July 18th Severe Weather Outlook

July 18th Severe Weather Outlook
We have decided to get an early jump on this particular outlook and whether or not the Storm Prediction Center ends up agreeing with a low end moderate risk or not is really irrelevant to what we are forecasting. There is going to be some very high CAPE in place or "fuel" as the cold front drops slowly towards the region. Temperatures out ahead of the cold front are going to be quite toasty and dew points are already climbing which is going to make it a very "soupy" feel to the day come tomorrow. When ever we have a cold front and associated trough dropping south from Canada into such a "hot" air mass this is always a recipe for what could be considered "explosive" development of thunderstorms.
We have been referencing last Saturday as a reference point for this event today..
Last Saturday was a very soupy feel to the day with the heat index near 105 degrees and the temperatures were in the 90s. We also had a temperature drop once the front finally cleared..Deja vu? Pretty much a similar set up but this time the fuel is a little higher then that time..and the front appears to be slightly stronger.
So lets look at the temperatures for later tomorrow..
http://www.twisterdata.com/data/models/nam/221/maps/2012/07/17/18/NAM_221_2012071718_F24_TMPF_2_M_ABOVE_GROUND.png
The NAM is suggesting that temperatures will be from 80 to about 100 degrees. This heat alone with out the severe aspect is very dangerous. Do yourself a favor and stay indoors till the sun goes down. Drink plenty of water , even if inside because you can still dehydrate when the heat outside is this bad..especially if your AC's are having issues working in this heat.
You can see the strength of this cold front , though the GFS is potentially over doing it ..once the front finally clears the area temperatures become at least 10 degrees cooler..
http://www.twisterdata.com/data/models/gfs/3/maps/2012/07/17/18/GFS_3_2012071718_F72_TMPF_2_M_ABOVE_GROUND.png
CAPE or Convective Potential Energy is showing to be as high as 4000 ..
http://www.twisterdata.com/data/models/gfs/3/maps/2012/07/17/18/GFS_3_2012071718_F24_CAPE_SURFACE.png
The NAM is in relatively good agreement with the GFS with high CAPE as well
http://www.twisterdata.com/data/models/nam/221/maps/2012/07/17/18/NAM_221_2012071718_F24_CAPE_SURFACE.png
Lift index across the area is at about negative 6 to negative 8.
http://www.twisterdata.com/data/models/gfs/3/maps/2012/07/17/18/GFS_3_2012071718_F30_LFTX_SURFACE.png
The one parameter on the down side is the SHEAR which is only about 30 knots across the red zone ..however..feel confident that the high CAPE amounts will cover the marginal shear.
http://www.twisterdata.com/data/models/gfs/3/maps/2012/07/17/18/GFS_3_2012071718_F30_SHRM_500_MB.png
HELICITY is not really a concern but the EHI is indicative of the potential for super cells across the region. Essentially PA east.
http://www.twisterdata.com/data/models/nam/221/maps/2012/07/17/18/NAM_221_2012071718_F30_EHI_3000_M.png
This is something that we will be re evaluating once 00z guidance comes out and will determine at that time "if" a greater then 2% tornado chance is needed.
At this point and time we feel that the main threat is going to be damaging winds that could be anywhere between 60-75 MPH. These storms will have the potential to cause power outages where they occur. These storms will also contain very heavy rain with PWATS in the order of 2.00+.. This means Flash Flooding is possible.
Stay tuned to your favorite weather source thru out the day tomorrow and we will be updating part of this with the EHI & Helicity after the 00z guidance comes out!