Alert archive / Florida / Severe Thunderstorm Warnings in 2020

Severe Thunderstorm Warning 178, NWS Jacksonville, FL

August 4, 2020Nassau County, Florida; Charlton County, Georgia

NWS Jacksonville, FL issued this severe thunderstorm warning at Aug 4, 2020, 7:24 PM EDT for Nassau County, Florida; Charlton County, Georgia. It was in force for 51 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 4, 2020, 7:24 PM EDT (23:24 UTC)
Expired
Aug 4, 2020, 8:15 PM EDT
In force
51 min
Issued by
NWS Jacksonville, FL
Area
Storm-based polygon
Hail
1.0 in
Wind
60.0 mph

Counties Nassau County, FL, Charlton County, GA

The radar

The Jacksonville radar (KJAX), 34 km from the middle of the area, began a volume at 23:26 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 12:00Z, 11.4 hours before the alert went out and 227 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, Tallahassee Rgnl, FL at 12:00Z on 2020-08-04Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 518 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, Tallahassee Rgnl, FL at 12:00Z on 2020-08-04The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 5 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
518 J/kg
Mixed-layer CIN
-80 J/kg
Mixed-layer LCL
1258 m above ground
0-6 km bulk shear
14 kt
0-1 km storm-relative helicity
5 m²/s²
0-3 km storm-relative helicity
64 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

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 4, 3:39 PM EDT, 3 hours 45 minutes earlier.

Area forecast discussion, Aug 4, 3:39 PM EDT, 3 hours 45 minutes before
Area Forecast Discussion
National Weather Service Jacksonville FL
339 PM EDT Tue Aug 4 2020

.NEAR TERM [Tonight and Wednesday]...Trailing trough from T.S.
Isaias extending into Ga will be a focus for scattered thunderstorms
to continue across se Ga through the the evening hours. Another
area for possible development will be near the ne Fl coast where
the east coast seabreeze is slowly moving inland. Warm and dry air
aloft will limit the severe potential with any isolated strong
storms resulting from boundary and cell mergers. Similar pattern
on Wednesday with a light sw flow favoring eastern zones for
afternoon/evening convection. Hot and humid conditions will
continue with low temperatures tonight mostly in the 75-80 degree
range. Heat indices will again reach near 105F Wednesday
afternoon.

.SHORT TERM [Wednesday night through Friday Night]...Troughing
will persist to the northwest with ridge to the southeast. A
southwest steering flow will decrease on Friday as the ridge
builds closer the area. Moisture will be at or above normal which
will mean scattered to numerous diurnal seabreeze storms.
Temperatures will be at or above average.

.LONG TERM [Saturday Through Tuesday]...Subtropical ridge will
remain just to the south through the period. Daily seabreezes
with ample moisture remaining over the area will result in
scattered to numerous thunderstorms each afternoon and evening.
Highest coverage of storms will be over inland areas as the
seabreezes move inland and merge over the interior. Steering winds
will be light and variable resulting in slow moving storms and
areas of locally heavy rainfall. The stronger storms will also
produce strong gusty winds and frequent ligthning strikes.

&&

.MARINE...Troughing will linger over the southeastern states
through Thursday along with prevailing south southwesterly winds
in place over our waters. The sea breeze will develop near the
coast each afternoon resulting in onshore winds over the near
shore waters. The Atlantic surface high pressure system will
build westward across the Florida peninsula late this week and
weekend with prevailing southerly winds. Scattered to numerous
thunderstorms will push into the coastal waters during the late
afternoon and evening hours through Thursday.

&&

.PRELIMINARY POINT TEMPS/POPS...

AMG  73  94  73  94  72 /  50  60  50  70  20
SSI  78  90  78  90  77 /  30  30  30  70  30
JAX  75  93  74  93  74 /  40  50  40  70  20
SGJ  75  90  74  90  74 /  30  30  30  70  20
GNV  74  93  73  91  73 /  10  30  30  70  20
OCF  74  91  73  91  73 /   0  40  30  70  20

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...None.
AM...None.

&&

In the hours before

Local storm report, Aug 4, 5:07 PM EDT, 2 hours 17 minutes before
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Special weather statement, Aug 4, 5:40 PM EDT, 1 hour 44 minutes before
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Special weather statement, Aug 4, 5:42 PM EDT, 1 hour 42 minutes before
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Local storm report, Aug 4, 5:57 PM EDT, 1 hour 27 minutes before
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Special weather statement, Aug 4, 6:03 PM EDT, 1 hour 21 minutes before
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Local storm report, Aug 4, 7:18 PM EDT, 6 minutes before
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The office that day

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

IssuedProductOfficeCountiesLasted
Aug 3, 11:24 PM EDTSpecial Marine WarningJAX66 min
Aug 4, 12:30 AM EDTSpecial Marine WarningJAX90 min
Aug 4, 1:30 AM EDTSpecial Marine WarningJAX78 min
Aug 4, 7:14 PM EDTSevere Thunderstorm WarningJAXClay, Duval46 min
Aug 4, 7:37 PM EDTSevere Thunderstorm WarningJAXDuval, Nassau53 min
Aug 4, 7:52 PM EDTSevere Thunderstorm WarningJAXClay, Duval, Nassau53 min
Aug 3, 9:09 PM EDTSpecial Weather StatementJAXWayne51 min
Aug 3, 9:52 PM EDTSpecial Weather StatementJAXWayne38 min
Aug 3, 11:15 PM EDTSpecial Weather StatementJAXGlynn15 min
Aug 4, 12:13 AM EDTSpecial Weather StatementJAXCamden32 min
Aug 4, 12:49 AM EDTSpecial Weather StatementJAXCamden41 min
Aug 4, 3:27 PM EDTSpecial Weather StatementJAXWayne48 min
Aug 4, 4:06 PM EDTSpecial Weather StatementJAXAppling39 min
Aug 4, 4:16 PM EDTSevere Thunderstorm WarningJAXAppling, Wayne44 min
Aug 4, 4:27 PM EDTSpecial Weather StatementJAXPierce48 min
Aug 4, 4:54 PM EDTSpecial Weather StatementJAXBrantley, Pierce51 min
Aug 4, 5:07 PM EDTSpecial Weather StatementJAXBacon38 min
Aug 4, 5:40 PM EDTSpecial Weather StatementJAXCamden50 min
Aug 4, 5:42 PM EDTSpecial Weather StatementJAXAtkinson48 min
Aug 4, 6:03 PM EDTSpecial Weather StatementJAXPierce42 min

Nearby

Severe Thunderstorm Warnings in Florida, 2020Severe Thunderstorm Warnings in Georgia, 2020Every severe thunderstorm warning 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.