Severe weather still expected, a deep dive into the forecast

Posted at 12:14 PM, Apr 11, 2019
and last updated 2019-04-11 13:14:16-04

We’re continuing to monitor the arrival of a storm system that looks like it will likely spark a round of severe weather this weekend.

While the forecast is one that’s going to evolve over the next few days these are the current (Thursday morning) thoughts on how things are evolving.

WHERE: There hasn’t been much movement in the outlook area, now that the event is in the three day window the Storm Prediction center has moved the northern half of the state to an Enhanced Risk, while the rest of Louisiana is under a Slight Risk.

SPC outlook area for Saturday.

WHEN: This question is a little more complicated based on the set up for Saturday and the potential for strong storms leading the front.

The main line of storms is expected to move through Saturday evening, with strong isolated storms firing up in the afternoon.

Those isolated storms will be harder to pinpoint as they’ll largely rely on atmospheric conditions on Saturday, more on that below.

IMPACTS: Damaging winds are going to be the main issue as the front moves through, however, isolated tornadoes are also going to be possible.

The tornado threat will exist primarily with the storms that pop up before the main line arrives, with enough instability isolated storms could become super-cells producing tornadoes.

While tornadoes can still exist along the main line those are much more isolated, short lived, and harder to spot.

Hail is going to be possible but not as intense as some of the other systems we’ve had in the recent past, though it should still be monitored.

This goes along with the usual frequent lightning and heavy downpours that typically accompany a systems like this one.

Flooding doesn’t look like it’ll be much of an issue with both the GFS and EURO bringing in less than impressive numbers.

Still 1-2″ of rain over a short amount of time can temporarily stress some of the low lying roadways as the event moves through Acadiana.

While not anticipating any widespread flooding we’ve all witnessed how quickly the Gulf of Mexico can produce rain so will monitor rain totals as the day unfolds.

EURO model prediction for rain totals.
GFS model prediction for rain totals.






FORECAST DISCUSSION: Wanted to give a slightly deeper dive into the forecast to give everyone an idea with some of the complexities of this forecast and things to look for as we wrap up the week.

One of the big question marks with the weather forecast is going to be the instability available for this system to work with, and it seems that the GFS and the EURO are both split on this issue.

The reason this is important is it will determine how strong not just the main line storms will be but also the storms out ahead of the system.

EURO model projections for instability.
EURO model projections for instability.

The EURO model has looked a little less robust on its Thursday morning model run, which is a trend that hopefully continues.

There’s still enough instability there for some severe weather but the lower these parameters the more the weather is kept in check.

One of the things to take note of (especially when compared with the GFS) is the timing of when the instability spikes.

CAPE (available energy) seems to peak in Acadiana Saturday evening which is when the main line comes swinging through, with fairly marginal numbers during the afternoon.

What this would mean is that the main line may be a little stronger as it swings through compared to what it would have the potential to do after a stormy afternoon.

If the EURO is to be believed it would indicate less pop up storms in the afternoon, with a more intense round of severe weather in the evening.

The outlook from the GFS, on the other hand, is almost entirely flipped from this scenario (although both predict showers and storms).

GFS model projections for instability.
GFS model projections for instability.

What stands out immediately compared to the EURO is the aggressive amount of instability the GFS has pinned for Saturday afternoon.

This would result in stronger potential for super-cell storms to develop out ahead of the line, making any pop up storm have the potential for severe weather.

As the evening approaches, however, instability would drop as the main line swung across south Louisiana.

If this scenario were to play out it would mean some very intense storms, but a little more isolated, in the afternoon.

As the main line swung through while bluster, loud and wet it may not have the severe potential that the early round of storms would possess.

The reason for this is that there’s only so much energy for the atmosphere to use so a round of strong leading showers would in turn exhaust it.

It’s similar to working out if you go for a run in the afternoon after resting all day you’re bound to turn in a faster time then if you spent the first half of the day running around using up all your energy.

WHAT TO WATCH FOR: As always the best way to figure out a forecast is to see how it trends as the time gets closer, for example has projected instability increased or decreased during Friday’s forecast.

One of the ways to get a sense of instability on Saturday is to keep an eye on the dewpoints, dewpoints in the 70s is a pretty good measure for moisture available.

The other thing will be sunshine, breaks in the cloud will lead to some extra heating which in turn will start to churn up the atmosphere.

Once that happens those isolated storms will start to grow and tap into the amount of energy the atmosphere has, this would be reminiscent of the GFS solution.

It’s still a little too early to pin point exactly how Saturday’s weather will unfold but hopefully this gives you a better idea of what to expect for the weekend.