY CONDITIONS EXPECTED THE REMAINDER
OF THE WEEK...WITH THE NEXT CHANCES ON SUNDAY WITH THE ARRIVAL OF A
COLD FRONT BY AFTERNOON AS ADVERTISED BY THE GFS AND ECMWF MODELS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 656 AM CDT MON JUL 27 2015

PATCHY IFR OR LOWER FOG/STRATUS IS IMPACTING CENTRAL ILLINOIS
EARLY THIS MORNING. THE LOW CLOUDS SHOULD BE RATHER SHALLOW AND
BURN OFF QUICKLY THIS MORNING. AFTER THE FOG/STRATUS BURNS OFF,
VFR CONDITIONS ARE EXPECTED TO PREVAIL AT LEAST UNTIL LATE
TONIGHT. THEN, ANOTHER ROUND OF FOG/STRATUS IS POSSIBLE. WHILE AN
ISOLATED SHOWER OR THUNDERSTORM CAN`T BE RULED OUT TODAY AROUND
THE HOURS OF PEAK HEATING, COVERAGE IS EXPECTED TO BE TOO LOW TO
MENTION IN THE TERMINALS AT THIS TIME.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...HJS
SHORT TERM...BAK
LONG TERM...GEELHART
AVIATION...BAK



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