Alert archive / Virginia / Mesoscale Discussions in 2017
Mesoscale Discussion 1621
The Storm Prediction Center issued this mesoscale discussion at Sep 5, 2017, 2:31 PM EDT for 4 states. It was in force for 59 min.
The area
The outline as issued.
The facts
- Issued
- Sep 5, 2017, 2:31 PM EDT (18:31 UTC)
- Expired
- Sep 5, 2017, 3:30 PM EDT
- In force
- 59 min
- Issued by
- the Storm Prediction Center
- Chance of a watch
- 40%
All 38 counties
Carroll County, MD, Frederick County, MD, Howard County, MD, Montgomery County, MD, Washington County, MD, Adams County, PA, Cumberland County, PA, Dauphin County, PA, Franklin County, PA, Fulton County, PA, Juniata County, PA, Lebanon County, PA, Perry County, PA, York County, PA, City of Fairfax, VA, City of Harrisonburg, VA, City of Manassas, VA, City of Manassas Park, VA, City of Winchester, VA, Clarke County, VA, Culpeper County, VA, Fauquier County, VA, Frederick County, VA, Greene County, VA, Loudoun County, VA, Madison County, VA, Page County, VA, Prince William County, VA, Rappahannock County, VA, Rockingham County, VA, Shenandoah County, VA, Warren County, VA, Berkeley County, WV, Hampshire County, WV, Hardy County, WV, Jefferson County, WV, Morgan County, WV, Pendleton County, WV
The radar
The Sterling radar (KLWX), 59 km from the middle of the area, began a volume at 18:33 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.
The nearest sounding before it
Washington/Dulle, VA (KIAD), launched 12:00Z, 6.5 hours before the alert went out and 66 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
- 4 J/kg
- Mixed-layer CIN
- -324 J/kg
- Mixed-layer LCL
- 1529 m above ground
- 0-6 km bulk shear
- 40 kt
- 0-1 km storm-relative helicity
- 8 m²/s²
- 0-3 km storm-relative helicity
- 79 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
484
ACUS11 KWNS 051831
SWOMCD
SPC MCD 051831
PAZ000-MDZ000-VAZ000-WVZ000-051930-
Mesoscale Discussion 1621
NWS Storm Prediction Center Norman OK
0131 PM CDT Tue Sep 05 2017
Areas affected...Eastern WV Panhandle...northern VA...portion of
western MD Panhandle into northwest MD
Concerning...Severe potential...Watch possible
Valid 051831Z - 051930Z
Probability of Watch Issuance...40 percent
SUMMARY...A broken band of storms extending from northeast WV
through the western MD Panhandle into south-central PA could produce
locally strong to damaging winds, as they advance east into the
Shenandoah and Cumberland Valleys and the piedmont regions of
northern VA to south-central/southeast PA.
DISCUSSION...Early-mid afternoon objective analyses indicated the
environment east of the higher terrain from northern VA to
south-central/southeast PA has become moderately unstable owing to
stronger surface heating and dew points in the 60s. Radar imagery
indicated a broken band of storms continued to develop and
strengthen some in intensity along a cold front moving across the
Appalachians this afternoon from eastern WV to central PA. These
storms could become stronger as they advance east into the corridor
of stronger instability, effective bulk shear of 40-50 kt, and
steeper low-level lapse rates, with the potential for isolated
strong to damaging wind gusts.
..Peters/Thompson.. 09/05/2017
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...CTP...LWX...
LAT...LON 39117699 38667746 38357797 38217848 38267901 38627942
38977932 39367885 39917829 40157807 40387772 40617733
40547682 40477642 40237631 39117699SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 5, 3:26 PM EDT | Severe Thunderstorm Watch | SPC | Baltimore, Carroll, Cecil, Frederick, Harford, Howard and 3 more | 5 hr |
| Sep 5, 5:00 PM EDT | Mesoscale Discussion | SPC | Baltimore, Carroll, Cecil, Harford, Howard, Kent and 2 more | 90 min |
| Sep 4, 10:26 PM EDT | Mesoscale Discussion | SPC | Erie | 64 min |
Nearby
Mesoscale Discussions in Virginia, 2017Mesoscale Discussions in Pennsylvania, 2017Mesoscale Discussions in West Virginia, 2017Every mesoscale discussion 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.