Sunday, April 15, 2012

UPDATED: Details on potential severe weather threat overnight


Following yesterday's Central Plains severe weather outbreak, Mid-Southerners are a little uneasy about the threat here as the same storm system makes it's way through the region tonight.  Fortunately for us, the impressive dynamics that spawned nearly 100 tornado reports (at last count, that number will likely fall a little as reports are verified) on Saturday are much weaker and will be well-removed from this portion of the country as the system moves east.  However, a potent cold front will still push a line of storms through the region during the overnight hours.
Reports of severe weather in the Plains on Saturday, April 14, 2012
The Storm Prediction Center has placed western sections of the Mid-South under a Slight Risk for severe weather this evening and tonight (updated graphic below).  This is due to strong to severe thunderstorms, some with damaging wind and hail threats, that have fired ahead of the cold front over western MO, eastern OK, western AR, and far northeast TX.  As this system moves east, this evening, storms are likely to coalesce into a squall line as they move through central and eastern AR.  As they do, however, the atmosphere they are moving into is not quite as unstable.  Part of this lessening in instability is due to timing - the storms will be moving into the area after peak heating when instability typically wanes.  However, because they will build up a head of steam moving across AR, some of the storms will still have the potential to bring strong to severe straight line wind (50-60 mph) and small hail.  And, as we typically warn in these scenarios, spin-ups within the squall line have the potential to drop brief tornadoes, though the threat of tornadic damage is not high.
Updated 8pm severe weather outlook from SPC showing a slight risk for the metro tonight
As for timing, models indicate storms could initially arrive in the metro anytime between 9pm and 1am and would last on the order of 2-4 hours.  MWN is forecasting the storms to arrive during that window (or 11pm to midnight) and last for 3-4 hours projected from the current location and movement of the line in Arkansas.  The line is generally following the lead of the high resolution model data from early this afternoon.

Hi-res computer model (HRRR) output showing "forecast radar" as of midnight CDT
In summary, Memphis metro residents should be prepared for the possibility of a narrow line of storms moving through the metro around 11pm to midnight bringing the possibility of strong straight-line wind and an isolated threat of hail or an isolated tornado. The line will be followed by general thunderstorm activity that will last into the wee hours Monday morning.  All of this activity will be out of the area prior to the Monday morning rush hour.  Only a few lingering showers are possible early Monday morning.

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