Friday's Snow Event Had an Impressive Duration of Low Visibility in Snow

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE CHICAGO IL
705 PM CST MON JAN 23 2012 /805 PM EST MON JAN 23 2012/

...THE JANUARY 20TH WINTER STORM BROUGHT AN IMPRESSIVE DURATION OF
LOW VISIBILITY IN SNOW...

THE JANUARY 20TH SNOW EVENT PRODUCED A WIDESPREAD FIVE TO NINE
INCHES OF SNOW ACROSS NORTHERN ILLINOIS AND FAR NORTHWEST INDIANA.
RATES OF SNOWFALL WERE ESPECIALLY HEAVY DURING THAT
AFTERNOON...WITH WIDESPREAD VISIBILITY OF ONE QUARTER MILE OR
LOWER. THIS INCLUDES AT HEAVILY TRAFFICKED CHICAGO OHARE /ORD/ AND
MIDWAY /MDW/ INTERNATIONAL AIRPORTS. THE COMBINATION OF QUICKLY
ACCUMULATING SNOW AND LOW VISIBILITY OFTEN GREATLY SLOW IF NOT
COMPLETELY HALT AIR TRAFFIC.

AT ORD...THE JANUARY 20TH SNOW EVENT BROUGHT VISIBILITY TO ONE
QUARTER OF A MILE IN SNOWFALL AND FOG FOR JUST OVER FOUR
CONSECUTIVE HOURS. SINCE 2007...ONLY THE FEBRUARY 1-2 2011
HISTORIC BLIZZARD PRODUCED A LONGER STRETCH OF BOTH SNOW AND ONE
QUARTER MILE OR LESS VISIBILITY OBSERVATIONS FOR A LONGER DURATION
AT ORD. THAT EVENT HAD LONGER THAN 14 HOURS OF SUCH OBSERVATIONS.

AS FOR MDW...THE JANUARY 20TH SNOW EVENT BROUGHT VISIBILITY TO ONE
QUARTER OF A MILE IN HEAVY SNOWFALL FOR EXACTLY FOUR CONSECUTIVE
HOURS. SINCE 2007...ONLY THE FEBRUARY 1-2 2011 HISTORIC BLIZZARD
PRODUCED A LONGER STRETCH OF BOTH SNOW AND ONE QUARTER MILE OR
LESS VISIBILITY OBSERVATIONS FOR A LONGER DURATION AT MDW.

ITS INTERESTING TO NOTE THAT BLOWING SNOW WAS NOT A FACTOR IN THE
JANUARY 20TH EVENT...WITH WINDS GENERALLY AROUND 10 MPH. THIS
HELPS TO QUANTIFY JUST HOW INFREQUENT A SEVERAL HOUR PERIOD OF
SUCH SNOWFALL RATES AND ASSOCIATED LOW VISIBILITY IS IN CHICAGO.

$$

MTF/CM

 



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