Alert archive / Arkansas / Mesoscale Discussions in 2011

Mesoscale Discussion 671

April 30, 201135 counties in Arkansas; Dunklin County, Missouri

The Storm Prediction Center issued this mesoscale discussion at Apr 30, 2011, 6:31 PM CDT for 35 counties in Arkansas; Dunklin County, Missouri. It was in force for 29 min.

The area

The outline as issued.

The facts

Issued
Apr 30, 2011, 6:31 PM CDT (23:31 UTC)
Expired
Apr 30, 2011, 7:00 PM CDT
In force
29 min
Issued by
the Storm Prediction Center
All 36 counties

Baxter County, AR, Clay County, AR, Cleburne County, AR, Conway County, AR, Craighead County, AR, Crittenden County, AR, Cross County, AR, Faulkner County, AR, Fulton County, AR, Garland County, AR, Greene County, AR, Independence County, AR, Izard County, AR, Jackson County, AR, Lawrence County, AR, Lonoke County, AR, Marion County, AR, Mississippi County, AR, Monroe County, AR, Montgomery County, AR, Perry County, AR, Poinsett County, AR, Pope County, AR, Prairie County, AR, Pulaski County, AR, Randolph County, AR, Saline County, AR, Searcy County, AR, Sharp County, AR, St. Francis County, AR, Stone County, AR, Van Buren County, AR, White County, AR, Woodruff County, AR, Yell County, AR, Dunklin County, MO

The radar

The Little Rock radar (KLZK), 83 km from the middle of the area, began a volume at 23:34 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.

The nearest sounding before it

Little Rock, AR (KLZK), launched 12:00Z, 11.5 hours before the alert went out and 161 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, Little Rock, AR at 12:00Z on 2011-04-30Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 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, Little Rock, AR at 12:00Z on 2011-04-30The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 306 square meters per square second.19395878Sfc1 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
0 J/kg
Mixed-layer CIN
No buoyant parcel
Mixed-layer LCL
1478 m above ground
0-6 km bulk shear
44 kt
0-1 km storm-relative helicity
306 m²/s²
0-3 km storm-relative helicity
537 m²/s²
Significant tornado parameter
0.0
Supercell composite
1.9

Open this sounding in Storm Lab

The text

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

979 
ACUS11 KWNS 302332
SWOMCD
SPC MCD 302331
TNZ000-ARZ000-MSZ000-MOZ000-010000-

MESOSCALE DISCUSSION 0671
NWS STORM PREDICTION CENTER NORMAN OK
0631 PM CDT SAT APR 30 2011

AREAS AFFECTED...CENTRAL AND NRN AR

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 302331Z - 010000Z

MUCH OF CENTRAL AND NRN AR IS BEING MONITORED FOR A SEVERE WEATHER
WATCH ISSUANCE EARLY THIS EVENING.  SPC COORDINATION WITH AFFECTED
WFOS MAY BE NEEDED SOON...WITH PROBABILITY OF A WATCH ISSUANCE BY
00Z IS 80 PERCENT.

REGIONAL RADAR IMAGERY AND LIGHTNING DATA SHOWED A CONTINUED
INCREASE IN TSTM COVERAGE AND INTENSITY ACROSS WRN TO NERN AR DURING
THE LAST 1-2 HOURS.  SLY WINDS INTO THIS REGION ARE RESULTING IN
SURFACE DEWPOINTS RISING THROUGH THE 60S.  THIS COUPLED WITH
MIDLEVEL LAPSE RATES OF 7-7.5 C/KM IS SUPPORTING MODERATE
INSTABILITY /MLCAPE 1000-1500 J PER KG/ DEVELOPING NEWD.

WHILE MUCH OF THIS REGION HAS BEEN CLOUDY THROUGH THE DAY AND
INITIAL ACTIVITY LIKELY ROOTED ABOVE THE SURFACE...FORECAST
SOUNDINGS SUGGEST THE WARM/MOIST BOUNDARY LAYER MAY BECOME REALIZED
AS THE CAP BASED AROUND 700 MB IS REDUCED.  THIS PROCESS MAY BE
UNDERWAY NOW...BASED ON THE INCREASE IN ACTIVITY AND IS LIKELY
SUPPORTED BY A WEAK MIDLEVEL IMPULSE TRACKING NEWD ACROSS NERN TX.
EFFECTIVE BULK SHEAR TO AROUND 50 KT WILL SUPPORT ORGANIZED STORMS
AND AS THE CAP WEAKENS...STORMS SHOULD BECOME SURFACE BASED.  THIS
WILL RESULT IN AN INCREASED TORNADO POTENTIAL...IN ADDITION TO THE
THREAT FOR HAIL AND DAMAGING WINDS.

..PETERS.. 04/30/2011

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

ATTN...WFO...MEG...LZK...

LAT...LON   34969029 34409185 34379419 35499347 36399262 36499007
            35739002 34969029

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Apr 30, 4:58 PM CDTMesoscale DiscussionSPCLittle River, Sevier92 min
Apr 30, 5:55 PM CDTTornado WatchSPCHempstead, Howard, Little River, Miller, Sevier8 hr
Apr 30, 6:48 PM CDTTornado WatchSPCArkansas, Clark, Cleburne, Conway, Craighead, Cross and 27 more7 hr

Nearby

Mesoscale Discussions in Arkansas, 2011Mesoscale Discussions in Missouri, 2011Every 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.