Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 130505 AAA
AFDLOT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1205 AM CDT SUN JUL 13 2014

.MESOSCALE DISCUSSION...
1204 AM CDT

AREA OF RAIN WITH EMBEDDED CONVECTION...PARTIALLY FROM DECAYED
MCS...CONTINUES TO SHIFT EAST DRIVEN BY STRONGER MID-LEVEL WINDS
AND ELONGATED SHORT WAVE. RAINFALL RATES OF ONE HALF TO
SPORADICALLY ONE INCH PER HOUR ARE BEING OBSERVED BASED ON
OBSERVATIONS AND RADAR ESTIMATED TOTALS. RAINFALL SHOULD LAST
AROUND 2-3 HOURS IN THE CHICAGO METRO AREA AND ADJACENT LOCATIONS.

HAVE COORDINATED WITH THE NORTH CENTRAL RIVER FORECAST CENTER ON
THEIR FLASH FLOOD GUIDANCE FOR THE SOUTHERN CHICAGO METRO AREA.
GIVEN CONFIDENCE IS HIGH FROM THEM IN LOW VALUES OF ONLY 1.25 TO
2.00 INCHES IN THREE HOURS FOR FLOODING...DUE TO THE HEAVY
RAINFALL OBSERVED EARLY SATURDAY MORNING...HAVE GONE AHEAD AND
ISSUED A FLASH FLOOD WARNING FOR THE CENTRAL TO SOUTHERN CHICAGO
METRO AREA.

PROPAGATION IS EXPECTED TO CONTINUE EAST-SOUTHEAST...THOUGH SOME
SLOWING IS EXPECTED FOR AREAS ALONG AND SOUTH OF THE KANKAKEE
RIVER AS THE 30-40 KT LOW-LEVEL JET OFFSETS SOUTHWARD MOVEMENT.
THIS COULD CREATE TRAINING AND FLOODING PROBLEMS...AGAIN
PARTICULARLY FOR THE AREAS HIT HARD ON SATURDAY MORNING /SUCH AS
WESTERN FORD AND SOUTHERN LIVINGSTON COUNTIES/.

MTF

&&

.DISCUSSION...
311 PM CDT

THIS AFTERNOON...
THE SURFACE LOW IS OVER NORTHERN MANITOBA AND THE UPPER LEVEL LOW IS
STACKED JUST ABOVE IT.  STILL HAVE MOSTLY CLOUD SKIES WITH A FEW
BREAKS OF SUN AND WE ARE SLOWLY RECOVERING FROM THIS MORNING/S
CONVECTION.  THE 18Z DVN SOUNDING FEATURED 1.7 INCHES OF PWAT AND
AROUND 1500 J/KG OF CAPE. THE SOUNDING ALSO HAD A STOUT CAP AT 850MB
WHICH MATCHES WELL WITH THE LATEST AMDAR SOUNDINGS.  LAPSE RATES TO
950 MB WERE SURPRISINGLY STEEP GIVEN THE THICK CLOUD COVER. WITH THE
CAP IN PLACE AND SLOW RECOVERY NOT EXPECTING MUCH CONVECTIVE
ACTIVITY AHEAD OF THE MAIN LINE OF STORMS. IN GENERAL EXPECTING
CLOUDS TO CONTINUE THIN AND TEMPS RISE INTO THE MID 80S BY LATE THIS
AFTN.  IT WILL CONTINUE TO BE MUGGY AS PWAT VALUES INCREASE TO
AROUND 2 INCHES.

THIS EVENING AND TONIGHT...
AN UPPER LEVEL SHORTWAVE CURRENTLY OVER IOWA WILL MOVE OVER THE CWA
THIS EVENING ADDING FORCING FOR STORMS. A SURFACE LOW IS OVER
NORTHERN MANITOBA AND ITS COLD FRONT STRETCHES FROM NORTHWEST
WISCONSIN THROUGH CENTRAL IOWA.  A LINE OF STORMS WILL FORM ALONG
THE FRONT AND SLOWLY PUSH SOUTH THROUGH THE CWA THIS EVENING AND
OVERNIGHT. 850MB STEERING FLOW WILL BE WEST AT 30-40 KT AHEAD OF THE
LINE BUT ONLY AROUND 15 KT FROM THE NORTH BEHIND THE FRONT. TIMING
DIFFERS BETWEEN THE MODELS BUT THINKING A BLEND OF OUR LOCAL ARW AND
THE RAP LOOK REASONABLE. THE NAM LOOKS TOO FAST WHILE THE HRRR LOOKS
TOO SLOW.

THE LINE MAY PRODUCE SEVERE WIND GUSTS IN EXCESS OF 60 MPH...BUT THE
MAIN CONCERN WILL BE FLASH FLOODING. PWAT VALUES REMAIN HIGH AT
1.7-1.8 INCHES AND VALUES WILL INCREASE TO AROUND 2 INCHES BY THIS
EVENING.  HAVE ISSUED A FLASH FLOOD WATCH FOR THE ENTIRE WARNING
AREA FOR THIS EVENING THROUGH TOMORROW MORNING.  TOTAL RAINFALL FROM
THIS STORM WILL BE IN EXCESS OF 1 INCH. THE HIGHEST TOTALS WILL
LIKELY BE ALONG THE IL/WI STATE LINE WHERE RAINFALL TOTALS WILL
EASILY APPROACH 2 INCHES.  IN ADDITION...SOME AREAS THIS MORNING
FROM COOK COUNTY SOUTH THROUGH PONTIAC AND GIBSON CITY SAW MULTIPLE
INCHES OF RAIN OVERNIGHT INTO THIS MORNING. THESE AREAS WILL BE THE
MOST SUSCEPTIBLE TO FLASH FLOODING AS WATER LEVELS ARE ALREADY
HIGH.

TEMPERATURES WILL QUICKLY FALL BEHIND THE LINE OF STORMS AND LOWS
WILL BE IN THE UPPER 60S TO LOWER 70S.

SUNDAY AND MONDAY...
THE UPPER LEVEL LOW SPLITS SUNDAY NIGHT AND THE FIRST TROUGH AXIS
MOVES THROUGH MONDAY NIGHT.  AT THE SURFACE A SECOND COLD FRONT
MOVES THROUGH SUNDAY AND THEN STALLS OUT JUST SOUTH OF THE CWA
MONDAY MORNING. THE HIGHEST INSTABILITY VALUES WILL BE SOUTH OF I-80
SO ONLY HAVE A CHANCE OF STORMS SOUTH OF I-80. NOT EXPECTING MUCH IN
THE WAY OF PRECIP AT THIS TIME.

A BAND OF SHOWERS AND STORMS MAY FORM SUNDAY NIGHT FIRST ALONG THE
IL/WI STATE LINE AND THEN SPREAD SOUTH AS A VORTICITY STREAMER FROM
THE UPPER LEVEL LOW PUSHES SOUTH THROUGH THE REGION.  THE SHOWERS
MAY PERSIST INTO LATE SUNDAY NIGHT AND BY THEN ONLY EXPECTING
SHOWERS.  CONFIDENCE IS MEDIUM WITH THE STORMS DEVELOPING AND
COVERAGE.

YET ANOTHER COLD FRONT COMES THROUGH MONDAY AND HAVE A CHANCE OF
SHOWERS AND STORMS MONDAY AFTERNOON AND EVENING.  THE BIGGER STORY
WILL BE THE COOL AIR THAT FOLLOWS THE COLD FRONT.  HIGHS ON SUNDAY
WILL BE IN THE LOWER 80S WHILE MONDAY/S HIGHS WILL BE IN THE MID TO
UPPER 70S.  MONDAY NIGHT LOOKS CRISP WITH LOWS IN THE LOWER 50S.

EXTENDED...TUESDAY THROUGH FRIDAY...
THE UPPER LEVEL TROUGH SLOWLY LIFTS NE THROUGH THURSDAY WHILE A
SURFACE HIGH BUILDS OVER THE REGION TUESDAY NIGHT. THE EXTENDED
LOOKS DRY WITH BELOW NORMAL TEMPERATURES.

JEE

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* TSRA 0400Z-0700Z WITH IFR VISIBIILTY IN HEAVY RAIN AND GUSTY
  WINDS AT THE LEADING EDGE.

* MVFR CIGS THROUGHOUT THE NIGHT WITH TEMPORARY IFR LIKELY DURING
  THE TSRA.

* SMALL CHANCE FOR SHRA/TSRA LATE SUNDAY AFTERNOON/EARLY SUNDAY
  EVE.

//DISCUSSION...UPDATED 03Z...

PREV DISCUSSION...UPDATED 00Z...

A SURFACE WARM FRONT IS DRAPED ACROSS NORTHERN IL...PRETTY NEAR THE
CHICAGO AREA TERMINALS. THIS WILL SERVE AS A FOCUS FOR STORMS AS
THE EVENING PROGRESSES...WITH STORMS LIKELY TO EXPAND EASTWARD
THROUGH MID-EVENING AS AN UPPER DISTURBANCE MOVES OVER THE AREA.
IT STILL REMAINS TRICKY TO TIME THE FIRST STORMS...BUT THE
GREATEST COVERAGE LOOKS TO BE THE TIMES WITH PREVAILING TSRA IN
THE TAFS. DUE TO A SUBSTANTIAL AMOUNT OF MOISTURE...HIGH RAINFALL
RATES AND LOW VISIBILITY...POTENTIALLY TO LIFR...IS TEMPORARILY
EXPECTED.

PATCHY MVFR CIGS HAVE BEEN SEEN ALONG AND NORTH OF THE WARM FRONT
AND THAT SHOULD CONTINUE UNTIL THE STORM ARRIVAL TIME. IN THE WAKE
OF THE STORMS...LINGERING MVFR CIGS MAY PERSIST FOR UP TO SEVERAL
HOURS.

WINDS ARE SOUTH-SOUTHWEST AT MUCH OF THE TAF SITES EARLY THIS
EVE AND THAT SHOULD CONTINUE. AS STORMS MOVE OVER...OF COURSE SOME
VARIABILITY CAN BE EXPECTED. A LARGE WELL-DEFINED COMPLEX OF
STORMS IS NOT EXPECTED...WHICH CAN SOMETIMES RESULT IN A SOUTHEAST
WIND AFTERWARD.

THE INITIAL COOL FRONT WILL MOVE THROUGH OVERNIGHT TURNING WINDS
TO THE NORTHWEST. A SECONDARY STRONGER ONE WILL MOVE THROUGH LATE
IN THE DAY SUNDAY. THIS COULD TRIGGER A FEW SHOWERS OR
STORMS...THOUGH THERE IS LIMITED FORCING.

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* HIGH IN TSRA TIMING. HIGH IN AT LEAST TEMPORARY IFR VISIBILITY
  DURING THE TSRA.

* HIGH THAT MVFR CIGS WILL CONTINUE AFTER THE STORMS FOR AT LEAST
  A COUPLE HOURS...WITH POSSIBLE IFR CIGS. LOW IN PRECISE
  DEPARTURE TIME.

* LOW IN ANY SHRA/TSRA SUNDAY AFTERNOON/EARLY SUNDAY EVE.

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...CHANCE OF AFTERNOON TSRA.
TUESDAY...CHANCE OF SHRA.
WEDNESDAY-FRIDAY...VFR LIKELY.

MTF

&&

.MARINE...
423 PM CDT

SOUTHERLY FLOW PERSISTING OVER THE ENTIRE LAKE THIS AFTERNOON AS
HIGH PRESSURE REMAINS SITUATED OVER THE ATLANTIC COAST...AND AS A
TROUGH OF LOW PRESSURE AND ASSOCIATED FRONTAL BOUNDARY ARE JUST
WEST OF THE LAKE. AS THESE SOUTHERLY WINDS BECOME MORE SOUTHWEST
AND THEN EVENTUALLY WEST TONIGHT WITH THE PASSAGE OF THIS
TROUGH...DO EXPECT SPEEDS TO REMAIN IN THE 10 TO 20 KT RANGE.
EXPECTED COMPLEX OF SHOWERS AND THUNDERSTORMS WILL LIKELY PROVIDE
ERRATIC WINDS LATER THIS EVENING AND OVERNIGHT...AS WELL AS THE
POSSIBILITY FOR SLIGHTLY HIGHER SPEEDS. DO EXPECT MORE OF A WEST
NORTHWEST WIND ACROSS THE LAKE ON SUNDAY...AS A SECONDARY
TROUGH/FRONT MOVE SOUTHEAST THROUGH THE GREAT LAKES REGION.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FLASH FLOOD WATCH...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039 UNTIL 1 PM SUNDAY.

IN...FLASH FLOOD WATCH...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 1
     PM SUNDAY.

LM...NONE.
&&

$$

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