Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 232000
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
300 PM CDT THU APR 23 2015

.SHORT TERM...(TONIGHT)
ISSUED AT 300 PM CDT THU APR 23 2015

NORTHWESTERLY FLOW ALOFT HELPING TO KEEP SOME COLD AIR OVER THE
REGION ALOFT. COLD AIR WILL BE THE MAIN ISSUE AGAIN OVERNIGHT AS THE
HIGH PRESSURE RIDGE AT THE SFC MOVES OVERHEAD. WINDS WILL BECOME
LIGHT AND VARIABLE UNDER THE RIDGE...CLOSE TO CALM, PARTICULARLY IN
THE EASTERN HALF OF CENTRAL ILLINOIS OVER TO THE INDIANA BORDER.
CLEAR SKIES AND LIGHT/CALM WINDS WILL SET UP FOR EFFICIENT
RADIATIONAL COOLING WITH A RELATIVELY DRY AIRMASS.  TEMPS WILL DROP
CONSIDERABLY WITH THE FAR EAST TO SEE THE POTENTIAL TO DROP TO RIGHT
AT FREEZING...IF NOT A DEGREE OR TWO LOWER IN LOW LYING AREAS.
FREEZE WARNING NEEDED AGAIN FOR THE INDIANA BORDER, WITH THE
REMAINDER OF THE AREA FROM ROUGHLY GALESBURG TO EFFINGHAM AND POINTS
EAST UNDER AT LEAST A FROST ADVISORY.  SOME PATCHY FROST STILL
POSSIBLE FROM HAVANA THROUGH SPRINGFIELD AND TAYLORVILLE AS WELL.

&&

.LONG TERM...(FRIDAY THROUGH THURSDAY)
ISSUED AT 300 PM CDT THU APR 23 2015

AN UPPER LEVEL LOW CURRENTLY OVER SOUTHERN CA WILL BEGIN TO EJECT
RAPIDLY EASTWARD TONIGHT AS A NORTHERN STREAM WAVE AND JET STREAM
CARVES OUT ON THE WEST COAST. THE SOUTHERN CA WAVE WILL APPROACH
FRIDAY STEADILY SPREADING HIGH AND MID CLOUDS INTO CENTRAL IL.
CONSIDERABLE LOW LEVEL DRY AIR WILL BE IN PLACE AS THE SYSTEM
APPROACHES...AND THIS WILL TAKE MOST OF THE DAYLIGHT HOURS FRIDAY TO
SATURATE. CURRENT INSTABILITY/SHEAR PROFILES INDICATE SEVERE
THUNDERSTORM POSSIBILITIES ARE LIKELY TO REMAIN SOUTHWEST OF
ILLINOIS THROUGH FRIDAY NIGHT...THEN SHIFT EASTWARD INTO SOUTHERN
ILLINOIS SATURDAY. SPC DAY 3 CONVECTIVE OUTLOOK CONTINUES TO
ADVERTISE A MARGINAL RISK FOR SEVERE STORMS SOUTH OF I-70.
INSTABILITY PROFILES INDICATE INSTABILITY FAVORABLE FOR
THUNDERSTORMS SPREADING NORTHEASTWARD ACROSS THE FORECAST AREA
FRIDAY EVENING...THEN SLIDING SOUTHEASTWARD OUT OF THE AREA SATURDAY
EVENING. CURRENT MODEL DIFFERENCES IN EXACT LOW TRACK INDICATE SOME
CONTINUED UNCERTAINTY IN EXACT DETAILS ON THIS STORM SYSTEM.

TRAILING THE SATURDAY SYSTEM...DEEP NORTHERLY FLOW OUT OF ONTARIO
WILL USHER IN MORE COOL AND DRY AIR FOR SUNDAY AND MONDAY...WITH
MOSTLY CLEAR SKIES...HIGHS AROUND 60...AN LOWS DROPPING BACK TO
AROUND 40 OR THE UPPER 30S.

LATEST MODELS TRACK THE NEXT SYSTEM FOR MIDWEEK THROUGH THE GULF
STATES...LIKELY KEEPING PRECIPITATION LARGELY TO THE SOUTH OF THE
CENTRAL IL FORECAST AREA FOR THIS TIME PERIOD. A NORTHERN STREAM
SHORTWAVE COULD POTENTIALLY BRING ENOUGH LIFT FOR SOME SHOWERS
WEDNESDAY...BUT ANY IMPACTS LOOK MINOR.

HIGH PRESSURE EXPECTED TO BUILD IN FOR LATE WEEK BRINGING WARMER
TEMPERATURES AND DRY CONDITIONS.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1253 PM CDT THU APR 23 2015
HIGH PRESSURE AND CLEAR SKIES THROUGH THE SHORT TERM...NWRLY
WINDS...WITH SOME INCONSISTENT GUSTING THROUGH THE AFTERNOON, BUT
NOT NEARLY AS HIGH WINDS AS THE LAST COUPLE OF DAYS, GENERALLY
ABOUT 5 KTS OVER SUSTAINED. CLEAR THROUGH THE OVERNIGHT WITH WINDS
BECOMING INCREASINGLY LIGHT AND VARIABLE UNDER THE SFC RIDGE.
WINDS MORE SOUTHEASTERLY AFTER SUNRISE IN THE MORNING AND BIG
QUESTION FOR TOMORROW IS THE ARRIVAL OF SOME CLOUDS AROUND
5KFT...MODEL TIME HEIGHTS SHOW THE MOISTURE MOVING IN FROM THE
SOUTHWEST, BUT SOME VARIATION AS TO THE TIMING BEFORE 18Z. VFR
THROUGHOUT.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
FROST ADVISORY FROM 1 AM TO 8 AM CDT FRIDAY FOR ILZ027>031-037-
038-042>045-053>056-061-062-066>068-071>073.

FREEZE WARNING FROM 1 AM TO 8 AM CDT FRIDAY FOR ILZ046-057-063.

&&

$$

SHORT TERM...HJS
LONG TERM...ONTON
AVIATION...HJS


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