Alert archive / Florida / Mesoscale Discussions in 2011

Mesoscale Discussion 757

May 12, 201112 counties in Florida

The Storm Prediction Center issued this mesoscale discussion at May 12, 2011, 1:59 PM EDT for 12 counties in Florida. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: May 12, 2011, 1:59 PM EDT (17:59 UTC)
Expired: May 12, 2011, 4:00 PM EDT
In force: 2 hr
Issued by: the Storm Prediction Center

Counties Broward County, FL, Charlotte County, FL, Collier County, FL, Glades County, FL, Hendry County, FL, Highlands County, FL, Lee County, FL, Martin County, FL, Miami-Dade County, FL, Monroe County, FL, Okeechobee County, FL, Palm Beach County, FL

The radar

The Miami radar (KAMX), 85 km from the middle of the area, began a volume at 18:00 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

Miami, FL (KMFL), launched 12:00Z, 6.0 hours before the alert went out and 82 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: 1881 J/kg
Mixed-layer CIN: -68 J/kg
Mixed-layer LCL: 978 m above ground
0-6 km bulk shear: 31 kt
0-1 km storm-relative helicity: -3 m²/s²
0-3 km storm-relative helicity: 8 m²/s²
Significant tornado parameter: -0.0
Supercell composite: -0.4

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

242 
ACUS11 KWNS 121759
SWOMCD
SPC MCD 121759 
FLZ000-122000-

MESOSCALE DISCUSSION 0757
NWS STORM PREDICTION CENTER NORMAN OK
1259 PM CDT THU MAY 12 2011

AREAS AFFECTED...SOUTH FL

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

VALID 121759Z - 122000Z

ISOLATED SVR STORMS WITH LARGE HAIL AND DMGG WINDS WILL BE POSSIBLE
OVER SOUTH FLORIDA THIS AFTERNOON.

THE AIR MASS OVER SOUTH FLORIDA CONTINUES TO DESTABILIZE THIS
AFTERNOON...WITH THE 12Z MIAMI SOUNDING ASSIMILATED WITH 17Z SFC
OBSERVATIONS YIELDING MLCAPE VALUES ON THE ORDER OF 2500-3000 J/KG.
THIS HAS OCCURRED AS SFC TEMPERATURES WARMED INTO THE UPPER 80S TO
LOWER 90S...WITH DEWPOINTS FROM THE MIDDLE 60S TO LOWER
70S...BENEATH A MODESTLY STEEP MID-LEVEL LAPSE RATE ENVIRONMENT --
I.E. 700-500-MB LAPSE RATE OF 6.6 C PER KM BASED ON 12Z MIAMI
SOUNDING.

MEANWHILE...VISIBLE SATELLITE IMAGERY REVEALS SEVERAL BOUNDARIES
THAT WILL LIKELY PLAY A ROLE IN INITIATING/ENHANCING CONVECTION THIS
AFTERNOON. FIRSTLY...AN ELONGATED NW-SE-ORIENTED CONVERGENCE BAND
EMANATING FROM A LARGE CYCLONIC GYRE CENTERED OVER THE WRN ATLC
CURRENTLY EXTENDS OVER THE SERN PENINSULA...AND IS SHIFTING SWWD.
INTERSECTING THIS BAND ARE N-S-ORIENTED CONVERGENCE-ENHANCED CUMULUS
LINES OVER THE SRN PENINSULA. DEEP CONVECTION HAS ALREADY STARTED
INITIATING AT THE INTERSECTION POINTS OVER PORTIONS OF MIAMI-DADE
COUNTY. MEANWHILE...A LAKE BREEZE OFF LAKE OKEECHOBEE IS MOVING
SWD...AND WILL ALSO LIKELY ENHANCE CONVECTION.

WITH CONTINUED DIABATIC HEATING...THE PRESENCE OF THE AFOREMENTIONED
BOUNDARIES...AND THE POTENTIAL DEVELOPMENT OF A SEA BREEZE OFF THE
WRN FLORIDA COAST...SCATTERED THUNDERSTORMS WILL LIKELY ERUPT DURING
THE NEXT COUPLE OF HOURS OVER SOUTH FLORIDA. THE DEGREE OF UPWARD
POTENTIAL BUOYANCY WILL LIKELY RESULT IN VIGOROUS UPDRAFTS. SOME
MULTICELLULAR ORGANIZATION IS ANTICIPATED...GIVEN EFFECTIVE BULK
SHEAR MAGNITUDES OF 25 TO 30 KT. THIS IS IN ASSOCIATION WITH
ENHANCED NNWLY FLOW OVER THE ERN PERIPHERY OF THE SERN CONUS RIDGE.
ISOLATED INSTANCES OF LARGE HAIL AND DMGG WINDS WILL BE POSSIBLE.
DUE TO THE LIMITED AREAL EXTENT OF ANY SVR THREAT...A WW IS
UNLIKELY.

..COHEN.. 05/12/2011

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...MFL...MLB...KEY...TBW...

LAT...LON   24668057 25068124 25918178 26948212 27188180 27468130
            27438068 26928024 25158003 24668057

Nearby

Mesoscale Discussions in Florida, 2011 Every mesoscale discussion in 2011

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.