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March 25, Thursday Severe Weather
nrgjeff posted a topic in Tennessee ValleyThursday will be a regional severe wx outbreak. @CheeselandSkies I think SPC was waiting for American guidance to come toward the ECMWF. It was stubbornly slow this time. Regardless of how we got here, we are at hatched ENH Day 3 now. First thing I noticed with 12Z guidance is that 500/200 mb winds are forecast WSW. Some of the sloppy South days those winds are SSW. From the SW is plenty of turning. From the WSW as forecast offers robust turning with height. No strange 700 mb winds, smooth forecast hodographs. LLJ is still forecast S or SSW, correct for South severe, even on the squirrelly GFS runs. Winds of course strengthen with height too. Warm sector looks a little bigger than last week defined by northward extent of the synoptic warm front. That does not necessarily mean intense severe weather farther north. That'll depend on the outflow boundary situated south of the warm front, and influenced by midday rain. Undisturbed warm sector soundings should have a little EML and lots of instability. Background pattern is there for a severe weather outbreak. Mesoscale details remain up in the air as usual Day 3, including the size of the region impacted.
Jan. 12-13, 2018 winter storm Nowcast and Forecast
nrgjeff posted a topic in Tennessee ValleyTime for a thread! Looks like possible heavy snow inside our Region. Some areas could get ice under the snow. Dynamic system with strong push of low level cold air is forecast.. First the ice consideration is due to rapid low level CAA into West Tenn. and West Ky. Mid levels still warm at onset, part of the TROWAL, so it could be ice. Hopefully not but... More interesting is the TROWAL forecast from the Mid-South to Kentucky. Could go as far north as Indiana. Could slide right across our region. Wouldn't that be great? Euro seems too far north; yes, it's still my favorite model. In this seasonably cold winter GFS needs more respect. NAM follows it more east/south. So, I'm confident enough to start a thread for our Region. TROWALs are great in the South, because they let us kind of cheat and get snow without cold air solidly in place. This time, confidence is added by robust low level CAA too. Upstairs WAA goes into a core that is cold enough for snow, convenient. Dynamic cooling plays a role. Snowfall rates can approach/match those in other robust WAA conveyor belts (in contrast to meh comma heads). Big challenge is that a TROWAL is basically a mesoscale feature. It will be tough to pin down the big winners early. Rest of us can hope for that low level CAA to change over other parts of the rain shield, but it will be difficult. Mid-levels (700 mb) will not be ideal for snow production outside the TROWAL. However thickness crashes farther upstairs and that low level CAA... Did we get slammed about this time in Jan. 2011, a similar analog year?