high risk

overnight convection? the CAMs say maybe; the radar is really lighting up to our southwest

no doubt. I'm not sure how much instability we can get this afternoon, and the rising heights argue against widespread coverage, but the deep layer shear is still there for some modest wind potential if storms can develop.

interesting that some of the CAMs have some scattered convection breaking out in the DC area later this afternoon due to a weak shortwave

yeah, it gets a nice head start with a 2" event Monday late afternoon.

Yeah, the 850 wind and PWAT really show the setup for the potential predecessor event Monday evening. Moisture will be streaming north well out ahead of the center of the storm and boosting precipitable water totals. I didn't include 250 winds, but you can see in those charts that we're in the right rear quadrant of the upper jet which enhances lift. So we have upper dynamics, a front, and tropical moisture - that can lead to some super impressive QPF that the models (especially the globals) will struggle to predict.

While there will be a sharp cutoff for the batch of heavy rain close to the storm center Tuesday morning that *could* end up further east, there is still real potential for significant amounts further west Monday night. Dynamics with the upper jet orientation will have a stream of tropical moisture surging north well out ahead of Isaias' center (2"+ PWATs) which will certainly lead to some healthy localized totals.

the PWs are really impressive, and earlier HRRR runs looked wet and suggested backbuilding, but that model has really backed off now.

certainly some chance of SVR this evening and later tomorrow, but I'm really starting to like the look for late Monday. NAM nest has an impressive connective signature in an environment with some shear. My biggest concern, though, is that the model looks slow with Isaias, so we could have a much wetter environment Monday than progged (and more of a flash flood thread than a SVR threat)

Great post! The orientation of the upper jet here would definitely put in a favorable region for ascent. If we combine that with the 850 winds and PW, the winds show a clear connection to the tropical moisture feed, and that's reflected in the very impressive precipitable water values. This is, of course, contingent on the further west track, although I think that *some* tropical moisture gets here Monday regardless.

I'm not writing it off, but I'm not very excited right now. Far more interested in a potential PRE on Monday.

I have to admit that I wasn't paying close attention to tomorrow, but the HRRR and the Hi-Res Windows all some some impressive cells across northern VA later Saturday. Wind profiles have some definite directional shear, although there is probably too much weakness in the speeds in the lower levels to have a robust TOR threat. Slight risk seems completely justified to me.

actually, the deep layer shear needed for an organized severe threat is overall lacking today, which explains the lack of a slight risk. that said, I do think we'll see a few isolated severe warnings later today.

very pleasantly surprised to get a heavy shower. All of the guidance I had seen today had this activity dying out well before reaching the I-95 corridor.

still a fair amount of model support for a Delmarva landfall, including the 18z HMON and HWRF

I'm not ready to buy in to heavier rain making it back to the I-95 corridor, but I'm definitely not ruling it out. The NAM nest is certainly most aggressive, but there is some support from other CAMs for the precip bands extending further west, although even those solutions make it clear that the NAM nest is too fast. It's also worth noting that the GFS tends to not generate sufficient precip on the west side of east coast storms, although there is more evidence for that with winter storms than with tropical hybrids.

Watching the 5th good cell today miss me by a couple of miles. Still stuck at a trace.

Yeah, this is comedy watching the whiffs here today. HRRR still says I get soaked in a few hours. Debating whether to water the garden.....

Exact same situation here just down the road. I rarely get pissed off at the weather. Right now, I'm really pissed off at the weather.

looking out my window here in Howard County, it looks like the atmosphere is trying to initiate locally

really need some patience. The CAMs were not forecasting an early show here. It will take time for the PA/NJ complex outflow to surge west and southwest, with development building along it back into northeast MD. There is still a legit question of whether there will be decent coverage in the DC/Baltimore corridor, but IF it happens, it won't be for several hours (and could even be an evening show).

No doubt that the eastern shore is the best place to be for organized SVR later today. For those west of the bay, we need the outflow to surge further west. It's worth noting that both the NAM nest and HRRR don't have too many storms in the DC area, as they both mix out the dew points a bit this afternoon. (HRRR is most aggressive.) Some of the other CAMs (the ARW2 of particular note) do not mix out the low-level moisture as much, as they have more coverage of storms west of the bay.

outflow made it all the way down to southern Howard County. Really nice!

Somewhat brief but torrential here in southern Howard too.

Thanks again for posting this. Tropical Tidbits has now corrected their plotting error as of the 18z cycle today.

great catch! If you look at the Tropical Tidbits 24h precip maps, it looks pretty clearly that the site is accidentally aggregating 24h totals, so I think it's a plotting error (or an error in the grib2 files) and not a new "biblical wet bias" in the new version.