high risk

8 minutes ago, yoda said:

00z NAM Nest has a large UD Helicity Swath just north of DC metro around 19z-21z (basically IAD to BWI)

     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.

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.

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.

4 hours ago, Eskimo Joe said:

Big red flag for tomorrow.is how underwhelming the event has been today in the Midwest. Was expected to be a squall line, instead it's mostly clusters.

   Is this really underwhelming?     Maybe for western OH, but......

12Z CAMs are all over the place.     Summary:

NAM Nest  

FV3   

HRRR    

ARW2         (for Howard County:   ) 

ARW    

30 minutes ago, Kmlwx said:

If my memory isn't failing me yet (it probably is) I do think that the HRRR had a tendency in past severe seasons to pull dew points way too far down. But I'm sure the NAM could be too moist. 

   Yes, the NAM is typically too moist, but the HRRR absolutely overmixes.

1 hour ago, Kmlwx said:

Liking the looks of many of the CAMs - but they are all still at range. Will be interesting to see how the modeling trends tomorrow. 

      Definitely an overall very interesting 00Z suite.     While there are still some valid questions about debris from Sunday convection and how the Monday storms evolve. I would think that much of the area wakes up tomorrow in a Day 2 SLGT.    

edit:   I totally missed SPC updating the Day 3 to put us in a SLGT, so this post was pretty useless.   I guess it's possible that parts of the area could get a Day 2 ENH, but the question marks listed might preclude that for now.

3 hours ago, George BM said:

I'm actually mildly surprised that they put us in a MRGL for Day 3 as I personally don't see any glaringly obvious signs of models decisively backing off on Mondays potential yet (still better than usual MLLRs leading to sufficient CAPE w/ at least modest deep-layer shear). We'll see what transpires with CAMs and future SPC outlooks.

    I was surprised too.     The 12z NAM Nest and HiResW FV3 definitely make the case for at least a SLGT.    The CAPE is big-time Monday afternoon, timing of the forcing is ideal, and shear is decent, with even some modest low-level shear.    Verbatim, the NAM Nest is a "south of I-70 show", while the FV3 lets northern areas get in on the show too.

14 minutes ago, WxUSAF said:

Dover radar looks good. What’s the ground truth @Herb@MAWS @Scraff?

    The Dover radar has been very misleading for us, but the nice looking band over eastern Howard County now is producing moderate rain.

1 hour ago, yoda said:

30-40kts of deep layer shear should be enough, though it would be nicer to see 40-50kts IMO

         That's what I'm getting at.     The shear appears so far that it will be sufficient for severe, but with some pretty impressive analogs being tossed around, I would expect to see some much higher values.

HRRR has been pretty consistent (with some support from other CAMs too) about some heavy showers mainly on the east side of the Potomac later tonight.

I had doubts about the timing of the system, but there seems to be some increasing agreement on better timing.    The wind fields overall still don't look great, but it's impossible to ignore several impressive ingredients that may be in place.

Wednesday is the synoptic rain, but it looks to go more convective on Thursday and beyond.   With PW values progged to exceed 2" for multiple days, it certainly seems like at least isolated instances of high QPF totals and flash flooding will occur, even if the areal-averaged QPF amounts don't suggest the threat.

54 minutes ago, 87storms said:

Hopefully, we can get some sun to fuel the next round tomorrow, but it looks like Thursday has more in the way of t-storm potential.

      Tomorrow is a low overcast, seasonably chilly day with steady rain arriving - there isn't even a hint of instabilty.  Agree that convective chances increase Thursday and ramp up further Friday.

9 hours ago, WxUSAF said:

Guidance now has a piece of the energy stay north and bring rain in Thursday. Been low consistency obviously.

       Tonight's GFS and CMC have it here now on Wednesday.    Really hope this is legit.

The HRRR has been quite emphatic that this morning line would crap out as it arrived (with redevelopment to our east-northeast);  it still really likes the idea of a more significant round 2 later this afternoon (although it verbatim screws the crew along I-70).

The question now is whether there is a modest line at the end of the "event" during the latter part of the rush hour.     HRRR still says yes, but it's hard to have confidence in the idea.

6 hours ago, nw baltimore wx said:

18z looks a little better but I don’t like relying on getting under a thunderstorm to get the goods. We need a day long soaker.

    That's not happening tomorrow, but I am hopeful of potentially 2 rounds of convection:   one perhaps mid-morning or midday and another late.   The 00Z WRF-ARW2 perhaps shows this idea the best.       Unfortunately, there is enough "bad look" in some of the other CAMs to make me think that not everyone is going to cash in.

21 hours ago, Kmlwx said:

I always say it - but often times things seem to speed up as we get closer. Not always - and may be solely anecdotal...but if lines of storms are expected 4-8pm - can usually bet on something coming through between 2 and 5

    I totally hear you on this, but I think there are 2 different types of "speeding up" with convection here.     There is the synoptic speed up, where the timing of the front and associated forcing end up arriving earlier, and things erupt on the other side of the Bay.     Then there is the speed up of just the actual propagating convection itself - the front is handled well and all, but the line perhaps initiates slightly earlier than progged and then moves east faster.

The 100 PoP in my NWS point-n-click forecast for tomorrow is..... brave.

Day 3 MRGL is east of here, but the 12Z NAM Nest an HiResW FV3 have slower timing of the front, so convection is better timed for much more of the area.    Lapse rates are iffy, but shear is workable.     If this trend continues, Day 2 products issued tomorrow would move the MRGL back into our area.         

Let's get the timing first.    Then we can work on upgrading the environment to make it to SLGT.    

9 hours ago, high risk said:

  Curious as to why you would say that.    HRRR has been pretty consistently showing some pretty substantial low-level smoke concentrations persisting through tomorrow.     00Z cycle this evening 21h forecast valid later Friday afternoon:

 

 

        So far, yesterday's HRRR smoke output does not not appear to have a good handle on today.    

37 minutes ago, Eskimo Joe said:

Unless we can get some backend smoke, this event looks to be over. Hope everyone enjoyed theirJebwalk in the haze.

  Curious as to why you would say that.    HRRR has been pretty consistently showing some pretty substantial low-level smoke concentrations persisting through tomorrow.     00Z cycle this evening 21h forecast valid later Friday afternoon:

Consistent with reports in this thread, low-level smoke concentrations are dropping in areas north and northwest of DC.   Still lousy air but some modest improvement:

 The HRRR smoke products have been consistently showing this scenario.    Here is the latest run's forecast for low-level smoke later this afternoon.

  Tomorrow, unfortunately, looks worse again:

20 minutes ago, Hank Scorpio said:

Wonder if the winds just shifted or something, because we just had a huge drop in the amount of smokiness in Leesburg

   The HRRR smoke very clearly shows the low-level smoke concentrations dropping this afternoon, especially for areas northwest of DC.