Historic/Record Halloween Snowstorm (Oct 30-31st) Update #5

(9:00PM - 10/28/19) A rare and potentially historic/record breaking snowstorm is set to affect the state, from tonight through Thursday evening. Two periods of accumulating snow are likely across portions of the state, with several inches of accumulation likely for some areas. The first period of snow will affect portions of Northern and Central Illinois, tonight through Wednesday morning. The second period of snow will affect much of Northern and portions of Central Illinois, Wednesday evening through Thursday evening.

As a storm system has begun to develop in the southern Mississippi Valley, advection and overrunning precipitation has developed this evening across the Southern Mississippi Valley. This blossoming large area of precip will spread across the state tonight. As this occurs, precip will push into colder air in place across portions of Northern and Central Illinois. This will lead to a narrow corridor of snow, which will occur from tonight through Wednesday morning. This axis will likely be fairly narrow, across portions of Northern and Central Illinois. Within this corridor, moderate to heavy snow will be likely at times. Several inches of snowfall accumulation is likely, with upwards of 3-6" being possible in the heart of this axis, with locally higher amounts possible. By mid-late Wednesday morning, precip will gradually change from snow to rain for most areas. Rain will then be possible for most areas through the day on Wednesday, the one exception possibly being near the Illinois/Iowa border. 

As the storm system organizes and lifts northeastward across the Ohio Valley Wednesday night, colder air will begin to wrap into the system. This will allow rain to gradually change back to snow across Northern Illinois and portions of Central Illinois, Wednesday night into Thursday morning. Snow will then continue across these areas into later Thursday afternoon, gradually ending from west to east by evening. Several inches of accumulation will be likely on Thursday for aforementioned areas, with upwards of 3-6" being possible for some areas, and locally higher amounts possible

It should be noted that this will be a heavy and wet snow for affected areas. With many trees still holding leaves, the extra weight from the snow could lead to tree damage and power outages. across portions of Northern and Central Illinois. As winds increase on Thursday, this could worsen the potential. 

Below is our TAM snowfall forecast for this event. This forecast map is the combined final expected snowfall totals for the entire event, including both periods of accumulating snow expected.

While this snowstorm will not be noteworthy a few months from now in the heart of winter, it is quite significant for this time of year and by October standards. This snowstorm has the potential the be one of the biggest, if not the biggest snowfall on record for October in some affected areas. Thursday will also likely end up being the snowiest Halloween on record for many affected areas, with some places likely crushing the current standing records. To top it off, some places will likely approach, if not succeed the all-time record snowiest October on record. October snowfall statistics for a few selects cities are below. Many of these listed current records will be in jeopardy. 

.....Chicago.....
Snowiest October Days: 3.8" - 10/19/1989 & 3.0" - 10/20/1952
Snowiest Halloween: 0.1" - 2014
Snowiest Octobers: 6.3" - 1989 & 4.4" - 1967
.....Rockford.....
Snowiest October Days: 5.0" - 10/23/1929 & 2.0" - 10/27/1925 + 10/29/1917
Snowiest Halloween: 0.1" - 2014
Snowiest Octobers: 5.0" - 1929 & 3.0" - 1917
.....Moline.....
Snowiest October Days: 6.5" - 10/26/1967 & 2.9" - 10/25/1898
Snowiest Halloween: T - 1954/1939/1926/1918/1917/1908
Snowiest Octobers: 6.6" - 1967 & 2.9" - 1898 .....(Already at 1.1" this month to date)
.....Peoria.....
Snowiest October Days: 3.3" - 10/23/1929 & 1.9" - 10/29/1925
Snowiest Halloween: T - 1918
Snowiest Octobers: 3.3" - 1929 & 1.9" - 1925

​​JP

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