Alert archive / Maryland / Mesoscale Discussions in 2013

Mesoscale Discussion 1879

September 12, 201317 counties in Maryland; 17 counties in Virginia; 7 counties in West Virginia

The Storm Prediction Center issued this mesoscale discussion at Sep 12, 2013, 1:29 PM EDT for 17 counties in Maryland; 17 counties in Virginia; 7 counties in West Virginia. It was in force for 91 min.

The area

The outline as issued.

The facts

Issued: Sep 12, 2013, 1:29 PM EDT (17:29 UTC)
Expired: Sep 12, 2013, 3:00 PM EDT
In force: 91 min
Issued by: the Storm Prediction Center
Chance of a watch: 40%

All 41 counties

Allegany County, MD, Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Carroll County, MD, Cecil County, MD, Charles County, MD, City of Baltimore, MD, Frederick County, MD, Garrett County, MD, Harford County, MD, Howard County, MD, Kent County, MD, Montgomery County, MD, Prince George's County, MD, Queen Anne's County, MD, Washington County, MD, Arlington County, VA, City of Alexandria, VA, City of Fairfax, VA, City of Falls Church, VA, City of Manassas, VA, City of Manassas Park, VA, City of Winchester, VA, Clarke County, VA, Fairfax County, VA, Fauquier County, VA, Frederick County, VA, Loudoun County, VA, Page County, VA, Prince William County, VA, Rappahannock County, VA, Shenandoah County, VA, Warren County, VA, Berkeley County, WV, Grant County, WV, Hampshire County, WV, Hardy County, WV, Jefferson County, WV, Mineral County, WV, Morgan County, WV

The radar

The Sterling radar (KLWX), 13 km from the middle of the area, began a volume at 17:29 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 watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

Severe Thunderstorm Watch 525Sep 12, 2:50 PM EDT

The nearest sounding before it

Phillips Aaf/Abe, MD (KAPG), launched 12:00Z, 5.5 hours before the alert went out and 119 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: 1009 J/kg
Mixed-layer CIN: -79 J/kg
Mixed-layer LCL: 970 m above ground
0-6 km bulk shear: 12 kt
0-1 km storm-relative helicity: 35 m²/s²
0-3 km storm-relative helicity: 39 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.

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SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 12, 2:50 PM EDT	Severe Thunderstorm Watch	SPC	Anne Arundel, Baltimore, Calvert, Caroline, Carroll, Cecil and 12 more	6 hr
Sep 12, 4:24 PM EDT	Mesoscale Discussion	SPC	Anne Arundel, Baltimore, Caroline, Cecil, Harford, Howard and 6 more	66 min
Sep 12, 3:16 PM EDT	Mesoscale Discussion	SPC	Alleghany, Augusta, Bath, Bland, Buchanan, Craig and 12 more	59 min

Nearby

Mesoscale Discussions in Maryland, 2013 Mesoscale Discussions in Virginia, 2013 Mesoscale Discussions in West Virginia, 2013 Every mesoscale discussion in 2013

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.