Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 311505
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1005 AM CDT FRI OCT 31 2014

.MESOSCALE DISCUSSION...
1001 AM CDT

WE ARE CURRENTLY WATCHING THE PROGRESS OF A SECONDARY INVERTED
SURFACE TROUGH...WHICH IS CURRENTLY RACING SOUTHWARD DOWN CENTRAL
LAKE MICHIGAN. OBSERVATIONS OVER AND NEAR THE LAKE INDICATE THE
PRESENCE OF GOOD CONVERGENCE ALONG THIS BOUNDARY. THE FIRST
MORNING VISIBLE SATELLITE IMAGES ALSO INDICATE CONVECTIVE
STRUCTURES DEVELOPING WITHIN THE BAND OF RAIN/SNOW SHOWERS
CURRENTLY SHIFTING SOUTHWARD JUST EAST OF MKE. OVERALL IT APPEARS
THIS AREA OF SNOWFALL WILL PIVOT SOUTHWARD ACROSS NORTHWESTERN
INDIANA WITHIN THE NEXT 2 HOURS (BY 1630Z). HOWEVER...I AM ALSO
CONCERNED THAT SOME OF THESE HEAVIER CONVECTIVE SNOW SHOWERS MAY
IMPACT PORTIONS OF NORTHEASTERN ILLINOIS...INCLUDING DOWNTOWN
CHICAGO THROUGH LATE MORNING. IN FACT...SOME OF THE LATEST RADAR
IMAGERY IS ALREADY INDICATING SOME BANDS OF PRECIP MOVING INTO
NORTHERN COOK COUNTY. IT APPEARS THE WINDS WILL BECOME MORE
NORTHERLY IN THE WAKE OF THIS SURFACE TROUGH...AND WIND SPEEDS
COULD ALSO INCREASE A BIT HIGHER THAN CURRENT WIND SPEEDS. WE WILL
CONTINUE TO WATCH OBSERVATION TRENDS...AND HANDLE THIS SNOWFALL
ACROSS THE CHICAGO AREA WITH GRAPHICAL NOWCASTS AT THIS TIME. IT
DOES APPEAR THIS INITIAL BURST OF SNOW WILL BE SOMEWHAT SHORT
LIVED ACROSS THE CHICAGO METRO AREA. WHILE SOME MINOR
ACCUMULATIONS ARE CERTAINLY POSSIBLE WITH THIS ACTIVITY...WE HAVE
NO IMMEDIATE PLANS TO EXPAND THE CURRENT WINTER WEATHER HEADLINES.

FOLLOWING THIS INITIAL BOUNDARY AND BURST OF SNOW...HI RES GUIDANCE
CONTINUES TO INDICATE THAT BANDS OF LAKE EFFECT RAIN/SNOW SHOWERS
WILL CONTINUE TO DEVELOP AND IMPACT MUCH OF THE AREAS CURRENTLY
UNDER THE WINTER HEADLINE ACROSS NORTHWESTERN INDIANA. HOWEVER...WE
WILL NEED TO WATCH FOR THE POTENTIAL OF THE LAKE EFFECT BANDS THIS
AFTERNOON TRYING TO WORK MORE WEST INTO EASTERN ILLINOIS. SOME
GUIDANCE DOES SUGGEST THAT THE LAKE EFFECT BANDS WILL EFFECT AREAS
NEAR...OR EVEN ALONG THE ILLINOIS...INDIANA STATE LINE....AND
POSSIBLY PARTS OF CHICAGO AS WELL. HOWEVER...GIVEN THE MODEL
DIFFERENCES...AND UNCERTAINTY STILL INHERENT IN WHERE ANY LAKE EFFECT
BAND...OR BANDS WILL SET UP...I WOULD LIKE TO WATCH THE EVOLUTION OF
CONDITIONS OVER THE LAKE BEFORE PUSHING SNOWFALL AMOUNTS...AND WINTER
HEADLINES FARTHER WEST.

NO BIG CHANGES ARE PLANNED FOR THE UPDATE. HOWEVER...I WILL LIKELY
ADD A MENTION OF LIGHT SNOW/FLURRIES FOR AREAS A BIT FARTHER INLAND
ACROSS NORTHEASTERN ILLINOIS BASED ON REPORTS OF LIGHT SNOW...AND
RADAR TRENDS.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* OFF AND ON FLURRIES LATE THIS MORNING AND AFTERNOON WITH THE
  POSSIBILITY OF SOME TEMPORARY SNOW SHOWERS NAMELY AT MDW.

* NORTHWEST WINDS SHIFTING NORTH TOWARD 16Z-17Z WITH GUSTS OF 35
  TO 40 KT. GUST SPEEDS WILL BE ERRATIC AND 40 KT GUSTS SHOULD BE
  SPORADIC.

* PERIODIC MVFR CIGS THROUGH THE MORNING AND POSSIBLY INTO THE
  AFTERNOON...ALTHOUGH SHOULD REMAIN ABOVE 2000 FT.

* LAKE EFFECT SNOW SHOWERS COULD AFFECT MDW FROM EARLY EVENING
  ONWARD.

MTF/MDB

//DISCUSSION...UPDATED 14Z...

NORTH-NORTHWEST WINDS HAVE BEEN VERY STEADY AT 340-350 AT ORD AND
MDW. A SECONDARY COLD FRONT/TROUGH IS MOVING SOUTHWARD DOWN LAKE
MICHIGAN AND WISCONSIN AND THIS WILL TURN WINDS MORE DUE NORTH.
THIS IS SLIGHTLY LATER FOR DUE NORTH THAN PREVIOUS TAF. WIND SPEED
THINKING REMAINS THE SAME.

CONVECTIVE CLOUD TOPS ARE BEGINNING TO SHOW UP ACROSS THE CENTRAL
AND SOUTHERN PART OF THE LAKE SO IT IS POSSIBLE WE BEGIN TO SEE
SOME LIGHTNING AS WELL.

PREV DISCUSSION...UPDATED 12Z...

NORTHWEST WINDS HAVE BEEN STEADILY INCREASING EARLY THIS MORNING
AS STRONG HIGH PRESSURE APPROACHES FROM THE NORTHWEST. ONE UPPER
WAVE AND ASSOCIATED -SHRA IS DEPARTING WHILE ANOTHER IS APPROACHING
FROM THE NORTH. A PUSH OF COLDER AIR WITH THE NEXT WAVE IS
RESULTING IN A BAND OF SNOW SHOWERS WHICH HAS BEEN REDUCING VSBY
TO AROUND A MILE AT TIMES...AT LEAST BRIEFLY. EXPECT A 1-2 HR
WINDOW OF -SHSN AT THE TERMINALS OVER THE NEXT 2-3 HRS. VARIABLE
MVFR-VFR CIGS WILL CONTINUE THROUGH MUCH OF THE MORNING BEFORE
STEADIER VFR IS EXPECTED ACROSS THE ILLINOIS TERMINALS WITH
SCATTERING OF CLOUDS WEST.

WINDS WILL TURN TO THE NORTH WITH THE PASSAGE OF THE UPPER WAVE
THIS MORNING AND EXPECT TO SEE A SURGE IN GUSTS AT THAT TIME. 35
TO 40 KT GUSTS ARE EXPECTED BUT AM NOT HIGHLY CONFIDENT IN HOW
FREQUENTLY 40 KT MAY BE REACHED. IT APPEARS THAT MID MORNING MAY
BE ONE POTENTIALLY PRIME PERIOD BEHIND THE UPPER WAVE/PRECIP WITH
THE NEXT POTENTIALLY FAVORED TIME BEING MID AFTERNOON IF SKIES CAN
SCATTER. IT MAY BE THAT AN OCCASIONAL 40 KT GUST OCCURS AT ANY
POINT THROUGH THE DAY. WINDS WILL EASE THIS EVENING.

LAKE EFFECT PRECIPITATION IS EXPECTED TO DEVELOP MID TO LATE
MORNING AND FOCUS ACROSS NORTHWEST INDIANA WITH GYY POSSIBLY BEING
ON THE WESTERN FRINGE INITIALLY BUT LIKELY GETTING INTO THE PRIME
BANDING INTO THE AFTERNOON. GIVEN THEIR PROXIMITY TO THE FAIRLY
WARM LAKE A RAIN SNOW MIX IS FAVORED TURNING TO ALL SNOW IF VERY
INTENSE BANDING CAN OCCUR. THUNDER IS ALSO POSSIBLE AND WOULD
ENHANCE THE ALL SNOW POTENTIAL. AS A RESULT IFR VSBY WILL LIKELY
OCCUR AT TIMES BUT THERE ARE FACTORS THAT MAY LIMIT THE
ORGANIZATION OF THE PRECIP. WINDS WILL LIKELY GUST 40-45 KT WITH
50 NOT OUT OF THE QUESTION TOWARD MIDDAY. LAKE EFFECT PRECIP WILL
LIKELY TURN TO ALL SNOW THIS EVENING AND SHIFT WESTWARD TOWARD THE
IL/IN STATE LINE AND POSSIBLY BEGIN TO IMPACT MDW WITH LIGHT
ACCUMULATIONS POSSIBLE...MAINLY ON THE GRASS. SEVERAL HOURS OF
SNOW MAY OCCUR AT OR NEAR MDW. ADJUSTMENTS TO THE FORECAST DETAILS
THIS EVENING AT MDW/GYY AND EVEN ORD ARE LIKELY.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* LOW ON IF IFR SNOW SHOWERS MAY IMPACT MDW THIS AFTERNOON.
  MEDIUM THAT THEY WILL STAY EAST OF ORD.

* HIGH IN NORTHWEST WINDS TURNING DUE NORTH AND MEDIUM IN TIMING.
  HIGH IN WIND SPEEDS AND THAT ANY GUSTS TO 40 KT WILL BE
  TEMPORARY.

* MEDIUM IN MVFR CIGS. HIGH THAT THEY WILL REMAIN ABOVE 2000 FT
  AT ORD...MEDIUM AT MDW.

* MEDIUM IN LAKE EFFECT SNOW SHOWER POTENTIAL TONIGHT AT MDW...LOW
  AT ORD.

MTF/MDB

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

* SATURDAY NIGHT...DRY VFR. LIGHT/VARIABLE WINDS.
* SUNDAY...DRY/VFR. SOUTH WINDS 10-15 KT.
* MONDAY...SLIGHT CHANCE OF SHRA. GUSTY SOUTHWEST WINDS.
* TUESDAY...SHRA/MVFR LIKELY. SOUTHWEST WINDS.
* WEDNESDAY...DRY/VFR. SOUTHWEST WINDS.
* THURSDAY...DRY/VFR. WEST WINDS.

MDB

&&

.MARINE...
256 AM CDT

A MAJOR WIND EVENT CONTINUES TO TAKE SHAPE FOR LAKE MICHIGAN EARLY
THIS MORNING. FAIRLY BROAD LOW PRESSURE OVER LAKE HURON WILL TRACK
SOUTHEAST TO LAKE ERIE BY MIDDAY THEN CONTINUE TO THE CAROLINA COAST
TONIGHT AND MERGE WITH DEVELOPING LOW PRESSURE. VERY STRONG HIGH
PRESSURE STRETCHED ACROSS THE NORTHERN PLAINS INTO CENTRAL CANADA IS
THE KEY TO THE RAPIDLY INCREASING WINDS THAT ARE NOW REACHING THE
NORTHERN PORTION OF THE LAKE. THE PRESSURE GRADIENT WILL QUICKLY
INCREASE ACROSS THE LAKE INTO MID MORNING AS A COLD FRONT SWEEPS
ACROSS ALLOWING MUCH COLDER AIR TO SPREAD DOWN THE LAKE. NORTH WINDS
WILL LIKELY INCREASE TO STORM FORCE AROUND 50 KT FOR MOST OF THE
LAKE WITH THE FAR NORTHERN SECTION HOLDING AT GALES...THOUGH A FEW
50 KT GUSTS COULD OCCUR THIS MORNING. MAY SEE SOME 55 KT GUSTS AT
TIMES ACROSS THE SOUTH HALF OF THE LAKE...ESPECIALLY LATE THIS
MORNING INTO MIDDAY. THIS RAPID INCREASE IN WINDS AND STRONG
MIXING OVER THE LAKE WILL ALLOW FOR A RAPID BUILDING OF WAVES
THROUGH THE MORNING TO AROUND 20 FEET BY EARLY/MID AFTERNOON
ACROSS THE CENTRAL AND SOUTHERN PART OF THE LAKE. WILL CONTINUE
WITH 18-23 FT PREVAILING WAVES IN THE FORECAST FOR THESE AREAS.
WINDS WILL BEGIN TO EASE THIS EVENING AND TREND A BIT
NORTHEASTERLY. SHOULD SEE WINDS FALL BELOW GALE FORCE OVERNIGHT
BUT WINDS WILL BE SLOW TO DIMINISH SIGNIFICANTLY THROUGH MIDDAY
SATURDAY SO WAVES WILL LIKELY BE SLOW TO FALL AS WELL. WILL LEAVE
EXISTING GALE AND STORM WARNINGS AS-IS.

THE HIGH WILL PASS OVER THE LAKE SATURDAY EVENING THROUGH SUNDAY
KEEPING WINDS LIGHT BUT SOUTH TO SOUTHWEST WINDS WILL INCREASE
THROUGH THE DAY SUNDAY AND MAY PUSH 30 KT LATE SUNDAY
AFTERNOON/EVENING AS LOW PRESSURE TRACKS NORTHEAST ACROSS THE
NORTHERN PLAINS. SOUTHWEST WINDS WILL REMAIN STRONG THROUGH MONDAY
NIGHT THEN LET UP NORTH AS LOW PRESSURE TRACKS FROM THE SOUTHERN
PLAINS ACROSS NORTHERN LAKE MICHIGAN...WHILE THE SOUTH SEES BREEZY
CONDITIONS CONTINUE. WINDS TURN WESTERLY LATER TUESDAY AND
DIMINISH AS HIGH PRESSURE RIDGING EXTENDS ACROSS THE AREA.

MDB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...HIGH WIND WARNING...ILZ014 UNTIL 6 PM FRIDAY.

     LAKESHORE FLOOD ADVISORY...ILZ014 UNTIL 4 AM SATURDAY.

     WIND ADVISORY...ILZ005-ILZ006-ILZ012-ILZ013-ILZ020-ILZ022-ILZ023-
     ILZ033 UNTIL 7 PM FRIDAY.

IN...HIGH WIND WARNING...INZ001-INZ002 UNTIL 6 PM FRIDAY.

     LAKE EFFECT SNOW ADVISORY...INZ001-INZ002-INZ010-INZ011 UNTIL 10
     PM FRIDAY.

     LAKESHORE FLOOD ADVISORY...INZ001-INZ002 UNTIL 4 AM SATURDAY.

     WIND ADVISORY...INZ010-INZ011-INZ019 UNTIL 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-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-
     LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 7 PM FRIDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ563 UNTIL 10 PM FRIDAY.

     GALE WARNING...NEARSHORE WINTHROP TO WILMETTE HARBORS UNTIL 4 AM SATURDAY.

&&

$$

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