Alert archive / Florida / Mesoscale Discussions in 2021
Mesoscale Discussion 396
The Storm Prediction Center issued this mesoscale discussion at Apr 18, 2021, 1:16 PM EDT for Lake County, Orange County, Seminole County, Florida. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Apr 18, 2021, 1:16 PM EDT (17:16 UTC)
- Expired
- Apr 18, 2021, 3:45 PM EDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
Counties Lake County, FL, Orange County, FL, Seminole County, FL
The radar
The Melbourne radar (KMLB), 86 km from the middle of the area, began a volume at 17:17 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, 5.3 hours before the alert went out and 83 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.
- Mixed-layer CAPE
- 298 J/kg
- Mixed-layer CIN
- -75 J/kg
- Mixed-layer LCL
- 852 m above ground
- 0-6 km bulk shear
- 55 kt
- 0-1 km storm-relative helicity
- 75 m²/s²
- 0-3 km storm-relative helicity
- 145 m²/s²
- Significant tornado parameter
- 0.1
- Supercell composite
- 0.9
The text
As transmitted.
149
ACUS11 KWNS 181716
SWOMCD
SPC MCD 181716
FLZ000-181945-
Mesoscale Discussion 0396
NWS Storm Prediction Center Norman OK
1216 PM CDT Sun Apr 18 2021
Areas affected...East central Florida peninsula
Concerning...Severe potential...Watch unlikely
Valid 181716Z - 181945Z
Probability of Watch Issuance...20 percent
SUMMARY...Isolated to scattered thunderstorm development is possible
this afternoon across the Greater Orlando into Space Coast vicinity,
particularly closer to 4-6 PM EDT. This may include an isolated
supercell or two, posing a risk for large hail and locally strong
surface gusts.
DISCUSSION...Strong differential surface heating is ongoing along a
convectively reinforced surface boundary extending across the
peninsula, north of Tampa through the Greater Orlando Metropolitan
area and the Cape Canaveral vicinity. South of this frontal zone,
where dew points are around 70F, temperatures have warmed into the
80s. This appears to be contributing to mixed-layer CAPE on the
order of 1500-2000 J/kg, in the presence of strongly sheared
westerly deep-layer mean flow. The generally unidirectional wind
profiles include 40-50 kt in the 700-500 mb layer, weakening to
around 20 kt around the 850 mb layer.
This appears focused near the northern periphery of warmer and more
strongly capping layers aloft, associated with mid/upper subtropical
ridging, which remain evident in recent ACARS soundings from
Orlando. However, as near-surface convergence becomes increasingly
focused across the Orlando into Space Coast vicinity through mid to
late afternoon, potential for the initiation of isolated to widely
scattered thunderstorms is expected to increase.
Latest High-Resolution Rapid Refresh suggests that isolated
thunderstorm development is possible as early as 18-19Z, but
sustained thunderstorm development seems more probable a bit later
this afternoon, aided by increasingly divergent upper flow,
downstream of a mid-level impulse approaching the Florida Gulf
coast. If/when this occurs, the environment will be conducive to
storms capable of producing large hail and locally strong surface
gusts.
..Kerr/Guyer.. 04/18/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MLB...TBW...
LAT...LON 28818171 28928130 28908068 28408060 28228114 28288160
28488194 28818171Nearby
Mesoscale Discussions in Florida, 2021Every 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.