MESO: Mesoscale Discussion 1521

ACUS11 KWNS 202058
SWOMCD
SPC MCD 202058
MTZ000-202230-

MESOSCALE DISCUSSION 1521
NWS STORM PREDICTION CENTER NORMAN OK
0358 PM CDT FRI JUL 20 2012

AREAS AFFECTED...WRN INTO PARTS OF CNTRL MONTANA

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 202058Z - 202230Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...TRENDS ARE BEING MONITORED FOR THE POSSIBILITY OF AN
INCREASING SEVERE THREAT WHICH COULD REQUIRE A WW LATE THIS
AFTERNOON.

DISCUSSION...DEEPENING CONVECTIVE DEVELOPMENT IS ONGOING ACROSS THE
ROCKIES... WHICH WILL GRADUALLY SHIFT ACROSS AND EAST OF THE HIGHER
TERRAIN BETWEEN NOW AND 23-00Z...AS 20 KT SOUTHERLY DEEP LAYER MEAN
FLOW BEGINS TO STRENGTHEN SOME...WITH THE NORTHEASTWARD MIGRATION OF
A 40-50 KT 500 MB JET STREAK OUT OF OREGON. THE ENVIRONMENT EAST OF
THE HIGHER TERRAIN IS NOT PARTICULARLY UNSTABLE IN TERMS OF
CAPE...BUT LAPSE RATES ARE STEEP...AND THE BOUNDARY LAYER IS
BECOMING DEEPLY WELL MIXED. AIDED BY INCREASING SHEAR...AND
LARGE-SCALE FORCING ASSOCIATED WITH THE APPROACHING SHORT WAVE
TROUGH...ISOLATED STRONG/SEVERE STORM DEVELOPMENT...INCLUDING THE
RISK FOR SUPERCELLS...DOES NOT APPEAR OUT OF THE
QUESTION...PARTICULARLY TO THE WEST AND SOUTHWEST OF CUT BANK.

..KERR/HART.. 07/20/2012

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

ATTN...WFO...BYZ...TFX...MSO...

LAT...LON 48251525 48811292 48491094 47000984 46191101 45651300
47601506 48251525

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