<p>According to the <a href="https://www.washingtonpost.com/weather/2019/01/31/brutal-cold-outbreak-is-breaking-records-midwest-thursday-morning/" rel="nofollow noreferrer">Washington Post</a>: </p>

<blockquote>
  <p>The cold snap is smashing all-time records in Northern Illinois. The state could have a new low temperature record as of Thursday morning, after Mount Carroll plummeted to minus-38 Thursday morning. The temperature was measured by a trained weather observer, according to the National Weather Service. The data will be examined by the Weather Service and the state climatologist to be certified as Illinois' lowest temperature. </p>
</blockquote>

<p>National Weather Service lists -38  °F as the low at Mount Carroll here: </p>

<blockquote>
  <p><a href="https://w2.weather.gov/climate/xmacis.php?wfo=dvn" rel="nofollow noreferrer">https://w2.weather.gov/climate/xmacis.php?wfo=dvn</a>  </p>
</blockquote>

<p><a href="https://en.wikipedia.org/wiki/Mount_Carroll,_Illinois" rel="nofollow noreferrer">Mount Carroll</a> held the record from 1930 to 1999.  </p>

<p><strong>Update</strong> from <a href="https://stateclimatologist.web.illinois.edu/2019/03/06/il/" rel="nofollow noreferrer">https://stateclimatologist.web.illinois.edu/2019/03/06/il/</a>:  </p>

<blockquote>
  <p>After a comprehensive review, the State Climate Extremes Committee (SCEC) unanimously voted to validate the -38 degrees reading as the new official state record minimum temperature. This committee ensures that the observation is meteorologically plausible, is within a range that the reporting instrument can detect, and that the instrument is in proper working order.</p>
</blockquote>

CC BY-SA 4.0
2019-01-31T18:38:24.533Z
Very interesting, and I'll be curious to see what comes of that! I also edited a couple points in my own answer to clarify that these general networks of personal weather stations *could* include more reliable data, additional information is needed for quantitative use of any particular measurements.
dplmmr
CC BY-SA 4.0
2019-01-31T18:41:36.970Z
@dplmmr in the OP, two of the stations used Davis Vantage Vue and one used AcuRite Pro Weather Center instruments
DavePhD
CC BY-SA 4.0
2019-01-31T19:15:08.787Z
Good info, I'd assume the characteristics will be checked, along with things like siting location that have a big impact on the measurements (with some confidence in things like that given by the owner being a trained observer).
dplmmr
CC BY-SA 4.0
2019-01-31T21:50:01.267Z
@dplmmr if the state climatologist considers a measurement to be a possible state record, this committee is supposed to investigate https://www.ncdc.noaa.gov/extremes/scec/
DavePhD
CC BY-SA 4.0
2019-01-31T22:03:35.783Z
Thanks, I only knew the generalities of record event verification but hadn't seen the specific steps and reports. This has been a fascinating development, and I'll be really curious to follow the reporting for the case.
dplmmr
CC BY-SA 4.0
2019-02-06T16:47:41.373Z
@dplmmr http://www.mycarrollcountynews.com/news/article_5dbb0b50-2a26-11e9-9984-e7ab9d729979.html that's the latest info
DavePhD
CC BY-SA 4.0
2019-03-27T02:48:50.053Z
This has been pretty fascinating to watch, and provides a good case study into how temperature measurements are made and verified - particularly in the modern era, where we have instant access to any number of weather observations both official and unofficial.
dplmmr
CC BY-SA 4.0
2019-01-31T18:04:10.883Z
2019-03-26T18:20:42.987Z
2019-03-26T18:20:42.987Z
DavePhD
<p><strong>The record is unlikely to change, at least based on the particular measurements provided in the initial question.</strong></p>

<p>According to the Illinois State Climatologist Office at the <a href="https://www.isws.illinois.edu/statecli/General/averages.htm" rel="nofollow noreferrer">link you provided</a>, the -37°F temperature record was discarded for lack of quality assurance: "However, that observation came from a small airport station designed for aviation purposes and was not part of the climate network in Illinois. As a result, the data were not always archived and no quality control procedures were applied to the data."</p>

<p>From the URLs in your question, the recent weather observations you refer to exist within <a href="https://www.wunderground.com/weatherstation/overview.asp" rel="nofollow noreferrer">Weather Underground's network of personal weather stations</a>. In other words, they are often relatively inexpensive sensors that are owned and maintained by private individuals, and their measurements will not have the accuracy required to be included in the official temperature records for the state. The actual temperature at the Sinnissippi Point station may or may not have been colder than Illinois' verified lowest temperature, but without additional info (e.g. knowledge of specific instruments/sites and operator, as implied in the answer by @DavePhD) the official record will not change based on that measurement.</p>

CC BY-SA 4.0
2019-01-31T17:18:16.153Z
My understanding is that the surface observational data assimilated into operational forecast models typically comes from only a set of "official" stations with at least some known maintenance/quality control criteria, not the set of all possible weather stations.
That's mainly based on my recollection of what I've learned from the US forecast model community, and based on results from some searching (e.g. the UK community: https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/qj.2372) it seems to hold up at least to some extent. But that's probably a topic worthy of its own entire question.
dplmmr
CC BY-SA 4.0
2019-01-31T17:41:00.853Z
This report of -35 °F https://www.wrh.noaa.gov/mesowest/timeseries.php?wfo=ilx&sid=KSFY&num=72 looks more official.  But that doesn't specify what the minimum was, only reports at 20 minute intervals.
DavePhD
CC BY-SA 4.0
2019-01-31T17:50:38.177Z
That looks like the same class of Automated Weather Observing System (AWOS) mentioned by the State Climatologist Office for the -37 °F measurement, and the reports around that time don't have any error codes. So a site like that could conceivably produce an official record low temperature if it passed a more detailed quality control analysis (although in this case I wouldn't be surprised if it doesn't get any special attention since it wouldn't quite make a major new record).
dplmmr
CC BY-SA 4.0
2019-02-01T16:45:21.293Z
@gansub it's worth noting, the new IBM global modeling effort is supposed to more heavily use such independent sensors more... will thus be something interesting to compare against and see if it is helpful or harmful to forecasts
JeopardyTempest
CC BY-SA 4.0
2019-01-31T16:48:01.277Z
2019-01-31T21:58:55.997Z
2019-01-31T21:58:55.997Z
dplmmr
<p>The <a href="https://www.isws.illinois.edu/statecli/General/averages.htm" rel="nofollow noreferrer">State Climatologist Office for Illinois</a> says the all time low temperature of Illinois was -36 °F, with a report of -37 °F in 2009 being disqualified.   </p>

<p>This morning, the station <a href="https://www.wunderground.com/personal-weather-station/dashboard?ID=KILOREGO7#history" rel="nofollow noreferrer">Sinnissippi Point</a> reported: </p>

<blockquote>
  <p>6:00 AM -37.6 °F<br>
  6:15 AM -37.8 °F<br>
  6:30 AM -38.3 °F<br>
  6:45 AM -38.5 °F<br>
  7:00 AM -38.4 °F<br>
  7:15 AM -38.9 °F<br>
  7:30 AM -38.7 °F<br>
  7:45 AM <strong>-39 °F</strong><br>
  8:00 AM -37.7 °F  </p>
</blockquote>

<p><a href="https://www.wunderground.com/personal-weather-station/dashboard?ID=KILGALEN16#history/tdata/s20190131/e20190131/mdaily" rel="nofollow noreferrer">Galena</a> was slightly lower reporting: </p>

<blockquote>
  <p>6:48 AM -39 °F<br>
  6:53 AM -39 °F<br>
  6:59 AM -39.2 °F<br>
  7:04 AM -39 °F<br>
  7:09 AM -39.2 °F<br>
  7:14 AM -39 °F<br>
  7:19 AM -39 °F </p>
</blockquote>

<p>and other stations (such as <a href="https://www.wunderground.com/personal-weather-station/dashboard?ID=KILSTOCK8" rel="nofollow noreferrer">North Fork Plum River</a>: -36.8 °F; <a href="https://www.wunderground.com/personal-weather-station/dashboard?ID=KILDURAN2" rel="nofollow noreferrer">Hawkeye Observatory</a>: 37.4 °F) are reporting temperatures near -37 °F.  </p>

<p>Was a new record set this day? Or is there some reason to disqualify or consider unofficial today's reports.  </p>

<meteorology><temperature>
Did temperature for the US state of Illinois reach an all-time record low 1/31/2019?
DavePhD
# Did temperature for the US state of Illinois reach an all-time record low 1/31/2019?

(Asked by: username_0 on 2019-01-31)

The [State Climatologist Office for Illinois](https://www.isws.illinois.edu/statecli/General/averages.htm) says the all time low temperature of Illinois was -36 °F, with a report of -37 °F in 2009 being disqualified.

This morning, the station [Sinnissippi Point](https://www.wunderground.com/personal-weather-station/dashboard?ID=KILOREGO7#history) reported:

> 6:00 AM -37.6 °F  
> 6:15 AM -37.8 °F  
> 6:30 AM -38.3 °F  
> 6:45 AM -38.5 °F  
> 7:00 AM -38.4 °F  
> 7:15 AM -38.9 °F  
> 7:30 AM -38.7 °F  
> 7:45 AM **-39 °F**  
> 8:00 AM -37.7 °F

[Galena](https://www.wunderground.com/personal-weather-station/dashboard?ID=KILGALEN16#history/tdata/s20190131/e20190131/mdaily) was slightly lower reporting:

> 6:48 AM -39 °F  
> 6:53 AM -39 °F  
> 6:59 AM -39.2 °F  
> 7:04 AM -39 °F  
> 7:09 AM -39.2 °F  
> 7:14 AM -39 °F  
> 7:19 AM -39 °F

and other stations (such as [North Fork Plum River](https://www.wunderground.com/personal-weather-station/dashboard?ID=KILSTOCK8): -36.8 °F; [Hawkeye Observatory](https://www.wunderground.com/personal-weather-station/dashboard?ID=KILDURAN2): 37.4 °F) are reporting temperatures near -37 °F.

Was a new record set this day? Or is there some reason to disqualify or consider unofficial today's reports.

**Tags:** meteorology, temperature


---

## 2 answers

### Answer by username_1 on 2019-01-31. Score: 8

**The record is unlikely to change, at least based on the particular measurements provided in the initial question.**

According to the Illinois State Climatologist Office at the [link you provided](https://www.isws.illinois.edu/statecli/General/averages.htm), the -37°F temperature record was discarded for lack of quality assurance: "However, that observation came from a small airport station designed for aviation purposes and was not part of the climate network in Illinois. As a result, the data were not always archived and no quality control procedures were applied to the data."

From the URLs in your question, the recent weather observations you refer to exist within [Weather Underground's network of personal weather stations](https://www.wunderground.com/weatherstation/overview.asp). In other words, they are often relatively inexpensive sensors that are owned and maintained by private individuals, and their measurements will not have the accuracy required to be included in the official temperature records for the state. The actual temperature at the Sinnissippi Point station may or may not have been colder than Illinois' verified lowest temperature, but without additional info (e.g. knowledge of specific instruments/sites and operator, as implied in the answer by @username_0) the official record will not change based on that measurement.

> **Comments:**
> **username_1**: My understanding is that the surface observational data assimilated into operational forecast models typically comes from only a set of "official" stations with at least some known maintenance/quality control criteria, not the set of all possible weather stations. That's mainly based on my recollection of what I've learned from the US forecast model community, and based on results from some searching (e.g. the UK community: https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/qj.2372) it seems to hold up at least to some extent. But that's probably a topic worthy of its own entire question.  
> **username_0**: This report of -35 °F https://www.wrh.noaa.gov/mesowest/timeseries.php?wfo=ilx&sid=KSFY&num=72 looks more official.  But that doesn't specify what the minimum was, only reports at 20 minute intervals.  
> **username_1**: That looks like the same class of Automated Weather Observing System (AWOS) mentioned by the State Climatologist Office for the -37 °F measurement, and the reports around that time don't have any error codes. So a site like that could conceivably produce an official record low temperature if it passed a more detailed quality control analysis (although in this case I wouldn't be surprised if it doesn't get any special attention since it wouldn't quite make a major new record).  
> **username_2**: @gansub it's worth noting, the new IBM global modeling effort is supposed to more heavily use such independent sensors more... will thus be something interesting to compare against and see if it is helpful or harmful to forecasts  

---

### Answer by username_0 on 2019-01-31. Score: 6

According to the [Washington Post](https://www.washingtonpost.com/weather/2019/01/31/brutal-cold-outbreak-is-breaking-records-midwest-thursday-morning/):

> The cold snap is smashing all-time records in Northern Illinois. The state could have a new low temperature record as of Thursday morning, after Mount Carroll plummeted to minus-38 Thursday morning. The temperature was measured by a trained weather observer, according to the National Weather Service. The data will be examined by the Weather Service and the state climatologist to be certified as Illinois' lowest temperature.

National Weather Service lists -38 °F as the low at Mount Carroll here:

> <https://w2.weather.gov/climate/xmacis.php?wfo=dvn>

[Mount Carroll](https://en.wikipedia.org/wiki/Mount_Carroll,_Illinois) held the record from 1930 to 1999.

**Update** from <https://stateclimatologist.web.illinois.edu/2019/03/06/il/>:

> After a comprehensive review, the State Climate Extremes Committee (SCEC) unanimously voted to validate the -38 degrees reading as the new official state record minimum temperature. This committee ensures that the observation is meteorologically plausible, is within a range that the reporting instrument can detect, and that the instrument is in proper working order.

> **Comments:**
> **username_1**: Very interesting, and I'll be curious to see what comes of that! I also edited a couple points in my own answer to clarify that these general networks of personal weather stations *could* include more reliable data, additional information is needed for quantitative use of any particular measurements.  
> **username_0**: @username_1 in the OP, two of the stations used Davis Vantage Vue and one used AcuRite Pro Weather Center instruments  
> **username_1**: Good info, I'd assume the characteristics will be checked, along with things like siting location that have a big impact on the measurements (with some confidence in things like that given by the owner being a trained observer).  
> **username_0**: @username_1 if the state climatologist considers a measurement to be a possible state record, this committee is supposed to investigate https://www.ncdc.noaa.gov/extremes/scec/  
> **username_1**: Thanks, I only knew the generalities of record event verification but hadn't seen the specific steps and reports. This has been a fascinating development, and I'll be really curious to follow the reporting for the case.  
> **username_0**: @username_1 http://www.mycarrollcountynews.com/news/article_5dbb0b50-2a26-11e9-9984-e7ab9d729979.html that's the latest info  
> **username_1**: This has been pretty fascinating to watch, and provides a good case study into how temperature measurements are made and verified - particularly in the modern era, where we have instant access to any number of weather observations both official and unofficial.  

---

