Mesoscale Discussion 657

Issued

May 1, 2012, 11:08 PM CDT (04:08 UTC)

Expired

May 2, 2012, 1:15 AM CDT

In force

2 hr

Issued by

the Storm Prediction Center

The Des Moines radar (KDMX), 108 km from the middle of the area, began a volume at 04:10 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.

567 
ACUS11 KWNS 020408
SWOMCD
SPC MCD 020408 
IAZ000-NEZ000-020615-

MESOSCALE DISCUSSION 0657
NWS STORM PREDICTION CENTER NORMAN OK
1108 PM CDT TUE MAY 01 2012

AREAS AFFECTED...PORTIONS IA AND ERN NEB.

CONCERNING...SEVERE THUNDERSTORM WATCH 224...

VALID 020408Z - 020615Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 224
CONTINUES.

SUMMARY...EXPECT INITIALLY SEPARATE AREAS OF CONVECTION OVER NWRN IA
AND ERN NEB TO CONSOLIDATE AND SHIFT EWD ACROSS WW AREA.  AS THIS
OCCURS...INITIAL HAIL THREAT WITH ERN NEB CONVECTION SHOULD
TRANSITION MORE TOWARD DAMAGING GUSTS...WITH LARGE HAIL STILL
POSSIBLE...WHILE DAMAGING WIND REMAINS PRIMARY CONCERN OVER NWRN IA.
NRN PORTION OF IA MCS SHOULD WEAKEN AFTER CROSSING FRONTAL ZONE
OUTLINED BELOW.

DISCUSSION...4Z SFC MESOANALYSIS SHOWED QUASISTATIONARY FRONT FROM
W-CENTRAL IL NWWD ACROSS OTM AND MCW AREAS THEN NWD INTO EXTREME SRN
MN...WHERE IT WILL CONTINUE TO BE OVERTAKEN BY MCS.  BOUNDARY LAYER
E OF THIS FRONT WILL REMAIN CHARACTERIZED BY PROGRESSIVELY DEEPER
AND LOWER-THETAE AIR...AND RELATED STRENGTHENING OF MLCINH WITH EWD
EXTENT.  SOME PARTS OF TSTM COMPLEX MAY BE MAINTAINED ATOP ERN IA
AIR MASS BY INCREASING ELEVATED BUOYANCY.  THIS WILL BE RELATED TO
WAA AND MOISTURE TRANSPORT FOSTERED BY 50-60 KT SWLY LLJ...WHICH
WILL HAVE PASSED THROUGH 850-MB MOISTURE MAX ANALYZED AT 00Z NEAR
TOP.  HOWEVER...SVR GUST POTENTIAL WILL BE REDUCED EWD FROM FRONT BY
STABLE LAYER.

FARTHER SW ACROSS WRN/CENTRAL IA...MLCINH WILL BE WEAKER AND SLOW TO
BUILD...GIVEN RELATIVELY HIGH BOUNDARY-LAYER THETAE AND PROSPECT OF
STG LIFT FROM FORCED ASCENT ASSOCIATED WITH GROWING CONVECTIVE
COMPLEX.  FCST SOUNDINGS AND MODIFIED RAOBS SUGGEST MLCAPE INCREASES
FROM AROUND 500 J/KG...IN NARROWING WARM SECTOR NEAR MN BORDER...TO
ABOVE 2500 J/KG OVER SERN NEB.  SUBTLE LARGE-SCALE ASCENT FROM APCHG
CENTRAL/ERN NEB SHORTWAVE TROUGH SHOULD HELP TO MAINTAIN STEEP LAPSE
RATES AND BUOYANCY OVER PRECONVECTIVE AIR MASS...IN CONJUNCTION WITH
FAVORABLE LOW-LEVEL MOISTURE.  EFFECTIVE SHEAR MAGNITUDES IN 40-50
KT RANGE WILL CONTINUE...AND MAY INTENSIFY SLIGHTLY AS GRADIENT
WINDS ALOFT RESPOND TO APCHG PERTURBATION.  AS SUCH...SVR THREAT
SHOULD CONTINUE ACROSS REMAINDER WW AREA IN SERN NEB/IA...AND MAY
EXTEND TO PORTIONS OF CENTRAL/SRN IA NEAR AND W OF FRONT BUT NOT YET
IN ANY WW.

..EDWARDS.. 05/02/2012

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

ATTN...WFO...DVN...ARX...DMX...FSD...OAX...GID...

LAT...LON   40399849 42039702 42609599 42719513 43369446 43389216
            42459217 42059219 41389241 40929398 40589577 40409707
            40399849

Mesoscale Discussions in Iowa, 2012Mesoscale Discussions in Nebraska, 2012Every mesoscale discussion in 2012

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.