high risk

13 minutes ago, dailylurker said:

Where is everyone? Hangovers? Tomorrow looks interesting. I'm going to head out towards Hagerstown tomorrow for work. I'm thinking about doing some storm chasing on my way back east alone 70. That area looks twisty. 

     The previous dozen posts discussing the higher end potential for tomorrow aren't enough for you?     

     I'm still thinking SLGT for tomorrow for areas west and southwest of DC with the MRGL expanded into the DC-Baltimore corridor.    Maybe we end up SLGT, but instability looks very limited.   There might be more of a flash flood threat, although the dry week we just had might preclude that.

     I'm fully expecting a Day 2 ENH for Monday.    I think that there is enough in the CAMs to pull the trigger.

2 hours ago, yoda said:

I've never seen such high numbers of STP that the 18z NAM NEST shows across our area 

Granted it's just one model run and it'll probably be different at 00z, but 6 to 8?  Wow

Good amount of PDS TOR tags too on the soundings across the region 

@high risk @Eskimo Joe @Kmlwx

       It's partially driven by huge CAPE numbers which are being caused by the usual NAM bias of having dew points that are too high.    That said, the shear will be good, and it will still be a very volatile environment on Monday.

1 hour ago, Eskimo Joe said:

I'll put all my chips in on Sunday.

     Sunday is challenged by very limited instability.    But if we can get more unstable than currently progged, any storm that interacts with the boundary to the southwest could spin for a bit.     I like the chances of evening convection moving southwest to northeast, but we have work to do to have it be severe.

Looking at the morning CAMs, looks good for widespread Sunday evening convection.    Low-level shear is interesting near the warm front, so the potential is there for a few spin-ups, but lack of instability and lack of discrete cells should temper the threat (maybe higher south and west of DC).  

Monday has good potential to be an ENH day.

1 hour ago, Kmlwx said:

"couple of tornadoes" or "isolated tornadoes" are such blanket terms. 

It's those super rare times when you see "significant tornadoes" or "isolated strong tornado" that your ears perk up. 

       Yes, but they usually don't throw those terms around beyond day 2.    Their usage of that wording reflects that the progged shear and especially the low-level shear Monday have been progged to be seasonably strong.      I personally don't like them discussing tornado threats at this range, but I do understand what they're seeing.

I haven't been a big fan of today's potential, because while there is some decent flow in the upper levels, the shear through the majority of the cloud layer sucks.   That said, as others have pointed out, there is modest CAPE and decent downdraft CAPE, so there is *some* potential.     IF the HRRR idea of an organized line with a coldpool is correct, the threat might be a bit higher than thought:

Finally seem to be getting consensus now on a single line impacting much of the area, or at least from Alexandria or so northward.     Looks like an early show, with the line initiating near the I-81 corridor by late morning and rolling into the DC metro area sometime between 1 and 3pm.    The lack of lead convection increases the severe threat, and there is probably enough deep layer shear to justify the SLGT risk, although the lack of shear in the sfc-4 km depth might temper the threat a bit.

With only one round of convection, and it progged to be progressive, the flash flood threat is a bit lower than initially thought.    That said, 2" PW values will create torrential downpours, and the areas that are soggy from the past few days will likely have problems.

I completely understand the lack of trust in the guidance, given the past few days, but the HRRR wants to light up the DC-Baltimore corridor between 5PM and 10PM in the last two cycles.

17 minutes ago, Kmlwx said:

That's the only activity that looks remotely interesting for the moment. Will see how this stuff looks as it heads into Loudoun - but pretty unimpressive thus far. That cell you mentioned might end up being what the 6z NAM showed with the UH track - but perhaps a little further south than forecast. 

   As you and I both noted earlier, the morning CAMs had the current cells coming off of the mountains and evolving into the show.    But the new HRRR doesn't do much with them and instead initiates the show later.    Certainly seems plausible with the current cells struggling.

1 hour ago, George BM said:

Watching what that batch of convection in eastern WV will do over the next few hours.

    Would expect an MD within the next hour as that convection approaches the better environment.    The CAMs all turn that into either the show or part one of the show.

49 minutes ago, Kmlwx said:

FV3 (0z run) looks abysmal for storm chances for many this afternoon. ARW and ARW2 look a bit better but not spectacular. HRDPS looks splotchy but passable for now. Yet another day of model solutions all over the map. 

  12Z FV3 looks better, at least for the north side of DC.     All of the CAMs look good for *some* coverage of storms, although there will be winners and losers for sure.    And the area of highest potential is still all over the map.    It's worth noting that several other CAMs have joined the NAM Nest with a weak surface low forming, which creates a mesoscale corridor of good wind profiles, and there are now modest to impressive single UH tracks in several solutions.

  Of course, need to get these damn clouds and morning showers out of here......

1 hour ago, yoda said:

Lol at the impressive UD Helicity swath just north of the DC metro this afternoon on the 06z NAM NEST 

      That is super impressive!    It seems to be associated with a very weak surface low pressure center that backs and strengthens the low-level winds.    Outlier for now, but it's worth noting that the forecast soundings across the board do support at least brief supercell structures this afternoon.     NAM Nest scenario aside, the low-level winds are too weak for tornadoes, but I'd certainly take a few supercells rolling through.

2 hours ago, Kmlwx said:

Can't believe I forgot about that one - would tend to agree. 

    I hated that event.      Was likely to be a pretty big day, but a dying derecho rolled through during the early morning.    It still had enough punch for some wind events in northern MD, but its main contribution to the day was to severely reduce the instability.       A small complex with an embedded supercell actually tracked across Montgomery County during the mid and late afternoon with a fairly long-track (but overall weak) tornado, while another derecho tracked through the southern half of VA, far southern MD, and NC.    Without the lead dying derecho, it would have been a pretty massive afternoon in the DC/Baltimore area too.

5 hours ago, high risk said:

Sign me up for today's 12Z HRRR.       Round 1 with severe chances later this afternoon, round 2 of noisy storms late tonight, and round 3 with severe chances later tomorrow.

Most of the CAMs are bullish for later today.    While mid-level lapse rates aren't awesome, they're sufficient, and the deep-layer shear is seasonably strong.   Could be a decent coverage of wind reports.    HRRR is an outlier for the late night MCS, so I'll assume for now that it's unlikely.     Shear isn't as strong Monday afternoon, so SVR would be more scattered, but the shear looks to still be sufficient for storm organization.

    Not sure at all where we stand here at 20Z, but it's certainly not playing out as progged this morning.    The CAMs looked great for the late afternoon period, but it's not cranking so far.     The recent HRRR runs look awful, but I'm not totally sure to trust them fully, given their poor handle on the low-level moisture evolution.

Sign me up for today's 12Z HRRR.       Round 1 with severe chances later this afternoon, round 2 of noisy storms late tonight, and round 3 with severe chances later tomorrow.

Most of the CAMs are bullish for later today.    While mid-level lapse rates aren't awesome, they're sufficient, and the deep-layer shear is seasonably strong.   Could be a decent coverage of wind reports.    HRRR is an outlier for the late night MCS, so I'll assume for now that it's unlikely.     Shear isn't as strong Monday afternoon, so SVR would be more scattered, but the shear looks to still be sufficient for storm organization.

3 hours ago, BlizzardNole said:

LWX discussion of thunderstorms in a nutshell:  today east of I-95; Saturday west of blue ridge.  The Drought of '23 rolls on

They’ve updated that to match the recent HRRR runs which initiate storms west of here by early afternoon and move a modest complex through the western burbs later today 

1 hour ago, Kmlwx said:

HRRR looks semi decent for at least storms today - severity to be determined. 

      Yeah, chances of more widespread storms today seem much higher.    But the overall environment is far less favorable for severe:   less CAPE, weaker lapse rates, and weaker shear.     The one "sneaky factor" we have is a fair amount of downdraft CAPE, so perhaps if the storms organize and form a cold pool, we could get some decent gusts.

10 minutes ago, Eskimo Joe said:

I really do hate it when I'm right. The mid level cloud deck screwed us today. If we had stayed clear, I would've been eating crow.

    Honest question:   instability is only very slightly better south of here.   We're talking like 3000 surface-based CAPE vs. 2500 or so.    That discrepancy shouldn't really make a difference.     Both mid and low level lapse rates look very similar on the mesoanalysis as well.

10 minutes ago, Terpeast said:

7.6 C/km is no slouch. Especially now that the cloud deck has already cleared

     And replace that 84/66 at the surface with the 87/72 at DCA. and the CAPE values shoot up.

devil's advocate time:  while we're lamenting the clouds, it has still gotten quite warm (still mid to upper 80s).   In theory, the reduction in heating might limit the boundary layer mixing, and I wonder if losing a couple of degrees with low-level temps might be a good tradeoff to potentially avoid a collapse of the low-level dew points.     Pure speculation, but maybe the clouds aren't completely our enemy here.

1 hour ago, Kmlwx said:

HRRR is still pretty meh

   The way that the HRRR mixes out the low-level moisture this afternoon makes it impossible for that model to generate any substantial convection.    What alarms me now is that most of the other CAMs made a big jump this morning to mix a lot more strongly.   They're overall not to HRRR levels, but it's significant, and their simulated reflectivities look really discouraging.

    The 12Z IAD raob has a LOT of dry air just above the boundary layer, way more than progged in recent days.  So the idea of mixing leading to low-level drying may very well be legitimate.    Let's watch the evolution of surface dew points over the next few hours and wait for the 18Z raob. 

18 minutes ago, RickinBaltimore said:

It's summer. We get storms, sometimes heavy. People forget that. Hell I can do the weather in summer here: "Hazy, hot and humid with a chance of afternoon or evening thunderstorms, some may be severe."

Sorry to be so snarky but I agree with you, the hyperbole is over the top. 

            But this isn't a standard summer day where thunderstorms will form, and couple of them might put out a couple of localized downbursts as they collapse.     We have an unseasonably strong upper trough arriving from the west and potentially better mid-level lapse rates than we commonly see here.      There are still fail scenarios, but there is absolutely higher-end potential today, even if we don't attain it.   

            That said, the communication from the media has been all about the high-end scenario and not the fail scenario, and it's going to be unfortunate if a lower-end scenario verifies.  I have no idea how they can appropriately cover the two scenarios without confusing a lot of people, especially when they only have time for a quick soundbite.

1 hour ago, Kmlwx said:

  The good news is that it already looks better for northern areas just an hour later.    Still plenty of fail modes today, but it's hard to take any HRRR solutions seriously, as I can't imagine how our dew points crash into the upper 50s / lower 60s on southerly winds.

3 minutes ago, yoda said:

02z HRRR has some explosive development in the i81 corridor at teh end of its run that looks like it matches the 00z NAM Nest a bit

    If you look at the forecasts valid at 20Z, they align with the line forming out to the west, but the HRRR doesn't have the lead storms that the NAM Nest has.   Probably not surprising, given the mixing out of the HRRR moisture.