Severe Weather Southeast Louisiana, April 4, 2011
Posted: Sat Apr 02, 2011 6:03 pm
April 2, 2011
this Saturday afternoon
550 PM CDT
Alright Gang ~~ Time for cyclogenesis to start rolling-out his PRELIMINARY thoughts on your big severe weather event up and coming for late Monday afternoon and Monday night, April 4, 2011. NOTICE--->> The SPECIFICS of this writing is applicable to SOUTHEAST LOUISIANA WEATHER ONLY!
I. Summary of the Bottom Line
First and foremost, let me say this: I believe this weather event will be "earmarked" with a HIGH WIND and DAMAGING wind potential, above all else, with secondary threats for HAIL, and then TORNADOES. Although, for c.y.a. reasons, I do believe your SPC will issue a Tornado Watch for all the area by late Monday afternoon, April 4th. This watch, followed by severe weather warnings, will commence from late Monday afternoon in to Monday night.
II. Initial Capping
I expect there to INITIALLY be a low-to-mid level capping inversion take shape EARLY Monday and early Monday afternoon. Anytime I see forecast 850 mb temps of 16 to 17° C and 700 mb forecast temps of 7 to 7.5° C, it offers the "smell" of cap to me. Surely enough, your GFS indicates 87 J/kg of conv. inhibition early Monday afternoon, and a cap strength of 2° C. Now, severe weather lovers, do not despair, as a cap is a good thing to have. It prevents "grungeola" piles of trash showers from developing too early and trashing over the atmosphere, (over-turning), and lets the HEAT of the day to BUILD over the region, to unleash in an explosive, yet nevertheless, pleasing ways for storm lovers to enjoy.
Look for this capping to be overcome by early evening as the cold front rapidly approaches, cooling aloft commences, and the stronger forcing / increasing wind speeds necessary for severe storms arrives at that time later on.
III. Model Inter-comparisons.
This was no easy, nor clear-cut solution to this Saturday morning's 12Z Saturday morning suite of models. We have an equal diversion of solutions on the short-wave troughs trajectory.
#1.) Your GFS is joined by the WRF and a little lesser extent the UKM in keeping a further NORTH track of the short-wave trough's path, passing NORTH of Southeast Louisiana.
#2.) Your ECMWF is joined by the NGP's, JMA, and to some extent the C-gem, although it's slower than the former 3 in this sentence.
I've seen this crap go on before between these models' differences, and the ECMWF has won-out in the past with a further South track, getting the severe weather potential more accurate.
However, I do respect the 500 mb patterns of the UKMET, and right now, it's about as close to a compromise between the GFS & ECMWF as there is, although it's tending to side just a little closer to GFS, but still offers a compromise between the 2.
I'm not ready to deduce & release a formal, structured writing to my weather e-mailing recipients, nor put on my website because of these VERY IMPORTANT model differences, that have consequences on the EXTENT of severe here.
IV. Justification for HIGH WIND & WIND DAMAGE threat
Whenever I see hodographs that tend toward straight-lined hodographs late in the afternoon, and winds veering at 850 mb to nearly westerly, out ahead of the front, this combined with HIGH Capes on the order of 1500 to 2000 J/kg and LI's of -5 to -7 and Showalters of -1.7 to -3, it indicates the magnitude of instability will just as equally as good as the last event we just completed, on the night of the 29th. Only this time, there will be MORE wind involved. Still, I'd prefer to see 0 - 6 km shears of better than the forecasted 30 to 36 kts.
This deep shear of 0-6 km forecast is more contingent upon the path & track of the short-wave trough. A further southward track will increase the belts of winds at all levels with a further south track, than a further North track.
I don't think there's going to be a whole lot of activity well in advance of the front due to this capping I mentioned above. By the time storms ignite, the winds in the lower levels of the troposphere will have already veered, decreasing the helicity, tending toward straight-lined hodographs, a uni-directional wind profile which will be MORE SUPPORTIVE of a SQUALL LINE formation. Some of you have come to know a squall line as a QLCS, which is short for Quasi-Linear Convective System, for those of you SPC worshippers. That's the language they use for a "squall line" Or LEWP's for "Line-echo Wave Pattern" So that's the lingo on that.
In fact, I think it may even be possible that a gust front will precede the squall line, whereby, just immediately AHEAD of the cold front the low-level winds will have already veered owing to a mesoscale gust front, which will come from the rain-cooled air, which will serve as a way of under-cutting the surface-based instability, and then the storm evolution becomes what I like to call, "outflow dominated" storms. This most often occurs with "anafronts". So I think that most of the storm activity will be confined right along the front, a little behind it, but NOT much ahead of the front in Southeast Louisiana.
Any further Southward track of the short-wave trough's positioning as the ECMWF, NGP's, JMA, and C-GEM models show, and we'll have a much less of a capping inversion to worry about, as there'll be greater height falls farther south, which implies colder-air advection, and a quick erosioning of the cap, along with increased belts of winds at all levels. This is why the forecast PATH & AMPLITUDE of this trough is EXTREMELY PIVOTAL in determining the EXTENT and SEVERITY of the severe weather this far South in Southeast Louisiana.
I do expect a Severe Weather Watch -- (likely a Tornado Watch) -- and several warnings to be issued in Southeast Louisiana starting late Monday afternoon to our North and spreading in to the rest of Southeast Louisiana during the early evening hours.
Because of the fast-moving nature of this cold front, these storms will be fast-racers, and not stick around and dump rainfall like that mini-MCS complex did on Tuesday night the 29th. So it's going to be in "in-and-out" kinda system -- not go on for a lengthy, 6 to 12 hours as the last one did. Also for that reason, the durations of heavy rainfall will be shorter -- much shorter than last time; this is why you're not seeing a whole lot of QPF in the models, because squall lines get in-and-out in a quick hurry. Blink; and you might miss it!
Okay, that's all for this edition.
-- cyclogenesis
this Saturday afternoon
550 PM CDT
Alright Gang ~~ Time for cyclogenesis to start rolling-out his PRELIMINARY thoughts on your big severe weather event up and coming for late Monday afternoon and Monday night, April 4, 2011. NOTICE--->> The SPECIFICS of this writing is applicable to SOUTHEAST LOUISIANA WEATHER ONLY!
I. Summary of the Bottom Line
First and foremost, let me say this: I believe this weather event will be "earmarked" with a HIGH WIND and DAMAGING wind potential, above all else, with secondary threats for HAIL, and then TORNADOES. Although, for c.y.a. reasons, I do believe your SPC will issue a Tornado Watch for all the area by late Monday afternoon, April 4th. This watch, followed by severe weather warnings, will commence from late Monday afternoon in to Monday night.
II. Initial Capping
I expect there to INITIALLY be a low-to-mid level capping inversion take shape EARLY Monday and early Monday afternoon. Anytime I see forecast 850 mb temps of 16 to 17° C and 700 mb forecast temps of 7 to 7.5° C, it offers the "smell" of cap to me. Surely enough, your GFS indicates 87 J/kg of conv. inhibition early Monday afternoon, and a cap strength of 2° C. Now, severe weather lovers, do not despair, as a cap is a good thing to have. It prevents "grungeola" piles of trash showers from developing too early and trashing over the atmosphere, (over-turning), and lets the HEAT of the day to BUILD over the region, to unleash in an explosive, yet nevertheless, pleasing ways for storm lovers to enjoy.
Look for this capping to be overcome by early evening as the cold front rapidly approaches, cooling aloft commences, and the stronger forcing / increasing wind speeds necessary for severe storms arrives at that time later on.
III. Model Inter-comparisons.
This was no easy, nor clear-cut solution to this Saturday morning's 12Z Saturday morning suite of models. We have an equal diversion of solutions on the short-wave troughs trajectory.
#1.) Your GFS is joined by the WRF and a little lesser extent the UKM in keeping a further NORTH track of the short-wave trough's path, passing NORTH of Southeast Louisiana.
#2.) Your ECMWF is joined by the NGP's, JMA, and to some extent the C-gem, although it's slower than the former 3 in this sentence.
I've seen this crap go on before between these models' differences, and the ECMWF has won-out in the past with a further South track, getting the severe weather potential more accurate.
However, I do respect the 500 mb patterns of the UKMET, and right now, it's about as close to a compromise between the GFS & ECMWF as there is, although it's tending to side just a little closer to GFS, but still offers a compromise between the 2.
I'm not ready to deduce & release a formal, structured writing to my weather e-mailing recipients, nor put on my website because of these VERY IMPORTANT model differences, that have consequences on the EXTENT of severe here.
IV. Justification for HIGH WIND & WIND DAMAGE threat
Whenever I see hodographs that tend toward straight-lined hodographs late in the afternoon, and winds veering at 850 mb to nearly westerly, out ahead of the front, this combined with HIGH Capes on the order of 1500 to 2000 J/kg and LI's of -5 to -7 and Showalters of -1.7 to -3, it indicates the magnitude of instability will just as equally as good as the last event we just completed, on the night of the 29th. Only this time, there will be MORE wind involved. Still, I'd prefer to see 0 - 6 km shears of better than the forecasted 30 to 36 kts.
This deep shear of 0-6 km forecast is more contingent upon the path & track of the short-wave trough. A further southward track will increase the belts of winds at all levels with a further south track, than a further North track.
I don't think there's going to be a whole lot of activity well in advance of the front due to this capping I mentioned above. By the time storms ignite, the winds in the lower levels of the troposphere will have already veered, decreasing the helicity, tending toward straight-lined hodographs, a uni-directional wind profile which will be MORE SUPPORTIVE of a SQUALL LINE formation. Some of you have come to know a squall line as a QLCS, which is short for Quasi-Linear Convective System, for those of you SPC worshippers. That's the language they use for a "squall line" Or LEWP's for "Line-echo Wave Pattern" So that's the lingo on that.
In fact, I think it may even be possible that a gust front will precede the squall line, whereby, just immediately AHEAD of the cold front the low-level winds will have already veered owing to a mesoscale gust front, which will come from the rain-cooled air, which will serve as a way of under-cutting the surface-based instability, and then the storm evolution becomes what I like to call, "outflow dominated" storms. This most often occurs with "anafronts". So I think that most of the storm activity will be confined right along the front, a little behind it, but NOT much ahead of the front in Southeast Louisiana.
Any further Southward track of the short-wave trough's positioning as the ECMWF, NGP's, JMA, and C-GEM models show, and we'll have a much less of a capping inversion to worry about, as there'll be greater height falls farther south, which implies colder-air advection, and a quick erosioning of the cap, along with increased belts of winds at all levels. This is why the forecast PATH & AMPLITUDE of this trough is EXTREMELY PIVOTAL in determining the EXTENT and SEVERITY of the severe weather this far South in Southeast Louisiana.
I do expect a Severe Weather Watch -- (likely a Tornado Watch) -- and several warnings to be issued in Southeast Louisiana starting late Monday afternoon to our North and spreading in to the rest of Southeast Louisiana during the early evening hours.
Because of the fast-moving nature of this cold front, these storms will be fast-racers, and not stick around and dump rainfall like that mini-MCS complex did on Tuesday night the 29th. So it's going to be in "in-and-out" kinda system -- not go on for a lengthy, 6 to 12 hours as the last one did. Also for that reason, the durations of heavy rainfall will be shorter -- much shorter than last time; this is why you're not seeing a whole lot of QPF in the models, because squall lines get in-and-out in a quick hurry. Blink; and you might miss it!
Okay, that's all for this edition.
-- cyclogenesis
