Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS01 KWNS 241959
SWODY1
SPC AC 241957

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0257 PM CDT THU JUL 24 2014

VALID 242000Z - 251200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE NRN PLAINS
AND UPPER MIDWEST...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF NC...

...SUMMARY...
A FEW SEVERE THUNDERSTORMS WITH LARGE HAIL AND DAMAGING WINDS WILL
OCCUR FROM EASTERN MONTANA INTO NORTH DAKOTA FROM LATE THIS
AFTERNOON THROUGH TONIGHT. STRONG STORMS CAPABLE OF LOCALLY DAMAGING
WINDS MAY AFFECT PARTS OF THE CENTRAL AND SOUTHERN APPALACHIANS AND
THE SOUTHERN MID-ATLANTIC STATES TODAY. ISOLATED STRONG TO SEVERE
STORMS WITH HAIL ARE EXPECTED THIS AFTERNOON AND TONIGHT FROM
SOUTHEAST NORTH DAKOTA AND EASTERN SOUTH DAKOTA INTO PARTS OF IOWA
AND MINNESOTA.

SEVERAL CHANGES HAVE BEEN MADE TO THE OUTLOOK FOR THIS ISSUANCE. THE
FIRST CHANGE IS TO EXTEND THE SLIGHT RISK AREA IN THE NRN HIGH
PLAINS FURTHER TO THE WEST. RAP MESOSCALE ANALYSIS IS SHOWING
MODERATE INSTABILITY AS FAR WEST AS HARVE MT WITH CONVECTION
APPROACHING FROM THE SOUTHWEST. THE HRRR MODEL GRADUALLY INTENSIFIES
THESE STORMS...MOVING THE CONVECTION ACROSS NE MT LATE THIS
AFTERNOON WHERE WIND DAMAGE AND HAIL WILL BE POSSIBLE. THE SECOND
CHANGE TO THE OUTLOOK IS TO REMOVE THE SIGNIFICANT WIND PROBABILITY
HATCHED AREA FROM THE NRN PLAINS. ALSO...HAVE MADE THE 30 PERCENT
WIND DAMAGE PROBABILITY SMALLER THERE. ALTHOUGH THE DEVELOPMENT OF A
BOWING LINE SEGMENT STILL REMAINS POSSIBLE...SEVERAL SHORT-TERM
MODEL FORECASTS SUGGEST THAT THE SUPERCELL MODE MAY BE MAINTAINED
INTO THE EARLY EVENING. THIS WOULD RESULT IN A THREAT FOR LARGE HAIL
AND HAILSTONES GREATER THE 2 INCHES IN DIAMETER WILL BE POSSIBLE
WITH THE MOST DOMINANT CORES. THE THIRD CHANGE TO THE OUTLOOK IS TO
NARROW THE SLIGHT RISK AREA ACROSS NC TO COINCIDE WITH THE MAX IN
INSTABILITY AND DEEP-LAYER SHEAR. ISOLATED DAMAGING WIND GUSTS STILL
APPEAR POSSIBLE IN CNTRL AND ERN NC LATE THIS AFTERNOON DUE TO STEEP
LOW-LEVEL LAPSE RATES AND UNIDIRECTIONAL WIND PROFILES.

..BROYLES.. 07/24/2014

.PREV DISCUSSION... /ISSUED 1129 AM CDT THU JUL 24 2014/

...ERN MT INTO ND...
A VIGOROUS UPPER LOW OVER SRN BC AND ASSOCIATED SHORT WAVE TROUGH
EXTENDING SWD INTO THE PACIFIC NW ARE EXPECTED TO MOVE ENEWD TOWARD
THE CANADIAN PRAIRIES THROUGH TONIGHT...WITH STRONG WSWLY WINDS
ALOFT PROGRESSING ENEWD ACROSS MT AND ND.  THE PRIMARY 500 MB HEIGHT
FALLS AND DYNAMIC FORCING FOR LARGE SCALE ASCENT WILL REMAIN NORTH
OF THE INTERNATIONAL BORDER.  AT THE SURFACE...A STRONG COLD FRONT
WILL MOVE EWD ACROSS ERN MT THIS AFTERNOON AND CONTINUE EWD ACROSS
THE DAKOTAS TONIGHT.

WARM TEMPERATURES AND A CAPPING INVERSION ALOFT ASSOCIATED WITH THE
EML IS LIKELY TO LIMIT THUNDERSTORM DEVELOPMENT TO THE SOUTH OF THE
UPPER LEVEL JET...WITH 12Z MODEL GUIDANCE INCLUDING
CONVECTION-ALLOWING MODELS INDICATING THE PRIMARY STORM AXIS WILL BE
FROM NERN/EAST CENTRAL MT ACROSS PARTS OF ND LATE THIS AFTERNOON AND
TONIGHT.  THE STEEP MID-LEVEL LAPSE RATES COUPLED WITH INCREASING
LOW-LEVEL MOISTURE IN THE WAKE OF CURRENT ELEVATED STORMS IN ERN ND
WILL RESULT IN STRONG INSTABILITY WITH CAPE EXCEEDING 2500-3000 J/KG
THIS AFTERNOON AND EVENING AHEAD OF THE COLD FRONT AND HIGH PLAINS
N/S TROUGH.  INCREASING CONVERGENCE ALONG THE FRONT AND SOME ASCENT
ALOFT WILL GRADUALLY WEAKEN THE CAP RESULTING IN CONVECTION
INITIATION BY MID-LATE AFTERNOON OVER MT...WITH ACTIVITY INCREASING
IN COVERAGE ACROSS ND INTO TONIGHT.  STRONG DEEP LAYER SHEAR WILL
FAVOR UPDRAFT ROTATION WITH INITIAL SUPERCELLS CAPABLE OF VERY LARGE
HAIL...SEVERE WINDS AND AN ISOLATED TORNADO OR TWO.  THERE IS
POTENTIAL FOR THE STORMS TO MERGE INTO A BOWING LINE SEGMENT AND
SPREAD RAPIDLY EWD ACROSS ND DURING THE NIGHT...WITH A CONTINUING
THREAT FOR DAMAGING WINDS AND LARGE HAIL.

...SERN ND/ERN SD/SWRN MN AND IA...
CURRENT ELEVATED STORMS OVER SERN ND AND ERN SD WILL POSE A THREAT
FOR ISOLATED LARGE HAIL THIS AFTERNOON...SEE MCD 1457 FOR NEAR-TERM
DETAILS.  IN ADDITION...ELEVATED STORMS ARE EXPECTED TO
PERSIST/REDEVELOP TONIGHT ALONG THE ERN EDGE OF THE EML/CAP WITHIN A
STRONG WARM ADVECTION ZONE WITHIN THE 850-700 MB LAYER...IN
ASSOCIATION WITH AN INTENSIFYING LOW LEVEL JET.  LARGE HAIL WILL BE
THE PRIMARY THREAT FROM THESE ELEVATED STORMS.

...PARTS OF VA AND NC...
STRONG STORMS ARE OCCURRING OVER ERN NC AT THIS TIME WITHIN AN
ENVIRONMENT CHARACTERIZED BY A VERY MOIST AIR MASS WITH SURFACE DEW
POINTS IN THE 70S AND SUFFICIENT SHEAR /25-30 KT IN THE LOWEST 6 KM/
TO ENHANCE STORM ORGANIZATION AND INTENSITY.  OTHER STORMS ARE
EXPECTED TO DEVELOP IN THE WAKE OF THESE CURRENT STORMS WHERE
VISIBLE IMAGERY INDICATES BREAKS/THINNING OF CLOUDS WHICH WILL
PROMOTE STRONGER DIABATIC HEATING AND DESTABILIZATION.  WATER VAPOR
IMAGERY SHOWS A WELL-DEFINED SHORT WAVE TROUGH CROSSING THE CENTRAL
APPALACHIANS REGION WHICH IS EXPECTED TO AID IN DEVELOPMENT OF
ADDITIONAL STORMS THIS AFTERNOON AND EVENING.  STRONGER CELLS WILL
HAVE POTENTIAL TO PRODUCE DAMAGING WIND GUSTS AND ISOLATED LARGE
HAIL.



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