Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 270750
AFDILX

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

.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 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1154 PM CDT SUN JUL 26 2015

FOG FORMATION IS THE MAIN CONCERN FOR THE REST OF THE NIGHT. BMI
DROPPED TO 1/4SM FG FOR A WHILE ALREADY THIS EVENING, ALTHOUGH WEB
CAMS FROM AROUND BLOOMINGTON/NORMAL DO NOT SHOW MUCH IN THE WAY
OF FOG AWAY FROM THE AIRPORT. HAVE INCLUDED A TEMPO FOR VLIFR FOG
AT BMI LATER TONIGHT. THE NAM AND HRRR ARE SHOWING AREAS OF DENSE
FOG ACROSS CENTRAL IL. WILL INCLUDE 1/2SM FG IN A TEMPO FOR DEC
AND CMI, WITH TEMPOS FOR 3/4SM AND 1SM FOR PIA AND SPI
RESPECTIVELY.

THE CIRRUS OVERCAST FROM CONVECTION IN THE PLAINS MAY REACH PIA
AND SPI LATER TONIGHT, HELPING TO KEEP DENSE FOG FROM FORMING.
EASTERN AREAS MAY SEE ENOUGH CLEAR SKIES FOR A HIGHER POTENTIAL OF
LOCALLY DENSE FOG.

ONCE THE FOG CLEARS AFTER SUNRISE, VFR CONDITIONS SHOULD PREVAIL
THE REMAINDER OF THE TAF PERIOD.

EASTERLY WINDS SHOULD PREVAIL ACROSS THE AREA AS WE REMAIN BETWEEN
A TROUGH ACROSS SOUTHERN ILLINOIS AND A STATIONARY FRONT ACROSS
NORTHERN IL. WIND SPEEDS SHOULD PREVAIL AT LESS THAN 10KT.


&&

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

$$

SHORT TERM...BAK
LONG TERM...GEELHART
AVIATION...SHIMON


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