Alert archive / Massachusetts / Mesoscale Discussions in 2018

Mesoscale Discussion 1221

August 2, 2018Essex County, Middlesex County, Suffolk County, Massachusetts

The Storm Prediction Center issued this mesoscale discussion at Aug 2, 2018, 5:33 PM EDT for Essex County, Middlesex County, Suffolk County, Massachusetts. It was in force for 117 min.

The area

The outline as issued.

The facts

Issued: Aug 2, 2018, 5:33 PM EDT (21:33 UTC)
Expired: Aug 2, 2018, 7:30 PM EDT
In force: 117 min
Issued by: the Storm Prediction Center
Chance of a watch: 5%

Counties Essex County, MA, Middlesex County, MA, Suffolk County, MA

The radar

The Boston radar (KBOX), 54 km from the middle of the area, began a volume at 21:33 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

Chatham, MA (KCHH), launched 12:00Z, 9.6 hours before the alert went out and 146 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: 808 J/kg
Mixed-layer CIN: -140 J/kg
Mixed-layer LCL: 626 m above ground
0-6 km bulk shear: 29 kt
0-1 km storm-relative helicity: 44 m²/s²
0-3 km storm-relative helicity: 23 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.3

Open this sounding in Storm Lab

The text

As transmitted.

977 
ACUS11 KWNS 022134
SWOMCD
SPC MCD 022133 
MAZ000-NHZ000-022330-

Mesoscale Discussion 1221
NWS Storm Prediction Center Norman OK
0433 PM CDT Thu Aug 02 2018

Areas affected...Central and northeast MA

Concerning...Severe potential...Watch unlikely 

Valid 022133Z - 022330Z

Probability of Watch Issuance...5 percent

SUMMARY...Isolated strong/damaging wind gusts remain a threat across
central into northeast Massachusetts and extreme southeast New
Hampshire this evening (until 8 PM EDT), as storms track across this
region.

DISCUSSION...At 2130Z, mosaic radar imagery showed a band of storms
extending from south-central MA into central CT, tracking to the
northeast at 25 kt.  These storms were located in vicinity of a cold
front which extended from ME through central MA to western CT into
NJ and southeast PA.  The warm sector across central and eastern MA
is moderately unstable with effective bulk shear of 40-50 kt
oriented parallel to the front.  This should maintain the linear
structure, while steep surface to 3 km lapse rates and DCAPE
exceeding 1000 J/kg enhance the potential for locally strong wind
gusts.  Given the spatial limitations of this severe threat, a
severe thunderstorm watch is not warranted as storms will spread
across central into northeast MA and extreme southeast NH.

..Peters/Hart.. 08/02/2018

...Please see www.spc.noaa.gov for graphic product...

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

LAT...LON   42067206 42637174 42897084 42677065 42277099 42067191
            42067206

Nearby

Mesoscale Discussions in Massachusetts, 2018 Every mesoscale discussion in 2018

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.