Mesoscale Discussion 1740
The Storm Prediction Center issued this mesoscale discussion at Sep 13, 2021, 7:23 PM CDT. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Sep 13, 2021, 7:23 PM CDT (00:23 UTC)
- Expired
- Sep 13, 2021, 9:30 PM CDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
The radar
The Houston radar (KHGX), 111 km from the middle of the area, began a volume at 00:23 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
Corpus Christi, TX (KCRP), launched 00:00Z, 0.4 hours before the alert went out and 228 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
- 36 J/kg
- Mixed-layer CIN
- -242 J/kg
- Mixed-layer LCL
- 656 m above ground
- 0-6 km bulk shear
- 15 kt
- 0-1 km storm-relative helicity
- -68 m²/s²
- 0-3 km storm-relative helicity
- -42 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
501
ACUS11 KWNS 140023
SWOMCD
SPC MCD 140023
TXZ000-140230-
Mesoscale Discussion 1740
NWS Storm Prediction Center Norman OK
0723 PM CDT Mon Sep 13 2021
Areas affected...Parts of the middle Texas coast
Concerning...Severe potential...Watch unlikely
Valid 140023Z - 140230Z
Probability of Watch Issuance...20 percent
SUMMARY...Supercell structures capable of producing tornadoes may
approach a small portion of middle Texas coastal areas east of
Palacios for a period this evening, but the risk for tornadoes
across and inland of mid and upper Texas coastal areas appears
rather low through tonight.
DISCUSSION...As Tropical Storm Nicholas slowly approaches the
Matagorda Bay vicinity, numerous cells with embedded mesocyclones
have been evident offshore, within a broad area of convection and
bands north-northeast through east of the circulation center. This
is within the sector of strongest southerly to south-southeasterly
low-level flow, which is contributing to large clockwise curved
low-level hodographs, and has supported the advection of mid/upper
70s surface dew points in at least a narrow corridor as far
northwest as the Brazos 451 Oil Platform.
There appears at least some potential that this environment could
advect into immediate coastal areas east of Palacios during the next
few hours, with a window of opportunity for a supercell structure
capable of producing a tornado or two. Otherwise, it appears that
environmental conditions supportive of tornadoes will generally
remain offshore through the overnight hours. Latest forecast
soundings for upper Texas coastal areas, suggest that relatively
stable boundary-layer conditions will be maintained through
daybreak.
..Kerr/Edwards.. 09/14/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...HGX...
LAT...LON 28779586 28869559 28939531 28859508 28359400 27839420
27579477 28269511 28599595 28779586Nearby
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.