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George BM

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    July Discobs 2019

    in Mid Atlantic

    Posted

    11 minutes ago, yoda said:

    STW for Calvert County for ping pong ball sized hail and winds to 60... but its moving north at 10mph, which is interesting 

    There are some left-movers that are trying to move northeast from central Virginia. They're worth watching especially from I-95 and southeastward where there's been more sunshine.

     

    2019 Mid-Atlantic Severe Wx - General Discussion

    in Mid Atlantic

    Posted 

    SEL7
   0-CWZ000-010100-

   URGENT - IMMEDIATE BROADCAST REQUESTED
   Severe Thunderstorm Watch Number 547
   NWS Storm Prediction Center Norman OK
   115 PM EDT Wed Jul 31 2019

   The NWS Storm Prediction Center has issued a

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

   * Effective this Wednesday afternoon and evening from 115 PM
     until 900 PM EDT.

   * Primary threats include...
     Scattered damaging wind gusts to 70 mph possible

   SUMMARY...Scattered thunderstorms are expected to develop this
   afternoon within a warm/unstable air mass.  A few clusters of severe
   storms are expected to form, capable of locally damaging wind gusts.

   The severe thunderstorm watch area is approximately along and 75
   statute miles east and west of a line from 45 miles south southeast
   of Washington DC to 25 miles north northwest of Boston MA. For a
   complete depiction of the watch see the associated watch outline
   update (WOUS64 KWNS WOU7).

   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.

   &&

   AVIATION...A few severe thunderstorms with hail surface and aloft to
   1 inch. Extreme turbulence and surface wind gusts to 60 knots. A few
   cumulonimbi with maximum tops to 500. Mean storm motion vector
   25030.

   ...Hart

    July Banter 2019

    in Mid Atlantic

    Posted

    1 hour ago, JakkelWx said:

    Had a weird dream last night that 2 feet of snow fell imby in the middle of July.

    I dreamt that there was a supercell thundersnow storm the night before last and that people were getting blown around like they were leaves when the tornado blew through the campus.

    July Discobs 2019

    in Mid Atlantic

    Posted

    On 7/25/2019 at 11:08 AM, terpodion said:

    I live in New Jersey and we get thunderstorms all summer long. We are used to it. But Monday we had a line of them move through and they were very, very strong. There was a lot of damage. I had no electricity for 26 hours, some people still have no power.

    My question is why were these storms so intense? Was this a derecho? I have asked this question on other forums and haven't gotten a decent answer. Perhaps an actual meteorologist can answer this for me. Thanks. 

    Well I'm certainly no meteorologist but I do know somethings about meteorology so here it goes.

    This past Monday, as you probably know, was the last day of the heatwave in the region. Very hot surface temperatures usually correspond with very steep low-level lapse rates which can help with higher winds aloft being mixed down to the ground say with, for example, a line of thunderstorms ;). Now this past Monday NJ had an area of 3,000+J/kg of mlcape (Mixed-layer convective available potential energy), which is fairly high (higher than usual), due to the high heat and humidity (surface temps in the 90's and dewpoints in the 70's). With you being in central NJ that means your area missed the previous days storms. This is important because it means that nothing was able to stabilize and moisten the atmosphere. That means that there was some drier air aloft (10,000-20,000ft) for Monday afternoon in your area. So, when strong heating of a moist boundary-layer (the layer below the cumulus clouds) helped cumulus clouds grow into cumulonimbus clouds the water droplets evaporated in the dry air which causes it to cool and sink creating a downdraft. On Monday afternoon there were also some stronger winds aloft around the 700-600mb layer (10,000-15,000ft above the ground) of around 35-40 kts. That can help storm clusters generate a cold-pool and with warm/moist air being forced upwards ahead of the storms and the rain cooled air (the cold-pool) sinking as they move through this creates a feedback loop allowing the storms to accelerate forward to 35-40kts (40-46mph) or faster especially if instability is strong (which it was on Monday). The storms on Monday blasted through your area at 50-60 mph and with the steep low-level lapse rates in place a lot of that wind energy was able to reach the ground. The result is widespread 50-60 mph wind gusts. However, with stronger downdrafts embedded within the line of storms they could've added 15-20+mph to the 50-60 mph winds in localized areas.

    This is my two cents on Monday's storms in your area. I'm no meteorologist or expert for that matter and I probably look like a total fool to those experts. Oh well, I live and I learn and boy do I have a lot to learn in this field. I also apologize for the horrible grammar. I hope you were able to understand something through all that. Hopefully an actual expert can clarify what the heck I just tried to say lol.

    • Like 9

    July Discobs 2019

    in Mid Atlantic

    Posted

    7 minutes ago, MN Transplant said:

    Hard to tell with the rounding, but DCA is something like 87/76 right now on a river wind.  IAD appears to have ticked up to 91 already.

    My station is 92/79 for a 108 HI.

    IAD now 93F as of 11:02am edt, Wednesday, July 17, 2019

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