2020 Mid-Atlantic Severe Weather - General Thread

[Kmlwx]

I re-positioned to my parent's house over closer to Silver Spring for today. I think I might still be just a hair too far east based on what the HRRR is showing. 

[Kmlwx]

The Herderps still really likes DC proper with a blob. 

[George BM]

SLGT shifted ENE to the Potomac river. (1300z update)

[Kmlwx]

3 minutes ago, George BM said:

SLGT shifted ENE to the Potomac river. (1300z update)

I'd feel pretty good about being in Northern Virginia this afternoon if you like storms. Especially from like Sterling to La Plata and SW of there. DC proper and MBY is more of a question mark. 

[Rhino16]

30 minutes ago, Kmlwx said:

The Herderps still really likes DC proper with a blob. 

I’m glad to know someone else also says HerDerps...

[Kmlwx]

Just now, Rhino16 said:

I’m glad to know someone else also says HerDerps...

How can you not...it's just so perfect. 

Honestly - it hasn't been terrible with at least outlining where storms may be in the anecdotal times I've watched it. NAM nest is a snoozer for most of us today. 

[George BM]

Mesoscale Discussion 1373
   NWS Storm Prediction Center Norman OK
   0300 PM CDT Sat Aug 01 2020

   Areas affected...northern Virginia...eastern West Virginia...much of
   Maryland...and the District of Columbia

   Concerning...Severe potential...Watch possible 

   Valid 012000Z - 012200Z

   Probability of Watch Issuance...40 percent

   SUMMARY...Convection over eastern West Virginia will gradually
   spread eastward, posing a risk for damaging wind gusts and perhaps
   an isolated tornado.  A WW may eventually be needed pending
   convective trends.

   DISCUSSION...Isolated convection has developed across portions of
   eastern West Virginia over the past hour or so, with one cell
   showing signs of broad/weak rotation aloft.  The airmass supporting
   these storms has become moderately unstable, with 70s F dewpoints
   and 80s F surface temperatures resulting in 2000-2500 J/kg along and
   south of a warm front located from PIT to WAL.  The cells are also
   in a weakly forced synoptic environment, with a mid-level trough
   located well west of the region. Nevertheless, weak inhibition and
   buoyancy in tandem with weak surface confluence has fostered initial
   development in eastern West Virginia.  This regime should continue
   through the evening, with 30-40 knots of deep shear fostering
   organization.  Damaging wind gusts will be the primary threat with
   this activity, although a tornado cannot be ruled out given favored
   cellular storm mode and potential for updraft interactions with the
   aforementioned warm front.  Convective trends are being monitored,
   and a Severe Thunderstorm Watch may be needed especially if a
   greater concentration of convection can be achieved through
   nightfall.

   ..Cook/Bunting.. 08/01/2020

[Chase]

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
416 PM EDT Sat Aug 01 2020
 
Day 1
Valid 2016Z Sat Aug 01 2020 - 12Z Sun Aug 02 2020 

..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE OHIO 
VALLEY AND ADJACENT PARTS OF THE EASTERN U.S...

...Ohio Valley into the Mid Atlantic...
We continue with a broad Slight Risk area that encompasses various 
threat areas associated with an anomalously deep upper trough. A 
well defined surface wave will lift through the Ohio Valley this 
evening. Cells in the warm sector will be moving fairly quickly, 
but the combination of moderate instability and precipitable water 
values well over 1.50 inches will yield heavy short term rain 
rates capable of producing flash flooding in sensitive basins. Out 
along the warm front, storms initiating off the Blue Ridge or more 
generally in the very moist and unstable air mass pooled along the 
Virginia portion of the warm front will have potential to produce 
very heavy downpours. Increasing inflow speeds could yield pockets 
of training or propagation back into the inflow if organized 
clusters can persist into the evening hours. Overnight the 
emphasis will shift to the deformation zone of the deep layer 
cyclone approaching northwest Ohio and southeast Michigan. Strong 
lift will work with instability rooted at mid levels to produce 
some slow moving convection, with local inch per hour rates likely.

Finally, a threat exists over eastern North Carolina and southeast 
Virginia for the next few hours, as the sea breeze and presence of 
a lingering frontal zone will yield a local maximum of storm 
initiation, allowing for cell mergers within a very moist and 
unstable environment. The latest 12Z HREF exceedance probabilities 
are quite impressive -- with probs of >1"/hr rates peaking over 
80% across this area between 20-00Z, with probs of >2"/hr rates 
equally as impressive during the same time (40-60%).

[high risk]

certainly some chance of SVR this evening and later tomorrow, but I'm really starting to like the look for late Monday.    NAM nest has an impressive connective signature in an environment with some shear.   My biggest concern, though, is that the model looks slow with Isaias, so we could have a much wetter environment Monday than progged (and more of a flash flood thread than a SVR threat) 

[thunderman]

Not really a whole lot yet across central and northern Virginia (as expected). 
Convection starting to fire in central Virginia along I64 and I'd expect this to continue north over the next few hours.  Good instability and wind profile for storms in a moist environment across central and northern parts of the state.  I wouldn't be surprised at all to see a few SVR warned cells between now and 10PM and maybe a TOR warning or two.
 

 

[Rhino16]

Tornado Warning in Botetourt VA.

[yoda]

2 minutes ago, Rhino16 said:

Tornado Warning in Botetourt VA.

Confirmed TOG 

[Rhino16]

And what’s the weird snake-like Thing doing near virginia beach making it’s way north? Looks like an outflow puff(?) that’s making the snake?

[MN Transplant]

10 minutes ago, Rhino16 said:

And what’s the weird snake-like Thing doing near virginia beach making it’s way north? Looks like an outflow puff(?) that’s making the snake?

Storms firing along an outflow boundary from prior storms.  A nice example.

[Rhino16]

2 minutes ago, MN Transplant said:

Storms firing along an outflow boundary from prior storms.  A nice example.

Very good example. Cool to watch.

[thunderman]

Mesoscale Discussion 1375
   NWS Storm Prediction Center Norman OK
   0605 PM CDT Sat Aug 01 2020

   Areas affected...Eastern West Virginia...Northern
   Virginia...Southern Pennsylvania...Maryland...Delaware

   Concerning...Severe potential...Watch possible 

   Valid 012305Z - 020100Z

   Probability of Watch Issuance...40 percent

   SUMMARY...A wind damage threat may develop across parts of the
   Mid-Atlantic this evening. Weather watch issuance could be needed
   across the region depending upon convective trends.

   DISCUSSION...The latest surface analysis shows a 1007 mb low in the
   Ohio Valley with a quasi-stationary front extending eastward from
   the low into southern Pennsylvania. South of the front, a moist
   airmass is in place with dewpoints in the lower to mid 70s. In
   response, the airmass has become moderately unstable and MLCAPE is
   estimated by the RAP to be in the 1000 to 2000 J/kg range across
   much of the moist sector. Scattered thunderstorms are ongoing across
   the Ohio Valley extending eastward into western Maryland and
   northern Virginia. This activity will continue to move eastward into
   the Mid-Atlantic over the next few hours. In addition to the
   instability, deep-layer shear on the order of 30 to 35 kt will be
   supportive of at least an isolated wind damage threat. However, the
   threat could be more substantial if convective coverage increases.
   If that occurs, weather watch issuance would need to be considered.

   ..Broyles/Hart.. 08/01/2020

[Eskimo Joe]

Glad to see you back Joey!

[Kmlwx]

That cell near Bath has some spin in it. 

[Ian]

put this in the wrong thread earlier I guess... impressive

 

[thunderman]

Interesting storm near Clear Springs, MD.

 

[NorthArlington101]

Interesting storm near Clear Springs, MD.

 

TOR possible tag. I’d warn that, IMO

[LP08]

2 minutes ago, NorthArlington101 said:

TOR possible tag. I’d warn that, IMO

Of all the pity warnings we get...I agree 

[boviscopophobic]

Well, I wish I'd gone south! This cell was weakly rotating for hours but didn't end up doing anything. Taken near Edinburg, VA.

 

[jewell2188]

Radar trends are rather sad. Not sure why a FFW was issued. These few storms are racing! 

[high risk]

53 minutes ago, jewell2188 said:

Radar trends are rather sad. Not sure why a FFW was issued. These few storms are racing! 

    the PWs are really impressive, and earlier HRRR runs looked wet and suggested backbuilding, but that model has really backed off now.

[thunderman]

Madison County cell showing some weak rotation.

[yoda]

Day 2 MRGL risk (Thursday) for a few damaging wind gusts possible

[thunderman]

Could have a good downburst or two tomorrow.  Instability and shear should support a few organized updrafts.  Heavy column with PWATS of 1.5+ should make make damaging winds and heavy rainfall the main threat.  Notable flash flood threat, for places that get storms … which may end up being in distinct swaths, with storm motion and low level SRW roughly converging.   3 hour FFG is also under 2 inches most everywhere from Isaias.

[Kmlwx]

Hell of a derecho going through the Midwest right now. One measured gust was to 106mph! 

[ErinInTheSky]

WOW this derecho! PDS to Chicago.