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high risk

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Everything posted by high risk

  1. high risk
    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:
  2. high risk
    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.
  3. high risk
    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.
  4. high risk
    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.
  5. high risk
    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.
  6. high risk
    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......
  7. high risk
    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.
  8. high risk
    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.
  9. high risk
    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.
  10. high risk
    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.
  11. high risk
    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
  12. high risk
    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.
  13. high risk
    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.
  14. high risk
    And replace that 84/66 at the surface with the 87/72 at DCA. and the CAPE values shoot up.
  15. high risk
    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.
  16. high risk
    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.
  17. high risk
    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.
  18. high risk
    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.
  19. high risk
    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.
  20. high risk
    Very impressive signal. It forms a discrete cell out ahead of the main line in the early-mid afternoon when surface winds will be somewhat more backed, leading to a shear profile that would actually support some healthy rotation. But this is somewhat of an outlier solution.
  21. high risk
    Monday obviously has the higher end potential, but it looks like all of the CAMs have widespread afternoon convection on Tuesday. If you toss the NAM Nest low 70s dew points, the CAPE is modest in most solutions, and shear is weak, but there is a healthy amount of downdraft CAPE. I would think that the outlook for Tuesday will expand the MRGL back to the west over more of the area.
  22. high risk
    not totally worthy of being mentioned in the severe thread, but for those of us who have been anxiously awaiting nocturnal convection, some of the CAMs say that at least several of us will be woken up later tonight by a round of storms. Radar is trying to light up a bit to our west.
  23. high risk
    Is this really underwhelming? Maybe for western OH, but......
  24. high risk
    12Z CAMs are all over the place. Summary: NAM Nest FV3 HRRR ARW2 (for Howard County: ) ARW
  25. high risk
    Yes, the NAM is typically too moist, but the HRRR absolutely overmixes.
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