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susqushawn

8/13 Double Barrel Risk Of YAWN

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On Tuesday, the aforementioned low pressure, associated with a
decaying MCS from the source region, will push a frontal boundary
into the forecast area. The exact placement of this boundary will
dictate the resulting convective evolution throughout the day
Tuesday, nevertheless the environment is likely to be favorable for
strong to severe thunderstorms developing during the afternoon.
Being that this event will be driven by primarily by mesoscale
processes, details are still a bit unclear at this range, however
all severe weather modes (including damaging winds, tornadoes, and
large hail) will be possible Tuesday afternoon and evening. Deep
layer shear is forecast to be in the 35-40 kt range with MLCAPE
values of 1000-2000 J/kg. Some guidance has impressive low-level
wind shear profiles and low-level curvature to the hodographs for
this time of year. Precipitable water values will be high as well
(well over 2") so flash flooding will be a threat where the heaviest
storms begin to train over the same areas. Tuesday will be a hot and
humid day with temps ranging from the mid 80s north to low to mid
90s south and dewpoints rising into the low to mid 70s outside of
the highest terrain.
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Definitely looking like a flash flood risk later tuesday into tuesday night with that low pressure pass as currently modeled. Pretty strong area of low pressure combined with very moist air along and south of its track. 

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Enhanced risk for Tuesday. A lot of potential, but not sure how things set up. (Warm front placement being key). I’ll touch on it by 12z runs later today. 

1CCC0969-77EA-47F0-AABF-DC48CB91D737.gif

8EC25B73-403F-4B21-85A0-978A1730D73D.png

CFABDF21-A4EE-4058-9094-CBA9E6969C53.png

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18 hours ago, tombo82685 said:

Definitely looking like a flash flood risk later tuesday into tuesday night with that low pressure pass as currently modeled. Pretty strong area of low pressure combined with very moist air along and south of its track. 

When has there been a recent precipitation event without flash flooding?

SREF predicted calibrated severe is highest from Philly west.  This remains true into the night.  Nothing lacking with predicted effective bulk shear >30 knots everywhere.

SREF_03HR_SVR_PROBS__f042.gif.ac9a6732eb93b3c63b2b0f100a765ba1.gif

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2 hours ago, Rainshadow said:

When has there been a recent precipitation event without flash flooding?

SREF predicted calibrated severe is highest from Philly west.  This remains true into the night.  Nothing lacking with predicted effective bulk shear >30 knots everywhere.

SREF_03HR_SVR_PROBS__f042.gif.ac9a6732eb93b3c63b2b0f100a765ba1.gif

What does the 1-15 scale correlate to?  % likelihood?  Is a 10 10x greater probability than a 1?

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2 hours ago, Rainshadow said:

98ewbg.gif

day2otlk_0600.gif

 

 

What's the thought on the enhanced risk moving further North? 

 

 

 

 

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I was looking at NAM/hrrr and obviously they’re a little out of range but it looks like morning showers tomorrow possibly? Will that effect heating/sun potential for afternoon storms?

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53 minutes ago, cbelke said:

 

 

What's the thought on the enhanced risk moving further North? 

 

 

 

 

Overnight strong MCS brings cloud cover and rain in the AM, should have breaks buy mid-afternoon as that moves out to sea with ingredients in place for storms to fire up and maintain. 

I see little potential north of Lehigh Valley given track of surface low over that area and less instability north.  Surface winds back along the warm front out ahead, hence the curving hodographs and non-zero risk for tornadoes.  It won't take long for storms to fire when those early clouds do clear out then we'll see if anvil blowout rolls in.  Either way it's a good setup and good timing of low.  Even with cloud debris its volatile enough

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1 hour ago, cbelke said:

 

 

What's the thought on the enhanced risk moving further North? 

 

 

 

 

Going to depend on Low track, thats what's setting the severe boundaries. You want to ideally be south of low track 

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Given the way this season has been going, folks in New Jersey should be stocking their shelters and tornado safe rooms today.

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HWO pretty much covers every possibility. No mention of lightning but I guess that's a given.

A storm system will impact the region on Tuesday. Storms will be
capable of producing damaging winds, tornadoes, large hail, and heavy
rainfall that could lead to localized flash flooding.

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38 minutes ago, tombo82685 said:

Going to depend on Low track, thats what's setting the severe boundaries. You want to ideally be south of low track 

Just browsing around the different models, but it appears the low is trending South, at least to me it does. 

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Looks like the SPC removed the specific mention of tornadoes tomorrow with the latest update:

https://www.spc.noaa.gov/products/outlook/day2otlk.html

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1219 PM CDT Mon Aug 12 2019

   Valid 131200Z - 141200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE CENTRAL APPALACHIANS EASTWARD TO THE MID-ATLANTIC...

   ...SUMMARY...
   Severe storms are expected Tuesday afternoon and early evening over
   the Middle Atlantic into the Ohio and Tennessee Valleys. Other
   strong to severe storms are possible over the Upper Mississippi
   Valley and the central High Plains.

   ...Mid-Atlantic/Ohio and Tennessee Valleys...
   A subtle cyclonic mid-level flow pattern will be in place on Tuesday
   from the north-central states eastward into the Northeast. At the
   surface, a cold front will advance southward into the Mid-Atlantic
   extending west-southwestward into the mid Mississippi Valley. A
   surface low along the front will move eastward across the central
   Appalachians. Surface dewpoints ahead of the front should be in the
   lower 70s contributing to a corridor of moderate instability by
   afternoon. Scattered thunderstorms are forecast to develop along the
   front during the afternoon from southern Ohio eastward across the
   Virginias into Maryland. Cells may tend to organize into lines and
   MCS development will be possible from late afternoon into the early
   evening.

   NAM forecast soundings along the front from West Virginia into
   northern Virginia and southern Maryland suggest that MLCAPE values
   could reach 2500 J/kg at peak heating. Winds are veered to the
   southwest at the surface with about 30 kt of westerly flow in the
   mid-levels. This combined with steep lapse rates in the lowest 3 km
   AGL will be favorable for damaging wind gusts associated with line
   segments.  If a cold pool can develop with a larger-scale line
   segment, then numerous damaging wind gusts will be possible from
   eastern West Virginia eastward to Delaware and southern New Jersey. 

 

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23 minutes ago, greg ralls said:

Looks like the SPC removed the specific mention of tornadoes tomorrow with the latest update:

https://www.spc.noaa.gov/products/outlook/day2otlk.html


   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1219 PM CDT Mon Aug 12 2019

   Valid 131200Z - 141200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE CENTRAL APPALACHIANS EASTWARD TO THE MID-ATLANTIC...

   ...SUMMARY...
   Severe storms are expected Tuesday afternoon and early evening over
   the Middle Atlantic into the Ohio and Tennessee Valleys. Other
   strong to severe storms are possible over the Upper Mississippi
   Valley and the central High Plains.

   ...Mid-Atlantic/Ohio and Tennessee Valleys...
   A subtle cyclonic mid-level flow pattern will be in place on Tuesday
   from the north-central states eastward into the Northeast. At the
   surface, a cold front will advance southward into the Mid-Atlantic
   extending west-southwestward into the mid Mississippi Valley. A
   surface low along the front will move eastward across the central
   Appalachians. Surface dewpoints ahead of the front should be in the
   lower 70s contributing to a corridor of moderate instability by
   afternoon. Scattered thunderstorms are forecast to develop along the
   front during the afternoon from southern Ohio eastward across the
   Virginias into Maryland. Cells may tend to organize into lines and
   MCS development will be possible from late afternoon into the early
   evening.

   NAM forecast soundings along the front from West Virginia into
   northern Virginia and southern Maryland suggest that MLCAPE values
   could reach 2500 J/kg at peak heating. Winds are veered to the
   southwest at the surface with about 30 kt of westerly flow in the
   mid-levels. This combined with steep lapse rates in the lowest 3 km
   AGL will be favorable for damaging wind gusts associated with line
   segments.  If a cold pool can develop with a larger-scale line
   segment, then numerous damaging wind gusts will be possible from
   eastern West Virginia eastward to Delaware and southern New Jersey. 

 

Still a 5% in the wording. 

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Well, to ones surprise, the 12k nam is still way overdone.  The other CAM models are showing issues with early crapvection polluting the airmass. You can see the limited cape on these models.

 

things to look for. Morning frontal location. Early convection and clearing out afterwards?? If we don’t recover, there won’t be much of a threat. 

1CDC4394-FD16-471B-BC66-FF480464DABA.png

04BB3BBA-8217-4DBE-AE6F-3D77F650015B.png

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1 hour ago, cbelke said:

Just browsing around the different models, but it appears the low is trending South, at least to me it does. 

If that’s the case then you shift severe south. All depends on low track. 

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From above..We can still see training storms, just reduces the stronger severe threat.

 

That being said, we we start seeing favorable clearing, that’s the increased threat area. Pretty good directional shear. AOA 35-40KNOTS. strong trigger. 

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3k NAM has the leftover MCS rolling through around 16-20z. That’s not ideal. It does recover enough for Immediate SEPA for evening storms, but would have to think that limits the higher end potential. 

Always a waiting game with these set ups. 

2517D088-6AE3-4308-89F5-5DE23064C203.png

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I know a few people on the forum don't enjoy convective season, but things like this are one of the reasons I like it so much. I love waiting to see what happens knowing that there is good potential, but also a few things that could go wrong.

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 I think I'm selling on tomorrow severe wise. Just don't think we are going to clear out enough to really get instability going. Trend over last 24 hrs has been for the area of low pressure to track a bit further south which would cause more cloud debris as we get into more of the stratiform type rain.  Heavy rain threat is there though, PWATS over 2"

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14 minutes ago, tombo82685 said:

 I think I'm selling on tomorrow severe wise. Just don't think we are going to clear out enough to really get instability going. Trend over last 24 hrs has been for the area of low pressure to track a bit further south which would cause more cloud debris as we get into more of the stratiform type rain.  Heavy rain threat is there though, PWATS over 2"

I concur.

If I'm agreeing with you, you should be scared. :ohmy:

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36 minutes ago, cbelke said:

I concur.

If I'm agreeing with you, you should be scared. :ohmy:

Maybe your latitude, but places farther south are still under the proverbial gun.

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8 hours ago, susqushawn said:

What does the 1-15 scale correlate to?  % likelihood?  Is a 10 10x greater probability than a 1?

I believe it is a straight percentage. 

 The calibrated guidance is actually a conditional probability of a severe thunderstorm (conditional on the occurrence of a thunderstorm).  Presently, the conditional probability assigned to each grid point is simply the maximum calibrated probability from any of the 21 layers.  The unconditional (or total) probability of severe is then the product of the conditional severe probability and the calibrated probability of a thunderstorm described in Bright et al. (2005).  Forecasts are produced for 3h valid periods (e.g., 18 UTC through 21 UTC) from forecast hour 03 through forecast hour 87.

I use it more as a geographic reference (as to where) and also see if the prob increases as we get closer in time (which it should if the threat has legs).  As has been discussed, there has been a southward drift of severe potential.

SREF_03HR_SVR_PROBS__f030.gif.7e89455ef6c584d75468483c23a6ec89.gif


 
 

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2 hours ago, tombo82685 said:

 I think I'm selling on tomorrow severe wise. Just don't think we are going to clear out enough to really get instability going. Trend over last 24 hrs has been for the area of low pressure to track a bit further south which would cause more cloud debris as we get into more of the stratiform type rain.  Heavy rain threat is there though, PWATS over 2"

I'm not really impressed, either... I feel that events with (relatively) higher shear seem to get more attention from the SPC, and given that there is some directional component, I certainly understand why! But I don't think that tomorrow seems like an enhanced risk day...

 

Moist skew-t profile with skinny cape makes me hedge against much severe tomorrow, though thunderstorm days like these, with the moist profile + low level shear & some curvature in hodograph, makes me think there's a potential for a couple weakly rotating storms that could produce a tornado. Strong wind gusts don't seem particularly likely given there not being much DCAPE without any dry air aloft, though these adequate shear + thin, unimpressive CAPE days make me think of weak/meh QLCS's.

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