Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 291808
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
108 PM CDT WED JUL 29 2015

.UPDATE...
ISSUED AT 1046 AM CDT WED JUL 29 2015

COLD FRONT HAS MOVED THROUGH MOST OF THE CWA THIS MORNING WITH
SOME SLIGHTLY COOLER AND DRIER AIR MOVING INTO THE REGION FROM THE
NW. NWRLY WINDS ALSO BEHIND THE FRONT. SOME SLIGHT ADJUSTMENTS TO
THE FORECAST TO REPRESENT CURRENT CONDITIONS AND LESSEN THE POPS
BEHIND THE BOUNDARY FOR THE MORNING AND EARLY AFTERNOON.

&&

.SHORT TERM...(TODAY)
ISSUED AT 309 AM CDT WED JUL 29 2015

A COLD FRONT, CURRENTLY EXTENDING FROM THE WESTERN GREAT LAKES INTO
THE CENTRAL PLAINS, WILL SWEEP THROUGH CENTRAL AND SOUTHEAST
ILLINOIS TODAY. CURRENT INDICATIONS ARE THAT THE FRONT WILL CLEAR
THE FORECAST AREA TO THE SOUTH AND EAST BY EARLY AFTERNOON.

SHOWERS AND THUNDERSTORMS REMAIN POSSIBLE UNTIL FRONTAL PASSAGE.
HOWEVER, THE OUTFLOW BOUNDARY FROM THE COMPLEX CURRENTLY CROSSING
CENTRAL ILLINOIS, WHICH IS APPROACHING THE I-72 CORRIDOR, IS LIKELY
TO SCOUR OUT MUCH OF THE LOCAL AIRMASS AND LIMIT THE POTENTIAL FOR
DIURNAL DEVELOPMENT. ALSO, THE RELATIVELY EARLY ARRIVAL OF THE FRONT
WILL REMOVE MUCH OF THE THREAT FOR DIURNAL STORM DEVELOPMENT ANYWAY.

DO NOT PLAN TO ISSUE A HEAT ADVISORY FOR ANY OF THE FORECAST AREA
TODAY. LOCATIONS SOUTH OF I-70 MAY STILL BE ABLE BREAK 90 DEGREES
BEFORE THE FRONT ARRIVES. IF THIS OCCURS, THERE MAY BE A FEW HOUR
WINDOW WHERE HEAT INDEX VALUES REACH ADVISORY CRITERIA. HOWEVER, IF
THE OUTFLOW BOUNDARY MAKES IT SOUTH OF I-70, THE THREAT OF THIS
OCCURRING IS MUCH LESS LIKELY. IN ANY EVENT, DO NOT FEEL AN ADVISORY
IS WARRANTED FOR BORDERLINE HEAT INDEX VALUES THAT ONLY LAST A
COUPLE HOURS. BEHIND THE FRONT, WE WILL RECEIVE WELCOME RELIEF FROM
THE RECENT OPPRESSIVE HEAT/HUMIDITY.

.LONG TERM...(TONIGHT THROUGH TUESDAY)
ISSUED AT 309 AM CDT WED JUL 29 2015

WELCOME PERIOD OF LESS HUMID CONDITIONS ON TAP THE NEXT FEW
DAYS...AS UPPER RIDGE BEGINS TO RE-ESTABLISH ITSELF ACROSS THE
WESTERN U.S. STRONG UPPER LOW OVER LAKE WINNIPEG EARLY THIS MORNING
ONLY WILL MAKE SLOW NORTHEAST PROGRESS INTO HUDSON BAY BY THURSDAY
AFTERNOON...BEFORE TAKING UP SEMI-PERMANENT RESIDENCE IN THE
VICINITY THROUGH A GOOD CHUNK OF NEXT WEEK. THIS WILL RESULT IN A
PERSISTENT NORTHWEST FLOW INTO THE GREAT LAKES REGION...AS A BROAD
TROUGH ENVELOPS THE MIDWEST. WE`LL STILL BE CLOSE ENOUGH TO THE
FRINGE OF THE THERMAL RIDGE THAT AIR TEMPERATURES WILL BE IN THE MID-
UPPER 80S THROUGH THE REST OF THE WORK WEEK...WITH SOME MODEST
COOLING THIS WEEKEND AS THE BROAD TROUGH DIGS FURTHER. HOWEVER...
SOME MODEST INCREASE IN DEW POINTS IS ON TAP BY THE WEEKEND.

WITH THIS PATTERN...THE MAIN CHALLENGE FOR PRECIPITATION WILL BE
TIMING OF A SERIES OF SHORTWAVES ZIPPING THROUGH THE NORTHWEST FLOW.
ONE SUCH WAVE SHOULD BE MOVING THROUGH LATER ON FRIDAY. THE GFS IS
MOST BULLISH ON SPREADING SHOWERS/STORMS AS FAR SOUTH AS SOUTHERN
ILLINOIS BY SATURDAY MORNING...WHILE THE NAM AND CANADIAN MODELS
FOCUS IT CLOSER TO THE GREAT LAKES AND THE ECMWF IS DRY. FORECAST
SOUNDINGS FROM THE GFS ARE FAIRLY DRY...SO ITS SOLUTION OF
WIDESPREAD SHOWERS/STORMS IS A BIT SUSPICIOUS. THUS...WILL BE
KEEPING THE FORECAST DRY AT THIS TIME. NEXT WAVE SATURDAY
NIGHT/SUNDAY HAS A LITTLE MORE AGREEMENT AMONG THE VARIOUS MODELS
WITH SCATTERED STORMS...BUT TIMING OF THE SUBSEQUENT ONE FOR MONDAY
AND MONDAY NIGHT WIDENS. THE LATEST ECMWF IS A BIT MORE PROMINENT
WITH THE WAVES AND COOLER AIR NEXT WEEK (850 MB TEMPS DOWN TO 15C BY
TUESDAY VS 20C ON THE GFS)...BUT THE LONGER RANGE MODELS HAVE
STRUGGLED A BIT THE LAST COUPLE DAYS WITH THIS SOUTHWARD PUSH OF
COOLER AIR...SO WE`LL SEE WHAT THE NEXT SET OF MODEL UPDATES HAVE IN
STORE.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 105 PM CDT WED JUL 29 2015
FOR THE MOST PART, EXPECTING CLEARING BEHIND THE COLD FRONT THAT
HAS PASSED THROUGH ALL OF THE ILX TERMINALS, ALTHOUGH NOT
IMMEDIATE. IN ADDITION TO THE SCT CIRRUS, A SMALL PATCH OF IFR
CIGS MOVING JUST BEHIND THE BOUNDARY FOR THE NEXT FEW HOURS WILL
AFFECT DEC AND CMI. THEN SCATTERED CIRRUS ANTICIPATED THROUGH THE
OVERNIGHT WITH NORTHWESTERLY WINDS BECOMING MORE WESTERLY TOWARDS
MORNING. DRIER DWPTS FILTERING IN SHOULD MITIGATE THE FOG THREAT,
BUT WILL KEEP AN EYE ON THE XOVER TEMPS.

&&

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

$$

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


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