Severe Storm Outlook Narrative (AC)
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000
ACUS11 KWNS 272333
SWOMCD
SPC MCD 272332
SDZ000-MTZ000-WYZ000-280130-

MESOSCALE DISCUSSION 1556
NWS STORM PREDICTION CENTER NORMAN OK
0632 PM CDT MON JUL 27 2015

AREAS AFFECTED...PORTIONS OF ERN MT...WRN SD...NERN WY

CONCERNING...SEVERE THUNDERSTORM WATCH 456...

VALID 272332Z - 280130Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 456
CONTINUES.

SUMMARY...THE RISK FOR SVR TSTMS CONTINUES ACROSS WW 456.

DISCUSSION...WATER VAPOR LOOPS SUGGEST THAT THE SPATIAL GAP BETWEEN
STRONG DCVA PRECEDING A BECOMING-NEGATIVELY-TILTED MID-LEVEL
SHORTWAVE TROUGH OVER WRN/CNTRL MT AND MODERATELY TO STRONGLY
UNSTABLE AIR SAMPLED OVER ERN MT INTO THE WRN DAKOTAS AND NERN WY IS
CLOSING. A CORRESPONDING UPSWING IN THE NUMBER AND INTENSITY OF
TSTMS IS ONGOING BASED ON THE LATEST VISIBLE SATELLITE AND MOSAIC
RADAR IMAGERY...AND THIS WILL CONTINUE AS THERMODYNAMIC PROFILES
ALOFT COOL WITH FORCED ASCENT DRIVING ADIABATIC COOLING. CONVECTION
WILL LIKELY BECOME SCATTERED TO NUMEROUS ACROSS THE WATCH AREA IN
THE NEXT FEW HOURS...WITH A MIX OF BOWING SEGMENTS AND OCCASIONAL
SUPERCELLS AFFECTING THE AREA.

THE GGW VWP SAMPLES 40-50 KT OF MERIDIONAL FLOW IN THE 4-6-KM-AGL
LAYER OFFERING STRONG DEEP SHEAR FOR ORGANIZED CONVECTION. SVR WIND
GUSTS AND LARGE HAIL WILL BE LIKELY...AND SIGNIFICANTLY SVR
WIND/HAIL CANNOT BE RULED OUT OWING TO THE STEEP-LAPSE-RATE PROFILE
IN PLACE. AREAS OF GREATEST CONCERN INCLUDE THE ERN ONE-THIRD OF MT.
THIS IS WHERE BUOYANCY IS MOST SUBSTANTIAL...AND A TIGHTENING
CROSS-FRONTAL ISALLOBARIC COMPONENT IS OCCURRING ACROSS A
FRONTOGENETIC COLD FRONT ADVANCING EWD OVER CNTRL MT. A TORNADO
CANNOT BE RULED OUT WITH ANY MORE DISCRETE SUPERCELL STRUCTURES IN
ERN MT...PARTICULARLY IN PROXIMITY TO...AND ON THE COOL SIDE OF A
COLD-FRONT-PRECEDING...WAVY...QUASISTATIONARY BOUNDARY ANALYZED FROM
NERN MT TO THE BIG HORN MOUNTAINS. THIS IS WHERE STRONG DIRECTIONAL
SHEAR IN THE LOW LEVELS IS ENHANCING SRH TO AROUND 150-200 M2/S2 IN
THE 0-1-KM-AGL LAYER BASED ON THE GGW VWP. HOWEVER...POTENTIAL MODE
TRANSITIONS TO QUASI-LINEAR COMBINED WITH THE OVERTAKING
FRONTOGENETIC BOUNDARY MAY LIMIT THE SVR RISK.

MORE ISOLATED SVR CONVECTION CONTINUES IN A PRESENTLY
WEAKER-FORCING-FOR-ASCENT REGIME INTO WRN SD...WHERE SUPERCELL
STRUCTURES HAVE BEEN NOTED. SUCH ACTIVITY WILL LIKELY CONTINUE IN
THE SHORT TERM WITH SVR HAIL/WIND POTENTIAL...AND AN UPSWING IN
CONVECTIVE COVERAGE MAY OCCUR IN THE NEXT FEW HOURS AS MID-LEVEL
HEIGHT FALLS CONTINUE TO OVERSPREAD THE AREA.

..COHEN.. 07/27/2015

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

ATTN...WFO...UNR...BYZ...GGW...

LAT...LON   45740377 45630247 44910151 43930138 43430155 43260220
            43260294 43630387 44100478 44520568 44860648 45570741
            46780783 47790805 48340795 48730730 48660633 47400517
            46140444 45740377



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