Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 261739
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1239 PM CDT SUN JUL 26 2015

.UPDATE...
ISSUED AT 1030 AM CDT SUN JUL 26 2015

INITIAL MCS THAT TRACKED INTO WEST-CENTRAL ILLINOIS EARLIER THIS
MORNING HAS DROPPED SOUTHEASTWARD INTO SOUTHERN ILLINOIS AND IS
NOW APPROACHING THE OHIO RIVER. MEANWHILE...SECOND CONVECTIVE
SYSTEM THAT FORMED FURTHER UPSTREAM IS FOLLOWING IN ITS FOOTSTEPS.
15Z/10AM RADAR SATELLITE/RADAR IMAGERY SHOWS THIS FEATURE CROSSING
THE MISSISSIPPI RIVER FROM JUST SOUTH OF MOLINE TO QUINCY. WHILE
CLOUD TOPS HAVE GENERALLY BEEN COOLING WITH TIME...ONE CLUSTER OF
STRONGER/ELEVATED CONVECTION IS EVIDENT ACROSS NORTHEAST MISSOURI
JUST S/SW OF QUINCY. THIS ACTIVITY WILL LIKELY FOLLOW THE
PREVAILING INSTABILITY GRADIENT AND TRACK SOUTHEASTWARD TOWARD THE
SAINT LOUIS AREA. MESOANALYSIS REVEALS A STABLE/CAPPED AIRMASS
ACROSS CENTRAL ILLINOIS THANKS TO THE CLOUD DEBRIS AND SHOWERS
FROM THE EARLY MORNING MCS. THINK THE APPROACHING SYSTEM WILL
SPILL INTO THE AREA OVER THE NEXT COUPLE OF HOURS BEFORE GRADUALLY
DISSIPATING BY EARLY TO MID AFTERNOON. GIVEN RADAR TRENDS...HAVE
INCREASED POPS TO LIKELY ALONG/WEST OF THE I-55 CORRIDOR FROM NOW
THROUGH EARLY AFTERNOON. FURTHER EAST...HAVE MAINTAINED HIGH
CHANCE POPS. ONCE THE SECONDARY MCS PASSES TO THE EAST...VERY
LITTLE RE-DEVELOPMENT IS ANTICIPATED LATER THIS AFTERNOON DUE TO
SYNOPTIC SUBSIDENCE IN THE WAKE OF THE SYSTEM AS EVIDENCED ON
LATEST WATER VAPOR IMAGERY AND OVERALL LACK OF STRONG INSTABILITY.
HAVE THEREFORE DECREASED POPS TO JUST SLIGHTS ACROSS THE WESTERN
HALF OF THE CWA AFTER 22Z.

&&

.SHORT TERM...(TODAY)
ISSUED AT 251 AM CDT SUN JUL 26 2015

FORECAST CONCERNS FOR TODAY ARE SIMILAR TO YESTERDAY: HOW EXTENSIVE
WILL CONVECTIVE DEVELOPMENT BE, AND WHAT IMPACT WILL THE EXPECTED
CONVECTION/CLOUD COVER HAVE ON PEAK AFTERNOON HEAT INDEX VALUES.

AT FIRST GLANCE THE OVERALL SCENARIO LOOKS PRETTY SIMILAR TO
YESTERDAY AS WELL. CAPE VALUES ARE PROGGED TO TOP OUT IN THE 3000-
4000 J/KG RANGE OVER MOST OF THE FORECAST AREA, ALONG WITH MODEST
BULK SHEAR VALUES OF 25 TO 35 KTS. HOWEVER, TODAY WE ARE LIKELY TO
BE IMPACTED BY TWO MCVS INSTEAD OF ONE, THE FIRST ASSOCIATED WITH
THE MCS TRACKING ESE OUT OF NORTHERN MISSOURI, AND THE SECOND
ASSOCIATED WITH THE MCS TRACKING SOUTHEAST ACROSS IOWA. THE IOWA MCV
SHOULD ARRIVE LATE ENOUGH TO BE ABLE TO WORK ON DIURNALLY ENHANCED
INSTABILITY. ALSO, WHILE THERE ARE NOT ANY FRONTAL EXPECTED TO PUSH
INTO THE AREA TODAY, THE REMNANT BOUNDARY FROM YESTERDAY AS WELL AS
OUTFLOW/DIFFERENTIAL HEATING BOUNDARIES FROM NEARBY CONVECTION AND
CONVECTIVE DEBRIS WILL PROVIDE NEEDED LOW LEVEL FOCUS. THE BOTTOM
LINE WITH RESPECT TO STORMS TODAY IS THAT WHILE THE SCENARIO IS
STILL NOT IDEAL, EXPECT THE STORMS TO BE MORE NUMEROUS THAN
YESTERDAY.

AS FAR AS HEAT IS CONCERNED, THE LOCAL AIRMASS IS NOT EXPECTED TO
UNDERGO MANY CHANGES IN LOW LEVEL MOISTURE/THERMAL PROPERTIES SINCE
YESTERDAY. HOWEVER, EXPECT MOST AREAS TO BE AT LEAST A COUPLE
DEGREES COOLER THAN YESTERDAY DUE TO MORE WIDESPREAD DEBRIS CLOUD
LIMITING INSOLATION, AS WELL AS MORE NUMEROUS SHOWERS/STORMS.

.LONG TERM...(TONIGHT THROUGH SATURDAY)
ISSUED AT 251 AM CDT SUN JUL 26 2015

MAIN CONCERN IN THIS PART OF THE FORECAST REMAINS WITH THE BUILDING
HEAT WAVE. UPPER LEVEL RIDGING WILL CONTINUE TO AMPLIFY AND SHIFT
EASTWARD LATER THIS WEEKEND...AS AN UPPER LOW CURRENTLY OVER
NORTHERN BRITISH COLUMBIA DROPS SOUTHWARD THROUGH THE PACIFIC
NORTHWEST THEN TRACKS ALONG THE CANADIAN BORDER. 925 MB TEMPERATURES
EXPECTED TO INCREASE TO THE 24-25C VICINITY BY LATE MONDAY AND TO
NEAR 27C BY TUESDAY AFTERNOON. WITH EVAPOTRANSPIRATION HELPING TO
BOOST DEW POINTS INTO THE MID-UPPER 70S BOTH MONDAY AND
TUESDAY...HEAT INDEX VALUES CONTINUE TO RISE TOWARD CRITICAL
LEVELS...100-105 ON MONDAY AND 105-110 TUESDAY ESPECIALLY ACROSS THE
WESTERN CWA. SOME INDICATIONS THIS COULD CONTINUE TO BE A CONCERN
ACROSS THE EAST ON WEDNESDAY AS WELL...BEFORE THE ARRIVAL OF A COLD
FRONT. HEAT ADVISORY WILL BE NEEDED AT SOME POINT...BUT STILL A BIT
OF A QUESTION REGARDING CONVECTIVE CLOUD DEBRIS LINGERING INTO
MONDAY TO PULL THE TRIGGER JUST YET.

IN TERMS OF THE CONVECTION...MODEL SOLUTIONS ON THE NEXT MCS
SYSTEM(S) TO DEVELOP SUNDAY NIGHT CONTINUE TO EXHIBIT A FAIR
SPREAD...WITH THE ECMWF AND CANADIAN MODELS MOST AGGRESSIVE WITH
IMPACTING US DIRECTLY AFTER MIDNIGHT...RANGING TO A DRY NAM SOLUTION
UNTIL MONDAY MORNING. THE MODELS HAVE NOT HAD THE BEST HANDLE ON
WHAT`S BEEN GOING ON THE LAST COUPLE NIGHTS...AND THUS CONFIDENCE ON
ANY GIVEN SOLUTION IS LOWER THAN NORMAL. WILL HAVE THE HIGHEST POP`S
DURING THE EARLY EVENING HOURS BASED ON WHAT WILL BE ONGOING
DURING THE AFTERNOON...THEN GRADUALLY DIMINISH THEM AS THE NIGHT
PROGRESSES. AS THE RIDGE BUILDS EASTWARD...WILL LIMIT POP`S TO
SILENT 20% CHANCES...ALTHOUGH THE GFS CONTINUES TO BE FAIRLY
HEALTHY WITH ITS RAIN TRENDS FOR A COUPLE DAYS. THE MAIN CHANCES
WILL LIKELY HAVE TO WAIT UNTIL THE MID WEEK FRONTAL
BOUNDARY...TIED TO THE UPPER LOW TRAVERSING THE BORDER NORTH OF
NORTH DAKOTA/MINNESOTA. HOWEVER...WITH THE RIDGE CONTINUING TO
KEEP A WEAK FLOW TO OUR SOUTHWEST...WILL ONLY GO WITH 30-40%
CHANCES WITH MORE OF THE MOISTURE DUE TO THE TROPICAL AIR MASS
ALREADY PRESENT.

ONCE THE FRONT PASSES...A WELCOME PERIOD OF COOLER AND LESS HUMID
AIR IS EXPECTED FOR THE LATTER PART OF THE WEEK...AS THE UPPER RIDGE
STARTS TO AMPLIFY ACROSS THE ROCKIES. WILL MAINTAIN A DRY FORECAST
LATE WEEK WITH HIGH PRESSURE OVER THE MID MISSISSIPPI VALLEY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1239 PM CDT SUN JUL 26 2015

DECAYING MCS CONTINUES TO TRACK ACROSS THE ILLINOIS RIVER VALLEY
EARLY THIS AFTERNOON...WITH 17Z/12 PM RADAR IMAGERY SHOWING ONLY
LIGHT SHOWERS REMAINING. HAVE INTRODUCED PREVAILING LIGHT RAIN AT
BOTH KPIA AND KSPI BETWEEN 18Z AND 19Z...BUT THINK THE PRECIP WILL
COMPLETELY DISSIPATE BEFORE PUSHING ANY FURTHER EASTWARD. WILL
HAVE TO KEEP AN EYE ON THE OUTFLOW BOUNDARY FROM THIS SYSTEM AS
ISOLATED CONVECTION MAY DEVELOP FURTHER EAST OVER THE NEXT COUPLE
OF HOURS. IN ADDITION...SEVERAL HIGH-RES MODELS ARE SUGGESTING
SCATTERED SHOWERS/STORMS MAY FIRE ALONG A STATIONARY FRONTAL
BOUNDARY DRAPED ACROSS NORTH-CENTRAL ILLINOIS THIS AFTERNOON INTO
THE EARLY EVENING. HAVE THEREFORE INCLUDED VCTS AT THE I-74
TERMINALS BETWEEN 20Z AND 02Z-03Z. ONCE ANY DIURNALLY DRIVEN
CONVECTION DISSIPATES...DRY CONDITIONS ARE EXPECTED FROM MID-EVENING
THROUGH MONDAY MORNING. DUE TO THE HIGHER DEWPOINT AIRMASS IN
PLACE ACROSS THE REGION AND CONTINUED LIGHT/VARIABLE WINDS...MAY
SEE SOME FOG OVERNIGHT AS WELL. DO NOT THINK IT WILL BECOME
WIDESPREAD OR DENSE...BUT WILL MENTION SLIGHTLY REDUCED VISBYS IN
THE TAFS LATE TONIGHT.

&&

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

$$

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



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