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

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000 FXUS64 KMRX 232026 AFDMRX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MORRISTOWN TN 322 PM EST FRI JAN 23 2015 .SHORT TERM (TONIGHT THROUGH SATURDAY NIGHT)...
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THE LOW PRESSURE SYSTEM MOVING THROUGH THE SOUTHERN APPALACHIAN REGION WILL CONTINUE TO BRING SCATTERED SHOWERS INTO THE AREA THROUGH THE NIGHT AND INTO SATURDAY MORNING. PRECIP THROUGH MUCH OF THE EVENING WILL REMAIN AS RAIN. AFTER MIDNIGHT...COLDER AIR WILL MOVE IN ON THE BACK SIDE OF THE SYSTEM AND THE RAIN WILL TRANSITION TO SNOW. LOWER ELEVATIONS NORTH OF TYS COULD SEE UP TO A HALF INCH...THE NORTHERN CUMBERLAND PLATEAU COULD SEE AROUND AN INCH. THE APPALACHIANS OF TN AND WISE AND RUSSELL COUNTIES SHOULD EXPECT 1 TO 3 INCHES AND WILL ISSUE AN ADVISORY FOR THESE LOCATIONS. SNOW SHOULD END FROM WEST TO EAST DURING SATURDAY MORNING. A WEAK WAVE MOVES THROUGH THE UPPER FLOW ON SATURDAY NIGHT. THIS WILL BRING IN SOME LOW LEVEL MOISTURE AND WEAK LIFT AND COULD SEE A FEW ISOLATED SNOW SHOWERS MOVE ACROSS FAR NORTHERN AREAS AND POSSIBLY FAVORED AREAS OF THE TN MOUNTAINS LATE SATURDAY NIGHT. .LONG TERM (SUNDAY THROUGH FRIDAY)...SUNDAY...CLOUDS WILL BE ON THE INCREASE OUT AHEAD OF OUR ALBERTA CLIPPER. NOW THAT THIS EVENT IS WITHIN THE RANGE OF THE NAM...THE EVENT BECOMES A LITTLE MORE TRICKY DUE TO SOME DISAGREEMENTS BETWEEN THE NAM AND GFS. THE NAM HAS THE BULK OF THE PRECIP BETWEEN 00Z AND 12Z MONDAY WHILE THE GFS IS MORE IN THE 06Z TO 18Z RANGE. THE NAM SOUNDINGS DON`T SHOW IT TO START SNOWING AT TRI UNTIL SOMETIME BETWEEN 06Z AND 09Z AND AT TYS UNTIL AROUND 09Z TO 12Z. BY 12Z PROFILES LOOK COLD ENOUGH FOR SNOW FROM KNOXVILLE NORTH...BUT BY THIS TIME THE MAJORITY OF THE PRECIP IS OVER WITH BESIDES SOME LINGERING LIGHT AND SCATTERED SNOW SHOWERS. IF THIS OCCURS...IT WILL BE HARD FOR THE VALLEY TO SEE ANY ACCUMULATION. THE NAM SHOWS SNOW STARTING ON THE NORTHERN PLATEAU AND SWVA BY AROUND 03Z TO 06Z MONDAY. SO THESE AREAS WOULD LIKELY STILL SEE SOME ACCUMULATING SNOWFALL. THE GFS BRINGS IN THE COLDER AIR A FEW HOURS LATER THAN THE NAM BUT THIS ALSO COINCIDES WITH THE LONGER LASTING MOISTURE. THE GFS SOUNDING PROFILES INDICATE THAT IT COULD STILL BE SNOWING FROM KNOXVILLE NORTH MONDAY AFTERNOON AT 18Z DUE TO 85OMB TEMPS AROUND -7C. THIS WOULD PROBABLY BE COLD ENOUGH TO SUPPORT SNOW ALL THE WAY DOWN TO THE SURFACE. SO IF THE GFS WERE TO BE TRUE...THEN I COULD STILL SEE THE LOWER ELEVATION CENTRAL VALLEY AREAS NORTH OF I-40 PICKING UP AROUND AN INCH OR SO WHERE THE NAM SOLUTION WOULD GIVE LITTLE TO NO ACCUMULATION. GOING WITH A BLEND OF THE TWO MODELS FOR THE LOWER ELEVATION ACCUMULATIONS. AGAIN...THE DIFFERENCES BETWEEN THE NAM AND GFS WOULD MOSTLY IMPACT SNOW ACCUMS ACROSS LOWER ELEVATION VALLEY AREAS. BOTH MODELS WOULD LIKELY STILL GIVE THE NORTHERN PLATEAU AND SWVA SOME ACCUMULATING SNOWFALL ALONG WITH SOME MINOR ACCUMULATIONS ACROSS NETN. THE NORTHERN PLATEAU COULD SEE 1 TO 2 INCHES...NETN 1 TO 2 INCHES...SWVA...1 TO 3 INCHES. SO AS IT STANDS...THIS SYSTEM IS STILL VERY MUCH UP IN THE AIR AS FAR AS CONFIDENCE IN SNOW TOTALS ACROSS THE LOWER ELEVATIONS. AS THE PREVIOUS DISCUSSION MENTIONED...THERMAL/MOISTURE PROFILES ALONG WITH THE TRACK WILL ULTIMATELY DETERMINE OUR SNOW TOTALS BUT BECAUSE MODELS AREN`T AGREEING ON ALL OF THESE THINGS IT`S HARD TO HAVE MUCH CONFIDENCE AT THIS POINT. ANOTHER ASPECT LEADING TO THE DIFFICULTY OF THIS FORECAST IS THAT BOTH MODELS DO SHOW SOME SLIGHT INSTABILITY WITH VALUES OF AROUND 100 J/KG SHOWING UP IN SOUNDINGS. THIS WOULD LEAD TO BANDING OF SNOW SHOWERS...WHICH CAUSES FORECASTING OF SNOW TOTALS TO BE VERY DIFFICULT. WHEN BANDING OCCURS...AN AREA UNDER ONE OF THESE SNOW BANDS COULD PICK UP A QUICK INCH OR MORE WHILE AN ADJACENT AREA OUTSIDE THE BAND SEES LITTLE TO NOTHING. MORE CONFIDENCE EXISTS WITH THE HIGHER ELEVATION FORECAST. STILL EXPECTING ELEVATIONS ABOVE ROUGHLY 3K FEET TO SEE SNOW FOR THE DURATION OF THE EVENT. EXPECT THE FAVORED NW FLOW SLOPES TO CONTINUE TO PICK UP SOME ACCUMULATIONS THROUGH TUESDAY NIGHT AS ANOTHER WEAK IMPULSE DIVES DOWN FROM THE NW MONDAY NIGHT THROUGH TUESDAY NIGHT. THIS WOULD ALLOW FOR ACCUMULATING SNOWS ACROSS THE HIGHER ELEVATIONS FROM SUNDAY NIGHT THROUGH LATE TUESDAY NIGHT INTO EARLY WED MORNING. FAVORED NW FLOW SLOPE AREAS COULD PICK UP ANYWHERE FROM 3 TO 6 INCHES DURING THIS TIMEFRAME WITH THE HIGHEST PEAKS RECEIVING LOCALLY HIGHER AMOUNTS. THE BULK OF THE HIGHER ELEVATION ACCUM THOUGH WILL LIKELY COME BETWEEN 03Z TO AROUND 18Z MONDAY. THE MONDAY NIGHT TUESDAY IMPULSE WILL PROVIDE ADDITIONAL MINOR ACCUMS. THIS IMPULSE WILL ALSO RESULT IN SOME SNOW SHOWERS ACROSS THE LOWER ELEVATIONS BUT NOT EXPECTING ACCUMULATIONS OTHER THAN TRACE AMOUNTS. HOWEVER...SWVA COULD RECEIVE AN INCH OR SO WITH THIS EVENT. WEDNESDAY THINGS BEGIN TO CLEAR OUT AS THE WESTERN RIDGE OF HIGH PRESSURE BEGINS TO PUSH THE TROUGH TO OUR EAST. RIDGING CONTINUES UNTIL THURSDAY BUT HEIGHTS BEGIN TO FALL THURSDAY NIGHT INTO FRIDAY AS ANOTHER WEAK SYSTEM APPROACHES. THIS SYSTEM WILL GIVE US ANOTHER SHOT OF SOME LIGHT PRECIP. SO...TEMPERATURES WARMING WEDNESDAY AND THURSDAY AND THEN DROPPING AGAIN FRIDAY WITH THE FRONTAL PASSAGE. WILL CONTINUE TO HIGHLIGHT CLIPPER IN THE HWO.
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&& .PRELIMINARY POINT TEMPS/POPS...
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CHATTANOOGA AIRPORT, TN 35 45 32 54 / 70 30 10 20 KNOXVILLE MCGHEE TYSON AIRPORT, TN 34 42 31 50 / 80 50 10 40 OAK RIDGE, TN 34 42 32 49 / 90 40 10 40 TRI CITIES AIRPORT, TN 32 39 29 46 / 90 70 10 50
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&& .MRX WATCHES/WARNINGS/ADVISORIES...
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NC...NONE. TN...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 11 AM EST SATURDAY FOR BLOUNT SMOKY MOUNTAINS-COCKE SMOKY MOUNTAINS- JOHNSON-SEVIER SMOKY MOUNTAINS-SOUTHEAST CARTER-SOUTHEAST GREENE-UNICOI. VA...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 11 AM EST SATURDAY FOR RUSSELL-WISE.
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&& $$ MJB/SR

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