Alert archive / Maryland / Mesoscale Discussions in 2016

Mesoscale Discussion 1002

June 21, 20166 states

The Storm Prediction Center issued this mesoscale discussion at Jun 21, 2016, 12:00 PM EDT for 6 states. It was in force for 90 min.

The area

The outline as issued.

The facts

Issued: Jun 21, 2016, 12:00 PM EDT (16:00 UTC)
Expired: Jun 21, 2016, 1:30 PM EDT
In force: 90 min
Issued by: the Storm Prediction Center
Chance of a watch: 80%

All 49 counties

Kent County, DE, New Castle County, DE, Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Caroline County, MD, Carroll County, MD, Cecil 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, Queen Anne's County, MD, Talbot County, MD, Washington County, MD, Camden County, NJ, Cumberland County, NJ, Gloucester County, NJ, Salem County, NJ, Adams County, PA, Chester County, PA, Cumberland County, PA, Delaware County, PA, Franklin County, PA, Fulton County, PA, Lancaster County, PA, York County, PA, 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, Prince William County, VA, Rappahannock County, VA, Warren County, VA, Berkeley County, WV, Hampshire County, WV, Jefferson County, WV, Morgan County, WV

The radar

The Sterling radar (KLWX), 69 km from the middle of the area, began a volume at 16:02 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 278Jun 21, 1:05 PM EDT

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 4.0 hours before the alert went out and 67 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: 719 J/kg
Mixed-layer CIN: -132 J/kg
Mixed-layer LCL: 1478 m above ground
0-6 km bulk shear: 32 kt
0-1 km storm-relative helicity: 122 m²/s²
0-3 km storm-relative helicity: 143 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.2

Open this sounding in Storm Lab

The text

As transmitted.

194 
ACUS11 KWNS 211601
SWOMCD
SPC MCD 211600 
NJZ000-PAZ000-DEZ000-MDZ000-DCZ000-VAZ000-WVZ000-211730-

MESOSCALE DISCUSSION 1002
NWS STORM PREDICTION CENTER NORMAN OK
1100 AM CDT TUE JUN 21 2016

AREAS AFFECTED...PARTS OF SRN PENNSYLVANIA/NEW
JERSEY...MARYLAND/DELAWARE AND NRN VIRGINIA

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 

VALID 211600Z - 211730Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...INCREASING AND INTENSIFYING THUNDERSTORM ACTIVITY IS
EXPECTED ACROSS THE REGION...INCLUDING THE WASHINGTON D.C./BALTIMORE
METRO AREAS...BY MID AFTERNOON.  A SEVERE WEATHER WATCH IS LIKELY
WITHIN THE NEXT HOUR OR TWO.

DISCUSSION...THUNDERSTORMS HAVE INITIATED ALONG THE EASTERN SLOPES
OF THE ALLEGHENY MOUNTAINS...NEAR A SURFACE FRONT ACROSS SOUTHERN
PENNSYLVANIA...SOUTHWARD INTO PARTS OF NORTHWESTERN VIRGINIA.  A
DIVERGENT UPPER FLOW FIELD ON THE SOUTHERN PERIPHERY OF A BROAD
CLOSED LOW CENTERED NEAR HUDSON BAY APPEARS TO BE SUPPORTING
ACTIVITY...WHICH IS EXPECTED TO GRADUALLY INCREASE WHILE PROPAGATING
OFF THE HIGHER TERRAIN BETWEEN NOW AND 17-19Z.

A MOIST BOUNDARY LAYER /CHARACTERIZED BY SURFACE DEW POINTS OF 70F+/
ACROSS MUCH OF NORTHERN VIRGINIA INTO NORTHERN MID ATLANTIC COASTAL
AREAS IS DESTABILIZING WITH INSOLATION...WITH MIXED LAYER CAPE
ALREADY ESTIMATED ON THE ORDER OF 1500-2000 J/KG AND LOCALLY HIGHER.
 ALTHOUGH LOW/MID-LEVEL THERMAL LAPSE RATES ARE NOT PARTICULARLY
STEEP...SEASONABLY HIGH MOISTURE CONTENT PROBABLY WILL BECOME
INCREASING CONDUCIVE TO POTENTIAL FOR WET DOWNBURSTS WITH FURTHER
BOUNDARY LAYER HEATING THIS AFTERNOON.

BENEATH 40-50 KT WEST NORTHWESTERLY 500 MB FLOW...VERTICAL SHEAR
APPEARS MORE THAN SUFFICIENT FOR ORGANIZED CONVECTION.  THIS MAY
INCLUDE ISOLATED SUPERCELLS...WITH AT LEAST SOME POTENTIAL FOR
SEVERE HAIL.  THE EVOLUTION OF AN UPSCALE GROWING MESOSCALE
CONVECTIVE SYSTEM SEEMS POSSIBLE...WHICH COULD BE ACCOMPANIED BY
BROADER-SCALE DAMAGING WIND GUST POTENTIAL ACROSS THE
CHESAPEAKE/DELMARVA PENINSULA AREA BY LATE AFTERNOON.

..KERR/GUYER.. 06/21/2016

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

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

LAT...LON   40267803 40217689 40107573 39687462 38947498 38447598
            38547712 38577828 39107873 39947852 40267803

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jun 21, 1:06 PM EDT	Severe Thunderstorm Watch	SPC	Kent, New Castle, Sussex	9 hr
Jun 21, 6:30 PM EDT	Mesoscale Discussion	SPC	Kent, Sussex	90 min
Jun 21, 2:01 PM EDT	Severe Thunderstorm Watch	SPC	Garrett	8 hr
Jun 21, 3:34 PM EDT	Mesoscale Discussion	SPC	Calvert, Charles, Dorchester, Prince George's, Saint Mary's, Somerset and 1 more	86 min
Jun 21, 1:08 PM EDT	Mesoscale Discussion	SPC	Buchanan	97 min
Jun 21, 4:26 PM EDT	Mesoscale Discussion	SPC	Buchanan, Dickenson, Lee, Russell, Tazewell, Wise and 1 more	94 min

Nearby

Mesoscale Discussions in Maryland, 2016 Mesoscale Discussions in Virginia, 2016 Mesoscale Discussions in Pennsylvania, 2016 Every mesoscale discussion in 2016

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.