Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 270207
AFDILX

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

.UPDATE...
ISSUED AT 900 PM CDT SUN JUL 26 2015

ANY LINGERING SCATTERED SHOWERS WILL PRIMARILY DISSIPATE OR MOVE
EAST OF OUR COUNTIES IN THE NEXT HOUR OR SO. THE PROBABILITY OF
ADDITIONAL SHOWER OR STORM DEVELOPMENT LATER TONIGHT APPEARS LOW,
BUT ANY DEVELOP THEY WILL MAINLY BE FOCUSED ALONG AND SOUTH OF
I-72, WHERE A SURFACE TROUGH AXIS HAS STALLED OUT. WE KEPT ONLY
SLIGHT CHANCE POPS IN THE SOUTHERN COUNTIES OVERNIGHT, BUT MOST
AREAS WILL REMAIN DRY.

DEWPOINTS WILL REMAIN IN THE UPPER 60S TO AROUND 70 OVERNIGHT,
WHICH WILL CREATE FAVORABLE CONDITIONS FOR FOG FORMATION. MOST
AREAS SHOULD ONLY SEE 3-4 MILE VISIBILITY, BUT LOCALIZED AREAS
COULD DROP LESS THAN A MILE, PER HRRR OUTPUT. HAVE ADDED FOG TO
THE FORECAST FOR LATER TONIGHT, MAINLY NORTH OF I-70 FOR NOW. WILL
MONITOR FOR POSSIBLE NEED TO EXPAND FOG COVERAGE.

UPDATES THIS EVENING WERE MAINLY TO POP AND WEATHER, WITH MINOR
ADJUSTMENTS TO HOURLY TEMP, DEWPOINTS, AND SKY.

&&

.SHORT TERM...(TONIGHT)
ISSUED AT 251 PM CDT SUN JUL 26 2015

MORNING MCS HAS COMPLETELY DISSIPATED ACROSS CENTRAL ILLINOIS EARLY
THIS AFTERNOON...WITH 19Z/2PM RADAR IMAGERY SHOWING NO LINGERING
PRECIP.  THE FOCUS FOR ADDITIONAL CONVECTION THIS AFTERNOON AND
EVENING WILL SHIFT FURTHER NORTH AND EAST ALONG A NEARLY STATIONARY
FRONTAL BOUNDARY EXTENDING FROM NORTH-CENTRAL INDIANA INTO EASTERN
IOWA.  SCATTERED THUNDERSTORMS ARE ALREADY DEVELOPING ALONG THE
BOUNDARY WITHIN A NARROW INSTABILITY AXIS CHARACTERIZED BY SBCAPES
OF 1500 TO 2500J/KG.  HRRR HAS BEEN CONSISTENTLY SHOWING STORMS
FIRING ALONG THE FRONT THIS AFTERNOON, AS WELL AS ALONG AN OUTFLOW
BOUNDARY/DIFFERENTIAL HEATING BOUNDARY CREATED BY THE MORNING MCS.
GIVEN CURRENT SATELLITE/RADAR TRENDS...SEE NO REASON TO STRAY FROM
THIS SOLUTION.  AS A RESULT...HAVE FOCUSED HIGHEST POPS ALONG/NORTH
OF I-74 AND EAST OF I-55 THIS AFTERNOON INTO THE EVENING.  ANY
STORMS THAT DEVELOP WILL BE DIURNALLY DRIVEN AND WILL LIKELY
DISSIPATE AFTER SUNSET.  AFTER THAT...THE QUESTION BECOMES WHETHER
ANY NOCTURNAL CONVECTION CAN DEVELOP OVERNIGHT.  THE HRRR AND RAPID
REFRESH MODELS SAY NO...HOWEVER THE NAM KEEPS AT LEAST SCATTERED
PRECIP GOING.  THE MAIN 850MB JET WILL BE ORIENTED FROM THE SOUTHERN
PLAINS INTO THE DAKOTAS TONIGHT...SO THERE WILL NOT BE MUCH SUPPORT
FOR OVERNIGHT STORMS IN ILLINOIS.  WITH THAT BEING SAID...NAM DOES
SHOW A WEAK 20-25KT BRANCH OF THE LLJ NOSING INTO THE AREA.  WITH
THIS WEAK INFLOW COMBINED WITH THE PRESENCE OF THE STATIONARY
FRONTAL BOUNDARY IN THE VICINITY...HAVE OPTED TO MAINTAIN JUST
SLIGHT CHANCE POPS AFTER MIDNIGHT.  LOW TEMPERATURES WILL ONCE AGAIN
BE IN THE LOWER 70S.

.LONG TERM...(MONDAY THROUGH SUNDAY)
ISSUED AT 251 PM CDT SUN JUL 26 2015

WITH HIGH PRESSURE TO THE NORTHEAST AND A WEAK RESIDUAL BOUNDARY IN
OR CLOSE TO THE CWA...BELIEVE A SMALL CHANCE/SLIGHT CHANCE OF PCPN
WILL REMAIN POSSIBLE TOMORROW THROUGH TUE. THIS WILL ONLY BE SEEN
THROUGH MONDAY NIGHT IN THE WORDING...BUT WILL BE SEEN THROUGH TUE.
ONCE THIS WEAK BOUNDARY BREAKS DOWN ENOUGH TUE NIGHT SHOULD BE MOSTLY
DRY EXCEPT IN THE NORTHWEST OF THE IL RIVER WITH APPROACH OF THE
NEXT WEATHER SYSTEM. MODELS HAVE GOTTEN LITTLE FASTER WITH THIS
FRONT AND IT NOW ARRIVES EARLY ON WED IN THE AREA. CONVECTION WILL
BE POSSIBLE ALONG THIS FRONT WED AND THEN QUICKLY EXIT THE AREA LATE
WED AFTERNOON...SO WED NIGHT SHOULD BE DRY THROUGHOUT THE CWA.

TEMPS WILL BE QUITE WARM THROUGH WED WITH UPPER 80S TO LOWER 90S
POSSIBLE MON AND WED...AND LOWER TO MIDDLE 90S LIKELY FOR TUESDAY.
THIS HEAT WILL COMBINE WITH DWPTS IN THE 70S...UPPER 70S ON
TUESDAY...TO CREATE HEAT INDEX VALUES OF 90S TO 105 FOR MON AND
WED...AND 105-110 FOR TUESDAY. HEAT ADVISORY CRITERIA...105...WILL
BE CLOSE TOMORROW BUT ONLY IN EXTREME WESTERN COUNTIES. SO LEANING
AWAY FROM ADVISORY AT THIS TIME. CRITERIA IS MET ON TUE AND THEN
MAYBE IN THE SOUTHEAST PARTS OF THE CWA FOR WED. OVERNIGHT SHIFT CAN
GET ANOTHER LOOK FOR TOMORROW BECAUSE CLOUDS AND POSSIBLE PCPN COULD
BE A LIMITING FACTOR.

ONCE THE MID WEEK FRONT MOVES THROUGH DRY WEATHER IS EXPECTED THE
REST OF THE WEEK AND INTO THE WEEKEND. COOL CANADIAN HIGH PRESSURE
IS EXPECTED OVER THE AREA...WHICH WILL ALSO BRING IN DRIER DWPTS TO
THE AREA. THIS RIDGE DOES BEGIN TO BREAK DOWN OVER THE WEEKEND AND
WILL ALLOW A FRONT TO DROP INTO THE AREA FOR THE LAST PART OF THE
WEEKEND. FOR NOW WILL JUST HAVE A SLIGHT CHANCE OF PCPN FOR SAT
NIGHT AND SUNDAY. TEMPS WILL ALSO BE COOLER WITH AFTERNOON HIGHS
REMAINING IN THE 80S THROUGH THE PERIOD AND OVERNIGHT LOWS IN THE
60S.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 652 PM CDT SUN JUL 26 2015

A LINE OF SHOWERS AND ISOLATED STORMS CONTINUES TO LINGER NORTH OF
I-74 AND EAST OF I-57. THE ONLY TERMINALS AFFECTED OVER THE NEXT
COUPLE OF HOURS APPEAR TO BE BMI AND CMI. THE HRRR AND RAP MODELS
SHOW AN OVERALL WEAKENING OF THE CONVECTION BY 02-03Z, WITH LOSS
OF INSTABILITY. WILL CONTINUE WITH THAT TREND IN THE TAFS,
REMOVING ANY MENTION OF VCTS AFTER 02Z.

AN OUTFLOW BOUNDARY MOVING SOUTH, AS SEEN ON KILX RADAR, HAS
PRODUCED A WIND SHIFT FROM SW TO NNE WINDS AT BMI, WHICH SHOULD
ALSO OCCUR AT PIA BY 00Z. HAVE INCLUDED NNE WINDS AT BMI/PIA FOR
AN HOUR OR SO. OTHERWISE, WINDS SHOULD BECOME VARIABLE BY MID-
EVENING UNDER A WEAK PRESSURE GRADIENT.

FOG CONCERNS ARE INCREASING, AS HRRR COVERS PORTIONS OF CENTRAL IL
WITH DENSE FOG. HAVE LOWERED THE VIS IN THE TEMPO GROUPS TO 1SM
FOR SPI/DEC/CMI, AND 2SM FOR PIA/BMI. THE MAIN FOCUS TIME FOR
DENSE FOG APPEARS TO BE AROUND SUNRISE, OR THE 10Z-12Z TIME
FRAME.


&&

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

$$

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



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