Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 240822
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
322 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 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1203 AM CDT FRI APR 24 2015

WAVE OVER THE HIGH PLAINS WILL PUSH EASTWARD TODAY BRINGING
INITIAL MID-LEVEL MOISTURE INTO ILLINOIS TERMINALS DURING THE DAY
WITH VFR CIGS POSSIBLE AFTER 18Z. MAV GUIDANCE SUGGESTS THAT SOME
LIGHT PRECIP MAY BE POSSIBLE WITH THIS INITIAL LAYER...BUT THIS
APPEARS TO BE INCONSISTENT WITH GFS QPF FORECASTS. GIVEN DRY
BOUNDARY LAYER CONDITIONS FEEL ANY PRECIP WILL LIKELY NEED TO WAIT
UNTIL THE SIGNIFICANT SOUTHERN STREAM LOW KICKS OUT OF THE SW U.S.
AND INTO THE PLAINS.

MODELS DIFFER SOMEWHAT ON TIMING...WITH GENERALLY A SLOWING TREND
BETWEEN 12Z AND 00Z MODEL SUITES. WILL LOWER CIGS TO BORDERLINE
MVFR AND ADD A VCSH FOR THE LATER PERIOD OF THE TERMINAL AND HONE
TIMING WITH LATER ISSUANCES.

AS SURFACE HIGH PULLS EAST...SFC GRADIENT PICKS UP FRIDAY
AFTERNOON WITH MODELS SUGGESTING SOME MOMENTUM TRANSFER POSSIBLE
GIVEN THE DRY LOWER ATMOSPHERE AND SOME SUN EARLY ON. WILL PLAN ON
ADDING SOME GUSTS TO SOUTHEAST DOMINATE WINDS DURING THE
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...LAUFENBERG/BARKER



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