Area Forecast Discussion
Issued by NWS New Orleans/Baton Rouge, LA
Issued by NWS New Orleans/Baton Rouge, LA
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
984 FXUS64 KLIX 150914 AFDLIX Area Forecast Discussion National Weather Service New Orleans LA 414 AM CDT Sat Jun 15 2024 ...New SHORT TERM, LONG TERM, AVIATION, MARINE... .SHORT TERM... (Today through Sunday night) Issued at 250 AM CDT Sat Jun 15 2024 A highly subsident airmass associated with deep layer ridging centered directly over the forecast area will remain in place today. The end result will be very warm and dry conditions continuing with little in the way of cloud development anticipated even during peak heating hours. Temperatures will once again climb into the mid to upper 90s and heat index values will rise to between 100 and 105 degrees this afternoon. Tonight and Sunday will be a period of transition from the dry pattern in place the past few days to a much wetter period of weather expected for much of the upcoming week. This will be due to a flux of deep layer tropical moisture currently parked over the southern and eastern Gulf sliding to the northwest on the western periphery of the deep layer ridge axis that will remain centered over the Southeast CONUS. Tonight will remain dry through the evening hours, but gradually increasing moisture in the low levels will result in scattered showers and few weak thunderstorms pushing onshore by daybreak tomorrow. Further inland, the airmass will remain sufficiently dry and stable to keep rain shower activity at a minimum. This is well reflected by an expected PWAT gradient ranging from around 1.4 inches in southwest Mississippi to near 2 inches along the immediate coast of Louisiana by daybreak on Sunday. As the deep layer moisture continues to feed into the region on Sunday, PWATS will further increase to around 2 inches over the northern third of the CWA to around 2.3 inches along the Louisiana coast. These values are between the 90th and max PWAT readings typically seen in mid-June. Rainfall rates of 2 to 3 inches per hour can be expected by the afternoon hours, but storm motions of around 20 mph will help to limit rainfall totals a bit. Still, there will be a localized street flooding concern for areas with poor drainage capacity. Despite the very moist airmass in place, some lingering dry air in the mid- levels could become entrained into the deepest convection Sunday afternoon. Thus, there could be some stronger gusts of wind that occur with the most potent convective cells that form. This is supported by both fairly steep low level lapse rates in excess of 6.5 C/km and downdraft CAPE values of around 1000 J/KG. Conditions will remain unsettled Sunday night as a weak upper level vorticity maxima sliding up from the central Gulf taps into the very moist airmass in place. Despite some loss of instability as temperatures cool into the low to mid 70s, the slight increase in upper level lift will allow for continued development of thunderstorms offshore where the diurnal maximum will be reached. Mean storm motion will be onshore from the south-southeast at around 20 mph, and this will push these offshore storms inland as far north as the I-10 corridor through the night. Rainfall processes will be highly efficient at this point as any mid-level dry air is flushed out and temperatures start to warm aloft and would not be shocked to see rainfall rates of 3 to 4 inches per hour develop during the overnight hours. This will keep the risk of street flooding in poorly drained areas in place through the overnight hours. A flood watch for flash flooding will likely be needed for portions of the forecast area starting Sunday night. && .LONG TERM... (Monday through Friday) Issued at 250 AM CDT Sat Jun 15 2024 Monday and Tuesday will see the highest potential for flash flooding in the CWA as precipitable water values surge to around 2.5 inches across the entire region. H5 temperatures will be quite warm at -5C, and this will result in highly efficient warm rain processes continuing Monday into Tuesday. Numerous rounds of thunderstorms will redevelop over the same areas, and these thunderstorm complexes will be moving to the northwest at 25 to 30 mph. These storm complexes have the potential to produce localized rainfall rates as high as 5 inches per hour, and these high rainfall rates combined with already saturated soils will lead to excessive runoff into area rivers and drainage canals resulting in some more widespread flooding concerns beyond the normal street flooding observed with Summer storms. The pattern will begin to shift on Wednesday as the plume of deeper tropical moisture shifts to the west and increased upper level ridging builds over the area. This increased ridging will develop in advance of an inverted trough axis pushing westward from Florida. A sharp moisture gradient is expected to be in place by the afternoon hours with PWATS ranging from near 2 inches along the Atchafalaya Basin to around 1.5 inches across coastal Mississippi. These more average PWAT values will persist into Thursday night, and the end result will be a return to more typical convective coverage and normal Summer rainfall rates of 1 to 2 inches per hour. Storm motion will continue to be northwesterly at 25 to 30 mph, and this will help to limit rainfall totals. However, the already saturated soils will still lead to a higher than average flood threat as any rainfall quickly runs off into the drainage systems. Some localized street flooding will be a concern, but the more significant flood threat will be lower on Wednesday and Thursday. Temperatures will also warm back to more normal readings by Thursday as convective activity decreases back to the scattered diurnally driven activity typically seen in June. The inverted trough axis will finally move through the forecast area on Friday, and another surge of deeper tropical moisture and increased convective coverage will take hold of the area. PWATS are expected to climb back to near 2 inches, and rainfall rates of 2 to 3 inches per hour will be possible with the strongest thunderstorms that form. Once again, the saturated soils in place will result in higher than normal runoff and the threat of localized street flooding concerns. Temperatures will be near average in the upper 80s and lower 90s as the convection will still be highly diurnal despite the increased forcing aloft associated with the inverted trough axis. && .AVIATION... (06Z TAFS) Issued at 250 AM CDT Sat Jun 15 2024 VFR conditions will remain in place at all of the terminals through the end of the forecast period. Winds will shift due to an onshore component by 18z at GPT, NEW, and MSY as a sea- breeze/lake-breeze forms. && .MARINE... Issued at 250 AM CDT Sat Jun 15 2024 A tightening pressure gradient between a ridge over the Southeast CONUS and a strengthening area of low pressure in the Bay of Campeche will result in an extended period of small craft advisory conditions over the coastal waters during the upcoming week. These small craft conditions with winds of 20 to 25 knots and frequent gusts to 30 knots are expected to develop as early as tomorrow night, but more likely on Monday and then continue through Thursday. These winds extend across a long fetch from the eastern Gulf, and this will allow for a decent swell of 2 to 3 feet to move into the area. This swell will combine with wind waves of 5 to 7 feet to push offshore seas to around 10 feet during the week. Wave run-up along east and south facing shores will also be an issue through the week, and some minor coastal flooding is anticipated to occur during high tide cycles starting on Tuesday and continuing through Thursday. && .PRELIMINARY POINT TEMPS/POPS... MCB 97 72 93 72 / 10 10 60 50 BTR 97 74 92 75 / 10 10 80 60 ASD 96 75 89 75 / 10 30 80 70 MSY 94 78 88 77 / 10 30 90 80 GPT 94 78 88 77 / 10 30 80 70 PQL 95 76 89 76 / 10 30 80 70 && .LIX WATCHES/WARNINGS/ADVISORIES... LA...None. GM...None. MS...None. GM...None. && $$ SHORT TERM...PG LONG TERM....PG AVIATION...PG MARINE...PG