Severe Storm Outlook Narrative (AC)
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ACUS48 KWNS 170847
SWOD48
SPC AC 170845

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0345 AM CDT FRI APR 17 2015

VALID 201200Z - 251200Z

...DISCUSSION...
THE MEDIUM-RANGE MODELS BEGIN THE DAY 4 TO 8 PERIOD IN FAIRLY GOOD
AGREEMENT WITH AN UPPER-LEVEL TROUGH OVER THE MS VALLEY. AT THE
SFC...A COLD FRONT IS FORECAST TO BE DRAPED FROM THE TN VALLEY SWWD
TO THE LA COAST AND SRN TX COAST. THIS FEATURE IS FORECAST TO MOVE
QUICKLY SEWD ACROSS THE APPALACHIAN MTNS AND GULF COAST STATES ON
MONDAY/DAY 4. THE PATTERN WOULD SUPPORT POSSIBLE SEVERE THUNDERSTORM
DEVELOPMENT FROM THE MID-ATLANTIC SSWWD ACROSS THE CAROLINAS WHERE A
WIND-DAMAGE THREAT MAY DEVELOP MONDAY AFTERNOON. ON TUESDAY/DAY
5...THE COLD FRONT IS FORECAST TO STALL NEAR THE COASTS FROM LA EWD
TO THE FL PANHANDLE. SOME MOISTURE RETURN MAY TAKE PLACE ACROSS THE
SRN PLAINS WHERE ENOUGH INSTABILITY COULD SUPPORT AN ISOLATED SEVERE
THREAT TUESDAY AFTERNOON. ON WEDNESDAY/DAY 6...THE GFS AND ECMWF
SOLUTIONS CONTINUE MOISTURE ADVECTION IN THE SRN PLAINS BUT THE GFS
IS THE MORE AGGRESSIVE SOLUTION. THE GFS SOLUTION WOULD RESULT IN A
FAVORABLE SETUP FOR SEVERE STORMS IN THE SRN AND CNTRL PLAINS WHERE
LARGE HAIL AND WIND DAMAGE COULD OCCUR WEDNESDAY AFTERNOON AND
EVENING. THE GFS WOULD FAVOR SRN KS AND WRN MO WHILE THE ECMWF WOULD
FAVOR TX DURING THE DAY AND THE RED RIVER VALLEY POSSIBLY OVERNIGHT.
AT THIS POINT...WILL NOT ADD A SEVERE THREAT AREA DUE TO DIFFERENCES
IN THE SOLUTIONS. ON THURSDAY/DAY 7...MODEL SOLUTIONS ARE QUITE
DIFFERENT WITH THE GFS MOVING THE WARM SECTOR TO THE LOWER MS VALLEY
WHILE THE ECMWF IS SLOWER...KEEPING THE WARM SECTOR OVER PART OF THE
SRN PLAINS. FOR THIS REASON...UNCERTAINTY REMAINS HIGH LATE IN THE
DAY 4 TO 8 PERIOD.

..BROYLES.. 04/17/2015



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