Mesoscale Discussion 683

Issued

May 1, 2011, 3:18 PM CDT (20:18 UTC)

Expired

May 1, 2011, 4:45 PM CDT

In force

87 min

Issued by

the Storm Prediction Center

The Little Rock radar (KLZK), 116 km from the middle of the area, began a volume at 20:19 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.

976 
ACUS11 KWNS 012019
SWOMCD
SPC MCD 012018
ALZ000-TNZ000-MSZ000-MOZ000-ARZ000-LAZ000-TXZ000-OKZ000-012145-

MESOSCALE DISCUSSION 0683
NWS STORM PREDICTION CENTER NORMAN OK
0318 PM CDT SUN MAY 01 2011

AREAS AFFECTED...SRN/ERN AR...NWRN LA...NWRN MS...WRN TN...NERN TX

CONCERNING...TORNADO WATCH 262...

VALID 012018Z - 012145Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 262 CONTINUES.

LATEST SFC ANALYSIS DEPICTS A FRONT LYING ALONG THE AR/TN BORDER AND
EXTENDING SWWD INTO SWRN AR AND NERN TX...AND FARTHER SW INTO CNTRL
TX. THE FRONT HAS BECOME NEARLY STATIONARY ACROSS MUCH OF THE WW
AREA...WHILE A REMNANT BAROCLINIC ZONE /DRIVEN BY EARLIER CONVECTION
ON THE COOL SIDE OF THE BOUNDARY/ IS LIFTING NWD ACROSS SWRN TN. THE
MOST ROBUST CONVECTION THUS FAR HAS BEEN LIMITED TO PORTIONS OF
CNTRL AR INTO WRN TN. THE GREATEST SVR THREAT DURING THE NEXT COUPLE
OF HOURS WILL BE FOUND WITH THE QUASI-LINEAR CONVECTIVE STRUCTURE IN
WRN TN THAT JUST CROSSED THE MS RIVER...AND DISCRETE CONVECTION
DEVELOPING FARTHER SOUTH. THIS ACTIVITY WILL CONTINUE PROGRESSING
EWD AMIDST MUCAPE VALUES OF 1000-2000 J/KG AND EFFECTIVE BULK SHEAR
MAGNITUDES OF 60-70 KT. ENHANCED LOW-LEVEL WIND SHEAR /EFFECTIVE SRH
VALUES OF 200-400 M2 PER S2/ WILL BE FOUND INVOF THE REMNANT
BAROCLINIC ZONE. NEAR AND SOUTH OF THIS FEATURE...THE ABSENCE OF
GREATER CINH WILL LIKELY YIELD A GREATER CHANCE FOR SURFACE-BASED
STORMS...INCLUDING THE POTENTIAL FOR LARGE HAIL...DMGG WINDS...AND
TORNADOES. THE WW HAS BEEN EXPANDED EWD PER COORDINATION WITH WFO
MEG TO ADDRESS THIS EWD-SHIFTING THREAT. HOWEVER...THE SVR THREAT IS
EXPECTED TO DIMINISH AS THE STORMS DEPART THE AXIS OF GREATER
INSTABILITY WHILE ENTERING MIDDLE TN.

ALSO OF NOTE...THE THREAT FOR HEAVY RAINFALL WILL PERSIST WITH
CONTINUED CONVECTIVE REGENERATION ACROSS PORTIONS OF THE MID-SOUTH
REGION. STRONG MOISTURE TRANSPORT WILL LIKELY SUPPORT RAINFALL RATES
OF 1-2 IN/HR...WITH THE SFC FRONT REMAINING A NEARLY STATIONARY
FOCUSING MECHANISM FOR THE CONVECTION. THIS THREAT WILL CONTINUE
INTO THE EVENING AS DEVELOPING CONVECTION UPSTREAM MOVES INTO THE
AREA.

MEANWHILE...CONTINUED SFC HEATING OVER NERN TX...NWRN LA...AND SWRN
AR IS WEAKENING CONVECTIVE INHIBITION FOR SFC-BASED PARCELS INVOF
THE FRONT. THE 16Z SOUNDING FOR SHV MODIFIED FOR CURRENT CONDITIONS
INDICATES MLCAPE AROUND 2800 J/KG WITH LITTLE IN THE WAY OF CINH.
THE PRESENCE OF A WARM LAYER IN THE 700-800-MB LAYER HAS PREVENTED
THE INITIATION OF DEEPER CONVECTION THUS FAR. HOWEVER...LATEST
VISIBLE SATELLITE IMAGERY INDICATES THE RECENT DEVELOPMENT OF A
BROAD CUMULUS FIELD WITHIN 30 NM OF THE FRONT /ON THE WARM SIDE/
ACROSS NERN TX. CONTINUED DIFFERENTIAL HEATING ACROSS THE FRONT WILL
LIKELY PROMOTE INCREASING FRONTAL CONVERGENCE OVER THE NEXT COUPLE
OF HOURS. AS SUCH...THE 18Z RUN OF THE EXPERIMENTAL HRRR DEPICTS
CONVECTION DEVELOPING IN THIS AREA BETWEEN 22Z AND 23Z. FORECAST
SOUNDINGS AND OBSERVATIONS SUGGEST EFFECTIVE INFLOW LAYERS WILL BE
ROOTED AT THE SFC...AND SUPERCELLS CAPABLE OF PRODUCING DMGG WINDS
AND LARGE HAIL WILL BE OF CONCERN. EFFECTIVE SRH VALUES OF 300-400
M2/S2 INVOF THE FRONT OWING TO STRONGLY CLOCKWISE-CURVED HODOGRAPHS
IN THE LOW LEVELS WILL ALSO YIELD A THREAT FOR
TORNADOES...ESPECIALLY WITH ANY DISCRETE CONVECTION.

..COHEN.. 05/01/2011

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

ATTN...WFO...OHX...HUN...MEG...JAN...LZK...SHV...HGX...FWD...

LAT...LON   36298948 36248809 35318765 34508794 34378893 34118999
            33629095 33159176 32399316 31459464 31389563 31449666
            31899705 32419667 33199588 34429408 35929064 36298948

Mesoscale Discussions in Arkansas, 2011Mesoscale Discussions in Texas, 2011Mesoscale Discussions in Tennessee, 2011Every mesoscale discussion in 2011

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.