Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 062224 AAA
AFDLOT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
524 PM CDT MON JUL 6 2015

.MESOSCALE DISCUSSION...
524 PM CDT

CONTINUE TO MONITOR STORM TRENDS LATE THIS MUGGY AFTERNOON...WITH
SCATTERED STORMS POSING AN ISOLATED GUSTY WIND THREAT ALONG AND EAST
OF INTERSTATE 57 THROUGH 7 PM...AND AN ORGANIZED AREA OF STORMS
ALONG INTERSTATE 80 MOVING EAST TO REACH THE WESTERN PORTION OF
LASALLE COUNTY 630-645 PM.

STORMS IN THE SOUTHEAST FORECAST AREA HAVE SHOWN ISOLATED STRONG
DOWNDRAFT SIGNATURES ON RADAR. FOR THE MOST PART...THESE HAVE BEEN
SHORT-LIVED. SUCH A STORM DEVELOPED NEAR THE WFO HERE AROUND 3 PM
PRODUCING A 48 MPH GUST. THE COMBINATION OF LOW-LEVEL CAPE AND
ASSOCIATED DCAPE ALONG WITH RAINFALL LOADING WILL CONTINUE THIS AN
ISOLATED THREAT. WILL LIKELY KEEP HANDLING WITH SPECIAL WEATHER
STATEMENTS.

FURTHER WEST...A MORE ORGANIZED CLUSTER OF STORMS IS RIDING EAST AT
PRESENT NEAR I-80 SOUTHEAST OF THE QUAD CITIES. THESE HAVE HAD A
HISTORY OF SEVERE WEATHER AND RADAR CONTINUES TO SHOW
ORGANIZATION...WITH A SLIGHT WARM AIR ADVECTION-LIKE WING DEVELOPING
INTO SOUTHWEST LEE COUNTY. THERE COULD ALSO BE A SUBTLE SHORT WAVE
MAY BE HELPING DRIVE THIS TOO PER WATER VAPOR. AS THIS PASSED
NEAR/OVER THE DVN VAD PROFILER IT APPEARED A 35 KT WNW REAR-INFLOW
JET WAS TRYING TO ESTABLISH ITSELF AOB 850MB. THE AIR MASS AHEAD AND
TO THE SOUTH OF THESE STORMS IS STRONGLY UNSTABLE WITH CLEARING
ALLOWING FOR WARMING AND DEW POINTS IN THE MID 70S AIDING IN MLCAPE
VALUES AS HIGH AT 3000 J/KG. WHILE DEEP LAYER SHEAR IS WEAK TO
MARGINAL...THE AFOREMENTIONED TRENDS AND 20-25 KT OF 0-3KM SHEAR
ORIENTED DUE EAST INDICATE SOME SUSTAINABILITY AND POCKETS OF
SURGING WINDS ARE LIKELY WITH THESE STORMS THE NEXT COUPLE HOURS OR
SO. THESE MAY WANT TO TREND A LITTLE SOUTH OF EAST IN THAT TIME.
ALSO OF CONCERN IS VERY HEAVY RAINFALL AS PWATS REACH 98TH
PERCENTILE OR HIGHER WITH TWO INCH VALUES.

FURTHER NORTH ACROSS NORTHEAST IA INTO WI...NUMEROUS SHOWERS ARE
SEEN WITH THE COLD FRONT. SOME OF THIS ACTIVITY MAY WANT TO UPTICK
INTO THE EARLY EVENING...ALTHOUGH A LARGE AMOUNT OF MOISTURE
TRANSPORT TO TAP INSTABILITY FOR STORMS MAY BE ROBBED BY ONGOING
ACTIVITY IN WESTERN IL THROUGH KS.

MTF

&&

.SHORT TERM...
252 PM CDT

THROUGH TONIGHT...

A LINE OF SHOWERS IS MOVING THROUGH NORTHEAST IL WITH ADDITIONAL
SHOWERS AND STORMS OVER SOUTHERN AND EASTERN IOWA.  THE LINE OF
SHOWERS WITH A FEW EMBEDDED THUNDERSTORMS WILL CONTINUE EAST AND MAY
WEAKEN FURTHER AS THE OUTFLOW BOUNDARY HAS STARTED TO SEPARATE
ITSELF FROM THE LINE OF SHOWERS.  HEAVY RAIN...A FEW GUSTS OF
WIND...AND A FEW FUNNEL CLOUDS HAVE BEEN REPORTED WITH THIS LINE OF
SHOWERS. THE FUNNEL CLOUDS ARE FORMING AS BOUNDARIES INTERSECT...BUT
THE FUNNELS ARE NOT LOCATED UNDER ANY UPDRAFTS SO TORNADOES ARE NOT
EXPECTED.

TEMPERATURES ARE FALLING INTO THE 70S BEHIND THE LINE OF SHOWERS AND
WITH THE THICK CLOUD COVER...RECOVERY IS VERY SLOW AT BEST.
THEREFORE LOCATIONS OVER NORTHWEST IL ACTUALLY SAW THEIR HIGH TEMPS
EARLY THIS MORNING AS THEY WILL STAY IN THE 70S. HAVE FALLING TEMPS
ALSO ACROSS NW INDIANA AS THE STORMS ROLL THROUGH...BUT IF THE LINE
FALLS APART...TEMPS WILL LIKELY STAY IN THE LOW TO MID 80S.

THE COLD FRONT STRETCHES ACROSS NORTHWEST WI THROUGH SOUTHERN MN AND
NW IA AND IS PROGGED TO SWING THROUGH NORTHERN IL AND NW INDIANA
OVERNIGHT.  ANOTHER ROUND OF SHOWERS ARE EXPECTED AHEAD OF THE COLD
FRONT...BUT NOT EXPECTING MUCH IF ANY SEVERE WEATHER.  THE LATEST
RAP ANALYSIS SHOWS 500-2000 J/KG OF CAPE BEHIND THE LINE OF STORMS
OVER NORTH CENTRAL IL...WITH THE VALUES DECREASING AS YOU GET CLOSER
TO THE MISSISSIPPI RIVER.  SHEAR VALUES ARE ALSO AROUND ZERO...SO
ORGANIZED STORMS ARE NOT EXPECTED.  EXPECTING THE NEXT ROUND OF
SHOWERS AND STORMS TO MOVE INTO NW ILLINOIS AFTER 5PM CDT AND
CONTINUE ACROSS NORTHERN IL AND NW INDIANA THROUGH THE NIGHT. THIS
ROUND WILL ALSO HAVE LIGHTNING...HEAVY RAIN...AND PROBABLY SOME
GUSTY WINDS...BUT WIDESPREAD SEVERE WEATHER IS NOT EXPECTED.

GIVEN THE LOWER THAN EXPECTED HIGH TEMPS TODAY...LOWERED LOW TEMPS
TONIGHT AS WELL. DEW POINTS WILL REMAIN IN THE MID 60S TO AROUND 70
SO LOW TEMPS SHOULD STICK PRETTY CLOSE TO THE DEW POINTS. EXPECTING
LOWS TO VARY FROM THE MID 60S AROUND RFD TO AROUND 70 IN NW INDIANA.

JEE

&&

.LONG TERM...
325 PM CDT

TUESDAY THROUGH MONDAY...

THE FRONT WILL CONTINUE SHIFTING SOUTH THROUGH TUESDAY MORNING
WITH NORTHERLY WINDS AND COLD ADVECTION ENVELOPING THE AREA. SUCH
AS HAS BEEN THE TREND WITH THE SYSTEM...DID ALSO SPEED UP THE END
OF RAIN CHANCES ON TUESDAY. THINK SHOWER COVERAGE IN THE MORNING
WILL BE SCATTERED WITHIN POST FRONTAL FORCING...AND ANY THUNDER
LIKELY EVEN MORE ISOLATED. STRATUS IS LIKELY TO LINGER LONGER THAN
THE RAIN CHANCES AS THE COOL AIR COLLIDES WITH THE MOIST BOUNDARY
LAYER. IT IS CERTAINLY POSSIBLE CLOUDS STICK AROUND FOR SOUTHERN
AREAS AS WELL AS LOCATIONS NEAR THE LAKE THROUGH THE AFTERNOON.
HIGH PRESSURE SHOULD KEEP THE AREA MAINLY DRY INTO WEDNESDAY
MORNING.

TEMPERATURES BOTH TUESDAY AND WEDNESDAY LOOK TO BE WELL BELOW
NORMAL WITH HIGHS PRIMARILY IN THE LOWER 70S...WITH MID-UPPER 60S
NEAR THE LAKE SHORE. THESE READINGS ACROSS THE FORECAST AREA ARE
10 TO 15 DEGREES BELOW NORMAL FOR EARLY JULY. IN-BETWEEN ON
TUESDAY NIGHT...ANY CLOUDS SHOULD BE CONFINED TO THE SOUTHERN CWA
WHICH WILL ALLOW NORTHERN COMMUNICATIONS TO DIP INTO THE
50S...EVEN LOWER 50S FOR OUTLYING LOCATIONS.

BEYOND...SHORT WAVE IMPULSES LOOK TO BE KEY TO RAIN CHANCES WITH
ONE BECOMING MORE CONSISTENTLY TARGETED ON GUIDANCE WEDNESDAY
NIGHT. THE WINDOW OF INSTABILITY RETURN LOOKS LIMITED...SO THIS
COULD BE MAINLY JUST SHOWERS ESPECIALLY NORTH OF I-80. EACH
SUCCESSIVE IMPULSE APPEARS TO BRING THE THETA-E GRADIENT ALOFT
MORE SO OVER THE AREA WHICH WARRANTS STORM CHANCES ALMOST DAILY
LATE IN THE WEEK INTO THE WEEKEND. TEMPERATURES ALSO LOOK TO
REBOUND BACK TO NORMAL BY THE WEEKEND.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* THUNDERSTORMS POSSIBLE AFT 02Z AND CONTINUE THRU 4Z...THEN RAIN
  SHOWERS LINGER AFTER THUNDER ENDS.

* MVFR OR POSSIBLE IFR TUESDAY MORNING.

* NORTH-NORTHEAST WINDS OVER 10KT TUESDAY.

MM/BEACHLER

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

LINE OF SHOWERS AND THUNDERSTORMS DEVELOPED EARLY THIS AFTERNOON
AND PUSHED EAST OF MDW AND HAVE SINCE DISSIPATED. ADDITIONAL
THUNDERSTORMS WILL TRY TO DEVELOP AND MAY IMPACT ORD/MDW AS WELL
AS OTHER NORTHERN IL/NORTHWEST IN AIRFIELDS THIS EVE. SOME
THUNDERSTORMS MAY BECOME STRONG AND CREATE BRIEF GUSTS IN EXCESS
OF 35KT AND LOCALLY HEAVY DOWNPOURS WHICH COULD DECREASE
VISIBILITIES BRIEFLY.

PREVIOUS DISCUSSION UPDATED 18Z...

PRE-FRONTAL THUNDERSTORMS ARE FIRING ACROSS NORTHERN ILLINOIS
THIS AFTERNOON WITH CONDITIONS FAVORABLE FOR CONTINUED EASTWARD
EXPANSION. TIME OF ARRIVAL TOOL PUTS FIRST ROUND OF THUNDER TO
ORD/MDW CLOSE TO 20Z. AS THESE STORMS LOOK TO BE OUTRUNNING THE
MAIN STORM COMPLEX...THEY ARE LOSING THEIR INTENSITY. FOLLOWING
THE BRIEF FIRST ROUND OF THUNDER...EXPECT VCSH ON AND OFF UNTIL
THE NEXT ROUND OF TSRA APPROACHES. MODEL CONSENSUS STARTS THUNDER
AT ORD/MDW AGAIN NEAR 02-03Z...LASTING FOR ABOUT 3 HOURS.

LOOK FOR A WIND SHIFT TO THE NORTH BEHIND THE COLD FRONT ALONG
WITH LOW CLOUDS...BR...AND OCCL SHOWERS. LOW-BASED INVERSION
EARLY TUESDAY WILL KEEP MVFR LIKELY WITH A CHANCE FOR CEILINGS
DROPPING UNDER 1KFT. THE INVERSION SHOULD MIX OUT JUST AFTER 12Z
BUT MVFR CONDITIONS WILL REMAIN THROUGH MOST OF THE MORNING.

MM

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* HIGH THAT THUNDERSTORMS WILL OCCUR...MEDIUM ON TIMING.

* HIGH ON MVFR TUESDAY...MEDIUM LOW ON IFR OCCURRING.

* HIGH ON NORTH WINDS OVER 10KT.

MM/BEACHLER

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

TUESDAY NIGHT...VFR.

WEDNESDAY...CHANCE OF SHRA...SLIGHT CHANCE OF TSRA.

THURSDAY...CHANCE OF TSRA.

FRIDAY...CHANCE OF TSRA.

SATURDAY...CHANCE OF TSRA.

SUNDAY...CHANCE OF TSRA.

RODRIGUEZ

&&

.MARINE...
252 PM CDT

WIND GUSTS WERE NOT AS STRONG AS EXPECTED ACROSS THE NEARSHORE
WATERS TODAY AS THICK CLOUD COVER LIMITED MIXING. A LINE OF SHOWERS
THAT HAS A HISTORY OF PRODUCING GUSTS UP TO 30 KT IS MOVING ACROSS
THE NEARSHORE WATERS SO WILL KEEP THE SMALL CRAFT GOING THROUGH
00Z/7PM CDT TO ACCOUNT FOR SHOWER RELATED GUSTS. WINDS WILL PICK
BACK UP TOMORROW AND A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR
POINTS SOUTH OF CHICAGO FROM 9AM CDT TUESDAY THROUGH 4AM CDT
WEDNESDAY.  FLOW WILL BE ON SHORE SO WAVE HEIGHTS ALONG THE INDIANA
SHORE WILL GROW TO 4-7 FT AND THEN COME DOWN TUESDAY EVENING AND
NIGHT.  WINDS DIMINISH AS HIGH PRESSURE SPREADS OVER THE LAKE
WEDNESDAY MORNING. WINDS WILL BE LIGHT AND VARIABLE OVER THE NORTH
HALF OF THE LAKE INTO WEDNESDAY EVENING WHILE A WEAK LOW PASSES JUST
SOUTH OF THE LAKE WEDNESDAY NIGHT. WINDS WILL BE NORTHEAST THEN
NORTH THURSDAY AFTERNOON.  WINDS REMAIN LESS THAN 10 KT AS THE HIGH
SLOWLY SHIFTS EAST THROUGH THE END OF THE WEEK WITH THE NEXT LOW
IMPACTING THE LAKE EARLY NEXT WEEK. THERE WILL BE ADDITIONAL
PERIODIC CHANCES OF THUNDERSTORMS WEDNESDAY NIGHT AND THEN FROM
EARLY FRIDAY MORNING THROUGH EARLY NEXT WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...BEACH HAZARDS STATEMENT...ILZ014...9 AM TUESDAY TO 4 AM
     WEDNESDAY.

IN...BEACH HAZARDS STATEMENT...INZ001-INZ002...9 AM TUESDAY TO 4 AM
     WEDNESDAY.

LM...SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 7 PM MONDAY.

     SMALL CRAFT ADVISORY...LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...9 AM
     TUESDAY TO 4 AM WEDNESDAY.

&&

$$

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