Keeping in mind yesterdays Storm Prediction Center Outlook for Day 1 had a moderate risk area and a 15% hatched area for tornadoes ..The storm reports look like this so far...
Not one tornado was reported for the day thus far.
The above is our outlook for today the 18th. Once again the red zone is where we think the greatest risk of severe will be based off the NAM/SREF and ECM ..and also would be the area that would have a chance of a Tornado.
A stationary front goes from off the coast around the carolinas back towards the west across Ohio to Illinois to a low pressure on the Kansas /Missouri border to another area of low pressure around the panhandle of Tx with a cold front trailing off to the SW..
The stationary front will lift north as a warm front and the low pressures will move to the NE and in doing so a cold front will be marching to the east. It is this cold front that will be responsible for another day of severe weather across parts of the USA..
The timing of this cold front looks to be around 06 Z or 2 AM EST (1 AM CDT) across western KY and TN and closer to 8 AM friday morning EST (7 AM ) for central and Eastern Areas of KY and TN..
Due to the timing of this front we think that places in Western to Central KY and TN will be dealing with more in the way of Garden Variety type thunderstorms and heavy rains then actual severe weather. There could be some isolated severe in those regions which would be in the form of gusty winds with the front and possible hail..
12 Z ECM has no CAPE across any of KY or TN and CAPE is one ingredient necessary for severe weather. However ...lets take a look at the severe weather parameters from the NAM..
CAPE is generally 500-1500 which is on the meager side. Generally when one thinks of a severe outbreak they would like to see CAPE in the 2000 + range..
Lift index will be about -4 to -5 but greater across the south around Louisiana
Shear depending on what time of the day will be 30-50 knots and 60 + knots down across eastern TX but the greatest shear will be further to the west where 90 + will be.
Helicity a thin stripe stretching from N to S which is in the 500 range ..
EHI +1 or higher again allocated fairly well with the higher Helicity. Now keep in mind this image is at 5 PM in the afternoon ..so those that are in central and western KY and TN are not really dealing with any precipitation at that time frame as the front does not arrive till the overnight hours and by the time the front does arrive the EHI looks like this..
Well below 1 except for locations further to the south ..
Finally temperatures will be in the 70s and 80s..
So in summary the greatest parameters are actually to the west and south of KY and TN so we have put the greatest risk to allocate with the greatest parameters. As the storms move towards the east with the cold front they will be going into parameters which are not really conducive for severe weather and with the timing of the front and the heaviest precipitation any storms should weaken and the main threat would be garden variety thunderstorms with heavy rains. In areas to the west they will be looking at Gusty winds along with Large Hail and the potential for tornadoes...
Start off with the outlook itself which is posted above . We think the greatest threat for severe weather is going to be from OK then Northeast Into Missouri and East into Ark. This outlook is based on the NAM and the SREF with a blend of the ECM.
First the culprit responsible for this severe weather event will be a low pressure developing over the OK /TX border and then moving NE from that location with a cold front extending to its south... brief diagram showing this..
As the low pressure moves NE the cold front will press south and off towards the east. As is generally the case the greatest chance of severe is to the North of the area of low pressure and we see this being no different .
There will also be a stationary front draped across the region as well which turns to a cold front once across the east which was responsible for some of the severe weather which occurred on the 16th.
Once again we think that those located in TX will be spared the greatest severe due to two reasons.
Reason # 1 is the timing of the cold front which is going to be between 6 Z and 12 Z or 1 AM and 7 AM CDT.
Reason #2 is that the region is pretty well CAPPED up thru about 30 hrs... This is shown here with the CINH
Which this graph breaks down what those #s mean
| 0 - 50 | Weak Cap |
| 51 - 199 | Moderate Cap |
| 200+ | Strong Cap |
Also as the enhanced water vapor shows the greatest moisture is actually breaking out over Eastern TX and the eastern GOM..
The image below the satellite is the NAM which shows moisture from hrs 27 to 30 or 10 PM to 1 AM CDT and the moisture is North of the TX /OK border.
So we strongly believe that the greatest severe weather will be north of that region and this is also based on the parameters as well..
First off its going to be a hot day across the region with temperatures in the 80-90 degree range with dewpoints in the 60s..
Behind the front we will be looking at temperatures cooling into the 50s
When you have a temperature drop such as shown it generally brings about a severe weather event and this will be no different.
The red zone is based on the EHI and where there is no CINH to hinder the severe ..
In this same general location the Helicity is quite steep as well..
There is plenty of Lift in the atmosphere ..
And ample enough shear to create the potential for Tornadic activity within the red zone on the map.
This shows as much as 100 knots of shear coming into the region. This is probably over doing it but this is about as extreme as one can get when it comes to wind shear. CAPE which is like the fuel to add to the fire is also at 1000 or above ..
So we have all severe weather ingredients in place for severe weather to take place across the region.
Further to the east in locations like KY and TN the risk for severe is much lower due to low parameters in place. However the stationary boundary could act as a trigger for some severe storms where the main threats would be wind and or hail with some heavy rains.
For those in KY and TN your timing looks to be overnight thursday night between 2 AM and 8 AM for the front to cross and garden variety type storms with heavy rains.
We are going to stand in complete contrast to SPC with the Day 2 outlook they has issued yesterday afternoon at 17:30.
As you can see from the current radar you can almost pick out exactly where the cold front is . As all the heavy rain with some garden variety or non severe storms are along the front.
You can also see this on the surface map as of 11 PM
For the rest of tonight ..there should be heavy rain with nothing more then isolated severe as this batch of rain and the cold front makes its way to the east. It will be crossing western portions of TN and KY between 8 AM and 2 PM in the afternoon.
And in those areas rain will clear out between 2 PM and 8 PM.
Nothing is to impressed tonight with severe weather for Thursday. We have the SREF significant severe which looks like this..
Notice how you are missing the dark red other then in the GOM? This is not an impressive map.
The NAM severe parameters ..CAPE
The greatest CAPE is over the Southeast and this is at 5 PM right around the peak of daytime heating.
There is also sufficient lift in the atmosphere...
Helicity is greatest across the Northern Tier ..However ..EHI is only isolated locations of at or above 1..
The greatest parameter in favor of severe would be the shear and this is located over the southern sections..
As the triggers we have a semi quasi stationary front across the northern tier with an impulse or low pressure area traveling across it and across the south we have a cold front that will be making its way towards the east.
With the EHI not very impressive we are not seeing this as a tornado day..perhaps an isolated one here and there but nothing substantial. The main threats will be gusty winds with the front and hail with any of the severe storms..and of course heavy rains.
We are not going with a red zone because of the over all parameters not being impressive enough to warrant a red zone. Greatest potential lies over the Southeast region for the greatest chances of severe weather!
The first main severe weather event of the season should start to take shape tomorrow evening into the overnight hours. An arctic cold front will be making its way to the south and to the east along with its associated trough. Air out ahead of this cold front is warm..
As you can see by looking at the first image the air behind the front is colder ..of course it will not be that cold into the south. However .. the front will cause temperatures to drop from the warmer levels.
Timing. Timing of the front looks to be in the over night areas and should be pass the Falls region of TX by 12 Z wednesday or 8 AM wednesday morning.
During the day across the south we will be dealing with a CAPPED environment. You can see this when you look at the CINH which is an inhibitor to severe weather.
So we are really expecting nothing to fall across that area thru about 8 PM. The guidance is in good agreement with this as well..
The above is what falls by 2 AM.. and there after by 8 AM (which is when the front will have passed thru NC TX)
So lets take a look at the severe parameters that will be in place. And the first one we are going to look at is the shear. There is no doubt about it that the shear would certainly support a severe weather event with shear as high as 100 Knots.. Keep in mind though there is a CAP thru about 8 PM
CAPE is greatest at 30 hrs and again this is when things are just starting to get going in the south around the TX area. As you see they develop over the Falls to Jacks County area .. So this is the CAPE for 30-36 hrs ..
Now you can see here by 33 hrs the CAPE has shifted east away from the Falls region and is very minimal at about 250 ..
And by 36 it continues to shift further to the east. So the CAPE is supportive of severe weather and especially in areas to the east.
Next Parameter we are going to look at is the Lift Index which again there is plenty of lift in the atmosphere..
The final parameters we are going to look at is the EHI and the Helicity index. These are the parameters that are specifically used to look at what areas are likely to see tornadic activity.
You can see by these images that the EHI is greatest to the east of the Falls region and the areas that are above 1 stretch as far north as Iowa.
Just as the CAPE progressed east so does the EHI. Lets look at the helicity quickly..
Now this is at 33 hrs ..and remember by this point the EHI has shifted east so the Helicity while in place to the west is no longer lined up with the Greatest EHI but it is further to the east and stretching to the North as well.
So we have severe parameters in place that will create a severe weather event. With the CAP in place across the south till at least 8 PM and the timing of the precipitation being in the over night hours we think areas across the west in Tx with the parameters decreasing will end up having the risk of Large Hail and gusty winds. It is to the east and then north where the greatest CAPE, EHI, and Helicity is that we anticipate all modes of severe from Winds to Hail to Tornado potential.
The front will cross the south by about 8 AM wednesday morning but the area will continue to see rain falling across the region.
So with all the above stated...this is the day 1 outlook for the 9th
We will be monitoring the situation later in the afternoon and all evening long!
