Friday, February 17, 2012

Good News, Bad News for Parades

(Note: the graphics in the post below are a somewhat lower quality than usual because I'm writing this from home late Friday morning)

Let's start out with some good news...

Today's forecast is turning out to be a bust in a good sense. Rain chances now look quite low through the day, which is good news for tonight's Southdowns parade. A few isolated showers can't be ruled out this evening, but any rain would likely be light. Look for temperatures in the low to mid 60°s for most of the parade.

Now the bad news...

As we warned you yesterday evening, a Flash Flood Watch has been posted for the entire WAFB viewing area, beginning at 6 a.m. and continuing through 6 p.m. on Saturday.

Flash Flood Watch in effect 6 a.m. - 6 p.m. Saturday. Courtesy: NWS New Orleans/Baton Rouge.
This morning's computer guidance is in very good agreement on bringing heavy rains into the area. The latest 2 runs of the NAM model forecast 2.03" and 2.13" of rain for Baton Rouge, while the latest 2 runs of the GFS forecast 2.71" and 1.71". A look at the RPM forecast below shows it has just about all of southeast Louisiana receiving anywhere from 2" to 4"+ of rain on Saturday (as indicated by the red and maroon shaded areas).

RPM model forecast rainfall. The red and maroon shades over most of SE Louisiana indicate 2" to 4"+ of rainfall.
The computer guidance is also now in good agreement on bringing widespread shower and t-storm activity into the area as soon as Saturday morning and continuing into at least a portion of the afternoon. Below is a look at 4 different computer model projections for Noon on Saturday.

RPM model projection for Noon on Saturday. The red and pink shades would likely represent t-storms.
GFS model forecast for Noon on Saturday.
NAM model forecast for Noon on Saturday.
ECMWF (European) model forecast for Noon on Saturday.
One trend worth monitoring today is that the models seem a bit slower in having the rains exit on Saturday. Most of our guidance yesterday showed things ending pretty quickly during the early afternoon; the latest runs indicate rains could continue into late afternoon before exiting.

The good news this morning is that Baton Rouge Police and the board of Spanish Town have made what I think is a very wise decision to move the start time of the parade back to 3:30 p.m. That still seems to be a close call in terms of getting wet, but I'm still somewhat optimistic that the worst of the storms will be through by then. We'll have to take another look at it this evening.

As I also mentioned last night, I still think it's quite possible that much of southeast Louisiana could be under a tornado watch by Saturday morning. The atmosphere will have plenty of wind shear to work with...the question is actually whether it's too much shear. There is also some question as to whether there will be enough 'instability' to drive severe storms, but I think there will be.

The Storm Prediction Center still has the area under a 'slight' risk of severe weather on Saturday. They actually have the 30% chance of severe weather contour just south of Baton Rouge. The 30% area in the map below means they're forecasting a 30% chance of severe weather within 25 miles of any point in that shaded area.

Probability of severe weather within 25 miles of a given point on Saturday from the Storm Prediction Center.

So, the bottom line here is that tonight's Southdowns parade should be fine. The later start time for Spanish Town gives them much better odds of rolling without incident, although we will have to continue to monitor the timing of Saturday's rainfall. Assuming Poseidon follows Spanish Town, I would expect that parade to be fine, although there will be an increasing threat of gusty winds as the night wears on behind a cool front.

1 comment:

  1. Poseidon is not rolling this year.