Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 280141
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
841 PM CDT SAT JUN 27 2015

.UPDATE...
ISSUED AT 840 PM CDT SAT JUN 27 2015

A SHORTWAVE HIGH PRESSURE RIDGE WILL APPROACH FROM THE NW AND
CROSS OVER ILLINOIS OVERNIGHT BRINGING MOSTLY CLEAR SKIES THROUGH
THE EARLY PORTIONS OF THE NIGHT DUE TO SUBSIDENCE ASSOCIATED WITH
THE FEATURE. HIGH CLOUDINESS ASSOCIATED WITH A SHORTWAVE LOW
PRESSURE TROUGH FOLLOWING THE RIDGE WILL ARRIVE OVERNIGHT...WITH
INCREASING LOW AND MID CLOUD BY MORNING MAINLY NW OF THE ILLINOIS
RIVER. NORTH WINDS WILL DECREASE RAPIDLY IN THE EVENING...BECOMING
LIGHT AND VARIABLE...AS PRESSURE GRADIENTS DECREASE UNDER HIGH
PRESSURE. CURRENT FORECAST IS IN GOOD SHAPE WITH THESE FEATURES
AND NO UPDATES ARE PLANNED AT THIS TIME OTHER THAN MINOR
ADJUSTMENTS TO SHORT TERM TEMPERATURE/HUMIDITY/WIND TRENDS.

&&

.SHORT TERM...(TONIGHT)
ISSUED AT 253 PM CDT SAT JUN 27 2015

ISOLATED SHOWERS AND POSSIBLE THUNDERSTORMS WEST OF A GALESBURG TO
BEARDSTOWN TO JACKSONVILLE LINE AT MID AFTERNOON FROM VERY WEAK
SHORT WAVE MOVING SOUTH NEAR MS RIVER VALLEY WILL DISSIPATE BY 00Z/7
PM LEAVING DRY CONDITIONS ACROSS CWA TONIGHT. DIRUNALLY DRIVEN
SCATTERED CUMULUS CLOUDS TO DISSIPATE AT SUNSET AS WELL LEAVING FAIR
SKIES TONIGHT ACROSS CENTRAL/SE IL. STRONGER NORTHERN STREAM SHORT
WAVE ALONG THE SOUTHERN ONTARIO AND MANITOBA PROVINCE LINE WITH
CONVECTION AS FAR SOUTH AS NORTHERN MN AND EASTERN ND WILL DIVE SE
ACROSS MN/IA BY DAWN SUNDAY AND INCREASE CLOUDS LATER TONIGHT OVER
IL RIVER VALLEY...MAINLY NW OF IL RIVER. ANY CONVECTION FROM THIS
SYSTEM SHOULD STAY NW OF CWA THROUGH AT LEAST 12Z/7 AM SUNDAY. WEAK
SURFACE HIGH PRESSURE RIDGE OF 1017 MB OVER THE MO VALLEY TO DRIFT
OVER IL OVERNIGHT. SO BREEZY NORTH WINDS WITH GUSTS 15-25 MPH SHOULD
DIMINISH LIGHT AND VARIABLE LATER THIS EVENING. DEWPOINTS HAVE
SLIPPED INTO THE MID 50S TO NEAR 60F AT MID AFTERNOON AND THIS
SHOULD BE WHERE LOWS REACH CLOSE TO OVERNIGHT. LOWS IN MID 50S OVER
EASTERN IL AND UPPER 50S OVER THE IL RIVER VALLEY.

.LONG TERM...(SUNDAY THROUGH SATURDAY)
ISSUED AT 253 PM CDT SAT JUN 27 2015

MAIN CHALLENGE WILL BE TIMING OF INDIVIDUAL SHORTWAVES AND ASSOCIATED
PRECIPITATION CHANCES IN THE NORTHWEST FLOW ALOFT OVER THE EASTERN
U.S. AS A RATHER AMPLIFIED PATTERN TAKES HOLD ACROSS THE AREA THRU
THE WEEK. FIRST OF THE UPPER WAVES WAS TRACKING SSE ACROSS THE
NORTHERN PLAINS THIS AFTERNOON AND WILL BRING AN INCREASING CHANCE
FOR SHOWERS AND STORMS BACK INTO THE REGION SUNDAY AFTERNOON AND
NIGHT. MIXED LAYER CAPES AROUND 1500 J/KG BY AFTERNOON ACROSS THE
WEST...HOWEVER...STRONGER DEEP LAYER FLOW REMAINS JUST TO OUR WEST
INTO THE EVENING HOURS WITH MARGINAL LAPSE RATES...DEPENDING ON
WHICH MODEL YOU LOOK AT. THE NAM HAS SLOWED THE ONSET OF THE PRECIP
AND IS KEEPING THE DEEP LAYER SHEAR AND BETTER INSTABILITY JUST TO
OUR WEST. STILL COULD SEE STRONG WIND GUSTS WITH SOME OF THE MORE
ORGANIZED STORMS TOMORROW AFTERNOON INTO THE EVENING AS THE UPPER
WAVE TRACKS ACROSS OUR AREA. DUE TO THE PROGRESSIVE NATURE OF THE
SYSTEM...IT APPEARS QPF VALUES WILL BE HELD IN CHECK WITH MOST
AREAS SEEING A QUARTER TO ONE HALF INCH AMOUNTS LATE SUNDAY
AFTERNOON INTO THE OVERNIGHT HOURS.

THE SHORTWAVE WILL SHIFT OFF TO OUR EAST BY MONDAY MORNING WITH THE
HIGHER POPS OVER THE EAST. STILL ENOUGH COLD AIR ALOFT ASSOCIATED
WITH THE DEPARTING WAVE TO KEEP AT LEAST LOW CHANCE POPS GOING
DURING THE AFTERNOON. POPS ARE IN THE SLIGHT CHANCE RANGE MONDAY
NIGHT IN THE WAKE OF THE SHORTWAVE WITH LOW POPS HOLDING INTO
TUESDAY BEFORE THE NEXT SHORTWAVE DROPS INTO THE REGION FOR MAINLY
TUESDAY NIGHT. IF THE SOUTHWARD TREND IN THE MODELS CONTINUES...THE
HIGHER THREAT FOR SHOWERS AND STORMS WOULD BE OVER OUR SOUTHERN
AREAS...BUT FOR NOW... WITH SOME SPREAD IN THE MODEL SOLUTIONS FOR
THAT TIME FRAME...WILL KEEP THE 30-40 POPS GOING TUESDAY NIGHT INTO
WEDNESDAY. ANOTHER FAST MOVING WAVE EMBEDDED IN THE NORTHWEST FLOW
WILL APPROACH THE AREA LATE WEDNESDAY/WEDNESDAY NIGHT WITH MORE
ORGANIZED SHOWER AND THUNDERSTORM CHANCES ADVERTISED OFF THE LATEST
ECMWF...WHILE THE 12Z GFS AND GEM GLOBAL SOLUTIONS NOT SHOWING MUCH
REFLECTION QPF-WISE FROM THAT SHORTWAVE.

PATTERN NOT EXPECTED TO MAKE MUCH OF A CHANGE UNTIL LATE NEXT WEEK
MEANING THE DAILY THREAT FOR SCATTERED SHOWERS AND STORMS WILL
CONTINUE INTO THE END OF THIS FORECAST PERIOD. THE LATEST ECMWF DOES
OFFER SOME HOPE IN THE EXTENDED PERIOD AS IT SHIFTS THE STRONGER
FLOW FURTHER NORTH AS AN UPPER LEVEL RIDGE EXPANDS NORTHWARD INTO
THE CENTRAL PLAINS AND MIDWEST NEXT WEEKEND. THIS WOULD SHIFT THE
BETTER CHANCES FOR SHOWERS AND STORMS FURTHER NORTH AND BRING SOME
VERY WARM TEMPS BACK INTO THE AREA. HOWEVER...WITH AS MUCH WATER
AS THERE IS IN THE SOIL OVER A LARGE PORTION OF THE CENTRAL
U.S...IT SEEMS HARD TO BUY THE IDEA OF ANY PERSISTENT RIDGING
OCCURRING ACROSS THE MIDDLE OF THE COUNTRY. IT`S NOT THE FIRST
TIME THIS MODEL HAS TRIED TO AMPLIFY THE RIDGE OVER THE CENTER OF
THE NATION...ONLY TO HAVE PERSISTENT CONVECTIVE ACTIVITY ACROSS
THE NORTH-CENTRAL PLAINS KEEP THE PATTERN MUCH LESS AMPLIFIED WITH
THE STRONGER FLOW DISPLACED FURTHER SOUTH THAN FORECAST. WE CAN
ONLY HOPE WE SEE AT LEAST A TEMPORARY SHIFT IN THE PATTERN HEADING
INTO THE SECOND WEEK OF JULY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 653 PM CDT SAT JUN 27 2015

VFR CONDITIONS ACROSS CENTRAL IL TERMINALS THIS EVENING AS A WEAK
HIGH PRESSURE RIDGE APPROACHES FOR OVERNIGHT. WINDS N UP TO 10 KTS
AT 00Z...BECOMING LIGHT AND VARIBLE OVERNIGHT. SOME VISIBILITY
REDUCTIONS POSSIBLE LATE IN THE NIGHT DUE TO FOG EXCEPT MOST
MODEL GUIDANCE SUGGESTING AGAINST IT AT THIS POINT DUE TO LOWER
DEWPOINTS IN THE LOW 50S AND A GENERAL DECREASE IN MOISTURE WITH
HEIGHT. SCATTERED CUMULUS CLOUDS TO APPEAR AGAIN BY 15Z AS A LOW
PRESSURE SYSTEM APPROACHES FROM THE NORTHWEST. SHOWERS AND
THUNDERSTORMS WILL SPREAD INTO THE REGION 17-20Z WITH THIS
SYSTEM...ALONG WITH WINDS BECOMING S-SW 10-12 KTS. AT THIS
TIME...TIMING AND LOCATION UNCERTAINTIES WITH THUNDERSTORMS THAT
DEVELOP PRECLUDE MENTION OF IFR/MVFR CIGS/VSBYS ALTHOUGH STRONGER
STORMS WILL CONTAIN IFR CONDITIONS AS WELL AS GUSTY AND VARIABLE
WINDS.


&&

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

$$

UPDATE...ONTON
SHORT TERM...07
LONG TERM...SMITH
AVIATION...ONTON



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