Area Forecast Discussion
Issued by NWS New Orleans/Baton Rouge, LA
Issued by NWS New Orleans/Baton Rouge, LA
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560 FXUS64 KLIX 092044 AFDLIX Area Forecast Discussion National Weather Service New Orleans LA 344 PM CDT Thu May 9 2024 ...New SHORT TERM, LONG TERM, AVIATION, MARINE... .SHORT TERM... (This evening through Saturday night) Issued at 245 PM CDT Thu May 9 2024 A vigorous vorticity max and associated 100+ knot upper level jet streak is currently moving through Texas this afternoon and will pass through the Lower Mississippi Valley and Gulf South tonight into tomorrow morning. Strong deep layer ascent has been noted with this system over Texas today, and this same ascent will move through the forecast area tonight. This deep layer forcing will tap into a very moist and highly unstable airmass, and this will allow any convection that moves in from Texas to maintain itself through the overnight hours. In terms of moisture and instability, PWATS will be near 2 inches tonight and very steep mid-level lapse rates of around 8.0 C/KM will support MLCAPE values on the order of 3000 J/KG. Thus, there will be no form of capping inversion to inhibit updraft growth and sustainment over the area. Additionally, the steep lapse rates in place will also allow for easier downward transport of stronger winds aloft and this reflected by very high downdraft CAPE values of 1000 J/KG. The passage of the jet streak aloft will increase 0-6km shear values to around 60 knots and these stronger winds will easily descend toward the surface in the form of a rear inflow jet behind the developing convective line over east Texas later this evening. The latest CAMS have trended further to the south and there is more confidence that a strong bow echo will impact portions of Southwest Mississippi and portions of the Florida Parishes late this evening into the early morning hours tomorrow. Winds in excess of 60 knots are absolutely possible with this bowing segment. Large hail may also be a concern given the high MLCAPE values and steep mid-level lapse rates. Any wind driven hail would lead to additional damage to buildings and vehicles. The most likely timing for this bow echo to impact the area will be between 11 PM and 5 AM based on the latest guidance. The cold pool in the wake of the convection will allow a front currently draped over north Louisiana to surge southward late tonight into tomorrow morning, and fully expect to see the front clearing the CWA by late tomorrow morning. Strong dry air and negative vorticity advection will follow the front and the departing upper level vort max tomorrow into tomorrow night, and this will lead to rapidly clearing skies tomorrow afternoon. One caveat is that colder air is not expected to initially move into the area, and the combination of increasing solar insolation, weak downslope heating on the back of northerly winds, and dry air will allow temperatures to climb into the upper 80s and even lower 90s. The colder air will finally move in by tomorrow night, and temperatures will rapidly fall into the upper 50s and 60s by Saturday morning. Temperatures will be near average for Saturday with highs warming into the low to mid 80s and lows dipping back into the upper 50s and 60s Saturday night. && .LONG TERM... (Sunday through Wednesday night) Issued at 245 PM CDT Thu May 9 2024 Long term forecast looks active. Overall the medium range global models have the same general idea showing a very progressive pattern with multiple impulses and s/w moving through. Obviously there are timing issues between the models but they all show what could be 3 to 4 rounds or more of rain. Latest NBM is in full agreement. The biggest question is how much rain do we eventually get and temperatures. The amount of rain is extremely difficult to try and predict however the temperatures appear to be a little too warm if we are expecting as much rain and cloud cover. Made some small deviations a degree or two lower for highs but overall stuck with the latest NBM until we can get a better idea of timing. We begin with the end of the weekend and likely one last pleasant day however, there is a chance that rain tries to move in from the west as early as Sunday evening. The ridge aloft should start to move east of the area late Sunday as a deep s/w moves across the Continental Divide and into the Plains. That along with the southern stream will start to increase the mid lvl flow and we could see the first impulse move across the coast and Lower MS Valley Sunday evening and night. As we move into the work week moisture will increase quite significantly with PWs easily over 1.75" and possibly over 2" before sunrise Monday. PWs stay that high until midday/afternoon Tuesday when drier air from the north could infiltrate the region temporarily, PWs may fall below 1.25". However, this will be short lived as moisture looks to quickly rebound overnight Wednesday with PWs approaching 2" once again early Thursday morning. With moisture this abundant it will not take much to get convection to fire and with any disturbance/jet streak we could easily see numerous to widespread convection. How much rain is basically impossible to discern and multiple things go into this: - Instability: we will be unstable how unstable depends on timing and whether we get much sun. - Jet strength and placement: All levels, LL jet increasing or decreasing the LL convergence, Mid lvl adding that extra forcing, Upper lvl location enhancing the or hindering the diffluence/divergence aloft - Timing/strength/location of impulse and s/w`s: this sort of goes into the previous two but this also will determine where convection initiates and how it evolves. Also determine where and how strong any sfc features are which will also dictate precip placement. Depending on how these ingredients come together we could have multiple rounds of storms some of which could be quite efficient. At this time if everything runs similar to what is being advertised it is not out of the question to see widespread 4 to 7" of rain with locally higher amounts likely. Take that with a grain a salt though because again just one or two things slightly different will easily impact location, timing, and amounts. One example is if we get an MCS to develop over the coast and just into the Gulf as this would drastically lower the rain potential inland for that round. The rain is wanted but depending on things set up it could be a tad more than we really want. /CAB/ && .AVIATION... (18Z TAFS) Issued at 245 PM CDT Thu May 9 2024 Moist boundary layer conditions will continue to keep a scattered to broken strato-cumulus field in place at all of the terminals through 03z. Ceilings will range from 2000 to 3500 over this period. After 03z, a band of convection is expected to begin impacting the terminals. The highest threat of convection is at MCB, and have included a TEMPO group from 06z to 08z with stronger west winds, lower visibilities, and TSRA. Elsewhere, the convective chances are low, and only have VCTS wording in place at BTR, HDC, ASD, GPT, NEW, and MSY between 06z and 12z. Overall, prevailing ceilings of 800 to 1500 feet can be expected over this time period as the band of convection moves through. After 12z, rapidly improving conditions are expected as winds shift to the northwest in wake of a passing cold front. Drier air moving in will allow ceilings to mix out with VFR conditions expected by 18z. && .MARINE... Issued at 245 PM CDT Thu May 9 2024 Southerly flow near 15 knots will persist over the waters tonight in advance of an approaching cold front. The front will move through the water tomorrow morning, and a surge of colder air into the area tomorrow night will lead to a brief period of stronger offshore flow to near 20 knots. Seas will also remain somewhat elevated in the 3 to 5 feet range over this period. High pressure passing through the area Saturday into Saturday night will lead to lighter winds of 10 knots or less, calmer seas, and more variable wind directions. By Sunday, the development of a broad area of low pressure over the Plains and a high to the east will increase southeast gradient winds back into the 15 to 20 knot range. These stronger onshore winds and resultant higher seas will persist through Tuesday as the low tracks to the north of the area and the high remains in place. PG && .PRELIMINARY POINT TEMPS/POPS... MCB 67 85 59 81 / 60 20 0 0 BTR 73 88 64 84 / 30 10 0 0 ASD 73 90 63 85 / 30 30 0 0 MSY 76 88 69 83 / 20 20 10 0 GPT 73 90 64 85 / 40 40 0 0 PQL 72 90 62 86 / 40 40 0 0 && .LIX WATCHES/WARNINGS/ADVISORIES... LA...None. GM...None. MS...None. GM...None. && $$ SHORT TERM...PG LONG TERM....CAB AVIATION...PG MARINE...PG