Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN

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000 FXUS64 KMRX 212009 AFDMRX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MORRISTOWN TN 309 PM EST SUN DEC 21 2014 .SHORT TERM (TONIGHT AND MONDAY)... THE NAM AND GFS CONTINUE TO SHOW DIFFERENT SCENARIOS FOR THE SHORT TERM...WITH THE GFS KEEPING MEASUREABLE PRECIP TO OUR EAST TONIGHT...WHILE THE NAM CONTINUES TO BE THE WETTER MODEL. HOWEVER THE NAM HAS BEEN TRENDING DRIER COMPARED TO YESTERDAY. IT SHOWS MOISTURE CONFINED TO A SHALLOW LAYER BELOW 700 MB AND ISENTROPIC LIFT AT THE 290-295K LEVELS...MORE OF A DRIZZLE PROFILE THAN MUCH MEASUREABLE RAIN. A WEAK DOWNSLOPE WIND COULD FURTHER REDUCE QPF IN THE TN VALLEY. THE GOING FORECAST LOOKS GOOD TO HANDLE THIS PATTERN...WITH CHANCE POPS EAST TAPERING TO ONLY DRIZZLE WEST...SO NO MAJOR CHANGES WILL BE MADE. THE ISENTROPIC LIFT SHOWN BY THE NAM LIFTS NORTH OF THE OUR AREA BETWEEN 12-15Z...SO WILL END ALL RAIN CHANCES BEFORE NOON. HOW MUCH CLOUD COVER LINGERS BEHIND IS VERY UNCERTAIN...BUT WILL LEAN ON THE PESSIMISTIC SIDE AND KEEP MOISTLY CLOUDY CONDITIONS FOR MOST OF THE DAY WITH TEMPERATURES ON THE COOL SIDE OF MOS GUIDANCE. .LONG TERM (MONDAY NIGHT THROUGH SUNDAY)... THE BEGINNING OF THE LONG TERM PERIOD REMAINS ACTIVE AND THEN A QUIETER FINISH. STORMS...RAIN/WIND...AND SNOW STILL POSSIBLE. THIS IS BECOMING A TRICKY FORECAST. MONDAY NIGHT INTO TUESDAY FEATURE HEIGHTS QUICKLY BUILDING OUT AHEAD OF OUR IMPENDING STORM SYSTEM THAT WE HAVE BEEN DISCUSSING FOR A WHILE NOW. AS MENTIONED IN YESTERDAY`S DISCUSSION...THIS WILL KEEP MONDAY NIGHT AND TUESDAY UNSEASONABLE WARM AS DEEP SOUTHERLY FLOW WILL BE IN PLACE. LOWS MONDAY NIGHT STILL LOOK TO BE 10 TO 12 DEGREES ABOVE NORMAL. HIGHS ON TUESDAY WILL BE IN THE MID/UPPER 50S AND NEAR 60 IN A FEW SPOTS...GENERALLY 5 TO 10 DEGREES ABOVE NORMAL. START BRINGING IN RAIN CHANCES MONDAY NIGHT AND INCREASING THEM THROUGH THE DAY ON TUESDAY FROM SOUTH TO NORTH. IT WILL TAKE A WHILE FOR PORTIONS OF NEON AND SOFA TO SEE RAIN BECAUSE OF. STORMS...LATE TUESDAYS AFTERNOON INTO EVENING LOOKS TRICKY TO ME REGARDING STORMS. THERE IS THE POTENTIAL FOR OUR EXTREME SOUTHERN AREAS TO SEE A FEW STRONG STORMS...IT DEPENDS ON SEVERAL FACTORS. HOW MUCH INFLUENCE/IMPACT WILL THE CONVECTION THAT DEVELOPS FURTHER SOUTH HAVE ACROSS OUR AREA...WHERE WILL THE WARM FRONT BE DRAPED...HOW MUCH INSTABILITY WILL THERE BE? THE CERTAINTIES ARE...STRONG LIFT PRESENT...HIGH SHEAR AND HELICITY VALUES AND PLENTY OF MOISTURE. WILL HAVE TO CONTINUE TO CLOSELY WATCH THIS TO SEE HOW IT FURTHER UNFOLDS. LEFT THUNDER IN FOR KNOXVILLE AND SOUTHWARD FOR TUESDAY AFTERNOON INTO EVENING. FOR THE RAIN/WIND...IF THE CONVECTION TO OUR SOUTH REALLY BLOWS UP IT COULD LIMIT HOW MUCH PRECIP WE SEE. IT IS NOT UNCOMMON FOR STRONG CONVECTION TO OUR SOUTH TO INTERRUPT THE FLOW OF MOISTURE INTO OUR AREA. HAVING SAID THAT...I STILL THINK IT IS LIKELY WE SEE SOME DECENT RAINFALL ACROSS OUR SOUTHERN AREAS DUE TO THE EXISTING MOISTURE THAT WILL BE IN PLACE...THE PROXIMITY OF THE SURFACE LOW MOVING ACROSS...AND THE STRONG 850MB JET AXIS OVER OUR AREA. CURRENT GFS AND NAM SOUNDINGS CONTINUE TO SHOW PW VALUES RANGING FROM 1.40 TO 1.20 INCHES FROM SOUTH TO NORTH. THIS PUTS US AT 2SD ABOVE NORMAL FOR THIS TIME OF YEAR. I STILL DON`T THINK FLOODING WILL BE A CONCERN BECAUSE OF HOW QUICKLY THIS SYSTEM IS MOVING. HIGHEST RAINFALL AMOUNTS WILL LIKELY BE ACROSS THE SOUTHERN VALLEY WITH AMOUNTS FROM HALF AN INCH TO ONE INCH POSSIBLE IN SOME LOCATIONS. GUSTY WINDS FROM 20 TO 30KTS WILL LIKELY OCCUR ACROSS THE HIGHER ELEVATIONS FROM TUESDAY AFTERNOON THROUGH WEDNESDAY DUE TO THE 40 TO 50KT 850MB JET. BREEZY CONDITIONS ACROSS THE LOWER ELEVATIONS EXPECTED ON WEDNESDAY AS THE FRONT MOVES THROUGH. THE SNOW...FOR THE SNOW LOVERS IT IS NOT LOOKING TOO GOOD. FOR THE PAST FEW DAYS THE MODELS HAVE BEEN DELAYING THE ARRIVAL OF THE COLD AIR...AND THEY CONTINUE TO DO SO. THIS HAS TO DO WITH THE TRACK OF THE LOW. DUE TO THE DELAYED COLD AIR AND THE SPEED OF WHICH THE UPPER LOW RACES OFF TO THE NORTHEAST...THE SNOW POTENTIAL CONTINUES TO DECREASE. BY THE TIME THE COLD FRONT MOVES THROUGH ON WEDNESDAY...CHRISTMAS EVE...IT LOOKS LIKE THERE WILL BE LITTLE MOISTURE LEFT. BECAUSE OF THE SPEED OF THE LOW THERE WON`T BE MUCH TIME TO FUNNEL WRAP AROUND MOISTURE INTO THE AREA. THOUGH THERE LIKELY WON`T BE ANY ACCUMULATION ACROSS LOWER ELEVATIONS...MOST AREAS WILL STILL PROBABLY SEE LIGHT SCATTERED SNOW SHOWERS/FLURRIES ACROSS THE AREA THROUGH EARLY CHRISTMAS MORNING....WITH THE BEST CHANCES ACROSS NE TN AND SW VA. UPPER ELEVATIONS MAY STILL SEE SOME MINOR ACCUMULATIONS OF AROUND AN INCH OR TWO. MODELS CONTINUE TO SHOW THIS SYSTEM QUICKLY EXITING ON THURSDAY...CHRISTMAS DAY...AS IT RACES OFF TO THE NORTHEAST. WE MAY EVEN SEE SOME SUNSHINE BY THURSDAY AFTERNOON ACROSS THE PLATEAU AND SOUTHERN AREAS. ANOTHER QUICK MOVING WEAKER SYSTEM MOVES THROUGH FRIDAY INTO SATURDAY...BUT MODELS AREN`T HANDLING IT TOO WELL. WILL CONTINUE WITH POPS THOUGH UNTIL THERE IS BETTER RESOLUTION. THE SYSTEM SHOULD BE EXITING THE AREA BY SUNDAY. && .PRELIMINARY POINT TEMPS/POPS... CHATTANOOGA AIRPORT, TN 40 53 46 57 / 20 10 40 80 KNOXVILLE MCGHEE TYSON AIRPORT, TN 38 54 44 59 / 20 10 10 50 OAK RIDGE, TN 37 55 44 58 / 20 10 20 60 TRI CITIES AIRPORT, TN 35 51 39 57 / 40 20 10 20 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ DGS/SR

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