Area Forecast Discussion

KEY MESSAGES

- High pressure centered over the northern Gulf Coast will limit daily thunderstorm potential (20-30%) this week.

- Drier air will move into the region Thursday and Friday, which will lower heat indices and make conditions feel more comfortable.

- Precipitation chances increase Sunday into early next week as an area of low pressure moves into the northeastern Gulf.

DISCUSSION

(Today through Monday) Issued at 1240 AM CDT Tue Sep 15 2026

Evening upper air analysis and water vapor satellite imagery depict a mid-level ridge centered over the lower Mississippi Valley, with our CWA on the southwestern fringes of this ridge. Meanwhile at the surface, high pressure centered over southeastern Louisiana is resulting in light southerly flow across the area. A few patches of light fog/mist are possible overnight over the CWA as skies clear, particularly for any areas that received rain today. Any fog will dissipate quickly with sunrise.

The upper ridge is projected to build and expand across the Deep South Tuesday, with 500 mb heights nearing 99th percentile values for mid-September. Tropical moisture will remain present underneath the ridge, however, with PWAT in the 1.9-2.0 inch range (near 70th percentile). With SBCAPE projected to be in the 2000-2500 J/kg range, isolated convection is expected to develop in the afternoon. Pulse storms that mature and dissipate rapidly will remain the norm with deep layer shear virtually nonexistent. However, there may be some isolated wet microburst potential with any stronger updraft that does manage to develop, given modeled DCAPE in excess of 1200 J/kg and steep low-level lapse rates greater than 8.0 C/km. Outside of convection, high temperatures will be in the mid 90s, with heat indices in the 103-107 range. This is below heat advisory criteria, but heat safety precautions are urged nonetheless.

For Wednesday, though the upper-level ridge will remain firmly in place and continue to build over the upper South, guidance has been acrossconsistent in depicting a weak inverted shortwave trough tracking east to west across the CWA during the day. While the extra forcing from this feature could provide somewhat of a boost to convection, this will be tempered by a decrease in instability as the mid-levels warm with the building ridge. HREF mean SBCAPE is only in the 1000-1500 J/kg range, compared to 2000-3000 J/kg on previous days. Thus, expect another day with isolated afternoon showers and a few thunderstorms, more likely closer to the coast and farther from the influence of the ridge.

As the disturbance exits to the west, the upper-level ridge is expected to shift westward and elongate along an axis from central Texas into the mid-Mississippi Valley. This will set up a deep layer northeasterly to easterly flow that will advect much drier air originating from the Appalachian region into our CWA for Thursday and Friday. LREF mean PWAT falls to 1.1-1.2 inches across the region during this period (25th percentile relative to climatology), with some ensemble members even decreasing this below 1 inch. Most guidance has surface dewpoints dropping into the 60s with afternoon mixing for all but immediate coastal regions, with dewpoints in central Louisiana perhaps even falling into the 50s. This dry air will result in rain chances near zero across the CWA. While actual afternoon high temperatures will stay essentially unchanged in the 90s, the heat index will be significantly more tolerable with these lower dewpoints. The drier air will also allow overnight lows to cool to values not seen in some areas since early June, particularly along the I-49 corridor. NBM probabilities of temperatures below 70 degrees approach or exceed 50 percent in this area.

Deterministic and ensemble guidance is in agreement in moving a rather strong upper-level low across Florida and into the northern Gulf over the weekend, where it is expected to stall into early next week. This will come with a push of moisture as PWATs rise back to the 1.7-1.8 inch range. As a result, a gradual increase in rain chances is expected across the area for Sunday into early next week, particularly for lower Acadiana. Afternoon highs will decrease a few degrees heading into next week owing to the height falls and increased cloud cover and rain chances, while overnight lows tick up a couple of degrees.

64/Silas

AVIATION

(06Z TAFS) Issued at 1240 AM CDT Tue Sep 15 2026

VFR conditions with light and variable winds will generally prevail at all sites tonight, though brief MVFR visibility restrictions in fog are not out of the question. For tomorrow, isolated convection is expected to develop in the afternoon to evening before dissipating by sunset. Introduced a PROB30 group for TSRA at LFT/ARA where high-resolution guidance has more consistently shown activity during this time. Would not entirely rule out a shower/storm at other sites, more so BPT/LCH, but confidence is not high enough to mention there at this time.

64/Silas

MARINE

Issued at 1240 AM CDT Tue Sep 15 2026

High pressure over the northern Gulf will keep winds out of the south to southeast at 4-10 kt through Tuesday night, with seas 1-2 feet. A disturbance moving through the area Wednesday will strengthen easterly winds to 20-25 kt and increase wave heights to near 8 feet. Small craft advisories will likely become necessary for the Wednesday into Thursday time period.

FIRE WEATHER

Issued at 1240 AM CDT Tue Sep 15 2026

A moist airmass remains in place over the region with winds generally light out of the south to southeast. Most of the area will remain dry through Wednesday, though an isolated afternoon shower or thunderstorm cannot be ruled out. Afternoon MinRH will be 40-50 percent inland and 50-60 percent near the coast. For Thursday into the start of the weekend, much drier air will begin to move into the CWA, with afternoon MinRH decreasing to 30-40 percent inland and 40-50 percent near the coast. East winds around 5-10 kt are expected for this period.

LCH WATCHES / WARNINGS / ADVISORIES

LA...None. TX...None. GM...None.