Alert archive / Texas / Mesoscale Discussions in 2016

Mesoscale Discussion 409

April 18, 20164 counties in Texas

The Storm Prediction Center issued this mesoscale discussion at Apr 18, 2016, 12:02 AM CDT for 4 counties in Texas. It was in force for 118 min.

The area

The outline as issued.

The facts

Issued: Apr 18, 2016, 12:02 AM CDT (05:02 UTC)
Expired: Apr 18, 2016, 2:00 AM CDT
In force: 118 min
Issued by: the Storm Prediction Center
Chance of a watch: 20%

Counties Harris County, TX, Liberty County, TX, Montgomery County, TX, San Jacinto County, TX

The radar

The Houston radar (KHGX), 86 km from the middle of the area, began a volume at 05:04 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

Lake Charles Mun, LA (KLCH), launched 00:00Z, 5.0 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-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

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: 466 J/kg
Mixed-layer CIN: -20 J/kg
Mixed-layer LCL: 736 m above ground
0-6 km bulk shear: 21 kt
0-1 km storm-relative helicity: 88 m²/s²
0-3 km storm-relative helicity: 130 m²/s²
Significant tornado parameter: 0.2
Supercell composite: 1.8

Open this sounding in Storm Lab

The text

As transmitted.

431 
ACUS11 KWNS 180502
SWOMCD
SPC MCD 180502 
TXZ000-180700-

MESOSCALE DISCUSSION 0409
NWS STORM PREDICTION CENTER NORMAN OK
1202 AM CDT MON APR 18 2016

AREAS AFFECTED...SOUTHEAST TX INCLUDING THE NORTH HALF OF THE
HOUSTON METRO

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

VALID 180502Z - 180700Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...IN ADDITION TO THE HEAVY RAIN THREAT PER WPC MPD
127...LOCALLY STRONG WIND GUSTS WILL BE POSSIBLE WITH THE SLOW
NORTHEASTWARD-MOVING CONVECTIVE COMPLEX ACROSS THE NORTH HALF OF THE
HOUSTON METRO INTO ADJACENT PARTS OF SOUTHEAST TX.  GREATEST THREAT
FOR THESE ISOLATED STRONG WINDS SHOULD EXTEND FROM SOUTHERN GRIMES
AND HARRIS COUNTIES TO SAN JACINTO AND LIBERTY COUNTIES.

DISCUSSION...MOSAIC AND SINGLE-SITE RADAR IMAGERY SHOWED THE
EVOLUTION OF A WELL-ORGANIZED COMPACT CONVECTIVE SYSTEM WITH AN MCV
LOCATED NEAR THE BORDERS OF GRIMES/MONTGOMERY/HARRIS COUNTIES SINCE
0330-04Z. THE LEADING EDGE OF THIS SYSTEM EXTENDED FROM SOUTHWEST
MONTGOMERY TO WESTERN HARRIS COUNTIES...WHILE VELOCITY DATA PER
WSR-88D HGX RADAR INDICATED A REAR-INFLOW JET AND STRONG
SOUTHEASTERLY LOW-LEVEL WINDS ON THE LEADING EDGE.  50 KT WAS
DETECTED AT APPROXIMATELY 4500 FEET AGL IN NORTH-CENTRAL HARRIS
COUNTY AND UP TO 60 KT AT 55-60 KT AT APPROXIMATELY 7500 FEET IN
SOUTHWESTERN MONTGOMERY COUNTY.  

GIVEN THE MCV POSSIBLY LOCALLY ENHANCING NEARBY WIND FIELDS AND THE
AFOREMENTIONED WIND SPEEDS...LOCALLY STRONG WIND GUSTS THROUGH THE
PROCESS OF PRECIPITATION LOADING WITHIN DOWNDRAFTS WILL BE POSSIBLE
THROUGH AT LEAST 07Z AS THE CONVECTIVE SYSTEM SHIFTS SLOWLY TO THE
NORTHEAST.

..PETERS/EDWARDS.. 04/18/2016

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...HGX...

LAT...LON   29699566 30079577 30319598 30419593 30609557 30719509
            30599491 30329477 30009476 29849506 29699566

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Apr 17, 8:21 PM CDT	Mesoscale Discussion	SPC	Starr, Zapata	84 min
Apr 18, 4:29 AM CDT	Mesoscale Discussion	SPC	Kinney, Medina, Uvalde	61 min
Apr 18, 5:10 AM CDT	Mesoscale Discussion	SPC	Fort Bend, Harris, Liberty	95 min
Apr 18, 12:57 PM CDT	Mesoscale Discussion	SPC	Brooks, Cameron, Dimmit, Duval, Hidalgo, Jim Hogg and 10 more	2 hr
Apr 18, 3:21 PM CDT	Severe Thunderstorm Watch	SPC	Brooks, Cameron, Duval, Hidalgo, Jim Hogg, Jim Wells and 7 more	8 hr
Apr 18, 5:54 PM CDT	Mesoscale Discussion	SPC	Brooks, Cameron, Dimmit, Duval, Hidalgo, Jim Hogg and 10 more	2 hr

Nearby

Mesoscale Discussions in Texas, 2016 Every mesoscale discussion in 2016

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.