879
FXUS63 KILX 090456
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1156 PM CDT TUE JUL 8 2008
DISCUSSION
ISSUED 900 PM CDT TUE JUL 8 2008
BULK OF HEAVIER RAIN/STRONG STORMS ALONG PRE FRONTAL TROF HAVE PUSHED
SOUTH AND EAST OF FORECAST AREA. MEANWHILE...ADDITIONAL
SHOWERS/STORMS ALONG SURFACE COLD FRONT ARE PUSHING ACROSS EASTERN
IOWA/NORTHWEST ILLINOIS. THESE SCATTERED SHOWERS/STORMS WILL
LIKELY IMPACT PARTS OF CENTRAL/SOUTHEAST ILLINOIS THROUGH THE
NIGHT. THESE CELLS STILL HAVE THE POTENTIAL TO PRODUCE LOCALLY
HEAVY RAINFALL. HOWEVER...THE SEVERE THREAT SHOULD BE LOW DUE THE
LACK OF DIURNAL HEATING AND PREVIOUS CONVECTION ACROSS THE
FORECAST AREA.
WILL DO SOME ADDITIONAL CLEAN UP TO GRIDS/ZONES PER LATEST
TRENDS...BUT THE OVERALL FLAVOR OF THE FORECAST LOOKS PRETTY GOOD.
BAK
AVIATION
ISSUED 1156 PM CDT TUE JUL 8 2008
WEAK COLD FRONT CURRENTLY MAKING ITS WAY INTO CENTRAL ILLINOIS.
THIS FRONTAL PASSAGE WILL BRING THE PRECIPITATION RISK FOR THE 06Z
TAF PERIOD TO AN END. STILL...SHOWERS AND POSSIBLY A THUNDERSTORM
REMAIN POSSIBLE FOR THE NEXT FEW HOURS...PRIMARILY ACROSS
KSPI/KDEC/KCMI TERMINALS. CEILINGS...IF ANY...SHOULD BE IN THE
VFR CATEGORY AFTER SUNRISE...BUT A FEW PERIODS OF IFR CIGS ARE
POSSIBLE OVERNIGHT UNTIL DRIER AIR FILTERS IN BEHIND THE FRONT.
EXPECT WINDS TO BE 10 KTS OR LESS THROUGH THE PERIOD AS HIGH
PRESSURE BUILDS IN BEHIND THE FRONT.
BAK
PREV DISCUSSION
ISSUED 222 PM CDT TUE JUL 8 2008
SHORT TERM...TONIGHT THROUGH FRIDAY...
PRE-FRONTAL TROUGH EXTENDING FROM KANSAS CITY EASTWARD TO NEAR
PEORIA HAS BECOME ACTIVE WITH CONVECTION SINCE THERE HAS BEEN A FEW
HOURS FOR THE PREVIOUSLY OVERTURNED MORNING AIRMASS TO RECOVER.
EXPECT STORMS TO CONTINUE TO SPREAD EAST AND INCREASE IN AERIAL
COVERAGE THIS EVENING. HEAVY RAINFALL WILL BE POSSIBLE OVER
LOCALIZED CELL-TRAINING AREAS...BUT THE HIGHER COVERAGE OF RAINFALL
AMOUNTS OVER FLASH FLOOD GUIDANCE VALUES WILL BE TO THE SOUTH AND
WEST OF THE FORECAST AREA. ALONG WITH THE HEAVY RAINFALL...THE
PRIMARY SEVERE WEATHER THREAT WILL BE VERY FREQUENT LIGHTNING AND
STRONG WET MICROBURSTS. HIGH PRECIPITABLE WATER VALUES ALONG WITH
MODERATE INSTABILITY WILL CREATE FAVORABLE CONDITIONS FOR ENHANCED
WATER-LOADING AND RESULTING DAMAGING WIND GUSTS...BUT THE RELATIVELY
HIGH FREEZING LEVEL WILL HOLD DOWN HAIL SIZES.
THE MAIN COLD FRONT IS ONLY JUST NOW ENTERING CENTRAL IOWA...AND IS
EXPECTED TO ARRIVE IN OUR NORTHWESTERN COUNTIES JUST AFTER MIDNIGHT
AND LIE PRETTY MUCH ACROSS THE CENTER OF THE AREA BY 12Z WED. RAIN
WILL END WITH FRONTAL PASSAGE...BUT THIS WILL LIKELY NOT OCCUR
ACROSS THE SOUTHEAST UNTIL WEDNESDAY AFTERNOON. WILL THEREFORE
CONTINUE WITH CHANCE POPS DOWN THERE THROUGH THE DAY WEDNESDAY WHICH
IS SIMILAR TIMING TO THE PREVIOUS FORECAST PACKAGES.
HIGH PRESSURE WILL THEN DOMINATE THROUGH FRIDAY BRINGING DRIER AIR
AND SLIGHT COOLER TEMPERATURES.
LONG TERM...SATURDAY THROUGH TUESDAY...
MOST LONG TERM GUIDANCE IS NOW ON BOARD WITH THE THEME OF A STRONGER
UPPER LOW MOVING ACROSS SOUTHERN CANADA LATE THIS WEEK. THIS SHOULD
BUCKLE THE SOUTHEAST STATES UPPER RIDGE AND ALLOW A COLD FRONT TO
COME DOWN INTO THE MIDWEST ON SATURDAY. PREVIOUS FORECASTER PUT IN
CHANCE POPS FOR SATURDAY AND THIS TIMING STILL LOOKS ON TRACK. WILL
ALSO EXTEND THE CHANCE POPS INTO SATURDAY NIGHT. THE FRONT BEGINS TO
SLOW DOWN ON SUNDAY...AND ALTHOUGH OBJECTIVE GUIDANCE LOWERS THE
POPS WITH THE FRONT EXPECTED TO BE TO OUR SOUTH...WILL HAND ON TO
SLIGHT CHANCE POPS FOR SUNDAY IN CASE THE FRONT ENDS UP EVEN SLOWER.
TEMPERATURES WILL ALSO CORRESPONDINGLY BE COOLER SUNDAY THROUGH
TUESDAY WITH THE CANADIAN AIRMASS ACROSS THE AREA.
THE GFS AND ECMWF BEGIN TO DIFFER AGAIN ON HOW FAST THE FRONT
RETURNS TO THE NORTH BEGINNING TUESDAY. THE GFS APPEARS TOO
AGGRESSIVE IN CHEWING SUCH A STRONG LOW EASTWARD INTO THE THROAT OF
THE SURFACE RIDGE...BUT EVEN THE ECMWF HINTS AT THE FRONT
MOVING/MODIFYING NORTH BY THEN. SO AFTER A DRY SUNDAY NIGHT THROUGH
MONDAY NIGHT...WILL STICK IN SLIGHT CHANCE POPS FOR TUESDAY.
04
ILX WATCHES/WARNINGS/ADVISORIES
FLASH FLOOD WATCH UNTIL 8 AM CDT WEDNESDAY FOR ILZ049>054-061.
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