Alert archive / Georgia / Mesoscale Discussions in 2017

Mesoscale Discussion 1640

September 11, 201711 counties in Florida; 12 counties in Georgia

The Storm Prediction Center issued this mesoscale discussion at Sep 11, 2017, 4:58 AM EDT for 11 counties in Florida; 12 counties in Georgia. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Sep 11, 2017, 4:58 AM EDT (08:58 UTC)
Expired: Sep 11, 2017, 7:00 AM EDT
In force: 2 hr
Issued by: the Storm Prediction Center

All 23 counties

Alachua County, FL, Baker County, FL, Bradford County, FL, Clay County, FL, Duval County, FL, Flagler County, FL, Marion County, FL, Nassau County, FL, Putnam County, FL, Saint Johns County, FL, Union County, FL, Brantley County, GA, Bryan County, GA, Camden County, GA, Charlton County, GA, Chatham County, GA, Glynn County, GA, Liberty County, GA, Long County, GA, McIntosh County, GA, Pierce County, GA, Ware County, GA, Wayne County, GA

The radar

The Jacksonville radar (KJAX), 27 km from the middle of the area, began a volume at 09:00 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

Jacksonville, FL (KJAX), launched 00:00Z, 9.0 hours before the alert went out and 29 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: 270 J/kg
Mixed-layer CIN: 0 J/kg
Mixed-layer LCL: 514 m above ground
0-6 km bulk shear: 39 kt
0-1 km storm-relative helicity: 282 m²/s²
0-3 km storm-relative helicity: 319 m²/s²
Significant tornado parameter: 0.4
Supercell composite: 2.9

Open this sounding in Storm Lab

The text

As transmitted.

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SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 10, 10:33 PM EDT	Mesoscale Discussion	SPC	Alachua, Baker, Bradford, Brevard, Charlotte, Citrus and 37 more	87 min
Sep 10, 11:50 PM EDT	Tornado Watch	SPC	Alachua, Baker, Bradford, Clay, Duval, Flagler and 5 more	14 hr
Sep 11, 8:49 AM EDT	Mesoscale Discussion	SPC	Baker, Duval, Nassau, Saint Johns	116 min
Sep 11, 1:46 PM EDT	Tornado Watch	SPC	Bryan, Bulloch, Burke, Candler, Chatham, Effingham and 7 more	10 hr

Nearby

Mesoscale Discussions in Georgia, 2017 Mesoscale Discussions in Florida, 2017 Every mesoscale discussion in 2017

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.