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2020 Mid-Atlantic Severe Weather - General Thread


Kmlwx
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SPC morning Day 2 disco

  ...Upper Ohio Valley/Northeast States...
   A low-amplitude shortwave trough and a related belt of strong
   cyclonically curved west-northwesterly winds aloft (40-55 kt at 500
   mb) will overlie a south/southeastward-spreading front. The
   potential exists for early day convection across the region, and
   this convection and related cloud cover casts some uncertainty 1)
   regarding the exact degree of destabilization and 2) a preferred
   corridor of any higher coverage severe potential. 

   That said, moderate buoyancy (upwards of 2000 J/kg MLCAPE) is
   plausible near/south of the front and to the south of any residual
   early day precipitation/outflow. Storms will likely
   increase/intensify through early/mid afternoon near the effective
   front. The strong mid/high-level westerlies and 40+ kt effective
   shear would support some initial supercells along with
   well-organized southeastward-moving clusters. Damaging winds and
   severe hail are expected. Although low-level winds will tend to
   remain veered in areas near/south of the front, moderately strong
   low-level shear/SRH could yield a non-zero tornado risk during the
   afternoon and early evening hours.

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I'm kind of not that enthused about any particular days in this threat window. @Eskimo Joe seems like he might be right about tomorrow being a dying complex. Thursday's parameters aren't really there - Friday looks like the instability is focused to the north and west. Would be pretty DCish to fail on everything. 

However, I will say with all that's going on down in DC, the last thing we probably want is large scale power outages...

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    I actually thought that the overnight guidance took a nice step forward for tomorrow, with several CAMs bringing activity through the area either late Wednesday or Wednesday evening.  It's reflected in the HREFv3 (updated version coming later this year with extension to 48h) that shows decent changes of 40 dbz at both 21 and 00z tomorrow:     (to be clear, these aren't huge probs, but it's a step forward for sure)

href_onekmrefdprob40_CONUS_f45_CONUSPROBV3.gif.6028e7849f3bfb176d676995d76b98d2.gif

 

href_onekmrefdprob40_CONUS_f48_CONUSPROBV3.gif

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8 minutes ago, MN Transplant said:

The big problem we have tomorrow is that it is dry.  HRRR is putting the DPs in the 50s by later in the day.  Kills the instability and the line dropping down.

Verbatim, it would be a nice fast-moving line with good wind potential if CAPE ended up better than modeled... not that I'm implying that it will be.

 

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28 minutes ago, MN Transplant said:

The big problem we have tomorrow is that it is dry.  HRRR is putting the DPs in the 50s by later in the day.  Kills the instability and the line dropping down.

I've been watching some of what has been going on in MN/WI... and seems like HRRR was a big whiff

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2 hours ago, MN Transplant said:

The big problem we have tomorrow is that it is dry.  HRRR is putting the DPs in the 50s by later in the day.  Kills the instability and the line dropping down.

             There will be some drying, due to what looks like modest downscoping, but the HRRR tends to overmix.    I think that's why its dew points are a fair amount lower than most of the other guidance here tomorrow. 

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On 6/1/2020 at 10:04 AM, Kmlwx said:

A bit north of us - @mappy is in the slight. Obviously expect tweaks as we get closer. D3 is an eternity away in severe forecasting. Do we all need a refresher that on June 29, 2012...DC proper was not even in the slight risk until the 20z update. Moderate not until the 01z update. 

close to enhanced risk now. but not liking any of the models this morning. a dying complex heading south.... i'm not too hyped on this one

MD_swody1 (3).png

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14 minutes ago, dailylurker said:

Any prospects for rain? I don't bother with severe around here. Widespread severe has happened like twice in the 41 years of my life. 

today? only if you're lucky to get under a storm. 

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That being said - I wonder what models looked like on a day like June 29, 2012. I could see the one wild card being if a good cold pool can really get established and sustain activity. Not sure if that would be modeled well prior to initiation. 

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1 hour ago, Kmlwx said:

That being said - I wonder what models looked like on a day like June 29, 2012. I could see the one wild card being if a good cold pool can really get established and sustain activity. Not sure if that would be modeled well prior to initiation. 

       We didn't have too many CAMs back then.   The NAM nest was running, and it whiffed badly on that event.     The HRRR did ok, but it was experimental, and not many people saw it.

        A key for today will be dew points.   The HRRR is most aggressive in mixing them out (downsloping factor?).    Most guidance mixes them out to some extent but try to have them recover closer to 00z, especially across northern MD.      I certainly can't disagree with everyone ready to punt today, but I'm not ready to close the book quite yet, at least for those of us north of DC.

 

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1 minute ago, high risk said:

       We didn't have too many CAMs back then.   The NAM nest was running, and it whiffed badly on that event.     The HRRR did ok, but it was experimental, and not many people saw it.

        A key for today will be dew points.   The HRRR is most aggressive in mixing them out (downsloping factor?).    Most guidance mixes them out to some extent but try to have them recover closer to 00z, especially across northern MD.      I certainly can't disagree with everyone ready to punt today, but I'm not ready to close the book quite yet, at least for those of us north of DC.

 

In my mind - the only two things that could "save" today are 1) An aggressive cold pool that performs better than expected at sustaining some sort of complex. 2) @Eskimo Joe's reminder that sometimes these things sag a bit more south and east than expected. But the fat lady is warming up. 

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