Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 120613
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
113 AM CDT SAT JUL 12 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 06Z...

* MVFR AND POSSIBLE IFR CIGS DEVELOPING LATE TONIGHT AND
  PERSISTING INTO/THROUGH SATURDAY MORNING.

* CHANCE FOR TSRA LATE TONIGHT THROUGH MID AFTERNOON
  SATURDAY...WITH GREATER CHANCES LATE SATURDAY AFTERNOON INTO
  NIGHT. SOME STORMS COULD BE STRONG WITH GUSTY WINDS.

KMD

//DISCUSSION...UPDATED 06Z...

AFTER A SLOW PROGRESSION...CEILINGS ARE BEGINNING TO LOWER EAST OF
THE MISSISSIPPI RIVER EARLY THIS MORNING...THOUGH STILL PRIMARILY
SEEING THE MVFR CEILINGS ISOLATED AT THIS POINT. HAVE BACKED OFF
ON THE MVFR ARRIVAL BUT STILL FEEL THAT IN THE ISENTROPIC LIFT REGIME
AHEAD OF THE WARM FRONT IN NORTHERN AND EASTERN MISSOURI THAT THERE
WILL STILL BE SOME LOWER CEILINGS THIS MORNING. FORECAST
CONFIDENCE IS HIGH ENOUGH FOR 1000-2000 FOOT CEILINGS. SHOWER
ACTIVITY IS AT A MINIMUM WITH NO OBVIOUS UPPER LEVEL FORCING AT
THIS TIME...BUT STILL EXPECT AT LEAST SOME SHOWER ACTIVITY LATER
THIS MORNING.

INSTABILITY WILL BE ON THE INCREASE THROUGH THE DAY TODAY. STILL
HAVE SOME QUESTIONS ABOUT CONVECTIVE ACTIVITY DURING THE
AFTERNOON...BUT THE MOST ORGANIZED COUPLED FORCING FROM UPPER
LEVELS AND MOISTURE CONVERGENCE AHEAD OF THE APPROACHING COLD
FRONT. HEAVY RAIN AND GUSTY WINDS REMAIN THE BIGGEST
CONCERNS...AND IT COULD BE A LONGER PERIOD THUNDERSTORM ACTIVITY
AS THE FRONT IS NOT MOVING ALL THAT QUICKLY.

KMD


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN AT LEAST CIGS DOWN TO 2000 FT DEVELOPING LATE TONIGHT.
  LOW IN TIMING OF SCATTERING ON SATURDAY.
* MEDIUM IN NO TSRA THROUGH EARLY SATURDAY AFTERNOON. LOW IN
  WHETHER TSRA WILL HOLD OFF THE REMAINDER OF THE AFTERNOON.
* MEDIUM IN TSRA OCCURRING SATURDAY EVE.

KMD

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

SUNDAY-MONDAY...LOW CHANCES OF TSRA.
TUESDAY...SLIGHT CHANCE OF SHRA.
WEDNESDAY-THURSDAY...VFR LIKELY.

MTF

&&

.MARINE...
350 PM CDT

WITH HIGH PRESSURE OVER THE EASTERN GREAT LAKES AND A TROUGH OF
LOW PRESSURE AND FRONTAL BOUNDARY APPROACHING FROM THE WEST...A
TIGHTER PRESSURE GRADIENT OVER THE NORTHERN HALF OF THE LAKE IS
PROVIDING SOME HIGHER SOUTHERLY WINDS IN THE 15 TO 25 KT RANGE
THIS AFTERNOON WHILE SPEEDS REMAIN IN THE 10 TO 20 KT RANGE OVER
THE SOUTHERN HALF. DO EXPECT THE PRESSURE GRADIENT TO RELAX
TONIGHT INTO SATURDAY WITH SPEEDS DIMINISHING. CONFIDENCE IS LOWER
WITH REGARDS TO OVERALL WIND DIRECTION AND SPEEDS SATURDAY INTO
SATURDAY NIGHT AS PERIODS OF SHOWERS AND THUNDERSTORMS ARE
EXPECTED. THIS COULD PROVIDE SOME PERIODS OF ERRATIC WINDS...WITH
EVEN THE POTENTIAL FOR AN ONSHORE WIND COMPONENT TO DEVELOP IN THE
NEARSHORE SATURDAY AFTERNOON INSTEAD OF THE CURRENT FORECAST
OFFSHORE WINDS.

RODRIGUEZ

&&

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

$$

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