Area Forecast Discussion
Issued by NWS Central Illinois

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700
FXUS63 KILX 170501
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1201 AM CDT SUN MAY 17 2015

.UPDATE...
ISSUED AT 1001 PM CDT SAT MAY 16 2015
NOT MUCH IN THE WAY OF UPDATES THIS EVENING. HAVE PULLED BACK ON
HOURLY POPS, AND PULLED MIN TEMPS DOWN A DEGREE OR SO WITH VERY
LITTLE IN THE WAY OF CLOUD COVER SO FAR. SOUTHERLY WINDS EXPECTED
TO KEEP TEMPS IN THE MID TO UPPER 60S AGAIN TONIGHT. IN ADDITION,
SHORT RANGE MODELS PERSISTING IN DEVELOPMENT OF A LLVL CEILING
WITH PLENTY OF MOISTURE IN THE BOUNDARY LAYER. OBS STARTING TO
PICK UP ON SOME SCT LOW CLOUDS AND THE BEGINNING OF THAT TREND.

&&

.SHORT TERM...(TONIGHT)
ISSUED AT 301 PM CDT SAT MAY 16 2015

SCATTERED SHOWERS CONTINUE TO FORM IN THE WARM AND HUMID AIRMASS...
MORE CONCENTRATED ACROSS THE LOWER OHIO VALLEY NEAR A WEAK UPPER
WAVE. THUNDER HAS BEEN VERY ISOLATED THUS FAR...DESPITE CAPE`S OF
1500-2500 J/KG PER SPC AND LAPS MESOANALYSIS. ACTIVITY WILL CONTINUE
TO LIFT NORTHWARD THE REST OF THE AFTERNOON...THEN FADE EARLY
EVENING WITH LOSS OF DAYTIME HEATING. HAVE KEPT SOME LOW CHANCE
POP`S ACROSS THE SOUTHEAST CWA EARLY EVENING AS THE WAVE PASSES
BY...BUT WENT WITH MAINLY ISOLATED SHOWERS/STORMS ELSEWHERE. LITTLE
CHANGE NEEDED TO FORECAST LOWS OF 66-68 DEGREES.

.LONG TERM...(SUNDAY THROUGH SATURDAY)
ISSUED AT 301 PM CDT SAT MAY 16 2015

THE MAIN FORECAST CONCERN WILL BE THE POTENTIAL FOR STRONG/SEVERE
CONVECTION SUNDAY. MANY OF THE SHORT RANGE MODELS, INCLUDING THE
NAM, GFS AND SREF, INDICATE THAT INSTABILITY WILL BE MODERATE TO
STRONG WITH INCREASING DEEP LAYER SHEAR SUNDAY AFTERNOON INTO EARLY
EVENING. GUSTY SOUTH WINDS WILL CONTINUE TO TRANSPORT PLENTY OF LOW
LEVEL MOISTURE ACROSS THE ENTIRE REGION SUNDAY. AN UPPER LEVEL
JET MAX WILL ALSO BE TRANSLATING FROM THE SOUTHERN PLAINS INTO THE
UPPER MIDWEST PROVIDING PLENTY OF LARGE SCALE LIFT, ESPECIALLY
WEST OF THE IL RIVER VALLEY UP INTO WISCONSIN.

HOWEVER, ALL THIS BEING SAID, THERE ARE SOME PRETTY LARGE
CAVEATS SO THE POTENTIAL FOR SEVERE STORMS IS VERY CONDITIONAL BASED
ON THE AMOUNT OF STABILITY AND CLOUD COVER FROM EARLY MORNING STORMS
THAT MOVE FROM THE MISSOURI VALLEY INTO WEST CENTRAL IL...AND THAT A
SURFACE TROUGH/DRY LINE IS ABLE TO MOVE INTO IL DURING THE AFTERNOON-
EARLY EVENING.

AS A RESULT, WILL MAINTAIN LIKELY POPS DURING THE MORNING HOURS
ACROSS CENTRAL IL, THEN LOWER THEM TO THE LOWER CHANCE CATEGORY FOR
THE EARLY AFTERNOON AND BUMP THEM BACK UP FOR LATE AFTERNOON AND
EVENING. AT THIS TIME, WILL HOLD OFF ON MENTIONING SEVERE STORMS FOR
SUNDAY DUE TO THE AFOREMENTIONED REASONS AND REVISIT THIS WITH THE
SUNDAY MORNING FORECAST UPDATES.

BECAUSE THE SURFACE LOW IN THE NORTHERN PLAINS IS EXPECTED TO
OCCLUDE, THE ASSOCIATED COLD FRONT WILL NOT GET MUCH OF A PUSH
THROUGH OUR REGION UNTIL MONDAY AFTERNOON AND EVENING. THIS WILL
RESULT IN ANOTHER DAY OF TEMPERATURES AROUND 80 DEGREES IN MOST
AREAS AS BRISK SOUTHWEST WINDS AHEAD OF THE FRONT CONTINUE TO KEEP
WARM AIR IN THE REGION. THE SLOWER MOVING FRONT ALSO MEANS THAT
LINGERING LOW LEVEL MOISTURE COULD RESULT IN SCATTERED SHOWERS/T-
STORMS EAST OF CMI-DEC-TAYLORVILLE LINE FOR MONDAY.

HIGH PRESSURE NOSING INTO THE UPPER MIDWEST FOR TUESDAY WILL RESULT
IN CLEARING AND COOLER TEMPERATURES. THE HIGH WILL MOVE VERY LITTLE
MUCH OF THE WEEK, KEEPING US ON THE COOLER THAN NORMAL SIDE. THE
NEXT CHANCE FOR PRECIPITATION WILL BE IN THE FORM OF OVERRUNNING
SHOWERS WEDNESDAY-EARLY WED NIGHT AS A SHORTWAVE TROUGH FROM THE
CENTRAL PLAINS RIDES OVER THE SOUTHERN EDGE OF THE SURFACE HIGH.
UPPER LEVEL RIDING BUILDING IN FOR LATE IN THE WEEK WILL RESULT IN
WARMER TEMPERATURES FOR LATE NEXT WEEK. A SOUTHERLY RETURN FLOW IS
EXPECTED TO SET UP SATURDAY, WHICH MAY RESULT IN A CHANCE FOR MORE
THUNDERSTORMS FOR THE HOLIDAY WEEKEND.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1158 PM CDT SAT MAY 16 2015
NOT TOO MUCH OF A SHIFT. MVFR/IFR CIGS MOVING IN AND SPREADING
OVER CENTRAL IL. SOUTHERLY WINDS CONTINUE. SOME VIS REDUCTION
POSSIBLE WITH THE ENHANCED/TRAPPED LLVL MOISTURE. ISSUES FOR
TOMORROWS FORECAST REMAIN WITH MODELS CHALLENGED BY CONVECTION.
WITH TIMING ISSUES...VCTS STARTING ROUGHLY MIDDAY, THEN PULLING
BACK TO VCSH LATER IN THE EVENING AS THE MAJORITY OF THE PRECIP
STARTING TO LOOK RAGGED ON MODEL DEPICTIONS.

&&

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

$$

UPDATE...HJS
SHORT TERM...GEELHART
LONG TERM...MILLER
AVIATION...HJS



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