Day 4-8 Severe Weather Outlook

...DISCUSSION...
MEDIUM RANGE GUIDANCE HAS COME INTO DECENT AGREEMENT WITH THE SYNOPTIC EVOLUTION DURING THE D4-8 PERIOD, THOUGH NORMAL UNCERTAINTIES REMAIN WITH EVOLUTION OF SMALLER SCALE FEATURES. A LARGE MID TO UPPER LEVEL TROUGH SHOULD MOVE INTO THE WEST COAST REGION BY EARLY D5/SATURDAY, EVENTUALLY MOVING ACROSS THE ROCKIES INTO THE HIGH PLAINS D6/SUNDAY, WITH SURFACE CYCLOGENESIS OCCURRING OVER THE CENTRAL TO NORTHERN PLAINS. ANOTHER LARGE TROUGH AMPLIFIES AND DIGS INTO THE WEST COAST BY D7/MONDAY AND EJECTS EASTWARD THROUGH THE END OF D8/TUESDAY, POTENTIALLY PHASING WITH THE INITIAL TROUGH. 

A FAIRLY MOIST AIRMASS WILL ALREADY HAVE DEVELOPED ACROSS THE SOUTHERN PLAINS ON D5. STRENGTHENING SHEAR PROFILES CAN BE EXPECTED AS A RESULT OF STRONG SOUTHWESTERLY FLOW AHEAD OF THE TROUGH. DEVELOPMENT OF MODERATE INSTABILITY IS LIKELY SATURDAY AFTERNOON AND EVENING ACROSS THE SOUTHERN PLAINS, WHILE INCREASING HEIGHT FALLS AND SURFACE CYCLOGENESIS PROVIDES ENOUGH FORCING TO SUPPORT DEVELOPMENT OF ISOLATED TO SCATTERED STRONG TO SEVERE THUNDERSTORMS ALONG A LIKELY DRYLINE, SPREADING NORTHEASTWARD THROUGH THE EVENING AND OVERNIGHT HOURS ACROSS THE SOUTHERN PLAINS. CONTINUED DEEPENING OF THE SURFACE CYCLONE BY D6/SUNDAY ALONG WITH STRENGTHENING LOW-LEVEL WINDS SHOULD SUPPORT CONTINUED STRONG WARM AIR ADVECTION/MOISTURE TRANSPORT WELL NORTHWARD ACROSS THE GREAT PLAINS POTENTIALLY INTO THE UPPER MISSOURI VALLEY. STRONG DEEP-LAYER SHEAR OVER A CORRIDOR OF MODERATE TO STRONG INSTABILITY ALONG AND AHEAD OF A COLD FRONT OR DRYLINE WILL SUPPORT DEVELOPMENT OF SCATTERED TO NUMEROUS THUNDERSTORMS SUNDAY AFTERNOON AND EVENING. ALL SEVERE HAZARDS WITH MULTI MODAL STORM EVOLUTION CAN BE EXPECTED, INCLUDING A CORRIDOR OF POTENTIALLY GREATER SUPERCELL/TORNADO POTENTIAL ACROSS THE SOUTHERN PLAINS SUN EVENING WHERE MODEL GUIDANCE INDICATES A LIKELY OVERLAP OF STRONG INSTABILITY AND INTENSIFYING LOW-LEVEL SHEAR PROFILES DURING THIS TIME FRAME.

SEVERE POTENTIAL WILL PERSIST INTO D7/MONDAY. WITH THE EVOLUTION OF UPPER FEATURES, IT SEEMS REASONABLE THAT RATHER SLOW PROGRESSION OF THE SURFACE CYCLONE AND ASSOCIATED UPPER JET CAN BE EXPECTED. HOWEVER, POTENTIAL APPEARS TO BE INCREASING FOR A RATHER LARGE WARM SECTOR DEVELOPING ACROSS THE EASTERN GREAT PLAINS INTO THE MISSISSIPPI VALLEY AND MIDWEST AS THE SURFACE CYCLONE LIKELY STRENGTHENS, ALONG WITH DEEP-LAYER SHEAR ACROSS THE REGION. FAIRLY NUMEROUS SEVERE STORMS ARE POSSIBLE, WITH GREATEST CONFIDENCE OVER A CORRIDOR EXTENDING FROM THE EAST-CENTRAL PLAINS INTO THE OZARKS AND MID-MISSISSIPPI VALLEY. MULTI-MODAL STORM EVOLUTION WILL SUPPORT AN ALL-HAZARDS SEVERE THREAT, INCLUDING SUPERCELLS AND TORNADOES.

THE HIGHEST CONFIDENCE IN SEVERE POTENTIAL EXISTS ON DAY 6 AND DAY 7, WARRINTING 30% OUTLINES FOR BOTH OF THESE DAYS.

MODEL GUIDANCE BEGINS TO DIVERGE SOMEWHAT BY D8/TUESDAY THOUGH BOTH EURO AND GFS CONTINUE TO INDICATE A BROAD MOIST/UNSTABLE REGION OVERLAPPED WITH STRONG DEEP-LAYER SHEAR POTENTIALLY FROM THE ARKLATEX INTO THE OHIO VALLEY. A SEVERE THREAT SHOULD PERSIST INTO D8 AS A RESULT.