Alert archive / Maryland / Severe Thunderstorm Watches in 2017
Severe Thunderstorm Watch 448
The Storm Prediction Center issued this severe thunderstorm watch at Aug 12, 2017, 4:11 PM EDT for 13 counties in Maryland; 12 counties in Virginia; Berkeley County, Jefferson County, Morgan County, West Virginia. It was in force for 7 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 12, 2017, 4:11 PM EDT (20:11 UTC)
- Expired
- Aug 12, 2017, 10:51 PM EDT
- In force
- 7 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
All 28 counties
Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Carroll County, MD, Charles County, MD, City of Baltimore, MD, Frederick County, MD, Harford County, MD, Howard County, MD, Montgomery County, MD, Prince George's County, MD, Saint Mary's County, MD, Washington County, MD, Arlington County, VA, City of Alexandria, VA, City of Fairfax, VA, City of Falls Church, VA, City of Fredericksburg, VA, City of Manassas, VA, City of Manassas Park, VA, Fairfax County, VA, King George County, VA, Loudoun County, VA, Prince William County, VA, Stafford County, VA, Berkeley County, WV, Jefferson County, WV, Morgan County, WV
The radar
The Sterling radar (KLWX), 38 km from the middle of the area, began a volume at 20:10 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
- 10%
- One or more EF2 to EF5 tornadoes
- 2%
- Ten or more severe wind reports
- 30%
- One or more gusts of 65 knots or more
- 10%
- Ten or more severe hail reports
- 30%
- One or more hailstones of 2 inches or more
- 10%
- Six or more combined severe hail and wind reports
- 70%
Warnings issued inside it
8 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 12, 5:00 PM EDT | Severe Thunderstorm Warning | LWX | Frederick, Washington | 45 min |
| Aug 12, 5:56 PM EDT | Severe Thunderstorm Warning | LWX | Carroll, Frederick, Howard, Montgomery | 49 min |
| Aug 12, 5:58 PM EDT | Severe Thunderstorm Warning | LWX | Frederick, Montgomery | 47 min |
| Aug 12, 6:30 PM EDT | Severe Thunderstorm Warning | LWX | Montgomery | 17 min |
| Aug 12, 7:19 PM EDT | Severe Thunderstorm Warning | LWX | Anne Arundel, Baltimore, Howard, City of Baltimore | 41 min |
| Aug 12, 7:32 PM EDT | Severe Thunderstorm Warning | LWX | Montgomery, Prince George's | 43 min |
| Aug 12, 7:56 PM EDT | Severe Thunderstorm Warning | LWX | Anne Arundel | 49 min |
| Aug 12, 8:09 PM EDT | Severe Thunderstorm Warning | LWX | Anne Arundel, Calvert, Prince George's | 66 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, 8.2 hours before the alert went out and 36 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
- 248 J/kg
- Mixed-layer CIN
- -78 J/kg
- Mixed-layer LCL
- 772 m above ground
- 0-6 km bulk shear
- 42 kt
- 0-1 km storm-relative helicity
- 12 m²/s²
- 0-3 km storm-relative helicity
- 78 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 12, 5:17 PM EDT | Mesoscale Discussion | SPC | Baltimore, Carroll, Cecil, Frederick, Harford, Howard and 2 more | 88 min |
Nearby
Severe Thunderstorm Watches in Maryland, 2017Severe Thunderstorm Watches in Virginia, 2017Severe Thunderstorm Watches in West Virginia, 2017Every severe thunderstorm watch in 2017
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.