Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 231119
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
619 AM CDT THU APR 23 2015

.SHORT TERM...(TODAY)
ISSUED AT 328 AM CDT THU APR 23 2015

RIDGE OF HIGH PRESSURE CURRENTLY ALONG THE MISSISSIPPI RIVER WILL
EDGE SLOWLY EASTWARD TODAY, PROVIDING CENTRAL ILLINOIS WITH ABUNDANT
SUNSHINE AND LIGHTER WINDS THAN HAVE RECENTLY BEEN OBSERVED.  DUE TO
A WEAKENING PRESSURE GRADIENT AND LOWER MIXING HEIGHTS, WIND SPEEDS
TODAY WILL ONLY REACH THE 10 TO 15 MPH RANGE.  AFTER CHILLY EARLY
MORNING LOWS IN THE UPPER 20S AND LOWER 30S, MID-APRIL SUNSHINE
WORKING ON THE VERY DRY AIRMASS IN PLACE ACROSS THE REGION WILL
RESULT IN AFTERNOON HIGH TEMPERATURES IN THE UPPER 50S AND LOWER 60S.

.LONG TERM...(TONIGHT THROUGH WEDNESDAY)
ISSUED AT 328 AM CDT THU APR 23 2015

ANOTHER COLD AND POTENTIALLY FROSTY NIGHT IS SETTING UP TONIGHT, AS
THE RIDGE AXIS SLOWLY SHIFTS EASTWARD ACROSS THE AREA.  ONCE THE
ATMOSPHERE DECOUPLES, EXCELLENT RADIATIONAL COOLING CONDITIONS WILL
ALLOW TEMPERATURES TO RAPIDLY DROP AFTER SUNSET.  RATE OF COOLING
WILL EVENTUALLY BE OFFSET ACROSS THE WESTERN HALF OF THE KILX CWA AS
A LIGHT E/SE RETURN FLOW BEGINS TO DEVELOP ON THE BACK SIDE OF THE
DEPARTING HIGH OVERNIGHT.  HIGH/THIN CLOUDS WILL ALSO BE ON THE
INCREASE FROM WEST TO EAST LATE TONIGHT, ALTHOUGH MOSTLY CLEAR SKIES
ARE EXPECTED TO PERSIST.  OVERNIGHT LOWS WILL BE COLDEST ACROSS THE
E/NE WHERE READINGS WILL DROP TO AROUND 30 DEGREES, AND WILL BE
WARMEST ACROSS THE FAR SW AROUND JACKSONVILLE WHERE TEMPS WILL
REMAIN IN THE MIDDLE 30S.  HAVE INCLUDED PATCHY FROST ACROSS MUCH OF
THE AREA, EXCEPT WEST OF A CANTON TO TAYLORVILLE LINE WHERE TEMPS
MAY BE A LITTLE TOO WARM.  FROST/FREEZE HEADLINES MAY ONCE AGAIN BE
NEEDED TONIGHT, BUT HAVE OPTED TO ALLOW CURRENT HEADLINES TO EXPIRE
BEFORE ISSUING NEW ONES.

UPPER LOW CURRENTLY EVIDENT ON WATER VAPOR IMAGERY OVER SOUTHERN
CALIFORNIA WILL GET KICKED EASTWARD BY A NORTHERN STREAM WAVE COMING
ONSHORE IN THE PACIFIC NORTHWEST OVER THE NEXT 24 HOURS.  SEVERAL
MODELS ARE TRYING TO SPREAD CLOUDS/PRECIP INTO CENTRAL ILLINOIS AS
EARLY AS FRIDAY, BUT THINK AIRMASS WILL REMAIN TOO DRY TO SUPPORT
MEASURABLE PRECIP.  AS A RESULT, HAVE INCREASED CLOUDINESS AS THE
DAY PROGRESSES AND ONLY INCLUDED SLIGHT CHANCE POPS FOR SHOWERS
ACROSS THE FAR W/SW CWA. ATMOSPHERIC PROFILE WILL MOISTEN FROM THE
TOP-DOWN FRIDAY NIGHT, WITH SHOWERS BECOMING WIDESPREAD ACROSS
THE AREA AS THE UPPER LOW OPENS UP AND BEGINS TO APPROACH FROM THE
WEST. CORRESPONDING SURFACE LOW WILL DEVELOP IN THE LEE OF THE
ROCKIES ON FRIDAY, THEN WILL TRACK EASTWARD ACROSS THE MISSISSIPPI
RIVER VALLEY ON SATURDAY. 00Z APR 23 MODELS ALL SHOW A NORTHWARD
SHIFT IN THE TRACK, GENERALLY TAKING THE LOW FROM KANSAS CITY
SATURDAY MORNING TO AROUND EVANSVILLE BY SATURDAY EVENING. GFS IS
EVEN FURTHER NORTH WITH THE TRACK, BUT IT APPEARS TO BE AN
OUTLIER. GIVEN THE NORTHWARD SHIFT, HAVE INCREASED THUNDER MENTION
ACROSS THE SE CWA ON SATURDAY AS INSTABILITY PARAMETERS ARE
BECOMING MORE FAVORABLE FOR THUNDERSTORMS. IN FACT, LATEST SPC DAY
3 CONVECTIVE OUTLOOK SHOWS A MARGINAL RISK FOR SEVERE SOUTH OF
I-70.

ONCE THIS SYSTEM DEPARTS, COOL/DRY WEATHER WILL RETURN FOR SUNDAY.
AFTER THAT, MODELS ARE COMING INTO MUCH BETTER AGREEMENT CONCERNING
THE NEXT UPPER SYSTEM TO EJECT OUT OF THE DESERT SOUTHWEST NEXT
WEEK.  PREVIOUS RUNS OF THE GFS HAD SHOWN THIS FEATURE TRACKING
NORTHEASTWARD INTO ILLINOIS, RESULTING IN A PERIOD OF SHOWERY
WEATHER TUESDAY AND WEDNESDAY.  LATEST RUN HAS SHIFTED THE TRACK
MUCH FURTHER SOUTH, BUT NOT QUITE AS FAR SOUTH AS THE ECMWF/GEM,
WHICH BOTH TAKE THE LOW ALONG THE GULF COAST AND KEEP CENTRAL
ILLINOIS COMPLETELY DRY.  GFS IS TRYING TO PHASE AN APPROACHING
NORTHERN STREAM WAVE WITH THE EJECTING DESERT SOUTHWEST LOW, WHICH
COULD RESULT IN A MORE NORTHERN TRACK OF THE SYSTEM.  ECMWF/GEM KEEP
THE TWO SYSTEMS COMPLETELY SEPARATE, WHICH RESULTS IN CONTINUED
COOL/DRY WEATHER FOR ILLINOIS THROUGH THE REMAINDER OF THE EXTENDED.
AT THIS POINT, FEEL THE MORE CONSISTENT ECMWF/GEM SOLUTION IS THE
WAY TO GO, SO WILL KEEP MENTIONABLE POPS OUT OF THE FORECAST NEXT
WEEK.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)
ISSUED AT 619 AM CDT THU APR 23 2015

VFR CONDITIONS WILL PREVAIL AT ALL TAF SITES NEXT 24HRS. SKIES
SHOULD BE CLEAR THROUGH MOST OF THE PERIOD, WITH ONLY SOME HIGH
CLOUDS COMING IN TOWARD TOMORROW MORNING. WINDS WILL BE NORTHWEST
TODAY AND THEN BECOME LIGHT AND VARIABLE FOR THIS EVENING AND
TONIGHT.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
FROST ADVISORY UNTIL 8 AM CDT THIS MORNING FOR ILZ049>052-054-
056-061>063-066>068-071>073.

FREEZE WARNING UNTIL 8 AM CDT THIS MORNING FOR ILZ027>031-
036>038-040>048-053-055-057.

&&

$$

SHORT TERM...BARNES
LONG TERM...BARNES
AVIATION...AUTEN



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