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Jack’s

A Higher Threat Level

Posted on: 5:20 pm, April 27, 2014, by , updated on: 09:41pm, April 27, 2014

Sunday Night Update: The bulk of the rain and storms are exiting northeast of the Valley as of 9:30pm, leaving us with a calm night, for the most part, although a few additional showers and storms cannot be ruled out.

Meanwhile, a significant, and now deadly, severe weather event continues unfolding to our west, especially in Arkansas. These storms will likely become more linear and may approach the Valley near sunrise Monday morning as a weakening line of storms. The severe threat during the morning hours is expected to be limited, but some gusty winds will still be possible, and we’ll be monitoring the situation closely for any surprises.

-Brandon

From Chief Meteorologist Jason Simpson:

We are seeing a disturbing trend in model guidance for Alabama and Tennessee for Monday’s storms. The NAM in particular has not showed an overly impressive look to this system until now. It’s trending toward a much more significant tornado threat for Alabama, Tennessee, and even western Georgia for Monday afternoon through the pre-dawn hours on Tuesday. Here’s the latest timeline:

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The Bottom Line:

Prepare now for what could be a very significant severe weather event in North & Central Alabama as well as Middle Tennessee and West Georgia.

We still believe this will not climb to April 27th levels, but now that we’re 24 hours away from the beginning of the event, there is much more clarity in how this will shape up.

The NAM’s output is valued because it has a higher resolution than the others (like the GFS and ECMWF that we’ve shown up until now). It also produces a Storm Relative Helicity product; that helps us see the amount of shear available for severe thunderstorms to use in tornado production. I’ve highlighted the significant range with the yellow box. Watch how the 0-1km (lowest 1000 meters of the atmosphere) helicity increases dramatically from 6 PM to midnight:

Photo Gallery Expand 1 of 7
  • Helicity Forecast Panel - 7 PM Monday

  • Helicity Forecast Panel - 8 PM Monday

  • Helicity Forecast Panel - 9 PM Monday

  • Helicity Forecast Panel - 10 PM Monday

  • Helicity Forecast Panel - 11 PM Monday

  • Helicity Forecast Panel - 12 AM Tuesday

  • Helicity Forecast Panel - 1 AM Tuesday

The model is showing small areas of extreme helicity; don’t read too much into the exact position of that. High helicity doesn’t mean a tornado is forecast by the model. Those are just spots that we will have to watch in real time on Monday evening.

All of this means we have a higher-end threat of tornadoes than we’ve had in quite some time. It’s not going to be exactly like April 27th, March 2, or any other previous event. They’re all different in their own ways; it’s on us to be prepared for whatever comes our way.

Have a Plan:

Now is the time to prepare. Know where the safest place in your home is located; if you live in a trailer, do not stay there in a tornado warning. There are numerous community shelters; if one is not listed here on WHNT.com, that means it has not been declared “public shelter.” There may be some temporary shelters announced periodically, but those are the ones we know are available.

There are numerous resources for NOAA Weather Radio programming, shelters, and storm information on WHNT.com.

-Jason
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