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2023 Mid-Atlantic Severe Wx Thread (General Discussion)


Kmlwx
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The depiction on the 18z 3km NAM aligns pretty well with the SPC discussion for tomorrow-

A large scale mid/upper trough oriented from the lower Great Lakes to the central Appalachians will pivot east across the Mid-Atlantic and Northeast on Tuesday. Large scale ascent coupled with modest vertical shear (effective shear magnitudes around 30 kt) atop a seasonally moist/unstable airmass will support scattered strong to severe thunderstorms from early afternoon into early evening. Elongated/straight hodographs amid large instability above 850 mb and increasing westerlies to around 35 kt between 3-6 km suggest isolated severe hail will be possible with semi-discrete cells, especially around the Delmarva/Chesapeake Bay vicinity where midlevel lapse rates are forecast to be steepest (around 6.5-7 C/km). Strong heating will aid in steepening low-level lapse rates, and low-level winds will remain fairly light. This will promote potential for strong outflow and isolated damaging gusts. Some guidance suggests a forward propagating cluster may develop via consolidating outflow across the Chesapeake Bay vicinity late afternoon/early evening. As a result of these factors, the Marginal risk (level 1 of 5) has been expanded across the Mid-Atlantic and a Slight risk (level 2 of 5) introduced across the Delmarva vicinity.

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0z HRRR does it's usual thing of bringing dews way down - even into the lower 60s for some tomorrow afternoon. The 18z NAM had richer moisture as usual. Despite that, the HRRR does deliver some storms but it looks fairly garden variety. 

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URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 546
NWS Storm Prediction Center Norman OK
1210 PM EDT Tue Jul 25 2023

The NWS Storm Prediction Center has issued a

* Severe Thunderstorm Watch for portions of 
  Connecticut
  District Of Columbia
  Delaware
  Eastern Maryland
  New Jersey
  Southeast New York
  Eastern Pennsylvania
  Northern Virginia
  Coastal Waters

* Effective this Tuesday afternoon and evening from 1210 PM until
  800 PM EDT.

* Primary threats include...
  Scattered damaging wind gusts to 70 mph possible
  Isolated large hail events to 1.5 inches in diameter possible

SUMMARY...Thunderstorms will increase from northern Virginia into
eastern Pennsylvania this afternoon, then track eastward across the
watch area through the day.  Damaging winds are possible in the
strongest storms.

The severe thunderstorm watch area is approximately along and 70
statute miles east and west of a line from 10 miles west northwest
of Windsor Locks CT to 45 miles east southeast of Washington DC. For
a complete depiction of the watch see the associated watch outline
update (WOUS64 KWNS WOU6).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

REMEMBER...A Severe Thunderstorm Watch means conditions are
favorable for severe thunderstorms in and close to the watch area.
Persons in these areas should be on the lookout for threatening
weather conditions and listen for later statements and possible
warnings. Severe thunderstorms can and occasionally do produce
tornadoes.

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1 minute ago, Eskimo Joe said:

@Kmlwxdefinitely can see a westward moving outflow boundary from the first round of convection. Hopefully this can act as a mechanism for more storms later but I'm really pessimistic about it.

I'm right there with you. It's mostly evolving just as much of the guidance had been predicting with a focus S/E of DC. 

Looking more longer range - GFS is trying to signal (for multiple runs) Something in the first day or two of August with beefy parameters. Way too far out for now...but CIPS has also been lighting up in the 96-120hr frames. The super long range CIPS quiets down substantially - probably indicates some larger cold front to clear out the juice. 

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Well that was interesting. Thought I could beat it when I left work, and drove straight into it a few miles south of my house. Wind driven torrential rain, lots of small debris and some big branches down. Plenty of T&L. My driveway is a river. Appears this blew up right on the doorstep from the outflow from the initial line. 1.73".

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2 minutes ago, CAPE said:

Well that was interesting. Thought I could beat it when I left work, and drove straight into it a few miles south of my house. Wind driven torrential rain, lots of small debris and some big branches down. Plenty of T&L. My driveway is a river. Appears this blew up right on the doorstep from the outflow from the initial line. 1.73".

I hope all that nice stone didn’t get washed away!

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