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2023 Mid-Atlantic Severe Wx Thread (General Discussion)


Kmlwx
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The HRRR performed REALLY well today IMO. Several runs in a row had a big cell type signature going right through Central Maryland. More like a line segment - but certainly a big punch for a non SPC risk day. This either means we will now pay for this with several misses in the next few days...or we are going on a hot streak for severe. Won't know until it's done ;) 

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STW with TOR poss tag for C MD

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Baltimore MD/Washington DC
441 PM EDT Fri Jun 30 2023

The National Weather Service in Sterling Virginia has issued a

* Severe Thunderstorm Warning for...
  Baltimore City in northern Maryland...
  Northwestern Anne Arundel County in central Maryland...
  Eastern Howard County in central Maryland...
  Southwestern Baltimore County in northern Maryland...

* Until 530 PM EDT.

* At 441 PM EDT, severe thunderstorms were located along a line
  extending from Ellicott City to near Elkridge to Laurel, moving
  east at 15 mph.

  HAZARD...60 mph wind gusts.

  SOURCE...Radar indicated.

  IMPACT...Damaging winds will cause some trees and large branches
           to fall. This could injure those outdoors, as well as
           damage homes and vehicles. Roadways may become blocked by
           downed trees. Localized power outages are possible.
           Unsecured light objects may become projectiles.

* Locations impacted include...
  Baltimore, Columbia, Severn, Pikesville, Elkridge, Riviera Beach,
  Baltimore-Washington Airport, Historic Ellicott City, Fort
  Smallwood State Park, Glen Burnie, Ellicott City, Dundalk, Towson,
  Catonsville, Woodlawn, Milford Mill, Lochearn, Pasadena, Arbutus
  and Ferndale.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Remain alert for a possible tornado! Tornadoes can develop quickly
from severe thunderstorms. If you spot a tornado go at once into the
basement or small central room in a sturdy structure.

Torrential rainfall is occurring with these storms, and may lead to
flash flooding. Do not drive your vehicle through flooded roadways.

&&

LAT...LON 3927 7651 3920 7649 3920 7650 3919 7650
      3916 7648 3910 7684 3917 7688 3926 7687
      3938 7673 3938 7659
TIME...MOT...LOC 2041Z 251DEG 14KT 3928 7684 3920 7680 3909 7683

TORNADO...POSSIBLE
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...<.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...60 MPH
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Was mentioned in the obs thread but yes - not even a marginal risk, no mesoscale discussion - what an overperformer! Not seeing any LSRs yet - but assuming some lagged ones might pop up. I'd say this is a solid storm day given the silence from the SPC. 

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5 minutes ago, Kmlwx said:

Was mentioned in the obs thread but yes - not even a marginal risk, no mesoscale discussion - what an overperformer! Not seeing any LSRs yet - but assuming some lagged ones might pop up. I'd say this is a solid storm day given the silence from the SPC. 

The under the radar days outperform the big risk days lol

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Both Sat/Sun seem to favor south of the Potomac. But some cells do make it ahead of the main line on that NAM nest run. These things are super tricky to forecast...H5 would seem to argue the bend further south of us is real. 

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Just now, Kmlwx said:

Both Sat/Sun seem to favor south of the Potomac. But some cells do make it ahead of the main line on that NAM nest run. These things are super tricky to forecast...H5 would seem to argue the bend further south of us is real. 

Looks like a supercell into a bow echo for DC metro Sun afternoon?  Hours 42-45 on sim radar

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Just now, yoda said:

Looks like a supercell into a bow echo for DC metro Sun afternoon?  Hours 42-45 on sim radar

After today I'm almost inclined to use the HRRR as my "first guess" for both days :lol: - it really did pretty well on this morning's runs for this afternoon/evening. 

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1 minute ago, yoda said:

Looks like a supercell into a bow echo for DC metro Sun afternoon?  Hours 42-45 on sim radar

The 18z NAM kept me largely dry except for a few showers...and of course I bought tickets for the Baysox game tomorrow evening...fitting that the NAM seems to want to spoil that. The 12km NAM even looks solid. 

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I said earlier...result of today will either be that we pay with painful misses for a while...or we are on a temporary heater. 

Given the recent boring weather, and a hunch feeling...I do wonder if we string together a solid streak of storm days. 

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Just now, Kmlwx said:

I said earlier...result of today will either be that we pay with painful misses for a while...or we are on a temporary heater. 

Given the recent boring weather, and a hunch feeling...I do wonder if we string together a solid streak of storm days. 

Should be an intriguing Day 1 and Day 2 SPC OTLK... maybe even Day 3 lol

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^^ 
Wow...obviously two isn't enough of a sample size - but that's suggestive that there *could* be some sort of terrain or microscale influence there to get spin going. At least while I was watching/tracking during the storms earlier - that rotation formed pretty quick - granted I wasn't really looking at elevated tilts. 

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Just a cursory glance at the terrain map and map in general for that area - a few things grab my attention - 

1) Much less developed/urban sprawl areas versus other suburban areas closer in. 

2) Triadelphia Reservoir/Patuxent River in that area

3) Sort of evenly split distance between the city center of Baltimore/DC (think heat islands). Have to wonder if the UHI plays a role...totally speculative - but if you have one area warmer than others one would assume there could be some microclimate stuff going on like eddies of warmer areas and such. 

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The guidance is all over the place for both today and tomorrow. Pretty much every solution portrayed depending on which model you look at. Could be anything from getting blanked (for the most part) both days, to flush hits both days (maybe even multiple times). 

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HRRR seems to think the storms will make it roughly to the Chesapeake before petering out. FV3 (12z run) really doesn't have much for most of us. It's still anyone's guess...but I think the SPC expansion of the slight risk into the area is probably wise. It's pretty cloudy here in Central Maryland - but certainly moist...73+ degrees for the dewpoint IMBY right now. 

I'm guessing we will overperform simply because I have baseball tickets for tonight ;) 

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:lmao: and the slight risk is gone. 

I really hate to be one to criticize SPC...but the other day they added a hatched hail area and subsequently removed it. Today they have us in marginal, bump us to slight, and then trim the slight way back again. With more and more people directly consuming SPC outlooks...we can no longer make the excuse of "it's not even for public eyes unless they go looking for it" - this is very public knowledge now. 

They should have just kept us at marginal all the way until confidence was higher. 

Rant over...but this is 2nd time in recent days/weeks. 

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1730z SPC OTLK for tomorrow... still SLGT risk 

 

   ...Mid Atlantic/Ohio and Tennessee Valleys into Ark-La-Tex...
   Along and just south of the weak frontal zone, the boundary-layer
   may be initially impacted by a considerable amount of remnant
   convective outflow.  How the associated outflow boundaries evolve
   through midday Sunday remains unclear, but insolation along and to
   their south likely will contribute to steepening low-level lapse and
   moderate to large CAPE in the presence of seasonably high moisture
   content.  This appears likely to occur beneath a belt of 30-40+ kt
   (perhaps stronger where augmented by prior convection)
   west-southwesterly flow in the 850-500 mb layer, which may prove
   conducive to renewed strong and organizing convective development
   Sunday afternoon and evening.  Isolated supercell structures are
   possible initially, posing a risk for severe hail, before
   potentially damaging wind gusts with evolving clusters becomes the
   more prominent hazard.
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https://www.spc.noaa.gov/products/md/md1371.html

mcd1371.png

 

 

   Mesoscale Discussion 1371
   NWS Storm Prediction Center Norman OK
   1237 PM CDT Sat Jul 01 2023

   Areas affected...northern/central Virginia into portions of Maryland

   Concerning...Severe potential...Watch unlikely 

   Valid 011737Z - 011930Z

   Probability of Watch Issuance...20 percent

   SUMMARY...Isolated thunderstorms may produce locally strong gusts
   and hail through the afternoon.

   DISCUSSION...Isolated thunderstorms are developing along a surface
   trough near the higher terrain of west-central VA. Low to mid 70s
   surface dewpoints are contributing to 1000-1500 J/kg MLCAPE amid
   modest midlevel lapse rates. Continued heating will result in
   steepening low-level lapse rates the next few hours. Vertical shear
   is expected to remain weak, at or below 20 kt 0-6 km effective bulk
   shear. This will limit longevity/organization of strong updrafts.
   Nevertheless, high PW values and boundary-layer mixing to around 1
   km could support sporadic downbursts. While midlevel lapse rates and
   3-6 km flow will remain weak, large instability from 700-300 mb and
   somewhat elongated hodographs could support a few instances of
   near-1 inch hail. The overall threat is expected to remain marginal,
   and a severe thunderstorm watch is not expected at this time.

   ..Leitman/Grams.. 07/01/2023

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...PHI...AKQ...LWX...RNK...
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