Alert archive / Texas / Mesoscale Discussions in 2021

Mesoscale Discussion 120

February 18, 20219 counties in Texas

The Storm Prediction Center issued this mesoscale discussion at Feb 18, 2021, 10:07 AM CST for 9 counties in Texas. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued
Feb 18, 2021, 10:07 AM CST (16:07 UTC)
Expired
Feb 18, 2021, 12:30 PM CST
In force
2 hr
Issued by
the Storm Prediction Center
Concerning
Heavy snow

Counties Bandera County, TX, Bexar County, TX, Comal County, TX, Guadalupe County, TX, Kendall County, TX, Kinney County, TX, Medina County, TX, Real County, TX, Uvalde County, TX

The radar

The Laughlin AFB radar (KDFX), 44 km from the middle of the area, began a volume at 16:07 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 12:00Z, 4.1 hours before the alert went out and 317 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, Corpus Christi, TX at 12:00Z on 2021-02-18Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 4 joules per kilogram.LCLEL10008507005003002001001 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, Corpus Christi, TX at 12:00Z on 2021-02-18The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 93 square meters per square second.1939587897Sfc1 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
4 J/kg
Mixed-layer CIN
0 J/kg
Mixed-layer LCL
398 m above ground
0-6 km bulk shear
76 kt
0-1 km storm-relative helicity
93 m²/s²
0-3 km storm-relative helicity
249 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

472 
ACUS11 KWNS 181607
SWOMCD
SPC MCD 181607 
TXZ000-181830-

Mesoscale Discussion 0120
NWS Storm Prediction Center Norman OK
1007 AM CST Thu Feb 18 2021

Areas affected...southern portions of the Edwards Plateau

Concerning...Heavy snow 

Valid 181607Z - 181830Z

SUMMARY...Heavy snowfall will persist for a few more hours across
southern portions of the Edwards Plateau.

DISCUSSION...Strong 700mb frontogenesis has led to a narrow corridor
of heavy snow from near Del Rio, TX eastward to near San Antonio.
Snowfall rates as high as 1.5 inches per hour have been reported
beneath this band. This frontogenesis is expected to persist into
early afternoon before waning by mid to late afternoon which should
result in lessening snowfall rates. This area of frontogenesis is
expected to remain mostly stationary which will likely lead to very
heavy snow accumulations beneath this band, especially near Del Rio,
TX.

..Bentley.. 02/18/2021

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

ATTN...WFO...EWX...

LAT...LON   29770157 29969999 30059908 29959838 29899784 29659760
            29409777 29249854 29019950 28850016 28870055 29010077
            29260096 29400116 29540141 29620145 29770157

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Feb 18, 12:51 PM CSTMesoscale DiscussionSPCKinney, Uvalde3 hr

Nearby

Mesoscale Discussions in Texas, 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.