Alert archive / Florida / Mesoscale Discussions in 2021

Mesoscale Discussion 1755

September 15, 2021Baldwin County, Mobile County, Alabama; 6 counties in Florida; 6 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Sep 15, 2021, 12:26 PM CDT for Baldwin County, Mobile County, Alabama; 6 counties in Florida; 6 counties in Mississippi. It was in force for 3 hr.

The area

The outline as issued.

The facts

Issued
Sep 15, 2021, 12:26 PM CDT (17:26 UTC)
Expired
Sep 15, 2021, 3:00 PM CDT
In force
3 hr
Issued by
the Storm Prediction Center
Concerning
Severe potential...watch unlikely
Chance of a watch
20%

Counties Baldwin County, AL, Mobile County, AL, Bay County, FL, Escambia County, FL, Gulf County, FL, Okaloosa County, FL, Santa Rosa County, FL, Walton County, FL, George County, MS, Hancock County, MS, Harrison County, MS, Jackson County, MS, Pearl River County, MS, Stone County, MS

The radar

The Mobile radar (KMOB), 92 km from the middle of the area, began a volume at 17:27 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

Slidell Radar S, LA (KSIL), launched 12:00Z, 5.4 hours before the alert went out and 210 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, Slidell Radar S, LA at 12:00Z on 2021-09-15Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 84 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, Slidell Radar S, LA at 12:00Z on 2021-09-15The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 120 square meters per square second.1939Sfc1 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
84 J/kg
Mixed-layer CIN
-69 J/kg
Mixed-layer LCL
695 m above ground
0-6 km bulk shear
15 kt
0-1 km storm-relative helicity
120 m²/s²
0-3 km storm-relative helicity
285 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

726 
ACUS11 KWNS 151727
SWOMCD
SPC MCD 151726 
FLZ000-ALZ000-MSZ000-LAZ000-152000-

Mesoscale Discussion 1755
NWS Storm Prediction Center Norman OK
1226 PM CDT Wed Sep 15 2021

Areas affected...Southern MS...Southern AL...Western FL Panhandle

Concerning...Severe potential...Watch unlikely 

Valid 151726Z - 152000Z

Probability of Watch Issuance...20 percent

SUMMARY...Isolated transient supercells may affect of the Gulf Coast
region from Southern MS into the western FL Panhandle this
afternoon, posing a risk of waterspouts and a tornado or two.  A
watch is unlikely.

DISCUSSION...The remnant low of Nicholas is currently near Baton
Rouge, with a well-defined surface boundary extending eastward along
the MS/AL coast to off the coast of the FL Panhandle.  Backed
low-level winds in vicinity of this boundary, coupled with
moderately strong southerly winds aloft, are resulting in favorable
shear profiles for rotating storms.  VAD profiles at MOB/EVX sample
this environment reasonably well, with 0-3km SRH of around 150
m2/s2.  A few of the cells near Mobile Bay have recently shown signs
of weak rotation.  This trend will likely continue through the
afternoon as daytime heating slowly destabilizes the air mass and
the boundary lifts slowly northward toward the FL coast.  Widespread
precipitation is expected to limit destabilization very far inland,
with the primary risk remaining offshore and in the coastal
counties.  Current indications are that a watch is unlikely due to
the limited areal coverage and marginal nature of risk.

..Hart/Thompson.. 09/15/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...TAE...MOB...JAN...LIX...

LAT...LON   30068826 30218920 30318989 30548995 30858976 30988895
            30938754 30678638 30378562 29708489 29358502 29048546
            29238609 29858744 30068826

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Sep 15, 4:49 AM CDTMesoscale DiscussionSPCHancock, Harrison, Jackson116 min

Nearby

Mesoscale Discussions in Florida, 2021Mesoscale Discussions in Mississippi, 2021Mesoscale Discussions in Alabama, 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.