Alert archive / Maine / Mesoscale Discussions in 2020

Mesoscale Discussion 1221

July 14, 20204 counties in Maine

The Storm Prediction Center issued this mesoscale discussion at Jul 14, 2020, 9:43 AM EDT for 4 counties in Maine. It was in force for 92 min.

The area

The outline as issued.

The facts

Issued: Jul 14, 2020, 9:43 AM EDT (13:43 UTC)
Expired: Jul 14, 2020, 11:15 AM EDT
In force: 92 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 5%

Counties Cumberland County, ME, Lincoln County, ME, Sagadahoc County, ME, York County, ME

The radar

The Portland,ME radar (KGYX), 36 km from the middle of the area, began a volume at 13:46 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, 1.7 hours before the alert went out and 36 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: 472 J/kg
Mixed-layer CIN: -108 J/kg
Mixed-layer LCL: 844 m above ground
0-6 km bulk shear: 28 kt
0-1 km storm-relative helicity: 51 m²/s²
0-3 km storm-relative helicity: 102 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.9

Open this sounding in Storm Lab

The text

As transmitted.

720 
ACUS11 KWNS 141343
SWOMCD
SPC MCD 141343 
MEZ000-141515-

Mesoscale Discussion 1221
NWS Storm Prediction Center Norman OK
0843 AM CDT Tue Jul 14 2020

Areas affected...The southern Maine Coastal Region.

Concerning...Severe potential...Watch unlikely 

Valid 141343Z - 141515Z

Probability of Watch Issuance...5 percent

SUMMARY...One or two strong to severe storms are likely to persist
through mid-day.

DISCUSSION...A strong storm has persisted across York county for the
last hour and is expected to persist as it moves northeastward. The
12Z GYX RAOB is a good proximity sounding for this storm and it
shows effective shear around 25 kts with around 1300 J/kg MUCAPE.
Moderately steep mid-level lapse rates of 7 C/km are also aiding
updraft acceleration and hail formation. Storm observations support
this with MRMS MESH suggesting hail of 1.75 to 2" and some updraft
rotation as of 1330Z. In addition, there have been a few reports of
wind damage and hail up to 0.75" thus far. Based on this sounding,
the storm is likely elevated, but some modest surface heating ahead
of this storm may allow it to become surface based relatively soon.
Modifying this 12Z RAOB for the current surface observation in
Portland, ME of 73/65 yields 800 J/kg MLCAPE and only 50 J/kg CINH.
Therefore, only a few more degrees of heating may erode inhibition
enough to allow this storm to become rooted in the boundary layer.
This storm, or additional development in its vicinity, is expected
to persist for a few hours along the southern Maine coast, where
breaks in the clouds have allowed for some surface heating, with a
threat for isolated large hail and damaging winds.

..Bentley/Guyer.. 07/14/2020

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

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

LAT...LON   43497087 43657071 43927032 44096989 44076950 43846936
            43616978 43457024 43287041 43247054 43257067 43297073
            43337083 43497087

Nearby

Mesoscale Discussions in Maine, 2020 Every mesoscale discussion in 2020

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.