2023 Mid-Atlantic Severe Wx Thread (General Discussion)

[Eskimo Joe]

FWIW, the experimental HREF from SPC has us socked in with low level clouds tomorrow morning, but they seem to burn off by 11am. The guidance that is most aggressive with convection tomorrow seems to have two things in common:

1.) Clouds burn off by 10am - 12pm.

2.) Minimal mid and high level debris clouds from tonight's convection. 

If we wake up to a favorable visible satellite tomorrow, I do believe that we will realize a solid ENH to maybe low level MOD risk day. My thinking is entirely hinged on the ability of strong sunshine sustaining itself so storms can root to the surface and realize the low level instability. That would help us maximize the best helicity and shear. It would not surprise me to see a few tornadoes tomorrow, especially east of I-95 where storms can take advantage of the typical mesoscale boundaries near Chesapeake Bay. Flooding is not something I am terribly worried about. Storm motion seems rather progressive and it's been dry the past two weeks.

[Stormchaserchuck1]

It's only 88F today, not really high enough to validate all this high risk stuff. 

[Eskimo Joe]

18z HRRR does a DC split. Solid supercell driving right along I-70, another decent batch south of I-66. In between is pretty run-of-the-mill.

[AmericanWxFreak]

23 minutes ago, Stormchaserchuck1 said:

It's only 88F today, not really high enough to validate all this high risk stuff. 

Tomorrow is the higher risk day - but the 18z 3k NAM is beefier for that 02z-05z time frame tonight  

[09-10 analogy]

1 hour ago, Eskimo Joe said:

According to the IEMbot archives, only 6/13/2013 was the other time that a portion of Maryland was under a 45% Day 2 wind contour.

I've been wanting to find a resource that could tell me "when was the last time XXX had a ZZZ," so thanks! Now I just have to figure out how to negotiate my way through all that data. I knew the IEM page has archived AFDs and many other NWS products, but I didn't know it could drill down even deeper. 

[Eskimo Joe]

15 minutes ago, 09-10 analogy said:

I've been wanting to find a resource that could tell me "when was the last time XXX had a ZZZ," so thanks! Now I just have to figure out how to negotiate my way through all that data. I knew the IEM page has archived AFDs and many other NWS products, but I didn't know it could drill down even deeper. 

https://mesonet.agron.iastate.edu/plotting/auto/?q=92

[Kmlwx]

There are some cases when morning showers or convection (if it clears early enough) can actually juice up dew points and also lay down boundaries to enhance later activity. But it's always a game of balance. 

[yoda]

13 minutes ago, Kmlwx said:

There are some cases when morning showers or convection (if it clears early enough) can actually juice up dew points and also lay down boundaries to enhance later activity. But it's always a game of balance. 

Not saying it's the same at all, but didn't one of our June derechos have this type of potential scenario happen?

[Kmlwx]

1 minute ago, yoda said:

Not saying it's the same at all, but didn't one of our June derechos have this type of potential scenario happen?

Several higher end events I think have. BUT - like mentioned above it has to clear out soon enough and of course every other factor can't go wrong either. 

No massively high mid level lapse rates with this it seems - so failure modes are still very real 

[yoda]

6 minutes ago, Kmlwx said:

Several higher end events I think have. BUT - like mentioned above it has to clear out soon enough and of course every other factor can't go wrong either. 

No massively high mid level lapse rates with this it seems - so failure modes are still very real 

True, but I believe LWX mentioned in their AFD from this morning that we don't necessarily need a lot of sunshine to destabilize tomorrow due to the extreme shear

ETA - yup, it was this morning 

Let me preface the further detailed environmental analysis that
uncertainty remains regarding how morning cldcvr or convective
debris may impact the SVR potential in the afternoon. Latest
guidance moves clouds out by mid-late morning and quickly
destabilizes the region. Given the dynamics and kinematics at
play, a long period of heating may not be necessary for the
potential of this event to be realized

[WxWatcher007]

Can I ask a dumb question? Is it possible the 45% for DC is partially based on what you all saw last week? As in, we see a stronger wind forecast this time given what the last setup produced?

[midatlanticweather]

1 minute ago, WxWatcher007 said:

Can I ask a dumb question? Is it possible the 45% for DC is partially based on what you all saw last week? As in, we see a stronger wind forecast this time given what the last setup produced?

I believe it has to do with models and the small dry layer that models are advertising. This will bring the potential for hail as well as winds. Now, there are some Mets here that can be more technical than me for sure. 

[Stormchaserchuck1]

4 minutes ago, WxWatcher007 said:

Can I ask a dumb question? Is it possible the 45% for DC is partially based on what you all saw last week? As in, we see a stronger wind forecast this time given what the last setup produced?

That's probably true. 74* and Rain here, I don't see how this is going to get to be that strong. 

[WxWatcher007]

21 minutes ago, midatlanticweather said:

I believe it has to do with models and the small dry layer that models are advertising. This will bring the potential for hail as well as winds. Now, there are some Mets here that can be more technical than me for sure. 

Oh there’s an EML on the table tomorrow? That would explain it I think. I’ve been so busy I admittedly haven’t looked deeply. 

[canderson]

I’m up in Harrisburg but tomorrow will be a real deal from here south through this region. If I were chasing it’d set up in Hagerstown first and then if necessary move S toward Leesburg if necessary (but I doubt it would be - ability to move north into PA will be worthwhile). 

CAPE and shear are set up regardless of PM sun. 

[Eskimo Joe]

The 01z HRRR puts a lead cluster through Frederick and Carroll counties around 19z Monday, with a solid UHI track just north of Frederick City. Main line well to the west with several bowing segments across WV.

EDIT: After AM clouds, we break out into the warm sector with near full sun shine.

[Eskimo Joe]

00z NAMNEST is a legit bow right through the entire DC Metro. It also has a UHI track right through Frederick and Carroll counties similar to the 01z HRRR.

[Eskimo Joe]

00z NAM has a bowing segment similar to the 01z HRRR, but it's further north along the Mason-Dixon counties. 

[yoda]

45 percent wind and 5 percent tornado both increased in size on new Day 1

 

 

[Ellinwood]

gm

chasing this area today

[Eskimo Joe]

I'm up in Emmittsburg for class all week. I'll be watching storms through the window like I did as a kid.

[Kmlwx]

That chase area tends to do very well! 

[yoda]

23 minutes ago, Kmlwx said:

That chase area tends to do very well! 

If @Ellinwood is posting about chasing, does that mean we are at Level 4?

[yoda]

Is it clear out west along the i81 corridor right now?

[yoda]

Very detailed and well written AFD this morning about all threats even into tonight re tornado potential re-emergeing after the QLCS threat

 

NEAR TERM /THROUGH TONIGHT/...
This morning, low stratus is becoming more widespread east of the
Blue Ridge, and should cover most of that area by sunrise. To the
west, a combination of low stratus and patchy fog is expected. The
upper level clouds have mostly cleared, so once daytime heating
begins the stratus should burn off by late morning. Daytime heating
brings temperatures into the upper 80s to low 90s. Combined with dew
points in the low to mid 70s, expect peak heat indices between 100-
105 east of the Blue Ridge, and 95-99 west.

One feature that bears watching is a decaying MCS, with an apparent
MCV, that is moving into southern OH as of 3AM. This complex has a
high chance of bringing some light rain and cloud cover to our area
at some point this morning. That could disrupt some of the severe
potential for this afternoon, though the remnant MCV could also act
to enhance severe potential - IF it tracks through at the right
time. This something to closely follow this morning.

Looking ahead at this afternoon and evening, given that we
destabilize, all signs point to a likely widespread severe wind
event across our area, though all modes of severe weather are
possible. A large mid-level trough over the western OH Valley this
morning will move eastward toward the Central Appalachians, with two
surface lows noted early this morning - one over southern ON and the
other along the IN/IL border. These surface lows deepen through the
afternoon, with models indicating pressure in the low 1000mb range,
which is quite impressive for early August (for a non-tropical low).
Storms are expected to develop in a favorable environment today
where surface dew points in the low 70s and impressive mid-level
lapse rates of 6-7 C/km yield around 1500-2000 J/kg of MLCAPE
(SBCAPE up to 2500+ J/kg possible). Storms should easily become
organized with deep-layer shear of 35-50KT.

Multiple rounds of storms are likely to impact the area today. The
moist airmass, approaching PVA max, and remnant MCV could initiate
late morning to early afternoon activity west of I-81 into north-
central MD. There is some potential for a storm or two to become
severe, with damaging winds and hail as the main threats.

The main surge is expected to develop by mid afternoon as the strong
synoptic forcing arrives, and is enhanced by the existing terrain
circulation and lee-side pressure trough. Models are rather good
agreement on timing, indicating numerous storms developing west of
the Blue Ridge between 2PM-3PM. These initial semi-discrete/cluster
storms could pose a large hail threat, in addition to damaging wind
gusts and a tornado or two. These storms move east of the Blue Ridge
between 4PM-5PM, and likely congeal into a solid/quasi-solid line
that reaches the I-95 corridor between 6PM-7PM.

This QLCS will be capable of producing widespread damaging wind
gusts, in addition to the possibility of embedded QLCS tornadoes.
Tornadoes that develop within these squall lines typically have
little lead time due to their rapid genesis. It is important to take
immediate action if a Tornado Warning is issued for your area. The
hail threat should diminish as the line of storms pushes eastward.

Finally, as the main mid-level trough moves over our area it could
initiate an additional broken line of showers and thunderstorms
later this evening. A low-level jet will have developed by that
time, and model soundings respond to the increasing low-level shear
with very wide hodographs, especially east of the Blue Ridge. There
will be a conditional tornado threat that lasts past sunset, and
given the strong shear, it won`t take much instability for these
storms to intensify.

Be sure you have multiple ways of receiving severe weather alerts
today, and take immediate action if a severe thunderstorm or tornado
warning is issued for your location.

[Darkstorm]

Is it clear out west along the i81 corridor right now?

Yes at least Hagerstown it is


.

[MN Transplant]

1 hour ago, Ellinwood said:

gm

chasing this area today

That’s a good idea.  From everything I’ve read that location is now completely desiccated from the ongoing mega drought, so sight lines should be good.

[Kmlwx]

 

Worth noting that if you animate that - all of the low clouds over the metro area appear to be just low clouds - may be easy to burn those off as long as clouds to the west don't come in to complicate things. 

[Eskimo Joe]

Impressed at the lack of mid and upper level clouds. All we have to do is burn off this low level junk and we're golden.

[Kmlwx]

We've gotta figure out where we are on the scale  

Some might argue we're at 3 but maybe we are close to a 4?!