E-Portfolio Assignment #3
Above Image of the Tornado Watch that was by the Storm Prediction Center Counties Highlighted in Red were under this watch from 12 PM until 9 PM Eastern Time
For this assignment I will be looking at the Tornado Watch #150 from April 16 Th 2011 that was issued by the Storm Prediction Center for a round of storms that moved through the Carolinas and left a path of widespread damage and was responsible for at least 43 Deaths and Numerous injuries and property damage.
For the analysis of the weather patterns that lead up to this event we will first look at the synoptic or big picture weather players and then focus in on the mesoscale or small features that produced these deadly storms.
THE BIG PICTURE
First let’s start with the synoptic level features that were the key players in the outbreak of severe weather for April 16 Th, 2011 and to begin we will look at a 200MB map that shows a very powerful upper level jet was moving though the area with winds in excess of 100 knots from mid Alabama thru Virginia
Above 200mb map depicting a upper level jet moving through the Carolinas with winds in excess of 100 Knots Courtesy of National Weather Service WFO Wilmington, NC
Next we turn our attention to the 500 MB map below that shows a Strong mid latitude trough moving across the Ohio Valley that appears to be in a negative tilt.
Above 500mb map showing a negatively tilted mid level trough moving across the Ohio valley Image from National Weather Service WFO Wilmington, NC
Next as we look at a 500 MB map of Heights and vorticity
Above image from SPC and shows the 500mb heights and vorticity
On the above vorticity chart we can see a vort max over western north Carolina which placed the tornado watch to the east of the vort max and provide the upper-air divergence allowing parcels to rise and cool.
Lastly in the big picture we will look at the Surface Map
Surface Map From HPC Above map shows a Small warm front draped across North Carolina and a Occluded Cold Front and the associated Low pressure system from the Gulf of Mexico to the Great Lakes
The Surface map has a cold front moving into the area from the East as a Warm front is retreating to the north. The placement of the fronts had the tornado watch area in the warm sector ahead of the eastward moving cold front. The cold front and associated boundary layer were the initiating factor for this convection.
Now we turn to the Mesoscale features
To Begin I would like to look at a chart of MLCAPE
Above image courtesy of SPC and shows cape values in north and south Carolina between 250 and 500 J/kg
The above MLCAPE chart shows a small amount of cape in the area ahead of the cold front. This Cape which is the measure of convective available potential energy provided the energy necessary to fuel storms once the air parcels were lifted.
Next we will look at a graphic of 0-6 KM wind shear
Above image courtesy of SPC and shows a fairly strong amount of vertical wind shear in the Carolina region with values between 50 and 70 knots.
With the high values of wind shear as seen on the above map we would expect to see supercell thunderstorms to develop and move across the area.
Next we look at the chart of 0-1 km SR helicity
Above image from the SPC and Shows the 0-1km storm relative helicity and is a measure of the potential for cyclonic updraft rotation in right-moving supercells, and is calculated for the lowest 1-km and 3-km layers above ground level
With the above Helicity map we can see some fairly high number across much of the eastern seaboard with ranges over the Carolinas from 300 to 600 m2/s2. While there is no set threshold of when supercell’s will form number higher than 100m2/s2 indicate an increased threat of tornadoes with supercell’s.
Next I would like to point out the mesoscale discussion issued by the SPC for the approaching storms
Image from SPC and shows the outline for mesoscale discussion 455 and the weather watch 150 that was issued on April 16th 2011 for most of North and South Carolina as well as parts of Virginia
The above mesoscale discussion was issued by the SPC to discuss the impending severe weather threat for all of the Carolina’s and parts of Virginia and from reading the text they were forecasting a Strong risk of Severe weather along and ahead of the Cold front progressing into the area.
Next we will turn our attention to the Skew-T chart from 18z on April 16th 2011 to determine Storm Motion by using the Rasmussen Technique.
The Rasmussen Technique is Galilean invariant, and is a more sophisticated method of predicting storm motion. The Rasmussen Technique works in a variety of wind shear environments but requires wind observations and shear vectors to be plotted on a hodograph.
To determine the forecast storm motion for April 16th 2011 we will plot the following Skew-t on a hodograph
Above Skew-t Chart Courtesy of SPC and is a sounding from the Charleston weather office and shows cape values of 2500 J/KG and some fairly high Lapse Rates
If we use the above sounding to plot on a Hodograph using the Rasmussen technique we would come out with a storm motion near 240 degrees at 40 knots as seen below
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The above hodograph shows a storm motion of 240@40 Knots and was found by using the Rasmussen technique which consists of plotting the surface wind vector and then the four kilometer wind vector, draw a line between those two points then at the 60% point draw a line that represents 17 knots at a right angle to the wind shear vector that you just drew connection the two points, From there you would draw a line from the center of the hodograph until it intersects the 17 knot line and that line would be the storm motion. When you compare this with the storm motion that was listed in the PDS watch they are identical.
To wrap things up
So for this deadly tornado outbreak we had a strong upper level jet combined with a vigorous negatively tilted mild level trough moving across the Ohio Valley as well as a surface low pressure system and associated cold front draped across the the east coast states and a retreating warm front over north Carolina and when combined with some moderate CAPE values and strong vertical wind shear sparked storms along the cold front which took the form of clustered supercells and led to the storm reports seen below
SPC Storm reports image courtesy of Storm Prediction Center and shows 139 Tornado reports and 421 total reports
On the above storm reports image we can see a tight cluster of storm reports over north Carolina that was associated with these cell’s that can be seen on the radar image below
Radar Composite Imagery courtesy of UCAR and shows the supercells forming and moving into the area with favorable wind shear
And the above supercell’s produced numerous tornadoes as can be seen by the damage paths below
Damage path image courtesy of NWS Raleigh, NC WFO and shows multiple tornadoes across North Carolina
IN Research I found one interesting image to share and can be seen below 
Above image and quoted text below from Columbia, SC WFO
"This is a reflectivity volume loop of the storm that moved through near the Manning area around 330 pm. Notice the depth of the high reflectivity core (white and pink to over 40,000 ft) and also the overshooting tops when the updraft intensifies (light blue color)."
These Storms caused widespread damage in multiple areas and approximately 42 Deaths
