Alert archive / Virginia / Mesoscale Discussions in 2012
Mesoscale Discussion 1998
The Storm Prediction Center issued this mesoscale discussion at Sep 27, 2012, 3:18 PM EDT for 8 counties in Maryland; 18 counties in Virginia; Berkeley County, Jefferson County, West Virginia. It was in force for 117 min.
The area
The outline as issued.
The facts
- Issued
- Sep 27, 2012, 3:18 PM EDT (19:18 UTC)
- Expired
- Sep 27, 2012, 5:15 PM EDT
- In force
- 117 min
- Issued by
- the Storm Prediction Center
- Chance of a watch
- 20%
All 28 counties
Baltimore County, MD, Carroll County, MD, City of Baltimore, MD, Frederick County, MD, Howard County, MD, Montgomery County, MD, Prince George's County, MD, Washington 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, Culpeper County, VA, Fairfax County, VA, Fauquier County, VA, Loudoun County, VA, Madison County, VA, Page County, VA, Prince William County, VA, Rappahannock County, VA, Stafford County, VA, Warren County, VA, Berkeley County, WV, Jefferson County, WV
The radar
The Sterling radar (KLWX), 19 km from the middle of the area, began a volume at 19:18 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, 7.3 hours before the alert went out and 25 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.
964
ACUS11 KWNS 271918
SWOMCD
SPC MCD 271918
MDZ000-PAZ000-DCZ000-VAZ000-WVZ000-272115-
MESOSCALE DISCUSSION 1998
NWS STORM PREDICTION CENTER NORMAN OK
0218 PM CDT THU SEP 27 2012
AREAS AFFECTED...NRN VA THROUGH NRN MD AND EXTREME SRN PA
CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY
VALID 271918Z - 272115Z
PROBABILITY OF WATCH ISSUANCE...20 PERCENT
SUMMARY...STORMS ARE EXPECTED TO INCREASE IN COVERAGE FROM NRN VA
THROUGH NRN MD AND EXTREME SRN PA THIS AFTERNOON. A FEW MULTICELLS
MIGHT BECOME CAPABLE OF ISOLATED STRONG TO DAMAGING WIND GUSTS...BUT
AT THIS TIME OVERALL THREAT DOES NOT APPEAR SUFFICIENT TO WARRANT A
WW.
DISCUSSION...THIS AFTERNOON A QUASI-STATIONARY FRONT STRETCHES FROM
SRN NJ WWD TO NRN MD...CNTRL OH AND BEYOND. SOUTH OF THIS FRONT AND
EAST OF THE CNTRL APPALACHIANS...DIABATIC WARMING OF THE BOUNDARY
LAYER HAS BOOSTED MLCAPE TO BETWEEN 1000-1500 J/KG. MAGNITUDE OF
INSTABILITY WILL LIKELY REMAIN AOB 1500 J/KG DUE TO RELATIVELY WEAK
MID LEVEL LAPSE RATES. COMBINATION OF OROGRAPHIC FORCING AND DEEPER
ASCENT DOWNSTREAM FROM VORT MAX ADVANCING EWD THROUGH THE OH VALLEY
WILL CONTINUE TO PROMOTE STORMS DEVELOPING OVER THE HIGHER TERRAIN
OF NWRN VA. ACTIVITY WILL SUBSEQUENTLY MOVE THROUGH NRN PORTIONS OF
THE WARM SECTOR...POSSIBLY INTERACTING WITH THE STATIONARY FRONT.
THIS REGION IS EMBEDDED WITHIN WEAK LOW LEVEL WINDS...BUT MODEST 30
KT WLY FLOW ALOFT AND EFFECTIVE SHEAR AOB 35 KT. SHEAR/INSTABILITY
PARAMETER SPACE MAY PROMOTE A FEW SUSTAINED MULTICELL STORMS THAT
MIGHT BECOME CAPABLE OF PRODUCING LOCALLY STRONG TO DAMAGING GUSTS
AS LOW LEVEL LAPSE RATES STEEPEN.
..DIAL/MEAD.. 09/27/2012
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...CTP...LWX...
LAT...LON 39727788 39927695 39667637 38897670 38367750 38287838
38637861 39727788SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 27, 6:16 PM EDT | Mesoscale Discussion | SPC | Anne Arundel, Frederick, Howard, Montgomery, Prince George's, City of Baltimore | 29 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.