Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 240523
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1223 AM CDT FRI APR 24 2015

.UPDATE...
ISSUED AT 835 PM CDT THU APR 23 2015

ANOTHER CHILLY EVENING OVER CENTRAL THRU SOUTHEAST ILLINOIS WITH
THE CENTER OF THE COOL AIR MASS EXPECTED TO PUSH JUST TO OUR EAST
BY FRIDAY MORNING. DEW POINTS MIXED DOWN INTO THE 10 TO 15 DEGREE
RANGE THIS AFTERNOON SO ONCE AGAIN WITH THE COMBINATION OF A
MOSTLY CLEAR SKY AND A LIGHT WIND...WE SHOULD SEE EARLY MORNING
LOWS DIP TO BETWEEN 30 AND 35 DEGREES WITH THE COLDEST READINGS
TONIGHT EXPECTED ACROSS OUR EASTERN COUNTIES. SOME OF OUR MORE
FAVORED COLD AREAS MAY SEE THE MERCURY DIP BRIEFLY INTO THE UPPER
20S. HAVE MADE SOME MINOR TWEAKS TO THE EARLY EVENING AND
OVERNIGHT TEMPERATURES...BUT OVERALL...THE FORECAST IS HOLDING
WELL FOR THE REST OF TONIGHT INTO FRIDAY MORNING. AS A RESULT...
NO ZFP UPDATE WILL BE NEEDED AT THIS TIME.

&&

.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 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.

&&

$$

UPDATE...SMITH
SHORT TERM...HJS
LONG TERM...ONTON
AVIATION...LAUFENBERG/BARKER



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