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 070009
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
709 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 00Z...

* RAIN REDEVELOPING LATER THIS EVE...POSSIBLY OVERNIGHT. A FEW
  EMBEDDED THUNDERSTORMS.

* SOUTH WINDS ARND 10-14KT STEADILY TURNING WEST/NORTHWEST BY
  EARLY TUE MORNING. WINDS FLIP NORTHEAST AND INCREASE WITH GUSTS
  TO 22KT POSSIBLE TUE MIDDAY.

* MVFR CIGS POSSIBLE BRIEFLY WITH RAIN TONIGHT...THEN MORE LIKELY
  TUE MORNING. POSSIBLE TUE MORNING CIGS COULD DIP TO IFR.

BEACHLER

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

CHANNEL OF VERY WARM/MOIST AIR CONTINUES TO FEED NORTHEAST ACROSS
NORTHEAST IL/NORTHWEST IN. RAIN AND A FEW THUNDERSTORMS CONTINUES
TO DEVELOP THIS EVENING...HOWEVER EXPECT THE COVERAGE OF THUNDER
TO SLOWLY DIMINISH. RAIN MAY INCREASE IS COVERAGE AND INTENSITY
LATER THIS EVENING...HOWEVER SOME GUIDANCE IS INDICATING THAT AS
THE FRONTAL BOUNDARY SLOWLY DROPS SOUTHEAST OVERNIGHT...THIS MAY
DIMINISH AND RESULT IN SPOTTY SHOWERS OVERNIGHT. CLOUDS WILL
REMAIN THICK OVERNIGHT AND BASES MAY FLIRT WITH MVFR CONDS
OVERNIGHT. AS THE BOUNDARY ARRIVES OVERHEAD...MVFR CIGS WILL
SPREAD IN COVERAGE AND COULD PERHAPS DIP TO IFR CONDS ARND
DAYBREAK TUE. WINDS WILL BE SLOWLY TURNING NORTHWEST TO
NORTH...AND GUIDANCE CONTINUES TO INDICATE BY MID-MORNING TUE THAT
WIND SPEEDS WILL INCREASE AND COULD BECOME GUSTY TO 20-25KT.
CLOUDS WILL SLOWLY ERODE TUE AFTN...WITH VFR CONDS RETURNING.

BEACHLER


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

* HIGH CONFIDENCE IN RAIN MOVING OVER ORD/MDW...LOW CONFIDENCE IN
  TIMING AND INTENSITY.

* LOW CONFIDENCE IN COVERAGE/TIMING OF THUNDER...COULD ONLY CLIP
  MDW.

* HIGH CONFIDENCE IN WIND DIR/SPEED...HIGH IN GUSTS DEVELOPING TUE
  MIDDAY.

* MEDIUM CONFIDENCE IN CIGS...HIGH CONFIDENCE IN CIGS DIPPING TO
  MVFR CONDS.

BEACHLER

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

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

THURSDAY THROUGH SUNDAY...PERIODIC CHANCES FOR SHOWERS AND
THUNDERSTORMS.

BEACHLER

&&

.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.

&&

$$

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

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