(3:30PM - 3/29/19) Waves of rain and t'storms have spread across the state the past two days, with additional rounds rain and t'storms expected through Saturday evening.

The first wave of rain and t'storms pushed across Northern and Central Illinois Wednesday evening and night, with the second round having pushed across Central and Southern Illinois Thursday afternoon into this morning. Rainfall amounts from these combined rounds ranged from a trace to 0.25" across Northern Illinois, to 0.25-1.00" across much of Central and Southern Illinois.

The main round of rain and t'storms is still to come, from this evening into Saturday evening. Areas of rain and t'storms will spread across the state this evening, continuing in periods overnight and into Saturday afternoon, before ending from west to east by Saturday evening. The heaviest rainfall totals will likely be across Central Illinois, where upwards of 1.00-2.50" of rain is likely. Amounts across Northern Illinois will be 0.10-1.00", and 0.50-1.50" across Southern Illinois. 

These heavy rainfall totals will likely lead to minor to moderate flood potential. 

JP

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As we have stated in the last few articles, the Friday/Saturday period has always been the one that looked the most threatening to produce widespread heavy rains. It continues to look that way as we head into the afternoon and evening hours today as the area of low pressure system organizes and moves into and through the Midwest. This "event" will have the potential to produce significant rainfall amounts across portions of the state between this evening and early tomorrow morning, possibly upwards of two inches in spots.  

​I dig into the latest details below....

As we go through the day today, an large area of rain and embedded thunderstorms will organize to our west across the plains and then move into portions of Iowa and Missouri by the mid-late afternoon hours, as you can see below. The image is valid at 4pm and is still showing nearly all of Illinois still dry. 

Now, looking at a evolution of how this system plays out, this loop runs from 1pm this afternoon through 7am tomorrow morning, showing a large area of rain and thunderstorms moving east and ENE across a good portion of the state. Timing wise it looks like the brunt of the heavy rain and thunderstorm threat will come during the evening hours and through the overnight, with the northern half of the state seeing an end to precipitation by the early morning hours on Saturday. 

By early tomorrow morning, the area of low pressure will have moved east of Illinois and into southern lower Michigan which will mean the end of the rain threat across portions of the state behind the cold frontal passage. Warm and humid conditions will continue across southern Illinois however as you can see below where temperatures will still be in the mid to upper 50's ahead of the frontal passage. This will mean a continuation of rain across downstate while high pressure and more dry air moves in further north. 

This is just one models output of potential rainfall amounts and could be overdone somewhat but there is good agreement on widespread moderate to heavy rain and potential thunderstorms which would only increase that threat for significant rain totals. Some areas could see upwards of 1-2" of rain tonight and overnight from this system. Stay tuned for continued updates as the area of low pressure and associated rain move into Illinois later today and more so this evening. 

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We continue to eye the potential for multiple rounds of widespread rains and the threat of heavy rain, really beginning tomorrow night and through the day on Saturday. There will be a chance for some rain across the northern half of the state late tonight but the real threat begins later tomorrow. This will be brought on by several weather disturbances moving over a frontal boundary which will be the focal point for several chances of widespread rain. 

I dig into the details below, including timing and who could see the most rain from this...

As mentioned above, showers and maybe some isolated thunderstorms will push east and southeast late tonight and into tomorrow morning across a good portion of the state but we aren't expecting any heavy rain or flooding from this first appetizer of rain. The loop below runs from 7pm tonight through 7am tomorrow morning.

By Thursday afternoon and evening, a more formidable weather disturbance will push through the plains and into the Midwest, sparking the next round of rain and potential thunderstorms. As you can see below, this looks to be a more impressive and widespread area of rainfall as it moves through and out of Missouri late tomorrow night and into central and southern Illinois. Rainfall amounts with this wave of rain could easily reach a half inch to an inch in spots, especially across the southern half of the state. This loop runs from 3pm Thursday through 9am on Friday, showing the progression of that area of rain from the plains into the Midwest and our area. 

The biggest potential in all of this and the one with the most question marks is the system that could move through the Midwest Friday night and through the entire day on Saturday. Now, there remains some difference among model guidance with the handling of this system where some are further south and weaker and some (like the one below) are further north and stronger. The north and stronger solutions then lead to heavier rain amounts and further north across the state as well. This will have to be watched closely as a solution like the one shown would have some potential for not only heavy rain but also some backside snow....yes, I said that four letter word we all love and adore. 

Amounts are obviously still in question and up in the air so everything right now is more so just potential on what could fall so don't take these numbers below too seriously just yet. We will continue to send out updates as we get closer and model guidance begins to fine tune thoughts on both amounts and the location of heaviest rainfall. 

Our first TAM for the upcoming heavy rain event...

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(8:45PM - 3/26/19) A new storm system is expected to affect the region over the next several days, bringing the chance for heavy rain, t'storms and flooding to portions of the state.

Periods of rain and isolated t'storms will first be likely across Northern and Central Illinois from Wednesday evening through Thursday morning. After this time, periods of rain and t'storms will be likely across the entire state from Thursday afternoon into Saturday night. The combination of a stalled out frontal boundary across the state most of the period and high moisture content, will lead to the repeated rounds of rain and potentially heavy rainfall totals.

​Given repeated rounds of rainfall expected and rainfall totals upwards of 1-2" for a good chunk of the state...combined with the recent wet period and river/creek/stream flooding...additional flooding will be likely. Areas of highest risk will be those near rivers/creeks/streams that have recently seen flooding, with minor flood potential expected elsewhere.

Additionally, as colder air filters in on Friday night and Saturday, rain may turn to snow across portions of Northern Illinois. At this time only a dusting looks likely, though potential exists for slightly higher accumulations should some model guidance pan out.

JP

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A severe thunderstorm watch has been issued until 10pm for parts of southern and western Illinois. Thunderstorms have begun to fire across central Missouri and should strengthen as the evening progresses. These storms will eventually cross into Illinois. 

Large hail is expected to be the primary threat, along with some damaging winds. The tornado threat appears very low, but you can never rule one out when severe thunderstorms are present. 

Stay tuned to ISC as we will provide important updates as necessary. 

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(11:15AM - 3/24/19) A storm system pushing through the region has spread areas of rain and t’storms across the state this morning. This activity is likely to continue in periods into tonight across the state. A severe t’storm threat will also exist across Southern Illinois this afternoon and evening.

A warm front is pushing northward across Southern Illinois this morning and afternoon. South of this front an environment featuring low instability, modest moisture and modest shear will exist. As the low pressure and associated cold front approach the state during the afternoon, scattered t’storms will develop across Eastern Missouri into Southwest Illinois by mid-afternoon today. This activity will then push across much of Southern Illinois during the rest of the afternoon and evening. Given the environment in place, an isolated to widely scattered severe t’storm is possible, with the best chance being near and south of I-64 in Southern Illinois. All modes of severe weather are possible with any severe t’storm.

Below is our updated TAM severe weather threat forecast for this event.

(2:00AM - 3/24/19) A storm system pushing through the region will bring the chance for rain and t’storms across much of the state on Sunday. A severe t’storm threat will also exist across Southern Illinois Sunday afternoon and evening.

A warm front is expected to push northward across Southern Illinois Sunday morning and afternoon. South of this front an environment featuring low instability, modest moisture and modest shear will exist. As the low pressure and associated cold front approach the state during the afternoon, scattered t’storms will develop across Eastern Missouri into Southwest Illinois by mid-afternoon Sunday. This activity will then push across much of Southern Illinois during the afternoon and evening. Given the environment in place, and isolated to widely scattered severe t’storm is possible, with the best chance being near and south of I-64 in Southern Illinois. All modes of severe weather are possible with any severe t’storm.

JP

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After a somewhat chilly weekend and start of this week for some of us across the state, especially the northern portion of Illinois, there are growing indications and signals on medium range model guidance that a favorable pattern for warmer weather and above normal temperatures will develop by later this week. The entire week itself should be fairly quiet weather wise with near normal temperatures but things will improve by the end of this week as the large scale pattern changes to one that leads to a nice warm-up across the Midwest. 

I dig into the details below, including what days will be  warmest and how long will it last...

As we go through the majority of this week, our pattern will remain fairly stagnant and quiet but a slow moving upper level low will eventually be located across the western U.S. by Thursday and Friday and this will lead to a developing upper level ridge across the plains and eventually the Midwest. This upper level ridge is usually a good feature to look for when to expect warmer weather and above normal temperatures. By Friday afternoon (image below) the ridge axis (marked in red dashed lines) is centered off to our west. This will be the beginning of what looks to be a multiple day stretch of above normal temperatures across Illinois. 

As we get into the afternoon on Saturday, we can see now that both the upper level low shifted east to over the Rockies and the ridge axis has also shifted west, now located nearly overhead of us here in Illinois. This is a favorable pattern as mentioned for a good bet of above normal temperatures across the Midwest. 

As low pressure continues to inch closer across the plains, broad warm air advection (in red below) will commence and continue, especially during the second half of the weekend, which will help lead to that continued/multiple day stretch of warmth across our area. 

Getting a first look at potential daytime highs during this period, model guidance is in fairly good agreement on the surface high being overhead or near Illinois by Friday which would mean a good deal of sunshine and widespread mid to upper 50's and some 60's. 

By Saturday, the area of high pressure would move east, allowing for strengthening warm southerly winds to potentially boost temperatures into the 60's over a larger area. 

We will not get into Sunday just yet but this looks like a several day period of warm weather and above normal temperatures across a large area, including Illinois from late this weekend and through the upcoming weekend. It is certainly possible it continues into the beginning of next week as well so stay tuned! 

(11:00PM - 3/16/19) An update on the expected snow event for portions of the state tonight into tomorrow morning...

Scattered areas of snow will be pushing into the Quad Cities area within the next few hours. This activity will then push across portions of Northern and Central Illinois overnight and into Sunday morning, before ending by noon Sunday. Periods of moderate to heavy snow is possible at times. Scattered rain showers will also be possible for portions of Central Illinois.

Evening model guidance has come in slightly weaker and drier with this disturbance, with accumulations for most affected areas being around a dusting up to 1”...though isolated higher amounts are possible.

JP

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Everything looks to be on track with our quick moving and fairly weak weather disturbance that is currently pushing into portions of the Midwest this evening and will lead to a quick hitting round of accumulating snow across portions of Illinois later tonight and into tomorrow morning. As mentioned earlier, this will not be a big deal event but given we are now into the middle part of March, it is somewhat noteworthy and worth mentioning. 

The latest on this system follows below...

Our wave is currently moving across portions of Iowa this evening and will continue southeast into and through Illinois later tonight and through the overnight hours. 

As we get a look at current radar across the Midwest, we can see that precipitation continues to slowly develop to our west across Iowa and this will eventually move into portions of western and northwest Illinois later this evening. 

Snow will continue east and ESE overnight tonight in a fairly narrow corridor which continues to be well modeled on high resolution model guidance. Even though snow will fall over a small area, it could snow rather heavy or intense in the band given the favorable ingredients in place for a few hour period of heavy snow. This could lead to a quick 1-3" of snow in spots wherever this band establishes itself. 

Snow will quickly end from west to east early tomorrow morning with the rest of the day quiet and drying out with high pressure moving in from the west. Our thoughts on snow totals has not changed much and we will update the map below if need be later tonight.