Alert archive / Massachusetts / Mesoscale Discussions in 2012

Mesoscale Discussion 1941

September 8, 20124 states

The Storm Prediction Center issued this mesoscale discussion at Sep 8, 2012, 7:53 PM EDT for 4 states. It was in force for 97 min.

The area

The outline as issued.

The facts

Issued: Sep 8, 2012, 7:53 PM EDT (23:53 UTC)
Expired: Sep 8, 2012, 9:30 PM EDT
In force: 97 min
Issued by: the Storm Prediction Center

All 23 counties

Bristol County, MA, Dukes County, MA, Essex County, MA, Middlesex County, MA, Norfolk County, MA, Plymouth County, MA, Suffolk County, MA, Worcester County, MA, Androscoggin County, ME, Cumberland County, ME, Franklin County, ME, Kennebec County, ME, Oxford County, ME, Somerset County, ME, York County, ME, Belknap County, NH, Carroll County, NH, Hillsborough County, NH, Merrimack County, NH, Rockingham County, NH, Strafford County, NH, Bristol County, RI, Providence County, RI

The radar

The Portland,ME radar (KGYX), 24 km from the middle of the area, began a volume at 23:56 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 nearest sounding before it

Gray, ME (KGYX), launched 12:00Z, 11.9 hours before the alert went out and 23 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: 1021 J/kg
Mixed-layer CIN: -20 J/kg
Mixed-layer LCL: 466 m above ground
0-6 km bulk shear: 45 kt
0-1 km storm-relative helicity: 176 m²/s²
0-3 km storm-relative helicity: 216 m²/s²
Significant tornado parameter: 0.9
Supercell composite: 7.2

Open this sounding in Storm Lab

The text

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

281 
ACUS11 KWNS 082354
SWOMCD
SPC MCD 082353
MEZ000-MAZ000-NHZ000-RIZ000-CTZ000-090130-

MESOSCALE DISCUSSION 1941
NWS STORM PREDICTION CENTER NORMAN OK
0653 PM CDT SAT SEP 08 2012

AREAS AFFECTED...PORTIONS OF CT/MA/NH/RI TO WESTERN MAINE

CONCERNING...SEVERE THUNDERSTORM WATCH 639...

VALID 082353Z - 090130Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 639
CONTINUES.

SUMMARY...SEVERE TSTM WATCH 639 CONTINUES UNTIL 03Z. DAMAGING WIND
POTENTIAL WILL CONTINUE TO SPREAD ACROSS PORTIONS OF CT/MA/NH INTO
RI/WESTERN MAINE...BUT LIKELY ON AN INCREASINGLY MARGINAL/MORE
SPORADIC BASIS THROUGH MID EVENING. AN ADDITIONAL WATCH IS NOT
CURRENTLY ANTICIPATED TO THE EAST OF WW 639 INTO ADDITIONAL PARTS OF
MAINE.

DISCUSSION...A RELATIVELY LOW-TOPPED SQUALL LINE CONTINUES TO
STEADILY PROGRESS EASTWARD ACROSS CT/CENTRAL MA AND NH AS OF
2330Z...WITH THE MOST INTENSE PORTION OF THE LINE ACROSS SOUTHERN
NEW ENGLAND WHERE THE BOUNDARY LAYER REMAINS SLIGHTLY WARMER /AROUND
MIDDLE 70S F AS OF 23Z/ AND SOMEWHAT MORE UNSTABLE /AROUND 500 J PER
KG MLCAPE/. A 46 KT WIND GUST WAS RECENTLY /2309Z/ MEASURED AT
CHICOPEE-WESTOVER MA /KCEF/.

THE SQUALL LINE WILL CONTINUE TO POSE THE PRIMARY DAMAGING WIND
THREAT AS IT SPREADS EASTWARD TOWARD RI/EASTERN MA/WESTERN MAINE.
OTHER MORE ISOLATED SHOWERS/TSTMS HAVE SHOWN ROTATIONAL
CHARACTERISTICS AHEAD OF THE SQUALL LINE SINCE THIS AFTERNOON...BUT
THIS ACTIVITY SHOULD BE A WANING FACTOR AS THE BOUNDARY LAYER
CONTINUES TO COOL/CINH INCREASES. THESE SAME LOW-LEVEL THERMODYNAMIC
TRENDS SHOULD ACCOUNT FOR A GRADUAL LOSS OF UPDRAFT/DOWNDRAFT
INTENSITY WITHIN THE CONVECTIVE LINE OVER THE NEXT FEW HOURS...A
TREND PERHAPS ALREADY REFLECTED IN RECENT LIGHTNING DATA.
NEVERTHELESS...DAMAGING WINDS WILL NONETHELESS REMAIN POSSIBLE
ESPECIALLY ACROSS SOUTHERN NEW ENGLAND INCLUDING PORTIONS OF EASTERN
CT/EASTERN MA AND RI.

..GUYER.. 09/08/2012

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

ATTN...WFO...CAR...GYX...BOX...

LAT...LON   45437097 46196999 45396914 44666939 43067046 41987014
            41267062 42017232 43957144 45437097

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 8, 3:55 PM EDT	Mesoscale Discussion	SPC	Androscoggin, Cumberland, Oxford, York	65 min
Sep 8, 4:47 PM EDT	Severe Thunderstorm Watch	SPC	Androscoggin, Cumberland, Franklin, Kennebec, Oxford, Somerset and 1 more	6 hr
Sep 8, 10:39 AM EDT	Mesoscale Discussion	SPC	Berkshire, Franklin, Hampden, Hampshire	2 hr
Sep 8, 11:18 AM EDT	Tornado Watch	SPC	Hampden, Hampshire	10 hr
Sep 8, 12:40 PM EDT	Tornado Watch	SPC	Berkshire	7 hr
Sep 8, 1:30 PM EDT	Mesoscale Discussion	SPC	Berkshire, Hampden, Hampshire	60 min
Sep 8, 2:46 PM EDT	Mesoscale Discussion	SPC	Berkshire	59 min
Sep 8, 6:17 PM EDT	Mesoscale Discussion	SPC	Berkshire, Franklin	58 min

Nearby

Mesoscale Discussions in Massachusetts, 2012 Mesoscale Discussions in Maine, 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.