Alert archive / Virginia / Mesoscale Discussions in 2012

Mesoscale Discussion 1957

September 18, 20125 states

The Storm Prediction Center issued this mesoscale discussion at Sep 18, 2012, 8:49 AM EDT for 5 states. It was in force for 116 min.

The area

The outline as issued.

The facts

Issued
Sep 18, 2012, 8:49 AM EDT (12:49 UTC)
Expired
Sep 18, 2012, 10:45 AM EDT
In force
116 min
Issued by
the Storm Prediction Center
Chance of a watch
80%
All 127 counties

Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Carroll County, MD, Charles County, MD, City of Baltimore, MD, Frederick County, MD, Harford County, MD, Howard County, MD, Kent County, MD, Montgomery County, MD, Prince George's County, MD, Saint Mary's County, MD, Washington County, MD, Alamance County, NC, Anson County, NC, Caswell County, NC, Chatham County, NC, Cumberland County, NC, Davidson County, NC, Durham County, NC, Edgecombe County, NC, Forsyth County, NC, Franklin County, NC, Granville County, NC, Greene County, NC, Guilford County, NC, Halifax County, NC, Harnett County, NC, Hoke County, NC, Johnston County, NC, Lee County, NC, Montgomery County, NC, Moore County, NC, Nash County, NC, Northampton County, NC, Orange County, NC, Person County, NC, Randolph County, NC, Richmond County, NC, Robeson County, NC, Rockingham County, NC, Rowan County, NC, Sampson County, NC, Scotland County, NC, Stanly County, NC, Vance County, NC, Wake County, NC, Warren County, NC, Wayne County, NC, Wilson County, NC, Adams County, PA, Cumberland County, PA, Franklin County, PA, Lancaster County, PA, York County, PA, Albemarle County, VA, Amelia County, VA, Appomattox County, VA, Arlington 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 Alexandria, VA, City of Charlottesville, VA, City of Colonial Heights, VA, City of Danville, VA, City of Emporia, VA, City of Fairfax, VA, City of Falls Church, VA, City of Fredericksburg, VA, City of Hopewell, VA, City of Lynchburg, VA, City of Manassas, VA, City of Manassas Park, VA, City of Martinsville, VA, City of Petersburg, VA, City of Richmond, VA, City of Winchester, VA, Clarke County, VA, Culpeper County, VA, Cumberland County, VA, Dinwiddie County, VA, Essex County, VA, Fairfax County, VA, Fauquier County, VA, Fluvanna County, VA, Frederick County, VA, Goochland County, VA, Greene County, VA, Greensville County, VA, Halifax County, VA, Hanover County, VA, Henrico County, VA, King and Queen County, VA, King George County, VA, King William County, VA, Loudoun County, VA, Louisa County, VA, Lunenburg County, VA, Madison County, VA, Mecklenburg County, VA, Nelson County, VA, New Kent County, VA, Nottoway County, VA, Orange County, VA, Page County, VA, Pittsylvania County, VA, Powhatan County, VA, Prince Edward County, VA, Prince George County, VA, Prince William County, VA, Rappahannock County, VA, Richmond County, VA, Shenandoah County, VA, Spotsylvania County, VA, Stafford County, VA, Sussex County, VA, Warren County, VA, Westmoreland County, VA, Berkeley County, WV, Jefferson County, WV, Morgan County, WV

The radar

The Norfolk radar (KAKQ), 137 km from the middle of the area, began a volume at 12:51 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.

The nearest sounding before it

Roanoke, VA (KRNK), launched 12:00Z, 0.8 hours before the alert went out and 86 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-pSkew-T log-p diagram, Roanoke, VA at 12:00Z on 2012-09-18Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 293 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Roanoke, VA at 12:00Z on 2012-09-18The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 354 square meters per square second.19395878Sfc1 km3 km6 km9 kmRMLM
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
293 J/kg
Mixed-layer CIN
-5 J/kg
Mixed-layer LCL
586 m above ground
0-6 km bulk shear
46 kt
0-1 km storm-relative helicity
354 m²/s²
0-3 km storm-relative helicity
314 m²/s²
Significant tornado parameter
0.5
Supercell composite
6.0

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.

IssuedProductOfficeCountiesLasted
Sep 18, 10:54 AM EDTTornado WatchSPCAnne Arundel, Baltimore, Calvert, Carroll, Charles, Dorchester and 11 more9 hr
Sep 18, 11:14 AM EDTMesoscale DiscussionSPCCecil91 min
Sep 18, 11:19 AM EDTMesoscale DiscussionSPCAnne Arundel, Baltimore, Calvert, Caroline, Carroll, Cecil and 13 more86 min
Sep 18, 12:10 PM EDTTornado WatchSPCCaroline, Cecil, Kent, Queen Anne's, Talbot9 hr
Sep 18, 1:27 PM EDTMesoscale DiscussionSPCAnne Arundel, Baltimore, Calvert, Carroll, Charles, Dorchester and 10 more63 min
Sep 18, 1:56 PM EDTMesoscale DiscussionSPCCecil, Harford64 min
Sep 18, 3:52 PM EDTMesoscale DiscussionSPCAnne Arundel, Baltimore, Calvert, Charles, Dorchester, Howard and 7 more113 min
Sep 18, 4:21 PM EDTMesoscale DiscussionSPCCaroline, Cecil114 min
Sep 18, 6:15 PM EDTMesoscale DiscussionSPCSomerset, Wicomico, Worcester30 min
Sep 17, 8:14 PM EDTMesoscale DiscussionSPCCherokee, Clay, Graham, Haywood, Henderson, Jackson and 4 more2 hr
Sep 18, 12:23 AM EDTMesoscale DiscussionSPCAlexander, Buncombe, Burke, Cabarrus, Caldwell, Catawba and 14 more97 min
Sep 18, 9:45 AM EDTTornado WatchSPCAlamance, Anson, Chatham, Cumberland, Davidson, Durham and 25 more8 hr
Sep 18, 11:35 AM EDTMesoscale DiscussionSPCUnion85 min
Sep 18, 1:00 PM EDTTornado WatchSPCBeaufort, Carteret, Craven, Dare, Duplin, Greene and 9 more5 hr
Sep 18, 1:21 PM EDTMesoscale DiscussionSPCAlamance, Anson, Chatham, Cumberland, Davidson, Durham and 25 more84 min
Sep 18, 4:11 PM EDTMesoscale DiscussionSPCAlamance, Anson, Beaufort, Carteret, Chatham, Craven and 40 more94 min

Nearby

Mesoscale Discussions in Virginia, 2012Mesoscale Discussions in North Carolina, 2012Mesoscale Discussions in Maryland, 2012Every mesoscale discussion in 2012

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.