Follow up from yesterday: 2 tornadoes and many wind reports. This is typical of squall lines- lots of wind and a brief embedded tornado or two.
The Storm Prediction Center (SPC) has issued an Enhanced Risk for parts of the Mid-Atlantic today. The same system that has dumped severe weather in the eastern Plains and Dixie Alley is now headed for the Mid-Atlantic.
Associated with the Moderate Risk is a 10% Tornado Threat Ring.
Synoptically speaking, the 250 mb NAM chart shows a deep trough moving east towards the Atlantic Coast.
The 500 mb NAM chart shows strong Positive Vorticity Advection (PVA) moving through the Carolinas and southwestern Virginia by 21 Z.
The 700 mb NAM chart shows a line of rapidly-rising air ahead of the cold front as it moves through the same region.
The 850 mb NAM chart shows Cold Air Advection (CAA) as a cold front moving through the Appalachians. This CAA is not as strong as yesterday’s.
The surface dewpoints (HRRR) show no sharp dryline, though there is ample moisture ahead of the front.
CAPE will not be high, but it may be adequate, given the deep moisture and strong shear. It’s another low CAPE threat.
The NAM shows that the Supercell Parameter will be greatest in the Carolinas.
…same with the Significant Tornado Parameter.
The HRRR Simulated Reflectivity chart shows that this system remain linear as it tracks east. There is a leading band, and a following band. Locations impacted will want to be aware of this!
The 12Z upper air sounding from Charleston, SC, shows a lightly capped, but slightly energetic atmosphere. There was 523 J/kg of Convective Available Potential Energy (CAPE) and -49 J/kg of Convective Inhibition (CINH). There was a tiny cap, and the 0-3 km average lapse rate was 6.4 C/km. The Lifted Condensation Level (LCL) was only 103 m. The Supercell Parameter was 4.5.
The hodograph from Norman, OK, shows 25 kts of low-level shear and 39 kts of deep-layer shear.
Currently, the surface observations (from the SPC Mesoscale Analysis Map) show warm, humid, and sunny conditions ahead of the cold front. Winds from the south and southeast continue to advect warm, moist air ahead of the squall line. The Doppler RADAR overlay shows that the line has crossed over the Appalachians and is headed for the Piedmont.
Visible satellite imagery shows that this system is huge- it extends into Central America.
Overall, I think there is a strong severe threat today for the Mid-Atlantic. The Carolinas should keep an eye on the weather today, in particular, as they have the highest tornado threat.
It would not be a great day for chasing, given the linear nature of this system, and the terrain. However, I would probably hang out east of Columbia on I-20, heading towards Bishopville or Florence by the end of the day.
There are tornado watches up for farther south, and a current Mesoscale Discussion for a Severe Thunderstorm watch likely in my target region. Even so, I would stick with South Carolina. This is going to be an embedded, low-topped supercell day for the Carolinas. The shear is there, even if the CAPE is meager.
Thank you for reading my forecast.
The upper air soundings and mesoscale analysis plots are from the <a href=”http://www.spc.noaa.gov/” target=”_blank”>Storm Prediction Center</a> website.
The forecasted upper air soundings are from <a href=”http://www.twisterdata.com” target=”_blank”>TwisterData.com</a>.
The surface observation and upper level charts are from <a href=”http://weather.unisys.com” target=”_blank”>Unisys Weather</a>.
The satellite data is from <a href=”http://weather.msfc.nasa.gov/GOES/” target=”_blank”>NASA – MSFC</a>