high risk

Definitely. Somewhat active today and then perhaps active for several days starting Sunday, but Saturday looks like a winner.

Pretty clear signal for afternoon convection tomorrow, and the CAPE/shear combo currently proved would certainly suggest at least some chance of SVR.

This cell over southern Howard is insane - blinding rain and gusts to 35 kt or so.

I can't speak for the Euro, but the new version of the GFS that was implemented in March showed a notable right-of-track bias for TCs in retrospective hurricane season testing, especially for those moving north and then recurving. It has been slowly adjusting to the west with Elsa's track through the southeast and Mid-Atlantic.

Tornadoes are only a threat immediately along and on the east side of the track of the center. There isn't much guidance that takes the center west of the area, although some tracks are further west than others.

Yeah, the steering flow along the east coast in the 12z GFS has more of a southerly component than previous runs, which allows Elsa to come further west. It seems to be in response to the midwest upper trough being a little bit stronger. Will be interesting to see whether this cycle is a blip or is legitimately catching on to a trend.

Thanks for continuing the discussion and for posting the sounding. In the big picture for SB vs MLCAPE, MLCAPE seems to be more representative of the air feeding into a storm if the environmental is deeply mixed. Once you go into the evening, and decoupling begins, SBCAPE is arguably more representative, although there are certainly exceptions. In the IAD sounding above, it's certainly not well-mixed, especially with the low-level moisture profile, so perhaps SBCAPE is a better representation, although the higher moisture values drop off quickly above the ground. That moisture profile makes it pretty easy to see why MLCAPE is so much lower.... If, however, a parcel was surface-based, it did have some instability to work with, and there is some decent 0-3 km CAPE to help achieve stronger upward acceleration. Given the earlier rounds of storms, I would have expected the temperature profile to be more moist adiabatic, but it actually had some decent low-level lapse rates. All of that said, I don't understand getting a sustained low-level mesocyclone out of this environment. Deep layer shear was good, and you can make a case for some rotation in the storm. But getting that rotation in the low-levels is an entirely different ballgame, and the low-level shear was meh - confirmed by the unimpressive values of 0-1 and 0-3 km helicity values. Perhaps there was a leftover boundary oriented ESE to WNW through DC, and the storm rode along it, greatly improving the helicity (there was certainly some existing directional shear in the lowest 0.5 km or so). The low LCLs would have greatly improved the chances of getting something to the ground, and that's confirmed by the videos of the storm hugging the ground. The fact that this cell was the only one in the area after dark that went severe argues for some localized enhancement of the environment in that Reston-DC-Bowie corridor. Still, this sounding has sneaky severe potential, but it certainly doesn't scream 'tornado!'.

I don't understand this event at all. The parameters don't seem to support what seems to be a fairly impressive severe event (albeit along a narrow corridor) this evening.

Definitely. There have been a few lame runs here and there, but guidance has overall been fairly consistent showing that the severe threat was this afternoon, and the threat for widespread heavy rain is in the late evening and overnight hours. Radar shows that this scenario is on track.

It's worth watching, but by the time it gets here, we will be losing instability (although we'll still have a decent amount of CAPE to work with), and the shear is not nearly as good here as it is further northwest. Heck, the shear isn't even very good where the watch just got issued. If, however, a sfc cold pool can become established, the line can organize better. and we would have some modest severe potential in a few hours. The HRRR runs haven't been too excited, but the 18z NAM nest looks robust.

yeah, even if we don't focus on potential significant UH swaths, the signal for widespread, organized convection in the early/mid afternoon hours tomorrow is robust across the CAMs. The shear/instability profile combo should be sufficient for some of that to become severe. The only "concern" is weak lapse rates shown in several models, but I like our chances of being upgraded to SLGT in the new day 2 outlook.

Looks to me like Thursday afternoon has a good chance to eventually become a SLGT. Lapse rates aren't great, but the timing looks favorable, and the shear/instability combo as current progged would likely generate SVR. Expecting a very heavy rain threat too, particularly as additional rounds of convection move over the area after dark.

Most of the CAMs this evening have a few showers in the area Saturday morning. LWX hasn't picked up on this yet.....

if you're just looking for rain, the HRRR has been somewhat consistent with a batch of heavy downpours moving southwest to northeast across the DC metro area around 10/11 PM.

The shear/instability/forcing combo to our northwest is legit and covers a large area. For us, the shear isn't nearly as good, and forcing is weaker, but the CAMs certainly agree on some sort of broken line moving through the areas north of DC. If you're south of DC by more than a county, it's pretty clear that today ain't your day. Even though our shear isn't as good as areas in the ENH, I agree with GeorgeBM that the mid-level flow is good enough to move things along and generate some wind potential. Could be a second round of soakers (with more of a heavy rain than a severe threat) in the evening hours.

yeah, it somehow creates small pockets of dew points in the upper 70s which of course makes the CAPE values expose. Not sure why it's doing that, but it's obvious wrong. Of course, we have the HRRR at the other end of the spectrum with its standard aggressive mixing of the low-level moisture.

I have to agree that we're now in the "Monday or bust" realm, as the timing for Tuesday shows no indication now of slowing down enough for us. There is certainly an increasing signal here for scattered storms later Monday into Monday evening, and there may be enough dry air in the low levels for a few downbursts, but the much better deep layer shear will remain to our west and likely preclude a more organized SVR threat. At this point, I just want to be sure avoid missing out entirely on rain by the time we get to Tuesday evening.

The HRRR has the most aggressive solution among the CAMs, but there seems to be some consensus overall for a convectively-induced shortwave (of some intensity) to approach the area tomorrow during peak heating and generate at least scattered convection. The HRRR solution would certainly be worthy of a SLGT.

Yeah, Saturday's threat has lessened, but I'm not sure it's dead. I was worried about the two MCS events coming in from the Midwest would keep us cloudy and cool Saturday, but most of the CAMs heat us up pretty good regardless. The problem in the HRRR is that it destroys the moisture over us - the HRRR tends to overmix, so I'm somewhat inclined to toss. The NAM nest has a much better environment over us later Saturday, but the forcing arrives too late. I agree for now with SPC that there are too many potential negatives to go with more than a MRGL, but the chances of a decent event here aren't dead.

Shear and instability certainly look good for late Saturday, even if we get mucked up for a while with light showers and cloud debris in the morning from the decaying MCS. Low-level shear may even be sufficient to support a lower-end TOR threat. I'm intrigued. Could be another shot Tuesday.

Agreed. Westerly winds at 850 always makes me a little hesitant to get heavily invested, but I'm intrigued.

And I think you have to give points to the NAM nest which, although an hour or two slow, really filled in the line once the original cells got to Frederick.

good analysis. Several CAMs now show things coming together as the system approaches the I-95 corridor, so that scenario is plausible. I think that dews will rebound a bit this evening as mixing wanes, and the HRRR shows this.

18z NAM Nest shows that people in the DC-Baltimore corridor will make a series of "next", "DC split", and "radar looks awful" posts around 8pm but will be much happier 2 hours later.

Yeah, things look better. I'm going to backtrack a bit from my earlier pessimism. There is a pretty clear trend in the guidance for some sfc-based instability to be present when the storms arrive/develop this evening. It shows up well in the individual 00z HREF member CAPE plots. The older runs (labeled -12h) have limited instability over our area, but some of the newer runs (especially NAM nest and ARW) trended higher with sfc-based instability last night. From what I've seen so far, the trend will continue with today's 12z cycle.