October 18th Severe Chances

Folks we are going to start this off by looking at the Storm Prediction Center forecast and duly make note that this is a low confidence forecast.
We are not ourselves going to actually issue a map for today..Instead we are going to show you the reasons why we are not issuing a map for today...

If you recall we stated for yesterday for the KY and TN area there was no instability and without instability you do not have much chance of any type of widespread severe or concentrated severe and there was no reports in KY at all and isolated (3 or 4) in TN...no tornado's occurred there at all either despite the 5% risk that was in place...

So we are going to take a look at a few things already...
For starters temperatures are not forecasted to get out of the 60s across vast majority of the region..

In other words we really do not have much in the way of surface heat to work off of with this cold front approaching.

On neither the NAM nor the GFS do we see any type of Convective Available Potential energy. This is another similarity to yesterday in the TN/KY region.. See it must be understood that in order to have severe you need a match (CAPE) to feed into for severe to occur...

Another problem is the greatest lift is actually south of PA 

And the LI that is there in PA is right around 0. 

What about EHI? Well compared to yesterday (which produced 5 tornados on the day) ..

We really have a total lack of EHI that would come into play across the northern areas such as PA as well as areas to the south..

Meanwhile Helicity is greatest across NJ and into North Central NY and Central And eastern PA but we once again have the lack of Cape and EHI across the area..

Once again the only parameter that is in place that would be supportive of severe in PA is the SHEAR..

There is no lack of shear. Shear indeed is rather quite impressive but it was also this way yesterday in locations like TN/KY. Factor in that the moisture is not as robust with this system as it was yesterday..

The SREF latest run is not really impressed with any severe weather...

And you have to come to the logical conclusion that if there is going to be any severe it would have to be where the instability is located and this would be to the south of the PA region. Again we are not seeing anything on guidance that would indicate that anywhere in PA would get any type of tornado. We do not have strong surface heating in place...we have clouds already on the increase and temperatures are currently cold in the lower 40s... Lack of Parameters..
And the arrival of the cold front looks like timing wise across Western PA to be around or between 2 AM and 8 AM or 6 Z and 12 Z later tonight overnight into Friday morning..

So now with expected timing added to the above already parameters that are not really supportive with severe we can add to that the loss of what little daytime heating there is.

So across places in PA we are expecting to see rainfall and garden variety storms due to lack of any type of parameters. South of PA we could see some isolated severe ..some super cells are possible but there really is nothing to support much in the way of tornado's. We will not rule out an isolated one where the EHI is in isolated locales above or at 1.

All and all expecting more of a rainy day then a severe day by the time all is said and done!