Alert archive / Georgia / Tornado Watches in 2017

Tornado Watch 484

September 10, 201711 counties in Florida; 12 counties in Georgia

The Storm Prediction Center issued this tornado watch at Sep 10, 2017, 11:50 PM EDT for 11 counties in Florida; 12 counties in Georgia. It was in force for 14 hr.

The area

The outline as issued.

The facts

Issued
Sep 10, 2017, 11:50 PM EDT (03:50 UTC)
Expired
Sep 11, 2017, 1:51 PM EDT
In force
14 hr
Issued by
the Storm Prediction Center
Largest hail expected
0.5 in
Strongest gust expected
50 kt
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), 36 km from the middle of the area, began a volume at 03:54 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.

What SPC expected

The probabilities SPC published with the watch, for the watch area over its life.

Two or more tornadoes
40%
One or more EF2 to EF5 tornadoes
20%
Ten or more severe wind reports
10%
One or more gusts of 65 knots or more
10%
Ten or more severe hail reports
5%
One or more hailstones of 2 inches or more
5%
Six or more combined severe hail and wind reports
30%

Warnings issued inside it

20 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

IssuedProductOfficeCountiesLasted
Sep 11, 12:49 AM EDTFlash Flood WarningJAXFlagler, Marion, Putnam, Saint Johns5 hr
Sep 11, 1:35 AM EDTFlash Flood WarningJAXClay, Flagler, Putnam, Saint Johns3 hr
Sep 11, 2:02 AM EDTTornado WarningJAXNassau28 min
Sep 11, 2:10 AM EDTFlash Flood WarningJAXClay, Saint Johns3 hr
Sep 11, 2:31 AM EDTFlash Flood WarningJAXClay, Duval, Nassau, Saint Johns3 hr
Sep 11, 2:34 AM EDTTornado WarningJAXNassau6 min
Sep 11, 2:41 AM EDTFlash Flood WarningJAXClay, Duval, Saint Johns3 hr
Sep 11, 3:36 AM EDTTornado WarningJAXDuval24 min
Sep 11, 4:10 AM EDTFlash Flood WarningJAXDuval, Nassau3 hr
Sep 11, 5:14 AM EDTFlash Flood WarningJAXNassau3 hr
Sep 11, 5:18 AM EDTTornado WarningJAXCamden27 min
Sep 11, 5:34 AM EDTFlash Flood WarningJAXClay, Duval, Nassau, Saint Johns3 hr
Sep 11, 6:15 AM EDTFlash Flood WarningJAXBaker, Bradford, Clay, Columbia, Duval, Union3 hr
Sep 11, 6:22 AM EDTFlash Flood WarningCHSMcIntosh10 hr
Sep 11, 6:45 AM EDTFlash Flood Warning EmergencyJAXDuval6 hr
Sep 11, 8:09 AM EDTFlash Flood WarningJAXBrantley, Camden, Charlton, Glynn111 min
Sep 11, 8:16 AM EDTFlash Flood WarningCHSBryan, Chatham, Liberty, McIntosh8 hr
Sep 11, 9:41 AM EDTFlash Flood WarningJAXCharlton, Ware2 hr
Sep 11, 10:11 AM EDTTornado WarningCHSBryan, Chatham, Liberty15 min
Sep 11, 12:19 PM EDTFlash Flood Warning EmergencyJAXClay, Duval, Putnam, Saint Johns6 hr

Discussions around it

SPC mesoscale discussions over the same counties from four hours before the watch to its end.

The nearest sounding before it

Jacksonville, FL (KJAX), launched 00:00Z, 3.8 hours before the alert went out and 35 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-pSkew-T log-p diagram, Jacksonville, FL at 00:00Z on 2017-09-11Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 270 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Jacksonville, FL at 00:00Z on 2017-09-11The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 282 square meters per square second.193958Sfc1 km3 km6 km9 kmRMLM
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.

293 
WWUS20 KWNS 110347
SEL4  
SPC WW 110347
FLZ000-GAZ000-CWZ000-111500-

URGENT - IMMEDIATE BROADCAST REQUESTED
Tornado Watch Number 484
NWS Storm Prediction Center Norman OK
1150 PM EDT Sun Sep 10 2017

The NWS Storm Prediction Center has issued a

* Tornado Watch for portions of 
  Northeast Florida
  Southeast Georgia
  Coastal Waters

* Effective this Sunday night and Monday morning from 1150 PM
  until 1100 AM EDT.

* Primary threats include...
  A couple tornadoes possible

SUMMARY...The risk for a couple tornadoes will persist as Tropical
Cyclone Irma moves north this morning.

The tornado watch area is approximately along and 45 statute miles
east and west of a line from 65 miles north northwest of Brunswick
GA to 35 miles west southwest of Daytona Beach FL. For a complete
depiction of the watch see the associated watch outline update
(WOUS64 KWNS WOU4).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

REMEMBER...A Tornado Watch means conditions are favorable for
tornadoes and severe thunderstorms in and close to the watch
area. Persons in these areas should be on the lookout for
threatening weather conditions and listen for later statements
and possible warnings.

&&

OTHER WATCH INFORMATION...CONTINUE...WW 483...

AVIATION...Tornadoes and a few severe thunderstorms with hail
surface and aloft to 0.5 inches. Extreme turbulence and surface wind
gusts to 50 knots. A few cumulonimbi with maximum tops to 500. Mean
storm motion vector 11050.

...Grams

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Sep 10, 10:33 PM EDTMesoscale DiscussionSPCAlachua, Baker, Bradford, Brevard, Charlotte, Citrus and 37 more87 min
Sep 11, 4:58 AM EDTMesoscale DiscussionSPCAlachua, Baker, Bradford, Clay, Duval, Flagler and 5 more2 hr
Sep 11, 8:49 AM EDTMesoscale DiscussionSPCBaker, Duval, Nassau, Saint Johns116 min
Sep 11, 1:46 PM EDTTornado WatchSPCBryan, Bulloch, Burke, Candler, Chatham, Effingham and 7 more10 hr

Nearby

Tornado Watches in Georgia, 2017Tornado Watches in Florida, 2017Every tornado watch 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.