Monday, April 30, 2012

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.

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.

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.

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.

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.