high risk

8 hours ago, vortex95 said:

Deep layer shear is good tomorrow, and there an solid 250 mb jet involved, unlike last time, so better dynamically.  HRRR really makes the CAPE stand out over the entire bay.  PWATs come up nicely during the day, so do sfc dew points.

      Yeah, this is a pretty solid setup:  good dynamics, good deep layer shear, and moderate instability.   CAMs suggest that most areas north of DC are close to a lock to get storms, while there is a bit more uncertainty for areas south of DC.

6 hours ago, vortex95 said:

I don't think the AM convection Sunday will be a detriment for later.  There is solid support for the aftn-eve w/ a 700/500 trof moving in.  PWATs increase in the aftn to as high 2.5" on the GFS/ECMWF/NAM, and there is very good directional shear w/ nicely looped hodographs and strong veering 925/850 to 700/500.  Wind fields 925-500 ramp up in the aftn to 35-40 kt at all these levels.  So supercells likely and the 2% tor risk is warranted.  Could see upgraded to 5% given the strength of the 925 winds (30 kt+ is excellent and we have it fcst as high as 40 kt).

Everything moves steadily W to E, unlike the previous events that were NW to SE and that pushed all the moisture and boundary focus S, so solid recovery for instability after the AM convection is a good bet.

FF threat, as noted, is there are well.  RRFS is quite aggressive for cntrl and nrn VA showing up to 7.5" of rain.  This model tends to overdo things, but 4" in some locations high prob IMHO.
 

Everything you said about the environment later tomorrow is spot on, but the one parameter you left out is cape, and that could certainly prevent a bigger day tomorrow.   There is certainly solid model consensus for a “round 2” of storms later Sunday, but forecast soundings don’t look great.  I certainly agree, though, that IF we can destabilize, supercells and tornadoes are on the table. Otherwise, it’s a noisy heavy rain event. 

10 hours ago, yoda said:

LWX seems to be hitting the threat a bit harder in this afternoon AFD 

There are things to like for Sunday for sure, but a morning MCS appears fairly likely, which would wreck afternoon chances, except perhaps for southern areas.    Probably more of a heavy rain event for most of us, unless the MCS is fake or delayed. 

5 hours ago, WxUSAF said:

Seems a majority of guidance wants to bring some decaying showers/storms through the metro area after sunset towards midnight.

   It's a definite signal.   There is some disagreement on decaying, as it looks like the storms actually originate during the late evening hours over northern Virginia and then move east.

1 hour ago, vortex95 said:

00z HRRR shows decent storms this afternoon, but 01-06z, it oddly has very little.  The 00 and 06z RRFS is lacking in storm coverage as well.  06z 3 and 12km NAM do show plenty of tstms.

Not sure what is going on here.  It is not too warm aloft (700 temps 7-8 C and  1000-500 thickness 576-577), flow aloft is slightly cyclonic, and w/ temps maxing in the mid 90s and dews low-mid 70s, I see no reason why tstm coverage should not be sct-bkn.

Plenty of instability CAPE 2500-3500, lapse rates better than several days ago up to 6.5 C/km at mid-levels. PWATs around 2" so big rain potential again.  Winds aloft kind of MEH.  So expect multicellular clusters.
 

I share your confusion about why the HRRR and RRFS have switched to an unenthusiastic solution for this afternoon.  

As some of you have noted, there is absolutely low level shear today, and the low LCLs also suggest that a brief tornado or two is possible.   The overall strength of the wind fields probably doesn't support a more significant threat, but I would not be surprised to see a few tornado warnings.

58 minutes ago, WxUSAF said:

Yes. Probably @high risk can update us on that timeline but I thought it was like the end of August at one point? 

Current target is early October. 

19 hours ago, vortex95 said:

00z HRRR was good for big storm coverage in the DC Metro.  06z has backed off somewhat.  00z was putting it all in one big hit 3-7pm.  06z has sct storms in the area around 5pm, then good coverage e-cntrl and sern VA, then a second decent area coming from the PA border spreading SE 8pm-midnight.

00Z RRFS crushes DC metro at 5pm.  06z was a little less impressive but still solid.  It does have the best storms in the RIC area.

The MCS that moves from OH overnight to WV and wrn VA by noon appears to weaken enough and far enough away, so by peak heating, we should be ok in the much of the DMV.

The best winds at 500 and 250 are S of the DC Metro, so I see why 5% tor risk is in sern VA. The NAM has excellent 925 and 850 winds in the DC Metro w/ nice curved hodographs, but the RRFS is less impressive and the GFS/ECWMF as well.  Again, best winds fields are S and SE closer to the NC border.
 

           It was interesting how the overnight runs looked pretty good, and then the 12Z suite (and a HRRR cycle or two after that) didn't look as good, before the HRRR locked on to the solution by late morning.     And I'll be curious to see how many tornadoes are actually found.  There were probably way more warnings than needed, but I'm wondering if they'll find more than the current count of one (good video of a tornado on the Eastern Shore north of Cambridge).    Ultimately, we probably weren't far off from a more significant tornado event, but as you suggested in your post, the low-level winds were probably just a bit too weak, although I think that the low-level profile was slightly better than what the RRFS and GFS/ECMWF were suggesting last night.

13 hours ago, Eskimo Joe said:

Latest HRRR is very GFS-esque. Total whiff for everyone.

           The guidance trends were really interesting.   Things were looking encouraging for fairly significant storms in the early runs on Tuesday, and then the cycles right after the raob data became available looked fairly lousy (as noted in your post).   Then, the HRRR started locking in again on the more significant solutions.

7 minutes ago, Eskimo Joe said:

Watch box out to our north, $20 says it's going to be multiple watches.

    You're not exactly going out on a limb with that prediction....  

5 minutes ago, SnowenOutThere said:

I like that implies we will get upstream storms, so at the very least we should get a nice rainy/thundery evening from whatever remnants can make it our way. Sort of similar to our last setup and getting the MCS from WV. 

      Sort of.  That day involved some local storms that initiated followed by the main band along the forcing arriving from the northwest during the evening hours.   This looks to be a line forming just to our northwest during the early/mid afternoon and rolling through at dinner time before making a quick exit.   There is some curvature in the hodographs, so the tornado threat is definitely non-zero, although the forcing may result in a more linear structure.

       The box will go up for northern sections first, because there is good cam agreement on an initial wave of storms for northeast MD/PA/NJ earlier this afternoon.

The evening cams don't fully sort out the details, but if we look for some modest consensus, the morning MCS threat for most of us has decreased a lot.   And the severe threat ramps up quickly after lunch.   Even if some cloud cover reduces the heating, I don't think that's a big deal unless we stay really cool.   Full heating is not critical to this event, because we have forcing and good shear.   Some solutions still screw us in terms of coverage and rainfall, but again, I'm looking for some sort of consensus, and the screw outcomes are on the table but seemingly less likely.   Oh, and there is case to be made for including a corridor bounding roughly Rocky Mount, NC to Harrisburg to Trenton and all points to the east with a tornado threat (5%).    SPC might keep our local area in a 2, but a 5 would be justifiable, as some solutions keep the sfc low just to our west or northwest with modestly increasing low level flow during the afternoon beneath strengthening west-northwest mid-level flow..

2 hours ago, SolidIcewx said:

The debris ball on that tornado was insane

It was not an obvious tornado day either, and in fairness to the forecast, that appears to be the only high-end tornado event today. (Yes, there was more widespread wind damage).  It unfortunately got its act together in a very populated area. 

4 hours ago, Kmlwx said:

I still would generally favor south of DC for tomorrow. But the NAM nest and HRRR do get activity (some seemingly severe?) into all areas tomorrow. After shrinking the 15% contour to the south of us yesterday, CSU guidance has it back north of the M/D line. So that's good. 

We'll see (as always!)

   I think so too, but this is still really complicated, and the 12Z suite hasn't locked in on anything yet.   It *does* seem like while the main MCS will be west of here in the morning hours, some piece of it will approach and probably strengthen a bit.  If it arrives around commute time, it will probably be sub-severe, but if it's mid-morning, severe is possible.   Guidance then differs sharply on how much heating will occur behind any morning activity, but how much will it matter.   Steepening lapse and strong forcing might compensate for limited surface heating.   At least scattered storms are likely by mid-afternoon, and some solutions are widespread.   All hazards would be possible; the low-level winds are probably too weak for tornadoes, but the directional shear will be there, so it wouldn't take much to increase the tornado threat.

14 hours ago, Eskimo Joe said:

I'll still take the Euro over the GFS.

           I'd usually agree with you.  But as we now move into CAM range, recognizing that the U.S. CAMs all have some influence of the GFS, the solutions seem to be favoring the GFS more.   The idea of a deep sfc low over the St Lawrence Valley isn't dead in the Euro, but even its AI version likes a secondary low in the Mid-Atlantic.   Verbatim, some pretty strong forcing rolls through during the morning and midday hours, which screams flash flooding more than severe.   That said, 1) a surface low will be nearby, so you always need to watch for a tornado threat, especially if we can heat up before the forcing arrives   2) there is time to change some of the synoptic details

Multiple CAMs break out scattered showers (thunder?) in the area Sunday afternoon lasting into the evening.

11 hours ago, vortex95 said:

Yet another solid 500 trough for July,  This time actuality cuts-off and is slow to move out, so looks like Mon-Wed tstms each day in some form, and maybe Thu if the ECMWF is right.  Tue appears the best for svr wx currently.

         The Euro is a legit severe solution for Tuesday.   The GFS screams "dying MCS moves through at 9AM and kills off the afternoon threat".

HRRR wants to bring another line through the area in a few hours.    Verbatim, it's mainly for areas south of DC, but there are certainly cells further north in eastern WV than modeled.

The radar west of Philly is what our radar was supposed to look like now 

28 minutes ago, vortex95 said:

Yes, I do not like to see a big cluster of storms S of an area of interest.  It seems more often than not, that means the area to the N is ripped out!

    I don't like seeing that east-west line to our south at all.

1 hour ago, jewell2188 said:

On our way to a bust!

  It might temper the severe threat somewhat, but getting significant storms seems to still be on track.   Each HRRR cycle this morning has been catching on to the fact that we won't get the amount of heating previously expected, and it still initiates widespread heavy convection.

Heating is obviously a concern, but assuming we bust out into some partial clearing by late morning, HRRR and RRFS both have a couple of interesting lead cells followed by a squall line feature.

1 hour ago, vortex95 said:

Or the Ivan tor day in Sep 2004?  What, like 40 tors in VA alone, and many clustered right up to the MD/VA border just W of DC!  I think that day is the only SPC MDT ever issued for a TC tor event.

There were so many tors in VA that day, that if you look at a map for the CONUS showing which month tors are most common for each state, VA says "September" -- all b/c of that Ivan tor day!  It shows how a single outlier event can skew climo big time.

      SPC issued MDTs on back to back days with Ivan.   The first day over the southeast somewhat busted, as too much cloud cover limited instability.   On the second day, we did eventually get a MDT into parts of northern VA, but the threat was not obvious until it evolved in real time.    This was the initial outlook of the day.  The area with a 5% got a SLGT.    (The probabilities ramped up starting with the 1630Z outlook.)

Sign me up for the 00Z HRRR.

11 hours ago, stormy said:

Human forecasters act as the ultimate decision-makers in formulating a forecast. 

AI and advanced computer modeling are certainly incorporated into the process but humans provide oversight to any and all forecasts.

      This isn't true at all.    All NWS gridded forecasts use the NBM which combines lots of available computer models.   For Days 4-7, WPC can make some minimal edits and get some input from WFOs, but they mostly leave the NBM alone.   For Days 0-3, the WFOs can be a bit more heavy-handed, but they are still encouraged to limit their editing.