(11:45AM - 6/8/20) The remnants of Tropical Storm Cristobal are expected to move through the region on Tuesday and Wednesday, bringing the potential for heavy rain, flooding, high winds and severe t'storms to the region.
Since 1886, there have only been 15 instances of documented tropical cyclone remnants having directly affected Illinois, which makes what will occur this week fairly unusual and rare. Tropical Storm Cristobal will end up being the storm 16th such occurrence. The most recent occurrences were Tropical Storm Alberto in May 2018 and Hurricane Isaac in Aug/Sept 2012. The most notable and somewhat recent occurrence was Hurricane Ike in Sept 2008, which brought upwards of 6-12" of rain and record flooding to portions of the state, as well as widespread high/destructive winds to Indiana and Ohio.
We are now less than 12 hours out from the first impacts of what will be the remnants of Tropical Storm Cristobal beginning to affect the state. There continues to be a high amount of agreement among model guidance regarding track of this storm, as well as the effect it will have on the state with multiple types of significant weather. The remnants of Cristobal have already moved northward from the Gulf Coast, and are now soon to be moving into Arkansas. This system is expected to move up through Missouri, into the vicinity of the tri-state (MO/IL/IA) border area, then on up into Wisconsin...before exiting into Canada. It is also continuing to look likely that this will continue to be a warm core storm system and will hold on to tropical characteristics as it moves through the area...Which means it will likely still be a tropical depression as it moves through the region. This is something that is very rare, but not totally unheard of.
Heavy rain, flooding, high winds and severe t'storms/tornado threat will all be likely across the state during the period. We will break each threat down below individually...
Heavy rain and flood potential...
With the track of the storm system being near or just west of the Illinois border, the heaviest rainfall and highest flood threat will likely stay just west of the state. This is usually the case with weakening tropical systems or remnant tropical systems in our region, in that the heaviest corridor of rainfall and worst flooding is along and west of the track of the storm system. However, that does not mean the state is out of the woods. Northwest, Western and Southwest Illinois will be near the track of the storm system, and will still be in line for heavy rainfall, possibly upwards of 1.00-3.00". This will lead to a low flood threat for this area. Elsewhere across the state, periods of heavy rainfall will be likely, with rainfall totals under 1.50" and more of an isolated flood potential being possible.
High wind threat...
At this time there it looks as though there will be two periods of high wind potential across the state. The first period of high winds across the state will be from Tuesday morning into Tuesday night. During this time wind gusts of 35-60MPH will be likely, with higher gusts possible in Northeast Illinois and in/near t'storms. It should be noted that if there is significant cloud cover in place, it could hinder the higher end of the scale wind potential. On the flip side, if there is ample clearing, this could allow for more mixing of the atmosphere, which would mean the high end of the scale (or higher) wind potential being more likely. The second period of high winds across the state will be from Wednesday morning into Wednesday evening. During this time wind gusts of 30-50MPH will be likely. Given there will be two periods of high winds, the length of time high winds will be occurring and the severity of the high winds...Some damage and power outages will be possible, if not likely.
Severe t'storm/tornado threat...
The whole state will be in the eastern quad of this storms system, which is usually a favorable area for a severe t'storm/tornado threat with a remnant or weakening tropical system in our region. A very tropical environment will be in place during this period, which will differ from our normal severe t'storm environment we usually see in the spring/summer. This tropical environment will feature low instability, high moisture, high shear and high forcing. Several bands/arcs of convection will likely sweep across portions of the state, from early Tuesday morning through Wednesday morning. At this time we have much of the state in a minimal threat for severe t'storms. However, should clearing and more destabilization look likely on Tuesday, the severe t'storm/tornado threat could greatly increase. This is something that will be closely monitored for future updates. The main threats from any severe t'storm will be damaging winds and a few tornadoes. It should be noted that in this tropical environment, lightning will likely be limited with any given t'storm.
Below are the high wind, severe t'storm and flood forecasts for this event.
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