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2011 - Mid-Atlantic Severe Storm Thread


Kmlwx

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What does the "2" mean for sig tornado mean? Is that a likelihood of 2 tornados within 50 miles or something completely different?

It's simply a composite parameter. The higher the number the greater the chance for tornadoes. No bearing on number of tornadoes really.

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Technical Definition -

A multiple ingredient, composite index that includes 0-6 km bulk wind difference (6BWD), 0-1 km storm-relative helicity (SRH1), surface parcel CAPE (sbCAPE), surface parcel CIN (sbCIN), and surface parcel LCL height (sbLCL). This version of STP uses fixed layer calculations of vertical shear, and the surface lifted parcels, as an alternative to the "effective layer" version of STP.

The index is formulated as follows:

STP = (sbCAPE/1500 J kg-1) * ((2000-sbLCL)/1500 m) * (SRH1/100 m2 s-2) * (6BWD/20 m s-1) * ((200+sbCIN)/150 J kg-1)

When the sbLCL is less than 1000 m AGL, the sbLCL term is set to one, and when the sbCIN is greater than -50 J kg-1, the sbCIN term is set to one. Lastly, the 6BWD term is capped at a value of 1.5, and set to zero when 6BWD is less than 12.5 m s-1. A majority of significant tornadoes (F2 or greater damage) have been associated with STP values greater than 1, while most non-tornadic supercells have been associated with values less than 1 in a large sample of RUC analysis proximity soundings.

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Thank you. In that case, this looks like a growing potential as it keeps "improving" as we get closer. No one appears to be really excited about it here though. Maybe folks are at church?

And it's Sunday - we tend to not be too active here on Sunday's. Church and family functions I bet.

Come tomorrow AM if it still looks this robust you'll have all the severe weenies on board.

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I would look to see if central and southern VA and DC/MD (EDIT: and maybe WV? depends on strength of morning storms) get upgraded to a Moderate Risk either in the soon-to-be update or sometime tomorrow. Simply an awesome, awesome storm for February.

If they upgraded I would have to assume they would wait until tomorrow like you said last night. I have to imagine that even then, it's a long shot. Moderates are hard to get here even during our peak severe months. Do you really think we have a shot? I'm thinking perhaps a very high end slight at best.

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I would look to see if central and southern VA and DC/MD (EDIT: and maybe WV? depends on strength of morning storms) get upgraded to a Moderate Risk either in the soon-to-be update or sometime tomorrow. Simply an awesome, awesome storm for February.

The time of year isn't a worry for you? I know synoptics can beat down climo, but I find that early-season events tend to be "watered down" somewhat.

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If they upgraded I would have to assume they would wait until tomorrow like you said last night. I have to imagine that even then, it's a long shot. Moderates are hard to get here even during our peak severe months. Do you really think we have a shot? I'm thinking perhaps a very high end slight at best.

Parameters are looking good for a low-end moderate (if just because of the severe wind risk). 30% Day 2 is already high-end Slight Risk, and with things looking dicier with peak heating ahead of the storms in central VA in the mid/late afternoon, I think it would warrant bumping up the probabilities a bit from where they are now and into the Moderate Risk area.

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Parameters are looking good for a low-end moderate (if just because of the severe wind risk). 30% Day 2 is already high-end Slight Risk, and with things looking dicier with peak heating ahead of the storms in central VA in the mid/late afternoon, I think it would warrant bumping up the probabilities a bit from where they are now and into the Moderate Risk area.

I definitely have no argument there. My cautious side just always comes into play and especially with the time of year. But with SPC having bullish wording and such a large 30% area on a day 2 outlook it's possible.

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The time of year isn't a worry for you? I know synoptics can beat down climo, but I find that early-season events tend to be "watered down" somewhat.

While were are still in February, we're just one day shy of met. spring. This is already the second high-end Moderate Risk storm over the mid-country, and it's looking more potent than the first system in terms of severe thunderstorms. The time of the year is not a concern of mine.

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Clouds are a bit of a concern at the moment, but with the strong southerly advection of higher temps we'll still probably see SFC temps in the mid 60s without the Sun. Even if we have SCT BKN BKN throughout the day, all we'll need is some peaks of Sun here and there to hit the 70F mark.

we dont necessarily need sun but it helps. i'd be more concerned about showers etc but we usually dont get a lot of that in the warm sector -- our bigger issue is usually just scouring the clouds.

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we dont necessarily need sun but it helps. i'd be more concerned about showers etc but we usually dont get a lot of that in the warm sector -- our bigger issue is usually just scouring the clouds.

Agreed that, while showers are possible, the models are likely overplaying their overall appearance and limiting factors. While it is a concern, I wouldn't really count it against the setup overall.

on a side note: it's very nice out today. how can anyone like winter more than spring?

Very nice, indeed! So nice that the birds were in full chirping mode this morning. One of them decided it could be fun to fly into my window as hard as it could. Window's fine, but the bird isn't... it's quite deceased.

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Agreed that, while showers are possible, the models are likely overplaying their overall appearance and limiting factors. While it is a concern, I wouldn't really count it against the setup overall.

Very nice, indeed! So nice that the birds were in full chirping mode this morning. One of them decided it could be fun to fly into my window as hard as it could. Window's fine, but the bird isn't... it's quite deceased.

Bad omen for storms. :arrowhead:

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Agreed that, while showers are possible, the models are likely overplaying their overall appearance and limiting factors. While it is a concern, I wouldn't really count it against the setup overall.

the gfs definitely has a tendency to overdo lighter precip/showers/etc. overall the gfs/nam are fairly similar outside the surface pcp during the day. both seem to advertise a clocking prior to 0z.

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