Mesoscale Discussion 660

Issued

May 20, 2016, 2:33 PM CDT (19:33 UTC)

Expired

May 20, 2016, 5:00 PM CDT

In force

2 hr

Issued by

the Storm Prediction Center

Chance of a watch

20%

Counties Blount County, AL, Cullman County, AL, Fayette County, AL, Franklin County, AL, Jefferson County, AL, Lamar County, AL, Lawrence County, AL, Limestone County, AL, Madison County, AL, Marion County, AL, Marshall County, AL, Morgan County, AL, Pickens County, AL, Tuscaloosa County, AL, Walker County, AL, Winston County, AL, Lowndes County, MS, Giles County, TN, Lincoln County, TN, Moore County, TN

The Columbus AFB radar (KGWX), 97 km from the middle of the area, began a volume at 19:35 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.

837 
ACUS11 KWNS 201933
SWOMCD
SPC MCD 201933 
ALZ000-TNZ000-MSZ000-202200-

MESOSCALE DISCUSSION 0660
NWS STORM PREDICTION CENTER NORMAN OK
0233 PM CDT FRI MAY 20 2016

AREAS AFFECTED...PORTIONS OF NORTHERN ALABAMA...AND SOUTH MIDDLE
TENNESSEE

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

VALID 201933Z - 202200Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...A FEW THUNDERSTORMS ARE DEVELOPING IN A SOMEWHAT
DESTABILIZED AIR MASS AHEAD OF A LIFTING SHORTWAVE TROUGH THAT ARE
CAPABLE OF PRODUCING MARGINALLY SEVERE HAIL AND WIND GUSTS OVER THE
NEXT FEW HOURS.

DISCUSSION...A SMALL AREA OF DESTABILIZATION RESULTING FROM
AFTERNOON HEATING ON THE NORTHWEST SIDE OF THE GULF-COAST MCS...AN
INCREASE IN DEEP-LAYER SHEAR ASSOCIATED WITH A SMALL MID-LEVEL
WESTERLY SPEED MAX...AND SCATTERED THUNDERSTORM DEVELOPMENT IN THE
VICINITY OF A WEAK SURFACE LOW AND WARM FRONT...IS CONTRIBUTING TO A
THREAT FOR MARGINAL SEVERE HAIL AND WIND GUSTS IN THE NEXT FEW
HOURS.  ALTHOUGH MID-LEVEL LAPSE RATES ARE LIKELY RATHER POOR IN THE
WAKE OF THE MORNING CONVECTION...SURFACE TEMPERATURES HAVE RISEN TO
THE MID-UPPER 70S WITH SURFACE DEWPOINTS HOLDING IN THE UPPER 60S IN
A REGION EAST OF THE COLD FRONT AND SOUTH OF THE WARM FRONT
CONTRIBUTING TO SURFACE-BASED CAPE VALUES OF 500-1000 J/KG. THE
INITIAL STORMS FROM STARKVILLE MS TO FAR NORTHWESTERN AL HAVE
EXHIBITED NARROW UPDRAFTS AND WEAK REFLECTIVITIES...POSSIBLY
INDICATING THAT MID-LEVEL DRY AIR IS BEING ENTRAINED INTO THE
UPDRAFTS. HOWEVER...ANOTHER HOUR OF HEATING AND THE PROGRESSION OF
THE STORMS INTO MORE BACKED SURFACE WINDS COULD SUPPORT AN INCREASE
IN CONVECTIVE INTENSITY OVER THE NEXT HOUR OR TWO...AS INDICATED IN
RECENT HRRR AND HRRR-PARALLEL RUNS. THE THREAT IS EXPECTED TO
SUBSIDE NEAR SUNSET AS THE COLD FRONT AND SURFACE LOW COLLIDES WITH
THE STABLE AIR MASS LEFT OVER FROM THE MORNING CONVECTION.

..CONIGLIO/HART.. 05/20/2016

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

ATTN...WFO...OHX...BMX...HUN...MEG...JAN...

LAT...LON   34188838 34538797 34938752 35088739 35258699 35408661
            35328634 35088609 34848604 34538610 34118636 33708659
            33388701 32988763 32918776 32868811 33078844 33708850
            33848846 34188838

Mesoscale Discussions in Alabama, 2016Mesoscale Discussions in Tennessee, 2016Mesoscale Discussions in Mississippi, 2016Every mesoscale discussion in 2016

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.