Area Forecast Discussion
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000
FXUS63 KLOT 190542
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1142 PM CST TUE NOV 18 2014

.UPDATE...840 PM CST

GENERAL FORECAST STILL ON TRACK THROUGH WEDNESDAY MORNING AS
ANOTHER CLIPPER DROPS SOUTHEAST ACROSS THE DAKOTAS. SURFACE
ANALYSIS SHOWS THE ASSOCIATED WARM FRONTAL BOUNDARY TRACKING
EASTWARD INTO WESTERN MINNESOTA AND IOWA WITH A COLD FRONT RIGHT ON
ITS HEELS TO THE WEST. WARM ASCENT WILL SHARPEN ACROSS THE AREA
LATE TONIGHT AND FIRST THING WEDNESDAY MORNING LEADING TO TOP DOWN
SATURATION AND EXPANSION OF SNOWFALL. LATEST TRENDS SUGGEST THAT
THE FORCING WILL BE BETTER ORGANIZING AS THE SYSTEM PASSES OVER
CWA AND SOUTHERN LAKE MICHIGAN. THIS SUPPORTS A SHORT PERIOD WHERE
THERE IS DECENT ASCENT WITHIN THE FAVORED SNOW GROWTH
ZONE...PRIMARILY ACROSS THE NORTHEAST CWA. INITIAL SATURATION MAY
TAKE SOME TIME BUT THE FORCING SHOULD BE STRONG ENOUGH TO
OVERCOME THIS. THEREFORE AM THINKING THAT THERE WILL BE A 2-3 HR
BURST OF BRIEFLY TO OCCASIONALLY MODERATE SNOWFALL ACROSS THE
NORTHEAST CWA. SNOW RATIOS OF 17-20:1 AND THE FEW HUNDREDTHS OF
LIQUID EQUIVALENT CONTINUE TO POINT TO PEAK AMOUNTS OF ABOUT AN
INCH...THOUGH IT MAY FALL AT A RATE OF AROUND A HALF INCH PER
HOUR FOR AN HOUR OR TWO. TIMING STILL LOOKS ON TRACK WITH THE PEAK
WINDOW IN THE 6-9 AM TIME FRAME FOR THE CHICAGO MORNING RUSH AND
SLIGHTLY EARLIER AT ROCKFORD THOUGH SNOW INTENSITY MAY BE LOWER
THERE. HAVE GONE AHEAD AND INCREASED POPS ACROSS THE NORTHEAST CWA
CARRYING HIGHEST VALUES NORTH/EAST OF A HARVARD TO ROMEOVILLE TO
GIFFORD INDIANA LINE...INCLUDING THE BULK OF THE CHICAGO METRO
AREA IN THE 6 TO 9 AM TIME FRAME. SNOW POTENTIAL AND INTENSITY
TAPERS OFF AS YOU GO FURTHER SOUTH TOWARDS PONTIAC-WATSEKA-FOWLER.
OTHERWISE TEMPS SHOULD REMAIN FAIRLY STEADY THROUGH THE REST OF
THE EVENING BEFORE WARMING OVERNIGHT.

MDB

&&

.SHORT TERM...
241 PM CST

THROUGH THURSDAY...

JUST A FEW MORE DAYS OF THE PREVIEW OF WINTER 2014-15 BEFORE WE
TRANSITION BACK TO A MORE TYPICAL NOVEMBER-LIKE WEATHER. BEFORE THIS
TAKES PLACE WE HAVE SEVERAL MORE UNSEASONABLY COLD DAYS A QUICK SHOT
OF LIGHT SNOW AND EVEN A THREAT OF A MINOR ICING EVENT FRIDAY NIGHT.

VERY DEEP LONG WAVE TROUGH RESPONSIBLE FOR USHERING IN THIS RECORD
COLD AIR MASS IS FINALLY SHOWING SIGNS OF EASING ITS GRIP A
BIT...WITH HEIGHT RISES NOTED ON MORNING U/A ANALYSIS SPREADING EAST
FROM PLAINS TOWARD THE WESTERN GREAT LAKES. WHILE THE LONG WAVE
TROUGH IS BEGINNING TO LIFT OUT ANOTHER VIGOROUS SHORTWAVE OVER THE
NORTHWEST TERRITORIES IS DIVING SOUTH AND WILL RE-ENFORCE THE
WESTERN FLANK OF THE LONG WAVE TROUGH TOMORROW INTO THURSDAY SLOWING
ITS DEPARTURE.

ANOTHER SHORTWAVE ANALYZED AHEAD OF THE NORTHWEST TERRITORIES WAVE
WILL DIVE SOUTH INTO THE UPPER GREAT LAKES TONIGHT. RENEWED HEIGHT
FALLS IN ADVANCE OF THIS FEATURE WILL RESULT IN INCREASING/BACKING
LOW/MID LEVEL FLOW TONIGHT AND STRENGTHENING WARM AIR
ADVECTION/ISENTROPIC ASCENT. INITIALLY COLUMN WILL BE QUITE DRY BUT
CONTINUED ASCENT WILL RESULT IN TOP DOWN SATURATION AND SNOW
DEVELOPING VERY LATE TONIGHT INTO EARLY WEDNESDAY MORNING. DURATION
AND INTENSITY OF THE FORCING WILL RESULT IN BEST CHANCES OF SNOW
OVER NORTHEASTERN PORTIONS OF THE CWA WITH DECREASING CHANCES
FARTHER SOUTH/WEST. LIMITED MOISTURE AND QUICK MOVEMENT OF THE
SYSTEM SHOULD KEEP SNOW AMOUNTS LIGHT...BUT DOES LOOK LIKE A FEW
HOURS OF LIGHT SNOW COMMENCING RIGHT AROUND RUSH HOUR FROM ROCKFORD
SOUTHEAST THROUGH METRO CHICAGO INTO NW INDIANA. ABOVE AVERAGE
SNOW:LIQUID RATIOS OF 15-20:1 COULD RESULT IN THE FEW HUNDREDTHS OF
AN INCH OF QPF FLUFFING UP TO AROUND AN INCH OF SNOW. WHILE AMOUNTS
LOOK TO BE REMAIN LIGHT AND INTENSITY NOT TERRIBLY HEAVY THE
INOPPORTUNE TIMING COULD RESULT IN ADDITIONAL HEADACHES FOR MORNING
COMMUTERS...ESPECIALLY GIVEN THE VERY COLD PAVEMENT TEMPS.

IZZI

&&

.LONG TERM...
241 PM CST

THURSDAY NIGHT THROUGH WEDNESDAY...

ANOTHER LOBE OF ARCTIC AIR WILL FILTER INTO THE REGION IN THE WAKE
OF THIS SYSTEM LATER WEDNESDAY INTO THURSDAY. WHILE NOT AS EXTREME
AS WHAT IS OVER THE AREA NOW...STILL EXPECT TEMPS TO BE AROUND 20F
BELOW AVERAGE. BY THURSDAY NIGHT SKIES SHOULD CLEAR OUT AND SURFACE
RIDGE AXIS WILL PASS OVERHEAD AND COULD ALLOW FOR FAIRLY STRONG
RADIATIONAL COOLING TO TAKE PLACE...ESPECIALLY OVER SNOW COVERED
AREAS WHERE READINGS COULD DIP WELL INTO THE SINGLE DIGITS AND IF WE
GO CLEAR/CALM POSSIBLY NEAR ZERO.

WHILE LONG WAVE TROUGH WILL FINALLY LIFT OUT OF THE REGION FRIDAY
THE LOW LEVEL COLD AIR MASS WILL NOT BE DISPLACED QUITE AS
EXPEDITIOUSLY...SO DESPITE SOUTHERLY WINDS AND SUNSHINE TEMPS MAY
STRUGGLE TO REACH FREEZING. FAST ON THE HEELS OF THE DEPARTING
NORTHERN STREAM TROUGH WILL BE AN IMPRESSIVE SOUTHERN STREAM
SHORTWAVE. GUIDANCE CONTINUES TO SUGGEST THAT WARM AIR ADVECTION AND
ISENTROPIC ASCENT AHEAD OF THIS TROUGH WILL RESULT IN LIGHT
PRECIPITATION DEVELOPING FRIDAY NIGHT...ESPECIALLY LATE. FORECAST
SOUNDINGS CONTINUE TO SUPPORT FREEZING RAIN AND PERHAPS SOME SLEET
FRIDAY NIGHT INTO VERY EARLY SATURDAY MORNING BEFORE WAA SENDS TEMPS
CLIMBING ABOVE FREEZING. NOT LOOKING FOR A BIG ICE EVENT BY ANY
MEANS...BUT OFTEN TIMES IT IS THESE LOW QPF MINOR ICE EVENTS THAT
TURN INTO TREMENDOUSLY HUGE TRAVEL PROBLEMS. CLIMATOLOGICALLY IT
IS UNUSUAL TO GET FREEZING RAIN EVENTS IN NOVEMBER...THOUGH IT IS
FAR FROM CLIMATOLOGICAL NORM TO GET 10 DAYS IN A ROW OF SUB-
FREEZING TEMPS IN NOVEMBER EITHER!

DOES LOOK LIKE A SLOW MOVING AND POTENTIALLY WET SYSTEM WILL AFFECT
THE AREA OVER THE WEEKEND...THOUGH DETAILS ARE STILL SKETCHY THIS
FAR OUT. CONSIDERING MEDIUM RANGE MODELS ARE ATTEMPTING TO RESOLVE A
PHASING OF SOUTHERN AND NORTHERN STREAM SHORTWAVE ENERGY IT WOULD
SEEM LIKELY THAT THERE WILL BE MODEL VARIANCES OVER THE NEXT COUPLE
DAYS. DESPITE THE UNCERTAINTIES REGARDING THE DETAILS...GENERAL IDEA
OF MUCH MILDER AND WETTER SEEMS SOLID THIS WEEKEND. ANOTHER SHOT OF
COLD AIR ARRIVES EARLY NEXT WEEK...THOUGH LATEST GUIDANCE ISNT
POINTING TOWARD COLD OF THE MAGNITUDE OF THIS CURRENT BLAST.

IZZI

&&

.AVIATION...

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

* -SN MOVES IN EARLY THIS MORNING WITH MVFR VSBY AT FIRST. VSBY
  DROPS TO LIFR BY 12Z.

* MVFR CIGS ACCOMPANY SNOW..AND MAY SEE CIGS DROP TO IFR.

* -SN TAPERS TO FLURRIES BY MID MORNING.

* GUSTY WEST WINDS RETURN MID MORNING AND PERSIST THROUGH THE
  NIGHT. MAX GUSTS IN THE AFTN WILL BE ARND 25 KT.

JEE

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

A TROUGH OF LOW PRESSURE IS APPROACHING FROM THE WEST AND IT WILL
BRING SNOW AND LOWER CIGS WITH IT. SW WINDS WILL BECOME SSE FOR A
COUPLE OF HOURS EARLY THIS MORNING...BUT THEN QUICKLY RETURN TO
SSW. DID NOT MAKE ANY CHANGES TO SNOW IN THE TAF AS IT ALL LOOKS
VERY REASONABLE. SNOW MOVES IN EARLY THIS MORNING AND PICKS UP IN
INTENSITY ARND 12Z. AT LEAST IFR VSBY IS EXPECTED...AND WILL
LIKELY SEE A PERIOD OF LESS THAN ONE MILE VSBY. CIGS WILL ALSO
COME DOWN WITH THE SNOW AND HAVE HIGHER CONFIDENCE IN MVFR CIGS
VERSUS IFR GIVEN THE UPSTREAM OBSERVATIONS.

ACCUMULATING SNOW COMES TO AN END BY MID MORNING BUT FLURRIES
PERSIST THROUGH THE AFTERNOON. CIGS SLOWLY RISE AND GUSTY WEST
WINDS SET UP WITH MAX GUSTS ARND 25 KT. GUSTS WILL SLOWLY DIMINISH
THROUGH THE NIGHT.

JEE


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

* HIGH CONFIDENCE IN WIND FORECAST.

* HIGH CONFIDENCE IN SNOW AND LOWER CIGS & VSBY...MEDIUM-HIGH
  CONFIDENCE IN TIMING.

* MEDIUM CONFIDENCE IN CIGS REMAINING ABOVE IFR WITH SNOW.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

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

THURSDAY...VFR.

FRIDAY...CHANCE OF A WINTRY MIX OVERNIGHT. IFR LIKELY OVERNIGHT.

SATURDAY...CHANCE OF A WINTRY MIX EARLY THEN BECOMING RAIN. IFR
LIKELY.

SUNDAY....RAIN. IFR LIKELY.

MONDAY...CHANCE OF RAIN OR SNOW. MVFR TO IFR CIGS.

RODRIGUEZ

&&

.MARINE...
222 PM CST

WINDS ARE EXPECTED TO CONTINUE TO SLOWLY DIMINISH BELOW GALES LATE
THIS AFTERNOON AND EVENING AS A RIDGE OF HIGH PRESSURE BUILDS
TOWARDS THE LAKE. THE RIDGE WILL MOVE OVER LAKE MICHIGAN TONIGHT BUT
RIGHT ON ITS HEELS...ANOTHER COLD FRONT WILL SWEEP ACROSS THE LAKE
MIDDAY TOMORROW. WINDS BACK TO THE SOUTH/SOUTHWEST AHEAD OF THE
FRONT TONIGHT/EARLY TOMORROW...THEN TURN BACK WEST/NORTHWESTERLY IN
THE AFTERNOON AND EVENING. WINDS MAY ONCE AGAIN RETURN TO GALE FORCE
ACROSS LAKE MICHIGAN. A GALE WATCH WILL REMAIN IN EFFECT FOR THIS
PERIOD. WINDS WILL REMAIN ELEVATED THROUGH THURSDAY THEN BEGIN TO
DIMINISH THURSDAY NIGHT INTO FRIDAY AS ANOTHER HIGH APPROACHES LAKE
MICHIGAN.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 2 PM FRIDAY.

     GALE WATCH...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...3 PM WEDNESDAY TO 9 AM
     THURSDAY.

&&

$$

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