SPC MD 1641

MD 1641 CONCERNING SEVERE POTENTIAL…WATCH POSSIBLE FOR PORTIONS CENTRAL/SRN IA.


MESOSCALE DISCUSSION 1641
NWS STORM PREDICTION CENTER NORMAN OK
0558 PM CDT TUE AUG 06 2013

AREAS AFFECTED...PORTIONS CENTRAL/SRN IA.

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 062258Z - 070100Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...CONDITIONAL SVR THREAT EXISTS OVER DISCUSSION AREA...GIVEN
MAINTENANCE AND UPSCALE DEVELOPMENT OF ISOLATED/YOUNG CONVECTION NOW
EVIDENT.  DAMAGING GUSTS WOULD BE MAIN CONCERN...WITH ISOLATED/MRGL
SVR HAIL ALSO PSBL.

DISCUSSION...SFC MESOANALYSIS SHOWED CONFLUENCE LINE -- SEPARATING
WLY/SWLY FLOW FROM SSWLY/SLY WINDS...LOCATED FROM NEAR CID WSWWD
ACROSS NW CORNER OF MO TO KS/NEB BORDER S BIE.  SEPARATE/MORE
DIFFUSE CONFLUENCE LINE WAS DRAWN FROM BOONE COUNTY AND NRN OMA
SUBURBS.  WIDELY SCATTERED TCU/CB WAS EVIDENT ALONG AND BETWEEN
THESE BOUNDARIES...IN THERMODYNAMIC ENVIRONMENT CHARACTERIZED BY SFC
DEW POINTS UPPER 60S TO 70S F...AND MLCAPE GENERALLY 1500-2500 J/KG
IN MODIFIED RR SOUNDINGS.  VIS IMAGERY SHOWS FAIRLY ABRUPT NRN BOUND
TO CONVECTIVE FIELD AS WELL...NEAR AND N OF I-80...RELATED TO SRN
FRINGES OF INFLUENCE OF DRIER...MORE WELL-MIXED BOUNDARY LAYER OVER
NRN IA.  THOUGH CONFLUENT...SFC FLOW ALSO IS WEAK...GENERALLY 5-10
KT ACROSS MOST OF THIS AREA...WHICH WILL LIMIT
CONVERGENCE...STORM-RELATIVE INFLOW AND HODOGRAPH SIZE.  DESPITE
WEAK SFC WINDS...SPEED INCREASE WITH HEIGHT IS STRONG ENOUGH TO
YIELD 40-45 KT EFFECTIVE SHEAR MAGNITUDE...SUPPORTING SOME
ORGANIZATION POTENTIAL WITH ANY SUSTAINED TSTMS.

REF SPC MESOSCALE DISCUSSION 1640 FOR COVERAGE OF MORE IMMEDIATELY
PREFRONTAL SVR POTENTIAL NW AND W OF THIS REGIME.

..EDWARDS/THOMPSON.. 08/06/2013

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

ATTN...WFO...DVN...DMX...OAX...

LAT...LON   41009574 41849443 42549389 42299189 41039170 40669241
            40719489 41009574

via SPC Forecast Products http://www.spc.noaa.gov/products/md/md1641.html