Area Forecast Discussion
Issued by NWS New Orleans/Baton Rouge, LA
Issued by NWS New Orleans/Baton Rouge, LA
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770 FXUS64 KLIX 131118 AFDLIX Area Forecast Discussion National Weather Service New Orleans LA 618 AM CDT Thu Jun 13 2024 ...New AVIATION... .SHORT TERM... (Today through Saturday Night) Issued at 300 AM CDT Thu Jun 13 2024 Today will see increasing negative vorticity advection throughout the day as a ridge begins to expand eastward from the southern Plains and Texas. However, there should be enough residual moisture below 700mb to support the development of isolated to widely scattered convection along and south of I-10 with the greatest probabilities along the coast of Louisiana and offshore later this afternoon. PWATS from New Orleans southward will range between 1.75 and 2 inches due to this residual moisture, and lapse rates along the coast will support deeper convection that could produce some brief heavy downpours and locally gusty winds. Given this threat, have PoP values of 20 to 40 percent in place for locations south of I-10. To the north of I-10, the influence of the building ridge will induce enough subsidence to effectively cap off convective development. At most, some fair weather cumulus development can be expected this afternoon. Temperatures will be seasonably warm with highs in the upper 80s and lower 90s. Any convection will quickly dissipate early this evening with the loss of daytime heating and skies will clear. Late in the night, increasing low level instability over the warmer Gulf waters will support scattered shower and thunderstorm development during the diurnal minimum around daybreak. A few of these showers and storms may move toward the immediate coast and this reflected by 20 percent PoP. Overnight lows will be near average. The shower and thunderstorm activity will be even more suppressed on Friday and Saturday as deep layer ridging becomes centered over the region. Very dry air aloft associated with deep layer subsidence will effectively cap off any rain chances over most of the forecast area both days. This drier airmass will result in precipitable water values dropping to around an inch over northern zones and closer to 1.4 inches along the coast. These values are in the 10th to 25th percentile for mid-June. The only region that may see an isolated shower or thunderstorm develop will be along the immediate coast where low level convergence is enhanced along the sea-breeze. Otherwise, only fair weather cumulus development is anticipated each afternoon. Temperatures will also be warmer than average with readings in the mid to upper 90s expected. Fortunately, the drier air mixing down to to the surface will keep dewpoints just low enough to produce heat index values of 100 to 105. These values are below our advisory criteria, but those who are more susceptible to heat illness including the elderly should limit time outdoors on Friday and Saturday. && .LONG TERM... (Sunday through Wednesday) Issued at 300 AM CDT Thu Jun 13 2024 The deep layer ridge axis will shift to the east of the area on Sunday, and this will open the door for a plume of deeper tropical moisture to begin feeding into the region. Sunday will see PWATS rise back to average for mid-June, and this will allow for greater convective activity by Sunday afternoon. PoP values will range from 30 to 50 percent north of I-10 and 50 to 70 percent south of I-10. The highest rain chances will be along the immediate coast and offshore where the deepest moisture is expected. The influence of the departing ridge will still be felt, especially over northern zones, as drier air in the mid- levels lingers. This drier air aloft when combined with fairly steep low level lapse rates could lead to a few wet microburst events Sunday afternoon as convective updrafts punch above 20k feet. Fortunately, the storm motion will be around 10 knots, and this will help to limit the heavy rainfall threat over portions of the southshore on Sunday. The impact of the increased cloud cover and convective activity will keep temperatures closer to seasonal averages in the upper 80s and lower 90s. The convection will be less pronounced Sunday night with the loss of daytime heating, but a weak upper level impulse rounding the southwest periphery of the upper level high over the Southeast CONUS will keep isolated to scattered convective activity in place over inland zones through the overnight hours. More numerous showers and storms are expected over the warmer offshore waters as the diurnal minimum is reached toward daybreak and low level instability increases. An increase in dewpoints into the 70s will keep overnight lows a few degrees above average with readings only dipping into the lower 70s over southern Mississippi and the upper 70s south of I-10. Monday through Wednesday looks to be a much more unsettled stretch of weather as the region remains on the western periphery of a deep layer ridge and deep tropical moisture continues to feed into the region. PWATS will be in the 90th percentile or higher each day with readings of between 2 and 2.25 inches expected. The result will be numerous showers and thunderstorms forming each day as temperatures climb into the mid to upper 80s. This reflected by the high PoP values of 60 to 80 percent forecast each day. The convective activity will decrease in coverage a bit each night as temperatures cool back into the 70s, but will still be at least scattered in nature. Storm motion will remain decent at 10 to 15 knots on Monday and Tuesday with a further increase to around 20 knots on Wednesday. However, very high rainfall rates of 3 to 4 inches per hour with the strongest convection could lead to some localized flash flooding issues each day next week. The highest threat will be for urban drainage systems that could be easily overwhelmed by these excessive rainfall rates. && .AVIATION... (12Z TAFS) Issued at 616 AM CDT Thu Jun 13 2024 VFR conditions will be the rule at the terminals through tomorrow as a drier and more stable ridge of high pressure begins to build in from the west. However, there are decent probabilities of shower and thunderstorm development between 23z and 01z near HUM before this drier air fully moves in. Have opted to go with VCSH wording over this time period at HUM to reflect this shower and thunderstorm risk. PG && .AVIATION... (06Z TAFS) Issued at 300 AM CDT Thu Jun 13 2024 VFR conditions at at all terminals currently and likely through the rest of the period. Can`t rule out some very isolated convection along the immediate LA coast tomorrow, but not enough confidence to include VCTS for any terminals. && .MARINE... Issued at 300 AM CDT Thu Jun 13 2024 Through Saturday, high pressure building over the waters will keep a light south to southeast flow of 10 knots or less in place. Seas of 2 feet or less will accompany these lighter winds. The only concern will be the threat of isolated to scattered thunderstorm activity that could produce some waterspouts and gusty winds. By Sunday, the high will shift to the east and a developing area of low pressure in the Bay of Campeche will lead to a tighter pressure gradient across the northern Gulf. East and southeast winds will increase to 10 to 15 knots on Sunday, 15 to 20 knots on Monday, and then to 20 to 25 knots on Tuesday. Seas will respond to these increased winds and should be in the 5 to 7 feet range over the open Gulf waters by Tuesday. The prolonged nature of these stronger onshore winds will lead to some minor coastal flooding issues by Tuesday. && .PRELIMINARY POINT TEMPS/POPS... MCB 92 68 96 71 / 10 10 10 10 BTR 93 71 96 74 / 10 10 10 10 ASD 93 73 96 75 / 20 10 10 10 MSY 91 77 94 78 / 30 10 20 10 GPT 92 76 93 78 / 20 10 10 10 PQL 93 73 94 75 / 20 10 20 10 && .LIX WATCHES/WARNINGS/ADVISORIES... LA...None. GM...None. MS...None. GM...None. && $$ SHORT TERM...PG LONG TERM....PG AVIATION...PG MARINE...PG