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GMZ534 Lake Borgne- 349 Am Cst Sat Dec 9 2023
.small craft advisory in effect from late tonight through late Sunday night...
Today..South winds 5 to 10 knots. Waves around 2 feet. A slight chance of showers late this morning. A slight chance of showers and Thunderstorms early this afternoon.
Tonight..South winds 5 to 10 knots, becoming northwest 20 to 25 knots with gusts up to 30 knots after midnight. Waves 2 to 4 feet. A chance of Thunderstorms. Showers.
Sunday..Northwest winds 20 to 25 knots with gusts up to 30 knots. Waves 4 to 5 feet. A slight chance of showers and Thunderstorms in the morning.
Sunday night..North winds 15 to 20 knots with gusts up to 25 knots. Waves 2 to 4 feet.
Monday..Northeast winds 10 to 15 knots with gusts up to 20 knots, diminishing to 5 to 10 knots in the afternoon. Waves 2 to 3 feet in the morning, then 1 foot or less.
Monday night..Northeast winds 5 to 10 knots, increasing to 10 to 15 knots with gusts up to 20 knots after midnight. Waves 1 to 2 feet, building to 2 to 3 feet after midnight.
Tuesday..Northeast winds 10 to 15 knots. Waves 2 to 3 feet.
Tuesday night..Northeast winds 10 to 15 knots. Waves 2 to 3 feet.
Wednesday..Northeast winds 10 to 15 knots. Waves 2 to 3 feet.
Wednesday night..Northeast winds around 15 knots. Waves around 3 feet.
winds and waves higher in and near Thunderstorms.

GMZ500 349 Am Cst Sat Dec 9 2023
Synopsis for pascagoula to atchafalaya river out 60 nm..
light to moderate onshore flow of 10 to 15 knots can be expected in advance of an approaching cold front tomorrow afternoon. The cold front will sweep through the waters tonight, and winds will quickly shift to the northwest and increase in speed to 25 to 30 knots over all of the waters. These high winds will also push seas to between 6 and 10 feet over the open gulf waters and 3 to 6 feet in the sounds and lakes. These rough conditions will last through Monday morning before improving as high pressure briefly settles in. However, another low pressure system deepening over the central gulf on Tuesday through Thursday will increase easterly flow to near 20 knots. Seas will once again turn rough as the combination of wind waves and swell pushes seas to around 7 feet in the open gulf waters.

FXUS64 KLIX 090542 AFDLIX

Area Forecast Discussion National Weather Service New Orleans LA 1142 PM CST Fri Dec 8 2023

New UPDATE, AVIATION

UPDATE
Issued at 1130 PM CST Fri Dec 8 2023

Performed a late-nite update to refresh the forecast between the recent evening update and the upcoming morning forecast to catch on obs/trends. Seeing some patchy areas of fog already developing, but has refrained from becoming widespread or dense yet. Feeling more confident for areas that saw rain may see patchy fog going into daybreak and keeping the same idea going with low clouds elsewhere and mainly dry. Did slow the temperatures from dropping for areas east of I-55 to the MS coast where deeper Gulf return flow has persisted the strongest this evening, where dewpoints have either remained steady or slightly increased holding temperatures more steady versus dropping as they should.

Otherwise, no big changes into thoughts going into the day on Saturday. Starting to feel a bit more confident over the idea that convergent surface banding/feeder bands (perhaps even a pre- frontal trough axis) will form late morning into the afternoon hours which may be enough to get some scattered showers, few storms developing ahead of the approaching cold front. Shear is limited, but subtle enough to support a few organized updrafts albeit may be shallow depending on how quick the low-level inversion can either erode or forcing associated with any of these bands may be enough to pierce through it and get some convection going earlier on around mid/late afternoon. Something to watch, but will focus again the main activity along the actual front as it progresses east later Saturday evening for the threat of a few strong, possibly locally severe storms, with a few strong wind gusts, isolated tornadoes the main threats. Don't want to discount hail in any locally stronger updraft given relatively cold H5 temps in the -12/-13C range but again, will watch it. KLG

SHORT TERM
(This evening through Saturday night)
Issued at 252 PM CST Fri Dec 8 2023

The primary forecast concern for tonight will the risk of some locally dense fog developing over portions of Southwest Mississippi and the Northshore. This fog will be highly conditioned on boundary layer winds falling below 10 knots, and the confidence is not quite there to issue a dense fog advisory at this time. Otherwise, low overcast conditions and mild overnight lows in the upper 50s and lower 60s can be expected on the back of continued onshore flow.

Heading into tomorrow and tomorrow night, a strong positively tilted longwave trough will slide through the forecast area.
During the day tomorrow, deep layer southwest flow will strengthen as the trough axis approaches from the northwest. Any fog in the morning will quickly mix out as winds increase to between 10 and 15 mph. This deep layer onshore flow will also allow for continued warm air advection from the southern Gulf back into the region, and highs will easily climb into the mid to upper 70s. A few locations may even touch 80 in the afternoon. Moisture will gradually deepen through the day as this southwest flow persists, and this will allow precipitable water values to rise a good half an inch from the morning into the evening. PWATS will be approaching 1.5 inches by evening, and this will be enough moisture to support the development of scattered showers and a few thunderstorms as forcing gradually increases over the region.
Peak forcing will occur tomorrow night as the upper level trough axis and an attendant strong cold front sweep through the forecast area.

Sounding analysis indicates that a marginal degree of instability could take hold in advance of the front with MUCAPE values of 1000 to 1500 J/KG possible in the early evening. Shear values will also peak in this timeframe with 0-6km shear of 35 to 40 knots and directional shear of around 150 m2/s2. These values would be supportive of a few strong to severe storms, especially closer to the front over portions of Southwest Mississippi and northwest portions of metro Baton Rouge. By late evening into the overnight hours, conditions become much less favorable for strong to severe convection as shear values diminish and instability falls to 500 J/kg or less. In fact, most of the convection will likely become elevated and post-frontal by late evening. The progressive nature of the convection will also limit rainfall totals to generally around an inch or less.

By Sunday morning, the trough axis and front will be east of the area. Strong negative vorticity advection in the wake of the trough will lead to rapidly clearing skies through the day. A deep cold pool will also feed into the region, and 925mb temperatures will drop to around 40F. These values are supportive of surface temperatures in the mid to upper 50s Sunday afternoon.
Additionally, a very sharp pressure gradient between the trough and the high building in will lead to gusty winds of 15 to 20 mph through the day. Thus, despite the sunny skies expected by afternoon, a chilly and blustery day can be expected. Sunday night will also be cold with lows falling below freezing over the northern half of the CWA and into the upper 30s and lower 40s over the southern half. Winds will also remain elevated at around 10 to 15 mph, and this will push wind chill values into the 20s and lower 30s Sunday night.

LONG TERM
(Monday through Thursday night)
Issued at 252 PM CST Fri Dec 8 2023

By Monday the back side of the current trough is moving into slight ridging and southern branch flow. A surface high moves quickly across the area in the lea of the trough. Toward mid-week a low moves into the western US and provides a path for moisture return over the northern Gulf and into TX. By the end of the week there are some minor differences in global model solutions, but overall the low pressure moves slowly east while the ridging builds in amplitude over the eastern US.

All this results in chilly temps warming slightly through the end of the week and little to no rain. Early in the week we will have lots of sun, but will transition as the week progresses to seeing partly to mostly cloudy skies. Winds early in the week will be dominated by the surface high and generally light and variable followed by a shift to light and easterly for the remainder of the period. Of most note may be daytime RHs that may dip into the 40% range early in the week, but should increase as the additional moisture returns increase mid to late week.

NBM values are accepted, especially since there is very little variability in the ensemble members. However, slight downward adjustments to lows were made in cold air drainage areas on Monday and Tuesday.

AVIATION
(06Z TAFS)
Issued at 1130 PM CST Fri Dec 8 2023

Main focus in the 06-14Z time frame will be low CIGs and areas of sfc fog developing across a few area terminals. ATTM, trends matched with near-term guidance suggests best potential for reduced VIS/CIGs and areas of SFC fog to be for terminals along and east of I-55, but should be relatively patchy with some periodic/scattered areas of dense fog possible. Regardless of reduced VIS, CIGs will be low overnight for most terminals bouncing flight categories into IFR or lower at times through 12-14Z. Shortly after going into mid/late morning, some scattered SHRA might develop mainly across coastal areas, with more VCTS into the afternoon. Going beyond, a cold front and associated SHRA/TSRA is expected overnight Sat night into early Sunday, with an associated strong wind shift to follow the FROPA. Will begin approximate timing into upcoming TAF cycles. KLG

MARINE
Issued at 252 PM CST Fri Dec 8 2023

A rather rough period of weather is expected over the marine zones through the middle of next week as a series of weather systems impacts the northern Gulf. Initially, a strong cold front will sweep through the waters tomorrow night. In the wake of the front, strong winds of 25 to 30 knots with higher gusts and very rough seas of 6 to 10 feet will develop on Sunday and continue into Monday morning before easing. After a brief period of calmer conditions Monday afternoon into Monday night, another low pressure system developing in the central Gulf will begin to produce higher winds and seas over the waters on Tuesday.
Increasing easterly flow of 15 to 20 knots will combine with a long fetch and increasing swell train to push seas up to nearly 10 feet by Thursday over the outer waters.

PRELIMINARY POINT TEMPS/POPS
MCB 60 78 44 55 / 20 50 90 40 BTR 62 82 49 56 / 20 60 90 30 ASD 61 78 48 59 / 20 30 90 50 MSY 64 79 51 59 / 20 30 80 50 GPT 61 75 49 61 / 20 30 80 60 PQL 59 79 50 64 / 20 30 80 70

LIX WATCHES/WARNINGS/ADVISORIES
LA...None.
GM...None.
MS...None.
GM...None.

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