Severe Storm Outlook Narrative (AC)
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ACUS48 KWNS 200844
SWOD48
SPC AC 200843

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0343 AM CDT MON APR 20 2015

VALID 231200Z - 281200Z

...DISCUSSION...
THE MEDIUM-RANGE MODELS INCLUDING THE ECMWF AND GFS SOLUTIONS BEGIN
THE 4 DAY 8 DAY PERIOD WITH AN UPPER-LEVEL RIDGE OVER THE SRN PLAINS
EXTENDING NNWWD INTO THE CNTRL HIGH PLAINS. THE MODELS MOVE THIS
FEATURE EWD ON THURSDAY/DAY 4 ACROSS A WARM SECTOR OVER THE ERN
TWO-THIRDS OF TX...SRN OK AND LA. ISOLATED TO SCATTERED THUNDERSTORM
DEVELOPMENT WILL BE POSSIBLE ACROSS THE WARM SECTOR WHERE MODERATE
INSTABILITY AND STRONG DEEP-LAYER SHEAR SHOULD MAKE CONDITIONS
FAVORABLE FOR SEVERE STORMS. AN ENHANCED THREAT FOR WIND DAMAGE AND
LARGE HAIL COULD DEVELOP ACROSS THE REGION THURSDAY AFTERNOON AND
EVENING WHERE A SLIGHT RISK HAS BEEN ADDED. MODEL SOLUTIONS DIVERGE
SHARPLY ON FRIDAY/DAY 5 WITH THE ECMWF MOVING AN NEGATIVELY TILTED
UPPER-LEVEL LOW INTO THE CNTRL HIGH PLAINS WHILE THE GFS MOVES A
POSITIVELY TILTED UPPER-LEVEL TROUGH OVER THE SRN HIGH PLAINS AND
CNTRL PLAINS. THE ECMWF SOLUTION WOULD BE FAVORABLE FOR SEVERE
STORMS IN THE SRN AND CNTRL PLAINS WHILE THE FASTER GFS SOLUTION
WOULD BE FAVORABLE FOR SEVERE STORMS OVER THE LOWER TO MID MS
VALLEY. AT THIS POINT...AM LEANING TOWARD THE SLOWER ECMWF SOLUTION
WHICH WOULD MEAN A POSSIBILITY FOR AN ENHANCED SEVERE THREAT IN FROM
NORTH TX NWD INTO SRN KS. LARGE HAIL...WIND DAMAGE AND TORNADOES
WOULD BE POSSIBLE FRIDAY AFTERNOON AND EVENING IN THE SRN PLAINS.
THE POTENTIAL EXISTS FOR AN OUTBREAK OF SEVERE STORMS IF THE ECMWF
SOLUTION VERIFIES. AT THIS POINT...THE LARGE SPREAD IN MODEL
SOLUTIONS IS TOO GREAT TO ADD AN ENHANCED SEVERE THREAT FOR FRIDAY.
ON SATURDAY/DAY 6...THE MODELS MOVE THE SYSTEM QUICKLY EWD ACROSS
THE MS VALLEY WITH A ZONAL FLOW PATTERN DEVELOPING IN THE GULF COAST
STATES. THIS PATTERN WOULD MAKE THUNDERSTORM DEVELOPMENT POSSIBLE IN
THE GULF COAST STATES WITH A SEVERE THREAT POSSIBLE THERE DURING THE
AFTERNOON. EVEN SO...PREDICTABILITY REMAINS QUITE LOW LATE IN THE
DAY 4 TO 8 PERIOD.

..BROYLES.. 04/20/2015


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