Alert archive / Pennsylvania / Severe Thunderstorm Watches in 2018
Severe Thunderstorm Watch 346
The Storm Prediction Center issued this severe thunderstorm watch at Aug 21, 2018, 2:41 PM EDT for 4 states. It was in force for 7 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 21, 2018, 2:41 PM EDT (18:41 UTC)
- Expired
- Aug 21, 2018, 9:19 PM EDT
- In force
- 7 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1 in
- Strongest gust expected
- 60 kt
All 50 counties
Allegany County, MD, Carroll County, MD, Frederick County, MD, Garrett County, MD, Washington County, MD, Adams County, PA, Armstrong County, PA, Bedford County, PA, Blair County, PA, Cambria County, PA, Centre County, PA, Clarion County, PA, Clearfield County, PA, Cumberland County, PA, Dauphin County, PA, Fayette County, PA, Franklin County, PA, Fulton County, PA, Huntingdon County, PA, Indiana County, PA, Jefferson County, PA, Juniata County, PA, Mifflin County, PA, Perry County, PA, Somerset County, PA, Westmoreland County, PA, York County, PA, City of Harrisonburg, VA, City of Winchester, VA, Clarke County, VA, Fauquier County, VA, Frederick County, VA, Greene County, VA, Loudoun County, VA, Madison County, VA, Page County, VA, Rappahannock County, VA, Rockingham County, VA, Shenandoah County, VA, Warren County, VA, Berkeley County, WV, Grant County, WV, Hampshire County, WV, Hardy County, WV, Jefferson County, WV, Mineral County, WV, Morgan County, WV, Pendleton County, WV, Preston County, WV, Tucker County, WV
The radar
The State College radar (KCCX), 92 km from the middle of the area, began a volume at 18:44 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.
What SPC expected
The probabilities SPC published with the watch, for the watch area over its life.
- Two or more tornadoes
- 20%
- One or more EF2 to EF5 tornadoes
- 10%
- Ten or more severe wind reports
- 50%
- One or more gusts of 65 knots or more
- 20%
- Ten or more severe hail reports
- 5%
- One or more hailstones of 2 inches or more
- 5%
- Six or more combined severe hail and wind reports
- 70%
Warnings issued inside it
21 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 21, 2:55 PM EDT | Tornado Warning | CTP | Bedford, Somerset | 50 min |
| Aug 21, 3:00 PM EDT | Severe Thunderstorm Warning | LWX | Allegany | 45 min |
| Aug 21, 3:11 PM EDT | Severe Thunderstorm Warning | PBZ | Jefferson | 34 min |
| Aug 21, 3:12 PM EDT | Severe Thunderstorm Warning | CTP | Bedford, Fulton, Somerset | 63 min |
| Aug 21, 3:13 PM EDT | Severe Thunderstorm Warning | LWX | Allegany | 47 min |
| Aug 21, 3:32 PM EDT | Tornado Warning | LWX | Allegany | 28 min |
| Aug 21, 3:43 PM EDT | Severe Thunderstorm Warning | LWX | Allegany, Washington | 47 min |
| Aug 21, 3:56 PM EDT | Severe Thunderstorm Warning | LWX | Hampshire, Mineral | 49 min |
| Aug 21, 3:59 PM EDT | Severe Thunderstorm Warning | LWX | Allegany, Washington | 34 min |
| Aug 21, 4:15 PM EDT | Severe Thunderstorm Warning | CTP | Bedford, Franklin, Fulton, Huntingdon | 45 min |
| Aug 21, 4:32 PM EDT | Severe Thunderstorm Warning | LWX | Frederick | 43 min |
| Aug 21, 5:12 PM EDT | Severe Thunderstorm Warning | LWX | Washington | 48 min |
| Aug 21, 5:52 PM EDT | Severe Thunderstorm Warning | LWX | Washington | 38 min |
| Aug 21, 6:09 PM EDT | Severe Thunderstorm Warning | LWX | Frederick, Washington | 51 min |
| Aug 21, 6:22 PM EDT | Severe Thunderstorm Warning | LWX | Clarke, Frederick | 38 min |
| Aug 21, 6:59 PM EDT | Severe Thunderstorm Warning | LWX | Frederick, Washington | 46 min |
| Aug 21, 7:13 PM EDT | Flash Flood Warning | PBZ | Armstrong, Clarion, Indiana, Jefferson | 3 hr |
| Aug 21, 7:58 PM EDT | Severe Thunderstorm Warning | LWX | Frederick, Shenandoah, Warren | 47 min |
| Aug 21, 8:02 PM EDT | Tornado Warning | PBZ | Jefferson | 28 min |
| Aug 21, 8:02 PM EDT | Severe Thunderstorm Warning | LWX | Frederick, Shenandoah, City of Winchester | 43 min |
| Aug 21, 8:25 PM EDT | Severe Thunderstorm Warning | LWX | Washington | 50 min |
Discussions around it
SPC mesoscale discussions over the same counties from four hours before the watch to its end.
The nearest sounding before it
Washington/Dulle, VA (KIAD), launched 12:00Z, 6.7 hours before the alert went out and 143 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.
- Mixed-layer CAPE
- 187 J/kg
- Mixed-layer CIN
- -22 J/kg
- Mixed-layer LCL
- 597 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
- 183 m²/s²
- Significant tornado parameter
- 0.1
- Supercell composite
- 0.6
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 21, 2:16 PM EDT | Mesoscale Discussion | SPC | Allegany, Garrett | 119 min |
| Aug 21, 4:56 PM EDT | Mesoscale Discussion | SPC | Allegany, Carroll, Frederick, Garrett, Montgomery, Washington | 2 hr |
| Aug 21, 5:03 PM EDT | Mesoscale Discussion | SPC | Charles, Saint Mary's | 117 min |
| Aug 21, 7:06 PM EDT | Mesoscale Discussion | SPC | Anne Arundel, Baltimore, Carroll, Cecil, Frederick, Harford and 7 more | 84 min |
| Aug 21, 12:45 PM EDT | Mesoscale Discussion | SPC | Fayette, Greene, Washington, Westmoreland | 3 hr |
Nearby
Severe Thunderstorm Watches in Pennsylvania, 2018Severe Thunderstorm Watches in Virginia, 2018Severe Thunderstorm Watches in West Virginia, 2018Every severe thunderstorm watch in 2018
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.