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2023 Mid-Atlantic Severe Wx Thread (General Discussion)


Kmlwx
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1 minute ago, yoda said:

Guess we'll be on MCS watch late Friday?

The H5 indicates it would go south and west of us. There will seemingly be chance for storms (maybe severe) in the next week or so (not each day but mixed in). 

GFS seems to have a decent cluster come through Sunday PM. 

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Just now, Kmlwx said:

The H5 indicates it would go south and west of us. There will seemingly be chance for storms (maybe severe) in the next week or so (not each day but mixed in). 

GFS seems to have a decent cluster come through Sunday PM. 

Most likely... I just saw the MRGL risk on day 3 into our region.

Would like a decent MCS to come rolling through the region... we haven't had one of those in awhile

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Interesting mention for severe potential in the morning AFD from LWX. 

Quote

As this trough tracks to our northwest, south to southwesterly return flow will develop in response, drawing very warm and humid air into the region. Highs on both Sunday and Monday are expected to reach into the upper 80s and low 90s, with dewpoints climbing into the lower to middle 70s. Winds in the mid-upper levels of the atmosphere will also be on the increase as the trough approaches the area. Our positioning downstream of the approaching trough will also place us in a a favorable location for weak synoptic scale forcing for ascent. As a result, thunderstorms are expected to form across the area on both Sunday and Monday afternoon. With winds on the increase aloft, and increasing low- level moisture being drawn northward into the region, it appears as though this system may create a favorable overlap of moderate to high instability and appreciable wind shear, making strong to severe thunderstorms possible. Most model guidance shows around 30-40 knots of 0-6 km shear both days, which would be enough to get organized storms on its own. What`s particularly eye-catching though is that most of the shear occurs in the 0-3 km layer, with models showing 30- 40 knots of flow at 700 hPa, which is highly atypical for early July (above the 90th percentile, and nearing daily maxes for the IAD sounding site according to the SPC sounding climatology site). Severe thunderstorm potential will be dependent on a number of factors, including convection from preceding days, as well as how the large scale pattern evolves. Given that it`s 4-5 days out, a lot can change, but we`ll continue to monitor the potential for strong storms Sunday and Monday over the upcoming days.

 

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5 hours ago, yoda said:

Can someone explain to me or point me in the direction of where I can read up and learn about what @Kmlwx bolded above in this morning's AFD from LWX?  I understand the 0-6km as deep layer shear... so would 0-3km be low level shear?

Are they describing helicity without using the word? 0-3km does seem to be described as low level shear in my reading about helicity.

edit: please correct me if I’m wrong though! I want to learn too 

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14 minutes ago, yoda said:

Pretty impressive at range and especially overnight too

Hr 81 just south of DC is lol 

GFS has much less instability for the same time period. We'll see how the modeling coverages Saturday into Sunday. If nothing else it's more chances at thunder and lightning to at least spice up the boring weather!

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12 hours ago, Kmlwx said:

18z 12km NAM has some decent parameters flowing in on Sunday evening. But...it's also the NAM at range. 

 

11 hours ago, yoda said:

Pretty impressive at range and especially overnight too

Hr 81 just south of DC is lol 

I see we have a Day 3 SLGT for the region.

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3 minutes ago, yoda said:

12z NAM still has some pretty impressive soundings for Sunday into Monday... and has an MCS rolling through Saturday evening 

That MCS on the 12km NAM for Saturday favors Virginia heavily. Also, the timing for the Sunday PM stuff seems to be overnight on that run - not ideal for daytime heating but we'll see how it trends. 

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6 minutes ago, Kmlwx said:

That MCS on the 12km NAM for Saturday favors Virginia heavily. Also, the timing for the Sunday PM stuff seems to be overnight on that run - not ideal for daytime heating but we'll see how it trends. 

True, but still has really nice shear and CAPE values

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14 minutes ago, yoda said:

True, but still has really nice shear and CAPE values

And of course there's always exceptions to the nighttime rule. We've had plenty of prolific lightning producers overnight that aren't severe - but could qualify if lightning was a determining factor. I guess it will depend on whether the instability becomes elevated in the overnight period. At least we have some days to track. 

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Afternoon AFD from LWX seems to suggest we have 3 days of chances, Sat-Mon

is complicates the forecast and lowers uncertainty
wrt how much recovery there could be before the aforementioned
wave moves through. Overall chances for showers and
thunderstorms appear to be higher west of the Blue Ridge. The
environment looks seasonably moist with MLCAPE values near ~1500
J/kg and 20-25 kts of shear. Cannot rule out some strong to
severe storms. There is varying flow with height, so storms may
not initially move a lot resulting in a low end flood/flash
flood threat. Will also have to monitor upstream convective
activity for potential local impacts as some guidance has an MCS
in the Ohio Valley Saturday night or early Sunday morning. This
in turn complicates Sunday`s forecast.

Come Sunday, a potent trough will move through the Ohio Valley
with flow increasing ahead of this feature along with ample
moisture return. There is a notable overlap in CAPE and shear
Sunday, which could result in severe thunderstorms areawide.
Clear skies Sunday morning will result in a volatile
environment. Also possible convective debris Sunday morning
limits the convective potential locally.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Sunday night, all attention will turn to a very potent shortwave
trough over the Great Lakes. A strong MCS associated with this
system will make its way eastward across the Ohio Valley into Sunday
evening, before approaching the Allegheny Front Sunday night. The
biggest uncertainty lies with what it does after that. Decaying
MCS`s are one of the most difficult weather phenomena to predict,
and this is no exception. Guidance is still all over the place with
available instability east of the mountains overnight Sunday into
Monday. The most likely scenario is that the MCS decays as it
crosses the mountains, and areas see some residual showers and
clouds into Monday morning. However, should the higher end of
guidance hold true, we could see re-formation east of the Shenandoah
Valley somewhere. All in all, this is a very complex forecast, and
the Storm Prediction has our area highlighted with a Slight Risk as
a result, so it is something that is being closely monitored.

Beyond that, the primary upper trough should move through on Monday,
bringing another chance for afternoon showers and storms. The level
of severity is going to depend greatly on the events that occur
Sunday evening, and what amount of cloud debris is left over our
area. Best chance would be during the late afternoon/evening hours.
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