Clouds without Much Rain

It was a crazy Halloween weather-wise across our area, but most of us in St. Tammany and the immediate MS Gulf Coast wouldn’t have known. Here it was a cloudy day with a few piddly showers followed by an acceptable, but humid evening for the youngsters. But near the Lake on the Southshore, an east-west band of storms dumped 1-6 inches in the afternoon but ended by evening. The real fireworks happened north and east of Bogalusa where a huge thunderstorm developed after sunset and refused to move. Localized rainfall totals were estimated at 15” by radar. This WDSU rainfall graphic shows the areas and rainfall totals..

Let’s take a moment to explain what happened. Moist-low level air was blowing in from the Gulf, but for the most part was trapped under a temperature inversion at about 3,000 feet. Though there was upper level support for rising motion, this was generally trapped above the inversion. So, for most of us, this led to a cloud cover at the inversion with weak upward motion and drips of light rain. However, at a few spots there was enough low level convergence to force air upward and break through that inversion resulting in strong thunderstorm growth and excessive rain. So instead of many of us getting a quarter to a half inch last night, all the water vapor was sucked into the clouds to condense and fall as a deluge in that one area near Bogalusa. That type of behavior is almost impossible to predict.

Currently, though there have been showers along the Louisiana coast southwest of the city, clouds are thinning out to our west as upper air support moves eastward (see the line of storms extending south from the Panhandle in the visible satellite image). So, though we are still in the humid air, the heavy precipitation threat is over. We could see very light showers moving through tomorrow, but they won’t amount to anything.

The next weather maker will arrive Tuesday afternoon and perhaps linger through Wednesday morning. At this point, I’m not seeing a severe weather( or heavy rain )threat that I worried about last week. The upper level energy looks to track well north of us. Last week’s models had a hard time locating the jet stream locations over the mid-Pacific given a lack of data (That’s the biggest single need in forecasting that satellites don’t provide) and were too far south. What this means for us is several chances for showers and thunderstorms, but amounts will be modest without the threat of high winds. This is the ECMWF forecast for 3 AM Wednesday morning showing several bands of showers and storms extending to the Gulf Coast. Then, we’ll be in for a period of slightly cooler but noticeably less humid weather. for a few days before even cooler weather arrives for next weekend.

The Foreca graphic looks reasonable except that I disagree with the rainfall next Sunday. Starting tomorrow, expect a day similar to today except with a bit more sun. Again, I can’t dismiss a very light, probably won’t wet the ground shower. Tuesday starts out with more sun but showers arrive during the afternoon. Several broken bands will move through Tuesday night and should be over early Wednesday morning, except in BiIoxi where they could linger through midday. Then, lower humidity arrives with north wind for Thursday dropping Northshore lows into the 50s. Highs will gradually come down through the weekend.

Tuesday Nov. 10 and Wed. Nov. 11 should feature fine, sunny fall weather with highs in the mid 60s and lows in the 40s. Thursday will be a transition day with lows in the 50s and highs in the low 70s. Friday and Saturday Nov. 13 and 14 should see a return of Gulf moisture with a chance of showers and storms..

The chance of showers tomorrow on the Southshore is a bit higher and the probabilities for rain and amounts for Tuesday night’s system is a bit lower. Again, I disagree with the Sunday rainfall.