(2:00PM - 11/2/19) Post storm wrap up regarding the recent Tue-Thur, October 29-31st Halloween snowstorm that affected Northern and Central Illinois...

Two periods of snow occurred with this event, the first being Tuesday night-Wednesday morning and the second from Wednesday evening-Thursday afternoon. The first period of snow occurred in a narrow corridor across Western and Northern Illinois, producing upwards of 1-4" of snow. The second period of snow affected Northern and Central Illinois, producing widespread amounts of 3-6" across Northern Illinois, with locally higher amounts. 1-4" snowfall amounts were more common across Central Illinois.

Final storm snowfall totals, which includes both periods of snow, were 3-6" across much of Northern and Western Illinois, with locally areas of 6-9". Amounts tapered with southeast extend, to 1-4" across portions of Central and Eastern Illinois.

Below is a map representation of final snowfall totals across the state and adjacent areas. 

This snowstorm ended up shattering records for the snowiest Halloween across the state. Additionally, many areas ended up finishing with one of the snowiest Octobers on record, including featuring one of the snowiest October days on record.

​New records/2nd place in bold/italics.
.....Chicago.....
Snowiest October Days: 3.8" - 10/19/1989 & 3.4" - 10/31/2019
Snowiest Halloween: 3.4" - 2019 & 0.1" - 2014
Snowiest Octobers: 6.3" - 1989 & 4.6" - 2019
.....Rockford.....
Snowiest October Days: 5.0" - 10/23/1929 & 3.1" - 10/31/2019
Snowiest Halloween: 3.1" - 2019 & 0.1" - 2014
Snowiest Octobers: 5.0" - 1929 & 4.2" - 2019 
.....Moline.....
Snowiest October Days: 6.5" - 10/26/1967 & 3.1" - 10/31/2019
Snowiest Halloween: 3.1" - 2019 & T - 1954/1939/1926/1918/1917/1908
Snowiest Octobers: 6.6" - 1967 & 5.8" - 2019
.....Peoria.....
Snowiest October Days: 3.9" - 10/31/2019 & 3.3" - 10/23/1929
Snowiest Halloween: 3.9" - 2019 & T - 1918
Snowiest Octobers: 4.2" - 2019 & 3.3" - 1929
.....Springfield.....
Snowiest October Days: 2.6" - 10/29/1925 & 2.4" - 10/23/1929
Snowiest Halloween: 2.3" - 2019 & T - 1993/1951/1917
Snowiest Octobers: 2.8" - 1925 & 2.4" - 1929
.....Lincoln.....
Snowiest October Days:  2.7" - 10/23/1929 & 2.0" - 10/31/2019
Snowiest Halloween: 2.0" - 2019 & T - 1955/1930/1918
Snowiest Octobers: 2.8" - 1929 & 2.0" - 2019 
.....St. Louis.....
Snowiest October Days:  0.3" - 10/29/1913 & 0.2" - 10/23/1917
Snowiest Halloween: T - 2019/2017/1993/1954/1951/1905
Snowiest Octobers: 0.3" - 1913 & 0.2" - 1917

​JP

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(10:30AM - 10/31/19) A brief short term update regarding the historic/record breaking Halloween snowstorm continues to affect the state at this time...

A large area of snow is ongoing at this time across much of Northern and Central Illinois. Snowfall intensity is generally light to moderate, though isolated pockets of heavy snow are possible. Snowfall rates up to around 1" an hour are possible in the heaviest activity. Several inches of snowfall has already occurred across Northwest and Western Illinois, where snow is gradually ending. Across the remainder of Northern and Central Illinois, snow continues and will into the afternoon, gradually ending from west to east. Additional accumulation of a couple inches is likely across these areas. Final storm total accumulations from Tuesday night through this evening, which includes both rounds of snow that will have occurred, will be widespread in the 3-6" range across much of Northern and Western Illinois...with locally higher amounts possible. Amounts will taper to 1-3" from Chicago down into Eastern and Central Illinois. Refer to our update from last night for a visual of expected final snowfall accumulations... ​https://www.illinoisstormchasers.com/forecasts/historicrecord-halloween-snowstorm-update-9

​JP

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(10:00PM - 10/28/19) A rare and historic/record breaking snowstorm continues to affect the region, and will continue to affect the state through Thursday evening. One period of accumulating snow occurred last night into this morning across portions of Western and Northern Illinois. The second period of snow will affect much of Northern and Central Illinois, tonight through Thursday evening.

​The first period of snow occurred in a narrow corridor last night into this morning, across portions of Western and Northern Illinois. Upwards of 1-4" of snow occurred in this narrow axis, which ran extended from near a line in the vicinity of Galesburg to La Salle to Naperville. 

The second period of snow will occur across Northern and Central Illinois tonight through Thursday evening. A large area of precip has blossomed across the region this evening, as the storm system further organizes. As this is occurring, colder air is beginning to wrap into the system, which is allowing rain to gradually turn to snow from west to east across Northern and Central Illinois. As of this posting time, rain has turned to snow across much of Northwest, North-Central and Western Illinois. Rain will transition to snow across the remainder of Northern and Central Illinois overnight and into Thursday morning. Snow will then continue across these areas into Thursday afternoon, gradually ending from west to east. Several inches of accumulation will be likely tonight into Thursday afternoon for the aforementioned areas, with upwards of 3-6" being possible for a large portion of Northern and portions of Central Illinois, with locally higher amounts possible.

​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 (Tue night-Wed morning & Wed night-Thur eve).

As mentioned in previous posts... 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 by several inches. To top it off, some places will likely approach, if not surpass 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 .....(Already at 1.2" this month to date)
.....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 .....(Already at 0.5" this month to date)
.....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 .....(Already at 0.1" this month to date)

​JP

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(4:00PM - 10/30/19) While the rare October snowstorm that's affecting the region is grabbing all of the attention and headlines, of note the next few nights will be cold temperatures...Which will feature a hard freeze for much of the state, officially ending the growing season.

While a good portion of the state has already received a freeze this fall, with lows of 29-32...This period will feature the first hard freeze of the fall for much of the state. A hard freeze is temps 28 degrees or colder. This effectively marks an end to the growing season.

For tonight, of focus will be Northwest and Western Illinois...and vicinity. Across this area low temps will bottom out in the mid to upper 20's. While this area has already seen a freeze this fall with lows of 29-32, this will be the first hard freeze of the season...marking an end to the growing season.

For Thursday night, much of the state will see low temperatures in the 20's. The exception may be across portions of Northern and Central Illinois that have deeper snow cover following the end to the snowstorm on Thursday afternoon. Across these areas, low temps may bottom out in the upper 10's. Much of the state has already seen a freeze with low temps of 30-32, but this will be the first hard freeze of the fall...marking an end to the growing season.

Below freezing temps will also be likely across portions of the state Friday night, but by this time much of the state will have already seen a hard freeze/end to the growing season.

​​​JP

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​After a several hour period of moderate to heavy snow earlier this morning across portions of western Illinois on northeast into northern Illinois and the Chicago metro area that dropped a few inches of snow, temperatures have warmed with rain now being the dominant precipitation type, where it is still raining. Going forward a dry period will work its way into much of the state as I dig into the latest along with what to expect with for Halloween tomorrow as some towns and cities are already postponing trick-or-treating due to the cold and snow expected. 

Our upper level low continue to inch closer to the Midwest and here in Illinois and is currently ejecting out into the plains early this afternoon. It will then turn more east and ENE later today and tonight ahead of moving into our region. 

The image below is valid at 6pm this evening, showing nearly all of Illinois void of any precipitation as a good chunk of tonight will be dry. However, after about 7pm or so, widespread precipitation will develop to our west in response to the upper level low coming east into the Midwest. You'll see an animation of this below.

The loop below runs from 6pm this evening through 8pm tomorrow morning, showing precipitation blossoming to our west late tonight. As colder air works its way eastward, rain will gradually changeover to snow from west to east across northern and central Illinois during the overnight and morning hours tomorrow. After that, a 6-10 hour period will commence where precipitation will be all snow as well as accumulating, favoring just west of the Chicago metro area across north central and northwest Illinois back into western Illinois. Not only will it be snowing but temperatures will be slowly dropping into the low 30's and upper 20's by the late afternoon hours. Lastly, winds continue to look like they'll be problematic with gusts up to 30mph. Lastly, it continues to look like some horrid trick or treating weather and some towns and cities are already beginning to postpone it tomorrow so be on the lookout for that in your town. 

Below is our latest thought on snowfall totals. **This is combining both the round of snow this morning and what is to fall tomorrow and early tomorrow evening, not what is to be expected from here on out. Stay tuned for continued updates.**

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(5:45AM - 10/30/19) A brief short term update regarding the ongoing snowstorm across portions of the state...

As expected, precipitation overspread much of the state overnight. A narrow corridor of snow has been ongoing across portions of Western and Northern Illinois, where colder air has filtered in. Across these areas in this narrow corridor, 1-2" per hour snowfall rates with moderate to heavy snow is occurring. Several inches of snowfall accumulation will be possible in this narrow corridor. Just to the south, a sharp rain/snow line exists, with an area of mixed precip along this line.Further to the south, precip is rain across portions of Central and all of Southern Illinois.

​A full update will be posted early this morning.

​JP

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Well the storm system that we have been talking about for several days now is ongoing early this morning across portions of the state with a narrow band of moderate to heavy snow that has already dropped a few inches of the white stuff from portions of western Illinois up into the suburbs of the Chicago metro area. South of this narrow band of heavy snow, rain is the dominant precipitation type (with a small zone of a mix) given surface temperatures are warmer the further south you go. This is just the beginning and I'll dig into the latest and what's to come the next 36 hours or so.....

Our main upper level low that will be responsible for the second round of accumulating snow across portions of the area tomorrow is still well back to our west and southwest this morning, located over Colorado. It will continue out into the plains later today and eventually come ENE into the Midwest tonight and into tomorrow morning. 

To start, the loop below runs from 1am earlier this morning all the way till 9pm tomorrow night. As you can see, the model did pretty well with the narrow band of heavy snow right now and over the next few hours that led to a swath of a few inches so far this morning. Going forward, not much has really changed to the forecast with mostly rain and/or a break in the action expected this afternoon and this evening across much of the area as surface temperatures warm well into the 30's. As we get into tomorrow (Halloween), again....not much has changed so expect rain to flip back to snow from west to east across northern and central Illinois during the early to late morning hours. Once it flips, expect at least a several hour period of accumulating snow with some areas (northern Illinois favored) seeing several hour inches of snow from late morning to early evening tomorrow. 

Regarding the exact forecast for trick or treaters for the kids on Thursday afternoon and evening. All we have to say is don't shoot the messenger.....as its going to be some of the worst Halloween/trick or treating weather that most of us have seen around this area, especially across the northern half of the state or so. Not only will it still be snowing during the late afternoon and early evening hours, but temperatures will be continuing to drop and range from the upper 20's to low 30's by 5 or 6pm (5pm shown below). Lastly...to go along with those temperatures and falling snow, winds will be quite gusty with sustained winds of 10-20mph with gusts up to or even exceeding 30mph. 

Our latest thinking on expected snowfall totals is shown below as we continue to expect this to be a record breaking and historical Halloween snowstorm and one none of us might never see again this time of year. 

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​MP

(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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We continue to inch closer to the start of this storm system and impending snowstorm across portions of the state as accumulating snow continues to look very likely for some. The system itself is still slowly organizing well to our west but its effects will be felt as early as late tonight and early tomorrow morning for some. I dig into the latest details below....along with expected snowfall amounts.

Our storm system continues to slowly come south and southeast this afternoon across Nevada and Utah and by later tonight it will begin to turn more east and eject out into the plains with its sights set on the Midwest. This is quite the impressive upper level low and what will end up being our snow maker. 

Precipitation is still expected to develop this evening off to our southwest and move into a good portion of the state by late tonight with mostly rain for awhile. As precipitation moves further north, it will encounter colder temperatures where a narrow of snow is looking likely across portions of northern Illinois tomorrow morning. As you can see in the loop below that runs from 3pm today till 7pm on Thursday, temperatures will warm during the heart of the afternoon on Wednesday, leading to mostly rain for all of Illinois outside of maybe far northwest Illinois. As the upper level low approaches from the west, cold air advection will commence from west to east into portions of the state coinciding with another area of widespread precipitation coming back into the area from the southwest. 

As mentioned above, surface temperatures will fall into the upper 20's to low 30's by Thursday morning and afternoon from west to east with the visualization below. As this occurs, expect rain to flip back to snow across portions of northern and central Illinois. 

So to recap, the first round of accumulating snow will come very early tomorrow morning into the late morning hours in a corridor from western Illinois on northeast into around the Chicago metro and some portions of northern Illinois but.....this will most likely be a narrow band of snow so not a lot of people with see sticking snow. Rain will then be the norm Wednesday afternoon and evening and potentially a break in there at some point. As precipitation moves back in Thursday morning, expect a changeover back to snow by mid-late morning Thursday and continuing into the early evening hours across much of northern Illinois. Below is our first TAM/expected snowfall totals for the entire event from early tomorrow morning through Thursday night. Expected continued updates over the next 24 hours. 

We continue to watch and analyze the latest computer model guidance as it comes in last night and this morning and everything continues to point to a fairly impressive storm system affecting the Midwest, including here in Illinois. This system will bring some rain to the area but the big story will be the rarity of accumulating snow to portions of Illinois before and on Halloween and what could be several inches at that. I dig into the latest details below....

Our storm system this morning has now entered the western U.S. and will continue to dig south and southeast through some of today before turning more easterly and entering the plains. After that, it will set its sights on the Midwest and our area by later tomorrow and into Thursday. 

The loop below runs from 1pm this afternoon till 7am on Thursday. There is a lot going on in this loop so lets break it down into a few steps.

1. Precipitation (in the form of rain at first) will initially develop this afternoon and evening well to our southwest across the southern and central plains and spread northeast aided by a strong low level jet. 

2. As precipitation gains some ground northward, it will encounter colder temperatures at the surface and aloft, allowing for it to changeover to snow from about northern Missouri into portions of northern Illinois very late tonight and more so into the heart of the overnight hours. Model guidance continues to hint at a band of snow early Wednesday morning across portions of northern Illinois that could lead to a few inches of snow accumulations. 

3. As surface temperatures warm Wednesday afternoon, it is possible that most of the precipitation across the state flips over to all rain for a period outside of maybe far northwest Illinois. 

4. As surface winds turn out of the northwest late tomorrow night into Thursday morning, colder temperatures will advect into portions of the state from western Illinois on northeast into northern Illinois, changing precipitation back to snow as things stand now. This looks to be the next period of potential snow accumulations on Thursday afternoon and evening as temperatures cool into the low 30's. Wind will also be quite gusty out of the west and northwest during the day and evening hours on Thursday. 

Exact snowfall amounts and the location of the most snow is still not set in stone yet so continue to stay on the lookout for more updates as we near the start of this event late tonight and early tomorrow morning. 

To recap.....the first window for accumulating snow will exist very late tonight into a good portion of Wednesday morning (locations not yet determined as band of snow could be quite narrow. Rain then is expected Wednesday afternoon and evening before colder air works back into western and northern Illinois, going back to snow for a good portion of Thursday and into Thursday night with more snow accumulations look likely but amounts still up in the air. 

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