Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 300507
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1207 AM CDT TUE JUN 30 2015

.UPDATE...
ISSUED AT 924 PM CDT MON JUN 29 2015

THUNDERSTORMS ACROSS NORTHERN IL HAVING A HARD TIME MAINTAINING
STRENGTH AS THEY SPREAD SLOWLY SOUTHWARD TOWARD CENTRAL IL. THIS
IS DUE TO GENERAL SUBSIDENCE OVER CENTRAL IL THIS EVENING IN THE
WAKE OF A DEPARTING SHORTWAVE HEADING TOWARD EASTERN GREAT LAKES
WITH ANOTHER APPROACHING FROM NNW VIA SE MINNESOTA/SW WISCONSIN.
WITH SURFACE COOLING AFTER SUNSET...INSTABILITY DRIVING THE
THUNDERSTORMS JUST NORTH OF CENTRAL IL WILL DIMINISH...FURTHER
DECREASING THUNDERSTORM ACTIVITY. HAVE MADE SOME MINOR
ADJUSTMENTS TO EVENING THUNDERSTORM CHANCES IN EARLIER
UPDATES...BUT FORECAST LARGELY ON TRACK OVERNIGHT AS THE
APPROACHING SHORTWAVE REMAINS ON TRACK TO ARRIVE EARLY IN THE
MORNING...SPREADING SHOWERS AND THUNDERSTORMS INTO THE AREA. LOWS
EXPECTED IN THE MID 60S WITH LIGHT WEST WINDS TONIGHT.

&&

.SHORT TERM...(TONIGHT)
ISSUED AT 300 PM CDT MON JUN 29 2015

19Z/2PM SURFACE ANALYSIS SHOWS 1008MB LOW OVER EASTERN
INDIANA...WITH COLD FRONT EXTENDING SOUTHWESTWARD INTO THE OZARKS.
ALOFT...A DEEP TROUGH WITH SEVERAL EMBEDDED SHORT-WAVES REMAINS IN
PLACE ACROSS THE EASTERN CONUS.  WHILE ONE IMPULSE ASSOCIATED WITH
THE SURFACE LOW HAS PASSED WELL EAST OF ILLINOIS...TWO ADDITIONAL
FEATURES ARE NOTED ON UPSTREAM WATER VAPOR IMAGERY...ONE OVER
SOUTHERN LAKE MICHIGAN AND ANOTHER OVER EASTERN MINNESOTA/NORTHERN
WISCONSIN.  THE GREAT LAKES WAVE IS CURRENTLY TRIGGERING WIDELY
SCATTERED CONVECTION ACROSS MAINLY NORTHERN ILLINOIS INTO
NORTHERN/CENTRAL INDIANA.  A FEW SHOWERS ASSOCIATED WITH THIS
FEATURE WILL DRIFT SOUTHWARD INTO THE NORTHERN KILX CWA THIS
AFTERNOON INTO THE EARLY EVENING BEFORE DISSIPATING TOWARD SUNSET.
WILL INCLUDE LOW CHANCE POPS ALONG/NORTHEAST OF A RUSHVILLE...TO
DECATUR...TO PARIS LINE THROUGH MID-EVENING ACCORDINGLY. AFTER
THAT...THINK THERE WILL BE A LULL IN PRECIP CHANCES BEFORE THE
MINNESOTA WAVE APPROACHES FROM THE NORTH LATE TONIGHT.  HAVE
THEREFORE BROUGHT LOW CHANCE POPS AS FAR SOUTH AS I-70 WELL AFTER
MIDNIGHT TOWARD DAWN TUESDAY.  FURTHER SOUTHEAST...HAVE GONE WITH A
DRY FORECAST THROUGH THE ENTIRE NIGHT SOUTH OF THE I-70 CORRIDOR.

.LONG TERM...(TUESDAY THROUGH MONDAY)
ISSUED AT 300 PM CDT MON JUN 29 2015

THE 12Z EXTENDED MODELS ARE STARTING TO GIVE SOME HOPE TO LONGER DRY
PERIODS THIS WEEK, ESPECIALLY THE NORTHERN HALF OF ILLINOIS.

IN THE EARLY EXTENDED FOR TUESDAY, THE UPPER TROUGH IN THE EASTERN
CONUS AND THE RIDGE IN THE WEST WILL ALLOW A SHORTWAVE TO DROP SOUTH
THROUGH ILLINOIS LATE TONIGHT INTO TUESDAY, TRIGGERING SHOWERS AND A
FEW THUNDERSTORMS.

SOME WEAK RIDGING ALOFT MID WEEK OVER ILLINOIS COULD PUSH THE STORM
TRACK FOR THE WEDNESDAY NIGHT SYSTEM JUST SOUTHWEST OF OUR COUNTIES.
THE BETTER CHANCES FOR STORMS FROM THAT SYSTEM SHOULD REMAIN S OF I-
70, ALTHOUGH MODEL DIFFERENCES KEEP AT LEAST CHANCE POPS AS FAR
NORTH AS I-74. WE REMAIN IN THE SPC DAY 3 MARGINAL RISK FOR STORMS
SOUTH OF I-74, BUT OVERALL CHANCES OF SEVERE ARE RELATIVELY LOW.

THE NEXT STRONGER SHORTWAVE IS PROJECTED TO AFFECT OUR FORECAST AREA
ON FRIDAY, WITH THE ECMWF/GFS/CANADIAN HAVING RELATIVELY SIMILAR
TIMING AND LOCATION OF THAT SYSTEM. THE GFS IS THE OUTLIER WITH
PRECIP, GOING NEARLY DRY DURING THAT TIME. BETTER CHANCES FOR STORMS
FRIDAY APPEAR TO BE SOUTH OF I-74.

BEYOND THAT, MODEL DIFFERENCES BECOME MORE PROMINENT, WITH
VARIATIONS ON TIMING OF UPPER LEVEL RIDGING OR TROUGHING. GENERAL
CONSENSUS IS FOR SCATTERED SHOWERS/STORMS TO BE POSSIBLE AS THE
UPPER TROUGH AXIS REMAINS CLOSE-BY IF NOT DIRECTLY ACROSS ILLINOIS
FROM SW TO NE. FROM FRIDAY NIGHT THROUGH THE WEEKEND, WE TRENDED
DOWN WITH POPS TO SLIGHT CHANCE IN THE WEST, AND LOW CHANCE IN THE
EAST CLOSER TO THE POTENTIAL TRACK OF ANY SHORTWAVES.

IN THE FAR EXTENDED, THE GFS IS ADVERTISING A POTENTIAL SHIFT TO
LONG WAVE RIDGING ALOFT STARTING MONDAY, WHICH COULD TRANSLATE INTO
A SHIFT IN THE STORM TRACK NORTH OF ILLINOIS AND BUILDING OF SOME
HEAT IN OUR AREA. THE 12Z ECMWF HAS THE OPPOSITE SOLUTION, WITH
ANOTHER TROUGH PROGRESSING FROM THE NORTHERN PLAINS AND DIGGING INTO
ILLINOIS FOR THE FIRST HALF OF NEXT WEEK. HOPEFULLY THE DRIER GFS
PANS OUT SO WE CAN GIVE THE RIVERS A CHANCE TO RECEDE FROM NEAR
RECORD FLOODING IN SOME AREAS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1207 PM CDT MON JUN 29 2015

VFR CONDITIONS ACROSS CENTRAL IL TERMINALS WITH ISOLATED
THUNDERSTORMS KCMI-KPIA NORTHWARD. THUNDERSTORMS WILL CONTINUE
SLOW MOVEMENT TO THE SOUTH OVERNIGHT. INITIAL BROKEN LINE OF
THUNDERSTORMS SHOULD PASS BY CENTRAL IL TERMINALS BY 11-14Z SO
HAVE INCORPORATED A BREAK IN VCTS AT THAT POINT...BUT SHOULD
RETURN WITH AFTERNOON HEATING SO HAVE BROUGHT VCTS BACK INTO TAFS
17-18Z. EXPECTING LOW VFR CEILINGS WITH MOST
SHOWERS/STORMS...HOWEVER STRONGER STORMS COULD PRODUCE LOCAL MVFR
CIGS/VSBYS. TIMING/LOCATION UNCERTAINTIES REMAIN WITH REGARD TO
STRONGER STORMS THAT MAY PRODUCE MVFR CONDITIONS...SO NOT
MENTIONED IN TAFS AT THIS TIME. WINDS SW-NW 5-10 KTS
OVERNIGHT...VEERING SLIGHTLY NW AND INCREASING TO 10-12 KTS AFTER
17Z. WINDS CONTINUING TO VEER NORTHERLY AROUND 00Z AND WEAKEN TO
5-8 KTS.

&&

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

$$

UPDATE...ONTON
SHORT TERM...BARNES
LONG TERM...SHIMON
AVIATION...ONTON


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