Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 260453
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1153 PM CDT SAT JUL 25 2015

.UPDATE...
ISSUED AT 902 PM CDT SAT JUL 25 2015

UPDATES TO FORECAST ISSUED THIS EVENING TO ACCOUNT FOR
THUNDERSTORM ACTIVITY WHICH DEVELOPED ALONG A FRONTAL BOUNDARY
OVER THE NORTHERN STATE AS WELL AS A WEAKER FROM AROUND DECATUR TO
CHAMPAIGN. AT THIS TIME...WEAKENING SURFACE-BASED INSTABILITY HAS
RESULTED IN A DECREASE IN ACTIVITY...NOW LARGELY CONFINED TO AREAS
NORTH OF I-74 FROM AROUND BLOOMINGTON TO THE INDIANA BORDER.
ISOLATED STORMS SHOULD CONTINUE TO AFFECT THE I-74 CORRIDOR FROM
AROUND CHAMPAIGN EASTWARD THE NEXT FEW HOURS. OVERNIGHT...ALSO
MADE A FEW MODIFICATIONS TO SPREAD THUNDERSTORMS BACK INTO WEST
CENTRAL IL A FEW HOURS EARLIER IN RESPONSE TO A CONVECTIVE SYSTEM
DEVELOPING OVER NW MISSOURI PROGGED TO ARRIVE IN THE EARLY MORNING
HOURS. LOWS SHOULD REACH AROUND 70 FROM I-74 NORTHWARD...RANGING
UP TO 73 OR SO FROM SPRINGFIELD-LAWRENCVILLE SOUTHWARD.

&&

.SHORT TERM...(TONIGHT)
ISSUED AT 254 PM CDT SAT JUL 25 2015

19Z/2PM VISIBLE SATELLITE IMAGERY IS BEGINNING TO SHOW A CU-FIELD
DEVELOPING ALONG A WEAKENING FRONTAL BOUNDARY ACROSS NORTHERN
ILLINOIS.  THIS AREA HAS BECOME MODERATELY UNSTABLE AND
UNCAPPED...AS EVIDENCED BY LATEST MESOANALYSIS INDICATING SBCAPES OF
3000-4000J/KG FROM NEAR CHICAGO WESTWARD TO MOLINE.  RAPID REFRESH
CONTINUES TO SUGGEST WIDELY SCATTERED THUNDERSTORMS DEVELOPING ALONG
THE FRONT AFTER 3 PM THEN TRACKING E/SE THROUGH THE EARLY EVENING
HOURS BEFORE DISSIPATING AFTER SUNSET.  FURTHER SOUTH...AIRMASS
REMAINS CAPPED DUE TO AMPLE CLOUD DEBRIS FROM DECAYING MORNING MCS.
AS A RESULT...HAVE OPTED TO GO WITH A DRY FORECAST ACROSS MUCH OF
THE KILX CWA FOR THE REMAINDER OF THE AFTERNOON AND EVENING...WITH
ONLY SLIGHT CHANCE POPS ALONG/NORTH OF THE I-74 CORRIDOR IN CLOSER
PROXIMITY TO THE BOUNDARY.

ONCE ANY EARLY EVENING CONVECTION FADES...EMPHASIS WILL SHIFT TO THE
CENTRAL PLAINS WHERE YET ANOTHER NOCTURNAL MCS IS EXPECTED TO FORM.
850MB JET STREAK WILL DEVELOP ACROSS NEARLY THE EXACT SAME LOCATION
AS IT DID LAST NIGHT...BASICALLY FROM THE TEXAS PANHANDLE
NORTHEASTWARD INTO EASTERN NEBRASKA.  A CLUSTER OF STORMS WILL
DEVELOP ALONG THE NOSE OF THE JET WHERE IT INTERSECTS THE TRAILING
END OF THE FRONTAL BOUNDARY...PRIMARILY ACROSS EASTERN SOUTH
DAKOTA/NEBRASKA.  THESE STORMS WILL THEN TRACK E/SE TOWARD THE
MISSISSIPPI RIVER AFTER MIDNIGHT.  SCENARIO MAY BE VERY SIMILAR TO
WHAT HAPPENED THIS MORNING...WITH THE LATEST RAPID REFRESH SHOWING
STORMS CROSSING THE RIVER INTO WEST-CENTRAL ILLINOIS TOWARD DAWN.
HAVE THEREFORE CARRIED HIGH CHANCE POPS ALONG/SOUTHWEST OF A
GALESBURG TO TAYLORVILLE LINE AFTER 3 AM...WITH ONLY SLIGHT CHANCES
FURTHER EAST.  DUE TO THE HIGHER DEWPOINT AIR IN PLACE ACROSS THE
REGION...OVERNIGHT LOWS WILL BE WARMER THAN IN RECENT NIGHTS...WITH
READINGS ONLY DROPPING INTO THE UPPER 60S AND LOWER 70S.

.LONG TERM...(SUNDAY THROUGH SATURDAY)
ISSUED AT 254 PM CDT SAT JUL 25 2015

AN MCS WILL ONCE AGAIN COME INTO CENTRAL IL DURING THE MORNING TO
DIE...JUST LIKE TODAY. HOWEVER...THIS ONE WILL CONTINUE MORE INTO
THE REST OF CENTRAL IL...UNLIKE THE ONE THIS MORNING. SO WILL HAVE
POPS THROUGHOUT THE CWA TOMORROW. MODELS SHOW SOME UNCERTAINTY WITH
THE TRACK OF THE MCS AND HOW QUICKLY IT WILL DISSIPATE SO WILL KEEP
POPS BELOW LIKELY CATEGORY BUT KEEP A HIGH CHANCE OF POPS...MAINLY
IN THE WEST AND SOUTHWEST. WILL HAVE SLIGHTLY LOWER POPS FOR THE
AFTERNOON AS MCS SHOULD BE SIGNIFICANTLY DIMINISHED...THOUGH ANY
LEFTOVER OUTFLOW BOUNDARY WILL BE A FOCUS POSSIBLE REDEVELOPMENT OF
CONVECTION. COULD BE SOME CONVECTION FOR MON THROUGH TUE...BUT LOOKS
LIKE UPPER LEVEL RIDGE WILL BE BUILDING EARLY NEXT WEEK AND THIS BUT
A CAP ON CONVECTION. HOWEVER...WILL KEEP SLIGHT CHANCE OF PCPN FOR
MON THROUGH TUE AS MODELS STILL TRY TO DEVELOP SCATTERED CONVECTION
IN THE AREA.

WITH BUILDING RIDGE EARLY NEXT WEEK...TEMPS WILL GET QUITE WARM WITH
AROUND 90 AND HIGHER EXPECTED FOR MON AND TUE. THIS WILL COMBINE
WITH MID TO UPPER 70 DWPTS...RESULTING IN HEAT INDEX READINGS OF 100
TO AROUND 110...THE HIGHEST BEING TUE. CLOUDS AND PCPN TOMORROW WILL
PRECLUDE ANY ADVISORY TOMORROW...BUT ONE MIGHT BE NEEDED FOR MON AND
DEFINITELY FOR TUE.

A BETTER DEFINED FRONTAL SYSTEM WILL MOVE THROUGH THE AREA WED AND
WED NIGHT...BREAKING DOWN THE UPPER LEVEL RIDGE FOR SHORT PERIOD OF
TIME. CONVECTION IS EXPECT SO WILL HAVE CHANCE POPS FOR WED OVER THE
WHOLE AREA AND THEN JUST IN THE SOUTHEAST FOR WED NIGHT...GIVEN HOW
FAST THIS SYSTEM MOVES THROUGH. BEHIND THIS SYSTEM HIGH PRESSURE
WILL RETURN TO THE AREA FOR THE REST OF THE WEEK. THIS HIGH PRESSURE
WILL BE AROUND FOR A LITTLE BIT LONGER AND APPEARS TO BE DRIER WITH
DEWPOINTS AND COOLER.

WED DOES LOOK WARM AND HUMID AGAIN AHEAD OF THE FRONT AND HEAT INDEX
VALUES WILL BE AROUND 95 TO OVER 100 AGAIN...MEANING AN ADVISORY MAY
BE REQUIRED IN THE EAST AND SOUTHEAST WED. HIGH TEMPS PAST WED LOOK
TO BE IN THE LOWER TO MIDDLE 80S.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1153 PM CDT SAT JUL 25 2015

MOSTLY CLEAR SKIES AND LIGHT AND VARIABLE WINDS UNTIL A
THUNDERSTORM COMPLEX APPROACHING FROM NORTHERN MISSOURI ARRIVES
EARLY IN THE MORNING. THE COMPLEX WILL LIKELY CONTINUE TO WEAKEN
OVERNIGHT. FORECAST TRACK OF THIS SYSTEM ARRIVES AT KSPI
EARLIEST...AROUND 10Z...ALTHOUGH TIMING/TRACK STILL UNCERTAIN
WITH DISCREPANCIES IN SHORT-TERM MODEL SOLUTIONS. EVEN LESS
AGREEMENT FOR EASTERN TERMINALS KBMI-KCMI-KDEC.
NEVERTHELESS...CHANCES FOR THUNDERSTORMS WILL INCREASE INTO THE
AFTERNOON AND EVENING AS A MOIST AND UNSTABLE AIR MASS REMAINS
OVER THE AREA WITH A WEAK FRONTAL BOUNDARY DRAPED ACROSS THE
REGION. HAVE INCLUDED VCTS AT KPIA-KSPI IN EARLY MORNING BUT
WAITED UNTIL 17-18Z FOR SITES FURTHER EAST. WINDS LIGHT AND
VARIABLE BECOMING E-SE AROUND 5 KTS BY MORNING.

&&

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

$$

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



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