Tuesday, August 13th, 2013 severe threat

[weatherwiz]

After a very gorgeous weekend with little to no humidity and cooler temperatures, a warm front will begin to slowly lift through the region during the day on Monday and with the passage of the warm front we will once again see the return of higher dewpoints/humidity along with the threat for showers on Monday.  The humidity won't be around for long though as a rather strong cold front is expected to cross the region sometime either late Tuesday or overnight Tuesday into Wednesday.  Right now there are differences in some of the computer model data on the exact timing of the cold front. 

 

An amplifying trough moving across the Great Lakes and southeastern Canada will allow for winds aloft to increase over southern New England.  Computer model guidance suggests that winds at 700mb will increase on order of 30-40 knots with winds at 500mb increasing to as much as 40-50 knots across the region.  While the low-level jet doesn't appear all that great, we still see winds at 850mb increase to 25 to perhaps 30 knots.  The region will also be in the right entrance region of a rather potent 100-110 knot upper-level jet streak.  

 

As the trough approaches the region, temperatures in the mid levels of the atmosphere will also begin to cool as 500mb temperatures are modeled to drop as low as -12C to perhaps -13C.  With 700mb temperatures around +5C to begin the day (although cooling as the afternoon goes on) this should yield to some much better mid-level lapse rates than we have been dealing with as they should be on order of around 6-6.5 C/KM.  

 

As far as instability goes, that picture is much more unclear right now as we may be dealing with a bit of cloudiness which could hold back temperatures.  Given how 925mb temperatures are modeled to be around +20C with 850mb temperatures closer to +14C, that would yield max temps with full mixing well into the mid to upper 80's.  However, with clouds expected to be around we probably won't realize this full potential so temperatures should be closer to 80F, although with more sun these temperatures could easily be boosted higher, especially locally where there happened to be more breaks.  Dewpoint temperatures are expected to climb into the mid-60s.  

 

The combination of surface temperatures near 80F, dewpoints in the mid-60's, and modest mid-level lapse rates, should yield to surfaced-based Cape values around 1500-2000 J/KG with mixed-layer cape values around 1000-1500 J/KG and surfaced-based lifted index values around -3C to -4C.

 

When taking into account the combination of strong winds aloft and potential for some modest instability, and a cold front/trough sliding east, we will be looking at the potential for some t'storms during the day on Tuesday.  

 

We will have to watch the exact timing of the front, however, as if the front comes through very late on Tuesday or during the night, then the threat for t'storms will be much more decreased as instability will be minimized.  However, some computer model guidance does suggest a pre-frontal trough will setup just east of the Hudson River Valley and that would be a focus for t'storms.

 

Given the strong shear/cold temperatures aloft, any t'storm would have the potential to produce strong winds and perhaps some hail.  

 

[Damage In Tolland]

That said. Considering this has been a terrible storm season I hope that this one pans out for Wiz

[weatherwiz]

Might have some convective feedback issues as the 18z run really cranks a LLJ but the 18z NAM actually suggests another threat for an isolated tornado.  This run also is more in line with the GFS in terms of instability.  

[free_man]

Lets hope lapse rates are okay this time.

[free_man]

Lets hope lapse rates and instability work out. Decent front and prefrontal trof like mentioned.

[weatherwiz]

Lets hope lapse rates and instability work out. Decent front and prefrontal trof like mentioned.

 

I would think lapse rates should be better than they have been, though they could be weakened with a bunch of crap.  Just as long as they are at least 6 C/KM that's fine.  The bigger question I think will be cloud cover/instability.  Other than that dynamics certainly should be there.  Timing could be an issue too I suppose.  

[weatherwiz]

That said. Considering this has been a terrible storm season I hope that this one pans out for Wiz

 

What has sucked about this season is we have really yet to see an excellent setup...usually we get 2-3 per year but this year we've just dealt with these marginal setups which have been full of potential, it's just nothing has really come together...however, a few of those events did produce.  

 

In the end really, given the types of setups we have seen all summer, this hasn't been THAT terrible of a year as the percentage of them that have worked out is probably what you would expect.

[joey2002]

What has sucked about this season is we have really yet to see an excellent setup

 

Yeah, we haven't even seen 30% probs from SPC yet.

 

Lack of instability seems to be the major problem with a lot of our setups this year. 

[CoastalWx]

Yeah, we haven't even seen 30% probs from SPC yet.

 

Lack of instability seems to be the major problem with a lot of our setups this year. 

 

It's called SNE.

[weatherwiz]

Yeah, we haven't even seen 30% probs from SPC yet.

Lack of instability seems to be the major problem with a lot of our setups this year.

We have seen a ton of mod risks the past several years. There was a period from like 2001 until 2008 where the BOX CWA did not get into a mod risk

[CoastalWx]

We have seen a ton of mod risks the past several years. There was a period from like 2001 until 2008 where the BOX CWA did not get into a mod risk

 

Many that did not pan out.

[weatherwiz]

Many that did not pan out.

Some of those SEE TEX days from 2008 would have verified high end risk/low end mod better than some of the mod risks we've had.

[joey2002]

We have seen a ton of mod risks the past several years. There was a period from like 2001 until 2008 where the BOX CWA did not get into a mod risk

 

2011 had quite a few great setups, and last year was pretty good too.  This year...

[Quincy]

Wiz, SPC tossed you a See Text.

00z Euro doesn't look half bad. Decent timing of cold front and shows us breaking out a bit to start Tuesday.

[Damage In Tolland]

Hopefully a few storms can pop

[CoastalWx]

Looks like we could have a lot of mid level junky clouds if the GFS is right.

[weatherwiz]

Looks like we could have a lot of mid level junky clouds if the GFS is right.

 

I think we will have clouds to contend with, just a question of whether or not we can get any breaks

[Quincy]

It looks to follow the pattern of most of these setups this year...if history tells us anything, any severe reports are probably far and few between.

[OceanStWx]

It's called SNE.

 

A lot more failure modes around here. The sooner you come to grips with that the better. If I want supercells I'll book a flight to MCI or DEN and go from there.

[OceanStWx]

Some of those SEE TEX days from 2008 would have verified high end risk/low end mod better than some of the mod risks we've had.

 

There is a little bias in there though. A "see text" can really only fail on the higher end (i.e. like a slight or moderate type coverage), whereas a moderate is more likely to fail on the lower end (slight or see text coverage).

 

We really just remember the big "see text" days, but we don't remember the ones that work out or see no action at all.

[N. OF PIKE]

There is a little bias in there though..... We really just remember the big "see text" days, but we don't remember the ones that work out or see no action at all.

Yup

[weatherwiz]

There is a little bias in there though. A "see text" can really only fail on the higher end (i.e. like a slight or moderate type coverage), whereas a moderate is more likely to fail on the lower end (slight or see text coverage).

 

We really just remember the big "see text" days, but we don't remember the ones that work out or see no action at all.

 

It's also really hard to truly verify moderate risk criteria here.  When you see mod risks issued in the Plains for example, you have a much larger aerial coverage b/c the land mass is so much greater, while here our region is quite small and when we see mod risks they are typically confined to a much smaller area and we really have to see quite the setup in order to verify it, and usually we would need a major squall line...like a 7/18/06 type deal.  

[OceanStWx]

It's also really hard to truly verify moderate risk criteria here.  When you see mod risks issued in the Plains for example, you have a much larger aerial coverage b/c the land mass is so much greater, while here our region is quite small and when we see mod risks they are typically confined to a much smaller area and we really have to see quite the setup in order to verify it, and usually we would need a major squall line...like a 7/18/06 type deal.  

 

I think our "bigger" days end up being more isolated significant severe. You'll see one big supercell dropping 2" hail, or a micro/macroburst levels a forest. This instead of widespread severe damage. As we well know, it takes some sort of EML to give us widespread severe weather.

[CoastalWx]

It's also really hard to truly verify moderate risk criteria here.  When you see mod risks issued in the Plains for example, you have a much larger aerial coverage b/c the land mass is so much greater, while here our region is quite small and when we see mod risks they are typically confined to a much smaller area and we really have to see quite the setup in order to verify it, and usually we would need a major squall line...like a 7/18/06 type deal.  

 

Yeah, but with you on the HAM just wearing socks...it makes it easier to report every rotted limb down.

[CoastalWx]

A lot more failure modes around here. The sooner you come to grips with that the better. If I want supercells I'll book a flight to MCI or DEN and go from there.

 

I enjoy a good storm as much as anyone, but I just can't get too excited unless the potential really looks good. Different story up your way, but the dynamics usually lack down by me. Winter is more my bread and butter.

[weatherwiz]

I think our "bigger" days end up being more isolated significant severe. You'll see one big supercell dropping 2" hail, or a micro/macroburst levels a forest. This instead of widespread severe damage. As we well know, it takes some sort of EML to give us widespread severe weather.

 

Agreed....for us to see widespread severe weather or widespread significant severe it has to be a truly special setup.

[weatherwiz]

Yeah, but with you on the HAM just wearing socks...it makes it easier to report every rotted limb down.

 

 

[Ginx snewx]

We had much discussion about EMLs and SNE this past spring, some were very excited because of the drought some were not because they anticipated a regime change in the MW,seems the regime change won out. 

[OceanStWx]

We had much discussion about EMLs and SNE this past spring, some were very excited because of the drought some were not because they anticipated a regime change in the MW,seems the regime change won out. 

 

Flash flooding in the High Plains is not good for EMLs.

 

In all seriousness though, widespread rainfall in those parts really limits what kind of lapse rates can advect downstream.

[Ginx snewx]

Flash flooding in the High Plains is not good for EMLs.

 

In all seriousness though, widespread rainfall in those parts really limits what kind of lapse rates can advect downstream.

Yep