Discussion for June 1st ...We are going to start off by looking at the surface map to see what is happening. http://www.hpc.ncep.noaa.gov/sfc/90fwbg.gif Low pressure is located over Southern Indiana. Accompanying this low pressure is a warm front to the east and a cold front trailing to the south. This low pressure is anticipated to move NE and take on a negative tilt to the trough as it does so. This will push a warm front into the region. This warm front will be followed by a cold front..http://www.hpc.ncep.noaa.gov/basicwx/93fwbgus.gif It will be this area of low pressure and the associated frontal systems that will bring the severe weather potential into the region.. So lets get down to the specific Parameters... TEMPERATURES are only going to be in the 60-80 degree range across the Northeast..Higher temperatures in the SW portion in the TX region of 80-90 degrees.http://www.twisterdata.com/data/models/nam/221/maps/2012/06/01/00/NAM_221_2012060100_F18_TMPF_2_M_ABOVE_GROUND.png ..DEWPOINTS will be in the 60-70 range ..http://www.twisterdata.com/data/models/nam/221/maps/2012/06/01/00/NAM_221_2012060100_F18_DPTF_2_M_ABOVE_GROUND.png..CAPE is not all that impressive it is only in the 500-1500 range and generally that would fall into the marginal category when it comes to Instability.. http://www.twisterdata.com/data/models/nam/221/maps/2012/06/01/00/NAM_221_2012060100_F21_CAPE_SURFACE.png ..LIFT INDEX is from 0 to about -7 depending where you are located..http://www.twisterdata.com/data/models/nam/221/maps/2012/06/01/00/NAM_221_2012060100_F21_PLI_30_0_MB_ABOVE_GROUND.png... Now where it gets a little on the dicey side is the EHI..Remember that anything at 1 or below that super cells are not likely but 1 and above super cells become more likely.. 1 to 5: Possibility of F2, F3 tornadoes ..http://www.twisterdata.com/data/models/nam/221/maps/2012/06/01/00/NAM_221_2012060100_F21_EHI_3000_M.png ..So you can see why things become a little bit on the dicey side here.. Another part of the dicey forecast is the HELICITY... to freshen peoples memories here is what the Helicity represents..Interpretation of values:
*150-300 Possible Super cell
*300 to 400 Super cell Severe Favorable
*400+ Tornadic Thunderstorms Favorable ..and here is what the Helicity looks like http://www.twisterdata.com/data/models/nam/221/maps/2012/06/01/00/NAM_221_2012060100_F21_HLCY_3000_M_ABOVE_GROUND_0_M_ABOVE_GROUND.png ..So as you can see we have two very favorable parameters in place for Tornadic Activity across PA.. We have no lack of SHEAR either with 30 knots and above in place...http://www.twisterdata.com/data/models/nam/221/maps/2012/06/01/00/NAM_221_2012060100_F21_SHRM_500_MB.png ...Now one thing that may hinder Tornadic potential could be cloud cover that is presently moving into western PA..http://weather.unisys.com/satellite/sat_ir_us_loop-12.gif ..So what we are going to do is we are going to make one more map and this is going to be PA based and it is going to be based on Tornado potential only. We already know that the severe zone always represents the places with likely hood of hail and or wind... and the percentages of Hail are at 15% and winds we place at 15%.
Here is the tornado potential only map:
Those in southwest PA we feel you will be dealing with more along the lines of heavy rainfall potential and garden variety storms> it is possible that some isolated severe could occur but we think the initiation of the severe will be NW of you and east..
We encourage people across the state of PA ..to pay attention to there local weather source!
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