Alert archive / Florida / Mesoscale Discussions in 2021
Mesoscale Discussion 400
The Storm Prediction Center issued this mesoscale discussion at Apr 20, 2021, 8:32 AM EDT for 7 counties in Florida. It was in force for 58 min.
The area
The outline as issued.
The facts
- Issued
- Apr 20, 2021, 8:32 AM EDT (12:32 UTC)
- Expired
- Apr 20, 2021, 9:30 AM EDT
- In force
- 58 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
Counties Brevard County, FL, Hillsborough County, FL, Manatee County, FL, Orange County, FL, Osceola County, FL, Polk County, FL, Seminole County, FL
The radar
The Tampa radar (KTBW), 77 km from the middle of the area, began a volume at 12:30 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
Tampa Bay, FL (KTBW), launched 12:00Z, 0.5 hours before the alert went out and 77 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
- 617 J/kg
- Mixed-layer CIN
- -48 J/kg
- Mixed-layer LCL
- 608 m above ground
- 0-6 km bulk shear
- 43 kt
- 0-1 km storm-relative helicity
- 117 m²/s²
- 0-3 km storm-relative helicity
- 250 m²/s²
- Significant tornado parameter
- 0.7
- Supercell composite
- 7.3
The text
As transmitted.
621
ACUS11 KWNS 201233
SWOMCD
SPC MCD 201232
FLZ000-201330-
Mesoscale Discussion 0400
NWS Storm Prediction Center Norman OK
0732 AM CDT Tue Apr 20 2021
Areas affected...central Florida
Concerning...Severe potential...Watch unlikely
Valid 201232Z - 201330Z
Probability of Watch Issuance...20 percent
SUMMARY...Thunderstorms will pose a risk for isolated marginally
severe hail through the morning, but a brief tornado and gusty winds
will also be possible. Overall threat appears somewhat marginal, but
trends will continue to be monitored.
DISCUSSION...Early this morning a stationary front is situated
across central FL from just south of the Tampa Bay area to south of
Melbourne. Widely scattered thunderstorms have been on the increase
during the past hour in response to deep forcing for ascent
accompanying a low-amplitude shortwave trough moving through the
northern Gulf. The low-level response to this feature has been
modest with the Tampa VWP indicating 20 kt southwesterly flow in the
1-2 km layer, though some increase in the low-level winds (up to 30
kt) might occur later this morning. Instability remains marginal due
to weak mid-level lapse rates with 1000 J/kg MUCAPE supported by
upper 60s F near-surface dewpoints. Storms still appear slightly
elevated, but advection of warmer air from the south could
eventually boost surface temperatures to in excess of 75 F during
the morning. The gradual warming of the boundary layer and modest
increase in low-level winds might promote further storm
intensification. Effective bulk shear around 45 kt will support a
few supercell structures with marginally severe hail the main
threat, but as storms transition to surface-based, some threat will
exist for a brief tornado.
..Dial/Grams.. 04/20/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MLB...TBW...
LAT...LON 28068064 27858137 27308230 27438270 27928280 28518232
28758074 28068064SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 20, 4:35 PM EDT | Mesoscale Discussion | SPC | Brevard, Hardee, Highlands, Hillsborough, Indian River, Okeechobee and 4 more | 115 min |
Nearby
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.