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

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS64 KMRX 202022 AFDMRX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MORRISTOWN TN 322 PM EST SAT DEC 20 2014 .SHORT TERM...(TONIGHT THROUGH MONDAY)...CLOUDS ARE SLOWLY ERODING FROM THE WEST THIS AFTERNOON...AND MOST OF THE TN VALLEY SHOULD BE CLEAR BEFORE MIDNIGHT IF THE TREND CONTINUES AND IF THE HRRR IS ACCURATE. WITH THE EXPECTED CLEARING AND CALM WINDS...CONDITIONS APPEAR FAVORABLE FOR FOG TONIGHT. CROSSOVER TEMPERATURES ARE ESPECIALLY FAVORABLE NORTH...SO WILL MENTION PATCHY/AREAS OF FOG THERE AS WELL AS SW NC. FOG SHOULD BE SLOW TO DISSIPATE DUE TO THE LOW SUN ANGLE AND WEAK MIXING TOMORROW MORNING. THE REST OF THE DAY SHOULD BE MOSTLY SUNNY...WITH HIGH CLOUDS INCREASING LATE IN THE DAY. A WEAK SHORTWAVE TROUGH IN THE SOUTHERN STREAM NOW OVER TX WILL BE LIFTING E-NE AND CROSSING OUR AREA SUNDAY NIGHT AND MONDAY. WITH THE JET POSITIONED FROM SOUTHERN AL TO THE NC COAST...THE MAJORITY OF LIFT AND DEEP MOISTURE APPEARS TO BE EAST OF OUR AREA. THE NAM PULLS MORE MOISTURE INTO OUR AREA THAN THE GFS...BUT EVEN THE NAM SHOWS THIS MOISTURE MAINLY BELOW THE -10C LEVEL...SUGGESTING THAT DRIZZLE IS MORE LIKELY THAN MEASURABLE RAINFALL. AS A RESULT...WILL CUT BACK POPS TO A CHANCE EAST TO NOTHING WEST...BUT MENTIONING DRIZZLE EVERYWHERE. QPF WILL BE REDUCED AS WELL...TO NO MORE THAN A TENTH IN THE MOUNTAINS. TEMPERATURE PROFILES IN ALL THE MODEL SOUNDINGS INDICATE ALL LIQUID PRECIP. THE TROUGH PASSAGE SHOULD BRING AN END TO ANY RAIN/DRIZZLE ON MONDAY AFTERNOON. .LONG TERM...(MONDAY NIGHT THROUGH SATURDAY)...QUITE THE ACTIVE LONG TERM PERIOD WITH A HIGHLY AMPLIFIED SYSTEM COMING IN FOR CHRISTMAS THAT WILL BRING...RAIN...MAYBE A FEW STORMS...WIND...AND PERHAPS SNOW. MONDAY NIGHT INTO TUESDAY HEIGHTS WILL BE QUICKLY BUILDING OUT AHEAD OF A DEEP TROUGH MOVING ACROSS THE CENTRAL U.S. AND SOUTHERN PLAINS. THIS WILL ALLOW FOR MONDAY NIGHT AND TUESDAY DAY TO BE UNSEASONABLE WARM. LOWS MONDAY NIGHT WILL BE 10 TO 12 DEGREES ABOVE NORMAL. HIGHS ON TUESDAY WILL BE IN THE MID TO UPPER 50S...5 TO 10 DEGREES ABOVE NORMAL. RAIN CHANCES INCREASE ON TUESDAY AS THIS HIGHLY AMPLIFIED AND DEEP TROUGH IS ON OUR DOORSTEP BY TUESDAY AFTERNOON. DID DECIDE TO INTRODUCE SLIGHT CHANCE OF THUNDERSTORMS FROM KNOXVILLE SOUTH TUESDAY AFTERNOON INTO TUESDAY NIGHT. CAPE IS VERY WEAK BUT SHEAR AND HELICITY ARE ROBUST...IN LARGE PART DUE TO A STRONG 850MB JET OF 40 TO 50 KTS THAT WILL BE IN PLACE. BETTER INSTABILITY EXISTS FURTHER TO OUR SOUTH AND SOUTHWEST BUT DID WANT TO MENTION A STORM OR TWO POSSIBLE ACROSS OUR CENTRAL AND SOUTHERN AREAS. ABUNDANT MOISTURE AND STRONG LIFT WILL LEAD TO SOME DECENT RAINFALL ACROSS THE AREA FOR TUESDAY NIGHT INTO WEDNESDAY...MORE SO ACROSS THE SOUTHERN AREAS. CURRENT GFS SOUNDINGS 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 DON`T THINK FLOODING WILL BE A CONCERN THOUGH BECAUSE OF HOW QUICKLY THIS SYSTEM IS MOVING. SO NOW THAT WE HAVE TALKED ABOUT RAIN AND STORMS...LET`S TALK ABOUT SNOW. CHRISTMAS EVE IS LOOKING TO BE RATHER NASTY WITH THE DEEP TROUGH AND ASSOCIATED SURFACE LOW MOVING ACROSS. LIGHT TO MODERATE RAIN CONTINUES WEDNESDAY MORNING WITH STRONG COLD FRONT MOVING THROUGH BY LATE AFTERNOON INTO EARLY EVENING. AS THE FRONT MOVES THROUGH EXPECT RAIN TO CHANGE TO SNOW ACROSS MUCH OF THE AREA ALONG WITH BREEZY WINDS. THE MILLION DOLLAR QUESTION IS HOW MUCH MOISTURE WILL BE LEFT. MODELS HAVE BEEN CONSISTENT IN SHOWING THE HIGHLY AMPLIFIED SYSTEM FOR SEVERAL DAYS OUT BUT HAVE NOT BEEN WITH THE EXACT PLACEMENT OF THE LOW. THE LATEST FEW MODEL RUNS OF THE ECMW AND THE GFS ARE TRENDING THE LOW FURTHER TO OUR WEST. THIS MEANS THAT THE BULK OF THE MOISTURE WILL HAVE PASSED OFF TO OUR EAST BEFORE IT GETS COLD ENOUGH TO SNOW BACK BEHIND THE COLD FRONT. IT LOOKS LIKE OUR SNOW WILL BE IN THE FORM OF WRAP AROUND MOISTURE. THE CHANGEOVER TO SNOW LOOKS TO OCCUR SOMETIME ON WEDNESDAY EVENING WITH SNOW LINGERING THROUGH EARLY CHRISTMAS MORNING. MOST OF THE PRECIP DURING THIS TIME FRAME SHOULD BE IN THE FORM OF SCATTERED LIGHT SNOW SHOWERS. LITTLE TO NO ACCUMULATION EXPECTED AT THIS TIME FOR LOWER ELEVATIONS. HIGHER ELEVATIONS MAY GET AN INCH OR TWO. AGAIN...ALL OF THE ABOVE DEPENDS ON THE TRACK OF THE LOW...BUT THIS IS HOW IT`S LOOKING FOR NOW. THIS SYSTEM QUICKLY EXITS ON THURSDAY...CHRISTMAS DAY...AS IT RACES OFF TO THE NORTHEAST. ANOTHER QUICK MOVING WEAKER SYSTEM MOVES THROUGH ON FRIDAY INTO SATURDAY THAT COULD BRING SOME LIGHT SHOWERS TO THE AREA. && .PRELIMINARY POINT TEMPS/POPS... CHATTANOOGA AIRPORT, TN 33 53 41 56 / 0 10 20 10 KNOXVILLE MCGHEE TYSON AIRPORT, TN 31 50 38 55 / 0 10 20 10 OAK RIDGE, TN 30 50 38 55 / 0 0 20 10 TRI CITIES AIRPORT, TN 30 48 35 51 / 0 10 30 40 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ DGS/SR

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.