Long Term Discussion

By: NWS
By: NWS

SOUTHERLY FLOW AHEAD OF AN APPROACHING SYSTEM WILL CONTINUE TO TRANSPORT MOISTURE INTO THE REGION. WITH THE MOIST FLOW AND WEAK ISENTROPIC ASCENT ACROSS THE WESTERN AREAS OF THE REGION IN THE AFTERNOON...A FEW LIGHT SHOWERS ARE POSSIBLE. THE MAIN ACTIVITY WILL HOLD OFF UNTIL WEDNESDAY NIGHT AND THURSDAY. WEDNESDAY NIGHT...THE MODELS SHOW AN UPPER LOW MOVING INTO SOUTHERN ARKANSAS DURING THE NIGHT TIME HOURS WHICH WILL DRIVE A SURFACE LOW PRESSURE SYSTEM INTO THE LOWER MISSISSIPPI RIVER VALLEY. WITH THE MAIN SYNOPTIC WARM FRONT LOCATED ALONG THE SOUTHERN TENNESSEE BORDER...OUR REGION WILL EASILY BE IN THE WARM SECTOR. HOWEVER...WE HAVE NOTED HERE MANY TIMES THAT IT IS A SECONDARY WARM FRONT THAT SEPARATES THE INITIAL MARITIME AIRMASS FROM A TRULY TROPICAL AIRMASS. THIS BOUNDARY WILL HAVE A LARGE INFLUENCE ON THUNDERSTORM AND SEVERE WEATHER POTENTIAL. THIS SECONDARY FEATURE LOOKS TO STILL BE OFFSHORE THROUGH MUCH OF WEDNESDAY NIGHT...THUS ISOLATED T IS INDICATED UNTIL THE FEW HOURS JUST BEFORE DAYBREAK ACROSS MUCH OF THE REGION. IN FACT...THE LATEST MODEL FORECASTS SHOW THAT ANY SURFACE BASED INSTABILITY WILL MATERIALIZE AFTER THIS FEATURE MOVES ASHORE...AROUND 12Z THURSDAY. SO WHILE AN ISOLATED STRONG STORM NEAR THE COAST CANNOT BE RULED OUT WEDNESDAY NIGHT...THE LATEST FORECASTS SHOW THAT THIS POTENTIAL WILL LIKELY BE CONFINED TO THURSDAY WHEN BETTER KINEMATICS AND INSTABILITY OVERLAP. NEVERTHELESS...POTENTIAL FOR SHOWERS AND ISOLATED THUNDERSTORMS WILL BE INCREASING THROUGH THE NIGHT...SO HAVE RAISED POPS INTO THE LIKELY CATEGORY FOR OUR WESTERN ZONES PRIMARILY BECAUSE REMAINING INCONSISTENCIES IN THE MODELS ARE WITH RESPECT TO SEVERE WEATHER POTENTIAL...AND NOT SO MUCH TIMING DISCREPANCIES. && .LONG TERM (THURSDAY THROUGH MONDAY). THE INITIAL PORTION OF THE LONG TERM FORECAST WILL BE DOMINATED BY THE POTENTIAL FOR SEVERE WEATHER ON THURSDAY. PREVIOUS MODEL CYCLES OF THE GFS WERE SHOWING MUCH OF THE FORCING FOR PRECIPITATION JUST AHEAD OF THE MAIN INSTABILITY AXIS...INDICATING A LESS ROBUST SEVERE WEATHER PICTURE. HOWEVER...THE 18/12Z GFS SHOWS MUCH BETTER SURFACE BASED INSTABILITY LINING UP JUST AHEAD OF THE MAIN FRONTAL CONVECTIVE BAND. WITH 0-6KM DEEP LAYER SHEAR IN THE 50 TO 60 KNOT RANGE IN OUR AREA...THE SEVERE WEATHER POTENTIAL IS INCREASED WITH THIS SOLUTION. THIS EVENT CERTAINLY HAS GREATER POTENTIAL FOR SEVERE WEATHER THAN THE LAST TWO SYSTEMS PRIMARILY BECAUSE OF A LONGER PERIOD (18 TO 24 HOURS) OF RETURN FLOW OFF THE GULF. NEGATIVES INCLUDE VERY COOL SHELF WATERS ALONG THE GULF COAST WHICH COULD SERVE TO STABILIZE AREAS WITHIN 50 MILES OR SO OF THE COAST. ADDITIONALLY...THE 18/00Z EURO AND NOW THE 18/12Z VERSION HAS NOT LOCKED ON TO THE MORE ROBUST GFS OR NAM SOLUTION. THE EURO PREFERS TO RAPIDLY TILT THE TROF STRONGLY NEGATIVE AND LIFT IT QUICKLY INTO THE LOWER MISSOURI RIVER VALLEY. THIS WOULD DECREASE THE OVERALL SHEAR VALUES ACROSS OUR REGION AS WELL AS WEAKEN ANY LARGE SCALE FORCING. SO WHILE THE SEVERE POTENTIAL IS HIGHER THAN SEEN IN THE LAST FEW EVENTS AT THIS TIME RANGE...THE REMAINING DIFFERENCES BETWEEN THE MODELS ARGUE AGAINST INCLUDING ANY MENTION IN THE FORECAST OF SEVERE STORMS UNTIL THESE INCONSISTENCIES ARE SORTED OUT. HOWEVER...SINCE THE TIMING DIFFERENCES ARE NOT THAT GREAT...WENT AHEAD AND INCREASED POPS ON THURSDAY TO 70 PERCENT TO MATCH WITH THE LATEST GUIDANCE. AFTER THIS SYSTEM ON THURSDAY...FAIR AND MILD WX SHOULD RETURN FOR FRI INTO SUN...WITH THE NEXT CHANCE OF RAIN (ALBEIT WITH A MUCH WEAKER COLD FRONT) NOT EXPECTED UNTIL AT LEAST LATE SUNDAY AND INTO MONDAY.


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