Mesoscale Discussion 2256
The Storm Prediction Center issued this mesoscale discussion at Oct 17, 2011, 3:39 AM CDT. It was in force for 3 hr.
The area
The outline as issued.
The facts
- Issued
- Oct 17, 2011, 3:39 AM CDT (08:39 UTC)
- Expired
- Oct 17, 2011, 6:15 AM CDT
- In force
- 3 hr
- Issued by
- the Storm Prediction Center
The radar
The Key West radar (KBYX), 36 km from the middle of the area, began a volume at 08:42 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
Key West, FL (KEYW), launched 00:00Z, 8.7 hours before the alert went out and 39 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
- 500 J/kg
- Mixed-layer CIN
- -2 J/kg
- Mixed-layer LCL
- 472 m above ground
- 0-6 km bulk shear
- 12 kt
- 0-1 km storm-relative helicity
- 131 m²/s²
- 0-3 km storm-relative helicity
- 128 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted, in the capitals the NWS used until 2016.
559
ACUS11 KWNS 170839
SWOMCD
SPC MCD 170839
FLZ000-171115-
MESOSCALE DISCUSSION 2256
NWS STORM PREDICTION CENTER NORMAN OK
0339 AM CDT MON OCT 17 2011
AREAS AFFECTED...PORTIONS LOWER-MIDDLE FL KEYS.
CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY
VALID 170839Z - 171115Z
RADAR AND SATELLITE TRENDS SHOW COVERAGE OF RELATIVELY DISCRETE
CONVECTION INCREASING FROM LOWER KEYS SEWD ACROSS STRAITS AT LEAST
180 NM PAST CAY SAL BANK AND JUST OFFSHORE N-CENTRAL CUBA.
WATERSPOUTS FROM ROTATING SHOWERS ARE POSSIBLE OVER WATERS NEAR
KEYS...AND A BRIEF TORNADO CANNOT BE RULED OUT OVER LOWER-MIDDLE
KEYS THROUGH REMAINDER MORNING.
DISCRETE CONVECTIVE ELEMENTS SHOULD REMAIN RELATIVELY SHALLOW AND
SMALL WITH LITTLE OR NO LIGHTNING PRODUCTION -- I.E. OCNL
WARM-CLOUD/MINI-SUPERCELLULAR SHOWERS. EXPECT WEAK MID-UPPER LEVEL
LAPSE RATES AND RELATIVELY BOTTOM-HEAVY PROFILE OF BUOYANCY. RICH
LOW-LEVEL THETAE AND 2.25-2.5 INCH PW SUPPORTS MLCAPE AROUND 500
J/KG OVER STRAITS...DECREASING NWD ACROSS FL BAY. LOWER-MIDDLE KEYS
AND ADJACENT WATERS LIE WITHIN NERN FRINGE OF ENHANCED
BOUNDARY-LAYER SHEAR...BASED ON EYW/MIA VWP...OBSERVED SFC WINDS AND
LOW-LEVEL MODEL ANALYSES. 0-1 KM SRH HAS BEEN HOLDING STEADY IN
250-300 J/KG RANGE FOR SEVERAL HOURS AROUND EYW...BENEATH 20-30 KT
SELY LLJ THAT LIKELY STRENGTHENS SOMEWHAT FARTHER SW TOWARD AREAS
OFFSHORE NWRN CUBA. BULK OF STRONGER AND MORE CONSISTENTLY
ORGANIZED CONVECTION SHOULD REMAIN S AND W OF LOWER KEYS...WHERE RUC
AND ETA-KF FCST SOUNDINGS SUGGEST COMPARABLE BUOYANCY AND LARGER
LOW-LEVEL HODOGRAPHS. HOWEVER...WIND PROFILES WILL CONTINUE TO
SUPPORT INTERMITTENT CONVECTIVE-SCALE ROTATION WITH CELLS APCHG
LOWER-MIDDLE KEYS.
REF NHC TROPICAL WEATHER OUTLOOKS -- WMO HEADER ABNT20 KNHC -- FOR
LATEST FCST GUIDANCE ON RELATED AREA OF LOW PRESSURE INVOF NERN
YUCATAN PENINSULA AND ITS POTENTIAL FOR TROPICAL DEVELOPMENT.
..EDWARDS.. 10/17/2011
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...KEY...
LAT...LON 24908058 24758090 24628122 24628146 24538172 24538181
24528221 24608220 24578199 24598172 24768145 24758131
24738114 24868082 24948067 24908058Nearby
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.