Area Forecast Discussion
Issued by NWS New Orleans/Baton Rouge, LA
Issued by NWS New Orleans/Baton Rouge, LA
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468 FXUS64 KLIX 232043 AFDLIX Area Forecast Discussion National Weather Service New Orleans LA 343 PM CDT Mon Sep 23 2024 ...New SHORT TERM, LONG TERM, AVIATION, MARINE... .SHORT TERM... (This evening through Wednesday night) Issued at 316 PM CDT Mon Sep 23 2024 Model agreement is high through the short term period and shows a deepening positively tilted trough axis tonight into tomorrow that takes a more neutral tilt by Tuesday night. At the same time, a fairly potent upper level low embedded within the larger trough will descend from the northern Plains and become detached from the northern jet stream on Wednesday. This low will continue to deepen over the Mid-Mississippi Valley into Wednesday night. In the low levels, a weak frontal boundary will gradually sink southeastward in advance of the trough axis. However, the parent low for this front will quickly advance to the east, and the front is expected to stall over the area on Wednesday. Although moisture values are marginal, enough forcing associated with increasing positive vorticity advection from the approaching trough axis and weak convergence along the front should be enough to produce scattered convective activity Wednesday into Wednesday night. Before Wednesday, dry mid- level conditions and lower than normal PWATS will greatly limit the convective potential on Tuesday. At most, an isolated shower or storm may develop across the far northwest portion of the CWA in southwest Mississippi along the weak frontal boundary. Temperatures will continue to run above average over this period with highs rising into the upper 80s and lower 90s both Tuesday and Wednesday and lows only dipping to around 70. && .LONG TERM... (Thursday through Sunday night) Issued at 316 PM CDT Mon Sep 23 2024 By Thursday, the tropical system moving through the eastern Gulf will drive the cold front over the area offshore resulting in significantly cooler high temperatures in the lower 80s. There is also expected to be a fairly sharp moisture gradient in place as the outer rain bands of the tropical system brush the Mississippi Coast and parts of Lower Plaquemines Parish. The result is POP of less than 20 percent for areas west of I-55 and 30 to 60 percent for locations further to the east. The highest POP values are across coastal Mississippi where some outer rain bands on the western periphery of the tropical system could pass through. Thursday will also be a breezy day with north winds of 15 to 20 mph and gusts up to 30 mph at times. As the system moves inland and away from the area Thursday night, strong negative vorticity and dry air advection will take hold of the forecast area. The end result will be a very dry and very stable airmass dominating the region from Friday through Sunday. PWATS will be well below normal and cloud development will be limited. Temperatures will also remain mild as northwest flow aloft ushers in a cooler airmass with lows falling into the 60s and highs only warming into the lower 80s on Friday and Saturday. Some warming back into the mid 80s is expected on Sunday as winds turn more southwesterly. Overall, have stuck with the NBM for forecast temperature and POP values in the extended period given the small spreads in the model solutions. && .AVIATION... (18Z TAFS) Issued at 316 PM CDT Mon Sep 23 2024 The primary forecast concern is the potential for IFR visibility and ceiling restrictions at MCB between 11z and 13z tomorrow morning. This period of IFR conditions will be tied into the strength of an expected surface based temperature inversion that forms as temperatures cool. Probabilities are high enough to warrant including these IFR conditions, and have gone with 300 foot ceilings and 1 mile visibility from 11z to 13z. Outside of this threat at MCB, VFR conditions are forecast at all of the remaining terminals through the end of the forecast period. && .MARINE... Issued at 316 PM CDT Mon Sep 23 2024 The main concerns for the marine forecast are directly related to Potential Tropical Cyclone 9. As this system intensifies into a tropical cyclone tonight into tomorrow and begins to move into the Gulf on Wednesday the pressure gradient over the coastal waters will begin to increase. Initially, benign conditions will persist over the waters through tomorrow, but winds will begin to increase from the northeast and east tomorrow night into Wednesday. By Wednesday night, small craft advisories will be needed as northeast winds increase to 20 to 25 knots over the open Gulf waters and sounds. These stronger winds will persist into Friday morning before finally easing as the tropical cyclone moves inland and weakens. The larger impact will be very high seas of 15 to 20 feet impacting the open Gulf waters east of the Mississippi River Thursday into Thursday night due to a combination of wind wave and swell activity. Seas of 10 to 15 feet can be expected west of the river and waves of 4 to 6 feet will impact the sounds over this period of time. && .PRELIMINARY POINT TEMPS/POPS... MCB 69 91 69 88 / 0 20 30 50 BTR 72 91 72 89 / 0 20 20 40 ASD 71 90 71 89 / 0 0 10 50 MSY 75 89 75 88 / 0 10 10 40 GPT 73 88 73 90 / 0 0 10 60 PQL 72 89 72 90 / 0 0 20 70 && .LIX WATCHES/WARNINGS/ADVISORIES... LA...None. GM...None. MS...None. GM...None. && $$ SHORT TERM...PG LONG TERM....PG AVIATION...PG MARINE...PG