Severe Storm Outlook Narrative (AC)
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ACUS48 KWNS 180842
SWOD48
SPC AC 180841

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0341 AM CDT SAT APR 18 2015

VALID 211200Z - 261200Z

...DISCUSSION...
THE MEDIUM-RANGE MODELS INCLUDING THE GFS AND ECMWF BEGIN THE DAY 4
TO 8 PERIOD WITH A BROAD CYCLONIC FLOW PATTERN OVER THE ERN
TWO-THIRDS OF THE NATION. THE MODELS KEEP THE SRN PLAINS RELATIVELY
DRY ON TUESDAY/DAY 4 EXCEPT FOR IN SRN AND CNTRL TX WHERE ISOLATED
SEVERE STORMS COULD DEVELOP TUESDAY AFTERNOON. ON WEDNESDAY/DAY
5...THE GFS SOLUTION AND TO A LESSER EXTENT THE ECMWF...INCREASE
LOW-LEVEL MOISTURE IN THE SRN PLAINS. BOTH SOLUTIONS HAVE AN
UPPER-LEVEL RIDGE EXTENDING NWWD FROM THE SRN PLAINS INTO THE SRN
ROCKIES AND SRN HIGH PLAINS. THIS COULD HELP TO KEEP THE SEVERE
THREAT ISOLATED ACROSS THE REGION WEDNESDAY AFTERNOON. BOTH
SOLUTIONS REMAIN IN REMARKABLY GOOD AGREEMENT AT UPPER LEVELS BUT
DIFFER ON WHERE THE MOIST AXIS WILL BE ON THURSDAY/DAY 6. THE
POTENTIAL FOR SEVERE STORMS LOOKS GREATER ON THURSDAY DUE A
MID-LEVEL JET MOVING INTO THE SRN PLAINS THURSDAY EVENING. SEVERE
STORMS WITH LARGE HAIL...WIND DAMAGE AND POSSIBLY A FEW TORNADOES
WILL BE POSSIBLE SOMEWHERE IN THE SRN PLAINS THURSDAY BUT
PREDICTABILITY IS LOW DUE TO DIFFERENCES IN THE SOLUTIONS ESPECIALLY
REGARDING LOW-LEVEL MOISTURE. ON FRIDAY/DAY 7...BOTH MODELS MOVE A
MID-LEVEL JET OUT OVER THE SRN PLAINS WITH AN ASSOCIATED SHORTWAVE
TROUGH IN THE SRN HIGH PLAINS. THIS PATTERN WOULD SUPPORT SEVERE
THUNDERSTORM DEVELOPMENT ACROSS PARTS OF THE SRN AND CNTRL PLAINS
EXTENDING EWD INTO THE LOWER MS VALLEY. AN ENHANCED SEVERE THREAT
WILL BE POSSIBLE ON EITHER THURSDAY/DAY 6 OR FRIDAY/DAY 7 BUT
PREDICTABILITY ON EXACTLY WHERE REMAINS LOW ATTM.

..BROYLES.. 04/18/2015


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