April 3-5 Severe Weather Outbreak Series: Storm Prediction Center Outlook (April 3)

Overall Risk:

The Storm Prediction Center upped the risk from Slight to Moderate in Northwest Missouri into East Kansas. The reason for that is not tornadoes, but for a threat of hail. That image will be shown below.
The next image will be the threat for large hail.

In the above image, we see the region of hail threat that sparked the moderate risk area. With that in mind, it can be expected storms with strong lifting will occur, lifting the raindrops up into the air, high enough to create hail.
The next image will be the tornado outlook.

The tornado risk above is aimed more towards North Illinois than anyone else. The Weather Centre indicates this goes along with Significant Tornado Parameters observed today.
Next image will be the threat of damaging winds.

The Damaging wind threat spans the tornado threat and hail threat, indicating the low level jet stream which will feed the storms will be strong tonight.
In summary, the worst weather is from North Illinois Southwest into Missouri and East Kansas.

April 3-5 Severe Weather Outbreak Series: 6z NAM/GFS Significant Tornado Parameters (April 3)

Images first from the NAM, then GFS.
NAM starting at hour 18

The NAM did push up on this Significant Tornado Parameter overnight, allowing for a hotspot to develop in North Central Illinois. There is where we are likely to see at least some weak tornadoes.
Next, we will feature the GFS, starting at hour 24.

The GFS definitely puts Northwest Illinois up as a hotspot for tornadoes, and it appears that is where the action will occur.

April 3-5 Severe Weather Outbreak Series: Supercell Parameter Concern- Southern Sector (April 2)

Images are from the NAM, starting at hour 33 and increasing by 3 hours every image.

This is an area of concern for the South, because supercells are much more of a deal than most people think. With proper winds, supercells are the most apt to produce tornadoes. Please watch out as we go into this event.

April 3-5 Severe Weather Outbreak Series: Supercell Parameter Concern- Northern Sector (April 2)

Above image is 18 hours out. All images below increase by 3 hours (example next image: 21 hours out.)

This is a series of images from the supercell parameter forecasts from the NAM.
We see a very defined area of supercell potential in the northern sector of the images. That said, the northern sector is likely to receive a multi-cell cluster of storm cells. These will be fed by the low level jet stream, which will provide fuel for the storms. The threat for damaging winds and tornadoes also increase.

April 3-5 Severe Weather Outbreak Series: Severe Weather Threat Indicator: April 4, 2011

April 3-5 Severe Weather Outbreak Series: 18z NAM/12z GFS Analysis

This is an analysis about the images issued previously in this post.

NAM ANALYSIS
The 18z NAM definitely pulled back on the way of tornado threat in North Illinois. However, that region is still outlooked as a big risk area, especially North Central Illinois.
The Weather Centre, seeing how volatile this situation may be, has issued an image for this situation.

The Weather Centre is concerned with the area outlined as an 'Elevated Tornado Threat' as a low level jet stream will provide the threat for damaging winds and tornadoes. With the Significant Tornado Parameter at levels that we view as extremely concerning, this will be a very tender and volatile situation.
More updates as they come.

April 3-5 Severe Weather Outbreak Series: 18z NAM/12z GFS Significant Tornado Parameter

NAM Model (Starting 27 hours out from now, going by 3 hours every image)

GFS Model

Write up issued next.

April 3-5 Severe Weather Outbreak Series: 12z NAM STP (Issued April 2)

The significant tornado parameter shot up in this NAM run in North Illinois. That area will be a good chasing area. However, it is incredibly hard, if not impossible, to predict areas where tornados may occur.

April 3-5 Severe Weather Outbreak Series: The Cap

This is part of the April 3-5 Severe Weather Outbreak series.
A cap is a region of negative buoyancy which suppresses the development of storms.
A strong cap is hard to break, thus storms may not develop.
A weak cap is easy to break, thus storms are likely to develop.
Regions with more negativity on the map indicate a stronger cap.
Below is a map of CIN (convective INhibition).

Here, we see a very strong cap over the Plains. That will be working to hold warm air in and make the atmosphere more unstable. Using this map, we can determine the Plains will likely get the brunt of this.
In the Souther Great Lakes, we see a much weaker cap. With that as weak as it is, it can be determined the worst weather will likely not occur there. That may be why the NWS office in that region only has North Illinois down for showers.
We will wait and see.

April 2: Significant Tornado Threat shifts North (April 3-5 Outbreak)

Upon immediate analyzation this morning of the Significant Tornado Parameter maps (STP), I discovered a couple new things.
1. The tornado threat had increased substantially across Central Illinois.
2. The tornado threat looms a bit larger over the Plains.
3. The tornado threat for where the storms began dropped off significantly.

However, some things stayed the same.
1. The system dropped off to the Southeast after hitting the Midwest.
2. The storms originated from the South Plains.

Just to give you an idea of how the threat shifted, below is Hour 48 from the NAM. Following that image will be hour 48 from the GFS model.

NAM 48 Hour Image above.

Now the 48 hour GFS image.

48 Hour GFS image above.

We do see a greatly differentiated threat with the models. 48 hours out is typically when the models have reached a consensus, but for difficult storms like this one, the consensus can be expected tomorrow morning.
(There is a new method for the GFS, but that is much less in terms of threat than the NAM as well. It is better to overguess and be wrong than underguess and have tragedy strike.)
I would take the NAM image, but Dr. Greg Forbes from The Weather Channel said that his specialized tornado forecast was 'moderate to high' a couple days ago. That is significant as his forecast is more short range.
That's the latest update on the storms. Another one will likely be issued tonight, separate from the forecast discussion.

Overall Severe Weather Risk April 3-5

This map is subject to potentially major changes.
The Weather Centre does believe the tornado threat will be in the Plains where the original squall line develops, with a fairly uncertain significant tornado risk in North Illinois.
The overall risk area for the first day expands across most of the Midwest and East Plains down south to the Gulf Coast.
The Risk Area for the day following will be the Southeast into the Eastern Seaboard.
This is definitely something to watch.

April 3-5 Tornado Threat Appears to be centered up North

The overall tornado threat will keep in the Plains, but the latest run of the Storm Prediction Center's SREF indicates the ingredients will come together to make up to a 20% chance of significant tornadoes in Illinois. North and Central Illinois, specifically.

Significant tornadoes are different from regular tornadoes. Significant tornadoes are strictly F2 or higher on the Fujita scale.
That said, with extreme caution, The Weather Centre is prepared to issue a dangerous situation bulletin going into the event.

Significant Severe Weather Outbreak Possible April 3-5

There is definitely potential for a significant severe weather outbreak for the Plains and South Plains into next week. We at The Weather Centre have obtained new images from an excellent source on this next outbreak.
First, let's outline where thunderstorms in general may occur.

The NAM is predicting that these storms will begin due to a low pressure system in the Oklahoma area. When these storms develop, it is crucial to know where the moisture output will be. With such a defined low pressure on this map, it can be expected a good moisture output will be present in the area.

These storms will develop into a squall line as another low pressure, with warm front and subsequent squall line. This squall line could be strong and very severe, with strong tornadoes possible. This is when we turn to another map, named the STP, or Significant Tornado Parameter. Below is that map with the same time period as the image directly above.

When such a parameter is as high as it is above, there is an extreme danger in that area.
Now, we will continue to the period where this risk moves north and east.

We definitely see a resurgence in this tornado risk as the cold front takes total control. A warm front will be dragging the moisture north.
A determining factor in tornadoes is also helicity, which is when there is updraft ROTATION in supercells. Values of 250 or higher indicate the greater potential for tornadoes.

Here, we see very high values of helicity on the brunt of the storm, suggesting tornadic supercells may occur at the beginning of the squall line.
This has been an in-depth forecast. This topic will be presented again in tonight's forecast discussion.