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Low-topped Convection March 1st, 2017

weatherwiz

By weatherwiz,
in New England

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weatherwiz

weatherwiz

Posted
Posted

Before getting into details I suppose I should add a disclaimer:

No...this is not calling for widespread severe weather or calling for a severe weather outbreak.  These setups which typically involve low-topped convection usually don't produce much in the way of severe weather here and anything is typically extremely isolated.  However, that doesn't mean discussion should be ignored.  While the majority of people don't see anything from these events, the people who do can get hit pretty hard.  It is for this that the awareness should be stated.  

With this said we are once again looking at a rather unusual setup as we begin the month of March.  A strong surface low progressing northeastward through the Oio Valley region through the US/Canadian border will allow for a southwesterly flow to develop across our region in the lower levels of the atmosphere which will work to push a warm front northward.  South of the warm front temperatures are expected to climb to near 60F with dewpoints into the mid 50's and perhaps near 60F.  This combined with very steep mid-level lapse rates, potentially in excess of 7.5 C/KM (especially down in CT) will yield the development of rather modest instability for March.  Computer forecast models are developing 250-500 J/KG of SBcape with 500-1000 J/KG of MUcape, and 250-500 J/KG of MLcape with lifted index values as low as -3C to -4C.  

In addition to the modest instability we will be dealing with very strong shear as well with 500mb winds in excess of 60-70 knots and 850mb winds in excess of 60-70 knots.  It doesn't appear, however, we will get enhanced support from any entrance regions of the mid to upper level jet.  

Anyways, Wednesday could transition to be a similar situation to Sunday where we see a low-topped squall line push into the region.  Surface winds may stay more SW as opposed to S or SE which could mean less of a stabilizing influence from Long Island Sound into Connecticut.  Given the parameters/shear we will once again have to watch for any convection as it approaches.  

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Typhoon Tip

Typhoon Tip

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Posted

I was just glancing at the NAM FRH grid and it has a 19 C, T1 temperature, with R1 over 70% at ALB, which means that's a warm humid airmass - certainly relative to the season that is true. 

We very recently saw what significant mechanical forcing can do the other night with an isolated tor in Conway Mass...  some 1,000 trees were pancaked. If this struck in a town center somewhere, we probably would have a 'holy schit' thread 5 pages deep by now... 

This synoptic evolution on Wednesday actually looks favorable from outside looking in, for a repeat of a mechanically forced situation.  Timing limits diabatic CAPE, but... this situation actually might benefit from an even better latent heat/theta-e transport as having be 16 to 20C in the T1 with 70% RH on those grids usually means you have DPs near 60F.  

'Course, this is the NAM - 

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weatherwiz

weatherwiz

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44 minutes ago, Typhoon Tip said:

I was just glancing at the NAM FRH grid and it has a 19 C, T1 temperature, with R1 over 70% at ALB, which means that's a warm humid airmass - certainly relative to the season that is true. 

We very recently saw what significant mechanical forcing can do the other night with an isolated tor in Conway Mass...  some 1,000 trees were pancaked. If this struck in a town center somewhere, we probably would have a 'holy schit' thread 5 pages deep by now... 

This synoptic evolution on Wednesday actually looks favorable from outside looking in, for a repeat of a mechanically forced situation.  Timing limits diabatic CAPE, but... this situation actually might benefit from an even better latent heat/theta-e transport as having be 16 to 20C in the T1 with 70% RH on those grids usually means you have DPs near 60F.  

'Course, this is the NAM - 

One difference I sort of see between Wednesday and Saturday is I think we had help from the RFQ of mid-level jet streak...doesn't seem to be the case here.  I think something like that really helps with mid/upper level forcing.  Anyways, we still have 90+ knots being forecasted at 500mb over us.  

If surface winds can remain more southwesterly I think that would enhance the likelihood for temperatures to push well into the 60's and perhaps even dewpoints climbing into the upper 50's and maybe even lower 60's.  More southerly winds and this is held back a bit.  The biggest key will likely be what happens with the lapse rates/remnant EML plume.  Both NAM/GFS have it but timing of it and such is different.  

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Typhoon Tip

Typhoon Tip

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36 minutes ago, weatherwiz said:

One difference I sort of see between Wednesday and Saturday is I think we had help from the RFQ of mid-level jet streak...doesn't seem to be the case here.  I think something like that really helps with mid/upper level forcing.  Anyways, we still have 90+ knots being forecasted at 500mb over us.  

If surface winds can remain more southwesterly I think that would enhance the likelihood for temperatures to push well into the 60's and perhaps even dewpoints climbing into the upper 50's and maybe even lower 60's.  More southerly winds and this is held back a bit.  The biggest key will likely be what happens with the lapse rates/remnant EML plume.  Both NAM/GFS have it but timing of it and such is different.  

yeah, like i said... just from a glance at the synoptics/grid ... I didn't look that specifically at timing those features... 

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weatherwiz

weatherwiz

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1 hour ago, CT Rain said:

Around 21z-00z... soundings are really impressive west of I-91. 

NAM is quite eye opening...however, 4km NAM not so much.  In fact, looking at 18z NAM bufkit for Waterbury is yielding over 350 J of 0-6km cape with nearly 50 m/s of shear and even nearly 300 J of hail cape.

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Damage In Tolland

Damage In Tolland

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BGW

 

  
Convective risk...
Remnant EML with mid lvl lapse rates reaching 6.5C/km and
7.0C/km moves over the region by late day tomorrow, allowing the
overall MU CAPE profiles to reach 500-1000j/kg, TT to reach 50+.
This could combine with the strengthening LLJ reaching nearly
60 kt. High shear values expected, with 0-6km shear nearly 50 kt
and 0-3km helicity values exceeding 200. Therefore, expecting
another high shear-low CAPE environment late tomorrow, similar
if not even with higher shear than this past Sat. While a bkn
convective line is the mode of choice here, SREF supercell
parameter/sig TOR parameters are high enough to warrant some
concern given the values mentioned above. Exacerbated by LCLs
below 1000ft. Therefore, can`t rule out a risk of strong winds
or even an isolated TOR in any T-storms that develop late in the
day
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CT Rain

CT Rain

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25 minutes ago, Damage In Tolland said:

BGW

 

  

Convective risk...
Remnant EML with mid lvl lapse rates reaching 6.5C/km and
7.0C/km moves over the region by late day tomorrow, allowing the
overall MU CAPE profiles to reach 500-1000j/kg, TT to reach 50+.
This could combine with the strengthening LLJ reaching nearly
60 kt. High shear values expected, with 0-6km shear nearly 50 kt
and 0-3km helicity values exceeding 200. Therefore, expecting
another high shear-low CAPE environment late tomorrow, similar
if not even with higher shear than this past Sat. While a bkn
convective line is the mode of choice here, SREF supercell
parameter/sig TOR parameters are high enough to warrant some
concern given the values mentioned above. Exacerbated by LCLs
below 1000ft. Therefore, can`t rule out a risk of strong winds
or even an isolated TOR in any T-storms that develop late in the
day

I love how you left out the second paragraph that talks about how the strongest forcing is south and that could be an issue.

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Hoth

Hoth

Posted
Posted

So what are the prime bust risks here (besides it's March)? Remnant EML is nice, low LCLs is nice, solid hodos, really nice lapse rates (thanks EML). Perhaps we don't destabilize enough, especially near the ocean? Or forcing is far enough south that we can't break the cap? These soundings I've seen posted were extremely impressive. If I woke up in May and saw that I'd say game on. But, per usual in NE, we have to ask, how can this go wrong?

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Dan

Dan

Posted
Posted
1 hour ago, Damage In Tolland said:

Hopefully scenes like this which are from my survey in Brimfield after the June 2011 Tor

http://1F094057-2F53-41F3-94CB-89842A011576_zps

http://1AD6B0DF-AEBF-4275-904A-0C6E588764E9_zps

You know, one of these days you are going to get your wish, I just hope for your sake it does not come with any deadly consequences.  I'm sure your opinion would change very quickly if the effects were close to home.   Wishing for damage, not a good idea.

 

 

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CoastalWx

CoastalWx

Posted
Posted
4 minutes ago, Dan said:

You know, one of these days you are going to get your wish, I just hope for your sake it does not come with any deadly consequences.  I'm sure your opinion would change very quickly if the effects were close to home.   Wishing for damage, not a good idea.

 

 

Agree.

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Typhoon Tip

Typhoon Tip

Posted
Posted

Indirectly related subject matter.. 

You know how some years have better convective character?  Like, just on the surface/average synoptic evolution, it may not be precisely clear why one year has better verification/witnessing over other years, but they do, when all other parametric observations being apparently equal. 

One thing I have noticed is that those years that do, seem to start early. It could just be "attention-honing" ...as in, you get something and that has a way of focusing one's attention, and thus they may remember more?  

I dunno.  But affectation aside (if that's all it is...), having two opportunities spanning a mere week at the end of February no less, is intriguing for me. Also, the flow tendency (all winter season) has been persistently fast and longitudinal.  

Longitudinal in Met parlance means the curve depth is shallow and the wave lengths are stretched/long-ish.  

Adding to that longitudinal tendency ... there's been surplus gradient and velocities.  These aspects seem would parlay favorably for a convection season ...pretty much everywhere across the conus where it counts.  One thing I have noticed over the years is that most big convective outbreaks occur because of open waves that have amplitude, but the vorticity is less generated in the curvature, and more so via speed shear. It's almost like the cyclone potential gets redistributed to the meso-scales and the supercells do all the expressing.  nice.   

 

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Damage In Tolland

Damage In Tolland

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14 minutes ago, Dan said:

You know, one of these days you are going to get your wish, I just hope for your sake it does not come with any deadly consequences.  I'm sure your opinion would change very quickly if the effects were close to home.   Wishing for damage, not a good idea.

 

 

Wanting to see  a tornado in the woods on  a hillside  is vastly different than wanting injuries and damage to life and property. Please don't ever insinuate that again 

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Dan

Dan

Posted
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2 minutes ago, Damage In Tolland said:

Wanting a tornado in the woods on  a hillside  is vastly different than wanting injuries and damage to life and property. Please don't ever insinuate that again 

No where did you say damage on a hillside.  Just because you show a pic of a hillside means nothing.  What about the other picture?

 

Its not just severe weather, ice storms, 38 hurricane damage, windstorms with trees breaking everywhere.  Great you love damage, but 99% of the people on this board don't wish for it.  That's my point.

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Damage In Tolland

Damage In Tolland

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3 minutes ago, Dan said:

No where did you say damage on a hillside.  Just because you show a pic of a hillside means nothing.  What about the other picture?

 

Its not just severe weather, ice storms, 38 hurricane damage, windstorms with trees breaking everywhere.  Great you love damage, but 99% of the people on this board don't wish for it.  That's my point.

Always trees . Never have I ever mentioned death or otherwise as you say. 

Think twice before making ghastly accusations 

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Dan

Dan

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Posted
Just now, Damage In Tolland said:

Always trees . Never have I ever mentioned death or otherwise as you say. 

Think twice before making ghastly accusations 

I never said that you said death.  

 

Just wishing for damage of any type many times causes injury or death, so why wish for it at all?  Why tempt fate?

 

You are completely missing the point.   I don't wish any harm to any person, friend or foe.   If that is how you take this conversation, so be it.

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CoastalWx

CoastalWx

Posted
Posted
7 minutes ago, Dan said:

I never said that you said death.  

 

Just wishing for damage of any type many times causes injury or death, so why wish for it at all?  Why tempt fate?

 

You are completely missing the point.   I don't wish any harm to any person, friend or foe.   If that is how you take this conversation, so be it.

Blinders.

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