Unusual Heat to end Thursday

Yes, the heat wave did not reach the extreme daytime highs that were forecast. Temperatures maxed out at 94 or 95 unless you live 50 miles inland, say in Washington Parish. There, highs did reach 98 to 100. But, the low temperatures along the I-10/12 corridor sure were high — in the 78-82 degree range. Nobody writes about that - preferring to show people sweltering on a sidewalk in the afternoon. But it’s the low temperatures that have really increased if you study global temperatures. The reason: Increased ocean temperatures leading to increased humidity.

The forecast is still on track for the upper level heat dome to move west. When this starts to happen, the atmosphere will first destabilize on Thursday meaning that upper level temperatures will cool enough to cause any cumulus that come along to grow into showers keeping the highs down a bit. Then, on Sunday, a deep trough for this time of year will nudge south from the Ohio Valley bringing a “cold” front through us Sunday morning. See the ECMWF forecast for 3 PM Sunday below where the dashed blue line shows the front.. Showers and storms will break out in the wee hours of Sunday morning ahead of this front through most of the Northshore (But see timing in section below). It’s in quotes because in August, the air won’t really be that cold with highs in the upper 80s. However, the mechanics of how this will bring more widespread storms is the same as if it were November.

Tomorrow temperatures will be the highest for the next week, though purists would argue that the upper 80s we could see this weekend won’t be much different. The graphic highlights the showers and storms on Thursday, but I think they overplay their hand here and underplay what’s coming in Sunday morning. Rainfall chances after this weekend are minor — typical widely scattered afternoon or evening showers with low rainfall amounts.

Back to Thursday…though there’s a chance for some showers in the early morning hours, I think the main event will start at noon or shortly afternoon in Washington Parish, Northern Pearl River County, and further east in Mississippi just north of I-10. Storms will move SW into most of St. Tammany during mid- to late afternoon, then into the Southshore by evening. We could see a half inch from these.

On Friday, the chance for afternoon storms and the amounts are greater than what’s depicted. On Saturday, if any showers happen it would be during the late afternoon or evening.

Next Sunday, the timing of the storms will vary across the region because it will be a slow moving system. Washington Parish and NW St. Tammany may see the showers and storms end before or at dawn with this system that moves from NW to SE. At the other extreme, Gulport/Biloxi and the Southshore may see showers and storms mid-day Sunday before ending during the afternoon. We'll take a closer look with the next forecast on Thursday.

Concerning rainfall, European long-range modeling paints most of August as slightly drier than normal in Louisiana and about normal in Coastal Mississippi. Temperatures will be about average.

Nothing going on in the tropical Atlantic. For the first three weeks of August, development odds favor the area off the Carolinas not the Gulf. That’s good news.

Foreca graphic for Pensacola Beach shows a nice Wednesday and typical scattered showers beginning next Tuesday. In between (Thursday - Sunday), higher than normal showers and storms with more clouds than sun. Watch those beach flags for rip currents during this period.