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

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000 FXUS64 KMRX 190733 AFDMRX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MORRISTOWN TN 333 AM EDT SUN APR 19 2015 .SHORT TERM (TODAY AND TONIGHT)...
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SHOWERS HAVE BEEN BLOSSOMING OVER AL OVER THE PAST HOUR...AND EXPECT THIS INTENSIFICATION TO CONTINUE AS AN UPPER JET STREAK NOSES INTO THE SE AND SURFACE CYCLOGENESIS OVER WEST TN STRENGTHENS THE LLJ. AGEOSTROPHIC CIRCULATIONS ASSOCIATED WITH THIS JET WILL PRODUCE STRONG FORCING OVER THE AREA FOR MOST OF THE DAY. DOWNSLOPE WINDS OF 40 KTS AT 850 MB MAY DELAY PRECIP IN THE TRI-CITIES AREA UNTIL THE AFTERNOON...BUT THIS WILL SOON BE OVERCOME BY THE MID/UPPER LEVEL FORCING. INSTABILITY IS WEAK AT THIS TIME...BUT EMBEDDED THUNDERSTORMS WITH GUSTY WINDS AND LOCALLY HEAVY RAINFALL WILL BE POSSIBLE EVERYWHERE DUE TO THE STRONG DYNAMICS ALOFT. THIS MAIN AREA OF LIFT BEGINS TO EXIT SOUTHERN AND WESTERN SECTIONS BETWEEN 18- 21Z...AND NORTHERN SECTIONS INCLUDING TRI-CITIES BETWEEN 21Z-00Z. THE NAM INDICATES A DRY WINDOW OF ABOUT 4-6 HOURS BEFORE BRINGING IN ANOTHER AREA OF CONVECTION...WHICH DEVELOPS OVER MIDDLE TN/NRN AL LATE IN THE AFTERNOON WITH A PRE-FRONTAL TROUGH. THIS AREA MAY HAVE THE GREATER POTENTIAL FOR SEVERE STORMS AS INSTABILITY IS MUCH MORE FAVORABLE...WITH MLCAPES REACHING NEAR 1500 J/KG SOUTH. DEEP LAYER SHEAR AND BRN VALUES INDICATE SUPERCELLS WITH DAMAGING WINDS AND LARGE HAIL WILL BE POSSIBLE...AND LOW LCL HEIGHTS SUGGEST SOME TORNADO POTENTIAL AS WELL. HOWEVER...THE DISCONNECT FROM THE STRONGEST DYNAMIC FORCING MAY LIMIT THE SEVERE POTENTIAL. PLUS...THE GFS DOES NOT SHOW THIS AREA AT ALL...SO THERE IS SOME UNCERTAINTY WITH IT. AFTER CATEGORICAL POPS TODAY...WILL LOWER POPS BACK TO HIGH CHANCES TONIGHT. .LONG TERM (MONDAY THROUGH SUNDAY)... BY MONDAY MORNING MOST OF THE ISOLATED STORMS THAT FORMED ALONG THE PRE-FRONTAL TROUGH SHOULD HAVE MOVED OUT OF THE AREA OR WEAKENED OVERNIGHT. LOOKS LIKE THERE COULD BE A SECOND ROUND OF SHOWERS AND THUNDERSTORMS ASSOCIATED WITH A LINE OF CONVECTION MOVING OUT OF ARKANSAS AND MOVING ACROSS TENNESSEE. THIS LINE WILL LIKELY WEAKEN AS IT MOVES ACROSS TENNESSEE AND HAVE LOST QUITE A BIT OF POWER BY THE TIME IT MOVES INTO OUR CWA. SURFACE PRESSURE GRADIENT TIGHTENS CAUSING WINDS TO PICK UP DURING THE DAY ON MONDAY. SHOULD SEE WIDESPREAD WINDS OF 10 TO 20 MPH WITH SOME HIGHER GUSTS MIXED IN. AT THIS POINT MODEL FORECASTS AND MODEL GUIDANCE SUGGESTS WINDS STAY BELOW ADVISORY CRITERIA, BUT WILL CONTINUE TO MONITOR AS THE COLD FRONT GETS CLOSER. THERE WILL ALSO BE A SLIGHT CHANCE FOR SOME STORMS MONDAY EVENING DEPENDING ON WHAT HAPPENS OVERNIGHT SUNDAY NIGHT. AT THIS POINT THINK THAT THE BEST ENVIRONMENT/LIFT WILL HAVE MOVED OFF TO OUR EAST LEAVING US TO BE MOSTLY DRY FOR THIS TIME PERIOD. IF SOMETHING CAUSES THE FRONT/REMNANT THUNDERSTORM ACTIVITY TO SLOW DOWN THEN OUR ENVIRONMENT WOULD SUPPORT STORMS THAT COULD CAUSE DAMAGING WINDS AND MAYBE EVEN SEVERE SIZE HAIL. AGAIN, THIS ALL DEPENDS ON THE LOCATION OF THE FRONT, AND LIKELY THESE STORMS WILL BE OFF TO THE EAST IN THE CAROLINAS BY MONDAY EVENING. REGARDLESS OF WHEN THE FRONT FINALLY MOVES THROUGH, DRIER AIR AND CLEARER SKIES WILL BE USHERED IN BEHIND IT. HIGH TEMPS WILL BE KNOCKED BACK BY ABOUT 5 - 10 DEGREES WHEN COMPARING MONDAY HIGHS WITH TUESDAY HIGHS. WE WILL GET A SHORT BREAK DURING THE MIDDLE OF THE WEEK WITH GENERALLY ZONAL FLOW ALOFT AND WEST/NORTHWESTERLY WINDS AT THE SURFACE. WEAK SHORT WAVE WILL QUICKLY MOVE ACROSS LATE WEDNESDAY LEADING TO A CHANCE FOR SOME SHOWERS, WITH BETTER CHANCES BEING CONFINED TO NORTHEAST TENNESSEE/SOUTHWEST VIRGINIA. COLD FRONT WILL THEN MEANDER INTO THE AREA AND STALL OUT SOMEWHERE IN THE VICINITY AT THE END OF THE WORK WEEK. THIS LEADS TO A DECREASE IN FORECAST CONFIDENCE AS LOCATION OF THIS FRONT WILL DETERMINE WHERE SHOWERS AND THUNDERSTORMS DEVELOP LEADING INTO THE WEEKEND. MODELS DEPICT THE FRONT MOVING SOUTH BEFORE ANOTHER SYSTEM MOVES IN SATURDAY LEADING TO A GOOD PORTION OF NEXT WEEKEND LIKELY BEING WET AND CLOUDY. MODELS THEN SHOW DRY WEATHER MOVING IN TO START THE WORKWEEK AT THE END OF THE FORECAST.
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&& .PRELIMINARY POINT TEMPS/POPS...
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CHATTANOOGA AIRPORT, TN 75 62 74 49 / 100 50 50 30 KNOXVILLE MCGHEE TYSON AIRPORT, TN 76 61 74 48 / 100 50 50 30 OAK RIDGE, TN 74 61 72 47 / 100 50 50 30 TRI CITIES AIRPORT, TN 74 55 74 46 / 100 50 70 40
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&& .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ DGS/ABM

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