Alert archive / Maine / Mesoscale Discussions in 2021

Mesoscale Discussion 1135

June 30, 202110 counties in Maine; 7 counties in New Hampshire

The Storm Prediction Center issued this mesoscale discussion at Jun 30, 2021, 4:16 PM EDT for 10 counties in Maine; 7 counties in New Hampshire. It was in force for 89 min.

The area

The outline as issued.

The facts

Issued: Jun 30, 2021, 4:16 PM EDT (20:16 UTC)
Expired: Jun 30, 2021, 5:45 PM EDT
In force: 89 min
Issued by: the Storm Prediction Center
Concerning: Severe thunderstorm watch 326

Counties Androscoggin County, ME, Cumberland County, ME, Hancock County, ME, Kennebec County, ME, Knox County, ME, Lincoln County, ME, Sagadahoc County, ME, Waldo County, ME, Washington County, ME, York County, ME, Belknap County, NH, Carroll County, NH, Cheshire County, NH, Hillsborough County, NH, Merrimack County, NH, Rockingham County, NH, Strafford County, NH

The radar

The Portland,ME radar (KGYX), 25 km from the middle of the area, began a volume at 20:20 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, 8.3 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.

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: 906 J/kg
Mixed-layer CIN: -60 J/kg
Mixed-layer LCL: 1312 m above ground
0-6 km bulk shear: 33 kt
0-1 km storm-relative helicity: 95 m²/s²
0-3 km storm-relative helicity: 102 m²/s²
Significant tornado parameter: 0.2
Supercell composite: 1.3

Open this sounding in Storm Lab

The text

As transmitted.

412 
ACUS11 KWNS 302016
SWOMCD
SPC MCD 302016 
MEZ000-NHZ000-302145-

Mesoscale Discussion 1135
NWS Storm Prediction Center Norman OK
0316 PM CDT Wed Jun 30 2021

Areas affected...Portions of southern NH and coastal ME

Concerning...Severe Thunderstorm Watch 326...

Valid 302016Z - 302145Z

The severe weather threat for Severe Thunderstorm Watch 326
continues.

SUMMARY...The greatest near-term severe threat across Severe
Thunderstorm Watch 326 should remain across parts of southern New
Hampshire and coastal Maine this afternoon.

DISCUSSION...A narrow corridor of moderate instability (MLCAPE of
1500 J/kg) remains present generally ahead of ongoing storms across
parts of southern NH and coastal ME. Recent VWP from KGYX shows
strong flow remains present in the 4-8 km layer AGL, with around
40-50 kt of westerly winds estimated. Convection has shown signs of
continued organization with around 40 kt of effective bulk shear,
and a mix of marginal supercells and multicells has been observed
over the past couple of hours. Occasional severe hail and strong to
locally damaging winds are expected to to remain the primary severe
threat as storms continue to move eastward towards the coast. The
greatest damaging wind threat may focus with a small cluster of
storms moving eastward across southern NH and vicinity, as low-level
lapse rates are steepest there.

..Gleason.. 06/30/2021

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

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

LAT...LON   42787248 43217233 43657167 44557001 44916908 45246733
            45056695 44786694 44486749 44076890 43537021 42937076
            42857114 42747150 42787248

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jun 30, 11:04 AM EDT	Mesoscale Discussion	SPC	Androscoggin, Cumberland, Franklin, Hancock, Kennebec, Knox and 8 more	116 min
Jun 30, 12:06 PM EDT	Severe Thunderstorm Watch	SPC	Androscoggin, Cumberland, Franklin, Hancock, Kennebec, Knox and 9 more	7 hr
Jun 30, 1:52 PM EDT	Mesoscale Discussion	SPC	Androscoggin, Cumberland, Oxford	83 min

Nearby

Mesoscale Discussions in Maine, 2021 Mesoscale Discussions in New Hampshire, 2021 Every mesoscale discussion in 2021

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.