Alert archive / Virginia / Mesoscale Discussions in 2017
Mesoscale Discussion 1739
The Storm Prediction Center issued this mesoscale discussion at Oct 23, 2017, 4:58 PM EDT for 25 counties in Virginia. It was in force for 92 min.
The area
The outline as issued.
The facts
- Issued
- Oct 23, 2017, 4:58 PM EDT (20:58 UTC)
- Expired
- Oct 23, 2017, 6:30 PM EDT
- In force
- 92 min
- Issued by
- the Storm Prediction Center
- Chance of a watch
- 40%
All 25 counties
Amherst County, VA, Appomattox County, VA, Bedford County, VA, Botetourt County, VA, Campbell County, VA, Carroll County, VA, Charlotte County, VA, City of Buena Vista, VA, City of Danville, VA, City of Galax, VA, City of Lynchburg, VA, City of Martinsville, VA, City of Radford, VA, City of Roanoke, VA, City of Salem, VA, Craig County, VA, Floyd County, VA, Franklin County, VA, Halifax County, VA, Henry County, VA, Montgomery County, VA, Patrick County, VA, Pittsylvania County, VA, Pulaski County, VA, Roanoke County, VA
The radar
The Roanoke radar (KFCX), 39 km from the middle of the area, began a volume at 20:59 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
Roanoke, VA (KRNK), launched 12:00Z, 9.0 hours before the alert went out and 33 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
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 2764 m above ground
- 0-6 km bulk shear
- 54 kt
- 0-1 km storm-relative helicity
- -65 m²/s²
- 0-3 km storm-relative helicity
- -202 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
954
ACUS11 KWNS 232059
SWOMCD
SPC MCD 232058
VAZ000-NCZ000-232230-
Mesoscale Discussion 1739
NWS Storm Prediction Center Norman OK
0358 PM CDT Mon Oct 23 2017
Areas affected...portions of southern VA
Concerning...Severe potential...Watch possible
Valid 232058Z - 232230Z
Probability of Watch Issuance...40 percent
SUMMARY...Severe threat may spread into portions of southern VA in
the next 1-2 hours. Given a lack of stronger instability, confidence
is low in convection maintaining organized severe threat. Trends
will be monitored closely for possible watch issuance in the next
hour or so.
DISCUSSION...The bowing segment of line of convection moving east
across western NC will continue to track northeast late this
afternoon. Several severe and tornado reports have been associated
with this convection across western NC and portions of Upstate SC.
However, it is uncertain how far northeast severe potential will be
maintained given very weak instability across southern VA where
surface heating has not been as strong and surface dewpoints are
lower than further to the southwest. That being said, strong deep
layer shear profiles could support strong wind gusts and perhaps
some rotating structures if the surging line can maintain
organization. This area will be monitored closely for possible watch
issuance by 22z.
..Leitman/Thompson.. 10/23/2017
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...AKQ...LWX...RAH...RNK...
LAT...LON 36658100 36968095 37328055 37618000 37737970 37797937
37667883 37407853 37017860 36647891 36477920 36528037
36518072 36658100SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Oct 23, 5:40 PM EDT | Tornado Watch | SPC | Amelia, Amherst, Appomattox, Augusta, Bedford, Botetourt and 38 more | 8 hr |
| Oct 23, 7:34 PM EDT | Mesoscale Discussion | SPC | Albemarle, Amelia, Amherst, Appomattox, Augusta, Bath and 25 more | 116 min |
Nearby
Mesoscale Discussions in 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.