Locations include: Ashton, Cortland, Crystal Lake, DeKalb, Franklin Grove, Gilberts, Malta, Mendota, Mundelein, Paw Paw, Rochelle, Rockford, Sandwich, Streamwood, and others.
A very cool Thursday Night set the stage, with temperatures in the 40s falling into the 30s in some places overnight. As temperatures cooled in the lowest few thousand feet of the atmosphere even more late overnight into early Friday morning, partially helped by saturating (a cooling effect) from the influence of a low pressure system overhead, snow reached a lower and lower altitude before melting. Eventually, it would begin reaching the ground just outside of the western Chicago metro around 5 am.
Here is a look at the anomalous weather system. On the weather balloon launches across North America on Thursday evening, the -30°C observed at 500mb (~18,000 ft) at NWS Davenport, IA was the third coldest in all of North America on the 00Z soundings (outside of two in far northern Canada). This speaks to just how deep the cold was, and enough so to briefly support a wet snow mixing in this morning.
Here is a water vapor image of the deep closed low over the area from early Friday morning.
Observations from Radar of Snow and Mixed Precipitation Progressing Closer to the Surface
Below is a look at a model analysis of the vertical profile of the atmosphere over the west metro of Chicago at 3 am this morning. As the atmosphere saturated with approaching rain, it cooled, and this brought enough of the profile below zero close enough to the ground to enable snow to reach the surface.
Rockford: May 24, 1925
Chicago: June 2, 1910
PUBLIC INFORMATION STATEMENT NATIONAL WEATHER SERVICE CHICAGO IL 603 PM CDT FRI MAY 16 2014 /703 PM EDT FRI MAY 16 2014/ ...SECOND LATEST SNOWFALL ON RECORD OBSERVED IN ROCKFORD TODAY... AT 706 AM CDT SNOW BEGAN OFFICIALLY FALLING AT THE GREATER ROCKFORD AIRPORT AND IT CONTINUED TO SNOW...MIXED AT TIMES WITH RAIN UNTIL 836 AM CDT. NO SNOW ACCUMULATED WHICH MAKES THE DAILY SNOWFALL TOTAL FOR ROCKFORD FOR TODAY A TRACE. ONLY ONCE BEFORE IN RECORDED WEATHER HISTORY FOR ROCKFORD HAS THERE BEEN A TRACE OF SNOW ON OR AFTER THIS DATE IN MAY AND THAT WAS BACK ON MAY 24TH 1925 WHEN A TRACE OF SNOW WAS REPORTED. $$ IZZI
This snowfall made it the longest snow season on record in Rockford. For more on this, see here.
For DeKalb, the 0.5" observed was the latest observed measurable snowfall on record. This breaks the record of May 11, 1966 (2.5").
Last Observed May Snowfall
Rockford: May 2, 2005*
Chicago: May 2, 2005 (prior to that, May 10, 1990)
* = Prior to May 16, 2014
:ID LOCATION HIGH LOW PCPN ORD: CHICAGO-O`HARE : 46 / 37 / 0.10 CNII2: CHICAGO-NORTHERLY ISL : 42 / 38 / MDW: CHICAGO-MIDWAY : 44 / 41 / 0.08 LOTI2: NWS CHICAGO-ROMEOVILLE : 43 / 38 / 0.23 RFD: ROCKFORD AIRPORT : 51 / 35 / 0.18 DPA: DUPAGE AIRPORT : 47 / 36 / 0.16 UGN: WAUKEGAN AIRPORT : 44 / 33 / 0.02 ARR: AURORA/SUGAR GROVE : 50 / 37 / 0.24 PWK: WHEELING/CHI EXEC : 47 / 35 / 0.15 VPZ: VALPARAISO IN : 43 / 35 / 0.03 : UNOFFICIAL SUPPLEMENTAL AWOS LOCATIONS : DKB: DEKALB : 45 / 32 / JOT: JOLIET : 43 / 39 / IKK: KANKAKEE : 45 / 41 / IGQ: LANSING : 42 / 39 / C09: MORRIS : 46 / 41 / VYS: PERU : 48 / 38 / PNT: PONTIAC : 46 / 45 / RZL: RENSSELAER IN : 48 / 41 / RPJ: ROCHELLE : 49 / 32 /
Chicago's Cold High Temperature on May 16th
PUBLIC INFORMATION STATEMENT NATIONAL WEATHER SERVICE CHICAGO IL 411 AM CDT SAT MAY 17 2014 /511 AM EDT SAT MAY 17 2014/ ...HIGH TEMPERATURE IN CHICAGO ON FRIDAY WAS NEAR RECORD TERRITORY... THE HIGH OF 46 DEGREES OBSERVED AT CHICAGO OHARE INTERNATIONAL AIRPORT ON FRIDAY MAY 16TH WAS ACTUALLY NOT A RECORD LOW MAXIMUM FOR THE DAY. THAT RECORD OF 44 SET IN 1891 JUST BARELY WAS PRESERVED. HOWEVER...THIS WAS IMPRESSIVE COLD FOR MAY...ESPECIALLY WITH IT BEING THE LATTER HALF OF THE MONTH. THE 46 DEGREES WAS THE COLDEST MAY HIGH TEMPERATURE IN CHICAGO SINCE 46 ON MAY 15TH 2011. WHEN LOOKING AT HIGH TEMPERATURES OBSERVED AFTER THE MID POINT OF MAY (MAY 16TH AND AFTER)...THIS WAS THE COLDEST IN CHICAGO SINCE 45 ON MAY 17 2002. MAYBE THE MOST STRIKING FACT WAS THIS WAS ONLY THE FIFTH TIME SINCE 1930 WITH A HIGH TEMPERATURE THIS COLD AFTER THE MIDPOINT OF MAY! COLDEST HIGH TEMPERATURES IN CHICAGO AFTER THE MIDPOINT OF MAY (MAY 16TH AND AFTER) SINCE 1930: TEMPERATURE DATE -------------------------- 46 MAY 16 1945 46 MAY 17 1945 46 MAY 24 1992 45 MAY 17 2002 46 MAY 16 2014 PRIOR TO 1930...THERE WERE 25 LATE MAY INSTANCES OF HIGHS THIS COLD IN CHICAGO...WHICH VERY LIKELY HAD TO DO WITH THE OFFICIAL OBSERVING LOCATION AT CHICAGO THEN BEING MUCH CLOSER TO LAKE MICHIGAN.
FOR MORE ON THE OFFICIAL OBSERVING LOCATION HISTORY IN CHICAGO SEE HERE.