Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 300819
AFDLOT

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

.SHORT TERM...

FORTHCOMING...

IZZI

&&

.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 06Z...

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

KREIN

//DISCUSSION...UPDATED 06Z...

THE REMAINDER OF THE NIGHT AND THROUGH MUCH DAY THURSDAY...
CONDITIONS WILL BE QUIET AT THE TERMINALS. THE STRATOCU DECK HAS
PUSHED WELL TO THE EAST...LEAVING MOSTLY CLEAR SKIES TO START THE
PERIOD. LATEST SATELLITE IMAGERY SHOWS AN AREA OF MID AND HIGH
CLOUD CROSSING THE UPPER MISSISSIPPI VALLEY ASSOCIATED WITH A MID
LEVEL IMPULSE...WHICH WILL OVERSPREAD THE TERMINALS FOR THE
REMAINDER OF THE OVERNIGHT HOURS. WITH SFC HIGH PRESSURE CENTERED
OVER NRN IL...WINDS WILL BE LIGHT AND VARIABLE FOR THE REMAINDER
OF THE NIGHT AND INTO TOMORROW MORNING. 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 CHANCE IS EXPECTED LATE TOMORROW NIGHT AS A STRONG COLD
FRONT PUSHES SOUTH ACROSS THE AREA. THE LATEST GUIDANCE SUGGESTS
THAT THE FRONT WILL PUSH THROUGH RFD BY ARND 04Z...AND THEN
QUICKLY PUSHING SOUTH THROUGH THE CHICAGO AREA TERMINALS BY
05-06Z. THIS WILL BE A VERY SHARP BOUNDARY AND WINDS SHOULD
QUICKLY SHIFT TO NWLY AND STRENGTHEN WITH GUSTS UP TO 30KT
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...BUT HAVE LOW CONFIDENCE IN THE TIMING
AND COVERAGE OF PCPN...SO WILL LEAVE ANY MENTION OF PCPN OUT OF
THE TAFS FOR NOW AND RE-EVALUATE WITH LATER UPDATES.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* 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.

KREIN

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

* FRIDAY...STRONG NORTH WINDS GUSTING TO 35 KT. CHANCE OF SHRA OR
  SHSN.
* SATURDAY...DRY/VFR. NORTHEAST WINDS.
* SUNDAY...DRY/VFR. SOUTH WINDS.
* MONDAY...CHANCE OF SHRA. GUSTY SOUTHERLY WINDS.
* TUESDAY...CHANCE OF SHRA. WESTERLY 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-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-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-LMZ741...6 AM FRIDAY TO 4 AM SATURDAY.

&&

$$

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