Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 251740
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1240 PM CDT SAT JUL 25 2015

.UPDATE...
ISSUED AT 1050 AM CDT SAT JUL 25 2015

AN MCS THAT DEVELOPED OVER EASTERN NEBRASKA LATE LAST EVENING
IS RAPIDLY DECAYING ACROSS CENTRAL ILLINOIS THIS MORNING. LATEST
RADAR SHOWS VERY LITTLE PRECIP REMAINING FROM THE SYSTEM
ITSELF...WITH ONLY A FEW LIGHT SHOWERS FROM MACOMB SOUTHWARD TO
NEAR SAINT LOUIS. FURTHER EAST...WIDELY SCATTERED SHOWERS HAVE
DEVELOPED ALONG THE RESULTING OUTFLOW BOUNDARY CURRENTLY
APPROACHING THE I-57 CORRIDOR. EXPECT THE MCS TO COMPLETELY
DISSIPATE OVER THE NEXT HOUR OR SO...WHILE SCATTERED
SHOWERS/THUNDER CONTINUE ALONG THE OUTFLOW ACROSS EAST-CENTRAL
ILLINOIS THROUGH EARLY AFTERNOON. AFTER THAT...CONVECTIVE
DEVELOPMENT LATER THIS AFTERNOON IS MORE UNCERTAIN. MCV FEATURE
ALREADY EVIDENT ON RADAR/SATELLITE IMAGERY WILL TRACK
SOUTHEASTWARD INTO SOUTHERN ILLINOIS...HOWEVER HIGH-RES MODELS ARE
SHOWING LITTLE TO NO THUNDER WITH IT. MOST MODELS SUGGEST WIDELY
SCATTERED SHOWERS/THUNDER DEVELOPING ALONG A WEAKENING COLD FRONT
ACROSS NORTH-CENTRAL ILLINOIS AFTER 3PM. DUE TO STABILIZING
INFLUENCE FROM MORNING MCS AND LACK OF A STRONG FOCUSING
MECHANISM...THINK RAIN CHANCES WILL REMAIN LOW ACROSS THE AREA
TODAY. HAVE THEREFORE ONLY CARRIED 20-30 POPS. FORECAST HAS BEEN
UPDATED TO BETTER REFLECT CURRENT SKY COVER AND POP TRENDS.

&&

.SHORT TERM...(TODAY)
ISSUED AT 315 AM CDT SAT JUL 25 2015

A COUPLE WEAK FRONTAL BOUNDARIES WILL MOVE INTO THE PORTIONS OF
CENTRAL AND SOUTHEAST ILLINOIS TODAY...CONTINUING TO WEAKEN AS
THEY DO SO. THE FIRST FRONT IS A COOL FRONT...AND CURRENTLY
EXTENDS FROM THE WESTERN GREAT LAKES SOUTHWEST TO WEAK LOW
PRESSURE IN NORTHERN MISSOURI. THE SECOND FRONT IS A WARM FRONT...
AND CURRENTLY EXTENDS FROM SOUTHEAST FROM THE WEAK LOW IN
NORTHERN MISSOURI INTO THE LOWER MISSISSIPPI VALLEY. THE MAIN
CONCERN FOR TODAY IS THE EXTENT OF THUNDERSTORM DEVELOPMENT THAT
CAN BE EXPECTED WITH THESE BOUNDARIES SLOWLY PUSHING INTO THE
AREA.

THERE IS NOT A WHOLE LOT OF CONVECTION ONGOING AT THE MOMENT...AND
WHAT THERE IS EXTENDS FROM THE CENTRAL PLAINS INTO MISSOURI WHERE
THE RICHEST LOW LEVEL INFLOW EXISTS. THESE STORM COMPLEXES ARE
TENDING TO FOLLOW THE 850MB-300MB THICKNESS...WHICH IS ALSO
FAIRLY CLOSELY ORIENTED WITH THE LOW LEVEL BAROCLINIC ZONE. THIS
TRAJECTORY...IF IT PERSISTS...IS NOT CONDUCIVE TO DIRECTLY
IMPACTING THE FORECAST AREA AND/OR LEAVING OUTFLOW BOUNDARIES IN
OUR AREA.

MOST OF THE SHORT-RANGE/MESOSCALE GUIDANCE IS NOT TOO BULLISH ON
PRECIPITATION DEVELOPING ACROSS THE AREA TODAY...ESPECIALLY WHEN
COMPARED TO SOME OF THE SYNOPTIC SCALE GUIDANCE. TEND TO AGREE WITH
THE DRIER HIGH RESOLUTION SOLUTIONS GIVEN THE LACK OF A STRONG FOCUS
TODAY (VERY MODEST UPPER FORCING AND WEAK SURFACE BOUNDARIES).
HOWEVER...CAN`T SUPPORT A DRY FORECAST EITHER...GIVEN THE CAPE
VALUES FORECAST TO REACH 3000-4000 J/KG THIS AFTERNOON...COUPLED
WITH BULK SHEAR VALUES OF 25-35 KTS. SO...PLAN TO KEEP POPS LOW
FOR NOW...UNTIL MOTHER NATURE DICTATES OTHERWISE.

IT WILL CONTINUE TO GET INCREASINGLY HUMID ACROSS THE AREA
TODAY...BUT CONVECTIVE DEBRIS/POSSIBLE RAINFALL MAY KEEP ACTUAL
TEMPERATURES SIMILAR TO WHERE THEY WERE YESTERDAY. THESE FACTORS
WILL KEEP HEAT INDEX VALUES BELOW ADVISORY CRITERIA...ALTHOUGH
THEY MAY BE APPROACHING 100 IN WESTERN PORTIONS OF THE FORECAST
AREA DURING PEAK HEATING.

.LONG TERM...(TONIGHT THROUGH FRIDAY)
ISSUED AT 315 AM CDT SAT JUL 25 2015

NOT MUCH CHANGE WITH THE BUILDING HEAT AND HUMIDITY...AS UPPER LEVEL
RIDGING BUILDS EASTWARD TOWARD THE MISSISSIPPI VALLEY THROUGH EARLY
NEXT WEEK. A DIGGING TROUGH ACROSS THE PACIFIC NORTHWEST...
ASSOCIATED WITH AN UPPER LOW CURRENTLY SPINNING OVER NORTHWEST
BRITISH COLUMBIA...WILL GRADUALLY CLOSE OFF AS IT SHIFTS ALONG THE
CANADIAN BORDER THROUGH THE WEEK. THIS WILL HELP SUPPRESS THE HEAT
OVER THE UPPER MIDWEST BY THURSDAY...WITH THE COOLER TREND
PERSISTING INTO LATE WEEK. IN THE MEANTIME...IT STILL APPEARS THAT
TUESDAY WILL SEE THE BEST SHOT FOR WIDESPREAD HEAT INDEX VALUES OF
100-105 DEGREES...ALTHOUGH THE SOUTHWEST THIRD OF THE FORECAST AREA
WILL START TO SEE THESE ARRIVE MONDAY.

STILL SOME QUESTIONS ON RAIN CHANCES TONIGHT DEPENDING ON WHAT
HAPPENS DURING THE DAY...BUT GENERAL MODEL CONSENSUS CONTINUES TO
POINT TOWARD AN MCS DEVELOPING ACROSS SOUTHERN IOWA/NORTHERN
MISSOURI WHERE THE LOW LEVEL JET WILL BE INCREASING THIS EVENING. AN
EAST-SOUTHEAST MOVEMENT MAY LEAVE PARTS OF THE FORECAST AREA DRY
THROUGH THE NIGHT...BUT HAVE KEPT THE HIGHER POP`S ACROSS THE WEST
WITH SOME LIKELY POP`S AROUND JACKSONVILLE AND RUSHVILLE AFTER
MIDNIGHT. WHAT`S LEFT OF THE MCS WILL BE DIMINISHING OVERHEAD ON
SUNDAY...AND WILL HAVE LIKELY POP`S FOR A GOOD PART OF THE AREA AT
LEAST DURING THE MORNING ON SUNDAY.

RAIN TRENDS WILL SLOWLY DIMINISH EARLY NEXT WEEK AS THE CAP
STRENGTHENS WITH THE ARRIVAL OF THE UPPER RIDGE...ALTHOUGH THE ECMWF
AND GFS BOTH HINT AT SOME SCATTERED AFTERNOON STORMS ON TUESDAY. THE
FRONT ASSOCIATED WITH THE BORDER LOW MAY PROVIDE MORE OF A FOCUS FOR
ORGANIZED CONVECTION AROUND MID WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1240 PM CDT SAT JUL 25 2015

MID/HIGH OVERCAST FROM DECAYING EARLY MORNING STORM COMPLEX
REMAINS IN PLACE ACROSS CENTRAL ILLINOIS EARLY THIS AFTERNOON.
MEANWHILE...SCT LOWER CLOUDS AT AROUND 1500-2500FT ARE BEGINNING
TO DEVELOP ACROSS NORTH-CENTRAL ILLINOIS AHEAD OF A WEAKENING COLD
FRONT. DUE TO STABILIZING INFLUENCE OF MORNING CLOUDS...HIGH-RES
MODELS GENERALLY KEEP MUCH OF THE AREA DRY THIS AFTERNOON. THE
EXCEPTION IS ALONG THE WEAK FRONT TO THE NORTH...WHERE THE RAPID
REFRESH SUGGESTS WIDELY SCATTERED CONVECTION WILL DEVELOP LATE
THIS AFTERNOON INTO THE EARLY EVENING. HAVE THEREFORE INCLUDED A
VCTS AT THE I-74 TERMINALS BETWEEN 21Z AND 04Z. MAIN AVIATION
FORECAST CONCERN WILL BE THE DEVELOPMENT AND TRACK OF ANOTHER
NOCTURNAL MCS TONIGHT. THIS SYSTEM WILL LIKELY DEVELOP IN NEARLY
THE SAME PLACE AS LAST NIGHTS SYSTEM DID...PERHAPS A BIT FURTHER
NORTH ACROSS EASTERN SOUTH DAKOTA/NEBRASKA. RAPID REFRESH SHOWS
THE STORM COMPLEX APPROACHING THE MISSISSIPPI RIVER BY 10Z...THEN
LIKELY SPILLING E/SE INTO CENTRAL ILLINOIS IN A DISSIPATING STAGE
SUNDAY MORNING. HAVE INCLUDED VCTS AT BOTH KPIA AND KSPI AFTER 13Z
ACCORDINGLY...BUT HAVE MAINTAINED A DRY FORECAST FURTHER EAST AT
THE REMAINING SITES DUE TO UNCERTAINTIES WITH THE TRACK AND SPEED
OF DISSIPATION OF THE EARLY MORNING CONVECTION. WINDS WILL BE
QUITE LIGHT THROUGH THE ENTIRE PERIOD...SWITCHING TO N/NE AS THE
FRONT SAGS THROUGH THE AREA BY SUNDAY MORNING.

&&

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

$$

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


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