Alert archive / Virginia / Mesoscale Discussions in 2009

Mesoscale Discussion 540

April 20, 2009Charles County, Saint Mary's County, Somerset County, Maryland; 19 counties in North Carolina; 67 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Apr 20, 2009, 4:57 PM EDT for Charles County, Saint Mary's County, Somerset County, Maryland; 19 counties in North Carolina; 67 counties in Virginia. It was in force for 93 min.

The area

The outline as issued.

The facts

Issued: Apr 20, 2009, 4:57 PM EDT (20:57 UTC)
Expired: Apr 20, 2009, 6:30 PM EDT
In force: 93 min
Issued by: the Storm Prediction Center

All 89 counties

Charles County, MD, Saint Mary's County, MD, Somerset County, MD, Alamance County, NC, Camden County, NC, Caswell County, NC, Chatham County, NC, Chowan County, NC, Durham County, NC, Franklin County, NC, Gates County, NC, Granville County, NC, Halifax County, NC, Hertford County, NC, Nash County, NC, Northampton County, NC, Orange County, NC, Pasquotank County, NC, Perquimans County, NC, Person County, NC, Vance County, NC, Warren County, NC, Albemarle County, VA, Amelia County, VA, Appomattox County, VA, Brunswick County, VA, Buckingham County, VA, Campbell County, VA, Caroline County, VA, Charles City County, VA, Charlotte County, VA, Chesterfield County, VA, City of Charlottesville, VA, City of Chesapeake, VA, City of Colonial Heights, VA, City of Danville, VA, City of Emporia, VA, City of Franklin, VA, City of Fredericksburg, VA, City of Hampton, VA, City of Hopewell, VA, City of Lynchburg, VA, City of Newport News, VA, City of Norfolk, VA, City of Petersburg, VA, City of Poquoson, VA, City of Portsmouth, VA, City of Richmond, VA, City of Suffolk, VA, City of Virginia Beach, VA, City of Williamsburg, VA, Cumberland County, VA, Dinwiddie County, VA, Essex County, VA, Fluvanna County, VA, Gloucester County, VA, Goochland County, VA, Greensville County, VA, Halifax County, VA, Hanover County, VA, Henrico County, VA, Isle of Wight 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, Lunenburg County, VA, Mathews County, VA, Mecklenburg County, VA, Middlesex County, VA, New Kent County, VA, Northampton County, VA, Northumberland County, VA, Nottoway County, VA, Orange County, VA, Pittsylvania County, VA, Powhatan County, VA, Prince Edward County, VA, Prince George County, VA, Richmond County, VA, Southampton County, VA, Spotsylvania County, VA, Stafford County, VA, Surry County, VA, Sussex County, VA, Westmoreland County, VA, York County, VA

The radar

The Norfolk radar (KAKQ), 86 km from the middle of the area, began a volume at 21:01 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

Roanoke, VA (KRNK), launched 12:00Z, 9.0 hours before the alert went out and 155 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: 23 J/kg
Mixed-layer CIN: -38 J/kg
Mixed-layer LCL: 526 m above ground
0-6 km bulk shear: 59 kt
0-1 km storm-relative helicity: 185 m²/s²
0-3 km storm-relative helicity: 217 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

<!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
Apr 20, 2:50 PM EDT	Tornado Watch	SPC	Calvert, Charles, Saint Mary's	7 hr
Apr 20, 7:15 PM EDT	Mesoscale Discussion	SPC	Saint Mary's	90 min
Apr 20, 12:42 AM EDT	Tornado Watch	SPC	Catawba, Cleveland, Gaston, Henderson, Lincoln, Mecklenburg and 2 more	5 hr
Apr 20, 12:22 PM EDT	Mesoscale Discussion	SPC	Beaufort, Bertie, Camden, Chowan, Craven, Edgecombe and 19 more	83 min
Apr 20, 2:09 PM EDT	Mesoscale Discussion	SPC	Alamance, Caswell, Durham, Edgecombe, Franklin, Granville and 11 more	2 hr
Apr 20, 2:52 PM EDT	Mesoscale Discussion	SPC	Bladen, Brunswick, Columbus, Duplin, New Hanover, Pender	83 min
Apr 20, 3:16 PM EDT	Severe Thunderstorm Watch	SPC	Beaufort, Bladen, Brunswick, Carteret, Columbus, Craven and 25 more	6 hr
Apr 20, 4:55 PM EDT	Mesoscale Discussion	SPC	Beaufort, Bertie, Bladen, Brunswick, Carteret, Chowan and 20 more	95 min
Apr 20, 7:36 PM EDT	Mesoscale Discussion	SPC	Beaufort, Bladen, Columbus, Craven, Duplin, Greene and 12 more	84 min

Nearby

Mesoscale Discussions in Virginia, 2009 Mesoscale Discussions in North Carolina, 2009 Mesoscale Discussions in Maryland, 2009 Every mesoscale discussion in 2009

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.