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Severe Weather Threat Week...so many threats!!!


weatherwiz
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21 minutes ago, wxeyeNH said:

I posted a video of our severe thunderstorm from 2 days ago.  That video was not made at the height of the storm.  This one is.  The video  starts shortly after the rain came in.  Normally in the thunderstorms I have observed the strongest wind was with the gust front, just before the rain.  This was different.  Started out breezy with moderate rain and got progressively worse.  The hail got bigger and bigger and the biggest hail was at the tail end of the storm, not on the video. Things start to get crazy around the 1 minute mark.  

Initially the wind came in from the west but as the storm got going it veered to due south.  The bigger hail was at the end of the storm, not on the video.  From my observation the most and biggest hail fell about 1/2 mile south of me.  Interesting to note 1 mile north of me had very little wind.

Visibility dropped to perhaps 1/8 of a mile by 1:20 about the same as I see in a heavy snowsquall.  I also notice something that I have never seen talked about.  The hailstones were hitting the Stratus funnel and bouncing right out.  Obviously each nickel to near quarter size hailstone is equal to a lot of water.  So the 1" of rain in the status might have been more.  Also I wonder if strong wind gusts reduce the accuracy of a rain gauge?

 

Wow!  Looks something like our 2nd TS on June 14, except you're far more exposed so much windier - probably topped out in the 40s here.  We had 0.92" of which at least 0.85" fell in a 10-minute period that included a minute of very light RA, and assumes the gauge caught the full amount.  Also, the 2nd half, when the visibility dropped to 100 yards in wind-torn mist and dimes were bouncing around, had by far the heaviest precip, RA+++ vs RA+ for the first downpour.  No Davis, just the Stratus, so the 10-minute average of 5.1"/hr means that second downpour was considerably more intense, but who knows about the rate.  

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31 minutes ago, wxeyeNH said:

I posted a video of our severe thunderstorm from 2 days ago.  That video was not made at the height of the storm.  This one is.  The video  starts shortly after the rain came in.  Normally in the thunderstorms I have observed the strongest wind was with the gust front, just before the rain.  This was different.  Started out breezy with moderate rain and got progressively worse.  The hail got bigger and bigger and the biggest hail was at the tail end of the storm, not on the video. Things start to get crazy around the 1 minute mark.  

Initially the wind came in from the west but as the storm got going it veered to due south.  The bigger hail was at the end of the storm, not on the video.  From my observation the most and biggest hail fell about 1/2 mile south of me.  Interesting to note 1 mile north of me had very little wind.

Visibility dropped to perhaps 1/8 of a mile by 1:20 about the same as I see in a heavy snowsquall.  I also notice something that I have never seen talked about.  The hailstones were hitting the Stratus funnel and bouncing right out.  Obviously each nickel to near quarter size hailstone is equal to a lot of water.  So the 1" of rain in the status might have been more.  Also I wonder if strong wind gusts reduce the accuracy of a rain gauge?

 

That's some good stuff there.... those gusts around 1:05 and onward are wild.

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 Also this is tomorrow, N/W areas maybe need to keep an eye out.

The strongest flow aloft is forecast from the Great Lakes to New
   England, which warrants an expansion of severe probabilities across
   portions of New England in this update.  Locally damaging winds are
   expected as multiple clusters/convective bands evolve with time,
   across the entire slight risk area.  In addition, a tornado or two
   will also be possible -- particularly across the Lower Great Lakes
   region and into western New England, where with isolated/rotating
   storms will be possible, given veering low-level winds beneath
   stronger west-southwesterlies through the mid troposphere.
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9 minutes ago, Henry's Weather said:

Either way though we're dealing with high dews though right? In my understanding that should increase the floor for ML instability 

Mid-level instability is more of a product of change of temperature with height (lapse rate). High dews can certainly help, But it’s not as much of a boost as a steep lapse rate. The greater the difference between the parcel temp and environmental temp, the more violently the parcel will accelerate. This helps to contribute to faster updrafts speeds which can be a significant driver in severe potential 

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2 minutes ago, weatherwiz said:

Mid-level instability is more of a product of change of temperature with height (lapse rate). High dews can certainly help, But it’s not as much of a boost as a steep lapse rate. The greater the difference between the parcel temp and environmental temp, the more violently the parcel will accelerate. This helps to contribute to faster updrafts speeds which can be a significant driver in severe potential 

Gotcha. But isn't it the case that if a parcel is saturated, it falls in temperature more slowly, thus increasing difference in temp of parcel and ambient atmosphere?

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45 minutes ago, Henry's Weather said:

Gotcha. But isn't it the case that if a parcel is saturated, it falls in temperature more slowly, thus increasing difference in temp of parcel and ambient atmosphere?

This is correct, which is why higher dewpoints are a good proxy for higher CAPE if you don't have access to CAPE forecasts. But no matter the dewpoint, the lapse rates really drive how significant the severe weather is. 

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FWIW someone directed me to this post on Facebook re: Monday 

                SNE weather 
“Tomorrow’s Severe Weather Event:
After looking at some of the latest computer models. I wouldn’t be surprised if we go from a Slight Risk of severe storms to Enhanced Risk of severe storms.
If everything continues to trend in the direction models are going, we could see a Tornado Watch go up for most of Southern New England (SNE).
Take any Tornado Warnings seriously tomorrow. Models are showing some very large values for this possibility. We don’t usually see values this high in SNE.
If the energy gets to around 4,000 j/kg, we could be talking about an outbreak. As of right now that doesn’t seem to be the case as these values have been running between 2,000 - 3,000 j/kg.”
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I don't know about tornado outbreak...I care less about CAPE for that and more helicity especially near the surface. I do think tomorrow has some potential for damaging winds and maybe a couple spinners if we don't get crapvection in the morning. 

SPC didn't hint at an ENH this afternoon, but let's see what tomorrow holds. It does look pretty legit on paper IMO. 

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15 minutes ago, WxWatcher007 said:

I don't know about tornado outbreak...I care less about CAPE for that and more helicity especially near the surface. I do think tomorrow has some potential for damaging winds and maybe a couple spinners if we don't get crapvection in the morning. 

SPC didn't hint at an ENH this afternoon, but let's see what tomorrow holds. It does look pretty legit on paper IMO. 

My primary concern for tornadoes would be from squall line type. 0-3 km shear is forecast to be in excess of 40 knots tomorrow. That's quite a bit, only need 30 kt perpendicular to the line to start spinning up mesos. 

Even if debris puts a lid on things, that kind of shear means any mesos that spins up could still find a way to force strong winds to the surface. 

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Just now, OceanStWx said:

My primary concern for tornadoes would be from squall line type. 0-3 km shear is forecast to be in excess of 40 knots tomorrow. That's quite a bit, only need 30 kt perpendicular to the line to start spinning up mesos. 

Even if debris puts a lid on things, that kind of shear means any mesos that spins up could still find a way to force strong winds to the surface. 

This convection tonight (which has held together a bit better than guidance indicated) could aid in some residual boundaries for tomorrow which could locally enhance potential 

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1 minute ago, OceanStWx said:

My primary concern for tornadoes would be from squall line type. 0-3 km shear is forecast to be in excess of 40 knots tomorrow. That's quite a bit, only need 30 kt perpendicular to the line to start spinning up mesos. 

Even if debris puts a lid on things, that kind of shear means any mesos that spins up could still find a way to force strong winds to the surface. 

Agree. I do think the shear forecast will make tomorrow interesting, even if instability is capped for lack of a better term. I am just dubious of the "outbreak" language in that FB post. 

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