SWOMCD
SPC MCD 201945
SDZ000-NDZ000-MTZ000-WYZ000-202045-
MESOSCALE DISCUSSION 0841
NWS STORM PREDICTION CENTER NORMAN OK
0245 PM CDT SUN MAY 20 2007
AREAS AFFECTED...PORTIONS SRN MT...NRN WY...WRN SD.
CONCERNING...SEVERE POTENTIAL...WATCH LIKELY
VALID 201945Z - 202045Z
CONDITIONS STEADILY WILL BECOME MORE FAVORABLE FOR SVR THROUGH LATE
AFTERNOON/EARLY EVENING...INCLUDING SUPERCELLS...AND WW PROBABLY
WILL BE REQUIRED.
SFC MESOANALYSIS SHOWS LOW NEAR GEY...WITH WAVY FRONTAL ZONE EWD
ACROSS AREA BETWEEN GCC-DGW...SRN BLACK HILLS...TO VICINITY MN/IA
BORDER. WY PORTION OF THIS BOUNDARY SHOULD RETREAT NWD AS WARM
FRONT DURING NEXT FEW HOURS...S OF WHICH NEAR-SFC AIR MASS SHOULD
BECOME MORE STRONGLY MIXED AND DRIER THAN THAT TO ITS N. MOIST AXIS
WILL BECOME EVEN MORE SHARPLY DEFINED N OF FRONT FROM NWRN SD WWD
OVER S-CENTRAL MT...SUPPORTING MLCAPES IN 800-1500 J/KG RANGE WITH
ADDITIONAL INSOLATION. MAIN FOCI FOR INITIATION WILL BE MOUNTAINS
INVOF WY/MT BORDER...THOUGH A FEW STORMS MAY DEVELOP IN MOIST
SECTOR. THICKENING HIGH CLOUDS WITH NWWD EXTENT...ACROSS SWRN
MT...MAY LIMIT HEATING AND CONVECTIVE DEVELOPMENT...AND THEREFORE
MAKE SVR POTENTIAL ACROSS CENTRAL/W-CENTRAL MT MORE CONDITIONAL THAN
THAT CLOSER TO WY BORDER.
DEEP-LAYER SHEAR SHOULD REMAIN RELATIVELY WEAK OVER SD...WITH BLACK
HILLS CONVECTION ALREADY PRODUCING OUTFLOW BOUNDARIES.
HOWEVER...SHEAR INCREASES WITH WWD EXTENT ACROSS THIS REGION...IN
PROGRESSIVELY CLOSE PROXIMITY TO APCHG ID PERTURBATION EVIDENT IN
MOISTURE CHANNEL IMAGERY. AS TROUGH MOVES NEWD OVER NEXT SEVERAL
HOURS...CONTINUED LOW LEVEL ISALLOBARIC/ISALLOHYPSIC RESPONSE WILL
YIELD STRONGER LOW LEVEL FLOW...AND BY EXTENSION...MORE FAVORABLE
DEEP-LAYER SHEAR AND STORM-RELATIVE INFLOW. LOW LEVEL HODOGRAPHS
APPEARED RATHER SMALL AT 19Z...WITH ONLY 10 KT FLOW OBSERVED THROUGH
LOWEST 2 KM AGL IN VWP AROUND BIL...HOWEVER RUC FCST SOUNDINGS
REASONABLY INDICATE DEVELOPMENT OF 0-3 KM SRH 200-400 J/KG BY 23-00Z
TIME FRAME. EFFECTIVE BULK SHEAR MAGNITUDE...ALREADY 50-60 KT OVER
S-CENTRAL MT...MAY INCREASE ANOTHER 10-15 KT AS LOW LEVEL WINDS
SHIFT TOWARD LARGER ELY COMPONENT AND STRENGTHEN.
.EDWARDS.. 05/20/2007
..PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...BIS...UNR...CYS...BYZ...GGW...RIW...TFX...
45621039 45971123 46621079 47020946 47000609 46130420
45990387 44840256 43880289 43480441 43520646 44070831
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