high risk

1500 is probably enough cape to handle that kind of instability, especially given that it's not "tall, skinny" cape, and there is enough low-level instability for good parcel accelerations. The forecasted soundings keep getting better, and SPC now has a day 2 MDT which looks justified. Still questions about evolution of elevated convection earlier in the day and resulting impact on how far north the warm front can get, but areas just south of wherever the warm front ends up look primed.

The problem seems to be that the sfc high to our northeast is moving out faster than was being shown, leading to the sfc winds shifting from north in the morning to southeast by the end of the day. In the NAM and GFS, that allows the sfc dew points, which start the day in the low teens, to recover to the low 30's by evening. That certainly won't get the job done. If we can somehow hold in northeast sfc winds for more of the day, we'll be able to keep the drier air in place and potentially reap some wet bulb benefits when the precip arrives.

NAM nest still shows that the front will sink back to the southwest later today and cool things down for those northeast of DC. HRRR seems to be coming on board.

While it's an obvious long shot, and I won't try to pretend otherwise, this is a chilly and very dry air mass that will settling in over us on Sunday. (The GFS shows dew points dropping perhaps into the single digits early Sunday). So IF the low can track south of us and we can get precip in here overnight Sunday, that could work for some of us.

There has been discussion about this line over in the severe thread. It's been going for a couple of hours now.

There are some small hints of it in the previous HRRR runs, but it's overall really tough for a model to get this, as it has to get the initial forcing and cold pool dynamics. Forecast soundings show a strengthening unidirectional wind profile and some downdraft cape......

This line is producing. I've seen a few events like this over the years, with a fast-moving line of low-topped showers requiring warnings. Will be interesting to see how far southeast they survive.

not at all saying that this will end up as a severe event, but the radar is supposed to look empty right now, regardless of whether we get severe. The guidance shows storms breaking out over central WV in the next 2 hours and then racing east-northeast.

lots of signal around 7 or 8pm, but a general 6-9pm range should cover it. overall severe threat seems fairly low but not non-zero, consistent with the SPC outlook. But lightning would be a nice early March bonus.

you have a very legit chance of seeing convection, for sure.

pretty stong agreement among the CAMs this morning that the threat later today is all north of the DC Beltway, and depending on your model of choice, it could well north.

right. because the HRRR is 5-8 degrees warmer.....

18z HRRR has a sfc-based bow echo moving across the areas north of the DC Beltway early Tuesday evening. It's an outlier solution in terms of having much warmer sfc temps than other guidance, but IF it were correct, it would be a SLGT risk day.

This post is spot-on. I can see why they didn't have any thunder marked around here on the prelim day 1, but the 12z guidance has clearly shifted towards more favorable parameters AND explicit convective signatures in the simulated reflectivity. It warrants a general thunder outlook in the new day 2 for sure, and it's honestly not that far off from a MRGL.

well, crap. Those got added in pretty late, so I guess that LWX had to look pretty hard to find them but in seriousness, the Culpepper reports don't totally surprise me, but the Fairfax reports do. I didn't see anyone in this forum report strong winds inside of the Beltway.....

O storm reports. Lack of sfc-based instability, ftw!

Perhaps the smallest amount of sfc-based instability for that cell to work with down by Culpeper, where sfc temps are 5-6 degrees warmer than around the DC Beltway and points north and east.

Agreed. We'll have no problems mixing behind the front.

Several of the morning CAMs show the same thing now. Seems like some showers break out ahead of the line in those runs and ruin the convergence.

This is a very good point! But that event had some actual sfc-based instability.

I still don't understand why SPC is now even considering an upgrade to SLGT, but there is no argument that if sfc-based parcels can find a way to be buoyant, the wind fields are amazing. A faster evolution of the event might allow the line to take advantage of daytime warming for the western part of the outlook, so I understand the outlook expanding west. I'm setting my goal for getting a torrential downpour and maybe hearing thunder. Seeing several consecutive HRRR cycles wanting to break up the line as it moves east is giving me some pause, though......

For sure. The reflectivity looks so impressive! But it's not surfaced-based. That said, there is some elevated cape, so while there wouldn't be any severe threat with that (assuming that the NAM nest is correct with the stable sfc layer), there would definitely be some chance of lightning. I would call that a win!

LWX is pretty bullish in their afternoon AFD, and as Yoda mentioned, the MRGL risk now comes into the DC metro area. I still, however, haven't seen guidance showing surface-based instability here. I do see good mid-level lapse rates, so there will likely be some elevated cape, and I certainly believe that some lightning is possible. Until, however, I see some sfc-based instability being progged, I can't buy in to SVR potential until you get well south of the DC Beltway.

I'm always interested in high shear low CAPE setups, but it could be a high shear NO CAPE setup. I tend to trust the NAM nest when it keeps us cool at the sfc in these events, but if the HRRR is right, it would be a SLGT risk day for sure.

So we're in to the range of the NAM nest now, and it has been emphatic for several consecutive cycles now that a strongly forced convective line will move through the area early Wednesday evening. But it's also been emphatic that the line will not be surface-based, and most of the guidance I've seen agrees with that, so the chances of taking advantage of the excellent shear profiles seems low. That said, the GFS is trying harder to find a tiny bit of sac-based instability, so I won't totally close the door, even though I'm really hesitant to consider the GFS it wants to scour out the low-level cold air.