Widespread, heavy rains possible over next week in Illinois

As of April 25, the statewide average precipitation for Illinois is 2.8 inches, which is 94% of normal. However, we have several opportunities for widespread rains this week and into the weekend, according to the NWS precipitation forecast.

The first round of rain on Wednesday and Thursday has potential rainfall amounts of 1 to 2 inches across most of Illinois, along with the chance for severe weather.

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There is a risk of severe weather along with this system.

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From the NWS Storm Prediction Center 

...Illinois into the Great Lakes...

   Instability and low-level moisture will be less in this region
   compared to farther south but sufficient for an organized severe
   threat given favorable wind profiles. The stronger storms will
   likely expand into this region during the late afternoon and
   evening, with a few supercells and bowing linear segments capable of
   damaging wind, large hail and a couple of tornadoes.

The second round of rain over the weekend has potential rainfall amounts of 2 to 5 inches in the southern half of Illinois and 1 to 2 inches elsewhere in the state. Keep in mind that this rain will be falling on soils already saturated from the mid-week rains, raising the potential for flooding. The cutoff for this map is Sunday morning and more rain is expected later in the day.

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Put that all together and we are faced with the potential for widespread heavy rains over the next 7 days, ranging from 2.5 inches in northwest Illinois to almost 7 inches in southwestern Illinois (below).

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Here is what the NWS office in Lincoln IL says about the situation.

Hydrologic Outlook
National Weather Service Lincoln IL
539 AM CDT Tue Apr 25 2017

...AREAS OF HEAVY RAIN ON WEDNESDAY AND AGAIN THIS WEEKEND...

A wet weather pattern will set up through mid week, and persist
into the upcoming weekend.

As a cold front approaches from the west, showers and
thunderstorms will begin spreading into areas west of I-55 later
tonight, and overspread areas to the east on Wednesday, before
exiting the region on Thursday. The heaviest rain from this system
is expected to be from about I-55 westward, where amounts of 1 to
1.5 inches are possible by Thursday morning. Over east central and
southeast Illinois, rainfall of a half to 1 inch is likely.

This weekend, a slow moving storm system will combine with copious
moisture in the atmosphere, to produce additional heavy rainfall.
Much of this is expected between late Friday night and Sunday
morning. While it is too early to give specifics, there are
indications that a few inches of rain are possible during the
period over portions of central and southeast Illinois.

Runoff from this heavy rain will cause rises on area rivers and
streams, and may eventually lead to flooding. Continue to monitor
the latest forecasts, as the rainfall timing and amounts will be
adjusted as the heavy rain events approach.

$$

Geelhart

Historically, the statewide average April temperature in Illinois has increased by 2 degrees over the past century. April precipitation has increased by about 25 percent over the past century.

National Climate Assessment for Illinois

Earlier this year the National Climate Assessment for Illinois was released, tracking the historical changes in temperatures and precipitation in Illinois. You can find the full report for Illinois and other states at the State Climate Summaries website.

Here is Key Message #1

Average annual temperature has increased by about 1°F since the beginning of the 20th century. There has been seasonal variation in this warming, with average spring temperature increasing by about 2°F and average summer
temperature increasing very little. Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century.

Key Message #2

Precipitation in spring and summer has generally been above average over the past two decades, affecting agriculture in both positive (adequate soil moisture) and negative (delays in spring planting) ways. Precipitation in winter and spring is projected to increase, which poses a continuing risk of spring planting delays.

Key Message #3

Severe flooding and drought have occurred periodically in recent years. Future increases in extreme precipitation events and in evaporation rates may increase the intensity of both floods and droughts.

You may notice that two out of the three messages relate to increases in precipitation and especially heavy rainfall events. The graphic I found most compelling was this one for the increasing number of 2-inch rain events with time. The caption explains how this graph was created. The increased frequency in 2-inch rain events seen since the early 1980s lines up very well with my experience and research over the years in Illinois.

il_obs-number-extreme-precip_v1_2
Figure 5: The observed number of days with extreme precipitation events (annual number of days with precipitation greater than 2 inches) for 1900–2014, averaged over 5-year periods; these values are averages from 43 available long-term reporting stations. A typical station experiences 1–2 such events each year. The number of extreme precipitation events has been above average since the 1990s. During the most recent 5-year period (2010–2014), Illinois experienced a record high number of events when stations averaged more than 2 events annually. The dark horizontal line is the long-term average (1900–2014) of 1.62 days per year. Source: CICS-NC and NOAA NCEI.

As shown in this map from the US EPA website, precipitation across Illinois has increased by 10 to 20 percent in the last 115 years. Many of the surrounding states have seen similar increases in precipitation.
precipitation-download3-2016

As noted in the first key message, Illinois has experienced warming in the past 115 years of about 1 degree F. However, warming has been more pronounced in the northern and western states.
temperature-download3-2016

Above-Average Temperatures Expected to Continue through Fall

The NWS released their latest forecasts for May and beyond. Currently, the Pacific Ocean is in the neutral phase between La Niña and El Niño. There is much debate on if and when El Niño should return. It could happen in late summer.  Meanwhile, the theme running through the outlooks is the increased risk of above-average temperatures through the fall. Illinois has been running warmer than average in the last few years. In 2016, 10 out of 12 months were above-average. So far, every month in 2017 has been above-average.

  • January 2017: 5.7 degrees above average
  • February 2017: 10.1 degrees above average
  • March 2017: 1.9 degrees above average
  • April 1-19, 2017: 6.5 degrees above average

May: eastern portions of Illinois have a slightly increased chance of being warmer than average. I am going out a little farther on the limb and say that all of Illinois has an increased chance of being warmer than average, based on recent trends and the climate models. Meanwhile, most of Illinois and the Great Lakes are expected to have an increased chance of below-average precipitation. Click to enlarge maps. Continue reading

April Showers Bring May Flowers?

The first part of April has been warmer and wetter than average across much of Illinois and the Midwest. As these maps show, there is a wide band of 1 to 3 inches of rain stretching from Kansas, through Missouri, Indiana, Michigan, and Ohio (click to enlarge) in April. These rains have helped ease concerns of any developing drought after the dry winter. In fact, the concerns have reversed and center around delays in field work from wet conditions. Continue reading

March in Illinois – Lots of Snow and Rain

March Temperatures: The statewide average temperature for March was 42.3 degrees, 1 degree above normal. Temperatures swung from periods several degrees above normal and several degrees below normal with little time in-between. Several sites reported temperatures reaching into the 80s. The warmest daily report was Belleville with 86 degrees on March 21. Chicago Midway reported a high of 82 degrees on March 24. Meanwhile, the coldest temperatures of the month were experienced in the northwest quarter of the state, including Altona and Illinois City with a low of 6 degrees on March 25.

March Precipitation: The statewide precipitation was 3.62 inches, 0.66 inches above normal. The highest monthly total precipitation was Lockport with 7.22 inches. Precipitation was greatest in a wide band from Quincy to Chicago with amounts between 3 to 6 inches, which is 1 to 3 inches above normal. The driest area was in southeastern Illinois with only 1 to 2 inches, which is 1 to 2 inches below normal. Click on the maps below for a closer view. Continue reading

Some Rain, Low Streams in Illinois

7-Day Rainfall (NWS)

Here are the 7-day totals for the central US, capturing the rainfall over the weekend. As forecasted, the heaviest rains were in Missouri and along the IL/MO border. Shades of green represent 0.5 to 2.0 inches.Most of IA, MI, IN, and OH received moderate amounts of rain from this system. However, large parts of Illinois received less than 0.5 inches (shaded in blue).

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Streamflows (USGS)

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Outlook for Spring – Warm

Notwithstanding this week, the outlook for this spring is warm. The Climate Prediction Center released their outlook on Thursday for April and beyond. Right now both El Niño and La Niña are out of the picture. However, there is much uncertainty for future conditions in the Pacific. Some models suggest that El Niño may return by late summer. As we move forward, we should get a clearer idea about El Niño.

April

For April, Illinois and much of the Midwest have an increased chance of above normal temperatures. Illinois has equal chances “EC” of above, below, or near-normal precipitation. I call EC a neutral forecast.

April – June

Continue reading