Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 280018
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
717 PM CDT THU AUG 27 2015

.SHORT TERM...(TONIGHT)
ISSUED AT 220 PM CDT THU AUG 27 2015

FOR TONIGHT...WEATHER WILL REMAIN QUIET ACROSS THE REGION AS A
LARGE AREA OF HIGH PRESSURE CENTERED OVER THE EASTERN GREAT LAKES
SLOWLY MOVES OFF TO THE EAST AND LOW PRESSURE DEEPENS OVER THE
CENTRAL PLAINS. THE DIURNAL CUMULUS SHOULD LARGELY DISSIPATE AT
SUNSET...BUT SOME MID AND HIGH CLOUD FROM ONGOING THUNDERSTORM
ACTIVITY OVER THE CENTRAL PLAINS WILL BEGIN TO OVERSPREAD THE
REGION TONIGHT. AS THE SURFACE PATTERN PROGRESSES...LOW LEVEL
FLOW WILL BECOME MORE SOUTHERLY...ALLOWING DEWPOINTS TO INCH A
LITTLE HIGHER OVERNIGHT. THE INCREASING MID AND HIGH CLOUD...
COMBINED WITH WINDS REMAINING AROUND 5 MPH OR SO OVERNIGHT SHOULD
PREVENT TEMPERATURES FROM DROPPING QUITE AS LOW AS LAST NIGHT DUE
TO REDUCED RADIATIONAL COOLING. OVERNIGHT LOWS SHOULD BE IN THE
MIDDLE TO UPPER 50S. HIGHER DEWPOINT DEPRESSIONS AND SOME
BREEZINESS SHOULD PREVENT MUCH IN THE WAY OF FOG DEVELOPMENT...
EXPECT PERHAPS IN SOME ISOLATED...SHELTERED AREAS.

.LONG TERM...(FRIDAY THROUGH THURSDAY)
ISSUED AT 220 PM CDT THU AUG 27 2015

THE TREND THROUGH THE LONGER TERM FORECAST PERIOD WILL BE FOR
INCREASING TEMPERATURES AND THE ONLY SIGNIFICANT CHANCE FOR PCPN
WILL BEGIN BY FRIDAY AFTERNOON OR EVENING AS THE SHORTWAVE
RESPONSIBLE FOR THE ONGOING CONVECTION OVER THE CENTRAL PLAINS
TRACKS ACROSS IOWA AND THROUGH THE UPPER MISSISSIPPI VALLEY AND
INTO SWRN WISCONSIN BY FRIDAY EVENING. INCREASING MOISTURE AND
INSTABILITY IN THE AIRMASS AHEAD OF A TRAILING COLD FRONT WILL AID
THE DEVELOPMENT OF SHOWERS AND SCATTERED THUNDERSTORMS AS THE
BOUNDARY SLOWLY SAGS THROUGH NWRN IL BY SATURDAY MORNING. THE
PROGRESSION OF THE MID LEVEL SHORTWAVE IS EXPECTED TO SLOW AND
BECOME ALMOST STATIONARY OVER THE WESTERN GREAT LAKES REGION AS
ADDITIONAL NORTHERN STREAM SHORTWAVE ENERGY PHASES WITH THE
INITIAL WAVE...ALLOWING THE FRONTAL BOUNDARY TO BECOME A MORE
EAST-WEST ORIENTED QUASI-STATIONARY FRONT ACROSS CNTRL IL. THE
LATEST GUIDANCE SUGGESTS THAT THE BOUNDARY WILL BE RELATIVELY
DIFFUSE...LIMITING SFC FORCING ACROSS CNTRL IL WHILE THE GREATEST
UPPER LEVEL FORCING REMAINS WELL TO THE NORTH OVER NRN IL/SRN
WI/SRN LAKE MICHIGAN. SO...WHILE THERE IS RELATIVELY HIGH
CONFIDENCE IN AT LEAST SCATTERED SHOWERS AND THUNDERSTORMS THROUGH
THE WEEKEND...FEEL THAT THE LACK OF WELL DEFINED FORCING
MECHANISMS SHOULD KEEP ACTIVITY ILL-DEFINED AND GENERALLY
SCATTERED.

BY EARLY NEXT WEEK...THE NRN STREAM SHORTWAVE SHOULD MOVE OFF TO
THE EAST WHILE THE SOUTHERN PORTION OF THE UPPER LEVEL WAVE LAGS
BACK OVER SRN MO/IL/IN...PERHAPS KEEPING A SLIGHT CHANCE FOR
LINGERING SHOWERS OVER FAR SOUTHERN ILLINOIS. UPPER RIDGING
BUILDING ACROSS THE MIDWEST WILL HELP CONTINUE THE WARMING TREND
THROUGH NEXT WEEK WHILE ENDING ANY SGFNT PCPN CHANCES. EXPECT THAT
TEMPS COULD REACH THE UPPER 80S BY MONDAY AND LOWER 90S FOR
TUESDAY THROUGH THURSDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 717 PM CDT THU AUG 27 2015

HIGH PRESSURE CENTERED OVER THE GREAT LAKES AND OHIO VALLEY WILL
MOVE EAST TONIGHT AND FRIDAY AS LOW PRESSURE CURRENTLY OVER THE
CENTRAL PLAINS MOVES TO NORTHEAST IOWA BY FRIDAY EVENING. LIGHT
SOUTHEAST WINDS EARLY THIS EVENING WILL BECOME LIGHT OVERNIGHT, THEN
BECOME MORE SOUTHERLY FRIDAY MORNING AS THE GRADIENT BEGINS TO
TIGHTEN AHEAD OF THE APPROACHING LOW. SPEEDS WILL LIKELY INCREASE TO
10-14KTS BY 16Z, THEN GUST TO 18KT OR HIGHER FRIDAY AFTERNOON.

SCT CU IN THE 3-4KFT RANGE WILL LINGER FOR A COUPLE HOURS THIS
EVENING, THEN SCT MID-HIGH CLOUDS WILL FILTER INTO IL ON NW FLOW
ALOFT. THERE IS SOME POTENTIAL FOR LIGHT/SHALLOW GROUND FOG
OVERNIGHT INTO FRIDAY MORNING BUT CONFIDENCE REGARDING HOW
WIDESPREAD IT MAY BECOME DUE TO QUESTIONS ON HOW MUCH HIGH CLOUDS
WILL BE ACROSS THE AREA LATE TONIGHT, SO NO MENTION WITH THIS
FORECAST.

&&

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

$$

SHORT TERM...KREIN
LONG TERM...KREIN
AVIATION...SHIMON



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