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.

First Significant Snow of the Winter in Illinois

It looks like winter has finally arrived – we knew it was only a matter of time.

Midwest

Here are the snowfall totals for the past 24 hours across the Midwest. The largest snowfall in the region was Davenport, IA, with 10.2 inches.

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Illinois

Here are the snowfall totals for the past 24 hours in Illinois. The official snowfall for Chicago was 6.4 inches, observed at Chicago O’Hare Airport. Rockford reported 5.3 inches. The largest snowfall in the state was 9.4 inches near Morrison (IL-WD-5). Other large totals include Elburn (IL-KN-96) with 9.0 inches and Dixon (IL-LE-10) with 8.5 inches. These are all CoCoRaHS volunteer observers, trained and using standard equipment to observe snowfall.

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5th Warmest November, 2nd Warmest Fall in Illinois

Temperature

This was the 5th warmest November on record for Illinois, based on preliminary data. The statewide average temperature was 47.4 degrees, and 4.9 degrees above normal. Here are the top ten warmest Novembers in Illinois since 1895:

  1. 2001 with 49.9°F
  2. 1931 with 49.1°F
  3. 1909 with 48.8°F
  4. 1999 with 48.4°F
  5. 2016 with 47.4°F 
  6. 2009 with 47.2°F
  7. 1902 with 46.9°F
  8. 1990 with 46.8°F
  9. 2015 with 46.6°F
  10. 1913 with 46.4°F

It was also the 2nd warmest fall on record for Illinois. The statewide average temperature for fall was 59.4 degrees, 5 degrees above normal. Only the fall of 1931 was warmer at 59.8 degrees. The climatological fall months are September, October, and November.

Precipitation

The statewide average precipitation for November was 2.51 inches, 0.96 inches below normal. Here are the maps for the total precipitation and departures from the 1981-2010 normals. Most of the state had below-normal precipitation with the driest spots in southern and western Illinois. The largest monthly total for November was 4.29 inches at the CoCoRaHS station (IL-FD-10) near Gibson City, IL, in Ford County.

The statewide average precipitation for fall was 8.20 inches, 1.74 inches below normal. While dry, it was not close to setting any kind of record. The driest fall on record was 1953 with only 3.93 inches of precipitation.

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Snow

Well … not much snow to report in November. Several sites in northern Illinois reported a trace of snow but only one site reported measurable amounts, Wonder Lake in McHenry County with 0.1 inches.

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The Edge of Drought – Southern Illinois

“The Edge of Drought” sounds like a soap opera or a catchy book title. However, southern Illinois is on the edge of a much larger drought in the southern US. The US Drought Monitor just released their latest map on Thursday, showing some of the southernmost counties in D1 (moderate drought). Other areas of Illinois are labeled D0 (abnormally dry).

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Here is a closer look at the Midwest where you can see the counties in Illinois.

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Because this is in fall, the impacts of drought are rather muted. So far there are no impacts on water supplies. However, there might be impacts on winter wheat and cover crops. Several counties in Kentucky and Indiana have had burn bans, as well as a few locations in Illinois.

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So what happened?

After a wet summer, this fall has been abnormally warm and dry. Here are the temperature and precipitation departures from normal since October 1 (click to enlarge). Rainfall was down 4 to 6 inches from normal in southern Illinois while temperatures were about 6 degrees above normal. The good news is that temperatures have really cooled off over the weekend and recent sub-freezing weather has brought the growing season to a close. Therefore, the demand on soil moisture and water supplies will be much lower. I rarely get worried about drought in the late fall and winter because of that.

And the forecast?

We are currently experiencing La Nina conditions in the Pacific Ocean. The drought outlook from the National Weather Service indicates that the southeastern drought is expected to persist this winter as there is an increased chance of drier than normal conditions in that area. As discussed in an earlier blog post, the NWS outlook for this winter has much of Illinois with an increased chance of above-normal precipitation. If this pans out, drought is not likely to spread in Illinois anytime soon.

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Latest NWS Outlooks for Next 3 Seasons

The NWS Climate Prediction Center released their latest outlooks for December, winter, spring, and summer. La Niña conditions are present and slightly favored to persist (~55% chance) through winter 2016-17. It is one of many players in our winter weather. Click to enlarge.

December

Illinois has equal chances (EC) of above, below, and near-normal precipitation and temperatures.

December-February

Illinois has an increased chance of wetter than normal conditions in the eastern two-thirds of the state. Above normal precipitation in winter typically translates into more snow.

March-May

Illinois has an increased chance of being warmer than normal in spring.

June-August

Illinois has an increased chance of being warmer than normal in summer.

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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These are average dates but the dates in a particular year can be much earlier or later. For example in Chicago, the date of the first snow ranges from October 12 to December 20 based on data from 1884 to present.

Normal November Snowfall

The early accumulations of snow are usually very modest in Illinois. Here is normal, or average, snowfall in November across Illinois, ranging from 1 to 2 inches in far northern Illinois to less than an inch for the rest of the state. The normal snowfall for November in far southern Illinois is zero. Notice that several of the sites in the southern half of the state have normal snowfall amounts greater than zero even though their average start dates are in December. In those cases, there were enough early snowfalls in November to affect the average snowfall in November.

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November – Warm and Dry Across US

Normally I write about Illinois, but the warm, dry weather experienced across Illinois so far in November covers a much larger area.

Here are the temperature departures from normal across the US. Almost all of the US has experienced well above-normal temperatures (except the East Coast). Illinois has been running about 8 degrees above normal. However, the temperature departures in the upper Midwest and the High Plains are 9 to 15 degrees above normal. The NWS forecast indicates that this pattern of warmer temperatures will persist for the rest of November.

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Here are the precipitation maps for November. Rains have been widespread across Texas New Mexico, and Arizona, as well as along the West Coast north of San Francisco. Some rain has fallen across central Illinois and parts of other Midwestern states. However, large areas of the US received less than 0.1 inches. Areas in gray have received no rain at all. 

The second map shows the precipitation as a percent of normal. Other than the Southwest, most of the US is well below normal on precipitation. Areas in red are less than 10% and gray areas are less than 2%.

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