high risk

18z IAD special rob has a 0-1 km helicity of 261 !!!

It's broad, but I would be erring on the side of extreme caution today if I were at LWX.

That cell just east of Waldorf looks great!

Spot on. At the least, they'd have to be sending kids home in torrential rain if they didn't alter the dismissal time.

DCA now 81/73 with a southeast wind. BWI is 79/75 with an east wind. We may not get the 2000 CAPE values that some guidance was showing yesterday, but it certainly seems like sufficient instability will be in place, at least along and east of the I-95 corridor.

Tornado watch coming soon.

Howard County schools closing 3 hours early. SPC Mesoanalysis shows that we have work to do in terms of instability along the I-95 corridor to ramp up the threat. The likely earlier arrival of the forcing will give less time for heating, but I'm absolutely not ready to lower the threat yet.

That would be good. My worries are that some schools will end up under tornado warnings, and they usually bring the kids to interior hallways, and that kind of crowding is not what we want during a pandemic......

School systems would be very wise to have an early dismissal at noon. It would be bad to potentially have to get kids home while there are active tornado warnings.

I don't like that the 00z HRRR run brings the TOR threat into our area by mid-afternoon Wednesday instead of late afternoon. Do not want kids on school buses as tornado warnings are issued.

Yes, most guidance had a modest chunk of the huge predicted rainfalls for PA occurring tonight.

You may be on to something here. I wasn't worrying too much about the late night threat due to what I thought would be a lack of instability, but even though it's somewhat of an outlier, the HRRR has a modest shear/instability combo here towards morning.

I'm WAY more worried about the TOR potential in the DC-Baltimore corridor than I am about flooding. That said, I think it's worth noting that while the major flooding potential is going to be in PA/WV/western MD tomorrow, there will absolutely be potential for FLASH flooding in the DC-Baltimore region. It's going to be a roughly 6 hour period late tomorrow with several bands of convection (with potential for TORs) that will have torrential rainfall. I can certainly see some localized 3-4" totals that will create major problems for the evening rush hour. Things will be worse if the warm advection rain later tonight ends up overperforming, which is always a possibility in this type of environment.

But that's not what the guidance shows. There is a lot of consensus that much of the area along and southeast of an IAD-FDK line will stay mostly dry tomorrow until the convection rolls in during the mid to late afternoon.

Interesting to see whether SPC will add a 10% TOR contour in the upcoming day 2 outlook. There is probably just enough uncertainty in the exact area to draw a 10 to make them wait until tomorrow to better define a higher threat area, but the setup as currently progged may support greater than a 5% TOR outlook. If you're looking for TORs, you can't ask for much more in this setup than what's currently shown: a dry slot keeping us dry through a big chunk of Wednesday, allowing surface heating to maximize instability ahead of strong forcing and strengthening wind fields at the right time of day.

Any chance you looked at the max by accident? That image matches your description. The mean isn't that aggressive for DC and areas right along I-95:

I'm in on SVR. I'm not in on widespread flooding rains until you get further north and northwest, although there will be isolated local flooding where recent heavy rains have occurred. Right now, guidance shows most of Wednesday being dry which will allow for some heating for sure. We then get some bands of convection arrive later in the day, with perhaps some moderate instability and likely strengthening low-level wind fields. If some of the more aggressive guidance is correct, these won't be little spin-ups in a big shield of rain; these will be legitimate supercells embedded in intense convective bands. This UH image from the 12z HRRR would warrant a potential ENH for tornadoes: There are plenty of ways that this could fail, and we often fail here, but this setup has *potential* to be a big deal if we legitimately heat up tomorrow. As for the rain, there could be some sneaky higher totals tonight, and those bands tomorrow evening will have torrential rainfall, but the heaviest rain will overall be too progressive, and the periods of intense rain will overall be relatively short-lived until you go further north.

I'm quite intrigued as well. The track to our northwest would allow for some heating before the main convective band arrives later in the day.

Increasing signal in the guidance this morning for widespread showers and storms this afternoon for those east of the Potomac, especially for northern/northeast MD. Models have had limited handle on the precip so far (to be kind), so I'm not totally sure how much I buy it, although radar seems to suggest that this scenario is plausible.

one last tornado warning on the MD/PA border, near @mappy

A few cells popping up in western Montgomery and near Culpepper. HRRR shows a strong line (or line with embedded supercells?) moving through DC and points north after dinner time.

The box is going to be justified, but in terms of tornado threat across MD, the earlier arrival of storms may limit that potential a bit, as the best low-level shear won't arrive until later in the afternoon.

Yeah, but those HRRR low dew points that we usually see are due to mixing, and even the HRRR can't overmix a tropical air mass like this.

NAM Nest seems to be an outlier with its very sparse coverage of cells this afternoon.

Oddly, the 00z NAM nest had better parameters but fewer storms than shown in previous runs. HRRR and HiRes Window ARW still look impressive.