Thursday, January 10, 2013

The skinny on possible severe weather this evening

UPDATED 9:15pm:  The slight risk area has been dropped from the Mid-South and bands of showers and a few thunderstorms are forming over northeast AR and west TN. Though brief heavy rain and wind gusts are likely with any showers, the severe weather risk appears to have not been able to materialize. As usual in the winter, instability was the biggest factor and there just wasn't enough to get strong storms to form.  Showers will linger through midnight or so.  Clouds will break apart in the morning leading to a partly cloudy afternoon with highs in the lower 70s!

UPDATED 6:30pm:  The Storm Prediction Center has issued a "mesoscale discussion" which basically outlines the state of the atmosphere and let's us know what they're thinking relative the potential for severe weather. In it, they state that a watch is unlikely (20% chance of issuance) due to a lack of suitable instability to promote widespread thunderstorm development.

SPC does not expect to have to issue a watch for the area tonight, though a few storms are still possible.
While some thunderstorms are still expected, most will be to our north and even those will have a hard time reaching a severe state. We still expect you could hear some thunder tonight between 8-11pm and the wind could get gusty in some storms.  By midnight, the threat will be over and we can look forward to a delightful spring day tomorrow!  Yes, a good deal of sunshine and 72 degrees is the definition of a spring day!  Enjoy it, more rain (lots of it) is on the way this weekend.

We'll be nowcasting throughout the evening on Facebook and Twitter. (Links at end of the post.)

UPDATED 5:40pm:  Storm Prediction Center graphics within the post below have been updated as of 5:30pm.  The tornado risk has been increased ever so slightly, though the risk is still very low (5%).  A period of dry weather this afternoon has allowed temperatures to climb into the mid to upper 60s with dewpoints also well into the 60s - favorable conditions for the possibility of severe storms.  We have also narrowed the "window of opportunity" to 8-11pm tonight.  We'll be nowcasting throughout the evening on Facebook and Twitter. (Links at end of the post.)

The Mid-South has entered a very unsettled, wet pattern that will continue into early next week. Despite a 12-hour period here and there with drier weather, the overall pattern will favor waves of rain and chances of thunderstorms until next Tuesday or Wednesday.

Rain encompasses the area this morning as moisture streams in from the south. Currently (9:45am), Tornado Watches are posted for portions of Louisiana and southern Mississippi where the greatest atmospheric instability (rising air) is located.  However, during the day, some of that instability will extend north towards our region as a potent upper level system nears the area from the west (see graphic below).

Upper-level energy, in the form of a low pressure center, will skirt the region, bringing a chance of strong storms this evening.
As the upper low approaches, thunderstorms are expected to develop later this afternoon in AR and move towards the metro. Besides heavy rain, some of these storms could bring the potential for strong to damaging wind with an isolated threat of hail or a tornado.  For this reason, the Storm Prediction Center has placed portions of the Mid-South under a Slight Risk of severe storms, primarily during the 8pm-11pm timeframe in the metro.

A Slight Risk means the threat for severe weather is elevated. In this case, damaging wind would be the primary threat
While atmospheric dynamics, such as wind energy, are sufficient for severe weather and moisture is in place, ongoing rainfall (especially if rain continues this afternoon) will inhibit the final ingredient needed for severe weather - instability. Should we get a break from the rain this afternoon (which models indicate is possible) and warmer dewpoints in the lower to mid 60s make it into the area, our severe chances would materialize. The Slight Risk is forecast due to this possibility.  If instability is more limited, strong storms would be possible but the severe weather risk would be limited as well. Once again, damaging wind is the main threat, but there is a non-negligible risk of a tornado as well.

Damaging wind (58+ mph) chances for tonight. Yellow area means there is a 15% chance that  wind gusts of 58+ mph will occur within 25 miles of any point in that area

While a tornado is possible with this threat, there is only a 5% chance of one occurring within 25 miles of the metro

As always, we'll keep you updated on social media throughout the day and tonight and will provide wall-to-wall coverage on Facebook and Twitter if thunderstorms form.  Download the MWN mobile apps for the most current information we publish, including radar, local conditions, the latest forecast, watches/warnings, and links to our social feeds.  Then, upgrade within the MWN app (on the Alerts tab) to StormWatch+ to receive pinpoint warning information delivered to your Android or Apple device, including Severe Thunderstorm and Tornado Warnings that will wake you up if need be.  All pertinent links are listed below.

Tomorrow we get a break from the rain as SPRING makes an appearance with highs in the lower 70s and partly cloudy skies! More rain, and potential thunder, arrives for the weekend. We'll have more on that tomorrow...

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