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Posted At: July 19, 2008 @ 2:18 PM

Posted By: Reed Timmer

A classic mid-summer severe weather pattern is in place across the upper Missouri River Valley this afternoon and evening, which basically means a very minimal tornado threat and rapid evolution into a mesoscale convective system (MCS)/derecho.  Thus, the main svr threat will be strong straight-line winds and large hail.  The basic ingredients for this textbook MCS pattern are weak low-level shear, high CAPE, a subtle disturbance embedded in northwesterly flow, and a diffuse surface pattern.  Storms are already exploding across southeast SD, but as expected, these storms have not exhibited supercellular structure.  The RUC forecast for 00z for 850 mb and CAPE below tell the story:

The SPC has issued an MD for this area, and a severe thunderstorm watch will likely be issued for this area.  There is a very small chance that if a cell can remain discrete through the evening while the LLJ intensifies, a brief tornado may touch down - but I'd say there is a better chance of winning the lottery.  We'll see though...  Crazier things have happened. 

Posted At: July 19, 2008 @ 10:31 AM

Posted By: Reed Timmer

TD Three is intensifying very slowly just off the SC/NC coast, with winds of 30 knots reported by a ship just southeast of the center.  The circulation center is clearly apparent on Wilmington radar, with the last few scans showing convection rotating entirely around.  The "donut hole" at the bottom center of the radar image below from just after 1500 UTC is where the approximate center of circulation is located.  Most models show very slow intensification if any due to dry air located just north of the system, but the NHC is predicting tropical storm status by the next advisory. 


The forecast track show below is right along the warm waters of the Gulf Stream, which favors continued intensification despite the dry air located to the north of the cyclone.  Typically re-curving systems encounter increased upper-level shear as they encounter the westerlies of Mid-latitudes, so TD3 will likely not attain hurricane status.  Stay tuned for updates!  My sister is currently located in New Bern, NC so I may have some pictures to post later today.