Alert archive / North Carolina / Mesoscale Discussions in 2012

Mesoscale Discussion 1789

August 19, 201231 counties in North Carolina; 8 counties in South Carolina; 4 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Aug 19, 2012, 9:53 AM EDT for 31 counties in North Carolina; 8 counties in South Carolina; 4 counties in Virginia. It was in force for 97 min.

The area

The outline as issued.

The facts

Issued: Aug 19, 2012, 9:53 AM EDT (13:53 UTC)
Expired: Aug 19, 2012, 11:30 AM EDT
In force: 97 min
Issued by: the Storm Prediction Center
Chance of a watch: 60%

All 43 counties

Beaufort County, NC, Bertie County, NC, Bladen County, NC, Brunswick County, NC, Camden County, NC, Carteret County, NC, Chowan County, NC, Columbus County, NC, Craven County, NC, Currituck County, NC, Dare County, NC, Duplin County, NC, Gates County, NC, Greene County, NC, Hertford County, NC, Hyde County, NC, Jones County, NC, Lenoir County, NC, Martin County, NC, New Hanover County, NC, Onslow County, NC, Pamlico County, NC, Pasquotank County, NC, Pender County, NC, Perquimans County, NC, Pitt County, NC, Robeson County, NC, Sampson County, NC, Tyrrell County, NC, Washington County, NC, Wayne County, NC, Berkeley County, SC, Charleston County, SC, Dillon County, SC, Florence County, SC, Georgetown County, SC, Horry County, SC, Marion County, SC, Williamsburg County, SC, City of Chesapeake, VA, City of Franklin, VA, City of Suffolk, VA, City of Virginia Beach, VA

The radar

The Wilmington radar (KLTX), 59 km from the middle of the area, began a volume at 13:55 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 585Aug 19, 10:35 AM EDT

The nearest sounding before it

Newport, NC (KMHX), launched 12:00Z, 1.9 hours before the alert went out and 122 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: 1089 J/kg
Mixed-layer CIN: -28 J/kg
Mixed-layer LCL: 821 m above ground
0-6 km bulk shear: 39 kt
0-1 km storm-relative helicity: 38 m²/s²
0-3 km storm-relative helicity: 75 m²/s²
Significant tornado parameter: 0.2
Supercell composite: 1.7

Open this sounding in Storm Lab

The text

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

336 
ACUS11 KWNS 191353
SWOMCD
SPC MCD 191353 
NCZ000-VAZ000-SCZ000-191530-

MESOSCALE DISCUSSION 1789
NWS STORM PREDICTION CENTER NORMAN OK
0853 AM CDT SUN AUG 19 2012

AREAS AFFECTED...THE CAROLINA AND SOUTHEAST VIRGINIA COASTAL PLAIN

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 191353Z - 191530Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...IT IS NOT CERTAIN THAT A WW WILL BE NEEDED...BUT TRENDS
ARE BEING MONITORED FOR THE POSSIBILITY OF AN INCREASING SEVERE
THREAT THAT COULD REQUIRE ONE LATE THIS MORNING OR EARLY THIS
AFTERNOON.

DISCUSSION...SEVERAL WEAK WAVES ARE EVIDENT ALONG A STALLED OR SLOW
MOVING SURFACE FRONT ROUGHLY EXTENDING ALONG THE I-95 CORRIDOR. 
VARIABILITY IS HIGH AMONG THE MODELS CONCERNING THESE FEATURES...
BUT IT APPEARS THAT ONE UPPER IMPULSE IS ALREADY BEGINNING TO
RAPIDLY LIFT NORTHEAST OF THE SOUTHERN APPALACHIANS...WITH PERHAPS
ANOTHER WEAKER IMPULSE BEGINNING TO LIFT NORTHEAST OF THE EASTERN
GULF STATES.

SOUTHWESTERLY MID/UPPER FLOW IS MODERATELY STRONG NEAR THE
FRONT...ALONG WHICH CLUSTERS OF STORMS ARE GENERALLY
CONCENTRATED...AND THIS IS PROVIDING MORE THAN SUFFICIENT SHEAR FOR
MID-LEVEL UPDRAFT ROTATION AND ORGANIZED CONVECTION. 
HOWEVER...LOW-LEVEL FLOW IS RATHER WEAK /20 KT OR LESS AT 850 MB/
AND NOT EXPECTED TO STRENGTHEN SUBSTANTIVELY.  FURTHERMORE
MID-LEVELS ARE RELATIVELY WARM WITH WEAK LAPSE RATES...AND LOW-
LEVEL LAPSE RATES ARE NOT LIKELY TO STEEPEN SUBSTANTIALLY AHEAD OF
ACTIVITY.  ON THE OTHER HAND...NEAR SURFACE AND DEEP LAYER MOISTURE
CONTENT IS HIGH...AND WILL CONTRIBUTE TO HEAVY PRECIPITATION LOADING
IN STRONGER CONVECTION.

IT CERTAINLY DOES NOT SEEM OUT OF THE QUESTION THAT AT LEAST
OCCASIONAL LOCALIZED STRONG SURFACE GUSTS WILL BE POSSIBLE WITH
SCATTERED EVOLVING STORM CLUSTERS...AS 25-30+ KT WEST SOUTHWESTERLY
DEEP LAYER MEAN FLOW ADVECTS THEM INTO AND ACROSS THE COASTAL PLAIN
THROUGH THE 15-18Z TIME FRAME.  BUT...SEVERE POTENTIAL BEYOND
THAT...AT LEAST IN THE NEAR TERM...REMAINS A BIT UNCLEAR.

..KERR/MEAD.. 08/19/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...AKQ...MHX...RAH...ILM...CHS...CAE...

LAT...LON   32668002 33338038 34147977 35147854 35897755 36767694
            36847595 35887546 35137563 33997723 33037900 32737960
            32668002

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 19, 10:33 AM EDT	Severe Thunderstorm Watch	SPC	Beaufort, Bertie, Bladen, Brunswick, Camden, Carteret and 29 more	7 hr
Aug 19, 1:38 PM EDT	Mesoscale Discussion	SPC	Beaufort, Brunswick, Camden, Carteret, Craven, Currituck and 10 more	97 min

Nearby

Mesoscale Discussions in North Carolina, 2012 Mesoscale Discussions in South Carolina, 2012 Mesoscale Discussions in Virginia, 2012 Every 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.