Fall and Winter Forecast for Illinois

Summary: The NWS Climate Prediction Center has issued their forecasts for September, September-November (Fall), and December-February (Winter). Illinois has an increased chance of being warmer than normal this fall, and wetter than normal this winter.

According to the Climate Prediction Center, the main factors in the forecast are the recent warming trends and the expected La Niña. While the conditions in the Pacific are in the neutral stage between El Niño and La Niña, there is a 55-60 percent chance of a weak La Niña during fall and winter.

Fall

The September forecast (top row) has Illinois and the Midwest with equal chances of being above, below, and near-normal on both temperature and precipitation. I call this a neutral forecast since there are no indications that we will be significantly cooler, warmer, wetter, or drier.

The September-November forecast (bottom row) has Illinois and the US with an increased chance of being warmer than normal. They are neutral on the precipitation forecast.

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Winter

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Forecast for October, Fall, and Winter – Warmer Than Average

The NWS Climate Prediction Center released their latest outlook for October and beyond. It looks like the warm-than-average weather is expected to continue for the next several months. The primary driver in the forecast is the ongoing El Niño in the Pacific Ocean basin.

October

Illinois has an increased chance of above-average temperatures for October. There is not much to report on precipitation in Illinois. We are between drier-than-average conditions to our northeast and wetter-than-average conditions to our southwest.

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October-December

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Latest Seasonal Forecasts for Illinois – A Mild Winter?

The NWS Climate Prediction Center released their latest seasonal forecasts today. Here are the results for Illinois. The biggest news is that Illinois has an increased chance of above-average temperatures and below-average precipitation for the winter months of December, January, and February. This forecast is based largely on the developing El Niño in the Pacific Ocean.

While the forecast of a milder winter may sound appealing, I would not leave the winter coat in the closet and throw away the snow shovel just yet. Two things to consider are: 1) this is not a 100% guarantee, other factors come into play in determining our winter weather, and 2) even a mild winter can contain short periods of intense cold and abundant snowfall.

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More on the seasonal forecast

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How February and This Winter Stacked Up in Illinois

Here are the time series plots of the statewide average temperature for February and winter (December-January-February) from 1895 to present (source: NOAA NCDC).

February

In the first plot, I have a red box around the temperature for 2014 and 2015. The only other time that we had a pair of extremely cold Februarys was 1978 and 1979. All the other cold Februarys were one-off events. According to NCDC, the statewide average temperature for February 2015 in Illinois was 19.5 degrees and the 9th coldest on record. Last February was nearly identical at 19.4 degrees.

plot1Winter

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Last Below Zero Weather of the Season? I Hope.

Here are the lows this morning, courtesy of the National Weather Service office in Lincoln. Areas in blue were below zero. Champaign-Urbana reached -9 degrees, breaking the old record of 4 degrees set in 1899.

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Of course, widespread snow cover (map below), clear skies, and calm winds were contributing factors in the hopefully last round of below-zero weather this season. nsm_depth_2015030605_Midwest

24 HOUR MINIMUM TEMPERATURE DATA IN DEGREES FAHRENHEIT,
FOR ILLINOIS AND THE SURROUNDING STATES, INCLUDING
24-HR DATA THROUGH 7 AM, FRIDAY MARCH 6, 2015.

 
  ILLINOIS 

    DANVILLE AIRPORT                      -10
    ELIZABETH                             -10
    FREEPORT                              -10
    MCHENRY                               -10
    ROCHELLE AIRPORT                      -10
    CHAMPAIGN WILLARD AIRPORT              -9
    DECATUR AIRPORT                        -9
    SIDELL 5NW                             -9
    STERLING AIRPORT                       -9
    PAW PAW 2NW                            -7
    WATSEKA                                -7
    MATTOON AIRPORT                        -6
    OGDEN                                  -6
    PANA SEWAGE PLANT                      -6
    PAXTON 2WSW                            -6
    ALTONA                                 -5
    AURORA AIRPORT                         -5
    DIXON                                  -5
    DWIGHT                                 -5
    LINCOLN NWS                            -5
    NEOGA 4NW                              -5
    ROBINSON WTYE                          -5
    ROCHELLE                               -5
    ROCKFORD AIRPORT                       -5
    ROSICLARE                              -5
    WAUKEGAN AIRPORT                       -5
    BARRINGTON 3SW                         -4
    EFFINGHAM 3SW                          -4
    KEWANEE                                -4
    PARIS SEWAGE PLANT                     -4
    RAMSEY                                 -4
    SULLIVAN 3S                            -4
    MONMOUTH                               -3
    MUNDELEIN 4WSW                         -3
    TUSCOLA                                -3
    BROOKPORT DAM                          -2
    CARBONDALE AIRPORT                     -2
    CHICAGO DUPAGE AIRPORT                 -2
    COAL CITY 4NNW                         -2
    KANKAKEE                               -2
    LACON AIRPORT                          -2
    PRAIRIE CITY 2S                        -2
    GRAND CHAIN DAM                        -1
    MINONK                                 -1
    MORRIS                                 -1
    MT VERNON                              -1
    OLNEY 2S                               -1
    BLOOMINGTON 5W                          0
    CHICAGO OHARE AIRPORT                   0
    GALESBURG                               0
    MOLINE AIRPORT                          0
    OTTAWA 5SW                              0
    SMITHLAND LOCK AND DAM                  0
    SPRINGFIELD CAPITAL AIRPORT             0
    WINDSOR SEWAGE PLANT                    0
    ELGIN                                   1
    JOLIET LOCK AND DAM                     1
    LAWRENCEVILLE-VINCENNES AIRPORT         1
    MACOMB AIRPORT                          1
    PERRY                                   1
    SPRINGFIELD NE                          1
    AURORA                                  2
    CASEY                                   2
    CHICAGO BOTANIC GARDENS                 2
    GLADSTONE LOCK AND DAM 18               2
    JACKSONVILLE                            2
    NEW BOSTON LOCK AND DAM 17              2
    NORMAL 4NE                              2
    PARK FOREST                             2
    WINCHESTER                              2
    GRIGGSVILLE                             3
    PEORIA INTERNATIONAL AIRPORT            3
    RUSHVILLE 4NE                           3
    WHEATON                                 3
    CHICAGO WHEELING AIRPORT                4
    JERSEYVILLE 2SW                         4
    PITTSFIELD                              5
    BENTLEY                                 6
    CHICAGO MIDWAY AIRPORT                  6
    NASHVILLE                               7
    QUINCY AIRPORT                          7
    QUINCY LOCK AND DAM 21                  8
    KASKASKIA LOCKS                        10
    CAHOKIA AIRPORT                        14

Winter Finishes Cold and Snowy in Illinois

The statewide average temperature for the three winter months of December, January, and February in Illinois was 26.1 degrees, 7.5 degrees below average. While cold, it was not nearly as cold as last winter’s 21.7 degrees. This winter ranks as the 30th coldest on record.

winterThis winter started off mild with an average December temperature of 33.9 degrees, 4 degrees above average.  The average temperature in January was 25.7 degrees, only 0.7 degrees below average, and the average in February was 18.6 degrees, 12.3 degrees below average. See figure to the left, click to enlarge. Last winter, all three months were well below average.

Snowfall

Snowfall was above average for the winter from December through February. Most of that fell in February. December was snow-free for most of the state except in the far west. Snowfall was common in January but below average except for a band across northern Illinois. Major snows occurred in February to bring up the winter snowfall totals across the state. Above-average snowfall occurred across northern and western Illinois as well as far southern Illinois. The maps below show the observed amounts and departure from average.

map2map3

Precipitation

map1The average precipitation for December-February was 4.97 inches, 1.85 inches below average. In fact, most of the Midwest received below-average precipitation this winter (figure left). Precipitation is a measure of both rainfall and the water content of any snow. While we received above-average snowfall, the water content of that snow was not always great. In a typical year we can get rain in winter, but not so much this winter. This kind of precipitation deficit would be a concern during the growing season. However, in winter the water demand is low.

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.