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 131925
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
225 PM CDT SUN APR 13 2014

.DISCUSSION...
225 PM CDT

MAIN FORECAST CONCERNS ARE IN THE SHORT TERM...WITH RAIN/THUNDER
TRENDS AND PRECIP AMOUNTS THROUGH TONIGHT AND THEN THE POTENTIAL FOR
A RAIN/SNOW MIX TOMORROW AS PRECIPITATION WINDS DOWN AND SYSTEM
PULLS AWAY. TEMP TRENDS ALSO RECEIVING ATTENTION...WITH NORTHEAST
WINDS OFF LAKE PRODUCING FOG/COOL TEMPS NEAR THE LAKE.

WEAK AREA OF LOW PRESSURE WHICH ACCOMPANIED OUR EARLY MORNING
CONVECTION HAD LIFTED OFF TO THE EAST DURING THE MORNING...WITH ITS
TRAILING COLD FRONT SAGGING ACROSS PARTS OF FAR NORTHERN ILLINOIS
AND BACK-DOORING DOWN THE ILLINOIS LAKE MICHIGAN SHORE INTO THIS
AFTERNOON. WITH WINDS SHIFTING TO THE NORTHEAST OFF THE LAKE...TEMPS
HAVE FALLEN INTO THE LOW-MID 40S ALONG THE LAKE WITH AREAS OF FAIRLY
DENSE FOG PUSHING A FEW BLOCKS INLAND AS WELL. FORECAST OF THESE
MESO/MICRO SCALE DETAILS WILL BE FRAUGHT WITH DANGER THROUGH THIS
EVENING...AS NEXT AREA OF LOW PRESSURE LIFTS NORTHEAST ACROSS THE
AREA OVERNIGHT AND BRINGS WINDS BACK TO THE SOUTH ACROSS PARTS OF
THE CENTRAL CHICAGO METRO AREA POTENTIALLY BRINGING TEMPS BACK UP
WELL INTO THE 50S/NEAR 60 LATER THIS EVENING. BEYOND THESE EFFECTS
WILL ALSO BE THE EXPECTATION OF SEVERAL ROUNDS OF RAIN/SHRA/THUNDER
THROUGH THE OVERNIGHT HOURS...AS SHORT WAVE TROUGH EJECTING FROM THE
SOUTHERN PLAINS PROPAGATES INTO THE REGION OVERNIGHT. SOME THREAT
EXISTS FOR LOCALLY HEAVY RAINFALL WITH ADDITIONAL PRECIP TONIGHT...
WITH PRECIPITABLE WATER VALUES JUST ABOVE 1 INCH PER 12Z RAOBS AND
NEARLY 200 PERCENT OF NORMAL FOR THIS TIME OF YEAR. SO FAR...AREAS
ALONG THE WISCONSIN/ILLINOIS HAVE BORDER RECEIVED THE GREATEST
RAINFALL SINCE SATURDAY MORNING WITH A COUPLE OF ROUNDS OF
THUNDERSTORMS PRODUCING 3/4 TO 1 1/2 INCHES ESPECIALLY OVER
WINNEBAGO...BOONE AND MCHENRY COUNTIES. ANOTHER 1-2" ARE POSSIBLE
FOR THESE AREAS THROUGH TONIGHT AS ADDITIONAL ROUNDS OF
THUNDERSTORMS LIFT ACROSS THE AREA IN ADVANCE OF THE APPROACHING
UPPER TROUGH. SOME AREAS ESPECIALLY NORTH OF A SQI-UGN LINE COULD
ULTIMATELY SEE AROUND 2.5 INCH STORM TOTALS. SYSTEM BEGINS TO
ACCELERATE A BIT LATE TONIGHT/MONDAY...WITH PRECIP DECREASING FROM
THE WEST DURING THE EARLY/MID MORNING HOURS AND THE LOW QUICKLY
LIFTING AWAY TO THE NORTHEAST. COLDER AIR SPILLING IN BEHIND THE
DEPARTING LOW WILL DECREASE THICKNESSES ENOUGH TO PRESENT THE
POTENTIAL FOR SOME WET SNOW/RAIN MIX TO DEVELOP MAINLY ACROSS NORTH
CENTRAL IL MONDAY...THOUGH WITH SURFACE TEMPS EXPECTED IN THE LOW
40S IN MANY AREAS AM NOT ANTICIPATING ANY ACCUMULATION OF
CONSEQUENCE. AFTER SATURDAY/S 70S AND 80 DEGREE TEMPS...MONDAY WILL
SERVE AS A BLUSTERY AND CHILLY REMINDER THAT SPRING HASNT COMPLETELY
SPRUNG FOR US JUST YET. WHILE THE MAIN LOW LIFTS QUICKLY AWAY DURING
THE MORNING...THE LARGE SCALE UPPER TROUGH AXIS CONTINUES TO DIG
ACROSS THE MIDWEST INTO MONDAY NIGHT...MAINTAINING THE POTENTIAL FOR
SOME ADDITIONAL LIGHT SNOW SHOWERS INTO MAINLY MONDAY EVENING.

HIGH PRESSURE RIDGE BUILDS ACROSS THE AREA TUESDAY WITH COOL BUT DRY
CONDITIONS FOR THE CWA...BEFORE ANOTHER LOW DEVELOPS OVER THE UPPER
MIDWEST WEDNESDAY AND BRINGS SOMEWHAT MILDER AIR BACK INTO THE
REGION. MODEL GUIDANCE IN DECENT AGREEMENT IN MOVING INVERTED
TROUGH/LOW PRESSURE AREA SLOWLY EAST ACROSS THE AREA
THURSDAY-SATURDAY WITH AN ATTENDANT PERIODIC LIGHT RAIN THREAT.
TEMPS HOWEVER LOOK TO MODERATE BACK INTO THE 50S/60S FOR THE MOST
PART...THOUGH WITH SOME COOLER READINGS ALONG LAKE MICHIGAN WITH AT
LEAST PARTIAL ONSHORE FLOW. LONGER RANGE...SOME INDICATION OF
COOLING BEHIND UPPER TROUGH MONDAY...THEN PERHAPS A MILDER PERIOD
INTO MID NEXT WEEK WITH BOTH GFS/ECMWF DEVELOPING BROAD UPPER
RIDGING OVER THE CENTRAL CONUS.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* EAST WINDS OF 10 TO 15 KT THROUGH THE EARLY TO MID EVENING.

* IFR CIGS ARRIVING THIS HOUR AND VSBY EXPECTED TO LOWER TO IFR BY
  19Z...THOUGH TIMING COULD BE DELAYED.

* PERIODS OF SHRA/TSRA THIS AFTERNOON AND EVENING...HEAVIEST COULD PRODUCE
  IFR VSBY.

* WINDS TURN NORTH AND GUST TO 25-30 KT LATE TONIGHT INTO MONDAY MORNING.

* RAIN POSSIBLY MIXING WITH OR CHANGING TO SNOW ON MONDAY AND
  ASSOCIATED CIG/VSBY IMPACTS.

RC

//DISCUSSION...UPDATED 18Z...

MULTIFACETED AVIATION CONCERNS THROUGH THE PERIOD. DUE TO WEAKNESS
IN PRESSURE PATTERN OVER THE TERMINALS...A LAKE ENHANCED FRONT IS
SURGING SOUTHWESTWARD AND HAS PUSHED THROUGH ORD/MDW AND GYY WITH
A WIND SHIFT TO EAST AND NORTHEAST. WARM MOIST AIR ALOFT ABOVE THE
DENSE MOIST MARINE LAYER HAS RESULTED IN IFR CIGS AND LOWERING
VSBY...WITH DENSE FOG ALONG THE LAKEFRONT. EXPECTING IFR VSBY TO
REACH ORD/MDW BY AROUND 19Z...THOUGH CONFIDENCE IS STILL ONLY
MEDIUM IN EXACT TIMING AND OCCURRENCE BASED ON UPSTREAM TRENDS AT
PWK. A WAVE OF SHRA AND EMBEDDED TSRA ALSO CURRENTLY LIFTING
NORTHEAST...WITH ADDITIONAL WAVES OF SHRA AND TSRA LATE THIS
AFTERNOON AND EVENING AND AT LEAST OCNL IFR VSBY IN THE HEAVIER
RAIN. AS LOW PRESSURE OVER THE SOUTHERN PLAINS LIFTS
NORTHEAST...WINDS WILL PICK UP OUT OF THE SOUTH-SOUTHWEST SOUTH OF
THE FRONTAL BOUNDARY...BUT THE CONVECTION IS LIKELY TO KEEP WINDS
OUT OF THE EAST AT ORD/MDW/DPA...POSSIBLY GOING BACK TO SOUTH AT
GYY AROUND 00Z. WINDS ARE EXPECTED TO SHIFT BACK TO GUSTY SOUTH-
SOUTHWEST AT ORD/MDW AND DPA BY MID TO LATE EVENING...WHICH COULD
TEMPORARILY LIFT CIGS BACK ABOVE IFR...THOUGH THIS IS NOT
CURRENTLY INDICATED IN TAF.

MUCH COLDER AIR WILL SURGE INTO THE AREA ON GUSTY NORTHERLY WINDS
LATE TONIGHT WHILE PERIODS OF RA/SHRA CONTINUE AS WELL AS IFR CIGS AND
VSBY REDUCTIONS. THE RAIN MAY LIGHTEN IN INTENSITY AND CIGS LOWER
BY MID MORNING MONDAY...THOUGH NORTHERLY WIND GUSTS COULD STILL BE
AS HIGH AS 30 KT ESPECIALLY FOR THE EASTERN TERMINALS. THE NEXT
CONCERN IS FOR ANOTHER UPPER LEVEL DISTURBANCE MOVING IN FROM THE
SOUTHWEST TOWARD MIDDAY MONDAY AS EVEN COLDER AIR ARRIVES WHICH
COULD RESULT IN A RAIN/SNOW MIX OR A CHANGE TO SNOW. UNLESS PRECIP
RATES ARE HEAVY AND THERE IS AN ACTUAL CHANGEOVER TO ALL SNOW AT
THE TERMINALS...WOULD EXPECT IMPACTS TO PRIMARILY BE TO VSBY AND
POSSIBLY LOWER CIGS THAN CURRENTLY INDICATED. FOR NOW HAVE A PROB
30 RASN MENTION IN THE ORD AND RFD TAFS...WITH SUBSEQUENT UPDATES
LIKELY TO ADD SOME BETTER DETAIL TO THIS POTENTIAL ON MONDAY.
WINDS ARE EXPECTED TO REMAIN CLOSE TO DUE NORTHERLY AND GUSTY
THROUGH THE AFTERNOON...THOUGH A SLOW DIMINISHING TREND IN SPEEDS
AND GUST MAGNITUDES IS PROBABLE.

RC

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN EAST WINDS THROUGH EARLY TO MID EVENING...MEDIUM
  CONFIDENCE IN TIMING OF SHIFT BACK TO SOUTH-SOUTHWEST THIS
  EVENING.

* HIGH CONFIDENCE IN IFR CIGS MOVING IN BY 19Z.

* MEDIUM IN VSBY LOWERING TO MVFR OR IFR IN BR...MEDIUM IN
  TIMING...AND MEDIUM HIGH IN POTENTIAL FOR IFR VSBY IN HEAVIEST
  SHRA/TSRA.

* MEDIUM CONFIDENCE IN OVERALL SHRA/TSRA TRENDS AND TIMING THIS
  AFTERNOON AND EVENING...WITH HIGH CONFIDENCE THERE WILL BE AT
  LEAST OCNL TSRA AT THE TERMINALS THIS AFTERNOON AND EVENING.

* HIGH CONFIDENCE IN SHIFT TO GUSTY NORTHERLY WINDS LATE
  TONIGHT...MEDIUM IN TIMING.

* LOW CONFIDENCE IN POTENTIAL FOR RASN MIX OR CHANGE TO SN AND
  ASSOCIATED VSBY/CIG IMPACTS MONDAY AFTERNOON.

RC

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

MONDAY NIGHT...-RASN PSBLY BCMG -SN AFTER MIDNIGHT. MVFR TO IFR
CIGS IMPROVING TO VFR.

TUESDAY...VFR.

WEDNESDAY...VFR.

THURSDAY...CHANCE OF RAIN OVERNIGHT...MVFR/IFR CIGS PSBL OVERNIGHT.

FRIDAY...CHANCE OF RAIN...MVFR TO IFR CIGS PSBL.

SATURDAY...CHANCE OF RAIN.

JEE

&&

.MARINE...
218 PM CDT

A FRONTAL BOUNDARY IN CURRENTLY IN PLACE ACROSS THE SOUTHERN TIP OF
LAKE MICHIGAN EARLY THIS AFTERNOON. LAKE INFLUENCES HAVE ALLOWED THE
WINDS TO SHIFT ONSHORE ACROSS THE INDIANA AND ILLINOIS NEAR
SHORES...WITH DENSE FOG ALSO RESULTING DUE TO THE HIGH DEW POINT AIR
ACROSS THE SOUTHERN END OF THE LAKE IN THE VICINITY OF THE FRONTAL
BOUNDARY.

WINDS WILL SHIFT BACK OUT OF THE SOUTH ACROSS FAR SOUTHERN TIP OF
THE LAKE EARLY THIS EVENING...AND THIS SHOULD IMPACT MAINLY THE
INDIANA NEAR SHORE WATERS. THIS WILL HAPPEN IN RESPONSE TO THE
APPROACHING SURFACE LOW...NOW IN PLACE ACROSS KANSAS AND OKLAHOMA.
SO...ALTHOUGH WINDS ARE CURRENTLY LIGHT OUT OF THE NORTH ACROSS THE
INDIANA NEAR SHORES...EXPECT THAT TO CHANGE EARLY THIS
EVENING...WITH WINDS LIKELY TO BECOME GUSTY FOR A PERIOD UP TO 30 KT
OUT OF THE SOUTH. WE CURRENTLY HAVE A SMALL CRAFT ADVISORY IN PLACE
TO COVER THESE STRONGER SOUTHERLY WINDS...HOWEVER...I DID PUSH OFF
THE START TIME OF THE SMALL CRAFT ADVISORY A FEW HOURS UNTIL THIS
EVENING WHEN THE WINDS ARE EXPECTED TO SHIFT.

AREAS OF FOG WILL LIKELY CONTINUE TO IMPACT SOUTHERN PORTIONS OF
THE LAKE THROUGH MUCH OF TONIGHT AS THE FRONTAL BOUNDARY CONTINUES
TO MEANDER ACROSS THIS AREA. WITH THIS IN MIND I WILL CONTINUE THE
DENSE FOG ADVISORY THROUGH LATE TONIGHT.

OTHERWISE...EXPECT WINDS TO INCREASE OUT OF THE NORTH...FIRST ACROSS
THE NORTHERN 1/2 OR SO OF THE LAKE THIS EVENING...WITH NORTHERLY
GALES LIKELY DEVELOPING BY LATE THIS EVENING. THESE NORTHERLY GALES
WILL THEN OVERSPREAD THE REST OF THE LAKE BY DAYBREAK MONDAY.
OVERALL...IT STILL APPEARS THAT THE MAGNITUDES OF THE WINDS WILL BE
UP AROUND 40 KT...WITH A FEW SHORT PERIODS OF SOME SLIGHTLY HIGHER
WINDS POSSIBLE TOWARDS DAYBREAK MONDAY. THESE GALES WILL GRADUALLY
EASE TO AROUND 30 KT BY EARLY MONDAY EVENING AND MONDAY NIGHT.

A PERIOD OF LIGHTER WINDS ARE EXPECTED TUESDAY INTO EARLY WEDNESDAY
AS A SURFACE RIDGE OF HIGH PRESSURE MOVES OVER THE LAKE.
HOWEVER...THE WINDS ARE EXPECTED TO INCREASE AGAIN OUT OF THE
SOUTHEAST BY THE MIDDLE OF NEXT WEEK AS OUR NEXT AREA OF LOW
PRESSURE BEGINS TO MOVE ACROSS THE MIDWEST.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 PM SUNDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

     DENSE FOG ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874...10 PM
     SUNDAY TO 3 PM MONDAY.

     GALE WARNING...LMZ080-LMZ675-LMZ777-LMZ779-LMZ876-LMZ878...3 AM
     MONDAY TO 3 PM MONDAY.

&&

$$

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.