643
FXUS64 KMRX 180341
AFDMRX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MORRISTOWN TN
1041 PM EST TUE DEC 17 2024
..NEW UPDATE
UPDATE
ISSUED AT 1020 PM EST TUE DEC 17 2024
KEY MESSAGES REMAIN IN GOOD SHAPE THIS EVENING. THE MAIN UPDATES
TO THE FORECAST HAVE FOCUSED ON FOG AND POPS. FOR FOG, HAVE
INTRODUCED AN SPS ACROSS THE FORECAST AREA HIGHLIGHTING AREAS OF
FOG WITH LOCALIZED DENSE FOG AND VISIBILITIES OF 1/4MI OR LESS.
WHILE SOME HI-RESOLUTION GUIDANCE SUGGEST THE COVERAGE OF DENSE
FOG MAY BRIEFLY INCREASE OVERNIGHT, SAID GUIDANCE ALSO SUGGEST A
LIGHT WIND DEVELOPING AS EARLY AS 4-6AM. THIS WOULD BE UNFAVORABLE
FOR INCREASED COVERAGE OF DENSE FOG AND IS THE REASON WHY AN SPS
WAS OPTED FOR RATHER THAN A DENSE FOG ADVISORY AT THIS TIME. FOR
PRECIPITATION, TRIMMED BACK/SLOWED DOWN THE ONSET OF SLIGHT
CHANCE/CHANCE PRECIPITATION INTO THE OVERNIGHT AS ISENTROPIC
ASCENT HAS PROVEN INSUFFICIENT AT THIS POINT. HAVE ALSO LIMITED
THE RELATIVELY HIGHER PROBABILITIES TO THE NORTHERN PLATEAU.
UPDATED ZONE FORECAST HAS BEEN PUBLISHED.
SHORT TERM
(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 315 PM EST TUE DEC 17 2024
KEY MESSAGES:
1. AREAS OF FOG TONIGHT WITH POOR VISIBILITY.
2. NEAR-RECORD TEMPERATURES FOR OVERNIGHT HIGH MINIMUMS AND FOR
DAYTIME HIGHS ON WEDNESDAY.
3. RAIN AND STORMS ON WEDNESDAY. AN ISOLATED DAMAGING WIND GUST AND
BRIEF TORNADO ARE POSSIBLE, THOUGH LOW PROBABILITY.
DISCUSSION:
TONIGHT:
LOW CLOUDS AND FOG ARE EXPECTED ACROSS THE AREA. THERE IS
MODERATE TO HIGH CONFIDENCE THAT 1 MILE OR LESS VISIBILITIES OCCUR,
AS NUMEROUS GUIDANCE SOURCES SHOW THIS. THERE IS LOW CONFIDENCE ON
HOW WIDESPREAD IT IS. SOME GUIDANCE KEEPS THE LOWEST VISIBILITIES
ISOLATED WHILE OTHER SOURCES SHOW IT TO BE MORE WIDESPREAD. THE
EVENING AND OVERNIGHT SHIFT WILL HAVE TO MONITOR TRENDS AND
OBSERVATIONS TO SEE IF A DENSE FOG ADVISORY WILL BE NEEDED.
TOMORROW:
IN THE MORNING, A WARM FRONT WILL BE LIFTING NORTH
THROUGH THE AREA. DURING THE AFTERNOON, A COLD FRONT WILL MOVE
THROUGH AND BRING A ROUND OF SHOWERS AND STORMS ACROSS THE AREA.
THERE CONTINUES TO BE SOME MINOR MODEL DIFFERENCES ON TIMING. MOST
OF THE CAMS SUGGEST THE LINE OF SHOWERS AND STORMS SHOULD BE MOVING
ONTO THE NORTHERN CUMBERLAND PLATEAU AROUND 16Z. THE NAM NEST SHOWS
A LATER ARRIVAL OF 21Z. STORMS THEN PROGRESS EAST SOUTHEAST THROUGH
THE REST OF OUR AREA THROUGH THE AFTERNOON.
RAIN:
THE HIGHER QPF AMOUNTS WILL LIKELY OCCUR WEST OF THE I-75 AND
I-81 CORRIDOR. QPF AMOUNTS WILL GENERALLY BE AROUND 0.5 INCHES.
AMOUNTS CLOSER TO 0.25 INCHES ARE EXPECTED EAST OF THE I-75 AND I-81
CORRIDOR.
TEMPERATURES:
SOUTHWEST FLOW AHEAD OF THE COLD FRONT WILL ALLOW
TEMPERATURES TO REMAIN VERY MILD OVERNIGHT. NEAR-RECORD HIGH MINIMUM
TEMPERATURES ARE EXPECTED WITH TEMPS IN THE LOW TO MID 50S.
TOMORROW, SOUTHWEST FLOW CONTINUES AND HIGH TEMPS WILL BE IN THE LOW
TO UPPER 60S, WHICH WILL BE NEAR-RECORD BREAKING ACROSS THE SOUTHERN
TN VALLEY.
WIND:
A 30 TO 40KT SOUTHWEST 850MB JET WILL BE IN PLACE THROUGH THE DAY ON
WEDNESDAY. THIS WILL ALLOW FOR WIND GUSTS FROM 30 TO 40 MPH ACROSS
THE HIGHEST ELEVATIONS OF THE EAST TN, SOUTHWEST VA, AND SOUTHWEST
NC MOUNTAINS.
STORMS:
HIGH SHEAR LOW CAPE SETUP FOR TOMORROW. THIS MEANS THAT ISOLATED
DAMAGING WIND GUSTS UP TO 60 MPH ALONG WITH AN BRIEF, ISOLATED,
TORNADO ARE POSSIBLE. THE PROBABILITY OF OCCURRENCE IS LOW, BUT
THERE ARE ENOUGH INGREDIENTS IN PLACE TO WARRANT MENTION OF AN
ISOLATED TORNADO. THE MAIN THREAT WINDOW WILL BE FROM ROUGHLY NOON
THROUGH 6 PM EST. A FEW THINGS THAT STAND OUT. 12Z HRRR SHOWS WEAK
HELICITY TRACKS ACROSS OUR AREA. NAM SOUNDINGS INDICATE 50 TO 100
J/KG 0-3KM CAPE, LOW LCL HEIGHTS, AND 0-1KM SHEAR OF 20 TO 30KTS.
HREF MUCAPE INDICATES A FEW HUNDRED JOULES. SPC CURRENTLY HAS MOST
OF OUR AREA WITHIN THE MARGINAL RISK FOR SEVERE STORMS.
LONG TERM
(WEDNESDAY NIGHT THROUGH NEXT TUESDAY)
ISSUED AT 315 PM EST TUE DEC 17 2024
KEY MESSAGES:
1. COOLER BEHIND THE FRONT FOR THE END OF THE WEEK INTO THE WEEKEND.
2. LIGHT SNOW CHANCES FOR SOUTHERN APPALACHIANS AND SW VIRGINIA
FRIDAY INTO SATURDAY.
3. DRY LATER SATURDAY AND THE DAYS LEADING UP TO CHRISTMAS EVE.
DISCUSSION:
EARLY THURSDAY AT THE START OF THE PERIOD, THE COLD FRONT AND DRIER
AIR WILL BE FILTERING INTO THE REGION. SHOWERS AND ISOLATED
THUNDERSTORMS WILL BE ENDING OVERNIGHT FROM WEST TO EAST. MUCH OF
THURSDAY INTO FRIDAY WILL BE DRY FOR MANY, BUT A SE DIVING SHORTWAVE
ACROSS THE OHIO VALLEY WILL FORM A WEAK FRONTAL SYSTEM WITH LITTLE
MOISTURE LATER FRIDAY INTO SATURDAY. WITH COLD AIR IN PLACE SATURDAY
MORNING, RAIN MAY CHANGE OVER TO LIGHT SNOW FOR FAR NORTHEASTERN
PARTS OF THE FORECAST AREA. QPF AMOUNTS FOR THIS FORECAST PACKAGE
LOOK LIGHT WITH TOTALS NO MORE THAN A TENTH OF AN INCH. WHICH
TRANSLATES TO UNDER AN INCH OF SNOW FOR PARTS OF THE SOUTHERN
APPALACHIANS FROM THE SMOKYS NORTHWARD AND HIGHER ELEVATIONS OF
SOUTHWEST VIRGINIA.
ONCE THE NORTHWEST FLOW ENHANCED PRECIPITATION PASSES, FLOW ALOFT
REMAINS NWLY WHILE SURFACE HIGH PRESSURE FROM MIDDLE CANADA MOVES TO
THE MID-ATLANTIC AND NORTHEAST, WHERE IT WILL REALLY STRENGTHEN. WE
WILL BE LOCKED UNDER THE INFLUENCE OF THE HIGH WITH DRY WEATHER
EXPECTED LATER SATURDAY THROUGH THE END OF THE TERM ON CHRISTMAS
EVE. WILL SEE IF THAT PERSISTS INTO CHRISTMAS DAY, BUT IT ISN'T PART
OF THE LONG TERM JUST YET. TEMPERATURE TRENDS FROM THE COLD FRONT ON
THE FRONT END TO THE WEAK FRONTAL SYSTEM FRI INTO SAT, WILL BE
DOWNWARD TRENDING. SAT INTO SUN LOOK STEADY, BUT VERY GRADUAL
WARMING POSSIBLE MONDAY AND CHRISTMAS EVE. STILL, THE TEMPERATURES
EXPECTED WILL BE BELOW CLIMATOLOGICAL NORMS FOR THIS PART OF
DECEMBER.
AVIATION
(00Z TAFS)
ISSUED AT 637 PM EST TUE DEC 17 2024
UNSETTLED WEATHER WITH POOR FLIGHT CONDITIONS ARE EXPECTED TO
CONTINUE THIS TAF CYCLE. LOW-LEVEL STRATUS HAS STARTED TO BUILD
INTO THE REGION BRINGING MVFR TO IFR CIGS. POTENTIAL FOR REDUCED
VISIBILITY WITH A MIST/FOG IS ALSO PRESENT INTO THE MORNING BUT
LOWER CONFIDENCE EXISTS WITH HOW HARD VIS MAY DROP DUE TO THE
IFR/MVFR CIGS REDUCING RADIATIONAL COOLING. A COLD FRONT WILL
BRING WIDESPREAD SHOWERS WITH THE POTENTIAL FOR EMBEDDED
THUNDERSTORMS TOMORROW AFTERNOON. SOUTHWESTERLY TO WESTERLY WINDS
WILL ALSO BECOME GUSTY AS THE FRONT PROGRESSES THROUGH THE AREA.
PRELIMINARY POINT TEMPS/POPS
CHATTANOOGA AIRPORT, TN 56 70 40 55 / 20 90 20 0
KNOXVILLE MCGHEE TYSON AIRPORT, TN 55 67 39 52 / 20 90 30 0
OAK RIDGE, TN 54 65 36 52 / 30 100 20 0
TRI CITIES AIRPORT, TN 51 65 36 50 / 10 90 50 0
MRX WATCHES/WARNINGS/ADVISORIES
NC...NONE.
TN...NONE.
VA...NONE.
SHORT TERM...
LONG TERM....KS
AVIATION...KRS
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