12/26/09 Northern IL surprise big snow event

[Thundersnow12]

This one goes down as my 2nd favorite snow event due to the surprise nature of it and +SN rates for several hours. Woke up around 10am to look at radar with already a few inches down from overnight after changing over to snow xmas night...the radar looked pretty interestin with SN across parts of northern IL thanks a strong wave rotating around the main system. We also had the help of a sfc convergence boundary oriented SW-NE from near PIA to northwest of ORD to help focus the heavy snowfall. I had 2"/hr rates for 3 straight hours.

link to Joe's maps from the other thread

http://www.americanw...ost__p__1030200

12z raob sounding from DVN that morning showing the nearly 400mb deep DGZ.

[Geos]

Yeah I remember that one. That storm started from snow on the 23rd went to sleet and freezing rain overnight 23/24, then the surprise snow on the 26th. Picked up 5.6" from that storm. I remember area rivers were flooded as well from the previous monthly snowfalls melting.

I remember similar systems in the last two years that have surprised the area by moving further NW at the last minute. I think one of those systems took a gulp of lake moisture also.

[Hoar_Frost]

This event actually had nothing to do with a northwest trend. The main lifting mechanism associated with this event was a 500-hPa low centred over northern Illinois around which vorticity maxima rotated. On the mesoscale, there was a surface convergence boundary (winds east-southeast on the more northern side, southwest on the more southern side) that oscillated somewhat from northeast to southwest but remained fairly focused overall in central Kane and northwest DuPage counties as well as the panhandle of Cook county during the midday and afternoon of 26 December. This convergence boundary was key in focusing the highest totals in the areas mentioned in the previous sentence.

In my backyard in Geneva (far north-central part of town near the high school), I had a 14.2" storm total from the mid-evening of the 25th through dusk or so on the 26th. Of that 14.2", about 11" fell during the six-hour period between 0900/26th and 1500/26th. The snowfall rate was about 2"/hour from 1100 to 1400; visibility during that period was often no more than about 100 yards. The usually-diligent city of Geneva Public Works ceased plowing operations during that event, it was so bad. Driving was quite treacherous, I recall, because it had been mild the day before (Christmas Day), with a bit of rain, so there was a layer of ice under the fluffy snow. The snow-liquid ratios were eye-catching on account of the deep dendritic growth zone, which is aptly illustrated in the sounding plot in Matt's post above this one; I had something like 42:1.

Looking through Joe's northern Illinois snow event thread linked from Matt's (Thundersnow) post above, I find that this event was the largest of the 2000's decade in terms of snow totals, perhaps slightly larger than the '99 blizzard, and so perhaps the largest since the blizzard in January 1979 (which had 16-17" locally). In my lifetime, this event probably ties with the '99 blizzard, only beaten by the GHD blizzard. It's also interesting to note from that other thread that the GHD blizzard may actually have been the largest snowfall in recent recorded history in my backyard; '79 and '99 were clearly less in terms of snow totals, and '67 was a little less, it appears.

[cyclone77]

Made a high-res loop for this event. Unfortunately the animation is a bit choppy as NCDC is missing some archived data from LOT for this event. Still gives you a decent idea on how things went down that day...

[Thundersnow12]

Can really see the SW-NE orientated sfc convergence boundary for awhile in that loop. Awesome stuff, man.