Alert archive / Virginia / Mesoscale Discussions in 2012
Mesoscale Discussion 2000
The Storm Prediction Center issued this mesoscale discussion at Sep 27, 2012, 6:16 PM EDT for 6 counties in Maryland; 14 counties in Virginia; Jefferson County, West Virginia. It was in force for 29 min.
The area
The outline as issued.
The facts
- Issued
- Sep 27, 2012, 6:16 PM EDT (22:16 UTC)
- Expired
- Sep 27, 2012, 6:45 PM EDT
- In force
- 29 min
- Issued by
- the Storm Prediction Center
- Chance of a watch
- 80%
All 21 counties
Anne Arundel County, MD, City of Baltimore, MD, Frederick County, MD, Howard County, MD, Montgomery County, MD, Prince George's County, MD, Arlington County, VA, City of Alexandria, VA, City of Fairfax, VA, City of Falls Church, VA, City of Manassas, VA, City of Manassas Park, VA, City of Winchester, VA, Clarke County, VA, Fairfax County, VA, Fauquier County, VA, Loudoun County, VA, Prince William County, VA, Rappahannock County, VA, Warren County, VA, Jefferson County, WV
The radar
The Sterling radar (KLWX), 6 km from the middle of the area, began a volume at 22:18 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 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, 10.3 hours before the alert went out and 14 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
- 392 J/kg
- Mixed-layer CIN
- -100 J/kg
- Mixed-layer LCL
- 938 m above ground
- 0-6 km bulk shear
- 25 kt
- 0-1 km storm-relative helicity
- -32 m²/s²
- 0-3 km storm-relative helicity
- 46 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.4
The text
As transmitted, in the capitals the NWS used until 2016.
835
ACUS11 KWNS 272217
SWOMCD
SPC MCD 272216
MDZ000-DCZ000-VAZ000-WVZ000-272245-
MESOSCALE DISCUSSION 2000
NWS STORM PREDICTION CENTER NORMAN OK
0516 PM CDT THU SEP 27 2012
AREAS AFFECTED...NRN VA INTO MD INCLUDING PARTS OF THE DC AND
BALTIMORE METRO AREAS
CONCERNING...SEVERE POTENTIAL...WATCH LIKELY
VALID 272216Z - 272245Z
PROBABILITY OF WATCH ISSUANCE...80 PERCENT
SUMMARY...A SEVERE TSTM WATCH WILL BE COORDINATED SHORTLY ACROSS NRN
VA INTO MD INCLUDING PARTS OF THE WASHINGTON DC AND BALTIMORE METRO
AREAS.
DISCUSSION...AT 22Z...MESOSCALE ANALYSIS SHOWED AN OUTFLOW BOUNDARY
EXTENDING FROM FAR NRN VA EWD TO INVOF WASHINGTON DC. THE AIR MASS
IN THIS REGION IS MODERATELY UNSTABLE WITH EFFECTIVE BULK SHEAR OF
30-35 KT WHICH IS SUFFICIENT FOR ORGANIZED STORM STRUCTURES
INCLUDING SUPERCELLS AS HAVE BEEN OBSERVED OVER NRN VA THUS FAR.
THIS TREND IS EXPECTED TO CONTINUE FOR ADDITIONAL STORMS...SOME
STRONG TO SEVERE...AS THE PROGRESSIVE SHORTWAVE TROUGH OVER WRN PA
ADVANCES EWD AIDING IN SUSTAINED UPDRAFTS.
..PETERS/CARBIN.. 09/27/2012
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...LWX...
LAT...LON 38847845 39377812 39517718 39377642 38987641 38667655
38587811 38627837 38847845SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 27, 3:18 PM EDT | Mesoscale Discussion | SPC | Baltimore, Carroll, Frederick, Howard, Montgomery, Prince George's and 2 more | 117 min |
| Sep 27, 6:36 PM EDT | Severe Thunderstorm Watch | SPC | Anne Arundel, Calvert, Charles, Howard, Montgomery, Prince George's and 1 more | 5 hr |
Nearby
Mesoscale Discussions in Virginia, 2012Mesoscale Discussions in Maryland, 2012Mesoscale Discussions in West Virginia, 2012Every mesoscale discussion in 2012
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.