Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 301416
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
916 AM CDT THU OCT 30 2014

.SHORT TERM...
343 AM CDT

FOR THE REMAINDER OF THE NIGHT AND INTO THURSDAY MORNING...WEATHER
CONDITIONS WILL REMAIN QUIET ACROSS THE REGION UNTIL A STRONG COLD
FRONT SWEEPS THROUGH THE AREA LATE TONIGHT.

UNDER CLEAR SKIES AND WITH DEWPOINTS IN THE MIDDLE 20S TO LOWER
30S...TEMPERATURES ACROSS THE REGION HAVE BEEN DROPPING FAST
OVERNIGHT UNDER FAVORABLE RADIATIVE COOLING.  HOWEVER...A WEAK
SHORTWAVE DROPPING SEWD THROUGH THE NRN PLAINS AND ACROSS THE MIDDLE
AND UPPER MISSISSIPPI VALLEY WILL BRING INCREASING MID AND HIGH
LEVEL CLOUDINESS...THROUGH THE EARLY MORNING HOURS...TEMPERING THE
TEMPERATURE DROP OFF.  HOWEVER...OVERNIGHT LOW TEMPERATURES WILL
STILL  DROP INTO THE UPPER 20S TO LOWER 30S ACROSS THE AREA AWAY
FROM THE CHICAGO METRO AREA URBAN HEAT ISLAND...WHERE TEMPERATURES
WILL ONLY DROP INTO THE  UPPER 30S TO LOWER 40S.  AT THE
SURFACE...HIGH PRESSURE IS SLIDING SEWD ACROSS THE REGION...KEEPING
WINDS NEAR CALM.  AS THE HIGH SLIDES INTO THE OHIO VALLEY LATER
TODAY...WINDS WILL BECOME MORE WLY...BUT WITH A WEAK GRADIENT IN
PLACE...WINDS SHOULD REMAIN LIGHT THROUGH THE DAY AND INTO THE EARLY
EVENING.  WITH HEIGHT FALLS ASSOCIATED WITH THE PASSAGE OF THE
SHORTWAVE AND A GENERAL COLD ADVECTIVE PATTERN IN PLACE
ALOFT...ANTICIPATE ANOTHER CHILLY DAY WITH HIGHS ONLY IN THE LOWER
TO MIDDLE 50S.

A STRONG COLD FRONT IS EXPECTED TO DROP OUT OF THE NRN PLAINS AND
PUSH INTO NWRN IL BY AROUND MIDNIGHT AND THE QUICKLY PUSH SEWD
ACROSS THE REGION...BRINGING A QUICK WIND SHIFT TO NWLY.  STRONG
COLD ADVECTION AND STRONG PRESSURE RISES OF 6MB/6HR WILL BRING
STRONG...GUSTY WINDS. LATEST FORECAST SOUNDING SHOW WINDS ARND 30
MPH AT THE TOP OF THE MIXED LAYER OVER LAND...WHICH WOULD
SUPPORT GUSTS NEAR 30 MPH AT THE SFC BY ARND DAYBREAK FRIDAY
MORNING.

KREIN

&&

.LONG TERM...
308 AM CDT

STRONG UPPER TROUGH/CLOSED LOW WILL CONTINUE TO DIG SOUTH THROUGH
THE WESTERN LAKES REGION FRIDAY. STRONG COLD AIR ADVECTION AND
TIGHTENING PRESSURE GRADIENT BETWEEN DEVELOPING SFC LOW TO OUR EAST
AND STRENGTHENING SFC HIGH APPROACHING FROM THE NORTHWEST WILL
RESULT IN STRONG NORTHERLY WINDS FRIDAY...ESPECIALLY NEAR THE LAKE.
FORECAST SOUNDINGS SUPPORT GUSTS TO AROUND 40 MPH MOST AREAS
FRIDAY...THOUGH THE LESSER FRICTION AND STRONGER INSTABILITY AND
RESULTANT MIXING NEAR THE LAKE SHOULD SUPPORT WIND GUSTS OF 50+ MPH
NEAR THE LAKE...ESPECIALLY COOK COUNTY AND NW INDIANA SHORE. COULD
BE A MARGINAL HIGH WIND WARNING FOR LAKE SHORE AREAS WITH A SOLID
WIND ADVISORY EVENT LIKELY. GIVEN THE UNCERTAINTY OPTED TO HOLD OFF
ON HEADLINES FOR NOW AND WILL LET LATER SHIFTS DECIDE.

THE FULL FETCH STORM FORCE WINDS WILL RESULT IN 20FT+
WAVES...PARTICULARLY FOR COOK COUNTY INTO NW INDIANA GIVEN THE
350-360 WIND DIRECTION. LAKE LEVELS ARE NEARLY 2 FEET HIGHER THAN
LAST YEAR AND PREVIOUS YEARS...SO EVEN THOUGH WAVES WILL NOT BE
QUITE AS HIGH AS SANDY A FEW YEARS AGO...THE LAKE SHORE FLOODING
IMPACT COULD BE SIMILAR. HAVE GONE AHEAD AND ISSUED A LAKESHORE
FLOOD ADVISORY TO HIGHLIGHT THE LIKELY COASTAL INUNDATION IMPACT
FROM THE LARGE AND BATTERING WAVES.

COULD SEE SOME SHOWERS ALONG THE COLD FRONT TONIGHT...BUT FRONT
SHOULD CLEAR THE AREA BY FRIDAY MORNING WITH SYNOPTIC PRECIP THREAT
LARGELY ENDING. HOWEVER...VERY IMPRESSIVE LAKE EFFECT SET-UP LOOKS
TO DEVELOP FRIDAY INTO FRIDAY EVENING WITH VERY HIGH LAKE INDUCED
EQUILIBRIUM LEVELS UP TO AROUND 20KFT AND UP TO NEARLY -30C. GIVEN
THE LIKELY PRESENCE OF SUPER COOLED LIQUID IN THE CLOUDS AND HIGH
EQUILIBRIUM LEVELS IT SEEMS QUITE LIKELY THAT ISOLATED THUNDERSTORMS
WILL OCCUR IN ADDITION TO FAIRLY WIDESPREAD SHOWERS FRIDAY. THESE
EARLY SEASON LAKE EFFECT EVENTS ARE ALWAYS TRICKY WITH P-TYPE AS THE
VERY COLD AIR ALOFT...AROUND -8 TO -10C AT 850MB WOULD SOLIDLY
SUPPORT SNOW DESPITE WARM WATER TEMPS IN THE 50S STILL. HAVE GONE
WITH RAIN OR SNOW SHOWERS FOR NOW...BUT THINK THE FARTHER INLAND
AWAY FROM THE LAKE YOU GET THE BETTER CHANCE WILL BE FOR ALL SNOW
SHOWERS FRIDAY AFTERNOON AND EVENING INTO NW INDIANA. GIVEN THE
POTENTIAL FOR THUNDERSTORMS AND ADDED DYNAMIC COOLING AM CONCERNED
THAT SOME PORTIONS OF NW INDIANA...ESPECIALLY A BIT INLAND FROM THE
LAKE...COULD END UP WITH A SLUSHY COUPLE INCHES OF SNOW ACCUMULATION
ON GRASSY SURFACES BY FRIDAY EVENING...THOUGH CONFIDENCE IS TOO LOW
TO HIT THAT TOO HARD AT THIS TIME. LOW LEVEL FLOW SHOULD SLOWLY VEER
SO THAT THE FOCUS FOR LAKE EFFECT PRECIP SHOULD START IN PORTER
COUNTY EARLY FRIDAY AND GRADUALLY SHIFT WEST INTO LAKE COUNTY
INDIANA FRIDAY AFTERNOON AND POTENTIALLY INTO SOUTHEAST COOK COUNTY
FRIDAY EVENING BEFORE INVERSION HEIGHTS CRASH AND LAKE EFFECT WINDS
DOWN LATE FRIDAY NIGHT.

THE COMBINATION OF STRONG WINDS AND UNSEASONABLY COLD TEMPS WILL
SEND WIND CHILLS DROPPING INTO THE 20S DURING TRICK OR TREATING
HOURS FRIDAY EVENING...WITH EVEN LESS FAVORABLE TRICK OR TREATING
WEATHER IN NW INDIANA UNDER THE LAKE EFFECT RAIN/SNOW SHOWERS. AFTER
THE UNSEASONABLY COLD TEMPERATURES AND WIND CHILLS FRIDAY INTO
FRIDAY NIGHT...LOOK FOR QUIET CONDITIONS OVER THE WEEKEND WITH VERY
SLOWLY MODERATING TEMPERATURES. PROGRESSIVE PATTERN SHOULD RESULT IN
TRANSIENT RIDGE MOVING EAST OF THE AREA EARLY NEXT WEEK WITH NEXT
SYSTEM BRINGING THE POTENTIAL FOR SHOWERS MONDAY NIGHT INTO TUESDAY.
TEMPERATURES SHOULD BE CLOSER TO SEASONAL NORMAL NEXT WEEK RETURNING
TO WHAT WILL FEEL LIKE THE RATHER PLEASANT 50S FOLLOWING FRIDAY`S
FLIRTATION WITH WINTER-LIKE TEMPERATURES.

IZZI

&&

.AVIATION...

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

* TIMING OF COLD FRONT PASSAGE WITH WIND SHIFT TO NWLY...GUSTS TO
  30KT AND CIGS LOWERING TO MVFR AND CHANCE SHRA.

* CHANCE SHRA WITH THE PASSAGE OF THE COLD FRONT.

KREIN/RODRIGUEZ

//DISCUSSION...UPDATED 12Z...

CONDITIONS WILL BE QUIET AT THE TERMINALS THROUGH MUCH OF THE
PERIOD...BUT A STRONG COLD FRONT MOVING THROUGH THE REGION LATE
TONIGHT WILL BRING STRONG NORTH WINDS.

HOWEVER...THIS MORNING...A MID LEVEL IMPULSE CROSSING THE MIDDLE
MISSISSIPPI VALLEY IS BRINGING INCREASING MID AND HIGH CLOUDINESS.
LATEST RADAR IMAGERY SHOWS SOME SCT SHRA OVER IOWA AND MISSOURI
ASSOCIATED WITH THIS SYSTEM...BUT WITH A VERY DRY AIRMASS IN
PLACE...DO NOT EXPECT ANY PCPN AT THE TERMINALS.  WITH SFC HIGH
PRESSURE CENTERED OVER SRN IL/IN...WINDS WILL BE LIGHT AND
VARIABLE INITIALLY...BUT AS THE HIGH SLIDES OFF TO THE
SOUTHEAST...WINDS SHOULD BECOME MORE SWLY-WLY THROUGH THE DAY AND
INTO THE EVENING...WITH SPEEDS REMAINING LESS THAN 10KT.

AN ABRUPT CHANGE IS EXPECTED LATE TONIGHT AS A STRONG COLD FRONT
PUSHES SOUTH ACROSS THE AREA. THE LATEST GUIDANCE SUGGESTS THAT
THE FRONT WILL PUSH THROUGH RFD BY EARLY EVENING...AND THEN
QUICKLY PUSHING SOUTH THROUGH THE CHICAGO AREA TERMINALS SHORTLY
THEREAFTER. THIS WILL BE A VERY SHARP BOUNDARY AND WINDS SHOULD
QUICKLY SHIFT TO NWLY. AS COLD ADVECTION AND STRONG PRESSURE RISES
DEVELOP BEHIND THE FROM...WINDS WILL STRENGTHEN WITH GUSTS UP TO
35-40 KT FOLLOWING THE FROPA. THERE WILL ALSO BE A SHALLOW BAND OF
MOISTURE WITH THE FRONT...AND EXPECT THAT CIGS SHOULD QUICKLY DROP
TO LOWER END MVFR LEVELS. THERE IS A CHANCE FOR SOME SHRA
FOLLOWING THE FROPA FOR A BRIEF PERIOD.

KREIN

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS UP TO THE TIMING OF THE
  COLD FRONT PASSAGE THURSDAY NIGHT.

* HIGH CONFIDENCE IN THE IMPACTS OF THE FROPA ON TERMINAL
  CONDITIONS...BUT MEDIUM CONFIDENCE ON THE EXACT TIMING.

* LOW CONFIDENCE IN TIMING AND COVERAGE OF PCPN WITH THE FROPA.

KREIN/RODRIGUEZ

//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...
319 AM CDT

SHARP UPPER TROUGH WILL DIG INTO THE WESTERN GREAT LAKES REGION
TONIGHT AND RESULT IN SURFACE LOW DEVELOPING AND SLOWLY INTENSIFYING
TONIGHT INTO FRIDAY OVER THE EASTERN LAKES. MEANWHILE...UPSTREAM
HIGH PRESSURE OVER THE CANADIAN PRAIRIES WILL STRENGTHEN AS IT MOVES
SOUTHEAST INTO THE NORTHERN PLAINS TONIGHT INTO FRIDAY. THE RESULT
WILL BE A VERY TIGHT PRESSURE GRADIENT DEVELOPING OVER THE AREA
LATER TONIGHT INTO FRIDAY AND WHEN COMBINED WITH THE EXTREME
INSTABILITY LIKELY TO DEVELOP AS A RESULT OF THE VERY COLD AIR ALOFT
MOVING IN...AM EXPECTING A PERIOD OF HIGH END GALES TO LOW END STORM
FORCE WINDS OVER THE LAKE LATE TONIGHT THROUGH FRIDAY NIGHT. CURRENT
INDICATIONS ARE THAT THE LONGEST DURATION AND HIGHEST PROBABILITY OF
STORM FORCE WINDS WILL EXIST OVER SOUTHERN LAKE MICHIGAN AND HAVE
OPTED TO UPGRADE TO A STORM WARNING THERE FOR FRIDAY...INCLUDING THE
NORTHWEST INDIANA NEARSHORE WATERS UP TO NORTHERLY ISLAND IN THE
ILLINOIS NEARSHORE. THE NORTHERN PORTIONS OF THE ILLINOIS NEARSHORE
MAY END UP WITH A MORE OFFSHORE FETCH IN THE 350-360 RANGE LESSENING
THE THREAT OF STORM FORCE WINDS A BIT. NORTHERN PORTIONS OF THE LAKE
COULD SEE STORM FORCE GUSTS FOR A TIME FRIDAY MORNING BUT DURATION
LOOKS TO BE LESS AND CONFIDENCE LOWER...SO JUST HINTED AT THIS
THREAT IN THE GLF. FULL FETCH NORTH STORM FORCE WINDS SHOULD HAVE NO
PROBLEM KICKING WAVES UP TO AROUND OR JUST ABOVE 20 FT OVER SOUTHERN
PORTIONS OF THE LAKE FRIDAY AFTERNOON AND EVENING. WINDS SHOULD
SUBSIDE RATHER QUICKLY FRIDAY NIGHT INTO SATURDAY AS THE PATTERN
REMAINS PROGRESSIVE AND THE HIGH PRESSURE RESPONSIBLE FOR THE STORM
EVENT MOVES INTO THE WESTERN LAKES REGION ALLOWING WINDS AND
EVENTUALLY WAVES TO SUBSIDE SATURDAY. LATER SUNDAY INTO EARLY NEXT
WEEK 25-30KT SOUTHERLY WINDS COULD DEVELOP AS HIGH PUSHES OFF TO THE
EAST AND NEW LOW PRESSURE DEVELOPS OVER THE NORTHERN PLAINS.

IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKESHORE FLOOD ADVISORY...ILZ014...11 AM FRIDAY TO 4 AM
     SATURDAY.

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

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

     STORM WARNING...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ870-LMZ872-LMZ874-
     LMZ876-LMZ878...6 AM FRIDAY TO 7 PM FRIDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ868...1 AM FRIDAY TO 10 PM FRIDAY.

     GALE WARNING...LMZ740...6 AM FRIDAY TO 4 AM SATURDAY.

&&

$$

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