Monthly Archives: February 2015

February – East Freezes While West Warms


This map was created by the PRISM climate group out of Oregon State University. You can visit their homepage at

While Illinois and the eastern half of the US freezes, temperatures in California and the West are well above average this month. Here is the map of temperature departures from average for the first 25 days of February. This pattern of extremes was the theme of 2014, diminished in December and January, only to return in February 2015. The temperature pattern is a result of a persistent ridge of high pressure in the West and a trough of low pressure in the East. This is discussed in some detail over at

Goldilocks’ Porridge: there is a tiny white strip on the map from Montana, through the Plains states, and into Texas, where temperatures are within a degree of average – not too hot, not too cold, but just right.

February On Track To Be Among The Coldest on Record for Illinois

image004February 2015 is on track to being one of the coldest February’s on record for Illinois. Data through February 24 puts the statewide average at 19.4° F. This is 11.5°F below average and slightly colder than last February’s 19.4°F. Before February, this was shaping up to be a mild winter with near to above-average temperatures (see graph to the left, click to enlarge).

At this point, February 2015 is ranked as the 8th coldest on record, edging out 2014 (see table below). The NWS forecasts show that temperatures for the rest of February will be 15 to 20 degrees below average. Therefore it is possible that it could move up the ranks. I will post more on this at the end of the month.

Ten Coldest February’s in  Illinois

  1. 1978 (16.9°)
  2. 1936 (17.2°)
  3. 1979 (17.4°)
  4. 1905 (17.6°)
  5. 1895 (17.7°)
  6. 1899 (18.0°)
  7. 1902 (19.2°)
  8. 2015 (19.4°) ** as of February 24
  9. 2014 (19.5°)
  10. 1914 (20.6°)

Statewide records go back to 1895.

Will Spring Ever Get Here? Yes It Will.

With snow this weekend and another round of cold temperatures expected in coming weeks, it feels like spring will never get to Illinois. But it will arrive someday – I promise.

Earth's orientation to the sun on the equinox.

Earth’s orientation to the sun on the equinox. Click to enlarge.

In coming weeks, many will point to the spring equinox as the start of spring, which is March 20 this year. The equinox is an astronomical event when the Earth’s axis is at a 90 degree angle to the sun (see figure). In theory, the length of day and night are the same around the world. However, due to how we calculate sunrise and sunset, and how the earth is not a perfect sphere means that the days and nights are not exactly equal in length on the equinox. However, that’s a story for another day.

The bigger problem with the equinox definition is that the spring and fall equinox*, as well as the winter and summer solstice, do not line up well with the annual march of temperature (see figure below for Chicago). With spring, temperatures on average are already warming significantly by March 21, compared to temperatures in January and February. By the arrival of the summer solstice, temperatures are already getting very close to their annual maximum.

image013As a result, many climatologists and meteorologists use calendar month definitions that line up better with the average annual changes in temperature. It works best for summer (June-August) and winter (December-February) in capturing the warmest and coldest periods of the year. In spring (March-May) and fall (September-November), it works well at capturing the strong transition in average temperatures. Several professional have called the period March-May “meteorological spring”, but it is based on climatological data so the better term is “climatological spring”.

Of course, all of this is a bit academic. We all carry our own definition of spring that is probably more in line with nature – the first signs of green grass, the buds swelling on trees and shrubs, increased activity in wildlife (especially birds). I think the one thing winter does best is to make us appreciate spring even more.

*the use of words like winter, spring, summer, and fall, are in reference to the Northern Hemisphere.

Outlook for March – Cold in Illinois

The NWS Climate Prediction Center released today their outlook for March and beyond. There is still a 50-60 percent chance of El Niño showing up in the next few months but likely to be both weak and short-lived. I do not think it will be a major player in 2015.


First of all for March, Illinois and the Great Lakes region have an increased chance of below-average temperatures. That is no real surprise given the cold weather of recent weeks and expected below-average temperatures in the 14 day outlooks. We have equal chances (EC) of above, below, and near-average precipitation. Click to enlarge maps.


After an expected colder than average March, we see a reverse pattern in Illinois and the Great Lakes region with an increased chance of above-average temperatures.



There is not much to report for the heart of this summer in Illinois. We have EC for both temperature and precipitation.


Three Dog Night for Illinois As Extremely Cold Air Arrives

A cold-air outbreak is expected to impact a large part of the US east of the Rockies. Lows tonight expected to drop below zero tonight (first map) across Illinois and most of the Midwest. These extremely cold temperatures will come close to the record lows for February 19 in many locations in the state, but is not likely to break them.

Strong winds out of north are expected as well, causing NWS to issue a wind chill advisory for Illinois as windchill values fall into the minus teens and twenties. Values in this range can lead to frostbite of exposed skin in 30 minutes or less, as well as greatly increase the risks of hypothermia. Stay tuned to your local forecasts as this situation develops.

Even before this cold air outbreak, the statewide average temperature for February in Illinois was 4.4 degrees below average.

nws1Note #1. You can see how windchill is calculated on this NWS web page.

Note #2. Three dog night is a folk expression of how many dogs you will need to stay warm at night [one dog night = cold, two dog night = colder, three dog night = coldest].