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2023 Mid-Atlantic Severe Wx Thread (General Discussion)


Kmlwx
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LWX CWA has two counties in the New STWatch issued by SPC just now

SEVERE THUNDERSTORM WATCH OUTLINE UPDATE FOR WS 528
NWS STORM PREDICTION CENTER NORMAN OK
615 PM EDT THU JUL 20 2023

SEVERE THUNDERSTORM WATCH 528 IS IN EFFECT UNTIL 300 AM EDT
FOR THE FOLLOWING LOCATIONS

MDC001-023-210700-
/O.NEW.KWNS.SV.A.0528.230720T2215Z-230721T0700Z/

MD
.    MARYLAND COUNTIES INCLUDED ARE

ALLEGANY             GARRETT
$$
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Not anything near as intense as June 2012 - but this is the kind of event where MAYBE some of us get surprised. Models can really struggle sometimes with eastern extent of a threat in a setup like this. It will be fighting the complete opposite of peak heating by the time it gets here - but I'll be watching. 

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27 minutes ago, Kmlwx said:

Not anything near as intense as June 2012 - but this is the kind of event where MAYBE some of us get surprised. Models can really struggle sometimes with eastern extent of a threat in a setup like this. It will be fighting the complete opposite of peak heating by the time it gets here - but I'll be watching. 

Agreed. This event is climatologically abnormal, and we don't have the rocket fuel to really goose the storms up. Still, we have some decent mid level instability, a belt of shear, and some really solid DCAPE.

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1 minute ago, Eskimo Joe said:

Agreed. This event is climatologically abnormal, and we don't have the rocket fuel to really goose the storms up. Still, we have some decent mid level instability, a belt of shear, and some really solid DCAPE.

Also, in addition to not having the triple digit heat that June 2012 had, this will be arriving substantially later. In fact, it will probably arrive so late that it makes little sense to "stay up" for the storms...I'll set an alarm for 2am perhaps and see how things look. 

I do like the look of the stuff over western Ohio - based on the H5 flow I'd think that would be more likely to be our stuff versus the NW PA stuff. 

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8 minutes ago, mappy said:

Wind threat? Should I bring in pool floats and stuff?

If it's easy - I'm not convinced the storms will make it here with much else than showers. But - some of the models do have something coming through. 

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11 minutes ago, Kmlwx said:

If it's easy - I'm not convinced the storms will make it here with much else than showers. But - some of the models do have something coming through. 

Thanks! I’ll reevaluate before going to bed. 

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8:30pm LWX AFD evening update

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Unsettled weather pattern is expected for tonight with strong
storms likely and severe storms possible. Current analysis
shows an MCS ahead of a cold front moving into Pennsylvania
while another area of convection approaches the Shenandoah
Valley from the southwest, which is in association with a weaker
shortwave/outflow boundary that is passing by to the south.

For this evening, the activity to our southwest will most likely
propagate into the central Shenandoah Valley and Potomac
Highlands. Note the west to southwest flow over western VA
converging into the south to southeast flow over the central
Shenandoah Valley. There is an area of higher MLCAPE over this
area as well. Therefore, showers and thunderstorms are likely to
develop this evening across this area, and with moderate
effective deep layer shear, some storms may become severe.
Damaging wind is the primary threat, but an isolated instance of
hail is possible as well. Also, there is a decent amount of
moisture pull, looking at the 925 and 850mb moisture transport
from the southwest. This, combined with a light low-level flow
means that some storms may hug terrain or convective boundaries,
causing a threat for flood/flash flooding. However, confidence
is too low for a watch at this time given a relatively stronger
steering flow. Will continue to monitor.

The other area of concern is the MCS moving through
Pennsylvania this evening. This line will most likely propagate
southeast into western MD close to midnight, before moving
through our area from northwest to southeast overnight. The
propagation of this system to the southeast is offset from the
steering flow, which is southwest to northeast as well as the
potent shortwave that will be passing by to the north.
Therefore, there is a chance that the outflow may outrun this
activity, causing it to be relatively weaker. However, there is
increasing CAPE and instability due to southerly winds ahead of
this system, despite it not being a favorable time for
convection. This increases the threat for severe storms. Given
the setup, damaging winds appear to be the primary threat,
especially near and north of Interstate 66 and US 50 into
eastern WV, northern VA, and northern/western MD, where the
forcing will be strongest. Isolated instances of flood/flash
flooding are possible due to the heavy rain and increasing
moisture ahead of this system. However, it should be
progressive (causing any training storms to be localized in
coverage). The low-level flow will be backed more to the
southeast and perhaps a bit stronger, especially near/east of
Interstate 95 in northeastern MD. An isolated tornado cannot be
ruled out as this activity approaches toward Friday morning.
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2 minutes ago, Kmlwx said:

0z HRRR kills off most of the activity for much of our area except for NE Maryland as LWX has been indicating. 

HRRR timing is not even close. Storms right now about to move into state college around 10ish and HRRR at 10 has the storms like 3 counties west of there. 

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2 minutes ago, TSSN+ said:

HRRR timing is not even close. Storms right now about to move into state college around 10ish and HRRR at 10 has the storms like 3 counties west of there. 

It also seems to interact with the activity over WV which seems to "aid" in killing off the line. Certainly the line still looks robust for right now. 

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It also seems to interact with the activity over WV which seems to "aid" in killing off the line. Certainly the line still looks robust for right now. 

The mountains love this type of system. If I can see lightning in the distance with remnant light showers, I’ll call it a win.
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1 minute ago, Kmlwx said:

It also seems to interact with the activity over WV which seems to "aid" in killing off the line. Certainly the line still looks robust for right now. 

I'm sure it will crap out though. I haven’t had a single thunderstorm this season yet. The heaviest rain I have had was late June and was only like .5” or something that day but was just a plain rainy day. Total rainfall since June 1st here only at 1.87”. 

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1 hour ago, Kmlwx said:

12z NAM nest goes kind of bonkers for parts of the area tomorrow afternoon - even has intense UH tracks over parts of the area. The other guidance is less impressive...but the FV3 is pretty good too. 

SLGT risk introduced for tomorrow east of the mountains. T/W/H 0/15/15

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