Alert archive / Vermont / Mesoscale Discussions in 2012

Mesoscale Discussion 1971

September 18, 20124 states

The Storm Prediction Center issued this mesoscale discussion at Sep 18, 2012, 4:41 PM EDT for 4 states. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Sep 18, 2012, 4:41 PM EDT (20:41 UTC)
Expired: Sep 18, 2012, 6:45 PM EDT
In force: 2 hr
Issued by: the Storm Prediction Center
Chance of a watch: 40%

All 22 counties

Franklin County, MA, Hampden County, MA, Hampshire County, MA, Middlesex County, MA, Norfolk County, MA, Worcester County, MA, Cheshire County, NH, Grafton County, NH, Hillsborough County, NH, Merrimack County, NH, Sullivan County, NH, Bristol County, RI, Kent County, RI, Providence County, RI, Washington County, RI, Caledonia County, VT, Lamoille County, VT, Orange County, VT, Rutland County, VT, Washington County, VT, Windham County, VT, Windsor County, VT

The radar

The Albany radar (KENX), 158 km from the middle of the area, began a volume at 20:41 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.

Severe Thunderstorm Watch 647Sep 18, 7:55 PM EDT

The nearest sounding before it

Albany, NY (KALY), launched 12:00Z, 8.7 hours before the alert went out and 136 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.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 2 J/kg
Mixed-layer CIN: -126 J/kg
Mixed-layer LCL: 572 m above ground
0-6 km bulk shear: 49 kt
0-1 km storm-relative helicity: 251 m²/s²
0-3 km storm-relative helicity: 226 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

054 
ACUS11 KWNS 182041
SWOMCD
SPC MCD 182041 
NHZ000-MAZ000-RIZ000-CTZ000-VTZ000-182245-

MESOSCALE DISCUSSION 1971
NWS STORM PREDICTION CENTER NORMAN OK
0341 PM CDT TUE SEP 18 2012

AREAS AFFECTED...A LARGE PART OF VT...WRN/SRN NH...A LARGE PART OF
MA...ERN CT...RI

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 182041Z - 182245Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...AREAS TO THE EAST OF WW 646 WILL BE MONITORED FOR THE
POSSIBLE ISSUANCE OF A WW LATER THIS AFTERNOON/EARLY EVENING.

DISCUSSION...WITH 0-1-KM BULK SHEAR INCREASING TO 40-55 KT OWING TO
A STRENGTHENING LOW-LEVEL JET STREAM...A CONDITIONAL SVR THREAT MAY
EVOLVE ACROSS PORTIONS OF NEW ENGLAND EAST OF WW 646.
HOWEVER...UNCERTAINTY AS TO WHETHER BOUNDARY-LAYER DESTABILIZATION
WILL BE SUFFICIENT FOR ANY SUBSTANTIAL SVR THREAT DOWNSTREAM OF WW
646 EXISTS...ESPECIALLY AS NOCTURNAL COOLING COMMENCES.
REGARDLESS...THE INFLUX OF RELATIVELY RICH LOW-LEVEL MOISTURE/WARMER
AIR MAY BE SUFFICIENT TO YIELD SOME THREAT FOR SVR WINDS AND PERHAPS
ONE OR TWO TORNADOES INTO THE EVENING HOURS...AS A SQUALL LINE
ARRIVES FROM THE WEST AND WAA-RELATED CONVECTION EVOLVES AHEAD OF
THE LINE. CONVECTIVE TRENDS WILL BE MONITORED FOR THE POTENTIAL
INCREASE IN BUOYANCY/SVR THREAT.

..COHEN/MEAD.. 09/18/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...GYX...BOX...BTV...OKX...ALY...

LAT...LON   44317308 44777282 44687206 43477159 41797104 41367158
            41457253 42797311 44317308

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 18, 11:14 AM EDT	Mesoscale Discussion	SPC		91 min
Sep 18, 3:26 PM EDT	Mesoscale Discussion	SPC		34 min
Sep 18, 3:38 PM EDT	Tornado Watch	SPC	Greater Bridgeport Planning Region, Northwest Hills Planning Region, Lower Connecticut River Valley Planning Region, Naugatuck Valley Planning Region, Southeastern Connecticut Planning Region	8 hr
Sep 18, 4:21 PM EDT	Mesoscale Discussion	SPC		114 min
Sep 18, 7:42 PM EDT	Mesoscale Discussion	SPC		63 min
Sep 18, 7:54 PM EDT	Severe Thunderstorm Watch	SPC	Capitol Planning Region, Northeastern Connecticut Planning Region	6 hr

Nearby

Mesoscale Discussions in Vermont, 2012 Mesoscale Discussions in Massachusetts, 2012 Mesoscale Discussions in New Hampshire, 2012 Every 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.