Alert archive / Virginia / Mesoscale Discussions in 2012

Mesoscale Discussion 1759

August 14, 20124 states

The Storm Prediction Center issued this mesoscale discussion at Aug 14, 2012, 2:07 PM EDT for 4 states. It was in force for 113 min.

The area

The outline as issued.

The facts

Issued: Aug 14, 2012, 2:07 PM EDT (18:07 UTC)
Expired: Aug 14, 2012, 4:00 PM EDT
In force: 113 min
Issued by: the Storm Prediction Center
Chance of a watch: 20%

All 49 counties

Anne Arundel County, MD, Baltimore County, MD, Carroll County, MD, City of Baltimore, MD, Frederick County, MD, Harford County, MD, Howard County, MD, Montgomery County, MD, Prince George's County, MD, Washington County, MD, Adams County, PA, Cumberland County, PA, Franklin County, PA, Fulton County, PA, York County, PA, Albemarle County, VA, Arlington County, VA, City of Alexandria, VA, City of Charlottesville, VA, City of Fairfax, VA, City of Falls Church, VA, City of Fredericksburg, VA, City of Harrisonburg, VA, City of Manassas, VA, City of Manassas Park, VA, City of Winchester, VA, Clarke County, VA, Culpeper County, VA, Fairfax County, VA, Fauquier County, VA, Frederick County, VA, Greene County, VA, Loudoun County, VA, Louisa County, VA, Madison County, VA, Orange County, VA, Page County, VA, Prince William County, VA, Rappahannock County, VA, Rockingham County, VA, Shenandoah County, VA, Spotsylvania County, VA, Stafford County, VA, Warren County, VA, Berkeley County, WV, Hampshire County, WV, Hardy County, WV, Jefferson County, WV, Morgan County, WV

The radar

The Sterling radar (KLWX), 46 km from the middle of the area, began a volume at 18:08 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, 6.1 hours before the alert went out and 54 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: 582 J/kg
Mixed-layer CIN: -23 J/kg
Mixed-layer LCL: 687 m above ground
0-6 km bulk shear: 49 kt
0-1 km storm-relative helicity: 9 m²/s²
0-3 km storm-relative helicity: 30 m²/s²
Significant tornado parameter: 0.1
Supercell composite: 0.3

Open this sounding in Storm Lab

The text

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

999 
ACUS11 KWNS 141808
SWOMCD
SPC MCD 141807
MDZ000-PAZ000-DCZ000-VAZ000-WVZ000-142000-

MESOSCALE DISCUSSION 1759
NWS STORM PREDICTION CENTER NORMAN OK
0107 PM CDT TUE AUG 14 2012

AREAS AFFECTED...PARTS OF ERN W VA...S CNTRL/SERN PA...CNTRL MD AND
N CNTRL VA...INCLUDING WASHINGTON D.C./BALTIMORE

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 141807Z - 142000Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...INCREASING STORM DEVELOPMENT IS POSSIBLE ACROSS THE REGION
THROUGH 20-22Z.  SEVERE WEATHER POTENTIAL...WHILE NOT
NEGLIGIBLE...SEEMS LIKELY TO REMAIN LOW...BUT TRENDS WILL CONTINUE
TO BE MONITORED.

DISCUSSION...CIRCULATION AROUND A WEAK CLOSED LOW TO THE LEE OF THE
CENTRAL APPALACHIANS IS MAINTAINING AN AXIS OF HIGHER SURFACE DEW
POINTS ACROSS THE DELMARVA PENINSULA...WEST NORTHWESTWARD ACROSS
MUCH OF CENTRAL MARYLAND AND ADJACENT NORTH CENTRAL VIRGINIA.  THIS
IS ALSO NEAR THE NOSE OF STRONGER BOUNDARY LAYER HEATING/MIXING TO
THE LEE OF THE CENTRAL APPALACHIANS...WHERE SURFACE TEMPERATURE WILL
APPROACH 90F THIS AFTERNOON...AND MIXED LAYER CAPE IS ALSO EXCEEDING
1000 J/KG.

DEEPENING CONVECTIVE DEVELOPMENT IS ALREADY UNDERWAY IN RESPONSE TO
DESTABILIZATION...NEAR THE BLUE RIDGE AND HIGHER TERRAIN TO THE WEST
AND NORTH...WHICH IS EXPECTED TO CONTINUE TO INCREASE AND SLOWLY
INTENSIFY THROUGH 20-22Z.  STRONGER DEEP LAYER MEAN FLOW AND SHEAR
GENERALLY APPEARS TO ACCOMPANY A 500 MB JET STREAK GRADUALLY
SHIFTING NORTHEAST OF NORTHERN MID ATLANTIC COASTAL AREAS.
HOWEVER...20-25 KT WEST SOUTHWESTERLY DEEP LAYER MEAN FLOW PROBABLY
WILL ADVECT STORMS OFF THE HIGHER TERRAIN...ACROSS NORTH CENTRAL
VIRGINIA/CENTRAL MARYLAND...WHERE PRECIPITATION LOADING AND FURTHER
STEEPENING OF LOW-LEVEL LAPSE RATES MAY BE SUFFICIENT TO SUPPORT
LOCALIZED STRONG WIND GUSTS.  MARGINALLY SEVERE HAIL ALSO MAY NOT BE
OUT OF THE QUESTION.  HOWEVER... FORCING TO SUPPORT AN EXPANDING
STORM CLUSTER APPEARS WEAK...OR IS STILL UNCERTAIN AT THE PRESENT
TIME.  AND...EVEN WITH NEAR SURFACE FLOW REMAINING BACKED TO A
SOUTHEASTERLY COMPONENT ACROSS MUCH OF MARYLAND...LOW-LEVEL SHEAR IS
WEAK AND NOT LIKELY TO STRENGTHEN SUBSTANTIVELY AT LEAST THROUGH THE
AFTERNOON HOURS.

..KERR/CARBIN.. 08/14/2012

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

ATTN...WFO...PHI...AKQ...CTP...LWX...

LAT...LON   39007890 40327804 40207640 39267617 37927766 38047878
            38467927 39007890

Nearby

Mesoscale Discussions in Virginia, 2012 Mesoscale Discussions in Maryland, 2012 Mesoscale Discussions in Pennsylvania, 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.