Severe Storm Outlook Narrative (AC)
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000
ACUS11 KWNS 280220
SWOMCD
SPC MCD 280219
SDZ000-NDZ000-MTZ000-WYZ000-280415-

MESOSCALE DISCUSSION 1558
NWS STORM PREDICTION CENTER NORMAN OK
0919 PM CDT MON JUL 27 2015

AREAS AFFECTED...PORTIONS OF THE WESTERN DAKOTAS AND EASTERN MONTANA

CONCERNING...SEVERE THUNDERSTORM WATCH 456...457...

VALID 280219Z - 280415Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH
456...457...CONTINUES.

SUMMARY...THE SVR RISK CONTINUES IN WWS 456 AND 457.

DISCUSSION...MULTIPLE CLUSTERS OF STRONG TO SEVERE
THUNDERSTORMS...WITH A HISTORY OF PRODUCING MEASURED SEVERE WIND
GUSTS...CONTINUE FROM ERN MT TO THE THE WRN DAKOTAS. SFC ANALYSIS
INDICATES A FRONTOGENETIC BOUNDARY OVERTAKING THE WRN EXTENT OF
MODERATE TO STRONG BUOYANCY OVER THE NRN HIGH PLAINS. THIS BOUNDARY
IS ANALYZED AS A N/S-ORIENTED COLD FRONT FROM THE ERN ONE-QUARTER OF
MT INTO CNTRL WY...AND IS ACCOMPANIED BY A STRONG PRESSURE RISE-FALL
COUPLET FROM W TO E ACROSS PARTS OF SRN MT/NRN WY. THIS HIGHLIGHTS
THE STRONG FORCING FOR ASCENT SPREADING ACROSS THE REGION...WITH THE
STRENGTHENING ISALLOBARIC WIND COMPONENT ENHANCING BACKGROUND FLOW
FOR SVR-WIND POTENTIAL WITH CONVECTION...AMIDST 30-45 KT OF DEEP
SHEAR ENCOURAGING ORGANIZED/SUSTAINED TSTMS.

THE BIS AND ABR 00Z RAOBS SAMPLE MODERATE TO STRONG BUOYANCY AND
LIMITED CAPPING...SUPPORTING CONTINUED EWD/NEWD SPREAD OF THIS
ACTIVITY...WITH LARGE DCAPE -- OVER 1000 J/KG -- ENHANCING
DOWNBURSTS AND THEIR PROPENSITY TO MANIFEST STRENGTHENING
LARGE-SCALE WIND FIELDS AS SVR WIND GUSTS AT THE SFC. RECENT
MEASURED GUSTS IN THE 50-60-KT RANGE HAVE BEEN REPORTED...AND
SIGNIFICANTLY SEVERE WIND GUSTS WILL ALSO BE POSSIBLE. CAPPI DATA
FROM 7 KM INDICATE RENEWED CONVECTION FROM SERN MT TO SWRN SD IN
ASSOCIATION WITH STRONG DCVA PRECEDING AN UPSTREAM POTENT
TROUGH...AND ADDITIONAL SVR RISK MAY CONTINUE BEHIND ONGOING
MULTICELL CLUSTERS.

ALL OF THIS ACTIVITY WILL CONTINUE SPREADING EWD/NEWD DURING THE
NEXT SEVERAL HOURS. POLEWARD MASS FLUXES ALONG A TROUGH-PRECEDING
LLJ -- ALREADY SAMPLED BY ABR/BIS VWPS AS SHOWING 20-30 KT OF FLOW
IN THE LOWEST 1 KM AGL -- WILL MAINTAIN AN INFLUX OF HIGH THETA-E
AIR IN THE BOUNDARY LAYER TO MAINTAIN CONVECTION THROUGH THE EVENING
AND INTO THE OVERNIGHT. SVR POTENTIAL WILL CONTINUE TO ACCOMPANY
THIS ACTIVITY.

..COHEN.. 07/28/2015

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

ATTN...WFO...ABR...BIS...UNR...BYZ...GGW...

LAT...LON   43360336 44190378 45580443 46300531 47560664 48790640
            48910311 48140140 44799971 43430021 43360336



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