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2021 Mid-Atlantic Severe Weather - General Discussion


Kmlwx
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18z NAM nest is lameeee for tomorrow. 

The 18z long range HRRR was pretty wild for Central Maryland tomorrow night. The timing isn't the best (overnight hours into Tuesday). If we can speed things up a bit maybe?

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8 minutes ago, Eskimo Joe said:

If we can speed things up tomorrow by just an hour or two and get a bit more clearing, someone could get smacked bigly.

Well if can can speed things up anyway. Tomorrow doesn't look to be plagued by clouds looking at CAM soundings. 

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10 hours ago, Kmlwx said:

CIPS for the 36hr mark (on the 12z run coming out now) is fairly bullish. Jun 2, 1998 is on the analogs lol

          I remember that event well.    It was just a couple of days after the historic May 31, 1998 northeast tornado outbreak (first ever high risk in that area), and another strong system came in on its heels.   Moisture had been shunted south by the cold front on the night of the 31st, and there was a question of how quickly it would return here.   SPC bought into the idea, issuing a MDT risk, but LWX wasn't buying it.    As a recall, their discussions were very bearish, and we had only a 30 PoP in the local forecast.    Dew points started the day quite low but ended up rebounding very well.

           Supercells erupted locally in the early evening.    During my drive home, I could see a wall cloud over DC (cell phone cameras weren't a thing then), and I then got golf ball hail in northern PG County - the only time I've ever experienced severe hail in 25 years of living in the DC area.    The big events were with the tornadic supercells to our northwest - there were early evening tornadoes very close to Pittsburgh and Buffalo among others in PA and WV, and the cells produced several late evening tornadoes in MD including the after-dark F4 in Frostburg.

 

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37 minutes ago, Eskimo Joe said:

If we can speed things up tomorrow by just an hour or two and get a bit more clearing, someone could get smacked bigly.

I'm not sure that's a big ask either - things do tend to come through a bit quicker than forecast on our severe events. Not totally buying into tomorrow - many of the CAMs are pretty lackluster...but I'm intrigued at least. IF things can line up I could see somebody getting a legit report out of this event. 

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Right now, I'm not optimistic about SVR in the local area tomorrow, as the timing just doesn't look good.      There are a few CAMs that break out a cell or two well out ahead of things during the afternoon, and any such cell could be SVR, but coverage will likely be sparse and perhaps non-existent.      I'm on board with a sharp increase in convection here after dark, and we'll probably have a sweet lightning show.    I'm just not seeing good sfc-based instability to take advantage of the stronger shear.      Maybe it will find a way to get it done, but I'm so far not seeing any guidance keep surface temperatures from falling fairly quickly after sunset.

Edit:   two possible pieces of hope:    1)  NAM nest has some convection in the early morning hours which could potentially leave an outflow boundary sitting around and lead to earlier initiation    2)  HiResW FV3 has an earlier arrival of storms tomorrow evening, but it is somewhat of an outlier

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NAM nest has the line arriving in the midnight timeframe tomorrow night. That's pretty poor timing. BUT - as I said above, we do tend to get things a bit earlier/faster than expected. Nonetheless, midnight is a pretty late window. Even an hour or two earlier might not be enough to get things done. 

If the timing on this was like 4-6 hours earlier, with the shear progged things would be really interesting. We'll see what the early morning runs show - and 12z will be useful as well...heck - with that timing even the 18z suite tomorrow will be useful :lol: 

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10 minutes ago, Kmlwx said:

NAM nest has the line arriving in the midnight timeframe tomorrow night. That's pretty poor timing. BUT - as I said above, we do tend to get things a bit earlier/faster than expected. Nonetheless, midnight is a pretty late window. Even an hour or two earlier might not be enough to get things done. 

If the timing on this was like 4-6 hours earlier, with the shear progged things would be really interesting. We'll see what the early morning runs show - and 12z will be useful as well...heck - with that timing even the 18z suite tomorrow will be useful :lol: 

      Hard to ignore that big UH track that the 00z HRRR showed, as you noted.    I do think that the NAM nest is (as always) too slow;   I'm still skeptical about whether even late-evening cells tomorrow can remain sfc-based, but I'll readily acknowledge that we have a shot.

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SLGT risk for today on new Day 1... 0/5/15... disco sounds intriguing 

...Mid-Atlantic/Upper Ohio Valley/Carolinas...
   An upper-level trough will move southeastward across the Great Lakes
   region today as a cold front advances southeastward into the central
   Appalachian Mountains. Ahead of the front, a surface low will move
   eastward into the Mid Atlantic as a corridor of maximized low-level
   moisture takes shape across the Atlantic Coastal Plain. Surface
   dewpoints are forecast to be in the mid to upper 60s F, which will
   result in the development of moderate instability during the
   afternoon. Model forecasts suggest that convection will first
   initiate to the northeast of the low during the morning near Lake
   Erie and Lake Ontario. Convective coverage should gradually expand
   along and ahead of the front from western Pennsylvania into central
   New York. This convection is forecast to develop into a cluster of
   thunderstorms, moving southeastward across southeast New York and
   north-central Pennsylvania during the late afternoon and early
   evening. The development of a quasi-linear convective system will be
   possible as this convection moves southeast into parts of the
   Mid-Atlantic, as is suggested by many of the new CAM solutions.

   RAP forecast soundings at 03Z along the path of the projected QLCS
   near Philadelphia have moderate instability, steep low to mid-level
   lapse rates and relatively strong deep-layer shear. MLCAPE is
   forecast to peak near 2000 J/Kg with 0-6 km shear around 50 kt. This
   will likely be favorable for severe storms along the leading edge of
   the QLCS. Supercells and organized multicell line segments will be
   possible from late afternoon to the mid evening as the QLCS moves
   across the Mid-Atlantic. Damaging wind gusts and hail be the primary
   threats.

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Double hmmm... evening AFD update from LWX 

A potent upper-level trough and associated surface cold front
will swing through the region Monday night into Tuesday. Although
uncertainty persists, there is some growing concern for a
severe weather threat focused during the evening hours Monday.
Most guidance projects instability /increasing/ during the
evening (1500-2000+ J/kg MLCAPE per latest HREF/SREF progs) on
the nose of a low-level theta-e ridge/moisture axis. Most
guidance also develops a meso/weak surface low overhead along
the approaching cold front as a strengthening mid/upper-level
jet buckles in response to an approaching shortwave. The
combination of ascent and instability along with deep layer
shear increasing to near 50 kt poses the threat for an organized
line of thunderstorms. Should such a line develop and become
organized just after peak heating over southwestern PA, the
environment would support a potentially widespread damaging wind
event as it progresses rapidly eastward across Maryland and
northern Virginia through the I-95 corridor and eventually
across the Chesapeake Bay. The timing after dark and modest low-
level flow, as well as the orientation of any line or cluster
that forms and leftover cloud debris tempering low-level
stability are factors which introduce uncertainty into the
forecast, but this scenario bears a close watch over the next 24
hours. In any case, it appears that the best potential for any
severe activity may focus mainly north of I-66/US-50.

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Well... morning AFD was short and sweet about today's threat lol... also mentioned Saturday as the next day to watch for severe 

A potent upper-level trough and associated surface cold front will
swing through the region tonight into Tuesday. A concern for severe
thunderstorms is present across much of central and northeast
Maryland, the metro areas of Baltimore and Washington D.C., eastern
West Virginia Panhandle and northeast Virginia. SPC has these areas
in a Slight Risk for severe thunderstorms through tonight. 1500-
2000+ J/kg of MLCAPE on the nose of a low-level theta-e
ridge/moisture axis are reasonably good values to support severe
thunderstorms.

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1 hour ago, yoda said:

06z NAMNEST runs a UD Helicity swath right through/just north of DC 04z to 06z time period.  Sim radar backs that up with a very intense line blowing through DC metro up the i95 corridor at same time

Nice summary here from MH AFD :

The best chance for severe weather will come this evening into
the overnight period, as upstream convection developing in the
vicinity of the surface cold front congeals and progresses
towards our area. The latest CAMS largely depict one or more
linear convective features moving towards the area overnight and
this evolution seems reasonable given the strong mid-lvl flow
and associated shear (500mb winds, and 0-6km shear will be in
the 90-95th percentile for mid June) which should help support
convective organization and maintenance. Although we may see a
shallow nocturnal surface inversion form, reasonably steep lapse
rates above this shallow layer should support wind gusts
reaching the surface in any well- organized convection. SPC
highlights this potential for damaging winds by placing the
majority of our area in a slight risk for severe weather today
(mostly for the evening-overnight period). Given the fast
propagation of the system, convective mode, and strong flow
aloft. damaging winds look to be the primary threat although
small hail will also be possible. The tornado threat will be
limited by the weak low-lvl wind fields (the wind field is very
"mid-lvl heavy" in this event). Heavy rain is certainly a
concern with any stronger convection with some signal for 1-2+
inch an hour rates, however suspect that the quick system motion
will make the hydro threat secondary to the wind threat.

The main forecast uncertainties are both the timing of the
latter round of convection, and also its spatial coverage. For
example, the latest CAMS have a spread of nearly 4 hours in
timing the QLCS passage which is not particularly surprising
given that the quick system motion, combined with the potential
for convectively-driven propagation effects related to cold
pools are a recipe for timing discrepancies. Additionally the
timing situation is further complicated by the fact that several
CAMS depict separate northern and southern linear segments
developing, while other CAMS show only a more consolidated
southern segment impacting our area. Generally suspect that the
most likely period for a potential QLCS would be 02- 08Z with
the best chance of severe winds being roughly TTN southward,
however if the northern segment is able to get going the risk
could both extend further northward and also begin earlier.

 

 

 

 

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Just now, Kmlwx said:

You got one foot in on this one? Or are you going for wedges in MoCo?

Yea I got a foot in this one I guess. It's kinda a NW flow event with decent shear. It's been wet recently so we might see more trees down than usual. I honestly could see a sneaky ENH upgrade at midday if things look a bit more certain.

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19 minutes ago, Eskimo Joe said:

Yea I got a foot in this one I guess. It's kinda a NW flow event with decent shear. It's been wet recently so we might see more trees down than usual. I honestly could see a sneaky ENH upgrade at midday if things look a bit more certain.

The wet ground is a good point. I'm really not sure what to think about this one - it seems the short range guidance is pretty consistent with having a little tongue of instability (despite the late night timing) match up with the shear. But timing is one of the primary things that likes to kill our chances around here (that and being socked in with clouds). 

I did notice SPC introduced the 2% tor probs with the last outlook update. Not much mention to go with it in the discussion, though. 

Probably as good of a look as we'll see during the doldrum periods of summer. Funny that you mentioned we'd already gotten beyond our severe season and this event kind of sneaks up. 

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*Puts weenie hat on* 

All the rain that fell to the west of the mountains yesterday will help keep dewpoints elevated in those areas when mixing occurs with the strong June sun today. 

*Takes weenie hat off* 

 

But seriously though how much of a factor is that? I'd thing that today's models take this into account?

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12z HRRR sends the complex towards us and then pops new cells almost right over the area. But they don't crank until they are a bit east. I like the general idea of the panels, though. Keeps me interested (for now). 

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The new 12z run of the NAM nest is perhaps an hour or so faster. If we add in that storms tend to clear the area faster than expected in most cases - that could bode well. Still bad timing - but a touch better. 

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51 minutes ago, Kmlwx said:

The new 12z run of the NAM nest is perhaps an hour or so faster. If we add in that storms tend to clear the area faster than expected in most cases - that could bode well. Still bad timing - but a touch better. 

        Yeah, things look better.    I'm going to backtrack a bit from my earlier pessimism.     There is a pretty clear trend in the guidance for some sfc-based instability to be present when the storms arrive/develop this evening.      It shows up well in the individual 00z HREF member CAPE plots.    The older runs (labeled -12h) have limited instability over our area, but some of the newer runs (especially NAM nest and ARW) trended higher with sfc-based instability last night.   From what I've seen so far, the trend will continue with today's 12z cycle.

 

Screen_Shot_2021-06-14_at_10_50.13_AM.png

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4 minutes ago, Eskimo Joe said:

Latest mesoanalysis shows ~900j/kg of DCAPE. Fairly confident we get under a watch at some point today.

Noticed this as well. Looks decent. 

1 minute ago, high risk said:

        Yeah, things look better.    I'm going to backtrack a bit from my earlier pessimism.     There is a pretty clear trend in the guidance for some sfc-based instability to be present when the storms arrive/develop this evening.      It shows up well in the individual 00z HREF member CAPE plots.    The older runs (labeled -12h) have limited instability over our area, but some of the newer runs (especially NAM nest and ARW) trended higher with sfc-based instability last night.   From what I've seen so far, the trend will continue with today's 12z cycle.imageproxy.php?img=&key=4c6452e0fc83486cimageproxy.php?img=&key=4c6452e0fc83486cimageproxy.php?img=&key=4c6452e0fc83486cimageproxy.php?img=&key=4c6452e0fc83486cimageproxy.php?img=&key=4c6452e0fc83486c

 

 

If we can nudge the timing even another hour or so earlier, I'll feel even better. Could be a fun night for lightning pictures. 

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