Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 302322 CCA
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
620 PM CDT THU OCT 30 2014

.DISCUSSION...

EARLY EVENING UPDATE...

MADE A FEW ADJUSTMENTS TO FORECAST TO INCREASE POPS ACROSS SOUTHERN
CWA WHERE WEST-EAST BAND OF MODERATE RAIN HAD DEVELOPED LATE IN THE
AFTERNOON...AND TO SLOW ARRIVAL OF POPS ACROSS THE NORTHERN COUNTIES
A BIT IN LINE WITH VARIOUS HIGH-RES NEAR TERM MODELS WITH APPROACH
OF COLD FRONT LATER THIS EVENING.

RAIN BAND ACROSS LIVINGSTON...FORD IROQUOIS AND BENTON COUNTIES
APPEARS TO BE ASSOCIATED WITH MID-LEVEL FRONTOGENETICAL FORCING WITH
INITIAL SHORT WAVE PROPAGATING SOUTHEAST ACROSS MO/IL INTO THE LOWER
OH AND TENNESSEE VALLEYS. THIS SHOULD SCOOT OFF TO THE SOUTHEAST
OVER THE NEXT COUPLE OF HOURS. FARTHER NORTHWEST...COLD FRONT WAS
DEVELOPING SOUTHEASTWARD ACROSS SOUTHEAST MINNESOTA AND
NORTHWEST/WESTERN WISCONSIN IN RESPONSE TO STRENGTHENING PRESSURE
RISES WITH STRONG HIGH BUILDING SOUTHEAST FROM CANADA. LITTLE IN
RADAR DETECTABLE PRECIP OCCURRING ACROSS THOSE AREAS AT THIS TIME
THUS HAVE SLOWED ARRIVAL AND SLIGHTLY LOWERED POPS FOR SHOWERS
ACROSS NORTHERN IL DURING THE EARLY EVENING HOURS...MORE ALONG THE
CONCENSUS OF THE RAP/HRRR/LOCAL ARW AND EVEN MANY OF THE SYNOPTIC
SCALE MODELS WHICH HOLD MEASURABLE PRECIP OFF LARGELY UNTIL MIDNIGHT
OR AFTER.

RATZER

PREVIOUS DISCUSSION FROM 332 PM CDT...

SHORT TERM...TONIGHT THROUGH SATURDAY...
THE MAIN FORECAST FOCUS THIS AFTERNOON CONTINUES TO CENTER AROUND
THE STORM SYSTEM EXPECTED IMPACT THE REGION LATE TONIGHT THROUGH
FRIDAY NIGHT. STRONG WINDS...AND THE POTENTIAL FOR SOME PERIODS OF
HEAVY LAKE EFFECT SNOW ARE THE PRIMARY CONCERNS.

WE ARE ISSUING A WIND ADVISORY FOR MOST OF THE EASTERN HALF OF THE
AREA...WITH THE EXCEPTION OF LAKE...PORTER...JASPER AND NEWTON
COUNTIES IN INDIANA...WHERE A WINTER WEATHER ADVISORY IS BEING
ISSUED. SEE BELOW FOR MORE DETAILS.

WATER VAPOR IMAGERY EARLY THIS AFTERNOON SHOWS A RATHER VIGOROUS
UPPER LEVEL IMPULSE NOW MOVING JUST EAST OF LAKE WINNIPEG AND OVER
FAR SOUTHWESTERN ONTARIO. THIS WAVE IS EXPECTED TO CONTINUE DIGGING
SOUTH-SOUTHEASTWARD TONIGHT ALONG THE EASTERN PERIPHERY OF AN UPPER
RIDGE...CURRENT CENTERED ACROSS THE INTER MOUNTAIN WEST. AS THIS
OCCURS...AN AREA OF SURFACE LOW PRESSURE WILL SHIFT SOUTHWARD ACROSS
LOWER MICHIGAN INTO FRIDAY MORNING. FARTHER NORTHWEST...A RATHER
STOUT 1036 MB HIGH IS ALSO EXPECTED TO RAPIDLY BUILD SOUTHEASTWARD
ACROSS THE DAKOTAS AND UPPER MIDWEST INTO FRIDAY. THIS STILL LOOKS
TO SET THE STAGE FOR STRONG NORTHERN WINDS ACROSS THE AREA DURING
THE DAY FRIDAY AS STRONG PRESSURE RISES AND STRONG COLD AIR
ADVECTION LEAD TO A QUICK RAMP UP OF NORTHERLY WINDS IN THE WAKE OF
A COLD FRONTAL PASSAGE LATE TONIGHT. MODEL SOUNDINGS ALL SUGGEST
MEAN MIXING LAYER WIND SPEEDS COULD TOP 40 KT ACROSS MAINLY THE
EASTERN HALF OF THE AREA INLAND FROM THE LAKE...MEANING WIND GUSTS
COULD EASILY REACH THIS MAGNITUDE IN MOST AREAS. HOWEVER...AREAS
DIRECTLY ADJACENT TO LAKE MICHIGAN IN NORTHEASTERN ILLINOIS AND
NORTHWESTERN INDIANA COULD EXPERIENCE EVEN STRONGER GUSTS UP AROUND
50 KT WITH THE STRONG NORTHERLY ONSHORE COMPONENT TO THE WINDS.
WINDS LOOK TO REMAIN INTO THE EVENING ON HALLOWEEN...THOUGH WIND
SPEEDS SHOULD GRADUALLY WEAKEN THROUGH THE NIGHT.

THE LAKE SHORE FLOOD ADVISORY WILL CONTINUE FOR AREAS NEAR THE LAKE
AS LARGE BATTERING WAVES IN EXCESS OF 20 FT APPEAR LIKELY...AND AS
THE PREVIOUS DISCUSSION MENTIONED...LAKE LEVELS ARE ABOUT 2 FT
HIGHER THAN PAST YEARS...WHICH COULD MAKE THE IMPACTS OF THESE WAVES
HIGHER THEN SIMILAR WAVE EVENTS IN THE PAST COUPLE OF YEARS.

DUE TO THE LIKELIHOOD OF THESE STRONG WINDS...WE HAVE ISSUED A WIND
ADVISORY FOR MUCH OF THE EASTERN HALF OF MY CWA. THIS
INCLUDES AREAS BASICALLY ALONG AND EAST OF A LINE FROM HARVARD
SOUTHWARD THROUGH KANKAKEE AND IROQUOIS COUNTIES. THE ONLY EXCEPTION
TO THIS WIND ADVISORY IS FOR LAKE COUNTY INDIANA...AS WELL AS
PORTER...JASPER AND NEWTON COUNTIES...WHERE A WINTER WEATHER
ADVISORY IS BEING ISSUED IN PLACE OF A WIND ADVISORY FOR THE
COMBINATION OF THESE STRONG WINDS AND ALSO THE INCREASING POTENTIAL
FOR SOME ACCUMULATING LAKE EFFECT SNOW ON FRIDAY INTO FRIDAY
EVENING.

PRECIPITATION WITH THE APPROACHING COLD FRONT AND UPPER LEVEL
IMPULSE
WILL LIKELY BEGIN TO ENTER FAR NORTHERN ILLINOIS AFTER 10 PM THIS
EVENING...AND BE IN THE FORM OF RAIN SHOWERS. THIS INITIAL ROUND OF
SHOWERS SHOULD MOVE SOUTHWARD ACROSS THE AREA THROUGH THE NIGHT...IN
CLOSE PROXIMITY THE INCREASING FRONTOGENESIS IN THE VICINITY OF THE
COLD FRONTAL BOUNDARY. THIS SHOULD BE A FAIRLY PROGRESSIVE AREA OF
SHOWERS...WITH MOST AREAS ACROSS NORTH CENTRAL ILLINOIS DRYING OUT
BY EARLY FRIDAY MORNING.

THE SECOND STAGE OF PRECIPITATION WILL BE MORE OF A TRUE LAKE EFFECT
SETUP. A COLD AIRMASS FEATURING -7 DEGREE C TEMPERATURES AT 850 MB
WILL MOVE OVER THE LAKE...WHICH IS CURRENTLY REPORTING A 53F (11.7C)
DEGREE WATER TEMPERATURE AT THE SOUTH BUOY. THEREFORE...DELTA T`S
SHOULD END UP VERY FAVORABLE AROUND 19 DEGREES C. IN ADDITION...DEEP
LAKE INDUCED INSTABILITY IS STILL EXPECTED...WITH EQUILIBRIUM LEVELS
LIKELY TO REACH OR EVEN EXCEED 16,000 FT AGL. THEREFORE...THE THREAT
FOR THUNDER AND LIGHTNING HAS NOT CHANGED...WITH CONVECTIVE
PROCESSES
LIKELY TO BE MORE THAN DEEP ENOUGH THROUGH THE -10 TO -20 LAYER TO
RESULT IN GOOD CHARGE SEPARATION.

IT LOOKS AS THOUGH THIS LAKE EFFECT BAND COULD BEGIN TO SET UP
ACROSS NORTHWESTERN INDIANA AND PERHAPS PORTIONS OF SOUTHEASTERN
COOK COUNTY BY LATE FRIDAY MORNING. HI RES GUIDANCE SUGGESTS
UNCERTAINTY ON THE EXACT AREAS THAT WILL GET THIS LAKE EFFECT
BANDING. SOME HAVE HINTED IN A FARTHER WEST BAND...WHICH WOULD
IMPACT MORE OF THE CHICAGO AREA. HOWEVER...I THINK AT THIS POINT
AREAS IN NORTHWEST INDIANA WILL BE MORE FAVORED...WITH THE
LIKELIHOOD OF A NEARLY DUE NORTH BOUNDARY LAYER FLOW SETTING UP OVER
LAKE MICHIGAN. THIS WOULD TEND TO FAVOR BETTER BOUNDARY LAYER
CONVERGENCE ALONG THE SOUTHERN TIP OF LAKE MICHIGAN FRIDAY
AFTERNOON...WHICH SUGGESTS THAT PORTER AND LAKE INDIANA WILL BE MORE
IN LINE WITH THE POTENTIAL HEAVIER PRECIPITATION. DUE TO THE STRONG
WINDS...IT IS ALSO LIKELY THAT THIS LAKE EFFECT PRECIP COULD BE
DRIVEN WELL INLAND ACROSS NORTHWESTERN INDIANA...POSSIBLY IMPACTING
MUCH OF JASPER AND PORTER COUNTIES AS WELL.

UNCERTAINTY IN PRECIPITATION TYPE IS STILL SOMEWHAT HIGH...AS
SOME WARMER AIR MOVING OFF THE LAKE SHOULD MAKE BOUNDARY LAYER
TEMPERATURES MARGINAL FOR SNOW TO REACH THE SURFACE. HOWEVER...WITH
THE AFOREMENTIONED CONVECTIVE INSTABILITY AND THE GOOD POTENTIAL FOR
SOME HEAVIER PRECIP RATES...IT IS VERY MUCH IN THE REALM OF
POSSIBILITIES THAT ENHANCED DYNAMIC COOLING COULD RESULT IN A COLD
ENOUGH BOUNDARY LAYER SUPPORTIVE OF HEAVY SNOW. IT APPEARS THAT
AREAS INLAND FROM THE IMMEDIATE LAKE SHORE WOULD HAVE THE BEST
POTENTIAL FOR SNOW...THOUGH EVEN AREAS ALONG THE LAKE COULD CHANGE
OVER/MIX WITH SNOW. OVERALL...WITH THE POTENTIAL FOR SOME HEAVIER
BANDS OF SNOW WITH SOME ACCUMULATIONS POSSIBLE (POSSIBLY A FEW
INCHES IN SOME AREAS) ALONG WITH THE VERY STRONG NORTHERLY
WINDS...WE HAVE CHOSEN TO ISSUE THE WINTER WEATHER ADVISORY FOR THE
4 NORTHWESTERN INDIANA COUNTIES. IF...HOWEVER...THE TRANSITION TO
SNOW DOES NOT PAN OUT AS CURRENT THINKING SUGGESTS...WINDS WOULD BE
THE MAIN HAZARD ON FRIDAY...AND THE WINTER WEATHER ADVISORY COULD
THEN BE REPLACED WITH A WIND ADVISORY. THEREFORE...IN SPITE OF THE
UNCERTAINTIES ON WHEN CHANGE OVERS TO SNOW WILL OCCUR AND HOW MUCH
SNOW WILL ACTUALLY FALL...WE FEEL AT THIS POINT...TO ERROR ON THE
SIDE OF CAUTION...AS THERE IS A POTENTIAL FOR SOME VERY HEAVY SNOW
IN ADDITION TO THE STRONG WINDS.

THE WINDS ARE EXPECTED TO GRADUALLY VEER MORE NORTHEASTERLY FRIDAY
NIGHT...AND THIS COULD ALLOW SOME OF THE LAKE EFFECT PRECIPITATION
TO GET INTO NORTHEASTERN ILLINOIS FOR A BRIEF PERIOD FRIDAY EVENING.
HOWEVER...MODEL GUIDANCE CONTINUES TO SUGGEST THAT INVERSION HEIGHTS
WILL CRASH IN A HURRY BY LATE FRIDAY EVENING AS HEIGHTS AND
TEMPERATURES BEGIN TO RISE ALOFT. THEREFORE...ANY SNOW SHOWERS THAT
GET INTO NORTHEASTERN ILLINOIS WOULD LIKELY BE LIGHT AND COME TO AN
END LATE FRIDAY NIGHT/EARLY SAT MORNING.

HIGH TEMPERATURES AREA-WIDE LOOK TO REMAIN IN THE LOWER 40S AT BEST
ON FRIDAY AND SATURDAY

LONG TERM...SUNDAY THROUGH WEDNESDAY...

HIGH TEMPERATURES WILL MODERATE INTO EARLY NEXT WEEK AS THE
WESTERN CONUS UPPER RIDGE BUILDS EASTWARD OVER THE REGION. ANOTHER
COLD FRONT LOOKS TO TAKE AIM ON THE AREA AROUND NEXT
TUESDAY...WHICH WILL RESULT IN OUR NEXT CHANCE OF SHOWERS.
OTHERWISE TEMPERATURES LOOK TO REMAIN NEAR NORMAL DURING THE LATER
HALF OF THE WEEK.

KJB

&&

.AVIATION...

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

* NO ISSUES IN THE NEAR TERM.

* SOUTHWEST WINDS SHIFTING TO THE NORTHWEST WITH FROPA
  TONIGHT...WITH GUSTS INCREASING THROUGH MIDDAY FRIDAY WHILE
  BECOMING MORE NORTHERLY.

* CHANCE OF -SHRA/-SHSN TONIGHT THROUGH EARLY FRIDAY MORNING.

* MVFR CEILINGS LATE TONIGHT INTO FRIDAY MORNING.

RODRIGUEZ/CMS

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

RELATIVELY QUIET CONDITIONS EARLY THIS AFTERNOON WILL CONTINUE THIS
AFTERNOON...WHILE SOUTHWEST WINDS PREVAIL AND MID/HIGH LEVEL CLOUD
COVER CONTINUE TO STREAM OVERHEAD. CONDITIONS WILL BEGIN
DETERIORATING TONIGHT AS SYSTEM/FRONT PUSH THROUGH THE REGION. THE
CURRENT SOUTHWEST WINDS WILL TURN WEST AND NORTHWEST TONIGHT WITH
WIND SPEED/GUSTS QUICKLY INCREASING. LOWERING CEILINGS TO MVFR WILL
ALSO OCCUR WITH THE ARRIVAL OF THIS WIND SHIFT...LIKELY PERSISTING
FOR MUCH OF FRIDAY MORNING. MOISTURE WILL ALSO BE SUFFICIENT FOR
RAIN SHOWERS TO INITIALLY BE POSSIBLE BUT WITH MUCH COLDER AIR
QUICKLY FILTERING IN...SNOW SHOWERS WILL THEN BE POSSIBLE. EXPECT
THESE RAIN/SNOW SHOWERS TO BE ON THE LIGHTER SIDE...WITH NO VIS
RESTRICTION EXPECTED AS WELL AS NO SNOW ACCUMULATION. THE WINDS WILL
CONTINUE TO SHIFT MORE NORTHERLY FRIDAY MORNING AND LIKELY REMAIN IN
THIS NORTH DIRECTION FOR MUCH OF FRIDAY. THIS ORIENTATION WILL
COINCIDE WITH VERY STRONG WINDS...WITH GUSTS ANTICIPATED TO BE
AROUND 40 KT. CONDITIONS SHOULD BE BACK TO VFR FOR THE REMAINDER OF
THE DAY/FORECAST PERIOD...BUT A TREND BACK TOWARDS DETERIORATING
CONDITIONS COULD BE POSSIBLE IF LAKE EFFECT PRECIP AND CLOUD COVER
MOVE TOWARDS THE TERMINALS FRIDAY EVENING.

RODRIGUEZ

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

* HIGH CONFIDENCE OF VFR CONDITIONS IN THE NEAR TERM.

* HIGH CONFIDENCE OF WIND DIRECTION AND SPEED/GUSTS...MEDIUM HIGH
  CONFIDENCE OF EXACT TIMING OF FROPA.

* HIGH CONFIDENCE OF -SHRA/-SHSN...MEDIUM CONFIDENCE OF DURATION.

* HIGH CONFIDENCE OF MVFR CEILINGS...MEDIUM CONFIDENCE OF DURATION.

RODRIGUEZ/CMS

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

* FRIDAY NIGHT...STRONG NORTH WINDS GUSTING TO 30 KT. CHANCE OF
  SHRA OR SHSN.

* SATURDAY...VFR. WX NIL. NORTHEAST WINDS 10-15KT.

* SUNDAY...VFR. WX NIL. SOUTH WINDS.

* MONDAY...CHANCE OF SHRA. GUSTY SOUTHERLY WINDS.

* TUESDAY...CHANCE OF SHRA. WESTERLY WINDS.

* WEDNESDAY...VFR. WX NIL. SOUTHWEST WINDS.

&&

.MARINE...
250 PM CDT

A VERY ACTIVE PERIOD OVER LAKE MICHIGAN BEGINNING LATER TONIGHT. THE
AREA WILL FIND ITSELF IN A FAVORABLE AND ANOMALOUS SYNOPTIC WEATHER
PATTERN FOR STRONG NORTHERLY WINDS...AND THIS WILL BE FURTHER AIDED
BY THE WARM WATERS/EXTREME INSTABILITY TO PRODUCE REGULAR HIGHER END
STORM FORCE GUSTS PERSISTING INTO FRIDAY. A STRONG COLD FRONT WILL
MOVE DOWN THE LAKE RAPIDLY FROM AROUND MIDNIGHT THROUGH 5 AM.
IMMEDIATELY BEHIND THIS A VERY TIGHT PRESSURE GRADIENT IN SYNC WITH
COLD AIR ADVECTION WILL PRODUCE A RAMP UP IN NORTHERLY WIND SPEEDS.
THE HIGHEST WIND SPEEDS OF STORM FORCE TO 50 AND POSSIBLY EVEN 55 KT
ARE EXPECTED LATE TONIGHT THROUGH MID FRIDAY AFTERNOON FOR THE
CENTRAL AND SOUTHERN PART OF THE LAKE...AND AFTER DAYBREAK THROUGH
THE DAY ON FRIDAY FOR THE NEARSHORE AREAS OF ILLINOIS AND INDIANA.
THE WAVE MAXIMUM OF OVER 20 FOOTERS IS EXPECTED TO DEVELOP OVER THE
CENTRAL PART OF THE LAKE EARLY FRIDAY MORNING AND EVOLVE SOUTHWARD
REACHING THE ILLINOIS AND INDIANA NEARSHORE FRIDAY AFTERNOON AND
EARLY EVENING. WAVES WILL BE VERY SLOW TO SUBSIDE THROUGH LATE
FRIDAY NIGHT AND EARLY SATURDAY. HIGH PRESSURE WILL MOVE QUICKLY
OVER THE LAKE SATURDAY NIGHT BEFORE SOUTHERLY FLOW RETURNS TO THE
LAKE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WIND ADVISORY...ILZ014...7 AM FRIDAY TO 10 PM FRIDAY.

     LAKESHORE FLOOD ADVISORY...ILZ014...11 AM FRIDAY TO 4 AM
     SATURDAY.

     WIND ADVISORY...ILZ005-ILZ006-ILZ012-ILZ013-ILZ020-ILZ022...7
AM
     FRIDAY TO 7 PM FRIDAY.

     WIND ADVISORY...ILZ023-ILZ033...10 AM FRIDAY TO 7 PM FRIDAY.

IN...LAKESHORE FLOOD ADVISORY...INZ001-INZ002...11 AM FRIDAY TO 4 AM
     SATURDAY.

     WINTER WEATHER ADVISORY...INZ001-INZ002-INZ010-INZ011...10 AM
     FRIDAY TO 10 PM FRIDAY.

     WIND ADVISORY...INZ019...10 AM FRIDAY TO 7 PM FRIDAY.

LM...GALE WARNING...LMZ080-LMZ366-LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-
     LMZ675-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-
     LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...7 PM FRIDAY TO
     4 AM SATURDAY.

     STORM WARNING...
LMZ080-LMZ366-LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-
     LMZ675-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-
     LMZ878...3 AM FRIDAY TO 7 PM FRIDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ563...1 AM FRIDAY TO 10
     PM FRIDAY.

     GALE WARNING...LMZ740...4 AM FRIDAY TO 4 AM SATURDAY.

     STORM WARNING...LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
FRIDAY
     TO 7 PM FRIDAY.

&&

$$

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