Friday, November 15, 2013

November 17 Potential Severe Weather Outbreak

There is potential for a severe weather outbreak this weekend, as an amplified storm system traverses the Plains, leading to an enhanced jet stream and an opportunity for a potentially significant squall line.

The image above shows the jet stream wind speed projection for Sunday evening. I drew in the black line to show the tilt of the storm system, which should be negatively-tilted for this event. The negative tilt matters in this situation, as negatively-tilted storms tend to produce more "intense" severe weather events than positively-tilted storm systems (which involve the storm pushing to the southwest). The jet stream should be absolutely screaming when this event begins, with the NAM forecast above maxing out above 110 knots. The active jet stream will lead to this event being maximized in the severity, in terms that whatever severe weather that occurs on Sunday should be of decent significance (i.e. damaging winds and possibly a tornado).

Simulated reflectivity projections from the NAM model indicate that a strong squall line should stretch from Ohio to the western tip of Tennessee by the evening hours on Sunday. Per hodographs from immediately out ahead of the squall line, any convection that forms before the squall line pushes through may be tornadic. In the same fashion, if the squall line itself is more of a coagulation of individual cells rather than a line of storms, there is a raised potential of tornadoes. At the time, storm motion (storm speed) around 50-60 knots to the east-northeast tells me that this will certainly be a big damaging wind threat. Lower level winds just 5000' off the ground will be over 60 knots, and if these winds translate to the surface, we could see a large-scale damaging wind event over the Ohio Valley.

Here's my current diagnosis of the situation.