Thursday, August 18, 2011

Short Range Forecast Discussion (For August 20-21)- Issued Morning August 18

Good morning everyone, we are here with a follow-up discussion from last night's potential for heavy rainfall/potential severe weather in the Plains.
A lot changed overnight. There is no longer a significant threat according to the models, but about 2 days away, we are watching the potential for a heavy rain/severe weather situation in the Lower Great Lakes.
Here's the NAM model at 7 PM CDT Saturday night.
The NAM has a low pressure system on the Tennessee/Illinois/Kentucky border. That low pressure system may lead to over an inch of rain in 6 hours in portions of Illinois. This would certainly have potential to provoke flooding. I would watch out for Illinois and Indiana in this situation.
The next model is the GEM Model, or a somewhat unreliable model from the Canadian weather center.
The GEM sides with the NAM model on this situation, but takes the low pressure system just a tad north of the NAM model. While that may not seem significant it actually brings the heavy precipitation farther north than the NAM. I have to say, for 2 days out, these two models are very close in their interpretations of what could happen.
The next model is the GFS, potentially the most reliable out of this trio of models.
The GFS lets this low pressure system fly north into North Central Illinois, where the heaviest precipitation will supposedly reside. It seems that, either way, the heaviest precipitation will hit the Illinois area. The question that the GFS brings in is how far north the dry slot of the low pressure system will be. Usually more concerning in winter storms, dry slots are slots of dry air that accompany a low pressure system.

The UKMET model has no low pressure system, no heavy precipitation. Thus, it is discounted.

In summary, there is a real chance that heavy precipitation could hit the Illinois/Indiana area this weekend. This is not set in stone, just an idea of what COULD happen.
We will brief you again tomorrow or tonight, but we will not be available from 5 pm to 8 pm.

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