2020 Mid-Atlantic Severe Weather - General Thread

[Newman]

The 12z 3k NAM sure is showing some curvy hodographs. This one right around the DC area at 18z:

[southmdwatcher]

Is that sounding above showing 0-3km CAPE at 164?

[Tater Tot]

When was the last time an outlook discussion used the term "Strong, long-track tornadoes" for an area that included Virginia? 

[Eskimo Joe]

Quote

Day 2 Convective Outlook AMEND 1
   NWS Storm Prediction Center Norman OK
   0320 AM CDT Sun Apr 12 2020

   Valid 131200Z - 141200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   SOUTHEAST GEORGIA...THE CAROLINAS AND VIRGINIA...

   AMENDED TO ADD PARTS OF PA/NJ INTO SLIGHT AND NY/MA INTO MARGINAL

   ...SUMMARY...
   Severe thunderstorms with tornadoes, damaging wind gusts and hail
   will be likely across parts of the Atlantic Coastal Plains into the
   central Appalachians on Monday.

   ...Atlantic Coastal Plains/Central Appalachians...
   A potent shortwave trough will move quickly northeastward across the
   Ohio and Tennessee Valleys tonight. The trough should be positioned
   over the central Appalachians at the start of the period. At that
   time, a 70 to 80 kt low-level jet will be located across the
   Carolinas and Virginia with an axis of moderate instability
   co-located with the jet. A band of convection, potentially severe,
   is forecast to be in northeast Georgia, the western Carolinas and
   western Virginia at 12Z. Other strong thunderstorms may be ongoing
   in the upper Ohio Valley. An 80 to 100 kt mid-level jet oriented
   along the western edge of the low-level jet will create very strong
   deep-layer shear favorable for severe thunderstorms. This band of
   convection is forecast to move quickly eastward across the Atlantic
   Coastal Plains during the morning and early afternoon. Farther
   north, strong convection should develop in weak instability but very
   strong shear as far north as Pennsylvania and southern New York.

   The main question with this outlook is convective mode. There are
   two possibilities.  The first is that the band of thunderstorms will
   have discrete elements and gaps that will be favorable for
   supercells and tornadoes. Forecast soundings at 15Z from southern
   Virginia southward into northern South Carolina show looped
   hodographs with 0-3 km storm relative helicities in the extreme
   catogory, generally near or above 600 m2/s2. This would support a
   threat for strong tornadoes associated with the more dominant
   supercells. A wind damage and hail threat would be likely with
   supercells and with the more organized line segments. 

   The second scenario would be that a squall-line is ongoing at 12Z
   from eastern Georgia northward into the western Carolinas and
   Virginia. In that case, widespread wind damage would be likely. A
   QLCS tornado threat would exist with the stronger bowing line
   segments. Hail would also be possible with the more intense parts of
   the line.

   At this time, the outlook reflects the first scenario in which more
   discrete cells are present across the warm sector at 12Z. In this
   case, a cluster outbreak of tornadoes would be possible and a strong
   long-track tornado or two can not be ruled out.

   ..Broyles.. 04/12/2020

 

[09-10 analogy]

45 minutes ago, Newman said:

The 12z 3k NAM sure is showing some curvy hodographs. This one right around the DC area at 18z:

Don't normally see too many PDS TOR soundings around here. 

EDIT: 

Just for the doing of it, looked up some parameters just prior to La Plata:

0-1 km SRH: 253 m2 s-2

0-3 km SRH: 243 m2 s-2

0-1 km bulk shear: 32 kt

0-6 km bulk shear: 53 kt

 

 

Taken from:

http://www.tornadohead.com/storhodos.htm

 

[Kmlwx]

Updated LWX disco snippet is dead on what I thought earlier

 

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

Really not much to add to the previous discussion. High impact
storm to affect the region Mon with significant risk of severe
thunderstorms including tornadoes. Planning to issue a Wind
Advisory for everywhere not included in a High Wind Watch.
While widespread damaging winds are certainly possible in a lot
of areas, these should be brief in nature and mainly
convectively driven. Believe those will be handled better with
SVRs or TORs as needed. Flooding rain threat seems to be
diminishing and not planning issuing any Flood Watches at this
time.

[high risk]

         I still have the same thoughts I had last night:   QLCS moves through the area during the early-mid morning hours with some discrete cells in the early afternoon.    The QLCS will have extreme shear - it's a question of instability, but IF we can get some sfc-based cape (and the chances seem to be going up), you have a threat of widespread wind damage and some tornadoes for sure.    The 2nd event will have more instability and reduced shear but still more than enough, and a more "classic" supercell mode would be favored with a legit TOR threat.   There are still uncertainties (how much instability for round 1?     how much coverage of storms for round 2?), but I think that a 10% TOR threat (and an ENH risk extended north into our area) would be justified in the updated day 2. 

   

[Kmlwx]

Just now, high risk said:

         I still have the same thoughts I had last night:   QLCS moves through the area during the early-mid morning hours with some discrete cells in the early afternoon.    The QLCS will have extreme shear - it's a question of instability, but IF we can get some sfc-based cape (and the chances seem to be going up), you have a threat of widespread wind damage and some tornadoes for sure.    The 2nd event will have more instability and reduced shear but still more than enough, and a more "classic" supercell mode would be favored with a legit TOR threat.   There are still uncertainties (how much instability for round 1?     how much coverage of storms for round 2?), but I think that a 10% TOR threat (and an ENH risk extended north into our area) would be justified in the updated day 2. 

   

Always glad to have your insight in our region. I would tend to think any hatching remains south of our area...at least with regards to TORs. I could see a hatched wind area come up to our area - especially if LWX is leaning more on the SVR TOR products to emphasize the wind threat rather than the wind advisory products. 

[high risk]

1 minute ago, Kmlwx said:

Always glad to have your insight in our region. I would tend to think any hatching remains south of our area...at least with regards to TORs. I could see a hatched wind area come up to our area - especially if LWX is leaning more on the SVR TOR products to emphasize the wind threat rather than the wind advisory products. 

     and likewise.     I agree that I'd wait on any hatching up here, but I personally see enough to go up a notch to ENH.

 

[Kmlwx]

The 15z RAP has over 2000J/kg of SBCAPE through a good chunk of the area around surrounding the 17z timeframe. 1km EHI approaching 4.5 in a pocket...SigTor 8-10 in a chunk of the area. Dang...

[yoda]

10% hatched tor is now literally just south of DC metro... EZF is included 

[Kmlwx]

2 minutes ago, yoda said:

10% hatched tor is now literally just south of DC metro... EZF is included 

You would track that line by the centimeter if you could

[yoda]

Just now, Kmlwx said:

You would track that line by the centimeter if you could

Its probably like 20 miles S of me lol... but I would expect it to come north more tomorrow tbh.  But that would depend on what goes on in the SE and western Carolinas tonight

[southmdwatcher]

Yeah that 10% hatched boundary looked like it stopped at the Rappahannock River on last nights graphics, it clearly includes southwestern part of Charles County now. So maybe 15 miles more northward. What happens with the QLCS and it's speed will probably have a large impact on our chances of tornadoes.

[MN Transplant]

12z euro still holds onto the widespread 60-70 mph gusts.  

[SomeguyfromTakomaPark]

2 minutes ago, MN Transplant said:

12z euro still holds onto the widespread 60-70 mph gusts.  

Across most of our CWA?

[southmdwatcher]

Euro has an area of 1000-2000 SB CAPE coming into the south side of DC area at 18z too, yeah not! Scratch that 21z information, somehow my F5/EuroWX switched over from Euro information to NAM.

[MN Transplant]

13 minutes ago, DCTeacherman said:

Across most of our CWA?

Yeah.  What I’m assuming is that the euro and NAM are mixing down the big wind aloft during the line that comes through mid-to-late morning.  So, not widespread and constant like March 2018.  
 

The euro then jacks up the CAPE following that line and has some semblance of storms in the early afternoon hours, but while the parameters are great, none of the models are throwing out any impressive storm signatures.  Not sure why that is.

[Eskimo Joe]

Couple of thoughts as we begin to close in on this event:

1.) I'm looking at the evolution of this event today across the south for timing, location of the warm front and low.  If we see things are staying further south or rushing along quicker than we could expect a more muted event here tomorrow.

2.) For tomorrow, the satellite and surface obs will be key.  If we somehow wind up socked in with east or northeast winds and 55 degrees at 10:00 or 11:00 am then we're probably going to bust.  

3.) I would argue the ceiling on this event is pretty high, at least for this area.  When even the GFS and Euro are pushing close to 1,200 SBCAPE up towards BWI then there's definitely some strong stuff at work and this isn't a case of the NAM et al being silly.

[CAPE]

Well, Mount Holly went with a fairly widespread High Wind Warning.  I thought it might only be hoisted for the immediate coastal counties of DE and NJ..

...HIGH WIND WARNING IN EFFECT FROM 6 AM TO 7 PM EDT MONDAY...

* WHAT...South winds 25 to 35 mph with 50 to 60 mph gusts
  expected.

* WHERE...Portions of central, northern and southern New Jersey,
  southeast Pennsylvania, northeast Maryland and central,
  northern and southern Delaware.

* WHEN...From 6 AM to 7 PM EDT Monday.

* IMPACTS...Damaging winds will blow down trees and power lines.
  Widespread power outages are expected. Travel will be
  difficult, especially for high profile vehicles.

* ADDITIONAL DETAILS...Thunderstorms are possible on Monday that
  could result in even stronger wind gusts.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

People should avoid being outside in forested areas and around
trees and branches. If possible, remain in the lower levels of
your home during the windstorm, and avoid windows. Use caution if
you must drive.

[yoda]

Seems like LWX is going for it in afternoon disco 

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
314 PM EDT Sun Apr 12 2020

.SYNOPSIS...

Low pressure over Oklahoma will strengthen rapidly as it tracks
across the Mississippi River Valley late tonight and into the
Great Lakes Monday with its associated cold front crossing the
area Monday afternoon. Unsettled conditions will persist through
the end of the week as waves low pressure track across the
southern mid-Atlantic states.

&&

.NEAR TERM /THROUGH MONDAY/...

Potential for a significant severe wx episode appears on tap for
Monday as strong wind fields develop in response to a deepening
low pressure center over the eastern half of the country. It
appears there could be two rounds of severe wx. The first one with
the initial surge of warm moist advection as warm front lifts
through the area. Model reflectivity from hi-res models indicate
possible QLCS with embedded tornadoes in the 09Z-15Z time frame
ahead of mid-level dry slot. Second round of severe wx will be
associated with secondary cold front and negatively tilted
shortwave trough moving through PA and grazing the northern fcst
area. Outside of t-storms expect winds to consistenly gust in
the 45 to 55 mph due to strong low-level wind fields (i.e. 60kt
at 925 mb and 70-kt at 850 mb). Biggest risk for severe wx will
be in the 09Z-18Z time frame.

[mappy]

There’s so much going on I can’t keep track lol

okay, two threats for tomorrow. Morning qlcs as mentioned, then possible more discrete cells later in the day

then high winds after that, right?

[Kmlwx]

3 minutes ago, mappy said:

There’s so much going on I can’t keep track lol

okay, two threats for tomorrow. Morning qlcs as mentioned, then possible more discrete cells later in the day

then high winds after that, right?

High winds seem like they will be with the activity and in the morning. 

[mappy]

1 minute ago, Kmlwx said:

High winds seem like they will be with the activity and in the morning. 

Oh.. high winds arent following the front? 

Just now, losetoa6 said:

Don't forget the snow event Wednesday morning 

lol didn’t know thee was a chance. It’s spring man 

[yoda]

Impressive... most impressive 

 

[MN Transplant]

5 minutes ago, mappy said:

Oh.. high winds arent following the front? 

lol didn’t know thee was a chance. It’s spring man 

No, this is an unusual wind setup for us.  We get this serious southerly low level jet sometimes, but we generally have a boundary layer that prevents it from getting to the surface.  This time there is all sorts of convection and the models think we’ll get it.  Even the 18z HRRR which looks relatively unimpressive reflectivity-wise, gets gusts to ~60 mph.

[mappy]

Just now, MN Transplant said:

No, this is an unusual wind setup for us.  We get this serious southerly low level jet sometimes, but we generally have a boundary layer that prevents it from getting to the surface.  This time there is all sorts of convection and the models think we’ll get it.  Even the 18z HRRR which looks relatively unimpressive reflectivity-wise, gets gusts to ~60 mph.

Ahh got it. Thanks. 

[osfan24]

I guess it's still early but it seems like there isn't all that much happening down south, thankfully. Seen a number of tornado warnings out but I haven't seen any official tornado reports or damage yet.

[canderson]

1 minute ago, osfan24 said:

I guess it's still early but it seems like there isn't all that much happening down south, thankfully. Seen a number of tornado warnings out but I haven't seen any official tornado reports or damage yet.

Monroe got hammered.

[osfan24]

Just now, canderson said:

Monroe got hammered.

Ahhh, just seeing that now on TWC. Does look like big damage there.