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394 FXUS64 KLIX 091002AFDLIXArea Forecast DiscussionNational Weather Service New Orleans LA402 AM CST Mon Dec 9 2024...New SHORT TERM, LONG TERM, AVIATION, MARINE....SHORT TERM...(Today through Tuesday)Issued at 358 AM CST Mon Dec 9 2024The next disturbance, which looks to be the strongest, comes in today just before noon. Again, there will be light to moderate showers around before and after this moves through, but the heaviest rain with this one should start just before noon today through about 7p. This is all due to the lift from the H3 jet moving over gently rising isentropic surfaces(warm front). But just how gentle is this slope? If we look at one sfc, we will use the 308PT sfc from the NAM12 but any other model will show relatively similar solutions. Draw a cross section through the warm front which means we draw a line perpendicular to the warm frontal interface. We then see the 308PT sfc move from 168 miles south of Galliano to 57 miles south of Galliano and rise from 775mb to 725mb. We need to look at a rise/run for a solution that shows how "steep" this rise is, so our rise is 775-725=50mb and our run is 168-57=111miles which gives 50mb/111mile=.45mb/mile. Now we can compare this to other frontal surfaces to see just how gentle or strong the slope is. If you were walking along a sidewalk with this slope, you would probably not be able to tell there was a slope. But if we give you a strong cold frontal slope that could be roughly as high as a 1 to 0, you would definitely know there was a slope which in this case is like climbing a wall. This is set into perspective when we are trying to see how much a sfc can lift and how rapidly it would do so. The 308PT sfc actually levels out at the warm front and the surfaces go parallel to each other. This occurs around Franklinton LA as of this morning around 230a. And this is also where we see the moderate to heavy rain being produced from this location northward. This means that the H3 jet is lifting the moisture up along these surfaces and since they rise gently, the ascent is gentle and gradual. But it brings a strong vertical depth of moisture up into these areas from the gulf, so there is plenty of moisture to drop out as rain. The warm front is along the line of moderate to heavy rainfall which starts for our area in Pearl River Co. over to Franklinton to just north of BTR then down to Lafayette and into eastern Cameron Parish before diving into the gulf. This boundary will stay in this position this morning, but models want to shove this back south late today toward the coast, or at least flatten out the isentopic surfaces down to the coast. This would simply help produce more rain closer to the coast like what is occurring north of the coast now. But with the help of the next distubance moving through the jet, it will help enhance the rainfall over these surfaces, which brings about the reason for the flood watch and higher amounts of rain totals later today.The warm front moves or expands northward again ahead of the next cold front for Tue as another disturbance in the H3 jet flow moves over and moderate to heavy rainfall begins again over areas that are already saturated. This looks to start around 3a Tue through about noon. It is about this time frame, noon, that we should see the cold front start to enter the NW corner of the area and move all this mess to the east exiting the area around or shortly after midnight Tue night/Wed morning. And this cold front can do that because of its strongly sloped surfaces(almost straight up vertically before leveling out horizontally) acting like a bulldozer. But this can also cause an abrupt lift to this moisture and it does which will be able to add to the rainfall as well.All of that to say we will be keeping headlines as they are with an additional 1 to 3 inches possible today through Tue.&&.LONG TERM...(Tuesday night through Sunday)Issued at 358 AM CST Mon Dec 9 2024Once the front moves through, strong winds will carry CAA and DAA along with it bringing highs back into the 50s by Wed and Thu and freezing temps for northshore areas for Wed night. A warming trend should take hold by the end of this week as winds shift from northerly to easterly then southerly as the sfc high moves in Thu and exits east Fri. The next front looks to approach by the weekend. We will need to get a bit closer to this timing to figure what this one will do.&&.AVIATION...(12Z TAFS)Issued at 358 AM CST Mon Dec 9 2024The mix of IFR, MVFR and even VFR cigs will remain through this taf pack. Each site will be in and out of every level through the day with the addition of -SHRA for the most part but there could be a few vis restrictions to IFR with +SHRA. Can't rule out TSRA but should not be as common.&&.MARINE...Issued at 358 AM CST Mon Dec 9 2024Headlines will be lowered this morning as southerly winds begin to ease. A cold front will move through Tue evening bringing strong NW winds around 25-35kt. There is the potential that a gale watch could be issued for these winds late Tue night or early Wed. Winds will ease through the day Wed and should be low enough Thu morning to drop all headlines.&&.PRELIMINARY POINT TEMPS/POPS...MCB 71 61 69 37 / 80 80 70 30 BTR 76 65 74 41 / 80 70 70 30 ASD 72 62 74 41 / 100 70 80 50 MSY 73 64 74 45 / 90 70 90 50 GPT 69 61 72 41 / 90 80 90 70 PQL 74 62 76 42 / 90 80 90 80 &&.LIX WATCHES/WARNINGS/ADVISORIES...LA...Flood Watch through Tuesday morning for LAZ039-056>060-064>071- 076>090.GM...Small Craft Advisory until 9 AM CST this morning for GMZ570-572.MS...Flood Watch through Tuesday morning for MSZ077-083>088.GM...Small Craft Advisory until 9 AM CST this morning for GMZ572.&&$$SHORT TERM...TELONG TERM....TEAVIATION...TEMARINE...TE
