Alert archive / Oklahoma / Mesoscale Discussions in 2011

Mesoscale Discussion 804

May 18, 201119 counties in Oklahoma; Clay County, Cooke County, Montague County, Texas

The Storm Prediction Center issued this mesoscale discussion at May 18, 2011, 2:44 PM CDT for 19 counties in Oklahoma; Clay County, Cooke County, Montague County, Texas. It was in force for 61 min.

The area

The outline as issued.

The facts

Issued: May 18, 2011, 2:44 PM CDT (19:44 UTC)
Expired: May 18, 2011, 3:45 PM CDT
In force: 61 min
Issued by: the Storm Prediction Center

All 22 counties

Blaine County, OK, Caddo County, OK, Canadian County, OK, Carter County, OK, Cleveland County, OK, Comanche County, OK, Cotton County, OK, Garfield County, OK, Garvin County, OK, Grady County, OK, Jefferson County, OK, Kingfisher County, OK, Logan County, OK, Love County, OK, Major County, OK, McClain County, OK, Murray County, OK, Oklahoma County, OK, Stephens County, OK, Clay County, TX, Cooke County, TX, Montague County, TX

The radar

The Norman radar (KTLX), 84 km from the middle of the area, began a volume at 19:41 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 watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

Tornado Watch 306May 18, 3:50 PM CDT

The nearest sounding before it

Norman, OK (KOUN), launched 12:00Z, 7.7 hours before the alert went out and 73 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: 2 J/kg
Mixed-layer CIN: -612 J/kg
Mixed-layer LCL: 934 m above ground
0-6 km bulk shear: 49 kt
0-1 km storm-relative helicity: 525 m²/s²
0-3 km storm-relative helicity: 713 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 10.1

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

911 
ACUS11 KWNS 181944
SWOMCD
SPC MCD 181944 
OKZ000-TXZ000-182045-

MESOSCALE DISCUSSION 0804
NWS STORM PREDICTION CENTER NORMAN OK
0244 PM CDT WED MAY 18 2011

AREAS AFFECTED...WRN/CNTRL OK...PORTIONS OF N TX

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 181944Z - 182045Z

THE POTENTIAL FOR CONVECTIVE INITIATION APPEARS TO BE INCREASING
THIS AFTERNOON ACROSS WRN OK AND PORTIONS OF N TX...ALTHOUGH SOME
UNCERTAINTY STILL REMAINS. THE ENVIRONMENT WILL BE FAVORABLE FOR
ISOLATED SUPERCELLS CAPABLE OF PRODUCING VERY LARGE HAIL AND
POSSIBLY TORNADOES. THE AREA IS BEING MONITORED FOR A POSSIBLE WW. 

STRONG DIABATIC HEATING ACROSS WRN OK HAS RESULTED IN AN EWD
ADVANCEMENT OF A SFC DRYLINE...POSITIONED FROM 40 SSW SPS TO FSI TO
40 NE CSM /PER 19Z SUBJECTIVE ANALYSIS/. THIS FEATURE IS ATTENDANT
TO A DEEPENING SFC LOW...AND A DIFFUSE BAROCLINIC ZONE/WARM FRONT
PROTRUDING ESE ACROSS CNTRL AND SERN OK. THERE IS SOME UNCERTAINTY
REGARDING CONVECTIVE INITIATION AS RECENT SFC OBSERVATIONS HAVE
INDICATED WINDS IN THE POST-DRYLINE ENVIRONMENT HAVE BACKED TOWARDS
THE S /LIMITING LOW-LEVEL CONVERGENCE/. THIS MAY BE OFFSET BY AN
AREA OF IMPLIED ASCENT THAT APPEARS TO BE SPREADING EWD OUT OF THE
SRN HIGH PLAINS...WHERE A BROAD SWATH OF CIRRUS HAS DEVELOPED IN
RECENT VISIBLE SATELLITE/WATER VAPOR IMAGES. AS THIS APPROACHES WRN
OK AND NW TX...WEAKENING CINH AND INCREASING MID-LEVEL ASCENT SHOULD
LEAD TO A MORE FAVORABLE ENVIRONMENT FOR CONVECTIVE INITIATION THIS
AFTERNOON.

RICH BOUNDARY LAYER MOISTURE AHEAD OF THE DRYLINE /LOWER-MID 60S SFC
DEW POINTS/ ALONG WITH STEEP MIDLEVEL LAPSE RATES IN EXCESS OF 7 DEG
C PER KM HAS YIELDED MLCAPE VALUES OF 1500-2000 J/KG...WHICH WILL
SUPPORT A THREAT FOR VERY LARGE HAIL. ADDITIONALLY...ENHANCED
LOW-LEVEL WIND SHEAR RESULTING FROM BACKED FLOW /PARTICULARLY WITH
NWD EXTENT/...ALONG WITH A FAVORED DISCRETE CONVECTIVE MODE DUE TO A
SIGNIFICANT ORTHOGONAL COMPONENT OF THE EFFECTIVE SHEAR VECTOR
RELATIVE TO THE DRYLINE...SHOULD SUPPORT A THREAT FOR TORNADOES IF
LONG-LIVED SUPERCELLS CAN DEVELOP. HOWEVER...CLOUD COVER ACROSS
CNTRL OK HAS LIMITED HEATING/INSTABILITY PRIMARILY E OF I-35...WITH
SOME QUESTION REGARDING MAINTENANCE OF THUNDERSTORMS MOVING E OFF
THE DRYLINE.

..ROGERS.. 05/18/2011

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

ATTN...WFO...FWD...OUN...

LAT...LON   36619876 36569810 36199732 34859686 33919697 33599725
            33679820 33849867 34339871 34969856 35659892 36239896
            36489880 36619876

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 18, 3:48 PM CDT	Tornado Watch	SPC	Alfalfa, Blaine, Caddo, Canadian, Carter, Cleveland and 24 more	3 hr
May 18, 6:48 PM CDT	Mesoscale Discussion	SPC	Alfalfa, Blaine, Caddo, Canadian, Carter, Cleveland and 19 more	87 min

Nearby

Mesoscale Discussions in Oklahoma, 2011 Mesoscale Discussions in Texas, 2011 Every mesoscale discussion in 2011

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.