Area Forecast Discussion
Issued by NWS Lake Charles, LA
Issued by NWS Lake Charles, LA
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343 FXUS64 KLCH 171214 AFDLCH Area Forecast Discussion National Weather Service Lake Charles LA 714 AM CDT Wed Jul 17 2024 ...New UPDATE... .UPDATE... Issued at 706 AM CDT Wed Jul 17 2024 Basis latest upper air sounding data illustrating a few layers of lowered RH being entrained from the NW into the mid levels, POPS have been adjusted for interior SETX and SWLA to reflect decrease chances of morning precipitation. Isolated to scattered convection remains in the forecast throughout the mid-afternoon with favorable lapse rates of 7 deg C / km above 3km AGL and sufficient surfaced based instability. 30 && .SHORT TERM... (Today through Friday night) Issued at 259 AM CDT Wed Jul 17 2024 Showers and storms are shifting onshore through the morning and mid afternoon hours under a slack high pressure regime locally across SETX and SWLA. An upper level low over SETX will continue to meander SW along the coast of Texas. This feature will exhibit localized speed divergence and lift aloft allowing the moist marine environment with southerly flow to enhance shower / storm activity throughout today. Guidance trims back the POPS to more isolated chances by the evening hours as much of this convection has surface based components that will be suppressed by latent heat released in the low level environment basis forecast sample soundings. In between showers / storms where possible breaks in cloud cover, many locations will see highs the upper 80s to lower 90s as well as on Thursday. The upper level feature begins to fill and weaken while shifting SE into the western Gulf of Mexico where it will open and merge with troughing along the northern portions of the Gulf of Mexico. Meanwhile a downstream shortwave associated with extensive frontal boundary will continue with shift toward the Canadian Maritimes / Gulf of Maine throughout the day. Trailing from the surface low in that region will be that cold front boundary curving SW across Appalachia NETX where a secondary sfc trough will deepen to further enhance the baroclinic environment along SETX and SWLA priming the area for more rainfall. Do note, forecast soundings during the period indicate PWATs measuring in excess of 2.00" at times. Therefore, localized flash flooding starting with low lying and urban areas is an impact to monitor through the Friday morning hours. However, an inhibiting factor will be the limited MLCAPE which trends further up in the lower troposphere during the nocturnal hours. Highs Friday will trend little cooler with the frontal boundary of the aforementioned pattern to the north of the area will begin to slow along the Gulf Coast, becoming stationary. Southerly low level flow will continue to abut this boundary as a secondary shortwave from the northern stream enhances upper level divergence over the SECONUS helping reform the boundary northward into early Saturday morning where further shower and storms are favorable. Kowalski / 30 && .LONG TERM... (Saturday through Wednesday) Issued at 259 AM CDT Wed Jul 17 2024 A wet pattern setting up for the long term. Consensus shows a surface frontal boundary will be stalled over the forecast area as the period begins that will start to wash out late in the weekend. A moist air mass will be in place over the forecast area during the weekend. Frontal convergence, along with a weakness aloft, will work with the moisture to produce widespread shower and thunderstorm activity. PWAT values over the weekend will be near the 90th percentile of daily SPC climo which is 2.15 inches. Mean relative humidity values from 100H-50H will be over 70 percent, so the convection will have a chance to be efficient precipitation producers. Mid level winds look to be light, that should mean slow moving convection that will make for the potential for mesoscale boundary collisions and cell mergers that will enhance rainfall with the result torrential downpours. With the potential for high rain rates, some drainage issues may come about for streets and urban areas. Therefore, WPC has outlined the portions of the forecast are in a Marginal Risk Potential (risk level 1 out of 4) for Excessive Rainfall that may lead to flash flooding or the flood potential between 5 to 14 percent. Early next week the forecast area will continue have a weakness aloft between an upper level trough extending from the Great Lakes down into Texas, and the sub-tropical ridge to the east. Meanwhile. a deeper south flow around the sub-tropical ridge will bring a surge of highly anomalous moist air into the region, with PWAT values well over the 90th percentile level and over 2.25 inches. Mean Relative Humidity in the 100H-50H layer is progged to be over 80 percent with warm cloud layer depth in the 13k to 15k foot range. Therefore, convection will likely be of the warm process highly precipitation efficient variety, which again means the likelihood of torrential downpours with high rain rates in a short period of time. If this scenario continues, then the excessive rainfall and flood potential risk will be extended into early next week. With the expected cloud cover and widespread convection, the heat is expected to be kept in check somewhat with max heat index readings mainly at or below 100 degrees for Saturday into early next week. 07/Rua && .AVIATION... (12Z TAFS) Issued at 630 AM CDT Wed Jul 17 2024 VFR conditions will persist for much of the day, particularly for more interior SETX and SWLA locations. A moisture gradient along SETX and Central LA will provide a focal point southwards for periodic VCSH and VCTS, particularly for near coastal site through the morning. Another round of VCTS expected through the mid- afternoon hours which may periodic lower conditions to MVFR / IFR temporarily. Winds outside of storms will remain variable southerlies through the afternoon. 30 && .PRELIMINARY POINT TEMPS/POPS... AEX 96 73 92 71 / 40 20 80 60 LCH 91 77 91 74 / 50 30 80 70 LFT 93 78 92 76 / 60 30 90 60 BPT 93 76 91 74 / 50 20 70 70 && .LCH WATCHES/WARNINGS/ADVISORIES... LA...None. TX...None. GM...None. && $$ SHORT TERM...30 LONG TERM....07 AVIATION...30