Alert archive / Virginia / Mesoscale Discussions in 2018

Mesoscale Discussion 1338

August 21, 2018Charles County, Saint Mary's County, Maryland; 49 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Aug 21, 2018, 5:03 PM EDT for Charles County, Saint Mary's County, Maryland; 49 counties in Virginia. It was in force for 117 min.

The area

The outline as issued.

The facts

Issued: Aug 21, 2018, 5:03 PM EDT (21:03 UTC)
Expired: Aug 21, 2018, 7:00 PM EDT
In force: 117 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 20%

All 51 counties

Charles County, MD, Saint Mary's County, MD, Albemarle County, VA, Amelia County, VA, Amherst County, VA, Appomattox County, VA, Augusta County, VA, Buckingham County, VA, Caroline County, VA, Charles City County, VA, Chesterfield County, VA, City of Buena Vista, VA, City of Charlottesville, VA, City of Colonial Heights, VA, City of Fredericksburg, VA, City of Hopewell, VA, City of Lexington, VA, City of Lynchburg, VA, City of Petersburg, VA, City of Richmond, VA, City of Staunton, VA, City of Waynesboro, VA, City of Williamsburg, VA, Cumberland County, VA, Dinwiddie County, VA, Essex County, VA, Fluvanna County, VA, Gloucester County, VA, Goochland County, VA, Hanover County, VA, Henrico County, VA, James City County, VA, King and Queen County, VA, King George County, VA, King William County, VA, Lancaster County, VA, Louisa County, VA, Mathews County, VA, Middlesex County, VA, Nelson County, VA, New Kent County, VA, Northumberland County, VA, Nottoway County, VA, Orange County, VA, Powhatan County, VA, Prince George County, VA, Richmond County, VA, Rockbridge County, VA, Spotsylvania County, VA, Surry County, VA, Westmoreland County, VA

The radar

The Norfolk radar (KAKQ), 121 km from the middle of the area, began a volume at 21:04 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 9.1 hours before the alert went out and 157 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 187 J/kg
Mixed-layer CIN: -22 J/kg
Mixed-layer LCL: 597 m above ground
0-6 km bulk shear: 32 kt
0-1 km storm-relative helicity: 122 m²/s²
0-3 km storm-relative helicity: 183 m²/s²
Significant tornado parameter: 0.1
Supercell composite: 0.6

Open this sounding in Storm Lab

The text

As transmitted.

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 21, 2:16 PM EDT	Mesoscale Discussion	SPC	Allegany, Garrett	119 min
Aug 21, 2:41 PM EDT	Severe Thunderstorm Watch	SPC	Allegany, Carroll, Frederick, Garrett, Washington	7 hr
Aug 21, 4:56 PM EDT	Mesoscale Discussion	SPC	Allegany, Carroll, Frederick, Garrett, Montgomery, Washington	2 hr
Aug 21, 7:06 PM EDT	Mesoscale Discussion	SPC	Anne Arundel, Baltimore, Carroll, Cecil, Frederick, Harford and 7 more	84 min

Nearby

Mesoscale Discussions in Virginia, 2018 Mesoscale Discussions in Maryland, 2018 Every mesoscale discussion in 2018

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.