Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 301725
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1225 PM CDT THU JUL 30 2015

.UPDATE...
ISSUED AT 1020 AM CDT THU JUL 30 2015

RIDGE OF HIGH PRESSURE EXTENDING FROM THE NORTHERN ROCKIES TO THE
MID-MISSISSIPPI RIVER VALLEY IS PROVIDING SUNNY AND WARM
CONDITIONS ACROSS CENTRAL ILLINOIS THIS MORNING. 15Z/10AM
TEMPERATURES HAVE ALREADY RISEN INTO THE UPPER 70S AND LOWER
80S...WELL ON THE WAY TO AFTERNOON HIGHS IN THE UPPER 80S.
CURRENT DEWPOINTS ARE HOVERING IN THE LOWER TO MIDDLE
60S...HOWEVER GIVEN A VERY DRY 12Z KILX UPPER AIR SOUNDING...AM
EXPECTING THOSE TO MIX OUT INTO THE MIDDLE TO UPPER 50S BY EARLY
THIS AFTERNOON. CURRENT FORECAST IS RIGHT ON TRACK...SO NO UPDATE
IS NEEDED AT THIS TIME.

&&

.SHORT TERM...(TODAY)
ISSUED AT 251 AM CDT THU JUL 30 2015

A SPECTACULAR SUMMER DAY IS ON TAP FOR CENTRAL AND SOUTHEAST
ILLINOIS TODAY. HIGH PRESSURE AT THE SURFACE AND NEUTRAL TO WEAKLY
CYCLONIC FLOW ALOFT WILL HELP ENSURE THIS FACT. THE AIRMASS IS MUCH
DRIER THAN WE HAVE SEEN LATELY SO CLOUD COVER WILL BE MINIMAL, AND
HUMIDITY WILL BE LOW. WHILE MOST LOCATIONS ARE LIKELY TO TOP OUT IN
THE UPPER 80S FOR DAYTIME HIGHS, LOW DEW POINT TEMPERATURES AND A
WESTERLY BREEZE WILL HELP KEEP CONDITIONS COMFORTABLE.

.LONG TERM...(TONIGHT THROUGH WEDNESDAY)
ISSUED AT 251 AM CDT THU JUL 30 2015

EVOLUTION OF THE UPPER PATTERN INTO THE WEST RIDGE/EAST TROUGH
CONFIGURATION IS UNDERWAY...AS THE LARGE UPPER LOW SPINS JUST SOUTH
OF HUDSON BAY. NOT MUCH CHANGE THROUGH EARLY NEXT WEEK FROM RECENT
MODEL RUNS...AS THE RIDGE BUILDS ACROSS THE ROCKIES AND THE LOW
WOBBLES OVER THE SAME GENERAL AREA. GETTING CLOSER TO MID WEEK...THE
GFS TRIES TO BUILD THE RIDGE SLOWLY EASTWARD INTO THE PLAINS...WHILE
THE ECMWF BREAKS IT DOWN. BOTH PATTERNS WOULD RESULT IN BELOW NORMAL
TEMPERATURES RETURNING BY TUESDAY...ALTHOUGH THE ECMWF WOULD FAVOR
MUCH COOLER CONDITIONS THAN THE GFS. RIGHT NOW...WILL GO A LITTLE ON
THE WARMER SIDE...BUT HIGHS IN THE 80 DEGREE RANGE MIDWEEK WOULD
STILL BE A FEW DEGREES BELOW NORMAL.

PERIODIC IMPULSES ROTATING AROUND THE UPPER LOW AND DOWN THE UPPER
SIDE OF THE RIDGE WILL BE THE MAIN CHALLENGE FOR THE NEXT FEW DAYS.
THE FIRST ARRIVES ON FRIDAY...AND THE SECOND ON SUNDAY. HAVE
INTRODUCED SOME ISOLATED THUNDERSTORMS FRIDAY AFTERNOON AND EVENING
WITH THE FIRST BOUNDARY. LATEST SPC DAY2 OUTLOOK INDICATES A FEW OF
THE STORMS MAY BE STRONG TO LOCALLY SEVERE...AS CAPES RISE OVER 2500
J/KG AND SOME 0-6KM SHEAR OF 30-35 KNOTS OCCURS ALONG THE FRONT. NOT
LOOKING FOR ANYTHING WIDESPREAD WITH THE RAIN AS FORECAST SOUNDINGS
DO NOT STAY MOIST FOR ANY DECENT PERIOD OF TIME. SECOND WAVE LATE
SATURDAY NIGHT AND SUNDAY IS A LITTLE MORE PRONOUNCED...AND MUCH OF
THE PRECIPITATION IS FAVORED JUST TO OUR NORTH...ALTHOUGH THE GFS
AND ECMWF DO BRING A BIT MORE OF A SOUTHWARD SURGE. THESE TRENDS
WERE LARGELY PRESENT IN THE PREVIOUS FORECAST...AND ONLY NEEDED SOME
MINOR TWEAKS.

CONVECTIVE ACTIVITY NEXT WEEK IS MORE UNCERTAIN DUE TO THE POTENTIAL
BREAKDOWN OF THE WESTERN RIDGE. BOTH AGREE THE NEXT WAVE SHOULD BE
COMING THROUGH MONDAY NIGHT...BUT THE ECMWF HANGS IT UP AS THE RIDGE
BREAKS DOWN AND ANOTHER IMPULSE ARRIVES IN THE SOUTHERN STREAM. THAT
SOLUTION WOULD FAVOR MORE EXTENDED RAINY PERIODS FROM TUESDAY
THROUGH WEDNESDAY NIGHT...WHILE THE GFS EXHIBITS MORE OF AN MCS
PATTERN FOR THE MIDDLE OF THE WEEK. WITH THE WIDE VARIETY...WILL
KEEP RAIN CHANCES MORE IN THE 30-40% RANGE FOR NOW WITH NO
SIGNIFICANT CONFIDENCE IN EITHER SOLUTION.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1225 PM CDT THU JUL 30 2015

VFR CONDITIONS WILL PREVAIL THROUGH THE ENTIRE 18Z TAF PERIOD.
HIGH PRESSURE WILL PROVIDE CLEAR SKIES AND LIGHT WINDS THIS
AFTERNOON THROUGH TONIGHT. A WEAK FRONTAL BOUNDARY WILL APPROACH
FROM THE NORTHWEST TOWARD MIDDAY FRIDAY...WITH THE NAM CU-RULE
SUGGESTING PERHAPS FEW-SCT CU DEVELOPING ALONG/AHEAD OF THE FRONT.
ANY ISOLATED CONVECTION WILL HOLD OFF UNTIL LATER FRIDAY
AFTERNOON.

&&

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

$$

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



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