September 18th Severe Weather Outlook...

September 18th Severe Weather Outlook...

While instability is NOT going to be off the walls and only meager at best ... Energy Helicity Index is on the impressive side ..Helicity Is on the impressive side and in addition to this SHEAR is o

n the impressive side..
Lets look at shear first ... we are going to look at 21 hours , 24 hrs and 27 hrs..and you can see that the shear goes from 30 knots to 70 knots +
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F21_SHRM_500_MB.png
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F24_SHRM_500_MB.png
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F27_SHRM_500_MB.png

So what this implies is that severe potential can indeed occur in the over night hours (despite unfavorable timing)

Here is the EHI
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F21_EHI_3000_M.png
You can see EHI is as high as 2-3 over East Central PA ...and at or above 1 in other areas..
HELICITY
Helicity is 350 + to 550 + ..
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F21_HLCY_3000_M_ABOVE_GROUND_0_M_ABOVE_GROUND.png
CAPE as we mentioned is meager with only about 500-1500
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F21_CAPE_SURFACE.png
Lift Index only to about negative 4
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F21_PLI_30_0_MB_ABOVE_GROUND.png
Dew Points will be in the 60-70 degree range...
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F21_DPTF_2_M_ABOVE_GROUND.png
Temperatures will not be overly too warm 70s to around 80 but the dewpoints are high so it will feel ..sticky outside..
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F18_TMPF_2_M_ABOVE_GROUND.png

What is going to be responsible for this is a very strong cold front coming in from the west. There will be strong winds out ahead of this front as well in addition to the severe potential which we explain with the map above...
http://www.hpc.ncep.noaa.gov/basicwx/92fwbgus.gif

In addition to the above will be heavy rains on the order of 1 to perhaps local areas of 3 inches..If we are able to get some more sunshine in early in the day this would add on to the instability available but with the shear, helicity and EHI at impressive levels we urge people out and about to keep there eyes to the sky...

We will be here all day monitoring conditions and posting watches etc ... and we will also be out filming whatever may effect our particular local area...