New Outlook for December – Wetter, Colder in Illinois

The NWS released their latest outlook for December. They have Illinois with equal chances (EC) of above, below, and near-normal temperatures for the entire month. However, the day to day forecasts out to 14 days show Illinois having colder than normal temperatures on most of the days. The NWS product for weeks 3 and 4 suggest that warmer-than-normal weather will return in the second half of December. In general, I have higher confidence in the forecasts out to 14 days.
The December outlook also shows Illinois with an increased chance of being wetter than normal. This is true in the shorter range forecasts out to 14 days as well. Considering it’s December, a forecast of colder and wetter than normal conditions sure sounds like a recipe for snow. As you may recall, last December was notable for having almost no snow.
Click to enlarge.

Will It Ever Snow Again in Illinois?

With the streak of warm weather this fall, thoughts of snow are far away – but not for much longer. The first significant winter storm for the Midwest is on the horizon on Thursday and Friday. It will likely hit Nebraska, the Dakotas, and Minnesota, but miss Illinois (blue shading on the map below).
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So when can we expect to see that first measurable snowfall (0.1 inches or more) in Illinois?
Here is a map that we constructed a few years ago using data from 1971-2000. No surprise – the earliest dates are in the Chicago area and cluster around November 20. For the rest of the northern half of the state, the average date is towards the end of November. In central Illinois, I have always considered Thanksgiving to be the start of the snowfall season. The average dates get dramatically later as you go southward, getting closer to Christmas by the time you get to Carbondale and southward.
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Continue reading “Will It Ever Snow Again in Illinois?”

February Snowfall in Illinois

Much of the southern third of Illinois received between 1 and 12 inches in this last winter storm. The highest amount reported was 12.5 inches at Smithland with several other stations reporting in the 7 to 8 inch range, including Jerseyville with 7.8 inches, Newton with 7.8 inches, and Brookport Dam with 8.8 inches.

map1The northern third of Illinois received a considerable amount of snow from the January 31 – February 2, 2015 storm.

As a result, total February snowfall has ranged from 15 to 20 inches in northeast Illinois and widespread amounts of 5 to 15 inches across the state (first map below). As a result for the month to date, most of the state is 1 to 8 inches above average except for the northeast which is 8 to 12 inches above average (second map below).

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First Half of May in Illinois – Warm, Wet, And Then Snow

According to preliminary records, the first half of May was both warmer and wetter than average for many locations in Illinois. The statewide average temperature was 61.2 degrees, about 1.4 degrees above average. Meanwhile, this morning there are reports of snow falling in northern Illinois. Talk about weather extremes. This was after last weekend when we saw widespread reports of highs in the upper 80s and low 90s.

The statewide average precipitation was 2.43 inches, 18 percent above average. Here is a screenshot of the last 14 days showing the widespread and heavy rainfall in much of the northeast, east-central, and southern parts of Illinois with many sites reporting between 3 to 6 inches of rain. Parts of western and central Illinois have not been as wet with amounts in the range of 1 to 3 inches of rain.
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Snow in May? Read more on the Chicago NWS page. It looks like Rockford set a new record for the latest report of snowfall in the season. The Chicago record still stands at June 2, 1910.

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Map courtesy of the Chicago NWS office.

First Half of February – Cold and Snowy

It is Valentine’s Day. It is also halfway through February. The statewide average temperature so far in February is 11.5 degrees, 14 degrees below the long-term average.

The accumulated snowfall for February 1-14, 2014, ranges from 4 to 5 inches in far southern Illinois to and from 5 to 15 inches in the rest of the state. The band of heaviest snow extends from Quincy to Chicago with amounts of 12 to 15 inches.

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The long-term average (1981-2010) February snowfall is presented in this map below. Comparing it with what snow has fallen so far shows that many places have already exceeded their February average by more than double.

Click to enlarge. Illinois State Climatologist Office.  ISWS.
Click to enlarge. Illinois State Climatologist Office. ISWS.

Right now almost all of Illinois is covered in snow, as shown by this image from the National Operational Hydrologic Remote Sensing Center. Southern Illinois is covered by 1 to 4 inches of snow, central Illinois by 4 to 10 inches, and northern Illinois by 10 to 20 inches.

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Click to enlarge. NWS National Operational Hydrologic Remote Sensing Center.

The water content of that snow pack is substantial in the northern half of the state with amounts of 1 to 4 inches (first map below) with higher amounts in states to the north, and upstream, of Illinois (second map). According to the National Weather Service, temperature are expected to be much warmer in the coming week with highs across the state above freezing from Monday through Thursday along with the possibility of rain. It is possible that the snow pack will be greatly reduced by the end of the week and likely gone for many areas in the southern and central Illinois.

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Click to enlarge. NWS National Operational Hydrologic Remote Sensing Center.

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First Major Snow for Some in Illinois

The recent winter storm dropped snow across western and northern Illinois. The first figure is a screenshot of a product found at http://www.srh.noaa.gov/ridge2/snow/
The Davenport, IA, NWS office provided a map with more detail on the heaviest snowfall amounts in northwestern Illinois (second figure). The heaviest snow in Illinois was 11 inches at Apple River Canyon in far northwestern Illinois.

Snowfall map for the period ending on the morning of December 21, 2012. Click to enlarge.
Snowfall map for the period ending on the morning of December 21, 2012. Click to enlarge.

Snowfall map for December 21, 2012, produced by the NWS office in Davenport, IA. Click to enlarge.
Snowfall map for December 21, 2012, produced by the NWS office in Davenport, IA. Click to enlarge.

End of the Snow Drought in Illinois

With the looming winter storm expected to reach Illinois on Wednesday and Thursday, we should see the end of the 2012 snow drought in Illinois. Last winter’s snowfall season was cut short by warm and dry conditions in February and March. Meanwhile, the start of this winter’s snowfall was much delayed by the warm, dry conditions of the past several weeks. As a result, many sites in northern and central Illinois approached or set their records for the longest snow-free period.
Here is the map of total snowfall for this winter through December 17, how much we normally get through December 17, followed by reports on the remarkable snow-free season in Illinois. A few sites in western Illinois reported snowfall this morning.
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Normal snowfall from November 1 to December 17 for the period 1981-2010.
Normal snowfall from November 1 to December 17 for the period 1981-2010.

Here is the report for Chicago. Here are additional reports for central Illinois and northwest Illinois.

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE CHICAGO IL
1153 AM CST MON DEC 17 2012 /1253 PM EST MON DEC 17 2012/
...LATEST ON SNOWFALL RECORDS...
SUNDAY DECEMBER 16TH MARKED THE 287TH CONSECUTIVE DAY WITHOUT
MEASURABLE SNOWFALL AT ROCKFORD...BREAKING THE PREVIOUS
CONSECUTIVE DAY RECORD THAT HAD BEEN SET IN 1922. THIS IS NOW THE
LONGEST PERIOD OF TIME WITHOUT MEASURABLE SNOWFALL IN ROCKFORD ON
RECORD. THE LAST DAY WITH MEASURABLE SNOWFALL WAS MARCH 4TH.
CHICAGO HAS ALREADY BROKEN THEIR RECORD.
ROCKFORD
RANK # DAYS DATES W/O MEASURABLE SNOW
 1) 287 03/05/2012-12/16/2012+
 2) 286 03/03/1922-12/13/1922
 3) 284 02/26/1908-12/05/1908
 4) 282 03/31/1939-01/06/1940
 5) 270 03/06/2011-11/30/2011
 270 03/10/1999-12/04/1999
CHICAGO
RANK # DAYS DATES W/O MEASURABLE SNOW
 1) 287 03/05/2012-12/16/2012+
 2) 280 03/01/1994-12/05/1994
 3) 277 03/10/1946-12/11/1946
 4) 269 03/11/1999-12/04/1999
ON AVERAGE...CHICAGO HAS 226 DAYS IN A ROW WITHOUT MEASURABLE
SNOWFALL /SEVEN AND A HALF MONTHS/ AND ROCKFORD HAS 233 /ALMOST
EIGHT MONTHS/.
GIVEN THE CURRENT FORECAST...IT APPEARS BOTH LOCATIONS COULD HAVE
THEIR RECORD SNOW DROUGHT PERIODS COME TO AN END ON WEDNESDAY NIGHT
OR THURSDAY...WITH EVEN THE POSSIBILITY OF A BRIEF SNOW EARLIER ON
TUESDAY MORNING.
HERE ARE SOME STATISTICS REGARDING FIRST/LAST MEASURABLE SNOWFALLS...
CHICAGO ROCKFORD
 EARLIEST: 10/12/2006 10/12/1909
1ST AVERAGE: NOV 16 NOV 20
 LATEST ??/??/2012 01/07/1940
EARLIEST: 02/27/1997 02/06/1911
LAST AVERAGE: APR 4 APR 1
 LATEST 05/11/1966 05/11/1966
HERE ARE THE LATEST FIRST MEASURABLE SNOWFALLS FOR CHICAGO AND
ROCKFORD...
CHICAGO ROCKFORD
1) ??/??/2012 1) 01/07/1940
2) 12/16/1965 2) 12/21/1996
3) 12/14/2001 3) 12/19/2001
4) 12/12/1946 12/19/1948
5) 12/10/2003 5) ??/??/2012
6) 12/09/2011 6) 12/14/1922
 12/09/1948 7) 12/12/1916
8) 12/07/1914 8) 12/11/1924
9) 12/06/1994 9) 12/10/1970
10) 12/05/1999 12/10/1932
 12/05/1984 11) 12/08/1956
 12/05/1973 12/08/1927
 12/05/1909 12/08/1914
$$
MTF/RODRIGUEZ

Chances of a White Christmas

What are the chances of a White Christmas (defined as at least an inch of snow on the ground on Christmas Day)? The National Climatic Data Center has updated their US map to show the current 1981-2010 averaging period. The odds are high in the Rocky Mountains, the upper Midwest, and the Northeast. However, a White Christmas is rarely, if ever, seen in much of the southern half of the US or along the West Coast.
We did a similar map with more detail for Illinois last year (second map).  It should come as no surprise that the highest odds are in northern Illinois.  In general, the odds are about 40-60 percent in the northern third of Illinois, 20-40 percent in central Illinois, and 0-20 percent in southern Illinois.
There can be large differences from site to site. Snowfall is notoriously difficult to measures with two nearby sites having different results due to exposure to sun and wind.

Chances of a White Christmas across the US. National Climatic Data Center (NOAA).
Chances of a White Christmas across the US. National Climatic Data Center (NOAA).

odds of a white Christmas
The odds of a white Christmas in Illinois, based on 1981-2010 data. Click to enlarge.