2020 Mid-Atlantic Severe Weather - General Thread

[Eskimo Joe]

On 4/23/2020 at 8:53 AM, George BM said:

While just about all ensembles have this trough staying over the eastern US for the remainder of the month into the beginning May I wonder if we can get into some W/NW flow action sometime early in May (2nd week?) as the trough slowly lifts and/or shifts eastward (as shown in a number of long range ens. ATM). Just speculation at this point of course... and me thinking out loud. 

You asked:

 

[poolz1]

Any potential for wed night/thurs?  Looks like the 3k has a nasty line coming through WV around midnight....some training looks possible with the slow eastward push.

[Eskimo Joe]

10 hours ago, poolz1 said:

Any potential for wed night/thurs?  Looks like the 3k has a nasty line coming through WV around midnight....some training looks possible with the slow eastward push.

More likely we get flooding.  If you read the morning AFD from LWX it sounds like we're getting a flood watch later today.

[high risk]

13 hours ago, poolz1 said:

Any potential for wed night/thurs?  Looks like the 3k has a nasty line coming through WV around midnight....some training looks possible with the slow eastward push.

       Yeah, wind profiles look awesome to our west Wednesday night, but instability is negligible.     On Thursday, the wind profiles along the I-95 corridor will be decent, but instability again looks to be effectively nada.     Agree with EJ that any threat would be flooding.     It had been looking like the axis of heavy rain Thursday afternoon would set up just to our east, but the 12z NAM is slower, and a heavy rain threat may set up for DC and points east.

[poolz1]

2 hours ago, high risk said:

       Yeah, wind profiles look awesome to our west Wednesday night, but instability is negligible.     On Thursday, the wind profiles along the I-95 corridor will be decent, but instability again looks to be effectively nada.     Agree with EJ that any threat would be flooding.     It had been looking like the axis of heavy rain Thursday afternoon would set up just to our east, but the 12z NAM is slower, and a heavy rain threat may set up for DC and points east.

06z euro with a slightly slower progression as well....Pretty consistent the last few runs for a 2-3" region-wide rain maker.  

Novice question....do you, or anyone, have any resources you can point me towards to help me understand how to assess the risk of severe from a sounding and other parameters?  I do understand the basics but the more I become interested in severe and heavy rains the more complex it seems compared to winter weather.  Never thought I would become interested in severe...but, it seems to have grown on me.

[Eskimo Joe]

NWS Charleston, WV just issued a flood watch for their eastern zones so I wonder if/when CTP and LWX will be hoisting a watch.

[osfan24]

3K NAM has been overdoing it lately, but looking at latest run, looks like it comes in pretty early tomorrow and is out of here in the afternoon. It moves through slowly, but not slow enough for training, and the line is pretty narrow, so its only about 4 hours of heavy rain in any one location.

[jewell2188]

12 minutes ago, osfan24 said:

3K NAM has been overdoing it lately, but looking at latest run, looks like it comes in pretty early tomorrow and is out of here in the afternoon. It moves through slowly, but not slow enough for training, and the line is pretty narrow, so its only about 4 hours of heavy rain in any one location.

Yeah looks pretty meh to me. 

[Vice-Regent]

Just now, jewell2188 said:

Yeah looks pretty meh to me. 

Again just east wins. Prevailing trend of the season thus far.

[arlwx]

From the latest LWX discussion:

(snip)
.SHORT TERM /THIS EVENING THROUGH FRIDAY NIGHT/...
Notable trends seen this cycle among global models were that
the GFS trended deeper/more amplified, closer to the Euro with
the upper level trof/closed low fcst to dig across the mid-Atlc
states Thu-Fri. Timing differences with respect to upper level
trof axis moving across the area have decreased significantly
and the rainfall potential has increased somewhat since 24 hrs
ago. Anticipating a widespread moderate to heavy rainfall event
late Wed night into early Thu evening with widespread 1.5 -2.5
inches with the potential for up to 4 inches (reasonable worst
case scenario) with heaviest amounts east of the Blue Ridge and
Catoctin mountains. Forcing and moisture will be plentiful with
instability lacking which would limit rainfall rates, but
prolonged period of the event, deep moisture, and strong upper
level divergence will compensate for lack of instability. While
heaviest amounts are expected east of the Blue Ridge, enough
spread is shown in the ensembles and difference percentiles to
include areas west of the Blue Ridge. Have issued a Flood Watch
for much of the area separated with two segments, a western
segment with beginning and ending time of 08Z-16Z Thu, and an
eastern segment running from 16Z Thu-02Z Fri.
(snip)

[arlwx]

If LWX is to be believed, I'd expect quite a few road closures due to small streams out of their banks. I DO hope Arlington has fixed its drains and alerted persons living/working in the usual suspect spots (think Westover, the area of South Glebe Road near the sewage plant, etc.).

[high risk]

While it looks like we'll hopefully avoid some of the nastier scenarios being depicted by various guidance in recent days, I don't think it's worthy of a 'meh' either.     We'll still have a 60+ knot low level jet, some very strong lift from multiple sources including upper difluence, and impressive PW values, and even hi-res guidance can often underdo precip in these events.    And while it looks to be fairly progressive, there are still some hints of a "round 2" Thursday afternoon in the HRRR and ARW2.     Certainly the best chances for big amounts are east of DC, but the chances of really huge totals seem lower now, they're not zero, and we'll still have to deal with issues associated with a heavy event in a short period of time at a minimum.

[George BM]

For the past several days I've been low-key watching the Sunday system for any severe potential and as of right now late Sunday has slight potential to get interesting should we have enough CAPE (which currently looks modest to perhaps locally moderate with LI of -3 to -5). Deep layer flow looks fairly strong (on the order of 50+ kts in the mid-levels). Should we be able to get enough sunshine for more moderate CAPE it could get interesting for some. Timing does look to be leaning a bit on the later side ATM.

Then there is also still the question of how far north this 'threat' will extend.

#Notanexpertopinion

#Justmy2cents

[high risk]

20 minutes ago, George BM said:

For the past several days I've been low-key watching the Sunday system for any severe potential and as of right now late Sunday has slight potential to get interesting should we have enough CAPE (which currently looks modest to perhaps locally moderate with LI of -3 to -5). Deep layer flow looks fairly strong (on the order of 50+ kts in the mid-levels). Should we be able to get enough sunshine for more moderate CAPE it could get interesting for some. Timing does look to be leaning a bit on the later side ATM.

Then there is also still the question of how far north this 'threat' will extend.

#Notanexpertopinion

#Justmy2cents

    Indeed!   check out the 12z NAM nest for Sunday afternoon.

[George BM]

48 minutes ago, high risk said:

    Indeed!   check out the 12z NAM nest for Sunday afternoon.

That's what pulled my arm enough for me to make the post about Sundays potential. 

[Kmlwx]

SARS putting out a decent amount of sounding analog results too...

[Eskimo Joe]

Sunday screams big hailers and structure for I-66 south.

[yoda]

2 minutes ago, Eskimo Joe said:

Sunday screams big hailers and structure for I-66 south.

I think it will depend on where the front (warm front?) sets up shop... could maybe be an isolated tornado if it rides the west to east front?

And big hailers are what to you?  The usual quarter to half dollar size around here or bigger?

[Eskimo Joe]

2 minutes ago, yoda said:

I think it will depend on where the front (warm front?) sets up shop... could maybe be an isolated tornado if it rides the west to east front?

And big hailers are what to you?  The usual quarter to half dollar size around here or bigger?

Couple of 1.5" stones based on the setup.  

[yoda]

1 minute ago, Eskimo Joe said:

Couple of 1.5" stones based on the setup.  

Ah, ping pong ball hail to maybe golf ball then... guess our ML Lapse rates are good enough?

[Eskimo Joe]

Just now, yoda said:

Ah, ping pong ball hail to maybe golf ball then... guess our ML Lapse rates are good enough?

Yea, good LIs are a sign of the capability to really sustain updrafts and we've seen some pretty cold temps upstairs of late so I could see a couple of big hailers ripple off the I-81 corridor and trek into NOVA.  Maryland is probably out of this one unless something big shifts in our favor.

[WEATHER53]

That storm had such odd verticle orientation both with mass and thin area of elongated heavy rain 

[yoda]

00z 12km NAM looks decent... has what looks to be a complex of storms (MCS?) Roll through the DC metro region around 03z MON

00z 3km NAM NEST looks intriguing from 00z to 04z MON... looks like a sup comes rumbling down i66 corridor from 02z to 04z

[Eskimo Joe]

Definitely looks like a I-66 to US 50 and points south risk.

[high risk]

The SPC outlook discussion is spot on.    Forcing is strong, but the soundings look very meh.    Best chance of severe will definitely be further south (as suggested by EJ), where temps will be warmer, giving some hope of modest cape, but it's pretty iffy there too.    For those north of DC like me, I'll be happy with thunder:  NAM nest looks great for that, but it's a bit of an outlier, with several other CAMS not showing good reflectivity signals north of 66 (VA) and 50 (MD).

[Kmlwx]

I want to witness comet sized hail. 

[Vice-Regent]

47 minutes ago, Kmlwx said:

I want to witness comet sized hail. 

You've come to the right place then. We are in the business of being the best weather region in the US.

[yoda]

6 hours ago, high risk said:

The SPC outlook discussion is spot on.    Forcing is strong, but the soundings look very meh.    Best chance of severe will definitely be further south (as suggested by EJ), where temps will be warmer, giving some hope of modest cape, but it's pretty iffy there too.    For those north of DC like me, I'll be happy with thunder:  NAM nest looks great for that, but it's a bit of an outlier, with several other CAMS not showing good reflectivity signals north of 66 (VA) and 50 (MD).

18z NAM soundings at KIAD for 00z MON and 03z MON looked pretty good to me... decent SBCAPE and shear... would suggest that the WF or west to east front is somewhere in C MD

Sim radar didnt look too bad on either of the 18z NAMs or RGEM... 18z long range HRRR did suggest though that the front is in N VA as it has best storms just south of me toward EZF

[Vice-Regent]

[yoda]

00z NAM and 3km NAM sim radar look interesting around 03z/04z MON... I guess some sort of an MCS?

Both 00z WRF-ARW and 00z WRF-ARW2 keep majority of storms down by EZF

00z WRF-NMM looks more like the NAM twins but is an hour or 2 faster

00z HRDRPS looks fun DC south