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Big Story Weather Special Storm Report – October 18, 2012

October 18, 2012

redOrbit Meteorologist Joshua Kelly

A potent weather system has been impacting regions from the Great Lakes to the Atlantic Seaboard. Where did this thing start and why was it so strong?

The first thing we will look at is the 300mb level upper level wind flow chart analysis which shows us the winds associated with the Polar Front Jet. The reason it is important to look at this chart is because we need to evaluate the strength of the cold air being pushed southward.

(Image courtesy of F-5 Data)

Now, looking at the 300mb chart above we take note of the very bright oranges and reds that are on the map. The one we need to look at the most is what is lying in Colorado to Northeast Mississippi. This region is supporting our surface weather feature. The winds at this level are between 100-130kts and this wind is pushing in the cold air from the Northwest. The reason it´s important to know about this is that cold air sinks towards the surface, so we are seeing all of this air from above sinking down towards the surface. Most of it is sinking near the Northeast corner of Mississippi and that is where yesterday´s severe weather event took place.

The second thing we need to look at is the moisture that was in place for this event. Looking at the image below we see all of those dark colors representing moist air near the surface.

(Images courtesy of F-5 Data)

Surface moisture is crucial in making clouds that will rise with the help of surface heating. So, if we look across the state of Mississippi, we can see that surface dew-points were around 60-70F. That means the air is pretty saturated. As the temps and dew-points get closer together the air becomes saturated. The right image is our surface temperatures, and you can also see that they are right at about 65-70F. This means that the air was near 100% saturated allowing the formation of clouds to occur. What type of clouds do we see here? We had cold air aloft moving in over warm air near the surface. This is known as COW (cold over warm). This type of air is the moist violent combination you can get it forms Cumulus-nimbus clouds that can lead to severe weather super cells. So, by putting the cold air together with the warm moist air, we were only missing one thing and that was the frontal boundary which can be identified on the image below.

(Image courtesy of Meteorologist Joshua Kelly via RedOrbit.com)

The importance of the frontal boundary in this was to allow the warm surface air to get forced upwards into the atmosphere. Warm air likes to rise, and when we have this strong jet stream pushing cold air. Cold air likes to sink and when it meets with this warm air we get what happened last night — tornadoes and severe weather.

Now let´s look at a map of the region that was impacted from the October 17, 2012 storms.

(Image courtesy of Meteorologist Joshua Kelly via RedOrbit.com)

Looking at the map above we can see that the green arrow was the warm and moist surface air moving into the region and behind the purple arrow was the cold air aloft that was sinking into the region. Now the dashed line ahead of the cold front represents where the squall line formed last night and this region was where we saw the most intense storms last night.

Here is a list courtesy of the National Weather Service of where the tornadoes did occur.

1. Clarendon  Arkansas
2. Near Jericho Arkansas
3. Northeast of Shelby Mississippi
4. West-Northwest of Louis Mississippi
5. Six miles northeast of Forest Mississippi
6. Two miles south of Conehatta  Mississippi

Along with that there were well over 90 damaging wind reports that scattered from Missouri southward into Mississippi and Arkansas, Tennessee and Louisiana.

All of these cells were found along that squall line which was ahead of the cold front. This morning the cold front and line of storms moved into the Gulf Coast region and here is some great images that I was able to capture of the lightning as it moved through the region.

Photos taken by Meteorologist Joshua Kelly RedOrbit.com

October 18, 2012: From the images above you can see the lightning sizzle through the sky in this great cloud to cloud strike. This type of lightning is very hard to catch with a camera as it flashes through the sky at rapid speeds. You can get very good images if you capture it with your video recorder first and then take it into a media player and capture the image in slow motion.

The thunderstorms began to move into the coast around 5am and left the area by 7am. The total significance of the storms that hit this region included the following information from my personal weather station.

WGEEK: October 18th 545AM Winds SW35mph | Total Rainfall 1.45in | Frequent lightning and also mini rain swirls flying down the road during the max winds.


Source: redOrbit Meteorologist Joshua Kelly

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