Cold Winters and What Subsequent Seasons May Be Like

 Cold Winters and Corresponding Springs & Summers

Considering Chicago's Different Observing Locations

Any Indication of the Spring Tornado Season?


Cold Winters and Corresponding Springs and Summers

A natural question after such a cold and active winter is what we might expect from this spring and summer. Does a really cold winter mean spring and summer will also be cooler than normal? A lot of atmospheric factors work together to influence seasonal temperatures from year to year, but with historical records we can at least see what has happened in the past after a really cold winter. Using data collected for the Chicago and Rockford area (141 and 121 years, respectively) we examined the top 20 coldest meteorological winters (Dec-Feb) on record and compared them to their subsequent spring (March-May) and summer (June-Aug) meteorological months. The seasons were organized by their departures from the long term average, with below average being <= -1°F from normal, at average being within 1° from normal, and above average being >=1°F from the long term average.  We also tried to take into account the different locations of Chicago's official observing site and that can be seen below.

Chicago 

Chicago’s normal meteorological winter temperature is 26.4°F. Here are the top 20 coldest winters for the Chicago area: 

Years

Average Winter Temperature

Winter Departure

1903-04

18.0

-8.4

1978-79

18.4

-8.0

1976-77

19.0

-7.4

1892-93

19.0

-7.4

1977-78

19.1

-7.3

1962-63

19.1

-7.3

1981-82

19.5

-6.9

1935-36

19.8

-6.6

1872-73

20.6

-5.8

1904-05

20.6

-5.8

1917-18

21.0

-5.4

1985-86

21.2

-5.2

1874-75

21.2

-5.2

1887-88

21.4

-5.0

1898-99

21.7

-4.7

1983-84

21.8

-4.6

1882-83

21.9

-4.5

1984-85

21.9

-4.5

1919-20

22.0

-4.4

2000-01

22.2

-4.2

For the Chicago area, seven of the meteorological springs following a Top 20 cold winter were also one of the top 20 coldest springs on record. More than half of those 20 spring seasons, 12 out of 20, could be considered as cooler than average.  Only one could be considered average spring (within 1°F of normal) and the remaining seven were warmer than average. Notably, the year 1977 had a winter temperature departure of -7.4, but a positive 8.4°F departure for spring, which made 1977 the second warmest spring on record for Chicago.

Chicago Spring Temperature Departures from Normal

Five Chicago summers following the cold winters were in the top 20 coldest summers on record. Just like spring, more than half of the summers (11 out of 20) qualified as cooler than average. Seven of 20 summers were around average, while only two were above average (both by less than 2°F). One of those summers, in 1875, is the coldest summer on record for Chicago with a -5.7°F departure from normal.

Chicago Summer Temperature Departures from Normal

The previous graphs were created for the Chicago area to depict temperature departures for the meteorological spring and summer following that specific year’s winter. Another graph demonstrates a combined seasonal state of a single year, by using spring and summer temperature departure data. Through observation, the years 1873, 1875, 1883, 1888, 1893, 1904, 1905, 1920, 1978, 1979, 1982, and 1984 remained with negative departure values for spring and summer for Chicago.

 Chicago Spring vs. Summer Departures

Rockford 

For Rockford, the normal meteorological winter temperature is 24.3°F. Here are the top 20 coldest winters for the Rockford area:

Year

Average Winter Temperature

Winter Departures

1978-79

                      14.1

               -10.2

1977-78

                      14.5

                 -9.8

1976-77

                      14.7

                 -9.6

1935-36

                      15.7

                 -8.6

1962-63

                      15.9

                 -8.4

1919-20

                      16.0

                 -8.3

1917-18

                      16.1

                 -8.2

1981-82

                      17.1

                 -7.2

1911-12

                      17.2

                 -7.1

1909-10

                      17.6

                 -6.7

1958-59

                      17.8

                 -6.5

2000-01

                      18.6

                 -5.7

1993-94

                      19.0

                 -5.3

1916-17

                      19.1

                 -5.2

1985-86

                      19.3

                 -5.0

1961-62

                      19.6

                 -4.7

1969-70

                      19.7

                 -4.6

2008-09

                      19.8

                 -4.5

1928-29

                      19.8

                 -4.5

1950-51

                      20.0

                 -4.3

Five of the Rockford meteorological springs following a Top 20 cold winter were also one of the top 20 coldest springs on record.  One of those five springs, in 1920, is the coldest spring on record for Rockford with a departure of -9.1°F from normal. The year, 1977, is the third coldest meteorological winter on record, but one of the top 20 warmest meteorological springs on record.  Furthermore, nine out of those 20 spring seasons could be considered as cooler than average, seven could be considered as average (within 1°F of normal), and four as above average.  As considered, the pattern for the Chicago and Rockford area conclude cooler than average spring seasons following those cold winters examined.

Rockford Spring Departures from Normal

Also, five of the Rockford summers following the cold winters were also in the top 20 coldest meteorological summers on record. The years, 1912 and 1917, are in the records as top 20 coldest meteorological winters, springs, and summer seasons for Rockford. The analyzed pattern continues to demonstrate cooler than average summers for both cities.  More than half of those 20 summer seasons, 11 out of 20, could be considered as cooler than average, eight could be considered average (within 1°F of normal), and just one as above average.

Rockford Summer Temperature Departures from Normal

The previous graphs were created for the Rockford area to depict temperature departures for the meteorological spring and summer following that specific year’s winter. Another graph demonstrates a combined seasonal state of a single year, by using spring and summer temperature departure data. Through observation, the years 1912, 1917, 1920, 1951, 1962, 1970, 1978, and 1979 remained with negative departure values for Rockford.

Rockford Spring vs. Summer Departures

Stephanie Gizzi
Student Volunteer
3/25/2014


Considering Chicago's Different Observing Locations

Chicago's official observing site has moved several times in the past 141 years, as can be seen here.  Prior to being at O'Hare from 1980-present and at Midway from 1942-1980, the official locations were closer to Lake Michigan.  Because of this, during spring and summer (lake breeze season) the temperature likely was naturally cooler at these near-lake locations than it was in outlying places like Midway and O'Hare at that time.  In an attempt to take that into account, two different averages were computed, one for prior to 1942 and one for after.  Below are results in the same format as above but looking at the departure from these possibly more representative averages.

Chicago Spring Departures Considering Different Observing Locations

Chicago Summer Departures Considering Different Observing Locations

 

Chicago Spring & Summer Departures Considering Different Observing Locations


Any Indication for the Spring Tornado Season?

Predicting the frequency and magnitude of the severe weather season for a particular area based on past or even current conditions is very challenging and has been shown to have varying degrees of skill.  What makes it so challenging and limits reliability is that severe weather events are tied to the combination of weather elements that can be quite transient from day to day and week to week, such as instability, wind shear, and especially an impetus or focus for storm development.  In addition, a single severe weather episode could have many high impact storms, producing significant tornadoes, but may be the only event of the spring. So predictability of impact is even more difficult.

That said, coming out of one of the coldest and snowiest winters on record indicates a weather pattern has been at least semi-established.  For instance, an active dynamic pattern with more frequent deep weather systems would likely produce regular high wind shear episodes.  Or for example, a persistent cold pattern with northwest flow may limit the degree of warmth and especially moisture toward producing instability.  Both of these have been patterns we have seen over the past weeks to months. Established patterns or characteristics of such and assuming they persist may give us a rough idea on the potential for severe weather frequency in the immediate upcoming months. 

One thing we know for certain is that the weather pattern has been active and at times progressive across the middle part of the U.S, with frequent weather systems.  Such an active pattern is a bi-product of a strong jet stream.  That can be seen looking at the past 60 days of 500mb wind speeds below.  Note the average of around 50 kt with the maximum located across a belt from the mid-Mississippi valley to the mid-Atlantic and northeast.

500mb wind speeds

We first looked into just the top 20 coldest winters seen further above on this page.  Tornado tallies began in earnest a little over a half century ago, so we looked at correlating April & May numbers from within in this era of reporting.  That allowed for nine of the top 20 coldest winters to be looked at.  What we found were varying numbers on a national to state to CWA scale.  The nation looked to be slightly above normal for tornadoes, with Illinois slightly below normal.

We then looked at taking into account more "big picture" patterns that are currently in place.  This included not only coming out of a very cold winter, but also a top 15 coldest March here in northern IL which we are on track for, a record to near-record low in tornadoes on the U.S. scale for March, the near record dryness across the southern Plains and southwest U.S. to start 2014, and finally the El Niño-Southern Oscillation (which has shown some skill for general severe weather predictability in certain phases for certain parts of the U.S.).  Below are the tornado tally results, with the departures from normal April & May tornado numbers listed in parentheses. 

Tornado Counts With Simliar Characteristics of Established Patterns

Note there is again a modest amount of variability. The 1996 year did have a high number of spring tornadoes in Illinois, but most of those were part of the largest outbreak on record for the state on April 19, 1996.  If it was not for that one day, that season would have been well below normal for April & May.  All years did have at least a tornado in the local area in April & May, with four of the six having significant (EF-2 or stronger) tornadoes. 

Takeaways from this would be that while it is very challenging to give an indication to a severe weather season's storm frequency and magnitude, the pattern presently established has not been one conducive for storms, due to regular cold and dry air intrusions.  Such a pattern has limited the tornadoes to a potential all-time record low across the nation in the month of March.  The frequency of low pressure systems (including multiple deep ones recently) and high shear episodes that can often be brought along with such scenarios may allow for severe weather episodes later this spring in the middle of the U.S., including possibly robust severe weather given the wind shear, if strong warmth and high moisture can be drawn back.  Such was the case with the November 17th outbreak.  This would require at least a partial pattern shift however, and that is not in the immediate forecast. 

Matt Friedlein
Lead Forecaster
3/29/2014


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