Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KLOT 112000
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
300 PM CDT FRI JUL 11 2014

.DISCUSSION...
259 PM CDT

SYNOPSIS...TONIGHT THROUGH SATURDAY NIGHT LOOK TO BE THE BUSIEST
WITH MULTIPLE CHANCES OF RAIN AND STORMS. THE BEST CHANCE FOR SEVERE
WEATHER WILL BE ALONG THE COLD FRONT TOMORROW EVENING...BUT COULD
SEE A FEW ISOLATED SEVERE STORMS TOMORROW AFTERNOON.  HEAVY RAIN IS
ALSO VERY LIKELY TONIGHT THROUGH SATURDAY NIGHT WITH A GOOD CHANCE
OF FLASH FLOODING.  TEMPERATURES TUMBLE AS COOLER AIR MOVES IN
MONDAY AND WE ARE LOOKING AT DRY AND COOLER THAN NORMAL CONDITIONS
FOR THE LATTER HALF OF NEXT WEEK.

REST OF TODAY AND TONIGHT...
AN UPPER LEVEL RIDGE STRETCHES FROM JAMES BAY THROUGH THE OHIO RIVER
VALLEY WITH A LARGE UPPER LEVEL HIGH PRESSURE SYSTEM ACROSS THE
SOUTHERN U.S.  A LOW IS OVER CENTRAL CANADA AND THIS PATTERN WILL
LEAVE US IN ZONAL FLOW ALOFT THROUGH TUESDAY.  AT THE SURFACE...HIGH
PRESSURE IS CENTERED OVER THE EASTERN GREAT LAKES WITH A LOW OVER
NORTHERN MANITOBA.  A TROUGH OF LOW PRESSURE EXTENDS SOUTH FROM THE
LOW THROUGH NW MINNESOTA AND THE CENTRAL PLAINS.

CONVECTIVE ACTIVITY IS EXPECTED TO FIRE OVER NORTHERN NEBRASKA TODAY
AND THAT COMPLEX WILL MOVE EAST.  EXPECTING THE STORM COMPLEX TO
TRAVEL ALONG THE INSTABILITY GRADIENT WHICH WOULD BRING THE SYSTEM
INTO IOWA AND THEN SINK SE THROUGH NORTHERN IL. GIVEN THE TIME OF
DAY AND LACK OF INSTABILITY OVER THE CWA...THINKING WE WILL FIRST
SEE RAIN SHOWERS MOVE INTO THE FAR WESTERN CWA LATE THIS EVENING.
MAY SEE SOME THUNDER AFTER MIDNIGHT...BUT CAPPED THE THUNDER
POTENTIAL IN THE CHANCE RANGE.

NOT EXPECTING ANY SEVERE WEATHER WITH THIS COMPLEX GIVEN MINIMAL
INSTABILITY AND WEAK SHEAR.  PWAT VALUES WILL INCREASE TO 2-2.3
INCHES BY SATURDAY MORNING SO HEAVY RAIN WILL BE THE GREATEST
THREAT.  STEERING FLOW WOULD SUGGEST THE STORM WOULD BE MOVING
SOUTHEAST AT 20-25 KT. AREAS SOUTH OF A FORRESTON TO KANKAKEE LINE
WILL SEE THE MOST RAIN WITH TOTALS OF 0.5-1.00 INCHES OR MORE
POSSIBLE.

WE WILL BE UNDER WAA TONIGHT AND TEMPS SHOULD REMAIN RATHER STEADY
WITH LOWS ONLY IN THE UPPER 60S.

SATURDAY AND SATURDAY NIGHT...
THE UPPER LEVEL LOW BEGINS TO SINK SOUTH WHILE THE SURFACE LOW ALSO
SINKS SOUTH INTO ONTARIO BY SUNDAY MORNING.  THE LOW/S SURFACE
TROUGH MOVES OVER THE REGION TOMORROW AFTERNOON.  THE STORM COMPLEX
FROM TONIGHT WILL BE EXITING THE REGION EARLY SATURDAY MORNING...AND
MOST AREAS SHOULD SEE A FEW DRY HOURS IN THE LATE MORNING. THE
WILDCARD WILL BE CLOUD COVER AND HOW LONG IT TAKES THE ATMOSPHERE TO
RECOVER FROM THE COMPLEX.  GUIDANCE CONTINUES TO INDICATE A QUICK
RECOVERY WITH CAPE VALUES PUSHING 2000 J/KG WEST OF A DIXON TO
WATSEKA LINE BY MID DAY TOMORROW.  AS SUCH HAVE CHANCES OF THUNDER
INCREASING THROUGH THE LATE MORNING AND EARLY AFTERNOON HOURS. THE
FIRST ROUND OF STORMS SHOULD BE SCATTERED WARM SECTOR STORMS THAT
INCREASE IN COVERAGE THROUGH THE AFTERNOON. A FEW MAY PULSE UP TO
SEVERE WITH HAIL AND WIND BEING THE MAIN SEVERE THREATS. PWAT VALUES
WILL REMAIN HIGH AT 2-2.3 INCHES SO HEAVY RAIN IS ONCE AGAIN THE
MAIN CONCERN. AREAS THAT RECEIVE HEAVY RAIN TONIGHT WILL BE PRIMED
FOR FLOODING AND FLASH FLOODING SATURDAY.

THE MAIN SEVERE WEATHER THREAT ROLLS THROUGH SATURDAY EVENING WITH
THE COLD FRONT. SIDED WITH THE SLIGHTLY FASTER NAM AND LOCAL ARW FOR
TIMING...BUT TIMING IS A BIG CONCERN WITH THIS SYSTEM AND CONFIDENCE
IS MEDIUM WITH TIMING.  WINDS IN EXCESS OF 60 MPH WILL BE THE MAIN
SEVERE THREAT WITH THE LINE OF STORMS. HOWEVER...CAPE VALUES WILL BE
UPWARDS OF 2500-3000 J/KG SO MAY SEE SOME HAIL. UPPER LEVEL LAPSE
RATES ARE NOT OVERLY IMPRESSIVE AND FORECAST SOUNDINGS SHOW LONG
SKINNY CAPE THAT WOULD NOT SUPPORT LARGE HAIL. PWATS OF 2+ INCHES
ARE STILL IN PLACE SO HEAVY RAIN IS ALSO EXPECTED.  WE COULD EASILY
SEE 1.5-2 INCHES OF RAIN WEST OF A ROCKFORD TO KANKAKEE LINE WITH
LOCALLY HIGHER AMOUNTS POSSIBLE FROM THE AFTERNOON THUNDERSTORMS.
FLASH FLOODING WILL BE VERY POSSIBLE.

TEMPS WILL COOL OFF QUICKLY BEHIND THE LINE OF STORMS AND LOWS WILL
BE IN THE UPPER 60S TO LOWER 70S.

SUNDAY AND MONDAY...
THE UPPER LEVEL LOW CONTINUES TO SHIFT SOUTH AND WE WILL BE IN ITS
TROUGH SUNDAY NIGHT THROUGH WEDNESDAY.  THE TROUGH AXIS MOVES
THROUGH TUESDAY.  AT THE SURFACE THE LOW PRESSURE TROUGH ASSOCIATED
WITH THE SURFACE LOW SHIFTS EAST OF THE REGION MONDAY NIGHT.

THE LINE OF SHOWERS AND STORMS WILL CONTINUE TO SHIFT SE OUT OF THE
CWA SUNDAY MORNING WITH WINDS BECOMING NORTH AND THEN NORTHWEST
BEHIND THE COLD FRONT.  A FEW WEAK SHORTWAVES/VORTICITY STREAMERS
WILL PASS OVER THE REGION SO HAVE A SLIGHT CHANCE OF SHOWERS AND
STORMS SUNDAY. NOT EXPECTING MUCH ACTIVITY OUTSIDE OF THE DEPARTING
LINE OF STORMS.  A STRONGER SHORTWAVE MOVES JUST SOUTH OF THE IL/WI
STATE LINE SO HAVE A CHANCE OF SHOWERS AND STORMS FOR THE NORTHERN
CWA SUNDAY NIGHT.

CHANCES OF THUNDER INCREASE MONDAY AS THE TROUGH AXIS APPROACHES THE
REGION. EXPECTING THE THUNDER TO BE VERY DIURNAL WITH JUST A CHANCE
OF SHOWERS OVERNIGHT.

FOR TEMPERATURES...SUNDAY WILL BE THE LAST DAY OF SUMMER WARMTH FOR
AWHILE WITH HIGHS IN THE LOW TO MID 80S.  COLD AIR FUNNELS IN MONDAY
WITH HIGHS IN THE MID TO UPPER 70S.

EXTENDED...TUESDAY THROUGH THURSDAY...
HIGH PRESSURE SPREADS OVER THE PLAINS EARLY NEXT WEEK AND MOVES OVER
THE CWA WEDNESDAY AFTERNOON/EVENING. THE HIGH REMAINS OVER THE
REGION THROUGH LATE NEXT WEEK. AS SUCH HAVE A DRY FORECAST FOR
TUESDAY NIGHT THROUGH THURSDAY.  TEMPERATURES WILL BE BELOW NORMAL
BUT HAVE A SLOW WARMING TREND GOING INTO LATE NEXT WEEK.

JEE

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* VARIABLE SSW-S WINDS THIS AFTERNOON 6-10 KT.

* TSRA CHANCES INCREASE OVERNIGHT...WITH LINGERING CHANCES
  SATURDAY...AND BETTER ORGANIZED POTENTIAL BY SATURDAY EVENING.

* MVFR CIG POTENTIAL SATURDAY MORNING.

MDB

//DISCUSSION...UPDATED 20Z...

WINDS HAVE BECOME A BIT STEADIER FROM THE SOUTH TO SOUTH-SOUTHWEST
FOR THE MOST PART BUT SOME VARIABILITY DOES CONTINUE ACROSS NE IL
AND NW IN...ESPECIALLY WITH SPEEDS WHICH HAVE RANGED FROM 3 TO 11
OR 12 KT AT TIMES. LAKE BREEZE BOUNDARY CONTINUES TO MOVE LITTLE
AND IS EXPECTED TO REMAIN EAST OF ORD/MDW. SOME LIGHT SHOWER
ACTIVITY HAS EXPANDED SOUTHWARD INTO FAR NORTHERN IL. LIGHT
SHOWERS CONTINUED TO MOVE EASTWARD TOWARDS THE MISSISSIPPI RIVER
AS WELL. THE ATMOSPHERE IS STILL FAIRLY DRY SO MUCH OF THE INITIAL
PRECIP WILL LIKELY HAVE A HARD TIME REACHING THE GROUND SO WILL
LEAVE THE TAFS DRY FOR NOW...BUT SOME LIGHT RAIN/SHOWERS ARE
POSSIBLE THIS EVENING AND MAY NEED TO BE ADDED TO THE TAF.

FROM 18Z...

HIGH PRESSURE CONTINUES TO MOVE OFF TO THE EAST RESULTING IN QUITE
A VARIABILITY IN WIND SPEED AND DIRECTION ACROSS CHICAGOLAND AND NW
INDIANA...WITH STEADIER SOUTH WINDS TO THE WEST TOWARD RFD. LAKE
BREEZE HAS DEVELOPED WITH RADAR SHOWING THE BOUNDARY A FEW MILES
INLAND FROM SHORE AND ORIENTED FROM NW TO SE. THERE HAS BEEN
LITTLE MOVEMENT IN THE LAST HOUR AND THIS MAY BE A RESULT OF THE
INTERMITTENTLY STRONGER SOUTH WINDS WHICH SHOULD BECOME STEADIER
THROUGH THE AFTERNOON. WILL KEEP THE LAKE BREEZE EAST OF ORD/MDW
AND CONTINUE WITH A SOUTHEAST DIRECTION AT GYY. SPEEDS HAVE RANGED
FROM CALM TO 15 KT BUT FEEL THAT THINGS WILL HONE IN ON THE 8-11
KT RANGE...THOUGH INFREQUENT GUSTS TOWARDS 15 KT ARE POSSIBLE. MID
AND HIGH CLOUD COVER WILL INCREASE THROUGH THE AFTERNOON WITH A
FEW SPRINKLES POSSIBLE TOWARD RFD BUT THE MAJORITY OF RADAR
RETURNS MOVING TOWARD THE AREA ARE FADING AND/OR NOT PRODUCING
PRECIP AT THE GROUND.

THUNDERSTORM CHANCES WILL INCREASE TONIGHT...WITH SOME CHANCE FOR
SHOWERS THROUGH THE EVENING...AS MOISTURE INCREASES AND A SERIES
OF UPPER DISTURBANCES APPROACH. BEST CHANCE STILL LOOKS TO BE LATE
TONIGHT OR EARLY SATURDAY MORNING AS A MORE FOCUSED UPPER TROUGH
PASSES. THERE THEN APPEARS TO BE A LULL IN BETTER ORGANIZED
ACTIVITY MID SATURDAY MORNING THROUGH THE AFTERNOON DEPENDING ON
HOW FAR NORTH A WARM FRONTAL BOUNDARY MOVES. CHANCES ARE TOO LOW
AND TOO UNCERTAIN TO INCLUDE IN THE TAF BEYOND 12Z THROUGH THE
AFTERNOON BUT TSRA CHANCES WILL BE THERE AND ADJUSTMENTS WILL
LIKELY BE NEEDED TO DETAILS. A COLD FRONT WILL CROSS THE AREA
SATURDAY EVENING/NIGHT BRINGING INCREASED CHANCES FOR STORMS AT
THAT TIME. WINDS WILL BE TRICKY SATURDAY BUT AT THIS POINT THE
MOST LIKELY DIRECTION IS SOUTHERLY AND THERE MAY BE GUSTS IN THE
15 TO 20 KT RANGE. SHOULD A BETTER ORGANIZED COMPLEX OF STORMS PASS
LATE TONIGHT THEN A SOUTHEAST DIRECTION MAY PREVAIL DURING THE
MORNING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WINDS THROUGH THE EVENING.

* MEDIUM CONFIDENCE IN TSRA OCCURRENCE TONIGHT OR EARLY SATURDAY
  MORNING. LOW CONFIDENCE IN TIMING. LOW CONFIDENCE IN EXTENT OF
  TSRA MID SATURDAY MORNING THROUGH MID AFTERNOON. MEDIUM
  CONFIDENCE IN OCCURRENCE LATER SATURDAY AFTERNOON/EVENING.

* MEDIUM CONFIDENCE IN MVFR CIGS SATURDAY MORNING...LOW CONFIDENCE
  IN DURATION.

MDB

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

SATURDAY NIGHT...TSRA WITH MVFR/IFR POSSIBLE.

SUNDAY THROUGH TUESDAY...PERIODIC CHANCES FOR TSRA/SHRA. PRIMARILY VFR.

WEDNESDAY THROUGH THURSDAY...SMALL CHANCES FOR SHRA. PRIMARILY VFR.

KMD

&&

.MARINE...
332 AM CDT

HIGH PRESSURE HAS SHIFTED TO THE EASTERN GREAT LAKES EARLY THIS
MORNING...AND WINDS HAVE TURNED MORE SOUTHERLY ACROSS THE LAKE.
EXPECT SPEEDS TO INCREASE TODAY IN RESPONSE TO A STRONGER GRADIENT
CREATED BY LOW PRESSURE CENTERED IN NORTHERN MANITOBA AND INTO THE
NORTHERN PLAINS. THE STRONGER GRADIENT WILL BE OVER THE NORTHERN
HALF OF THE LAKE...WHERE SOUTH WINDS INCREASE TO 15 TO 25 KT...WHILE
THE SOUTH HALF WILL SEE S TO SE WINDS AT 10-20 KT. WINDS DIMINISH
SATURDAY AS A TROUGH OF LOW PRESSURE MOVES OVERHEAD AND BECOME
SOUTHWEST SATURDAY NIGHT.

A LOW PASSES WELL NORTH OF THE LAKE SATURDAY NIGHT AND SUNDAY AND
ITS COLD FRONT SWINGS OVER THE LAKE SUNDAY MORNING. WINDS BECOME
WEST BEHIND THE FRONT MAINLY FOR THE NORTHERN HALF...AND THEN A
SECOND FRONT PUSHES DOWN THE LAKE SUNDAY NIGHT INTO MONDAY BEFORE
FINALLY CLEARING THE LAKE MONDAY EVENING.  WINDS WILL BECOME NORTH
TO NORTHWEST 10-20 KT BEHIND THE FRONT.  WINDS DIMINISH LATE TUESDAY
NIGHT AND THEN HIGH PRESSURE MOVES OVER THE LAKE WEDNESDAY NIGHT.

KMD

&&

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

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.