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2021 Mid-Atlantic Severe Weather - General Discussion


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17 minutes ago, MN Transplant said:

12z NAM 3k is a bit more frisky than prior runs.  Both the NAM and HRRR indicate that there may be a set of cells out in front of the main line, which is pretty common around here.

      Yeah, the signal for this started showing up yesterday, and even the Hi-Res Windows are buying in, although they disagree a bit on location and timing.   (The HiResW FV3 initiates the lead cells notably further north.)      Seems like several cells will race from south to north out ahead of the more organized line rolling east.    Still unclear how much instability will be available:  the HRRR is much warmer (but drier), while the NAM Nest is more moist (but cooler).   Perhaps there is a temperature/moisture "sweet spot" in there that could increase the potential for some hail and wind.

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1 hour ago, high risk said:

      Yeah, the signal for this started showing up yesterday, and even the Hi-Res Windows are buying in, although they disagree a bit on location and timing.   (The HiResW FV3 initiates the lead cells notably further north.)      Seems like several cells will race from south to north out ahead of the more organized line rolling east.    Still unclear how much instability will be available:  the HRRR is much warmer (but drier), while the NAM Nest is more moist (but cooler).   Perhaps there is a temperature/moisture "sweet spot" in there that could increase the potential for some hail and wind.

HRRR over-mixing coming into play again? BWI is already 77. Even Westminster is 72.

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4 minutes ago, Eskimo Joe said:

HRRR over-mixing coming into play again? BWI is already 77. Even Westminster is 72.

        HRRR seems to have a good handle on the environment.    It's going for roughly 80/58 by mid-afternoon which seems reasonable.   NAM Nest is too cool - it really raises the dew points later this afternoon, and I'm not sure that's going to be right.

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18 minutes ago, high risk said:

        HRRR seems to have a good handle on the environment.    It's going for roughly 80/58 by mid-afternoon which seems reasonable.   NAM Nest is too cool - it really raises the dew points later this afternoon, and I'm not sure that's going to be right.

Dewpoints along and east of I-95 are starting to tick into the low 60s. Get that west to US 15 baby.

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21 minutes ago, southmdwatcher said:

The storms along I64 started this morning down in North Carolina and have been moving northward steadily since then.

       Good point, and the HRRR is still struggling to initialize them.    The only guidance that explicitly showed this was the ARW2.    Some of the other guidance has shown cells developing later this afternoon south of DC and moving north, so I think that these solutions correctly captured the northward-moving forcing mechanism but struggled to initiate storms much earlier and much further south.

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NWS Baltimore-Washington (@NWS_BaltWash) Tweeted:
One of the biggest tidal flood events of the past 10-20 years (possibly since Hurricane Isabel at some locales), is expected Friday & Saturday. Those along tidal shores should get ready for exceptional tidal inundation!  Tidal forecasts here: https://t.co/Q2WdpDGgIJ https://t.co/LQkL80pzQs https://twitter.com/NWS_BaltWash/status/1453734194501206024?s=20

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1 hour ago, Bodhi Cove said:

NWS Baltimore-Washington (@NWS_BaltWash) Tweeted:
One of the biggest tidal flood events of the past 10-20 years (possibly since Hurricane Isabel at some locales), is expected Friday & Saturday. Those along tidal shores should get ready for exceptional tidal inundation!  Tidal forecasts here: https://t.co/Q2WdpDGgIJ https://t.co/LQkL80pzQs https://twitter.com/NWS_BaltWash/status/1453734194501206024?s=20

Awesome!  Will be heading down to Fells Point to see if it comes over the banks!  

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In addition to the coastal flood threat, areas generally south of DC are in a MRGL risk for damaging convective wind gusts Friday afternoon.      Several models are now showing a little bit of sfc-based instability Friday afternoon, which could allow some of the faster wind speeds just above the surface to mix down.     I'll note that  1) a few CAMs develop instability even further to the north than currently indicated in the MRGL region implying a more widespread threat  but  2) a lot of the stronger wind speeds above the surface will move off to the northeast before the instability develops which implies an overall lesser threat

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Take on severe potential from Mount Holly-

Severe thunderstorms/tornadoes: Instability will be quite limited. However, even with a marginal instability, a few thunderstorms are possible, primarily in Delmarva. Any thunderstorms in the vicinity of the occluded front will be developing in an area with significant wind shear and helicity. Thus, rotating storms will be possible in this area. The higher threat for this looks to be further south from our region near the front during the period of max mixing, but will have to watch if the front progresses north faster than currently forecast, the risk for rotating storms could develop as far north as northern Delmarva.

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