Alert archive / Mississippi / Mesoscale Discussions in 2021
Mesoscale Discussion 675
The Storm Prediction Center issued this mesoscale discussion at May 18, 2021, 4:17 PM CDT for Choctaw County, Sumter County, Washington County, Alabama; 23 counties in Mississippi. It was in force for 118 min.
The area
The outline as issued.
The facts
- Issued
- May 18, 2021, 4:17 PM CDT (21:17 UTC)
- Expired
- May 18, 2021, 6:15 PM CDT
- In force
- 118 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 5%
All 26 counties
Choctaw County, AL, Sumter County, AL, Washington County, AL, Clarke County, MS, Covington County, MS, Forrest County, MS, Greene County, MS, Jasper County, MS, Jefferson Davis County, MS, Jones County, MS, Kemper County, MS, Lamar County, MS, Lauderdale County, MS, Lawrence County, MS, Leake County, MS, Marion County, MS, Neshoba County, MS, Newton County, MS, Noxubee County, MS, Perry County, MS, Rankin County, MS, Scott County, MS, Simpson County, MS, Smith County, MS, Wayne County, MS, Winston County, MS
The radar
The Jackson/Brandon,MS radar (KDGX), 97 km from the middle of the area, began a volume at 21:17 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
Jackson, MS (KJAN), launched 12:00Z, 9.3 hours before the alert went out and 107 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
- 163 J/kg
- Mixed-layer CIN
- -21 J/kg
- Mixed-layer LCL
- 651 m above ground
- 0-6 km bulk shear
- 7 kt
- 0-1 km storm-relative helicity
- 116 m²/s²
- 0-3 km storm-relative helicity
- 241 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.2
The text
As transmitted.
501
ACUS11 KWNS 182117
SWOMCD
SPC MCD 182117
ALZ000-MSZ000-182315-
Mesoscale Discussion 0675
NWS Storm Prediction Center Norman OK
0417 PM CDT Tue May 18 2021
Areas affected...Portions of central...southern and eastern
Mississippi into extreme western Alabama
Concerning...Severe potential...Watch unlikely
Valid 182117Z - 182315Z
Probability of Watch Issuance...5 percent
SUMMARY...A couple brief tornadoes remain possible with the stronger
storms in close proximity to and ahead of the MCV. Given the sparse,
brief nature of the tornado threat, a WW issuance is not expected.
DISCUSSION...Semi-discrete, low topped supercells have developed
immediately ahead of an eastward propagating MCV over the past
couple of hours, with at least two brief tornadoes reported. These
storms are organizing in an environment characterized by modest
0-3km CAPE (100+ J/kg) and low-level vertically oriented voriticity,
but weak effective SRH (mainly under 100 m2/s2). The low-level CAPE
in place will allow for sufficient stretching of the vertical
vorticity to support the potential for a couple more
supercell/landspout hybrid tornadoes for at least a few more hours,
until boundary-layer cooling after peak afternoon heating gradually
erodes the severe threat. Given the sparse and brief nature of the
tornado threat, a WW issuance is not expected.
..Squitieri/Grams.. 05/18/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...BMX...MOB...JAN...LIX...
LAT...LON 31038992 31519030 32149022 32638984 33178938 33338892
33288866 33048839 32858822 32458807 31978801 31538798
31248809 31018854 31038992Nearby
Mesoscale 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.