Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 241134
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
634 AM CDT FRI APR 24 2015

.SHORT TERM...(TODAY)
ISSUED AT 322 AM CDT FRI APR 24 2015

HIGH PRESSURE WILL SLIDE OFF TO THE EAST TODAY, ALLOWING A
DEVELOPING STORM SYSTEM TO BEGIN TO APPROACH FROM THE WEST.  WHILE
GLOBAL MODELS KEEP PRECIP WEST OF ILLINOIS THROUGHOUT THE DAY,
HIGHER-RES MODELS SUCH AS THE NAM, HRRR, AND 4KM WRF-NMM SUGGEST A
FEW SHOWERS WILL SPREAD INTO AT LEAST THE WESTERN HALF OF THE CWA
DURING THE AFTERNOON.  REMAIN SKEPTICAL ABOUT THIS DUE TO THE VERY
DRY AIRMASS INITIALLY IN PLACE AS SHOWN BY THE 00Z KILX UPPER AIR
SOUNDING.  EVEN MODELS THAT DEVELOP SOME LIGHT PRECIP LATER TODAY
SHOW A SURFACE-BASED DRY LAYER BELOW 800MB. DUE TO THIS PERSISTENT
DRY LAYER, DO NOT THINK MEASURABLE PRECIP WILL OCCUR. HAVE INSTEAD
OPTED TO GO WITH JUST A CHANCE OF SPRINKLES ACROSS THE
CENTRAL/WESTERN ZONES THIS AFTERNOON.  THE DAY WILL START OUT MOSTLY
SUNNY, BUT WILL BECOME OVERCAST BY AFTERNOON AS MID-LEVEL CLOUDS
INCREASE.  AFTER CHILLY EARLY MORNING LOWS IN THE 30S, AFTERNOON
HIGHS WILL REACH THE LOWER TO MIDDLE 60S.

.LONG TERM...(TONIGHT THROUGH THURSDAY)
ISSUED AT 322 AM CDT FRI APR 24 2015

ATMOSPHERIC PROFILE WILL CONTINUE TO MOISTEN FROM THE TOP-DOWN THIS
EVENING, WITH FULL SATURATION NOT BEING ACHIEVED UNTIL AFTER
MIDNIGHT.  HAVE THEREFORE ALTERED THE POPS TONIGHT TO GO WITH CHANCE
DURING THE EVENING, THEN CATEGORICAL OVERNIGHT.  SHOWERS WILL
DEVELOP IN ADVANCE OF AN APPROACHING SURFACE LOW EARLY ON, THEN WILL
BECOME MORE WIDESPREAD AFTER MIDNIGHT AS A WARM FRONT LIFTS
NORTHWARD TOWARD THE AREA.  MODELS ARE IN GOOD AGREEMENT THAT THE
LOW WILL BE LOCATED NEAR KANSAS CITY BY 12Z SAT, WITH WARM FRONT
EXTENDING E/SE ACROSS SOUTHERN ILLINOIS.  THIS WILL PLACE THE ENTIRE
KILX CWA ON THE COOL/NORTHERN SIDE OF THE STORM SYSTEM.  FORECAST
SOUNDINGS THEREFORE REMAIN QUITE STABLE AT LOW-LEVELS OVERNIGHT, BUT
INDICATE MODEST ELEVATED INSTABILITY WITH MUCAPE VALUES OF 400-
800J/KG. HAVE THEREFORE INCLUDED THUNDER MENTION AFTER MIDNIGHT,
PARTICULARLY ACROSS THE SOUTHERN HALF OF THE AREA IN CLOSER
PROXIMITY TO THE STRONGEST FORCING ALONG THE WARM FRONT.  SOME OF
THE STORMS COULD BE CAPABLE OF PRODUCING HAIL AND LOCALLY HEAVY
RAINFALL.  LOW PRESSURE IS THEN EXPECTED TO TRACK E/SE INTO FAR
SOUTHERN ILLINOIS BY SUNDAY EVENING, ENSURING A COOL/WET DAY ACROSS
CENTRAL ILLINOIS.  WILL CONTINUE WITH CATEGORICAL POPS FOR SHOWERS,
WITH BEST CHANCE FOR THUNDER ALONG/SOUTH OF I-70.  A FEW OF THE
STORMS COULD BECOME SEVERE ACROSS THIS AREA SATURDAY AFTERNOON AS
MUCAPES INCREASE TO AROUND 1500J/KG AND 0-6KM SHEAR VALUES REACH
50KT.  STRONGEST INSTABILITY AND SHEAR PROFILES WILL REMAIN JUST
SOUTH OF THE AREA ACROSS FAR SOUTHERN ILLINOIS INTO WESTERN
KENTUCKY WHERE A SEVERE WEATHER OUTBREAK IS POSSIBLE.

SHOWERS WILL PERSIST INTO SATURDAY NIGHT BEFORE LOW GRADUALLY SHIFTS
SOUTHEASTWARD INTO THE APPALACHIANS BY SUNDAY.  ONCE THIS FEATURE
DEPARTS, THE REMAINDER OF THE EXTENDED LOOKS DRY AS MODELS HAVE NOW
COME INTO VERY GOOD AGREEMENT ABOUT THE NEXT SYSTEM EJECTING OUT OF
THE DESERT SOUTHWEST.  GFS/ECMWF/GEM NOW ALL TAKE THE LOW EASTWARD
ACROSS THE DEEP SOUTH, WHILE A NORTHERN STREAM WAVE REMAINS WELL TO
THE NORTH ACROSS THE UPPER MIDWEST/GREAT LAKES.  CENTRAL ILLINOIS
WILL REMAIN BETWEEN THESE TWO SYSTEMS, RESULTING IN DRY
CONDITIONS AND SEASONABLE TEMPERATURES IN THE 60S THROUGH THURSDAY.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 622 AM CDT FRI APR 24 2015

MID-DECK ASSOCIATED WITH WAVE OVER CENTRAL MISSOURI VALLEY MOVING
INTO TERMINALS THIS MORNING...HOWEVER THE MOISTURE IS PUSHING INTO
DRY LOW-LEVEL AIR AND WILL TAKE A WHILE FOR CIGS TO COME DOWN.
CIGS SHOULD REMAIN VFR INTO THE EVENING WHEN LOW-LEVEL RH
INCREASES IN RESPONSE TO INCOMING STRONG SOUTHWEST U.S. SYSTEM.
DRY BOUNDARY LAYER SHOULD HOLD OFF ANY SIGNIFICANT MEASURABLE
PRECIP UNTIL AFTER SUNSET. STRONG LIFT IS EVIDENT IN MODEL TIME
HEIGHTS AT THE WESTERN SITES AFTER 06Z WITH DEEPEST MOISTURE NEAR
SURFACE LOW TRACK AND WARM FRONT WHICH WOULD BE CLOSER TO KSPI.
WILL LOWER CIGS TO IFR THERE BY MORNING WHILE KEEPING MVFR CIGS
ELSEWHERE. WIDESPREAD PRECIP SHOULD BE FALLING AT MOST TERMINALS
BY THE END OF THE TAF VALID TIME.

WINDS SHOULD BE MOSTLY 100-150 DEGREES THROUGH THE VALID PERIOD AS
THE SFC LOW TRACK KEEPS CENTRAL ILLINOIS TERMINALS NORTH OF WARM
FRONT. SOME GUSTINESS IS POSSIBLE THIS AFTERNOON.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
FROST ADVISORY UNTIL 8 AM CDT THIS MORNING FOR ILZ027>031-037-
038-042>045-053>056-061-062-066>068-071>073.

FREEZE WARNING UNTIL 8 AM CDT THIS MORNING FOR ILZ046-057-063.

&&

$$

SHORT TERM...BARNES
LONG TERM...BARNES
AVIATION...BARKER


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