210 FXUS64 KMEG 281041 AFDMEG AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MEMPHIS TN 441 AM CST MON JAN 28 2013 .DISCUSSION... UNSEASONABLY WARM AIR WILL CONTINUE TO SPREAD INTO THE MIDSOUTH ON INCREASING SOUTH WINDS THROUGH TUESDAY LEADING TO A CHANCE OF SEVERE THUNDERSTORMS TUESDAY AFTERNOON AND NIGHT. EARLY THIS MORNING...A WARM FRONT WAS LIFTING NORTHEASTWARD THROUGH THE MIDSOUTH. TEMPERATURES ACROSS MUCH OF THE AREA WERE IN THE 50S AND LOWER 60S WITH A STRENGTHENING SOUTHERLY LOW LEVEL WIND FLOW. SHOWERS WERE SPREADING INTO NORTHEAST AR FROM THE SOUTHWEST IN ASSOCIATION WITH MOISTURE ADVECTION AND A WEAK UPPER LEVEL DISTURBANCE. FOR TODAY...SHOWERS WILL SPREAD MAINLY FROM NORTHEAST AR INTO PORTIONS OF WEST TN THIS MORNING AS THE WEAK UPPER LEVEL DISTURBANCE MOVES TO THE EAST. BREEZY SOUTH WINDS WILL PUSH HIGH TEMPERATURES INTO THE MIDDLE 60S TO NEAR 70 DEGREES. SKIES WILL BE MOSTLY CLOUDY WITH PARTIAL SUNSHINE THIS AFTERNOON MAINLY ACROSS PORTIONS OF NORTHEAST MS. A LARGE AND HIGHLY AMPLIFIED UPPER LEVEL TROUGH WILL MOVE TOWARD THE WESTERN PLAINS FROM THE WEST TONIGHT. A SURFACE LOW WILL MOVE INTO IA/WI BY SUNRISE TUESDAY WITH A COLD FRONT TRAILING INTO OK. STRONG SOUTHERLY LOW LEVEL FLOW WILL MAKE FOR A WARM NIGHT ACROSS THE MIDSOUTH. CONDITIONS WILL BE MAINLY RAINFREE TONIGHT WITH THE MIDSOUTH WELL ENTRENCHED IN THE WARM SECTOR AND MOSTLY CAPPED AHEAD OF THIS SYSTEM. THERE IS A CHANCE OF SHOWERS MAINLY ALONG AND WEST OF THE MS RIVER. AS THE STRONG UPPER LEVEL TROUGH AND ASSOCIATED COLD FRONT MOVES TO THE EAST...SHOWERS AND THUNDERSTORMS WILL SPREAD ACROSS THE MIDSOUTH FROM THE WEST BY LATE TUESDAY AFTERNOON INTO WEDNESDAY MORNING. MODELS ARE NOW IN FAIRLY GOOD AGREEMENT WITH THIS SYSTEM...WITH THE ECMWF AND NAM A LITTLE SLOWER THAN THE GFS. DID NOT CHANGE THE EARLIER POPS MUCH IF ANY WHICH IS A COMPROMISE IN THE TIMING. THERE REMAINS THE POTENTIAL FOR SEVERE THUNDERSTORMS WITH THE INSTABILITY REMAINING THE MAIN LIMITING FACTOR. WOULD ALSO LIKE TO SEE MORE OF MID LEVEL DRY SLOT PUNCHING IN FOR SEVERE WEATHER. NEVERTHELESS...THE 00Z MODELS INDICATED A LITTLE BETTER INSTABILITY AHEAD OF THIS SYSTEM THAN THE PREVIOUS MODELS. THE STORM PREDICTION CENTER HAS MOST OF THE MIDSOUTH IN A SLIGHT RISK FOR SEVERE THUNDERSTORMS. MODEL MIXED LAYER MOST UNSTABLE CAPES ARE FORECAST TO CLIMB TO BETWEEN 500 AND 800 J/KG WITH THE HIGHEST VALUES ADVECTING INTO EAST CENTRAL AR AND NORTHWEST MS BY TUESDAY EVENING. ACTUAL CAPE VALUES WILL BE DEPENDENT ON HOW MUCH SUN CAN BREAK THROUGH THE CLOUDS TUESDAY AFTERNOON. ATTM...HIGH TEMPERATURES ARE FORECAST TO CLIMB 25 DEGREES ABOVE NORMAL FOR THIS TIME OF THE YEAR WITH READINGS IN THE LOWER AND MID 70S. LIFTED INDICES DECREASE TO BETWEEN MINUS TWO AND MINUS FOUR. THE COLD FRONT IS FORECAST TO EXTEND FROM WESTERN AR INTO NORTHEAST TX BY SUNSET TUESDAY WITH A SECONDARY SURFACE LOW DEVELOPING OVER NORTHEAST MO. SURFACE DEW POINTS IN THE MIDDLE 60S WILL ADVECT AS FAR TO THE NORTHEAST AS TO NEAR MEMPHIS. WHILE INSTABILITY MAY BE MARGINAL...SHEAR VALUES WILL BE VERY HIGH WITH 0-1 STORM RELATIVE HELICITY CLIMBING TO NEAR 450 M2/S2 WITH GOOD VEERING OF A STRONG FIELD WIND FROM THE SURFACE UPWARD. 925 MB WINDS WILL INCREASE TO NEAR 60 KTS FROM THE SOUTH TUESDAY. MEANWHILE...BY SUNSET TUESDAY...500 MB WINDS WILL STRENGTHEN TO NEAR 75 KTS WITH 250 MB WINDS NEAR 115 KTS. THUNDERSTORMS ARE EXPECTED TO DEVELOP / SPREAD INTO CENTRAL AR TUESDAY AFTERNOON CONGEALING INTO A QUASI-LINEAR CONVECTIVE SYSTEM (QLCS) / SQUALL LINE BY LATE TUESDAY AFTERNOON WITH STRONG LINEAR FORCING AHEAD OF THE UPPER TROUGH. THE QLCS IS FORECAST TO MOVE INTO NORTHEAST AR BY LATE TUESDAY AFTERNOON...THEN IS FORECAST TO SWEEP ACROSS THE MIDSOUTH TUESDAY NIGHT AS THE UPPER LEVEL TROUGH SHOVES EASTWARD PUSHING THE ASSOCIATED COLD FRONT QUICKLY TO THE EAST. DAMAGING STRAIGHT LINE WINDS WILL BE THE MAIN SEVERE WEATHER THREAT. ISOLATED TORNADOES ARE ALSO POSSIBLE IN EMBEDDED BOWING LINE SEGMENTS / SUPERCELLS ALONG THE QLCS. HEAVY DOWNPOURS ARE LIKELY AS THE THUNDERSTORMS MOVE ACROSS THE REGION. PRECIPITABLE WATER VALUES ARE FORECAST NEAR 1.6 OR 1.7 INCHES WHICH IS IN THE 99TH PERCENTILE FOR THIS TIME OF THE YEAR. THINK MOST LOCATIONS WILL RECEIVE BETWEEN 1 1/2 AND 2 INCHES OF RAIN IN A SHORT PERIOD OF TIME. A WIND ADVISORY MAY BECOME NECESSARY FOR PORTIONS OF THE AREA TUESDAY INTO WEDNESDAY AS GRADIENT WINDS STRENGTHEN WITH THIS SYSTEM. DRIER AND COLDER AIR IS FORECAST TO GRADUALLY SPREAD INTO THE MIDSOUTH WEDNESDAY AS THE COLD FRONT MOVES EASTWARD. A STRONG PUSH OF ARCTIC AIR IS STILL FORECAST INTO THE MIDSOUTH THURSDAY NIGHT AND FRIDAY. THE LATEST MODELS WERE LESS ROBUST IN INDICATING SNOW WITH THIS PUSH OF COLD AIR THAN EARLIER MODELS. HOWEVER...DID LEAVE IN A SLIGHT CHANCE OF SNOW SHOWERS FOR ABOUT THE NORTHERN TWO-THIRDS OF THE MIDSOUTH. JCL && .AVIATION... 06Z TAFS MILD SUBTROPICAL AIR WILL CONTINUE TO FLOW THROUGH THE MIDSOUTH THROUGH THE NEXT 24 HOURS. ELEVATED MOIST LAYER... RESULTING IN MVFR CLOUDS... SHOULD DEVELOP PRIOR TO SUNRISE AND PERSIST INTO EARLY AFTERNOON. HAVE BUMPED UP NONCONVECTIVE WIND SHEAR SPEEDS A BIT... BASED ON KNQA/TMEM VAD WIND PROFILES. PWB && .PRELIMINARY POINT TEMPS/POPS... MEM 70 61 75 51 / 30 20 40 100 MKL 67 58 74 53 / 50 10 20 100 JBR 68 58 72 46 / 50 20 70 100 TUP 68 56 74 56 / 10 10 20 100 && .MEG WATCHES/WARNINGS/ADVISORIES... AR...NONE. MO...NONE. MS...NONE. TN...NONE. && $$