Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 041712
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1212 PM CDT FRI SEP 4 2015

.UPDATE...
ISSUED AT 1035 AM CDT FRI SEP 4 2015

WATER VAPOR LOOP INDICATING A SLOW MOVING UPPER WAVE OVER SOUTHERN
LOWER MICHIGAN WITH A SECONDARY CIRCULATION NOTED OVER SOUTHEAST
WISCONSIN THIS MORNING. MEANWHILE...AT THE SURFACE...HIGH PRESSURE
WAS LOCATED TO OUR SOUTHEAST WHILE A WEAK FRONTAL BOUNDARY/WIND
SHIFT LINE WAS ANALYZED OVER FAR NORTHERN ILLINOIS. ANOTHER HOT
AFTERNOON IN STORE FOR THE AREA WITH TEMPERATURES SOARING INTO
THE LOW TO MID 90S AND HEAT INDEX VALUES OF 95 TO 100. THE
AFOREMENTIONED SECONDARY WAVE TO OUR NORTH COMBINED WITH SOME
COOL AIR ALOFT...500 MB TEMPS WERE AROUND -10 DEGREES C...AND
MIXED LAYER CAPES OF AROUND 2500 J/KG COULD LEAD TO SOME ISOLATED
SHOWERS AND THUNDERSTORMS THIS AFTERNOON...ESPECIALLY ACROSS THE
NORTH AND EAST. CURRENT FORECAST HAS THIS WELL HANDLED AT THE
MOMENT SO OTHER THAN SOME MINOR CHANGES TO THE MORNING TEMPERATURE
TRENDS...THE REST OF THE FORECAST LOOKS FINE. WILL SEND OUT AN
UPDATED ZFP TO REMOVE THE MENTION OF MORNING FOG IN PARTS OF OUR
AREA.

&&

.SHORT TERM...(TODAY)
ISSUED AT 303 AM CDT FRI SEP 4 2015

SPRAWLING UPPER-LEVEL RIDGE EXTENDING FROM THE SOUTHERN PLAINS INTO
THE WESTERN GREAT LAKES WILL CONTINUE TO DOMINATE THE WEATHER ACROSS
CENTRAL ILLINOIS TODAY...LEADING TO MOSTLY SUNNY SKIES WITH HIGH
TEMPERATURES ONCE AGAIN TOPPING OUT IN THE LOWER TO MIDDLE 90S.  THE
ONLY POTENTIAL FLY-IN-THE-OINTMENT WILL BE AN UPPER LOW SPINNING
OVER MICHIGAN.  08Z/3AM WATER VAPOR IMAGERY SHOWS THE MAIN LOW OVER
LAKE HURON...HOWEVER A WELL-DEFINED CIRCULATION IS NOTED ROTATING
AROUND THE LOW ACROSS EASTERN WISCONSIN. MODELS TAKE THIS FEATURE
ON A SOUTHEASTERLY TRAJECTORY ACROSS SOUTHERN LAKE MICHIGAN INTO
FAR NORTHERN INDIANA...WITH MOST OF ITS ASSOCIATED CONVECTION
REMAINING N/NE OF THE KILX CWA. HOWEVER THIS WAVE WILL PASS CLOSE
ENOUGH TO THE AREA TO WARRANT A SLIGHT CHANCE POP ALONG/NORTHEAST
OF A LACON TO PARIS LINE DURING THE AFTERNOON.

.LONG TERM...(TONIGHT THROUGH Thursday)
ISSUED AT 303 AM CDT FRI SEP 4 2015

UPPER LOW WILL REMAIN IN PLACE OVER MICHIGAN THROUGH SATURDAY...WITH
THE GFS DEVELOPING PRECIP WELL TO THE SOUTH INTO PORTIONS OF NORTH-
CENTRAL ILLINOIS.  THINK THIS MAY BE A BIT TOO AGGRESSIVE GIVEN THE
WEAKENING TREND OF THE SYSTEM AND THE FACT THAT BOTH THE NAM AND
ECMWF SHOW DRY CONDITIONS ACROSS THE AREA.  WILL MAINTAIN JUST A
SLIGHT CHANCE POP NORTHEAST OF THE I-74 CORRIDOR...BUT IF CURRENT
TRENDS CONTINUE THIS MAY BE REMOVED BY LATER SHIFTS.  ASIDE FROM
THIS VERY SLIM CHANCE FOR RAIN ACROSS THE FAR NE CWA...HOT AND DRY
WEATHER WILL PREVAIL BOTH SATURDAY AND SUNDAY WITH HIGH TEMPERATURES
REACHING THE LOWER TO MIDDLE 90S.

AFTER THAT...THINGS GET A LITTLE MORE INTERESTING AS MAJOR PATTERN
CHANGE OCCURS NEXT WEEK.  MODELS ARE BEGINNING TO COME INTO BETTER
AGREEMENT CONCERNING THE TIMING OF THIS PROCESS...WITH CONSENSUS
BRINGING THE INITIAL WEAKENING COLD FRONT INTO CENTRAL ILLINOIS ON
MONDAY.  AS IS TYPICALLY THE CASE WITH A PATTERN CHANGE OF THIS
MAGNITUDE...MODELS HAVE BEEN TOO FAST WITH THE FRONT.  AS A
RESULT...HAVE TRIMMED POPS SUNDAY NIGHT TO FEATURE JUST LOW CHANCE
ACROSS THE ILLINOIS RIVER VALLEY LATE.  HAVE ALSO SLOWED THE
EASTWARD PROGRESSION OF PRECIP ON MONDAY...WITH AREAS EAST OF I-57
REMAINING DRY THROUGH THE ENTIRE DAY.  THE FRONTAL BOUNDARY WILL
BECOME PARALLEL TO THE UPPER FLOW AND WILL STALL ACROSS THE
AREA...KEEPING CHANCE POPS IN THE FORECAST MONDAY NIGHT THROUGH
TUESDAY NIGHT.  AS A MORE SIGNIFICANT UPPER WAVE DIVES SOUTHEASTWARD
OUT OF CANADA...IT WILL PUSH A STRONGER COLD FRONT INTO ILLINOIS ON
WEDNESDAY.  GIVEN AMPLE LOW-LEVEL MOISTURE...STRONG UPPER
DYNAMICS...AND ADEQUATE CONVERGENCE ALONG THE BOUNDARY...HAVE OPTED
TO CARRY LIKELY POPS ON WEDNESDAY.  FRONT WILL DROP SOUTHWARD INTO
THE OHIO RIVER VALLEY BY THURSDAY...RESULTING IN COOLER AND DRIER
CONDITIONS WITH HIGH TEMPERATURES DROPPING INTO THE MIDDLE TO UPPER
70S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z Saturday AFTERNOON)
ISSUED AT 1205 PM CDT FRI SEP 4 2015

VFR CONDITIONS ARE EXPECTED THRU MOST OF THIS FORECAST PERIOD.
ABOUT THE ONLY EXCEPTION WOULD BE IN THE 10Z-13Z TIME FRAME
WHEN SOME PATCHY FOG/HAZE MAY FORM IN A FEW LOCATIONS. SCATTERED
TO BROKEN MID LEVEL CLOUDS SEEN ON VISIBLE SATELLITE DATA EARLY
THIS AFTERNOON WITH SOME SCATTERD CUMULUS BELOW AT 4000-5000 FEET.
LIGHT SOUTH TO SOUTHWEST WINDS WERE REPORTED ACROSS THE AREA LATE
THIS MORNING INTO EARLY THIS AFTERNOON WITH LIGHT WINDS EXPECTED
OVER THE FORECAST AREA THROUGH TONIGHT. ISOLATED THUNDERSTORMS
WILL BE POSSIBLE AT KBMI AND KCMI IN THE 20Z-01Z TIME FRAME BUT
COVERAGE AT THIS TIME APPEARS TO BE TOO LIMITED TO INCLUDE IN
TAFS.

&&

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

$$

UPDATE...Smith
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Smith


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