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January 2013 General Discussion


Chicago Storm

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I'll clear off my driveway starting at about an inch, which I kind of have to do if it's going to be below freezing for awhile. My driveway is on an incline, so if the snow packs on and ice's up then it quite difficult to get traction going up the driveway! I like shoveling anyways, so I don't mind.

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Temps after the GHD Blizzard in 2011 dropped to -9F in Chicago and -20F in Rockford.  If you can believe it, the 850 mb temps were about 10 C warmer (!) at that time, versus what will occur over the next 2 days.  Lows are predicted near 0 in Chicago Monday night...but you have to imagine it would be -15 or so if there was snow cover...and possibly as low as -20F if there was snow cover over the entire Midwest.  

 

From NWS LOT:

 

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE CHICAGO IL
121 PM CST SUN JAN 20 2013 /221 PM EST SUN JAN 20 2013/

ON THIS DATE IN 1985....THE MORNING TEMPERATURE AT O`HARE BOTTOMED
OUT AN INCREDIBLE -27 DEGREES F. THIS SET THE ALL-TIME RECORD LOW
TEMPERATURE IN CHICAGO. IN ADDITION...ROCKFORD PLUMMETED TO
-26...WHICH IS THE SECOND LOWEST TEMPERATURE EVER RECORDED THERE.

INTERESTINGLY...AIR TEMPERATURES LATE TOMORROW OVER NORTHERN
ILLINOIS AT 850 MILLIBARS...OR JUST OVER 4000 FEET ABOVE THE
SURFACE...WILL BE NEAR -25 CELSIUS. TYPICALLY THE 850 MILLIBAR
LEVEL IS AT APPROXIMATELY 5000 FEET ABOVE THE GROUND...AND
TEMPERATURES HERE ARE A GOOD PROXY FOR HOW WARM OR COLD AN AIR
MASS IS. HOWEVER...IN THE CASE OF THE AIR MASS OVERHEAD
TOMORROW...IT WILL BE SO COLD THAT THE 850 MILLIBAR LEVEL WILL
ACTUALLY BE MUCH LOWER AND CLOSER TO 4000 FEET. THE TEMPERATURE AT
THIS LEVEL BACK ON 1/20/85 WAS ONE OF THE LOWEST OBSERVED IN THE
PAST 30 YEARS FOR OUR AREA...AT -31 C.

THEREFORE...THE AIR MASS TOMORROW WILL BE EXTREMELY COLD BY OUR
STANDARDS...ABOVE THE SURFACE...BUT THE LACK OF SNOW COVER IS A
BIG LIMITING FACTOR ON HOW COLD IT CAN GET AT THE SURFACE. ON
1/20/85...THERE WAS 7 INCHES OF SNOW ON THE GROUND AT O`HARE. IF
WE ACTUALLY HAD DEEP SNOW COVER TOMORROW NIGHT...IT IS IMPOSSIBLE
TO ESTIMATE JUST HOW COLD IT WOULD GET...BUT A GOOD INDICATOR IS
THE LAST TIME CHICAGO AND ROCKFORD WERE BELOW ZERO...FEBRUARY 10
2011. ON 2/10/11...THERE WAS NEARLY 20 INCHES OF SNOW ON THE
GROUND ACROSS THE AREA. ROCKFORD SET A NEW RECORD LOW OF -20
DEGREES F AND CHICAGO DIPPED TO -9 DEGREES. 850 MILLIBAR
TEMPERATURES THAT DAY WERE ACTUALLY COMPARATIVELY MILD TO TOMORROW
NIGHT AT AROUND -15 CELSIUS. CLOUD COVER IS ALSO A FACTOR THAT
LIMITS HOW COLD IT CAN GET...BUT BASED ON AIR TEMPERATURES ABOVE
THE SURFACE ALONE...IT IS POSSIBLE IF NOT LIKELY THAT TEMPERATURES
SEVERAL DEGREES COLDER THAN 2/10/11 WOULD HAVE OCCURRED EARLY THIS
TUESDAY IF WE HAD A DEEP SNOWPACK IN PLACE.

IN CLOSING...BECAUSE OF THE LACK OF SNOW COVER...THE ACTUAL AIR
TEMPERATURES DURING THE COLD SNAP WE ARE NOW IN WILL NOT BE NEARLY
AS COLD AS BACK ON 1/20/1985...POSSIBLY GETTING JUST BELOW ZERO IN
CHICAGO ON TUESDAY MORNING. NONETHELESS...WIND CHILL VALUES EARLY
TUESDAY WILL STILL BE AT DANGEROUSLY LOW LEVELS...APPROACHING 20
BELOW ZERO IN THE CITY AND 25 BELOW FOR AREAS NORTH AND WEST OF
CHICAGO.

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Looks like tomorrow could very likely be the coldest day of the whole winter.  Temps should hover at or below 10 all day, and then make a run at zero tomorrow night.  If we fail to go below zero tomorrow night there's a chance we could escape the winter without a below zero reading.  Had only 1 last season, which I thought was extraordinary.  To do this two seasons in a row is incredible.  MLI averages 10 subzero days a season. 

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Mississippi River effect snow !

River_Effect.png

 

Modis_2013Jan20.png

 

The combination of arctic air flowing across the ice-free portion of Lake Pepin allowed a snow band to form off the lake, impacting counties from Buffalo southeast through La Crosse and Vernon.

The radar image below shows the snow band when it was about at its maximum intensity at 6:16 am (click on the image to see a larger one). Due to the small size of Lake Pepin, the band was quite narrow, only about 3 miles in width.  However, visibilities lowered to 1/4 mile in the band!

Very cold temps, open water, gusty winds... 

 

Lake Pepin is just a dammed portion of the Mississippi (pool)...

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