634
FXUS64 KMRX 251124 AAA
AFDMRX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE MORRISTOWN TN
724 AM EDT MON OCT 25 2021
UPDATE
FOR 12Z AVIATION.
SHORT TERM (TODAY AND TONIGHT)
KEY MESSAGES:
1. A LINE OF SHOWERS WITH SOME EMBEDDED THUNDERSTORMS WILL CROSS THE
AREA FROM LATE MORNING THROUGH MID AFTERNOON. STRONG TO SEVERE WIND
GUSTS ARE POSSIBLE.
DISCUSSION:
CAMS SEEM TO HAVE A GOOD HANDLE ON THE CURRENT POSITION OF
CONVECTION ACROSS WESTERN KY AND NW TN. THERE IS GOOD AGREEMENT THAT
THIS LINE WILL REACH OUR PLATEAU COUNTIES AROUND 9-10 AM. THE LINE
IS EXPECTED TO WEAKEN, AS SHOWN BY THE HREF MAX REFLECTIVITY
PROBABILITY AND THE UPDRAFT VERTICAL VELOCITY DROPPING OFF QUICKLY
AS IT NEARS THE PLATEAU. AS USUAL WITH EVENTS LIKE THESE THIS TIME
OF YEAR, CAPE WILL BE THE LIMITING FACTOR FOR SEVERE POTENTIAL.
HOWEVER, WITH GOOD UPPER DIVERGENCE IN THE LEFT EXIT REGION OF THE
JET AND MIDLEVEL WINDS OF 50-60 KTS, SOME STRONG TO MARGINALLY
SEVERE WIND GUSTS CAN'T BE RULED OUT WITH DEEPER EMBEDDED CELLS. NE
TN/SW VA WILL HAVE THE BEST CHANCE OF THIS SINCE THERE WILL BE A
WINDOW OF SURFACE HEATING THIS MORNING FOR SLIGHTLY MORE
DESTABILIZATION. TORNADO POTENTIAL APPEARS LOW AS IT WILL BE
DIFFICULT TO GET SURFACE WINDS BACKED ENOUGH IN THE NORTHERN VALLEY
IN THE LEE OF THE MOUNTAINS, AND WE DO NOT HAVE A BOUNDARY IN PLACE
TO AID LOW LEVEL HELICITY. THE MAIN CONVECTIVE LINE SHOULD BE
EXITING OUR AREA BETWEEN 19-21Z.
FRONTAL PASSAGE WILL TRAIL CONVECTION BY A FEW HOURS, LIKELY
OCCURRING IN THE 22-02Z TIME FRAME. GUSTY WEST WINDS MAY ACCOMPANY
THE FROPA. COLD ADVECTION TONIGHT WILL BRING AN INCREASE IN CLOUD
COVER AFTER SUNSET, AND AN UPSLOPE FLOW COULD KEEP SOME LIGHT
SHOWERS GOING IN HIGHER ELEVATIONS.
DGS
LONG TERM (TUESDAY THROUGH SUNDAY)
KEY MESSAGES:
1. DRYING OUT TUES AND WED WITH BELOW NORMAL TEMPS TUES WARMING TO
AROUND NORMAL WED. PATCHY FROST POSSIBLE IN NE AREAS EARLY WED.
2. WIDESPREAD SHOWERS AND THE POTENTIAL FOR PERIODS OF HEAVY RAIN
MOVE IN WED NIGHT AND THURS WITH MUCH COOLER TEMPS AND SHOWERS
LINGERING FRI AND SAT.
3. DRYING OUT BY SUN, BUT TEMPS STILL A FEW DEGREES BELOW NORMAL.
DISCUSSION:
TUESDAY THROUGH WEDNESDAY...
DEEP SURFACE LOW PRESSURE WILL REALLY BOMB OUT TO 974-978 MB AND
REMAIN NEARLY STATIONARY OFFSHORE OF CT AND RI TUES WITH DEEP
MID/UPPER TROUGHING OVER THE EASTERN CONUS BEHIND THIS SYSTEM. THIS
WILL BRING A MUCH COOLER AND DRIER NW FLOW TO THE S APPALACHIANS.
SOME LINGERING MOISTURE AND UPSLOPING WILL KEEP A FEW SCATTERED
SHOWERS GOING FROM SW VA THROUGH THE EASTERN MOUNTAINS TUES BEFORE
STRONG SURFACE HIGH PRESSURE BUILDS S FROM THE OH VALLEY TUES NIGHT
AND WED WITH THE ASSOCIATED DRY AIR AND SUBSIDENCE BRINGING DRY
CONDITIONS. THE MID/UPPER TROUGH AXIS WILL SHIFT INTO THE NE CONUS
BY WED WITH SHORTWAVE RIDGING BUILDING ACROSS THE TN AND OH VALLEYS
AHEAD OF THE NEXT DEEP MID/UPPER TROUGH PROGRESSING INTO THE PLAINS.
THIS WILL LEAD TO MODERATING TEMPS WED. HIGHS TUES WILL STRUGGLE TO
CLIMB OUT OF THE UPPER 50'S BUT WILL REBOUND INTO THE MID 60'S WED.
STRONG RADIATIONAL COOLING TUES NIGHT WILL LEAD TO LOWS IN THE UPPER
30'S/LOW 40'S, SO PATCHY FROST IS POSSIBLE FROM THE N PLATEAU
THROUGH NE TN AND SW VA.
WEDNESDAY NIGHT THROUGH FRIDAY...
THIS WILL BE THE START OF A COOL, WET, UNSETTLED PERIOD AS THE
AFOREMENTIONED DEEP PLAINS MID/UPPER TROUGH SHIFTS INTO THE MS
VALLEY WED NIGHT AND THURS AND EVOLVES INTO A CLOSED LOW OVER THE
LOWER OH AND TN VALLEYS BY FRI. THE DETERMINISTIC ECMWF, GFS, AND
CMC ARE ALL IN SOLID OVERALL AGREEMENT ON THIS PATTERN EVOLUTION
WITH JUST SMALL DIFFERENCES ON THE PLACEMENT OF THE CENTER OF THE
VERTICALLY STACKED LOW BY FRI. FOR WED NIGHT AND THURS, THE DEEP
MID/UPPER TROUGH SWINGING INTO THE MS VALLEY AND BECOMING NEGATIVELY
TILTED WILL SUPPORT A DEEPENING SURFACE LOW AROUND SE MO AND WESTERN
KY AIDED BY THE LEFT EXIT OF A 110 KT H3 JET STREAK OVER THE DEEP
SOUTH. AN ASSOCIATED 30-50 KT SOUTHERLY LOW-LEVEL JET DEVELOPING
AHEAD OF THIS LOW OVER THE S APPALACHIANS WILL ADVECT COPIOUS
AMOUNTS OF MOISTURE INTO THE REGION WED NIGHT AND THURS, AS WELL AS
CAUSE POSSIBLE MOUNTAIN WAVE HIGH WINDS IN THE SMOKIES. A LOOK AT
THE NAEFS MEAN INTEGRATED WV TRANSPORT SHOWS VALUES NEARING THE 90TH
PERCENTILE INDICATING THAT MOISTURE FLUX COULD BE ANOMALOUS OVER OR
JUST E OF THE REGION DURING THIS TIME. THUS, EXPECT SHOWERS TO MOVE
IN FROM W TO E WED NIGHT WITH PERIODS OF HEAVY RAIN POSSIBLE THURS.
AT THIS TIME, INSTABILITY LOOKS VERY WEAK GIVEN CLOUDS AND
RELATIVELY COOL CONDITIONS, SO KEPT THUNDER OUT OF THE FORECAST. AS
THE SURFACE LOW PULLS A BIT FARTHER N INTO THE LOWER OH VALLEY THURS
NIGHT INTO FRI, A COLD FRONT WILL PUSH THROUGH THE REGION. H85 TEMPS
FALLING TO 1-3 C AND DEEP WRAPAROUND MOISTURE AS THE SYSTEM CLOSES
OFF AND BECOMES VERTICALLY STACKED WILL LEAD TO MUCH COOLER TEMPS
AND FREQUENT SHOWERS LINGERING THROUGH FRI, BUT PROBABLY NOT AS
HEAVY AS THE RAIN THURS. HIGHS THURS WILL BE IN THE LOW/MID 60'S
WITH ONLY MID/UPPER 50'S FRI. LOWS BOTH WED AND THURS NIGHTS WILL
BE IN THE UPPER 40'S/LOW 50'S.
FRIDAY NIGHT THROUGH SUNDAY...
DETERMINISTIC AND ENSEMBLE GUIDANCE IS IN OVERALL AGREEMENT THAT THE
CLOSED LOW WILL GRADUALLY LIFT OUT SAT WITH QUASI-ZONAL FLOW ACROSS
THE CONUS BY SUN AND A SURFACE HIGH BUILDING E FROM THE MID SECTION
OF THE COUNTRY. THUS, STAYED WITH NBM POPS WHICH HAS LINGERING
SHOWERS SCATTERED AROUND FRI NIGHT AND SAT BECOMING MOSTLY DRY BY
SUN EXCEPT FOR A FEW ISOLATED SHOWERS FROM NE TN INTO SW VA.
WELL BELOW NORMAL TEMPS CONTINUING SAT WILL MODERATE A BIT SUN.
GARUCKAS
AVIATION
12Z TAF DISCUSSION.
SHOWERS ARE APPROACHING THE AREA FROM THE WEST AND WILL MOVE
THROUGH THE TAF SITES BETWEEN 14-19Z. MVFR VIS AND CIGS WILL
ACCOMPLANY THE SHOWERS, WITH THE POSSIBILITY OF A SHORT-LIVED TS.
A COLD FRONT MOVES THROUGH SHORTLY AFTER THAT IN THE LATE
AFTERNOON, WHICH WILL SHIFT WINDS TO W-NW WITH GUSTS AT TIMES.
MVFR CIGS ARE EXPECTED TONIGHT IN THE COOLER AIR MASS BEHIND THE
FRONT.
DGS
PRELIMINARY POINT TEMPS/POPS
CHATTANOOGA AIRPORT, TN 73 49 65 46 68 / 70 10 0 0 0
KNOXVILLE MCGHEE TYSON AIRPORT, TN 70 48 60 42 66 / 90 10 10 0 0
OAK RIDGE, TN 69 48 60 42 66 / 90 10 0 0 0
TRI CITIES AIRPORT, TN 68 46 56 38 64 / 90 20 10 0 0
MRX WATCHES/WARNINGS/ADVISORIES
NC...NONE.
TN...NONE.
VA...NONE.
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