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

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000 FXUS64 KMRX 241856 AFDMRX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MORRISTOWN TN 256 PM EDT TUE MAR 24 2015 .SHORT TERM /TONIGHT AND WEDNESDAY/... CLEAR CONDITIONS THIS MORNING HAVE GIVEN WAY TO SCATTERED CU DEVELOPMENT ACROSS THE TENNESSEE VALLEY AND SOUTHERN APPALACHIANS... THANKS TO DIURNAL HEATING. WITH AMPLE SUNSHINE AND A SOUTHERLY FLOW...TEMPERATURES HAVE RISEN INTO THE LOWER 70S IN MANY AREAS AS OF 3 PM EDT...AND SHOULD TOP OFF IN THE MID 70S OVER A GOOD PORTION OF THE CENTRAL AND SOUTHERN VALLEYS BEFORE SUNSET. AN ISOLATED SHOWER OR TWO WILL BE POSSIBLE LATE THIS AFTERNOON AND EVENING ALONG THE EAST TENNESEEE MOUNTAINS...AND SW VIRGINIA/FAR NE TENNESSEE. HOWEVER...MOSTLY LOCATIONS WILL REMAIN DRY. MUCH OF THIS CU DEVELOPMENT WILL DISSIPATE WITH THE SETTING SUN...BUT SOME MID TO HIGH CLOUDS COULD MOVE IN LATE TONIGHT...AHEAD OF A FRONTAL SYSTEM TO THE NORTH AND WEST. SOME BREEZY/GUSTY SOUTHEAST GRADIENT WINDS WILL ALSO BE POSSIBLE AT TIMES OVER THE HIGHER TERRAIN OF THE EAST TENNESSEE MOUNTAINS AND THEIR SURROUNDING FOOTHILLS...IN RESPONSE TO A STRONGER LLJ MOVING FROM WEST TENNESSEE INTO CENTRAL KENTUCKY. HOWEVER...NOTHING ADVISORY-LEVEL IS EXPECTED TO OCCUR ATTM. SCT TO PERHAPS BKN DECKS OF CU WILL DEVELOP AGAIN TOMORROW. HOWEVER...WITH WINDS INCREASING FROM THE SOUTHWEST...GOOD WARM AIR ADVECTION /ALONG WITH SOME SUNSHINE/...WILL HELP TO PUSH HIGHS INTO THE LOW TO MID 70S ONCE AGAIN. SOME ISOLATED SHOWERS AND THUNDERSTORMS WILL AGAIN BE POSSIBLE ALONG THE PLATEAU AND MOUNTAINS...BUT MOST AREAS WILL REMAIN DRY. .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... WEDNESDAY NIGHT WILL FEATURE A STRENGTHENING DOWNSLOPE 850 MB FLOW THAT WILL KEEP MOST PRECIP EAST OF THE AREA AND KEEP MOST OF THE TN VALLEY DRY. BY THURSDAY MORNING...FORCING ASSOCIATED WITH THE APPROACHING UPPER TROUGH AND JET ENTRANCE REGION MOVES INTO MIDDLE TN...BRINGING SHOWERS TO OUR DOORSTEP FROM THE WEST. THE NAM HAS COME INTO BETTER AGREEMENT WITH THE TIMING OF THE GFS AND ECMWF...BUT IS STILL THE SLOWEST OF THE MODELS. THIS FASTER TREND OF THE NAM LENDS CONFIDENCE TO RAISING POPS TO CATEGORICAL THURSDAY AFTERNOON. WITH 850 MB THETA-E VALUES NEAR 320 K BEING MARGINAL FOR THUNDERSTORMS...WILL MENTION A SLIGHT CHANCE OF TSTMS. SEVERE THREAT LOOKS MARGINAL AT BEST WITH INSTABILITY BEING VERY LIMITED...BUT CANNOT ENTIRELY RULE OUT STRONG WIND GUSTS. PRECIP CHANCES DROP OFF QUICKLY AFTER MIDNIGHT WITH LOW AND MIDLEVEL DRY ADVECTION BEHIND THE COLD FRONT. THE MAIN UPPER TROUGH AXIS SHIFTS ACROSS THE AREA ON FRIDAY. LOW LEVEL COLD ADVECTION ALONG WITH VERY COLD MIDLEVEL TEMPS BENEATH THE TROUGH WILL CREATE SOME INSTABILITY FOR LOW-TOPPED CONVECTIVE SHOWERS THROUGH THE DAY. THE NAM AND GFS SHOW SNOW ACCUMULATION BEGINNING AS EARLY AS THURSDAY NIGHT...BUT SURFACE TEMPS WILL LIKELY NOT BE COLD ENOUGH BY THEN FOR ANY ACCUMULATION...AND MIDLEVEL MOISTURE LOOKS TOO LIMITED ABOVE THE DENDRITE GROWTH ZONE FOR MUCH SNOW FORMATION ALOFT. LOW LEVEL TEMPERATURES MAY BE FALLING THROUGH FRIDAY AFTERNOON AS THE GFS SHOWS STRENGTHENING COLD ADVECTION...AND THIS SHOULD CHANGE PRECIP TO SNOW SHOWERS IN SW VA AND HIGHER ELEVATIONS BY FRIDAY EVENING. THERE IS ONLY A SMALL WINDOW OF ADEQUATE MOISTURE DEPTH AFTER TEMPS DROP ENOUGH...SO SOME LIGHT ACCUMULATIONS WILL BE POSSIBLE NORTH AND IN HIGHER ELEVATIONS FRIDAY EVENING. LOWS SATURDAY MORNING WILL BE IN THE 20S TO LOWER 30S SOUTH. SATURDAY WILL BE ABNORMALLY COLD BUT MOSTLY SUNNY BEHIND THE EXITING TROUGH. THE GFS AND ECMWF BOTH SHOW A SHORTWAVE TROUGH MOVING BY QUICKLY IN THE NW FLOW...BUT WITH THE TIMING NEARLY 24 HOURS APART...SUNDAY AFTERNOON IN THE GFS...AND MONDAY IN THE ECMWF. WILL SPLIT THE DIFFERENCE AND HAVE CHANCE POPS NORTH SUNDAY NIGHT...WITH A BOOKEND SLIGHT CHANCE SUNDAY AND MONDAY MORNING. A WARMING TREND WILL START OFF NEXT WEEK...WITH HIGHS UP TO THE 60S BY TUESDAY. && .PRELIMINARY POINT TEMPS/POPS... CHATTANOOGA AIRPORT, TN 55 75 59 71 / 10 10 10 70 KNOXVILLE MCGHEE TYSON AIRPORT, TN 53 74 54 72 / 10 10 10 80 OAK RIDGE, TN 53 74 54 70 / 10 10 20 80 TRI CITIES AIRPORT, TN 49 70 50 73 / 20 10 20 80 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ AMP/DGS

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