Alert archive / Pennsylvania / Mesoscale Discussions in 2015

Mesoscale Discussion 408

April 20, 20154 states

The Storm Prediction Center issued this mesoscale discussion at Apr 20, 2015, 9:17 PM EDT for 4 states. It was in force for 88 min.

The area

The outline as issued.

The facts

Issued: Apr 20, 2015, 9:17 PM EDT (01:17 UTC)
Expired: Apr 20, 2015, 10:45 PM EDT
In force: 88 min
Issued by: the Storm Prediction Center

All 35 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, Charles County, MD, City of Baltimore, MD, Harford County, MD, Kent County, MD, Prince George's County, MD, Queen Anne's County, MD, Talbot County, MD, Cumberland County, NJ, Salem County, NJ, Adams County, PA, Berks County, PA, Chester County, PA, Columbia County, PA, Cumberland County, PA, Dauphin County, PA, Delaware County, PA, Juniata County, PA, Lancaster County, PA, Lebanon County, PA, Montgomery County, PA, Montour County, PA, Northumberland County, PA, Perry County, PA, Schuylkill County, PA, Snyder County, PA, Union County, PA, York County, PA

The radar

The Sterling radar (KLWX), 108 km from the middle of the area, began a volume at 01:18 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 00:00Z, 1.3 hours before the alert went out and 105 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: 460 J/kg
Mixed-layer CIN: -29 J/kg
Mixed-layer LCL: 1835 m above ground
0-6 km bulk shear: 47 kt
0-1 km storm-relative helicity: 176 m²/s²
0-3 km storm-relative helicity: 177 m²/s²
Significant tornado parameter: 0.1
Supercell composite: 3.2

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
Apr 20, 10:34 PM EDT	Mesoscale Discussion	SPC	Sussex, Warren	86 min

Nearby

Mesoscale Discussions in Pennsylvania, 2015 Mesoscale Discussions in Maryland, 2015 Mesoscale Discussions in Delaware, 2015 Every mesoscale discussion in 2015

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.