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

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000 FXUS64 KMRX 022034 AFDMRX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MORRISTOWN TN 334 PM EST MON MAR 2 2015 .SHORT TERM (TONIGHT AND TOMORROW)...
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TEMPERATURES RISING WHERE CLOUD COVER HAS THINNED...SO ADJUSTED TEMPERATURES TODAY AND TONIGHT TO REFLECT THIS. WARM FRONT WILL RISE NORTH THROUGH THE AREA THIS EVENING...WITH SHOWERS BEGINNING EARLY MORNING TUESDAY. FAR NORTHEAST TN AND SOUTHWEST VA COULD BE COLD ENOUGH FOR SOME SNOW FLURRIES...BUT ACCUMULATION IS EXPECTED TO BE LOW. OTHERWISE...SCATTERED RAIN SHOWERS EXPECTED THROUGH THE SHORT TERM WITH WINDS INCREASING TUESDAY AFTERNOON...MAINLY IN HIGHER TERRAIN. .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... VERY COMPLICATED FORECAST IN THE EXTENDED PERIOD WITH THE POSSIBILITY OF LOCALLY HEAVY RAINFALL TUESDAY NIGHT AND WEDNESDAY...AND WINTRY PRECIPITATION WEDNESDAY NIGHT INTO THURSDAY. HOWEVER...GREAT DIFFERENCES EXIST BETWEEN THE MODELS...WITH THE NAM A BIT DRIER AND WARMER FOR WEDNESDAY AND WEDNESDAY NIGHT...AND THE GFS COLDER AND WETTER. A WARM FRONT WILL MOVE INTO SOUTHWEST VIRGINIA TUESDAY EVENING... BRINGING SOME ADDITIONAL SHOWERS ACROSS THE AREA OVERNIGHT. SOME DOWNSLOPE WINDS ALONG THE MOUNTAINS AND SOUTHWEST WINDS ACROSS MUCH OF THE VALLEY /ALONG WITH THE CLOUDS/ WILL KEEP TEMPERATURES UP OVERNIGHT IN THE UPPER 40S TO MID 50S. A SLOW MOVING COLD FRONT TO OUR NORTHWEST WILL THEN SET THE STAGE FOR EVENTS WEDNESDAY AND WEDNESDAY NIGHT. THE NAM AND ECMWF MODELS HAVE CONTINUED THE SLOWER TREND AND SHOW THIS FRONT /ALONG WITH IT`S LIFT/PRECIPITATION FOCUS/ TO BE OVER CENTRAL KENTUCKY AND MIDDLE TENNESSEE. HOWEVER...SOME HEAVIER RAIN IS EXPECTED DURING THE DAY AND WILL FAVOR AREAS ALONG THE CUMBERLAND MOUNTAINS THAT STILL HAVE A SNOWPACK. THE WARM TEMPERATURES IN THE 50S TO EVEN LOW 60S /ALONG WITH THIS PRECIPITATION/ WILL MELT ANY REMAINING SNOW. THIS...COMBINED WITH THE HEAVY RAINFALL BETWEEN 1 TO 2 INCHES BY THE EVENING COULD LEAD TO AREAL AND RIVER FLOODING BEGINNING TUESDAY NIGHT THROUGH THE DAY ON THURSDAY. AS A RESULT...HAVE ISSUED A FLOOD WATCH FOR THIS PERIOD OVER THE NORTHERN PLATEAU AND SOUTHWEST VIRGINIA. ELSEWHERE...QPF AMOUNTS WILL BE LIGHTER...SO A FLOOD WATCH WAS NOT NEEDED ATTM. ATTENTION THEN TURNS TO THE COLD FRONT WHICH WILL LIKELY MAKE IT`S WAY THROUGH THE AREA BY LATE EVENING. A MUCH COLDER AIR MASS WILL FOLLOW WHICH WILL LEAD TO WINTRY PRECIPITATION ACROSS THE ENTIRE REGION. THERE IS STILL GREAT UNCERTAINTY REGARDING THE ARRIVAL OF THE SUBFREEZING AIR AND WHAT THE TEMPERATURE PROFILE WILL BE ACROSS MUCH OF THE VALLEY OVERNIGHT. THE SHALLOW NATURE OF THIS SUBFREEZING AIRMASS HAS BEEN KNOWN TO GET HUNG UP TO THE NORTH AND WEST OF THE PLATEAU...SIGNIFICANTLY DIMINISHING THE ICING THREAT ACROSS MUCH OF THE VALLEY IN SIMILAR SITUATIONS. SO THE QUESTION BECOMES...WHEN DOES THIS AIR BLEED INTO THE TENNESSEE VALLEY? HAVE SOME CONFIDENCE THAT AREAS ALONG THE NORTHERN PLATEAU AND CUMBERLAND MOUNTAINS OF EAST TENNESSEE WILL SEE SOME FREEZING RAIN ACCUMULATIONS...FOLLOWED BY 1 TO 3 INCHES OF SLEET/SNOW LATE WEDNESDAY NIGHT INTO THURSDAY. ELSEWHERE ACROSS THE VALLEY...SLIGHTLY WARMER SURFACE TEMPERATURES COULD KEEP PRECIPITATION A COLD RAIN THROUGH MUCH OF THE NIGHT...BEFORE A BRIEF CHANGE OVER TO SLEET AND EVENTUALLY SNOW AS PRECIPITATION TAPERS AND THE COLDER AIR ARRIVES. HAVE TRIED TO ACCOUNT FOR MODEL VARIABILITY...BUT FOR NOW HAVE FAVORED THIS THINKING OF GENERALLY LIGHT WINTRY PRECIPITATION ACROSS MUCH OF THE VALLEY FOR NOW. BY THURSDAY MORNING...COLDER AIR WILL QUICKLY MOVE IN...RESULTING IN A DECREASING TEMPERATURE THROUGHOUT THE DAY DUE TO STRONG COLD AIR ADVECTION. WITH CLEARING OCCURRING THURSDAY NIGHT...A VERY COLD FORECAST WILL BE IN STORE FOR THE REGION WITH LOWS IN THE SINGLE DIGITS TO TEENS BY FRIDAY MORNING. A GRADUAL RECOVERY WILL OCCUR BY THE WEEKEND WITH A DRY FORECAST UNTIL SUNDAY.
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&& .PRELIMINARY POINT TEMPS/POPS...
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CHATTANOOGA AIRPORT, TN 44 55 51 64 / 70 80 70 90 KNOXVILLE MCGHEE TYSON AIRPORT, TN 40 54 53 62 / 40 80 70 70 OAK RIDGE, TN 39 54 51 59 / 40 80 80 80 TRI CITIES AIRPORT, TN 34 52 49 60 / 30 70 70 70
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&& .MRX WATCHES/WARNINGS/ADVISORIES...
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NC...NONE. TN...FLOOD WATCH FROM TUESDAY EVENING THROUGH THURSDAY EVENING FOR CAMPBELL-CLAIBORNE-HANCOCK-MORGAN-SCOTT TN. VA...FLOOD WATCH FROM TUESDAY EVENING THROUGH THURSDAY EVENING FOR LEE-RUSSELL-SCOTT-WASHINGTON-WISE.
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&& $$ JW/AMP

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