Alert archive / Florida / Mesoscale Discussions in 2021

Mesoscale Discussion 1720

September 8, 202110 counties in Florida; 4 counties in Georgia

The Storm Prediction Center issued this mesoscale discussion at Sep 8, 2021, 10:37 PM EDT for 10 counties in Florida; 4 counties in Georgia. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Sep 8, 2021, 10:37 PM EDT (02:37 UTC)
Expired: Sep 9, 2021, 1:00 AM EDT
In force: 2 hr
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 5%

Counties Dixie County, FL, Gadsden County, FL, Hamilton County, FL, Jefferson County, FL, Lafayette County, FL, Leon County, FL, Madison County, FL, Suwannee County, FL, Taylor County, FL, Wakulla County, FL, Brooks County, GA, Grady County, GA, Lowndes County, GA, Thomas County, GA

The radar

The Tallahassee radar (KTLH), 54 km from the middle of the area, began a volume at 02:38 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

Tallahassee Rgnl, FL (KTLH), launched 00:00Z, 2.6 hours before the alert went out and 52 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: 35 J/kg
Mixed-layer CIN: -78 J/kg
Mixed-layer LCL: 965 m above ground
0-6 km bulk shear: 27 kt
0-1 km storm-relative helicity: 94 m²/s²
0-3 km storm-relative helicity: 129 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.2

Open this sounding in Storm Lab

The text

As transmitted.

618 
ACUS11 KWNS 090238
SWOMCD
SPC MCD 090237 
GAZ000-FLZ000-090500-

Mesoscale Discussion 1720
NWS Storm Prediction Center Norman OK
0937 PM CDT Wed Sep 08 2021

Areas affected...parts of the Florida Panhandle into extreme
southern Georgia

Concerning...Severe potential...Watch unlikely 

Valid 090237Z - 090500Z

Probability of Watch Issuance...5 percent

SUMMARY...A brief tornado may accompany any stronger, sustained
storm that manages to form. However, the severe threat is expected
to be quite brief and localized, and a WW issuance is not expected.

DISCUSSION...Tropical Storm Mindy has recently made landfall along
the FL panhandle coastline, with convective bands continuing to
pivot around the center within the northeast quadrant of the
cyclone. While a brief uptick in convective intensity was noted
earlier (including the possibility of a tornado in Wakulla County,
FL nearly 90 minutes ago), convection within the bands has more
recently waned in intensity. 02Z mesoanalysis shows up to 40 kts of
effective bulk shear within the northeast quadrant of Mindy, with
the TLH 0154Z VWP showing over 200 m2/s2 of 0-3km SRH. However, the
TLH 00Z observed sounding depicted a meager buoyancy profile, with
under 900 J/kg SBCAPE and very little MLCAPE (given a relatively dry
surface-850 mb layer for a tropical cyclone ambient environment).

Given the aforementioned vertical shear profile, a robust, sustained
low-topped supercell would be capable of producing a tornado.
However, the overall severe threat is expected to be very sparse and
brief given the meager buoyancy, and a Tornado Watch issuance is not
currently anticipated.

..Squitieri/Grams.. 09/09/2021

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

ATTN...WFO...JAX...TAE...

LAT...LON   29708454 30068476 30418483 30738460 30948425 31038373
            30918331 30698302 30518291 30268293 29938295 29578312
            29418343 29708454

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 8, 8:17 PM EDT	Mesoscale Discussion	SPC	Calhoun, Gadsden, Jefferson, Leon, Liberty, Wakulla	118 min

Nearby

Mesoscale Discussions in Florida, 2021 Mesoscale Discussions in Georgia, 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.