Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 142347
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
647 PM CDT SUN SEP 14 2014

.DISCUSSION...
240 PM CDT

MAIN FOCUS IS ON OUR NEXT RAIN CHANCE WHICH COMES VERY LATE TONIGHT
THROUGH MUCH OF MONDAY...AND A CONTINUATION OF COOL/BELOW AVERAGE
TEMPS FOR MID-SEPTEMBER.

IN THE NEAR TERM...A PLEASANT BUT STILL COOL WEATHER WAS IN PLACE
ACROSS THE REGION THIS AFTERNOON. SURFACE HIGH PRESSURE WAS CENTERED
OVER THE EASTERN GREAT LAKES...WITH RIDGING EXTENDING SOUTHWEST
ACROSS INDIANA AND ILLINOIS. THE RESULT IS MOSTLY SUNNY AND SLIGHTLY
MILDER CONDITIONS WITH TEMPS REACHING THE MID 60S IN MOST SPOTS AND
UPPER 60S IN A COUPLE IN THE WEST/SOUTH PARTS OF THE CWA. LIGHT
WINDS AND CLEAR SKIES THIS EVENING WILL ALLOW TEMPS TO FALL OFF
FAIRLY QUICKLY HOWEVER...WITH READINGS DROPPING THROUGH THE 50S THIS
EVENING AND INTO THE MID-UPPER 40S LATER TONIGHT BEFORE CLOUDS BEGIN
TO INCREASE AFTER MIDNIGHT.

THIS INCREASE IN CLOUD COVER LATE TONIGHT WILL BE IN ASSOCIATION
WITH A MID-LEVEL SHORT WAVE TROUGH CURRENTLY DIGGING SOUTHEAST FROM
SASKATCHEWAN INTO MONTANA PER AFTERNOON GOES VAPOR IMAGERY.
INCREASING SOUTHERLY LOW LEVEL FLOW WILL DEVELOP AS THIS WAVE DIGS
SOUTHEAST...WITH 925-850 MB LAYER MOISTURE TRANSPORT INCREASING ON
THE NOSE OF A 30-35 KT LOW LEVEL JET WHICH DEVELOPS FROM THE TX/OK
PANHANDLE REGION. THIS AXIS OF MOISTURE TRANSPORT EVENTUALLY WORKS
INTO NORTHERN MISSOURI AND WEST CENTRAL IL MONDAY MORNING AS THE JET
VEERS MORE WEST-SOUTHWESTERLY. WHILE A FEW SHOWERS MAY DEVELOP
ACROSS FAR NORTH CENTRAL IL PRIOR TO SUNRISE...IT APPEARS THAT THE
BEST FORCING WILL ARRIVE SHORTLY AFTER...AS MID-LEVEL VORT
APPROACHES. A COMBINATION OF 40-50 METER HEIGHT FALLS...UPPER
DIVERGENCE BENEATH THE RIGHT REAR ENTRANCE REGION OF A 100+ KT UPPER
JET STREAK OVER THE GREAT LAKES...AND DEVELOPING FRONTOGENETIC
FORCING WITHIN THE LOW-MID LEVELS SHOULD PROVIDE SUFFICIENT FORCING
FOR PRODUCING RAIN/SHOWERS ACROSS THE AREA DURING THE DAY MONDAY.
WITH VARIOUS MODEL QPF AMOUNTS IN THE 0.25 TO 0.35 RANGE...RAIN IS
EXPECTED TO TAPER OFF FROM THE WEST/NORTHWEST LATE MONDAY AFTERNOON
AND EARLY MONDAY EVENING AS THE RELATIVELY PROGRESSIVE DISTURBANCE
MOVES EAST OF THE FORECAST AREA. STRONG HEIGHT RISES THEN ACCOMPANY
DEVELOPMENT OF SURFACE HIGH PRESSURE ACROSS THE MID-MISSISSIPPI
VALLEY MONDAY NIGHT AND TUESDAY.

SURFACE HIGH PRESSURE IS EXPECTED TO LINGER ACROSS THE ACROSS THE
MIDWEST FOR MUCH OF THE REMAINDER OF THE WEEK...SETTING THE STAGE
FOR DRY WEATHER WITH COOL NIGHTS AND COOLER THAN AVERAGE BUT SLOWLY
MODERATING TEMPS THROUGH NEXT WEEKEND. AFTER CLOUD/PRECIP INFLUENCED
TEMPS ONLY IN THE UPPER 50S/LOWER 60S OVER MUCH OF THE AREA
MONDAY...DAYTIME HIGHS SHOULD MODERATE THROUGH THE 60S THROUGH
WEDNESDAY AND THEN FINALLY INTO THE 70S FOR THE END OF THE
WEEK/WEEKEND. COLDEST OVERNIGHT MINS LOOK TO BE LATE MONDAY NIGHT AS
HIGH PRESSURE BUILDS IN  WITH LOW 40/A FEW UPPER 30S...WITH LOWS
GRADUALLY MODERATING INTO THE 50S BY THE END OF THE WEEK.

UPPER PATTERN EVOLVES INTO A LONG WAVE TROUGH OVER THE EAST COAST
WITH AN UPPER RIDGE ACROSS THE ROCKIES BY FRIDAY. SLIGHT EASTWARD
PROGRESSION AND FLATTENING OF THE PATTERN ALLOWS RETURN OF
WARMER/HIGHER MOISTURE CONTENT AIR INTO THE REGION INTO THE WEEKEND.
THIS YIELDS AN INCREASING CHANCE OF SHOWERS/THUNDERSTORMS AS A
MID-LEVEL DISTURBANCE PROPAGATES THROUGH THE FLOW AND A SURFACE
TROUGH APPROACHES AND MOVES ACROSS THE AREA FRIDAY NIGHT THROUGH
SUNDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* SOUTHWEST WINDS TURN WESTERLY MIDDAY MONDAY THEN NORTHERLY LATE
  AFTERNOON. 350-010 DIRECTION POSSIBLE LATE AFTERNOON/EARLY
  EVENING WITH SPEEDS 10+ KT ALSO POSSIBLE FOR A FEW HOURS.

* RAIN INCREASES IN COVERAGE MID MORNING MONDAY...WITH STEADIEST
  RAIN MIDDAY/EARLY AFTERNOON BEFORE ENDING LATE AFTERNOON.

* CIGS LOWER LATE MONDAY MORNING WITH MVFR LIKELY BY AROUND
  MIDDAY. MVFR SCATTERS TO VFR LATE AFTERNOON/EARLY EVENING.

MDB

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE REMAINS SPREAD FROM THE ST. LAWRENCE VALLEY AND DOWN
THE OHIO VALLEY THIS EVENING KEEPING SOUTHWESTERLY WINDS ACROSS
THE TERMINALS. SPEEDS WILL DIMINISH TO A FEW KNOTS WITH SUNSET. AN
UPPER TROUGH MOVING ACROSS THE CANADIAN PRAIRIES INTO THE
NORTHERN PLAINS WILL TRACK SOUTHEAST ACROSS THE AREA MONDAY
AFTERNOON. MID AND HIGH CLOUDS WILL STREAM ACROSS THE AREA LATER
TONIGHT WITH RAIN/SHOWERS EXPECTED TO MOVE IN MID/LATE MONDAY
MORNING FROM WEST TO EAST. THE BULK OF THE FORCING WILL PASS
DURING THE MIDDAY/EARLY AFTERNOON HOURS LIKELY BRINGING MORE
WIDESPREAD RAIN TO THE AREA. RAIN LOOKS TO QUICKLY EXIT DURING THE
LATE AFTERNOON AS A SURFACE TROUGH PASSES. CIGS WILL LIKELY LOWER
TO MVFR INTO MIDDAY THEN LOWER END MVFR DURING THE EARLY
AFTERNOON. SOME BRIEF IFR IS ALSO POSSIBLE. WINDS WILL SHIFT
NORTHERLY WITH THE FRONTAL PASSAGE DURING THE LATE AFTERNOON AND
MAY GO AS FAR AS NORTH-NORTHEAST ACROSS NORTHEAST IL. HAVE REDUCED
CONFIDENCE IN WIND SPEEDS DURING THE MID AFTERNOON/EARLY EVENING
HOURS BUT 10-15 KT DOES LOOK POSSIBLE. SOME MVFR MAY LINGER INTO
EARLY EVENING BUT EXPECT A STEADY DECREASE IN COVERAGE BEHIND THE
TROUGH.

MDB


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH CONFIDENCE IN SOUTHWEST TO WEST WINDS MONDAY MORNING
  THROUGH MID AFTERNOON. HIGH CONFIDENCE IN SHIFT TO AT LEAST
  NORTHWEST...WITH MEDIUM CONFIDENCE IN NORTH AND LOW CONFIDENCE
  IN NNW. MEDIUM CONFIDENCE IN SPEEDS 10+ KT WITH THE NORTHERLY
  DIRECTION.

* HIGH CONFIDENCE IN RAIN SPREADING ACROSS THE AREA MONDAY. MEDIUM-
  HIGH CONFIDENCE IN TIMING.

* MEDIUM-HIGH CONFIDENCE IN MVFR CIGS OCCURRING MONDAY...MEDIUM
  CONFIDENCE IN TIMING/DURATION. LOW CONFIDENCE IN POTENTIAL FOR
  ANY IFR.

MDB

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. NORTHWEST WINDS BECOMING WEST.

WEDNESDAY...VFR. WEST WINDS BECOMING NORTHEAST.

THURSDAY...VFR. EAST WINDS.

FRIDAY...VFR. SOUTHEAST WINDS.

SATURDAY...VFR. BREEZY SOUTH-SOUTHWEST WINDS. CHANCE OF
THUNDERSTORMS.

MDB

&&

.MARINE...
144 PM CDT

HIGH PRESSURE CENTERED OVER THE OHIO VALLEY WILL CONTINUE TO
SLOWLY LIFT NORTHEAST...BECOMING CENTERED OVER NEW ENGLAND MONDAY
MORNING. ALONG THE WESTERN END OF THIS HIGH PRESSURE CENTER IS A
TIGHTER GRADIENT...WHICH HAS BECOME EVIDENT ALONG THE NORTHERN
PORTIONS OF LAKE MICHIGAN WITH WINDS GUSTING AT TIMES TO 30KT FROM
THE SOUTHWEST. A FRONTAL BOUNDARY WILL SWEEP ACROSS LAKE MICHIGAN ON
MONDAY TURNING WINDS WEST/NORTHWEST. THEN ANOTHER RIDGE OF HIGH
PRESSURE WILL BRING ANOTHER PERIOD OF LIGHTER WINDS TO THE LAKE
MONDAY NGT THRU TUE.

HIGH PRESSURE WILL THEN REMAIN IN PLACE THROUGH EARLY
THURSDAY...THEN LIFT NORTHEAST WITH FLOW TURNING SOUTHERLY AND A
TIGHTENING GRADIENT THURSDAY NGT THROUGH FRIDAY. AT THIS TIME IT
IS POSSIBLE WIND COULD GUST TO 30KT FRIDAY NIGHT INTO
SATURDAY...MAINLY FOR THE NORTHERN HALF OF THE LAKE.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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