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

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
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 181910 AFDMRX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MORRISTOWN TN 310 PM EDT SAT APR 18 2015 .SHORT TERM (TONIGHT AND SUNDAY)...CONVERGENCE ALONG THE SPINE OF THE APPALACHIAN MOUNTAINS (ALONG THE TN/NC STATE-LINE) WILL CONTINUE TO DEVELOP SCATTERED SHOWERS AND POSSIBLY A THUNDERSTORM. THESE SHOWERS WILL MOVE NORTH INTO THE VALLEY THE REST OF THE AFTERNOON/EVENING. GREATEST COVERAGE WILL BE ACROSS THE SMOKYS SOUTHWARD INTO SOUTHWEST NORTH CAROLINA. FOR TONIGHT...WARM FRONTAL BOUNDARY WILL LIFT NORTHEAST FROM THE GULF COAST STATES TOWARD EAST TENNESSEE. INCREASING MOISTURE AND INSTABILITY WILL ACCOMPANY THE FRONTAL BOUNDARY. THERE IS GOOD UPPER LEVEL SUPPORT AS WELL THE TENNESSEE VALLEY/SOUTHERN APPALACHIANS WILL BE UNDER DIVERGENCE ALOFT/DIRECT CIRCULATION. THIS WILL INDUCE A WAVE ALONG THE WARM FRONTAL BOUNDARY AS WELL. A PERIOD OF MODERATE TO HEAVY RAINS IS EXPECTED AS THE WARM FRONT MOVES NORTH WITH LOCALIZED RUNOFF ISSUES POSSIBLE...BUT NO WARRANTING A FLOOD WATCH. MODEL SHOWS WARM FRONTAL BOUNDARY NEAR TRI BETWEEN 18-21Z WITH DECENT SHEAR ALONG THE BOUNDARY. WILL NEED TO WATCH FOR ANY STRONG CONVECTIVE DEVELOPMENT NEAR THE WARM FRONT SUNDAY AFTERNOON. ACROSS THE REST OF THE AREA WILL BE IN THE WARM SECTOR WITH MODEL SOUNDINGS SHOW FAVORABLE MID-LEVEL DRY AIR AND CAPES FOR ISOLATED DAMAGING DOWNBURSTS. ALSO...LOW WBZ AND LARGE ENOUGH HAIL CAPES TO PRODUCE THE THREAT OF HAIL. .LONG TERM (SUNDAY NIGHT THROUGH SATURDAY)...BULK OF THE WIDESPREAD PRECIP SHOULD BE NORTH OF OUR AREA AS WE BEGIN THE LONGTERM FORECAST ON SUNDAY NIGHT. AT THIS TIME...LONGWAVE TROUGH AXIS STILL BACK TO OUR WEST ALONG THE MISSISSIPPI RIVER WITH TRAILING COLD FRONT. MODELS IN DECENT AGREEMENT THAT AFTER THE WIDESPREAD PRECIP MOVES NORTH SUNDAY AFTERNOON THAT WE WILL HAVE A SLIGHT BREAK IN THE ACTION TO START SUNDAY NIGHT. THE BREAK DOESN`T LAST LONG THOUGH AS CONVECTION LOOKS TO FIRE WITH APPROACHING PRE-FRONTAL TROUGH AND MOVE INTO OUR AREA BETWEEN 8 PM AND MIDNIGHT. WITH THE PRE-FRONTAL CONVECTION THERE COULD BE A FEW STRONG TO SEVERE STORMS AS THERE SHOULD BE ENOUGH INSTABILITY AND SHEAR TO PROMOTE THE OCCASIONAL STRONGER/LONGER-LIVED UPDRAFT. AS THE PRE-FRONTAL CONVECTION IS MOVING THROUGH OUR AREA CONVECTION ALONG THE FRONT IN WEST TN IS BECOMING LINEARLY ORGANIZED BY 06Z MONDAY ACCORDING TO THE 12Z NAM. THE NAM SHOWS THIS LINE OF STORMS LOSING STEAM AS IT ROLLS INTO OUR AREA EARLY MONDAY MORNING. DEPENDING ON HOW ORGANIZED THE LINE IS AND COLD POOL ESTABLISHMENT...WILL DETERMINE HOW STRONG THE STORMS ARE WHEN THEY ENTER THE CUMBERLAND PLATEAU. IF THE STORMS REMAIN STRONGER THE MAIN THREAT WOULD BE DAMAGING WIND GUSTS. MONDAY IS AN INTERESTING DAY BUT HOW IT PLAYS OUT DEPENDS ON WHAT HAPPENS WITH THE SUNDAY NIGHT/MONDAY MORNING CONVECTIVE LINE. IF THE 12Z NAM SOUNDINGS ARE CORRECT...CAPES JUMP UP TO AROUND 2000 J/KG ACROSS THE SOUTHERN VALLEY AND 1000-1500 ACROSS THE CENTRAL VALLEY AND NETN BY MONDAY AFTERNOON. WITH THE COLD FRONT STILL WELL BACK TO OUR WEST...NEW CONVECTIVE DEVELOPMENT LOOKS POSSIBLE ALONG AND OUT AHEAD OF THE FRONT FOR MONDAY AFTERNOON THROUGH EVENING. SOME OF THESE STORMS COULD BE SEVERE WITH THE MAIN THREATS BEING DAMAGING WINDS AND POTENTIALLY LARGE HAIL. SOUNDINGS ARE SHOWING QUITE A BIT OF DRY AIR IN THE MID LEVELS WITH THE CLASSIC INVERTED V LOOK AT THE SURFACE. THIS DRY AIR ENTRAINMENT COULD LEAD TO DAMAGING WINDS AT THE SURFACE. LOW WETBULB FRZ HEIGHTS WITH AMPLE CAPE IN THE HAIL GROWTH REGION MAY RESULT IN SOME LARGE HAIL. AGAIN...A LOT OF THIS DEPENDS ON HOW QUICKLY MONDAY MORNINGS ACTIVITY EXITS AND FRONTAL TIMING LATER IN THE DAY. STAY TUNED... DRY AIR AND COOLER TEMPS MOVE IN BEHIND THE FRONTAL PASSAGE MAKING TUESDAY LOOK LIKE THE BEST DAY OF THE WEEK. MOSTLY SUNNY SKIES AND TEMPS IN THE LOW TO UPPER 60S EXPECTED. ZONAL FLOW ESTABLISHES ITS SELF TUESDAY NIGHT WITH A WEAK AND SUBTLE SHORTWAVE ZIPPING THROUGH THE FLOW ON WEDNESDAY. THERE COULD BE A FEW LIGHT SHOWERS AROUND BUT MOST AREAS ON WEDNESDAY LOOK DRY. ANOTHER WAVE MOVES IN WEDNESDAY INTO THURSDAY THAT WILL INCREASE POPS ONCE AGAIN AREA-WIDE. COLD FRONT SAGS SOUTH THROUGH THE AREA LATE THURSDAY. FRONT MAY STALL OUT SOMEWHERE ACROSS OUR AREA INTO FRIDAY WHICH WOULD LEAD TO ADDITIONAL CHANCES FOR SCATTERED SHOWERS. THE NEXT SYSTEM MOVES IN ON SATURDAY AND INCREASES POPS ONCE AGAIN. DRY WEATHER LOOKS TO RETURN JUST BEYOND THE END OF THIS EXTENDED FORECAST. && .PRELIMINARY POINT TEMPS/POPS... CHATTANOOGA AIRPORT, TN 64 77 61 72 / 100 80 40 50 KNOXVILLE MCGHEE TYSON AIRPORT, TN 62 74 60 71 / 100 90 40 50 OAK RIDGE, TN 62 74 60 70 / 100 90 40 50 TRI CITIES AIRPORT, TN 59 68 56 69 / 70 100 60 60 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$

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