Sunday, September 18, 2011

Long Range Forecast: Cool Air moves East, Ridge builds in the West

This is the Long Range Forecast until September 26, 2011.
This period will feature the cool Canadian High pressure moving east and a building ridge of high pressure in the West in the Nevada region. That ridge will expand eastward and eventually begin affecting the Midwest and possibly even the East Coast. Here's the current 8 day temperature anomaly shown in Figure 1, the visual aid of the cool air moving east in Figure 2, and the building ridge in the West in Figure 3.
Figure 1

Figure 2

Figure 3 (Upper Right Image- red line moving far upward shows  the building high pressure.)

NAM projects Up to 2.4'' to Fall in Chicago Tonight

The NAM is projecting up to 2.4 inches of rain to fall in a very narrow strip which includes Chicago in a 24 hour period. This is an extremely heavy amount of rain in such a short period- something that could cause a flooding event.
Because this is a very intense amount of rain, we have looked into the possibility of a heavy rain cell occurring over this area due to its locality.
It does appear that from tonight into the 10 am period tomorrow morning may have several yellow cells appearing on radar over the same area in a very eerie coincidence. Yellow is defined as moderate rain on radar reflectivity.
We will closely watch this solution this evening to keep you in the know.

Your Weather Now: 9/18/11- 2:25 PM

Large patches of disorganized rain showers are moving eastward this afternoon across the Midwest. While this precipitation is mostly light rain, it is a nuisance. There does appear to be a bowing feature in southern Illinois which is likely producing heavier showers and thunderstorms, so be careful if you are around that area.

As of right now, temperatures compared to normal are in quite a hole, especially in the NW Illinois region back through South Wisconsin, Iowa, the south half of Minnesota and East Nebraska. That is the top left graph. The top right graph is current temperatures as of right now. The bottom two images show stations with temperatures in the coolest 10% vs. the 1981-2010 average (bottom right image), whereas the bottom left image shows stations in the warmest 10% vs. the 1981-2010 averages.

Cold Front to Ignite Showers this evening across the Midwest

A cold front will stretch down through the Midwest associated with a low pressure system in Canada. That front will ignite some showers going into the 7 pm hour this evening, with the heaviest precipitation from about 8pm-12am tonight. Here's this evening's forecast 500 mb chart, where we have outlined the cold front reaching down from Canada.
Since it is Fall, temperatures across the nation have gone to a point where the violent spring and summer thunderstorms are no longer something to worry about as much. They can be a threat, but not nearly as much as in the spring or summer. Thus, this evening, there will only be some showers and embedded thunderstorms. If you're really curious about where the convection/thunderstorms will occur, check the image below to see where convective precipitation will occur at around 1 am this evening.
The image is in millimeters, so it won't be as bad as you may initially think by looking at the map only without a legend.
Anyhow, below we have the overall set-up for this evening around 1 am below.
The image is from the GFS model, which gives the set-up. But the cool thing is that we have a model called the WRF that can show what the radar may look like in the future. That said, here is the forecast radar reflectivity for 1 am.
All in all, there will be several disorganized fragments of showers in the Illinois region, some more thunderstorms in the Arkansas region, and maybe some embedded thunderstorm pieces in the Wisconsin area into Michigan.
Stay with The Weather Centre for the latest information on this storm system.