Area Forecast Discussion
Issued by NWS Lake Charles, LA
Issued by NWS Lake Charles, LA
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030 FXUS64 KLCH 181826 AFDLCH Area Forecast Discussion National Weather Service Lake Charles LA 126 PM CDT Thu Jul 18 2024 ...New AVIATION... .SHORT TERM... (Today through Saturday night) Issued at 353 AM CDT Thu Jul 18 2024 An upper level trough shifts off the SETX Coast into the western Gulf. Concurrently, a shortwave trough with positive tilt further upstream over the central Plains will continue to amplify toward the ARKLAEX and Mississippi Valley into Sunday morning. Together, both features develop a series of minor perturbations in the pressure pattern aloft to sweep through the area, thus providing multiple rounds of Isolated to periodically widespread showers and storms through Sunday. In addition the frontal pattern along with increased cloud cover will trend down daytime high temperatures toward mid upper 80s through the start of the weekend. Should be noted, that sfc 3km moisture transport continues to remain from the Gulf / Caribbean driven easterlies which are forecast to develop a healthy moisture jet keeping the pattern fairly we throughout the remainder of the short term. That said, despite the influx of tropical moisture, per most recent guidance from NHC there is no tropical development forecast to develop in the next 7 days. Zooming in to the weather at hand, a southward moving cold frontal boundary over central LA continues to stall, becoming stationary along the SETX and SWLA Gulf Coast briefly. Last nights evening sounding data calculates PWAT of 1.88 which has been congruent with prior days forecast suite. With that in mind, northern portions of SETX and SWLA are in a Slight Risk (level 2 of 4) for excessive rainfall with the greater surrounding counties and parishes under a marginal risk(level 1 of 4). The stationary front will be the focal point for more widespread and heavier rainfalls to occur throughout today as it shifts southward. By tonight the front become stationary near the coast while the aforementioned shortwave amplifying south continues to shift east toward central AR. Additional speed divergence and vorticity are generated along central and southern portions of LA including SETX counties, therefore another night of nocturnal rainfall will occur into Friday morning. Here, the stationary front hangs along the coast remaining the focus area of thunderstorm genesis throughout the day. That said, periodic breaks to allow broken cloud cover is not out of the question. By Saturday morning, the parent shortwave shifts eastward over the TN while keeping a positive tilt toward the LA Gulf Coast lifting the boundary north again toward the ARKLTEX region. Upstream, another shortwave trough begins to deepen south of the central plains developing a weak surface trough over southern AR. Referring back to the earlier mentioned sfc- 3km moisture transport strengthening across the Gulf into the interior regions of TX / LA /MS, we continue to stay the course for further rounds of precipitation continuing into Sunday morning. Kowalski / 30 && .LONG TERM... (Sunday through Thursday) Issued at 353 AM CDT Thu Jul 18 2024 Still looking like a rather wet pattern setting up for the long term. Consensus of guidance is showing an upper level trough will be located from the Great Lakes into central Texas. Meanwhile, the Sub- Tropical Ridge will be centered over the western Atlantic off the east coast of Florida and the southeast US coast. This will allow for a weakness aloft to persist over the forecast area. This will likely provide little inhibition to get convection going. Plenty of Gulf moisture will be over the forecast area for Sunday into Monday with PWAT values between 2 and 2.15 inches which is between the 75th and 90th percentile of daily SPC climo. 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, and progged storm motion is around 10 knots. Therefore, slow moving convection with high rainfall rates could bring some drainage problems, not to mention 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 that could provide some drainage issues for streets and urban areas, WPC has outlined 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. As we get into Tuesday and further into the middle part of the week, no pattern change is noted. In fact, southwest flow is progged to increase ahead of the upper level trough that will increase surging East Pac moisture into the forecast area. Meanwhile, deep southerly flow around the sub-tropical ridge will bring surging moisture with origin from the northwest Caribbean and southwest Gulf of Mexico. The convergence of these moisture plumes will make for a tropical- like air mass with highly anomalous moist air over the forecast area. PWAT values well over the 90th percentile level and nearing max moving levels between 2.25 and 2.5 inches. The 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, and antecedent conditions become more moist from the expect rain over the weekend, then the flood potential risk may increase. However, still plenty of time to watch to see if this scenario becomes more likely. 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 Sunday into next week. 07/Rua && .AVIATION... (18Z TAFS) Issued at 125 PM CDT Thu Jul 18 2024 Local 88Ds show the convection which has been moving ewd across the forecast area is about to cross the Atchafalaya with thunder still being reported at the Acadiana terminals...will hold onto tempo TSRA there for an hour or two to account. Otherwise, CAM guidance indicates a quiet afternoon although have reinserted PROB30s to account for possible redevelopment with heating as satellite/88D imagery does show a MCV just to our northwest. CAM guidance is also depicting late night redevelopment via the MCV...PROB30s and VCs are being used all sites to handle the out hours of the TAF period for this. Otherwise, VFR conditions should prevail outside of convection. 25 && .MARINE... Issued at 335 PM CDT Wed Jul 17 2024 Not expecting the need for any headlines on the CWF over the next several days. 25 && .PRELIMINARY POINT TEMPS/POPS... AEX 89 71 86 70 / 70 70 80 30 LCH 90 74 88 75 / 70 80 80 70 LFT 92 76 89 76 / 90 70 90 60 BPT 91 74 90 74 / 70 70 80 60 && .LCH WATCHES/WARNINGS/ADVISORIES... LA...None. TX...None. GM...None. && $$ SHORT TERM...30 LONG TERM....07 AVIATION...25