Alert archive / Florida / Severe Thunderstorm Warnings in 2017

Severe Thunderstorm Warning 256, NWS Jacksonville, FL

August 18, 2017Duval County, Nassau County, Florida

NWS Jacksonville, FL issued this severe thunderstorm warning at Aug 18, 2017, 3:30 PM EDT for Duval County, Nassau County, Florida. It was in force for 15 min. No storm report in the archive falls inside the area while it was in force.

The area

The counties it named.

The facts

Issued: Aug 18, 2017, 3:30 PM EDT (19:30 UTC)
Expired: Aug 18, 2017, 3:45 PM EDT
In force: 15 min
Issued by: NWS Jacksonville, FL
Area: Storm-based polygon
Hail: 0.75 in
Wind: 60.0 mph

Counties Duval County, FL, Nassau County, FL

The radar

The Jacksonville radar (KJAX), 1 km from the middle of the area, began a volume at 19:33 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

Cape Canaveral, FL (KXMR), launched 12:00Z, 7.5 hours before the alert went out and 252 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: 222 J/kg
Mixed-layer CIN: -113 J/kg
Mixed-layer LCL: 1020 m above ground
0-6 km bulk shear: 16 kt
0-1 km storm-relative helicity: -64 m²/s²
0-3 km storm-relative helicity: -22 m²/s²
Significant tornado parameter: 0.0
Supercell composite: -0.2

Open this sounding in Storm Lab

What forecasters said that day

The local office's own words before this severe thunderstorm warning went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Jacksonville, FL wrote its last area forecast discussion before this severe thunderstorm warning went out at Aug 18, 2:44 PM EDT, 46 minutes earlier.

Area forecast discussion, Aug 18, 2:44 PM EDT, 46 minutes before

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Hazardous weather outlook, Aug 18, 3:00 AM EDT, 12 hours 30 minutes before

Hazardous Weather Outlook
National Weather Service Jacksonville FL
300 AM EDT Fri Aug 18 2017

AMZ450-452-454-470-472-474-FLZ020>025-030>033-035>038-040-124-125-
GAZ132>136-149>154-162>166-191000-
Coastal waters from Altamaha Sound to Fernandina Beach FL out
20 NM-
Coastal waters from Fernandina Beach to St. Augustine FL out
20 NM-
Coastal waters from St. Augustine to Flagler Beach FL out 20 NM-
Waters from Altamaha Sound GA to Fernandina Beach FL from 20 to
60 NM-
Waters from Fernandina Beach to St. Augustine FL from 20 to 60 NM-
Waters from St. Augustine to Flagler Beach FL from 20 to 60 NM-
Hamilton-Suwannee-Columbia-Baker-Inland Nassau-Inland Duval-Union-
Bradford-Clay-St. Johns-Gilchrist-Alachua-Putnam-Flagler-Marion-
Coastal Nassau-Coastal Duval-Coffee-Jeff Davis-Bacon-Appling-
Wayne-Atkinson-Ware-Pierce-Brantley-Inland Glynn-Coastal Glynn-
Echols-Clinch-Charlton-Inland Camden-Coastal Camden-
300 AM EDT Fri Aug 18 2017

...HOT AND HUMID WITH HEAT INDICES NEAR 105 DEGREES TODAY...

...SLOW AND ERRATIC STORM MOTION WILL PROMOTE LOCALLY HEAVY
RAINFALL THREAT THIS AFTERNOON AND EVENING...

This Hazardous Weather Outlook is for Northeast Florida,
Southeast Georgia and the Adjacent Coastal Waters.

.DAY ONE...Today and Tonight...

Heat Index values of 103 to 107 degrees are expected at many
locations this afternoon.

Scattered to Numerous afternoon and evening thunderstorms are
expected today...mainly across Northeast Florida. A few strong
thunderstorms will be possible with gusty winds and frequent
lightning strikes. Slow and erratic storm motion is expected with
locally heavy rainfall possible in the stronger storms from the
I-10 corridor southward across Northeast Florida.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday...

Scattered to numerous mainly afternoon and evening thunderstorms
are expected Saturday. Scattered afternoon and evening thunderstorms
will be possible at inland locations from Sunday through Thursday.
A few strong thunderstorms will be possible each day, with gusty
winds, frequent lightning strikes, and heavy downpours being the
main threats.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed.

For additional information, visit the National Weather Service in
Jacksonville website on the internet at weather.gov/jax.

In the hours before

Special weather statement, Aug 18, 1:38 PM EDT, 1 hour 52 minutes before

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Special weather statement, Aug 18, 1:53 PM EDT, 1 hour 37 minutes before

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Special weather statement, Aug 18, 2:25 PM EDT, 1 hour 5 minutes before

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Special weather statement, Aug 18, 2:39 PM EDT, 51 minutes before

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Special weather statement, Aug 18, 2:44 PM EDT, 46 minutes before

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Special weather statement, Aug 18, 3:01 PM EDT, 29 minutes before

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The office that day

Everything else NWS Jacksonville, FL issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 18, 12:44 PM EDT	Areal Flood Advisory	JAX	Duval	91 min
Aug 18, 12:49 PM EDT	Special Weather Statement	JAX	Clay	41 min
Aug 18, 12:53 PM EDT	Areal Flood Advisory	JAX	Clay	97 min
Aug 18, 12:54 PM EDT	Special Weather Statement	JAX	Alachua	51 min
Aug 18, 1:00 PM EDT	Special Weather Statement	JAX	Duval	30 min
Aug 18, 1:14 PM EDT	Areal Flood Advisory	JAX	Alachua	3 hr
Aug 18, 1:18 PM EDT	Special Weather Statement	JAX	Alachua	27 min
Aug 18, 1:38 PM EDT	Special Weather Statement	JAX	Alachua	22 min
Aug 18, 1:53 PM EDT	Special Weather Statement	JAX	Saint Johns	22 min
Aug 18, 2:00 PM EDT	Areal Flood Advisory	JAX	Alachua	2 hr
Aug 18, 2:02 PM EDT	Areal Flood Advisory	JAX	Saint Johns	118 min
Aug 18, 2:14 PM EDT	Areal Flood Advisory	JAX	Alachua	91 min
Aug 18, 2:25 PM EDT	Special Weather Statement	JAX	Saint Johns	50 min
Aug 18, 2:39 PM EDT	Special Weather Statement	JAX	Nassau	51 min
Aug 18, 2:44 PM EDT	Special Weather Statement	JAX	Suwannee	46 min
Aug 18, 3:01 PM EDT	Special Weather Statement	JAX	Columbia	44 min
Aug 18, 3:49 PM EDT	Special Weather Statement	JAX	Hamilton	41 min
Aug 18, 4:01 PM EDT	Special Weather Statement	JAX	Flagler	29 min
Aug 18, 4:26 PM EDT	Areal Flood Advisory	JAX	Marion	3 hr
Aug 18, 4:43 PM EDT	Areal Flood Advisory	JAX	Marion	3 hr

Nearby

Severe Thunderstorm Warnings in Florida, 2017 Every severe thunderstorm warning 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.