Discussion Concerning Multi-Day Severe Weather Threat (Tuesday-Wednesday)

This is a discussion concerning the multi-day severe weather potential for Tuesday and Wednesday. Further dates will not be included due to a lack of confidence.

Overview
Zonal flow of the jet stream aloft will carry several disturbances along its track. One of these disturbances will involve the lifting of a warm front north into the northern US, engulfing the Midwest and Plains in the warm sector of hot temperatures and humid air. As this happens, a cold front will eventually become present in the western portion of the Plains states before moving eastward.

Factors
Because this will be a zonal flow jet stream, indicating that the jet stream will be on the Canada/US border, that is where we will find the dynamics of shearing associated with this event. Bulk shearing will take place in Wisconsin, which is a reason for the slight risk included in the entire area of Wisconsin. However, slightly lower temperatures and associated dewpoints will act to level out the severe aspect. Nonetheless, the remains potential for some intense weather in that area.
Farther to the south, in north Illinois and the like, hotter temperatures and higher dewpoints will make for a hot, muggy day. Because dry air requires more heat to rise, expect convection to be fairly quick to get started. This may very well be hampered, however, especially without the aid of the jet stream, which will be displaced to the north. However, temperatures in the 70s-80s may be able to ignite some convection. If this happens, the main threats would include damaging wind and large hail. Tornadoes do not appear to be a concern south of Wisconsin, in north Illinois.

Caveats
As mentioned previously, dry air requires more heat to rise. This normally would push down convection chances in Wisconsin, but the presence of the jet stream will cover that loss.

Summary
In the end, I find it more likely that the Wisconsin/Illinois border and north will get in on some of the strongest convection, while areas like North Illinois and possibly southern Iowa may be slotted out of this event. Time will tell.

Storm Prediction Center Issues Slight Risk for Wednesday; Higher Risk Possible

Probability of Severe Weather

The Storm Prediction Center did issue a slight risk today, which was not a surprise to me. However, in the discussion associated with these images, they did mention the potential of a higher risk upgrade in the future. That said, I think there is potential for some more intense weather than what is being pictured here.

I do not have a lot of time to write this, but I can tell you that I will be following this event closely, as it originally started out in the 4-8 day range- something reserved for eventual moderate risk areas or the like.

Severe Weather Possible Today for Plains, Ohio Valley

Overall Risk

Hail Threat

Tornado Threat

There is a risk of severe weather today in the Plains and Ohio Valley.

The Plains will experience a typical dry line scenario, with storms igniting in western Oklahoma, northern Texas, and southwestern Kansas. These storms will likely have some form of rotation in them based on tornado threats, so people in those areas should keep an eye to the skies.

There is also an enhanced threat for large hail in the areas mentioned above. Because the storms may get so large and may have some rotation, it is very possible that the intensity of the storms will create abnormally large hail.

A frontal boundary is currently in the vicinity of southern portions of the Ohio Valley, and this should be the focus for some showers and storms to develop today. If they do develop, expect the main threats to be wind and hail, with a very low risk of a tornado.

Flash Flooding Likely in Plains as Heavy Rainfall Continues Today

There is a 'high' probability of excessive rainfall in Northern Oklahoma and southeast Kansas, with a moderate threat in northern Oklahoma, southeast Oklahoma, southwestern and central Missouri.

As of 6:26 AM CDT, several flash flooding events were ongoing. With another 1-3 inches of rain expected today, the situation will only get worse today and tomorrow before things begin to ease off.

I advise everyone in the 'high' risk area to prepare for evacuations if you are by an overflowing stream of creek. If you are driving and see a flooded roadway, remember: Turn around, don't drown.

Storm Prediction Center Removes Wednesday Threat; Severe Potential Still Remains

The Storm Prediction Center has deleted the outline for severe weather on Wednesday into Thursday as the zonal flow of the jet stream ('zonal', meaning the jet stream is moving on the US/Canada border) is progressing several disturbances that are all equally hard to track. However, I still believe there is a severe weather risk associated with this potential.

What we see here is a chart of 925mb dewpoints for 7:00 PM CDT on May 2nd. What I do when I see high dewpoints is look for equally heightened temperatures to indicate that the area in question is indeed under a warm sector of air- one that may produce strong to severe storms. As you can see, the GFS model has a wide swath of high dewpoints from Oklahoma to the Ohio Valley. However, I am more concerned with particularly the Midwest and South Plains, due to what seems to be almost a propulsion of higher dewpoints directly from Texas to the Midwest. I am concerned with the Southern Plains due to the extreme dewpoint gradient in western Texas and Oklahoma.

As explained, high dewpoints can indicate instability. The image above is instability values, and you can see just how intense this could get, with widespread values over 2000 units, sufficient for severe weather. As I had mentioned earlier, there appears to be a stream of high dewpoints from Texas directly into the Midwest. This is directly reciprocated into instability values from Oklahoma into Missouri and Illinois. I worry that early showers and storms may depress instability values, but it does appear that enough instability could be in place for some stronger storms later on.
Let's take a look at the GFS/ECMWF comparison of 850mb temperatures. First is the GFS, next is the ECMWF. Both are valid at 7:00 PM CDT May 2nd.

A comparison reveals that the ECMWF involves a hotter warm sector than the GFS does. This additional warm air could very well mean that the ECMWF is positioning the severe threat higher than the GFS is. However, due to the restriction of many ECMWF graphics, I am unable to confirm this.

In summary, just because the SPC has removed the risk does not mean the risk is not there, because I do believe it is based on what I have shown above.

Andrew