MARCH 2021

General Weather Discussions and Analysis
Cromagnum
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I just see rain this week. What was the concern with severe weather?
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don
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SPC Extended outlook has the eastern half of southeast Texas in risk of severe weather. The worst of the weather should be over dixie alley, but discreet supercells cannot be ruled out even here locally due to moderate shear and moderate CAPE values.

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0346 AM CDT Mon Mar 22 2021

Valid 251200Z - 301200Z

...DISCUSSION...
...Day 4/Thu - Eastern TX to the Central Gulf Coast States...

An upper shortwave trough over the Rio Grande/northern Mexico will
strengthen and become negatively tilted as it ejects northeast
across the Arklatex through Thursday evening, and to the Ohio Valley
by Friday morning. Intense shear will overspread the south-central
and southern U.S. ahead of the trough. Furthermore, strong low-level
warm advection will result in a broad warm sector ahead of a
deepening surface low and eastward-advancing cold front from the
Sabine Valley eastward across the central Gulf coast/TN Valley
vicinity.

Differences in the evolution of the surface low across the lower MS
and OH Valleys are still apparent in medium-range guidance. This is
mainly resulting in uncertainty in the position of the surface low
and cold front Thursday morning, and how far east each of these
features progresses by Friday morning. As a result, changes in
severe probabilities, especially on the western and northeastern
edges, are likely in the coming days. Nevertheless, weak to moderate
instability will overlap with favorable shear parameters and an
overall supportive pattern for severe convection. A couple of rounds
of severe storms could be possible, as some warm-sector development
may occur across the Lower MS Valley before a QLCS develops along
the surging cold front during the evening/nighttime hours. All
severe hazards will be possible with discrete warm-sector
supercells. Potential for damaging gusts and tornadoes will becoming
preferential with any upscale development along the cold front.
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Cpv17
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Models aren’t looking good for rain over the next week or two especially south of I-10.
Cromagnum
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Seeing talk of "mud showers" tonight. I just washed my truck before this evenings popcorn showers rolled through to get a free rinse. Guess that's going to be pointless afterall.
Cromagnum
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Hill Country was pretty bumpy last night.

Houston's turn for the AM commute.


...SIGNIFICANT WEATHER ADVISORY FOR GALVESTON...SOUTHEASTERN FORT
BEND...NORTHERN BRAZORIA...SOUTHWESTERN CHAMBERS AND SOUTHERN HARRIS
COUNTIES UNTIL 645 AM CDT...

At 601 AM CDT, Doppler radar was tracking a strenghtening strong
thunderstorms along a line extending from Sienna Plantation to near
Brazos Bend State Park. Movement was east at 35 mph.

Pea size hail and winds in excess of 40 mph will be possible with
these storms.

Locations impacted include...
Pearland, League City, southeastern Missouri City, Galveston
Causeway, Galveston Island West End, Texas City, Friendswood, Alvin,
Dickinson, La Marque, Santa Fe, southwestern Seabrook, Webster,
Hitchcock, Manvel, Kemah, Fresno, southern Clear Lake, Nassau Bay and
Danbury.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with these storms, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

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JDsGN
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That was an intense thunderstorm here in Cypress in Fairfield. Haven’t seen lightening like that in a long time.
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jasons2k
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Lots of lightning here but managed only .28”
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don
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The ingredients are there for some pretty strong storms but the situation is conditional based on rather the cap can break or not this Thursday.I think the cap may hold for now.
txbear
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don wrote: Tue Mar 23, 2021 4:02 pm The ingredients are there for some pretty strong storms but the situation is conditional based on rather the cap can break or not this Thursday.I think the cap may hold for now.
Ah there it is. I was waiting for that three-letter curse word to show up. Seems like we could've had a few rounds of severe weather with the recent setups of fronts and boundaries, but seems like the cap has kept that tampered down.

We've seen what can occur when the cap busts along the gulf coast (Dixie Alley, my goodness), but we don't see similar setups here. I can gather some of the differences between here and say West Texas/Panhandle and the like because we don't see the dry line and those types of dynamics. But I would gather that our conditions would mimic, to some extent, those in Dixie Alley. Our cap seems to be a bit more stout seems like one factor, but that's just speculation. Bit of a headscratcher for me.
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jasons2k
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We are closer to the dry Mexican highlands and SW flow aloft from there brings-in the cap.

SW flow aloft over much of “Dixie” is from the Gulf....moist, not hot and dry.

And yes there are often better jet dynamics to the north of here. One reason why the storms are so intense in OK, KS, AR, etc.

Thursday will be a close call. A few hours and a few degrees either way could make a big difference. I hope the system slows down just a tad and crosses later in the day, giving us a better chance of rain. One can hope...
txbear
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Thanks, jasons2k. Appreciate the context. A curious note is that the Panhandle and West Texas, etc also have the tradewinds blow out of the SW and W from the higher and drier elevations in Mexico and New Mexico as well (a lot more dry land to contend with).

But perhaps it has somewhat to do with a couple of things; 1) the boundaries between hot/dry and humid extend down the surface out there and are a bit more stark with less mixing and 2) the intensely higher humidity/dew points here suppress temps to the point of not being able to punch towers through the cap. Probably much more to do with the latter. My amateur postulation after having lived in both.

Yeah, definitely hoping for additional rain.
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jasons2k
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txbear wrote: Wed Mar 24, 2021 10:48 am Thanks, jasons2k. Appreciate the context. A curious note is that the Panhandle and West Texas, etc also have the tradewinds blow out of the SW and W from the higher and drier elevations in Mexico and New Mexico as well (a lot more dry land to contend with).

But perhaps it has somewhat to do with a couple of things; 1) the boundaries between hot/dry and humid extend down the surface out there and are a bit more stark with less mixing and 2) the intensely higher humidity/dew points here suppress temps to the point of not being able to punch towers through the cap. Probably much more to do with the latter. My amateur postulation after having lived in both.

Yeah, definitely hoping for additional rain.
Well, then we are getting into all sorts of subtleties that depend on the situation and we get into the actual meteorology.

I remember well - I took my first Met class at Texas Tech with Dr. Peterson. He said out there in Lubbock, as a general 'rule of thumb' in the springtime you needed a dew point of 50F or above for the environment to be conducive for thunderstorms. In short, what he was really saying is that if the dew point is above 50, you are going to be on the moist side of the dry line. But one of my biggest take-aways has been '50 -- only 50? Down in SE Texas you're gonna usually need mid 60's+ for any action.'

Why is that?

A big part of it is up there in the Panhandle and into OK, there is often a "triple point" centered around a low. The position of the low (to our NW) often means that flow into the low pressure, in the low and mid-layers, is from the southeast, off of the Gulf. It's relatively moist and unstable. All you need is some heating and/or a cold pocket to pass overhead and boom! You get the storms up there.

Keep in mind for as active as it gets up there in the Spring, they end-up with only 15-20" of rain for the year.

Down here, if the system is progressive, as the low moves across our longitude and passes to our north, the low-level and mid-level flow often shifts to the southwest. We become the victim of the cap and/or a pre-frontal trough with a SW wind shift. The position of that flow just depends on the trajectory of the system, whether or not it's positively or negatively-tilted on its approach, etc.

Speaking of the system tomorrow - my local NWS forecast has this through by 11am and they have lowered my rain chances. Any hopes of busting the cap seem to be dwindling.
txbear
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Definitely spot on with the triple-point. Any talk of that, and things always tend to get sporty in those parts. The shear and lift you can get around the triple point, or even just the dryline by itself, can really get things going. Dryline....now that's a term I haven't referenced in a long time.

No need to remind me of how actual little rainfall in total areas to the west of '35 really end up with; we had reservoirs drying up completely and water source scarcity was something else (still is, especially with the aquifers).

Great dialogue.
unome
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Cromagnum
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Cap firmly in place over us. Little to no rain expected with today's front.
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don
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Yep looks like only streamer showers today.Whats interesting is that the last 24 hours models have gotten a little more aggressive with next weeks system.This weekend into next week we could get some much needed rain as models are in pretty good agreement with two slow moving fronts next week.The first one comes this Sunday and stalls over the area as a coastal low develops and rides the front producing widespread rain.Models are not showing anything significant at the moment but even an inch or two would be nice, we'll see not getting my hopes up yet...
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jasons2k
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0.00”

And to think several days back, today’s “midweek system” looked so promising. Lucy is hanging around...
txbear
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Big ole' goose egg, thanks cap. Talk about a huge swing from the forecast not so long ago.

And on queue, Dixie Alley looks to be rather sporty. Crazy to see how active that "Alley" has become, and I'm not sure that their geology allows for the construction of basements/cellars. Although there are those reinforced closets/rooms that can be incorporated into the main structure of the house.
Cromagnum
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Meanwhile, Dixie Alley is doing what it does best this time of year...
Cpv17
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The latest Euro has some nice rain for us Sunday into Monday morning.
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