Thursday, February 16, 2012

Weekend Parade Outlook

For the second year in a row, we're looking at potentially dicey weather for the final weekend of Mardi Gras parades in the Baton Rouge area. I'll start with a look at the Southdowns parade, scheduled to roll at 7 p.m. on Friday.

Most of our guidance is now in good agreement on good rain chances on Friday. However, there are differences in both the timing and the intensity. After examining several models, it appears as though most point toward light to moderate rains, although the NAM model generates about an inch of rain in Baton Rouge on Friday. At this point, I'll consider that an outlier and lean toward lower rain amounts on Friday.

For the Southdowns parade itself, I think we'll have scattered showers around south Louisiana, but litte if any lightning/thunder. So, with that said, the parade should be able to roll as planned, although it could be wet at times. Below is a look at parade time Friday from 4 of our computer models. As you look at the image below, it's important to note that the ECMWF ('European') model is at a lower resolution than the others, so it is likely overdoing the scope of the rainfall.

(a) Titan9 RPM model. (b) NAM model. (c) GFS model. (d) ECMWF model.
While I believe Southdowns will be able to roll without major incident, things aren't so clear for Spanish Town on Saturday. A wave of low pressure forming in the western Gulf of Mexico is expected to track toward Louisiana on Saturday. The track of the low will be key. A track near or west of Baton Rouge would likely bring active weather into the area, including the threat of some severe storms. A track to our south or east would keep the active weather away, with just some soaking rains expected.

The image below shows the same 4 forecast model projections for Noon on Saturday. Note that 3 of the 4 models below paint a rather ugly picture for parade time on Saturday. Those same 3 models all have the low tracking near or west of Baton Rouge, implying both a threat of heavy rains and a few severe storms. Any severe storms could produce damaging winds and even isolated tornadoes.

The one model that keeps the low to our south is our Titan9 RPM model. This is a model that we typically lean heavily on in the 24-48 hour forecast range. However, at this point I'd have to consider it an outlier, so I tend to lean more heavily on the other models painting a wet and stormy picture for the first half of Saturday. Keep your fingers crossed that the other models fall in line with our Titan9 RPM, but for now, we'll go with the consensus.

(a) Titan9 RPM model. (b) NAM model. (c) GFS model. (d) ECMWF model.
As mentioned, a track near or west of Baton Rouge would likely lead to a threat of severe weather. The Storm Prediction Center agrees, outlining all of southeast Louisiana under a 'slight' risk of severe weather on Saturday.

Severe weather threat from 6 a.m. Saturday to 6 a.m. Sunday from the Storm Prediction Center.
The other concern is the potential for heavy rains. Again, the track of the low pressure center will determine which areas get dumped on. Below is a rainfall projection graphic from our Titan9 RPM model from 6 p.m. Friday through 6 p.m. Saturday.

Titan9 RPM model rain projection from 6 p.m. Friday through 6 p.m. Saturday.
Remember from our discussion above, our Titan9 RPM model tracks the low well southeast of Baton Rouge. As a result, you see the heaviest rains in this projection extending from Terrebonne & Lafourche parishes into metro New Orleans. However, if you move the low track farther inland, closer to Baton Rouge, it would be fair to assume that stripe of heavy rain would be closer to Baton Rouge as well. In the graphic above, the light green and yellow shadings are indicating anywhere from 2" to 4" of rainfall.

While our Titan9 RPM model keeps rain totals modest around Baton Rouge, a glance at projections from our other models shows 1" to 2" forecasted during the day for Baton Rouge.

The weather looks rather 'iffy' for Spanish Town, but rains should start to wind down from late afternoon into the evening on Saturday. I think there's a decent chance that Poseidon could roll as planned, although there may still be some rain in the area. Below are the 4 model projections for parade time for Poseidon.

(a) Titan9 RPM model. (b) NAM model. (c) GFS model. (d) ECMWF model.
 We'll take another look at the latest model runs later this afternoon or evening...

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