Current Set-up, Sat. 4/24

SPC outlook has been upgraded to a high risk for MS/AL/TN.  Lots of early morning action ongoing.  Very strong shear profiles are in place and expected to strengthen further through the day.  Forecast soundings from MS & AL show incredibly high helicities(exceeding 500m2/s2)  and fast storm motions (239/46 at Huntsville AL @21Z…also with a helicity >800m2/s2!), so any sustained supercell could spawn a long-track tornado.  Instability is forecasted to be moderate with CAPE running 1000-2000j/kg.  If any area destabilizes significantly with sun today, and any storm can stay discrete (storm coverage looks to be very high today), conditions could surely favor a significant tornado event.  I’m out for baseball for a while, post anything you see, and I will check back later….    -Dave

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28 responses to “Current Set-up, Sat. 4/24

  1. the moisture in the area is incredible with dewpoints in the low 70s–add this to the fact that temps themselves are in the mid-70s, and we’ve got one MOIST air mass

  2. Wow! Looking at parameters on the SPC mesoscale analysis page is enough to boggle the mind. The supercell composite value is 28 in Louisiana and southern Mississippi…I’ve never seen it that high! The shear values are also off the charts! It may not be great chase territory, but it can’t be much worse than some places here in Virginia.

  3. Tornado emergency now for Yazoo City, MS.

    The chase terrain in MS/AL/TN is pretty similar to much of eastern/central VA with the trees and hills. We would never say never about chasing in this region, but would allow a bit more of a safety margin in a situation like this because of the likelihood of truly violent tornadoes and the limited visibility.

  4. Even worse than the terrain is how rain-wrapped tornadoes usually get in the Gulf region. The Weather Channel has some live footage from a chaser near the Yazoo City tornado and it’s hard to make out much definition in the clouds.

  5. hokiestormchaser

    …just a quick update as things are unfolding pretty much as anticipated by the SPC. Instability remains modest by some standards, but as Chris mentioned shear is impressive. Back to the second part of the Blacksburg Cub’s double-header, and then I can look at the storms a bit more….-Dave

  6. …A TORNADO WARNING REMAINS IN EFFECT UNTIL 115 PM CDT FOR
    NORTHEASTERN YAZOO…WESTERN ATTALA AND SOUTHERN HOLMES COUNTIES…

    …THIS IS A TORNADO EMERGENCY FOR THE WARNED AREA…

    AT 1230 PM CDT…NATIONAL WEATHER SERVICE METEOROLOGISTS AND STORM
    SPOTTERS WERE TRACKING A LARGE AND EXTREMELY DANGEROUS WEDGE
    TORNADO. SIGNIFICANT DAMAGE HAS OCCURRED IN YAZOO CITY ALL ALONG
    THIS LONG TRACK TORNADO! THIS TORNADO WAS LOCATED NEAR MIDWAY MOVING
    NORTHEAST AT 50 MPH.

  7. Kevin,
    Agree with you wholeheartedly on ensuring a wider safety margin in that kind of sight-limited territory amid fast-moving tornadic storms like those we’re hearing about today. That’s the beauty of chasing the open Plains; you can get closer to the action without increasing the risk past safety margins because you can see further.

  8. also agreeing with chris, shear is off the charts! particularly low-level shear which in some places is 50 knots!! holy smokes!

    helicity is also ridiculous as well….just got home so didn’t see any action from the yazoo tornado mentioned above…

  9. Dave: How do the parameters today compare to what we saw in Kansas on 5/22 and 5/23 of our 2008 chase?

  10. In the post-storm assessment, it will be interesting how much of the path across Mississippi (red dots on the SPC reports map linked below) was a single tornado track or whether it was a tornado family with a recycling supercell.

    http://www.spc.noaa.gov/climo/reports/100424_rpts.html

  11. kevin i was wondering the same thing about the tornado reports. SPC was mentioning conditions would be ripe for long-tracked tornadoes so perhaps that will be the case?

    i’ve been watching the storms in TN a while now thinking they HAVE to go tornadic with the atmosphere they would be entering…sure enough tornado warnings are up there too!

  12. hokiestormchaser

    …lower CAPE (KS was over 3500), similar shear (both abundant…KS was 50-70kts deep-layer and similar today), low-level shear & helicity are higher today (30-40kts KS…upwards of 50kts today; 0-1kmSRH 350-400m2/s2 in KS vs. over 500m2/s2 today. Storm motion both days was FAST. This is consistent with what we’d expect…higher CAPE in late May, and higher shear earlier in the season. Storm coverage in both cases has somewhat limited the number of individual long-track tornadoes. Correct me if I remember this incorrectly, but Kev it seemed that nearly every strong cell that day in KS produced tornadoes in rapid-fire fashion. I am still amazed at how quickly the storms completed RFD cycles that day. Probably something similar today. -Dave

  13. You remember correctly. On 5/22/08 the tracks weren’t very long but the number of tornadoes was incredible … we were often watching multiple wall clouds, or would just lose sight of one tornado only to see another. 5/23/08 was a little more like today in the Deep South with longer tracks and more intense tornadoes.

  14. it’s very interesting to see how the storms lose their their tornadic signatures when they cross the border from MS into AL… i wonder if it’s because AL has much lower cape

  15. hokiestormchaser

    …it appeared that instability was certainly maximized over MS. The cells are taking on a more linear mode, but two of them toward the southern end of the line in Pickens AL & Noxobee MS are tornado-warned and look impressive on radar currently. If the linear tendency continues, we could transition into more of a straight-line wind threat. One caveat: the surface winds seem to be backing a bit more over central AL (more so than close to the AL/MS border region). Even if we move toward linear mode, I’d say the tornado threat isn’t over just yet, but they may be imbedded nasties this eve… -Dave

  16. major damage reported in yazoo…accounts of a mile-wide tornado

    http://www.cnn.com/2010/US/weather/04/24/tornado/index.html?hpt=T1

  17. http://www.cnn.com/2010/US/weather/04/24/tornado/index.html?hpt=T1

    reports of major damage in yazoo…accounts of a mile-wide tornado

  18. reports of major damage in yazoo with accounts of a mile-wide tornado

  19. At least 6 fatalities, per Associated Press.

    I was telling Dave earlier that this seems more like a March-type outbreak rather than late April, based on its location in the Gulf states and the type of high-shear, rain-wrapped monstrous tornadoes we saw today. It seems the severe weather season is running about 3-5 weeks late, probably owing to the frequent Arctic air masses and winter storms deeply cooling the Gulf. If this holds true through our May trip, we could well be Kansas and southward rather than farther north.

  20. hokiestormchaser

    …thoughts on today Kathryn??? -Dave

  21. i’m thinking i’ve got a HUGE folder of radar images, rucs, and SPC stuff galore waiting for you haha

    i’ve been watching the storms non-stop since about 3 o’clock and noticed a few things. first of all i am not surprised at all over how many tornado reports there have been today. like we’ve all discussed on the blog the shear and helicites were unbelievable. although this was enough to produce multiple tornadoes, i feel if the CAPE was higher it would have been a much more significant day.

    the lack of CAPE east is, in my opinion, what has inhibited the storms from becoming tornadic for the past few hours now. there are some exceptions because again, shear and helicity is enough to spawn some isolated tornadoes!

    as the cold front approached the winds went from backing to linear causing a lining out in most areas. i watched as the low and warm front approached TN and i was expecting MAJOR action there (winds were backed significantly). there were a couple tornado reports, but on a whole not as much as i think SPC expected. i also think this is because of lack of CAPE up there AND the low occluded quickly which in effect caused the winds to become vertical instead of staying backed.

    overall, i think today could have been bigger (i’m sure many people would disagree with me because after all, today was pretty big) but i really think if CAPE was higher then we really would have had problems.

    i see a bunch of tornado watches are still up, but i’m not so sure if they’re warranted. most storms now, with the onset of night, have less diurnal heating/less cape. some danger still resumes, but i think for the most part a lot of people will get a nice light show!

  22. hokiestormchaser

    …I think storm coverage/severity certainly warranted a high risk. As you noted, if instability had been an order higher…we could be looking at damage that was far worse. After dark now, there is a plume of high theta-e that lies west of the heavy rain mess in GA, so the AL storms may still be able to maintain some intensity for awhile(a by-product of a clean fetch of juice from the Gulf that isn’t that far away). -Dave

  23. oh yea, ‘high risk’ was definitely needed!

  24. I think your anlaysis is spot-on, Kathryn.

    Strictly from a chasing perspective … this is NOT what we want … murky, rain-wrapped wedges with little or no discernible structure racing through hilly, wooded terrain and, much worse, destroying populated areas and killing people. We want sharp, discrete supercells with gorgeous structure, dropping picturesque, backlit funnels over empty stretches of Plains regions with good road networks but few structures.

  25. dave, how do you think today would have been chase-wise?

  26. whoa, kevin, you read my mind haha!

  27. Dave and I often are on the same wavelength about things before we even talk about them … be very afraid if you’re operating on that same frequency. 🙂

    Very honestly, it would be extraordinary for us to chase in Mississippi — we’ve never done it. We’d be there if and only if there was nothing in the Plains for the foreseeable future and it was reachable after whatever we had done the day before. (If we’d gone to Nebraska and busted Friday, it would have been way, way out of play). The later we get in the season, the severe weather tends to shift north and west away from the Gulf states, so it’s unlikely we’d face a decision like this in mid to late May.

  28. haha i will be careful. but dave and i have e-mailed each other at the exact same minute before so i guess i should be marginally worried 😉

    i had a feeling the today would not be a good chase day…i’ve heard from multiple sources that the deep south simply is NOT the place to be on tornado outbreaks!

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