Low Topped Convective Potential Thursday, October 31, 2019 - Friday, November 1, 2019

[weatherwiz]

A vigorous trough is set to dig into the country's mid-section midweek, eject into the Ohio Valley and begin lifting as it approaches New England. Out ahead of it, an anomalously strong southerly flow will transport anomalous PWAT values into the region, along with llvl moisture and warmth. These two factors will help to contribute to at least some modest elevated instability along with the potential for weak sfc instability. 

Both the GFS/euro indicate a vigorous 500mb jet streak pushing through New England (80-100+ knots) will help to yield extreme upward vertical motion and forcing. The combination of strong dynamics, strong forcing, and (to some degree) instability will result in the potential for a low-topped squall line to organize and at least push into western sections. 

The line itself likely won't be associated with strong winds, but just out ahead of this line will be the potential for strong-to-damaging wind gusts..as is typically the case in these type of situations. There are some wildcards as to the potential extent of this activity, however, with sfc dewpoints into the 60's this may result in very weak capping aloft, so there is potential for very strong wind gusts not only from convection, but momentum transport. 

If the trough was not opening up and lifting to the northeast this would allow for a much stronger surge of CAA in the mid-level. This would be accompanied by steeper mid-level lapse rates and perhaps a much greater threat for widespread severe weather. As t stands now, torrential rainfall and strong/gusty winds look probable; including the risk for some embedded severe t'storms (though we'll have to see if we have enough for lightning generation) 

[Torch Tiger]

This is going to be a sneaky big event imo. 

[weatherwiz]

1 hour ago, Dr. Dews said:

This is going to be a sneaky big event imo. 

Damage for all 

[512high]

wiz, do you think this will be stronger then a week ago or so?  

[weatherwiz]

5 minutes ago, 512high said:

wiz, do you think this will be stronger then a week ago or so?  

I don’t 

[Torch Tiger]

This will definitely surpass the last event for many.

[Damage In Tolland]

Trees and wires downed 

[weatherwiz]

9 hours ago, Dr. Dews said:

This will definitely surpass the last event for many.

I disagree. The best winds in this case will have to be driven from convective processes...so any more significant or impressive gusts are going to be on the more isolated side...unless of course we deal with a pretty decent low topped line blow through. We won't see much pressure-gradient winds (well anything impressive anyways) this go-around. I would like to see steeper llvl lapse rates get involved to help with momentum transfer which would then result in bigger wind potential. 

[Torch Tiger]

1 hour ago, weatherwiz said:

I disagree. The best winds in this case will have to be driven from convective processes...so any more significant or impressive gusts are going to be on the more isolated side...unless of course we deal with a pretty decent low topped line blow through. We won't see much pressure-gradient winds (well anything impressive anyways) this go-around. I would like to see steeper llvl lapse rates get involved to help with momentum transfer which would then result in bigger wind potential. 

many areas didn't top 40mph in that last one...should be doable

[Torch Tiger]

want


The biggest question mark is on how much of the winds mix to
the surface. Strong low-level warm advection in the lowest part
of the column may keep stability profiles closer to weakly
stable until we get on the backside of the cold front; that
stability profile could in turn result in less of a percentage
of this strong jet to translate to surface gusts. Felt the most
confident on winds capable of producing damage across the Cape
and the Islands, into the southern coast of MA and towards Block
Island and Newport Counties. Even if 60 percent of the flow
mixed to the ground, that still gets you at least into Advisory
criteria, with potential for stronger. What may also transpire
is strong/damaging winds could accompany the front itself
embedded in the dynamic/strong cold frontal heavy showers
(accompanied by elevated instability/thunder). Do feel potential
exists for 40 to 60 mph gusts in the Watch area, especially in
the pre-dawn to early-mid Friday morning period. So this may be
a little bit different than prior strong wind events experienced
in October. Given the potential and the model
signals/consistency, think it was worth raising awareness with
the Watch at this point in time.

[weatherwiz]

NAM NEST anyways is quite aggressive with a very potent fine line of convection with widespread 50-60 knot gusts ahead of it. 

[weatherwiz]

When you think of the meteorology behind this...this is extremely beautiful. That's likely a big wind producer (with the winds on the leading edge) 

[Torch Tiger]

Too bad it fades coming NE..a little svr threat for the MA anyway

[Torch Tiger]

I missed the ENH upgrade.. guess that was predictable with 70F dews, strong forcing and high shear. If there's a little more Cape realized, look out

 

   ...Portions of the PA/NY vicinity southward/southwestward to the
   southern Appalachians...
   A zone of showers and thunderstorms should be ongoing at the start
   of the period from the mid Ohio Valley/Mid South region
   south-southwestward to the western Gulf of Mexico, in the vicinity
   of an advancing surface cold front.  A secondary area of showers --
   perhaps with some embedded lightning -- will be shifting quickly
   northeastward across the Carolinas/Virginia vicinity.  Only minimal
   severe risk -- mainly in the form of gusty winds or a brief tornado
   -- is apparent at this time within either of these areas of
   convection through the first several hours of the period.

   With time, the advance of the cold front across the southern, and
   then the central, Appalachians during the afternoon in conjunction
   with the strengthening upper system will result in gradual
   organization of a band of frontal convection.  Very strong flow
   aloft will aid in the convective organization, with upscale
   evolution toward a semi-continuous band of storms expected.  By late
   afternoon/early evening, storms will likely have become fairly
   well-organized, crossing south-central and southeastern PA, MD, VA,
   and the Carolinas along with attendant risk for strong/damaging wind
   gusts.  

   Low-level wind profiles will become supportive of supercells during
   the afternoon across the pre-frontal warm sector.  While suggestive
   of some tornado potential, pre-frontal warm-sector storms are
   largely not anticipated.  Still, a few mainly QLCS-type tornadoes
   will be possible, given the overall dynamic/kinematic set-up --
   particularly from late afternoon through mid evening.

   As storms near the coast overnight, gradual weakening of the
   convection -- and associated diminishing of the severe risk -- is
   expected, though limited wind risk will likely extend to near the
   mid Atlantic/Carolina coasts overnight.

[weatherwiz]

That line is going to mean some business I think. Even if radar isn't impressive...just ahead of that line will be a brief burst of some pretty strong winds. 

[weatherwiz]

GFS steepens the 950-900 lapse rate to over 7 C/KM just ahead of that line. Very small layer sure, but winds in that layer are very strong and just above. Very good bet we mix at least 50-55 mph gusts to the sfc ahead of that line 

[weatherwiz]

Already a TOR out...TN/VA border 

[weatherwiz]

Well...could be pretty active southwest of here later on

[weatherwiz]

Holy tomato

 

[OceanStWx]

Just now, weatherwiz said:

Holy tomato

Prime environment in the Mid Atlantic for mesovortices. 

[weatherwiz]

Just now, OceanStWx said:

Prime environment in the Mid Atlantic for mesovortices. 

The HRRR is pretty impressive. Generate an expansive corridor of ~500 J MLCAPE along with 100-150+ J 3km CAPE.

Not to mention how warm/moist the llvl airmass is. When you see a 100+ 500mb jet streak punching into this type of environment trouble is going to happen  

[weatherwiz]

I wonder if the high wind warnings issued for BOX across northern CT are to cover for the winds with that line (based on the time frame within the warning). since this may not have thunder/lightning instead of issuing SVR's its covered via the HWW 

[Cyclone-68]

Am I wrong or does it seem like the mid Atlantic gets a setup like this about once every year in the fall?

[weatherwiz]

3 minutes ago, Cyclone-68 said:

Am I wrong or does it seem like the mid Atlantic gets a setup like this about once every year in the fall?

You're not wrong. 

[bairn]

47 minutes ago, weatherwiz said:

Holy tomato

 

Hi Wiz, I live just west of Raleigh

Are these hww %s or tornadic?

Grew up in Danbury btw, and know Westconn very well.

Even briefly studied with the great Dr Mel

[Cyclone-68]

3 minutes ago, weatherwiz said:

You're not wrong. 

It seems to me back in the early 90’s we had something similar to this that DID affect further north and may have even caused a strong November tornado in eastern NY state somewhere?

[weatherwiz]

7 minutes ago, bairn said:

Hi Wiz, I live just west of Raleigh

Are these hww %s or tornadic?

Grew up in Danbury btw, and know Westconn very well.

Even briefly studied with the great Dr Mel

Yes, the left image is tornado probabilities and the right in damaging wind probabilities 

I wish I would have had the opportunity to have studied under Dr. Mel. that is very cool! 

 

7 minutes ago, Cyclone-68 said:

It seems to me back in the early 90’s we had something similar to this that DID affect further north and may have even caused a strong November tornado in eastern NY state somewhere?

November 16, 1989 there was a significant severe weather/tornado outbreak across southeast NY, NJ, and into mid-Atlantic 

[OceanStWx]

40 minutes ago, weatherwiz said:

I wonder if the high wind warnings issued for BOX across northern CT are to cover for the winds with that line (based on the time frame within the warning). since this may not have thunder/lightning instead of issuing SVR's its covered via the HWW 

If they are, it's not being messaged very well. That's a 7 hour long HWW. The real threat is going to be an hour tops. It's going to be quite gusty in the warm sector, but not 60 mph gusty in my opinion.

Given that the threat is convective in nature, I prefer handling that with short-fused warnings. 

[ineedsnow]

Why is the valley warned but not east of here?  What time will the line come through? 

[weatherwiz]

2 minutes ago, OceanStWx said:

If they are, it's not being messaged very well. That's a 7 hour long HWW. The real threat is going to be an hour tops. It's going to be quite gusty in the warm sector, but not 60 mph gusty in my opinion.

Given that the threat is convective in nature, I prefer handling that with short-fused warnings. 

That's what I'm a little confused about. This isn't a huge wind event outside of any convection (which still doesn't guarantee significant gusts but just increases likelihood). 

Did you see new MCD...95% chance of a WW...we don't even see those probs up this way with summer convective events