Thursday, February 16, 2012

Wet Weather Returns Friday, Saturday

By Jay Grymes & Steve Caparotta

We spent just about all of Thursday under the clouds, but at least it stayed mainly dry.  Watching Titan9 Doppler radar throughout the day showed that storms were very active about 20-60 miles off the Louisiana coast, all tied to a quasi-stationary front that meandered over the northern Gulf.  Unfortunately, that same front, further energized by mid/upper-level disturbances passing from west-to-east, is going to make for a couple of wet days for the WAFB viewing area.

Clouds will continue over the region tonight, but we will remain mainly-dry into Friday morning.  Temps will dip into the mid to upper 50°s by Friday’s sunrise, with a few showers possible for the morning commute, mainly closer to the coast.  We could also see some pockets of fog in the morning, but widespread fog isn’t likely as winds should be running out of the east at about 5-10 mph by sun-up, limiting fog to wind-shielded areas.

As the day progresses, however, rain chances will go from 20% to 30% in the early morning to 60% to 70% by the afternoon.  Friday afternoon temps should climb into the low to mid 60°s.  While rain is likely, we don’t expect any heavy rains through the day – Friday will be an “over-running,” gray-sky day with mid-level clouds and a passing upper-air disturbance generating mainly light rain for metro Baton Rouge.  Most of us will see less than one-quarter-inch of rain on Friday, with higher totals possible closer to the coast.  But we expect little if any thunderstorm development on Friday, so even if it’s still raining Friday evening, those rains should be light enough to allow the Krewe of Southdowns to roll if they so choose.

Saturday?  That looks like a very different story weatherwise.

Right now, Saturday not only looks like a wet day, but it could be very wet. In fact, the National Weather Service is hinting at the possibility of a Flash Flood Watch being posted as soon as Friday afternoon or evening.

Projected rainfall on Saturday from our Titan9 RPM model. The model shows most of the WAFB viewing area receiving 1" to 3" of rainfall during the day, with the potential for locally higher amounts.

In addition, the NWS Storm Prediction Center (NWS/SPC) has the entire WAFB viewing area included under a “Slight Risk” for severe weather on Saturday.

Most, if not all, of the computer weather forecast models that we review have a low pressure center developing along that same stationary front in the Gulf late Friday, with that low tracking east-northeast into southern Louisiana during the day on Saturday.  Since the models seem to agree on the basics, the only question that remains is “how far inland” does that low track?  The farther inland it goes, the stormier the weather could become for metro BR.

Plot of low pressure center locations at Noon on Saturday from 4 different computer models. The 3 highlighted models (NAM, ECMWF, GFS) imply a threat of heavy rain and strong storms because of a track near or to the west of Baton Rouge.
Plot of low pressure center locations at Noon on Saturday from 4 different computer models. The highlighted model (RPM) implys a lesser threat of heavy rain and strong storms because of a track south of Baton Rouge.
And at least for now, the timing couldn’t be much worse for a noon kick-off the Spanish Town Parade.  Our Titan9 model gets the weather rolling by or before 11:00 am.  The “stormiest” of Saturday’s weather could be exiting the WAFB viewing area to the east by the mid- to late afternoon, allowing for better weather for Saturday evening parades across most or all of southeast Louisiana.

And it all quiets down after that: the weather looks great for Sunday and Monday, with only a slight chance of showers during the latter half of “Fat Tuesday.”

No comments:

Post a Comment