Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 301946
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
246 PM CDT TUE JUN 30 2015

.SHORT TERM...(TONIGHT)
ISSUED AT 246 PM CDT TUE JUN 30 2015

18Z/1PM WATER VAPOR IMAGERY CONTINUES TO SHOW A DEEP TROUGH OVER THE
GREAT LAKES/OHIO RIVER VALLEY...WITH NORTHWESTERLY FLOW PREVAILING
FROM THE NORTHERN PLAINS TO THE TENNESSEE RIVER VALLEY.  TWO
DISTINCT SHORT-WAVES ARE EMBEDDED WITHIN THE FLOW...ONE OVER INDIANA
AND ANOTHER FURTHER UPSTREAM ACROSS SOUTHERN SASKATCHEWAN.  DESPITE
WEAK FRONTAL BOUNDARY DROPPING INTO NORTH-CENTRAL ILLINOIS THIS
AFTERNOON...UPPER SUPPORT IS VERY WEAK IN THE WAKE OF THE INDIANA
WAVE.  AS A RESULT...AM ONLY EXPECTING ISOLATED SHOWERS/THUNDER
AHEAD OF THE APPROACHING FRONT LATE THIS AFTERNOON INTO THE EARLY
EVENING.  MOST HIGH-RES MODELS SUGGEST THE GREATEST AREAL COVERAGE
OF PRECIP WILL BE ACROSS EAST-CENTRAL ILLINOIS.  HAVE INCLUDED 20-30
POPS EARLY THIS EVENING TO COVER ANY POTENTIAL CONVECTION ALONG THE
FRONT...BUT THINK THIS WILL QUICKLY DISSIPATE AFTER SUNSET.  FURTHER
NORTHWEST...A LARGE COMPLEX OF THUNDERSTORMS IS EXPECTED TO DEVELOP
AHEAD OF THE SASKATCHEWAN WAVE THIS EVENING...THEN TRACK
SOUTHEASTWARD TOWARD THE REGION OVERNIGHT INTO WEDNESDAY MORNING.
MODEL TRENDS HAVE BEEN SLOWING THIS SYSTEM AND TRACKING IT FURTHER
S/SW ACROSS MAINLY CENTRAL MISSOURI INTO SOUTHERN ILLINOIS.  HAVE
TRIMMED POPS CONSIDERABLY AFTER MIDNIGHT...WITH ONLY SLIGHT CHANCES
ALONG/SOUTHWEST OF A MACOMB...TO SPRINGFIELD...TO OLNEY LINE TOWARD
DAWN WEDNESDAY.  ELSEWHERE AROUND CENTRAL ILLINOIS...DRY CONDITIONS
WILL PREVAIL WITH PERHAPS SOME PATCHY FOG DEVELOPING.

&&

.LONG TERM...(WEDNESDAY THROUGH TUESDAY)
ISSUED AT 246 PM CDT TUE JUN 30 2015

DESPITE A LONG WAVE TROUGH REMAINING ACROSS THE EASTERN HALF OF THE
CONUS FOR MUCH OF THE NEXT WEEK, THERE STILL APPEAR TO BE A FEW DRY
PERIODS, ESPECIALLY FOR THE NORTHERN HALF OF ILLINOIS.

WEDNESDAY WILL START OUT WITH A STRONG MCS DEVELOPING IN NEBRASKA
AND A WARM FRONT EXTENDING EAST AHEAD OF THE LOW ACROSS MISSOURI AND
SOUTHERN ILLINOIS. THE 12Z MODELS HAVE ALL SLOWED DOWN THE
PROGRESSION OF THE LOW CENTER, WITH THE LOW PASSAGE NOW DELAYED
UNTIL THURSDAY. INCREASING WARM FRONTAL CIRCULATION ACROSS SOUTH-
CENTRAL ILLINOIS WILL BE THE FOCUS FOR SHOWERS AND STORMS TO DEVELOP
WELL AHEAD OF THE LOW, AS EARLY AS 12Z/7AM WEDNESDAY IN OUR SW
COUNTIES. SHOWERS AND STORMS WILL EXPAND EASTWARD DURING THE DAY,
WITH THE BEST CHANCES OF RAIN COMING WED NIGHT AS LOW CENTER REACHES
FAR SW IL BY 12Z/7AM THURSDAY. SHOWERS WILL BE CONFINED TO AREAS
SOUTH OF I-70 THURSDAY, AS THE LOW PROGRESSES INTO WESTERN KENTUCKY.

A STATIONARY FRONT LINGERING BEHIND THE LOW ACROSS SOUTHERN IL WILL
KEEP PRECIP CHANCES ACROSS OUR FAR SOUTHEASTERN COUNTIES FRIDAY
THROUGH SATURDAY NIGHT, WHILE THE REMAINDER OF OUR COUNTIES SEE A
POTENTIALLY DRY START TO THE WEEKEND. THE DRY TREND MAY END ON
SUNDAY AS A LOBE OF THE UPPER TROUGH SWINGS ACROSS IL. THE 12Z
ECMWF IS MORE AGGRESSIVE WITH PRECIP WITH THAT FEATURE, WITH THE
CANADIAN DRY AND THE GFS IN THE MIDDLE, SHOWING SCATTERED
AFTERNOON CONVECTION. WE KEPT CHANCE POPS FOR AREAS SOUTHEAST OF
THE IL RIVER FOR NOW.

A COLD FRONT ARRIVING FROM THE NORTHWEST ON MONDAY WILL PROMPT STORM
CHANCES ACROSS ALL OF IL. AS THE FRONT STALLS OUT ACROSS THE AREA,
RAIN CHANCES WILL LINGER THROUGH TUESDAY.

TEMPS ARE PROJECTED TO REMAIN BELOW NORMAL THROUGH FRIDAY, THEN
THE GFS ADVERTISES A WARMING TREND THIS WEEKEND INTO EARLY NEXT
WEEK AS AN UPPER LEVEL RIDGE TRIES TO BUILD INTO ILLINOIS. THE
ECMWF HAS CONTINUED TO DIFFER WITH THAT SOLUTION, INDICATING THE
ARRIVAL OF ANOTHER TROUGH FROM THE NORTHERN PLAINS EARLY NEXT
WEEK, AND A CONTINUATION OF BELOW NORMAL TEMPS. THE END RESULT IN
HIGHS WAS TO CLIMB TOWARD NORMAL EACH DAY SATURDAY THROUGH MONDAY,
WITH NORMAL BEING MID 80S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1238 PM CDT TUE JUN 30 2015

MAIN AVIATION FORECAST CONCERN IS THE DEVELOPMENT AND TRACK OF A
POTENTIAL STORM COMPLEX LATE TONIGHT INTO WEDNESDAY MORNING. MODEL
TRENDS HAVE BEEN SLOWER AND FURTHER SOUTH WITH THE
TRACK...GENERALLY FROM THE SOUTH DAKOTA/NEBRASKA BORDER THIS
EVENING ACROSS CENTRAL MISSOURI INTO SOUTHERN ILLINOIS BY
WEDNESDAY MORNING. BELIEVE THE CENTRAL ILLINOIS TERMINALS WILL BE
ON THE NORTHERN FRINGE OF THE PRECIP...SO HAVE ONLY INCLUDED MVFR
CEILINGS AND VCTS AFTER 13/14Z AT KSPI AND KDEC. FURTHER
NORTH...HAVE MAINTAINED DRY CONDITIONS AT THE I-74 TAF SITES. THE
ONLY OTHER ISSUE WOULD BE POSSIBLE FOG TONIGHT AS SKIES CLEAR AND
WINDS BECOME LIGHT/VARIABLE. FORECAST SOUNDINGS AND NUMERIC
GUIDANCE BOTH INDICATE SOME LIGHT FOG OVERNIGHT...SO HAVE LOWERED
VSBYS TO AROUND 3SM AFTER 09Z ACCORDINGLY.


&&

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

$$

SHORT TERM...BARNES
LONG TERM...SHIMON
AVIATION...BARNES



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