Southwest Pass of the Mississippi River to Port Fourchon Louisiana Marine Forecast
| Rest Of Tonight...South Winds 10 To 15 Knots. Seas 2 To 4 Feet. Dominant Period 5 Seconds. Patchy Fog In The Late Evening And Early Morning. |
| Monday...Southwest Winds 10 To 15 Knots Becoming Near 10 Knots Late In The Afternoon. Seas 2 To 4 Feet. Dominant Period 5 Seconds. Chance Of Showers In The Afternoon. Slight Chance Of Thunderstorms Late In The Afternoon. |
| Monday Night...South Winds 10 To 15 Knots Becoming Southeast After Midnight. Seas 2 To 4 Feet. Dominant Period 5 Seconds. Chance Of Showers And Slight Chance Of Thunderstorms. |
| Tuesday...East Winds 10 To 15 Knots. Seas 2 To 4 Feet. Dominant Period 5 Seconds. Chance Of Showers Through The Day. Slight Chance Of Thunderstorms In The Afternoon. |
| Tuesday Night...Southeast Winds 10 To 15 Knots Becoming South After Midnight. Seas 2 To 4 Feet. Dominant Period 4 Seconds. Chance Of Showers And Slight Chance Of Thunderstorms. |
| Wednesday...West Winds 10 To 15 Knots Becoming North 15 To 20 Knots In The Afternoon. Seas 2 To 4 Feet. Dominant Period 4 Seconds. Showers Likely In The Morning. Chance Of Thunderstorms Until Late Afternoon. Chance Of Showers In The Afternoon. |
| Wednesday Night...East Winds 10 To 15 Knots Becoming Southeast After Midnight. Seas 2 To 4 Feet. Dominant Period 5 Seconds. Slight Chance Of Showers After Midnight. |
| Thursday...South Winds 10 To 15 Knots. Seas 2 To 4 Feet. Dominant Period 5 Seconds. Chance Of Showers And Slight Chance Of Thunderstorms. |
| Thursday Night...South Winds 10 To 15 Knots. Seas 3 To 5 Feet. Dominant Period 5 Seconds. Chance Of Showers Through The Night. Slight Chance Of Thunderstorms After Midnight. |
| Friday...South Winds 15 To 20 Knots. Seas 3 To 5 Feet. Dominant Period 5 Seconds. Slight Chance Of Showers Through The Day. |
| Friday Night...South Winds 15 To 20 Knots. Seas 3 To 6 Feet. Dominant Period 6 Seconds. |
| Synopsis for Pascagoula to SW Pass Mississippi - GMZ501 Synopsis for SW Pass Mississippi River to Atchafalaya River- GMZ500 1007 PM CST Sun Dec 5 2021 High pressure remains anchored over the northwestern Gulf of Mexico. A cold front is expected to move through the central Gulf Coast region Monday afternoon and overnight before stalling. The front will then move north as a warm front thereafter on Tuesday. |
| Area Forecast Discussion National Weather Service New Orleans LA 554pm CST Sunday Dec 5 2021 /issued 356pm CST Sunday Dec 5 2021/ SHORT TERM (This evening through Tuesday Night)... Starting off with late this afternoon/early evening, overall is looking rather pleasant with only some patchy low-level cu or stratocu areawide bringing partly to mostly cloudy skies. Current state of the atmosphere reveals steady and persistent onshore moist return flow in progress with subtle veering low-level/near surface winds. We will continue.nue to see low-level flow slowly increase throughout the night tonight in response to a strengthening low-level jet/attendant tightening height gradient to nearby or just to our northwest. This is in association with a deepening positive-tilt shortwave trough axis and attendant surface low/cold front diving east and southeast into the Great Lakes/MS valley region overnight tonight that we will talk more about shortly. But meanwhile here, the first item to focus on will be the potential for fog once again later tonight and into early Monday. There are subtle environmental differences, including a slight increase in low-level winds mentioned before that could throw a wrench in either the expected coverage and/or density owing to a lower-confidence forecast. Combing through a large suite of model guidance this afternoon shows a bit of a spread, but enough to build a consensus especially after closely analyzing select short-range model soundings. The previous mornings fog processes have generally been a mixed/conglomerate radiative/advection process, with developmental emphasis moreso near areas near better moisture sources with air/water temperature differential (particularly near and within northern portions of the MS river where the thickest fog has been maintained now for the past several days). Closely looking at soundings show the increase in winds roughly from around 150-200m AGL and above, but with only very little increase below and to the surface. This will be important as winds are technically forecast to be just a few MPH higher than the previous mornings, but the question is how much will this harm the production of widespread, dense fog. Advertising for now that the potential of widespread dense fog will be lower than the previous few days, but not entirely out of the question especially anywhere where winds can shut down enough to aid in a more radiative fog development process. Otherwise, guidance also suggests shallow surface fog to maintain or increase along coastal Terrebonne parish, transporting inland given favorable wind advection regime. Because of this, will mention the greater potential for another round of fog for western areas, or generally along/west of I-55, with less potential east. Due to a lower confidence forecast, will hold off on any dense fog highligheights for now, and will refer to subsequent forecast shifts to re-analyze model guidance should the threat increase later this evening. Any fog around may linger, through mid-morning on Monday, but should be quick to dissipate as surface winds continue to increase out of the west/southwest. From here, the next focus as mentioned earlier will be on an approaching cold front and associated line of showers and storms entering our NW CWA areas late AM/early PM. Thumbing through individual HREF members shows somewhat ok confidence in regards to speed/timing with the main line, with the spread being around 50 miles or so on average from the slowest to fastest member. HRRR (High-Resolution Rapid Refresh) creeps this line in northwestern areas around noon as a few members have it in an hour or two earlier. The Storm Prediction Center does highlight a large portion of our CWA in a Marginal Risk for severe weather, highlighting particularly on low TOR and Wind probs. Taking a closer look at available shear with this line looking at the synoptic hour HRRR (High-Resolution Rapid Refresh) runs, we see a transitioning low-level vertical wind profile as this line progresses south and east. Early monday morning, surface winds begin more southerly (or from the SSW) which aids in a slight bump up in low-level 0-1/0-3 SRH of around 100-200m2/s2. But this is well ahead of the front with the line of showers then over northern LA/central MS. As the shortwave trough/attendant surface low continues to eject east into the Northeast, the aforementioned low-level jet discussed earlier flattens out and deamplifies with time. Surface winds transition more out of the southwest to eventual west-southwest which reduces necessary low- level shear/curvature to support the potential for rotating updrafts. Meaning, SRH lowers by the time the line enters out CWA likely becoming cold-pool dominant at some point, reducing the tornado risk. Having said all of that, storms within the line will need to be monitored across far northwestern areas, but the threat will likely diminish as the line sags south into central areas early afternoon. HRRR (High-Resolution Rapid Refresh) Neural Network Convective Hazard probabilities also illustrate this exact process with lowering probabilities as the line swings southeast aiding in confidence in the lowering TOR risk. Damaging winds may be the only (albeit still low) risk, with the potential for some sub-severe wind gusts along the line, particularly for northern and western areas of the CWA. We do see some very subtle phasing/matching of the weak subtropical jet lining up with the axis of the deeper shortwave trough axis to our north, but with max H5 winds in the 45-55kt range. Low-level winds diminish as mentioned earlier which reduces the threat even more to around 20-25kt meaning even where downward transfer occurs, even nearby the strongest updraft, we should only see generally sub-severe wind gusts in the 35-45mph range, maybe isolated higher but will remain also a minimal risk. Will just have to monitor for small bowing segments or for any cells that could initiate ahead/merge with the line over southern/southwestern MS and east of I-55 Monday afternoon; but the threat should diminish thereafter. Should mention the threat for hail is non-zero, with H5 temperatures in the -12 to -14C range, but should updrafts ascend high enough to tap into some of the colder air aloft, could see some isolated small hail collocated within any stronger storm. The line steadily diminishes as cold pooling overtakes the leading updraft ingest down to more of a line of showers across coastal LA and MS Monday afternoon/evening, with the stratiform precipitation shield diminishing with time. We should see the front settle into the northern Gulf Monday evening, eventually seeing most precipitation diminishing at that point only with perhaps some isolated/scattered showers around. Monday evening/night, a close upper-low over northern Mexico finally drifts east and weakens/stretches some, but provides enough downstream divergence coupled with lingering surface frontogenetic to re-enhance spotty shower coverage, mainly after midnight Monday night into Tuesday morning. Tuesday offers a bit of difficulty in the temperature forecast, but with persistent post-frontal moisture advection leading to mostly cloudy to even overcast skies, with some (but enough) ongoing low-level to near surface cold air advection, have decided to lean on the lower end of the very wide ensemble spread for MaxT's. This places many areas just around 2-3 degrees below deterministic values (upper 50's north/60's south). Be aware that this could be even cooler with thicker clouds or post-frontal showers, OR could lead in the wrong direction should Cold Air Advection relax and/or sunshine find it's way to the surface but will target temperatures below guidance for now given the setup at hand. What is left of the weakening shortwave impulse pushes east late Tuesday going into Tuesday night, leading to a drying trend but we may likely be stuck in low-level post- frontal clouds. LONG TERM (Wednesday through Sunday)... Clouds try to break up going into the daytime on Wednesday, with a steady return flow setting back up over the northern Gulf coast. This will lead to a warming trend starting mid-week, going into the rest of the week ahead. We see a weak/broad trough swing through Wednesday during the day, which tries to squeeze out some showers near our area, but better coverage will exist with surface cyclogenesis/frontogenesis over the mid-Atlantic states. We stay in this relatively moist environment thereafter as temperatures continue to build. Kept a warmer bias going on Thursday and Friday, placing areas into the 80's and overall pleasant. Late this week, large-scale ridging remains in control of the Gulf of Mexico, meanwhile deeper longwave troughing builds into the intermountan west. Trends with the GFS keeps this large NE to SW oriented positive tilt axis drifting east into the MS valley region late Saturday into Sunday, with some sharper curvature at the base of the trough pulling into the Arklatex region. The GFS and ECMWF (European Centre for Medium-Range Weather Forecasts) solutions are split on the amplitude/intensity of the "tip end" shortwave axis which has everything to do with the potential for severe weather downstream. The ECMWF suggests higher amplitude troughing to promote enough downstream divergence along the front to produce surface cyclogenesis, and should this happen this could help to back surface winds/increase shear ahead of what could be a quick-moving line of showers/storms. However, the GFS suggests less overall amplitude with the mid-level trough that never helps to deepen a surface low leading to less surface/low level backing in a primarily unidirectional vertical wind profile, limiting severe weather potential. Overall, many doubts here but will advertise the next chance of rain with this front at some point this upcoming weekend, with details including any severe weather potential forthcoming in the next several days. KLG Marine Onshore southerly flow will continue.nue to build later this evening through tonight and during the day on Monday, with exercise caution headlines in effect later this evening, tonight and through Monday. Some extension or upgrade to advisory criteria will be possible, but should remain generally in the 15-20kt range. The next front will swing through later Monday afternoon/evening before stalling over the northern Gulf. The front will return north with onshore flow persisting through the middle to later parts of the week. Additionally, southerly fetch increases as surface southerly winds build with increasing wave heigheights before the next cold front swings through following into next weekend. NOAA New Orleans LA Office: Watches - Warnings - Advisories LA...None. GM...None. MS...None. GM...None. |
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