Can any of the weather buffs explain what's about to happen in NOLA? (1 Viewer)

I get emails from a pro-met in the NOLA area. It's long.

March 3, 2008
this Pre-dawn Monday morning
213 AM CST



* * * Stormy weather headed for Southeast Louisiana late today & ESPECIALLY tonight, Monday NIGHT, 3/3/2008 * * *



* * * Expect a Tornado Watch will be issued late this afternoon into Monday night, 3-3-2008 * * *



* * * Also expect a few severe warnings to accompany the watch * * *



* * * 3 - Star Writing * * *



I. Introduction.


It's been a long time since I furnished you with a weather writing. This particular weather coming late today & tonight will be a dynamic storm situation which WILL have a Tornado Watch accompany the weather that it brings.


In the New Orleans area, expect the HEAVIEST thunderstorms to come Monday night, (tonight). However, a prelude to tonight's activities includes some pop-up showers that will begin during the mid-afternoon hours today, most prevalent north & west of the lake. By evening, expect more showers & storms to develop and move in to our area.


The Baton Rouge area will get more showers, first, during the afternoon today. Showers & thunderstorms this afternoon & evening, north & west of Lake Pontchratrain will need close surveillance for tornadic supercell potential, as the cap erodes & better moisture moves into the region. Then, EVERYONE gets the rain tonight, both sides of the lake.


I should say this: Supercell potential is the highest late this afternoon through early tonight.


Because I see a slow-down of the advancement of weather features, (LLJ, 850 DP axis, 700 RH's), between 6 PM & Midnight, heavy rainfall also could be channeled right over Southeast Louisiana for a period of hours tonight.


II. Priming the Pump.


Today, it'll be very warm with highs reaching near 80 degrees. Strong southeast winds of 20 mph & frequently gustier in the afternoon means a bad hair day. Moisture depth will increase on the heels of these strong winds, as a capping inversion whithers away by late afternoon.


A strong cold front will reach New Orleans a little after midnight late tonight, dropping temperatures down to 47 degrees by Tuesday morning & not rising but only 5 - 10 degrees from there. It's back to sweaters on Tuesday.



III. Timing of Thunderstorms & Severe Weather.


A few showers or thunderstorms will first start sprouting in the mid-afternoon hours today, with better coverage west and north of the lake. These daytime afternoon showers will NOT be the main show, though.


The heart or meat of the main bang of storms comes tonight on Monday night for New Orleans & southshore parishes. Late this afternoon, look for a Tornado Watch to expand eastward to include all of Southeast Louisiana.


I think for the New Orleans area, expect the HEAVIEST rain to fall between 6 PM and Midnight tonight.


However, I think that the severe weather threat will start earlier, as in 4 PM during peak heating time going to 11 PM.


Since there will be plenty of lingering moisture late tonight after midnight, I do think there will be some late night, post-frontal drip; residual patchy light rain or showers behind the front, too.


In other words, there will be some high-altitude overrunning light rain behind the frontal passage, very late tonight, as forecast 700 mb winds are to be from 210 degrees after the surface windshift to the northwest. Any patchy light rain AFTER midnight late tonight will be NON-severe.


The severe threat will be mostly between the hours of 3 PM & 11 PM late this afternoon & tonight for N.O., (slightly earlier northshore). And the heaviest rainfall for New Orleans to be between 6 PM & Midnight.


IV. Rainfall Amounts.


Recent, NEWER trends I've been watching show that projected rainfall totals look to be on the RISE, comparing with older data. The movement of weather features SLOWS DOWN between 6 PM & midnight tonight, possibly stalling-out the heavier rainfall channel over the SE Louisiana region, at that time.


I feel that a good, healthy swath of 1 - 3 inch rainfall totals can be expected across the better part of Southeast Louisiana; higher amounts north; lower amounts south. Isolated swaths of 3 - 4 inches in SW Miss, & northern northshore parishes.


Still, I'll give you what your most recent models data show, centered ON New Orleans: The range is between 0.76" to 2.12" for this storm event.


V. Severe weather types.


There is the risk for severe weather. I prefer the NORTHSHORE parishes as being the greater threat for severe weather occurrences. On the southshore, I'm not as impressed, however, nor as gung-ho with it as much as my colleagues at your S.P.C. There's only 4 different types of severe weather to watch for: tornadic; straight-lined wind damage; flooding; or hail.


I prefer to go with #1.) Brief/short flooding; #2.) Tornado #3.) Wind damage; and lastly #4.) Hail, in that order. The readers here need to understand that we DO NOT go into this storm event with the expectation that your location is going to get 'banged-up' & destroyed to get the classified severe weather. For most of us, it'll simply be just thunderstorms with heavy rainfall & gusting winds of 35 to 45 mph. But the TV set will make it look more (i.e. -- warnings issued).


The Nam's calculated top peak wind gusts were for 48 to 49 kts on Monday evening. That equates to 55 - 56 mph, BUT ONLY IN THE MOST HEAVY STORM. The highest hail stone size it calculates is 1/2" - 0.70".


Here's the high point about the severe weather talk. It deals with the tornado threat. There are certain criteria that are being met, that I talk in further detail ON MY WEATHER PRESENTATION, AUDIO/SLIDESHOW I gave you the link to yesterday. I encourage you to listen to it.


Lastly, I'll close with this: I reviewed a checklist, (Miller's), 21 assorted parameters for severe weather. Of the 21: 9 out of 21 showed weak potential for severe weather. 8 of 21 showed moderate potential for severe; and 4 of 21 showed strong potential for severe weather. That was centered on New Orleans. So, it'll be a little higher north of the lake.
 
It just rolled through up here. A nice helping of rain and a 10 degree drop. Not as bad as anticipated.
 
It dropped about 20 degrees here in Houston within just a few minutes time. Most of the bad rain was north of us; we got some light showers, followed by some strong winds and a bit heavier rain. Now it's overcast and much much cooler. Glad I sent the kids' jackets in their backpacks...it was 72 when they left this morning; it's 50 now.

New Orleans may be far enough south of the main weather system, like Houston, so that you don't get the severe stuff. You'll likely get more rain than we did, it looks like. We were under tornado watches too, but I never even heard a rumble of thunder.
 
beast
 

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I'm in West Monroe, northern LA.

It was so windy here a little earlier, it was freaking me out. I was playing the new Lost Video game, when the wind was just getting louder and louder. I looked out the window expecting to see rain, but it was just wind. The first thing I think is Tornado when things look like that. I think it has past us for right now till the next wave hits.
 

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