294
FXUS64 KMRX 231941
AFDMRX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MORRISTOWN TN
241 PM EST SUN FEB 23 2020
SHORT TERM (THIS AFTERNOON THROUGH MONDAY)
CURRENT WATER VAPOR IMAGERY AND RAP UPPER AIR ANALYSIS INDICATE A
CLOSED LOW ACROSS THE DESERT SOUTHWEST MOVING TO THE EAST. A LOW
AMPLITUDE RIDGE EXTENDS ACROSS THE LOWER MISSISSIPPI AND TENNESSEE
RIVER VALLEYS. AT THE SURFACE, A LOW PRESSURE IS TAKING SHAPE ACROSS
THE TEXAS PANHANDLE WITH A WARM FRONT THAT EXTENDS TO THE SOUTHEAST
INTO THE LOWER MISSISSIPPI RIVER VALLEY. CLOSER TO HOME, HIGH
PRESSURE CONTINUES TO SHIFT FURTHER TO THE EAST OVER THE ATLANTIC
WITH SOUTHERLY TO SOUTHWESTERLY FLOW IN THE LOW-LEVELS. HIGH CLOUDS
CONTINUE TO INCREASE ACROSS THE FORECAST AREA AHEAD OF THE
APPROACHING UPPER LEVEL TROUGH. CURRENT RADAR IMAGERY INDICATES
SOME WEAK RETURNS ACROSS NORTH ALABAMA AND MIDDLE TENNESSEE BUT THE
LOW-LEVELS ARE STILL RELATIVELY DRY AND DO NOT SEE ANY OBSERVATIONS
OF PRECIPITATION. CURRENT PW VALUES ARE IN THE 0.4-0.6 INCH RANGE AND
IT WILL TAKE SEVERAL HOURS FOR THE ATMOSPHERE TO SATURATED FROM THE
TOP DOWN.
THE MOISTURE ADVECTION AND LIFT TO THE NORTH OF THE WARM FRONT WILL
CONTINUE TO INCREASE OVERNIGHT WITH POPS INCREASING FROM SOUTHWEST
TO NORTHEAST. RAINFALL AMOUNTS OVERNIGHT ARE FORECAST TO BE LIGHT
WITH THE LOW-LEVELS REMAINING RELATIVELY DRY THROUGH DAYBREAK.
AMOUNTS WILL REMAIN BELOW A TENTH OF AN INCH THROUGH SUNRISE. MODELS
DO NOT DEPICT A REAL SURGE IN THE LOW-LEVEL WARM ADVECTION UNTIL
AFTER 12-15Z. THEREFORE, EXPECT THERE COULD BE A BRIEF WINTRY
MIXTURE FOR ELEVATIONS ABOVE 4 KFT AT THE ONSET OF THE
PRECIPITATION. DO NOT EXPECT ANY IMPACTS WITH ANY ACCUMULATIONS
UNDER HALF AN INCH BEFORE TEMPERATURES QUICKLY WARM AFTER SUNRISE
MONDAY. OVERNIGHT LOWS WILL RANGE FROM UPPER 30S TO LOW 40S FOR MOST
WITH LOWS AROUND FREEZING AT THE HIGHEST ELEVATIONS.
A WIDESPREAD SOAKING RAIN IS FORECAST FOR MONDAY. ISENTROPIC LIFT
WILL CONTINUE TO INCREASE ON THE NORTHERN SIDE OF THE WARM FRONT. PW
VALUES WILL CONTINUE TO RISE INTO THE 0.8-1.0 INCH RANGE. THESE
VALUES ARE NEAR THE 90TH PERCENTILE FOR LATE FEBRUARY. MODEL
SOUNDINGS INDICATE DEEP SATURATION THROUGHOUT THE ATMOSPHERE.
OVERALL, RAINFALL TOTALS WILL RANGE FROM 0.25-0.75 INCHES ON MONDAY.
THE LOWEST AMOUNTS ARE FORECAST ACROSS NORTHEAST TENNESSEE WHERE
THERE COULD BE SOME DOWNSLOPING. HIGHS ON MONDAY WILL RANGE FROM THE
UPPER 40S TO LOW 50S.
MA
LONG TERM (MONDAY NIGHT THROUGH SUNDAY)
A MID LEVEL SHORTWAVE LIFTING INTO THE OH VALLEY MON NIGHT WILL BE
IN THE PROCESS OF SHEARING OUT, SO ITS ASSOCIATED SURFACE LOW WILL
ALSO BE WEAKENING. THE WEAK COLD FRONT TRAILING BEHIND THIS SYSTEM
WILL MOVE THROUGH EARLY TUE, LIKELY IN THE 09-12Z TIMEFRAME. KEPT
CATEGORICAL POPS MON NIGHT. FORECAST SOUNDINGS CONTINUE TO SHOW
ELEVATED INSTABILITY ABOVE ABOUT 900 MB ON THE ORDER OF 300-500 J/KG
OVER THE SOUTHERN HALF OF THE CWA WITH LESS IMPRESSIVE AMOUNTS OVER
THE NORTH HALF. FOR THIS REASON, AND THE LARGE SCALE FORCING FOR
ASCENT AIDED BY CONVERGENCE AHEAD OF THE FRONT AND LEFT EXIT REGION
OF A 100-125 KT H3 JET STREAK, MAINTAINED A SLIGHT CHANCE OF THUNDER
BEFORE 09Z OVER THE SOUTHERN PLATEAU AND SOUTHEAST TN. POPS QUICKLY
DROP OFF TUESDAY BEHIND THE FRONT. SUBSIDENCE IN THE WAKE OF THIS
SYSTEM, CONTINUED WSW FLOW ALOFT, AND WEAK HEIGHT RISES AHEAD OF AN
INCOMING STRONGER MID/UPPER TROUGH WILL ACTUALLY ALLOW TEMPS TO WARM
MUCH ABOVE NORMAL TUE.
THE NEXT TROUGH MENTIONED ABOVE WILL DIG THROUGH THE UPPER MIDWEST
AND MISSISSIPPI VALLEY TUE NIGHT INTO WED, SIGNIFICANTLY
STRENGTHENING AS ITS ENERGY PHASES WITH WHAT'S LEFT OF THE TUE
SYSTEM OVER THE WESTERN GREAT LAKES. THE RESULT WILL BE AN
ANOMALOUSLY STRONG NEGATIVELY TILED TROUGH TAKING UP RESIDENCE OVER
THE CENTRAL AND EASTERN CONUS WED THROUGH THE WEEKEND WITH
REINFORCING SHORTWAVES, THAT WILL BE DIFFICULT TO TIME,
PERIODICALLY DROPPING THROUGH THE LONGWAVE TROUGH. THIS WILL LEAD TO
WELL BELOW NORMAL TEMPS AND PERIODIC CHANCES FOR RAIN/SNOW SHOWERS.
MOISTURE RETURN LOOKS LIMITED, BUT BASED ON STRONG DYNAMIC FORCING
FROM THE UPPER JET AHEAD OF THE ARCTIC FRONT, BROUGHT IN SLIGHT
CHANCE POPS TUE NIGHT OVER THE PLATEAU AND CHANCE ALL AREAS WED. ALL
GUIDANCE HAS SPED UP THE TIMING OF THE ARCTIC FRONT INTO WED
MORNING, SO TEMPS WILL FALL THROUGH THE AFTERNOON WITH ANY SHOWERS
CHANGING TO SNOW SHOWERS IN THE HIGHER ELEVATIONS DURING THE DAY AND
IN ALL AREAS WED NIGHT. AGAIN, MOISTURE WILL BE LIMITED, SO LIGHT
ACCUMULATIONS WILL BE CONFINED TO THE HIGHER ELEVATIONS OF THE
PLATEAU AND THE MOUNTAINS OF EAST TN AND SW VA LATE WED THROUGH WED
NIGHT.
GUIDANCE HAS CONTINUED TO TREND DRIER THURS WITH UNFAVORABLE FLOW TO
BRING IN GREAT LAKES MOISTURE, SO OPTED FOR DRY AND COLD CONDITIONS
WITH INCREASING SUNSHINE THURS THROUGH FRI.
TIMING DIFFERENCES CONTINUE AMONG THE GUIDANCE FOR ONE OR TWO
SHORTWAVES DROPPING DOWN THIS WEEKEND THAT COULD BRING SCATTERED
RAIN/SNOW SHOWERS. CONTINUED TO LEAN TOWARD THE SLOWER ECMWF WITH
SLIGHT CHANCE POPS FRI NIGHT AND SAT. DRY CONDITIONS EXPECTED SUN AS
HEIGHT RISES AND SURFACE HIGH PRESSURE FINALLY BUILD INTO THE
REGION.
HIGHS IN THE LOW 60'S TUE COOL INTO THE UPPER 40'S/LOW 50'S WED AND
UPPER 30'S/LOW 40'S THURS WARMING SLIGHTLY INTO THE LOW/UPPER 40'S
FRI. COOLER AGAIN SAT WITH UPPER 30'S/LOW 40'S BEFORE WARMING INTO
THE LOW/UPPER 40'S SUN. LOWS IN THE LOW/UPPER 40'S MON NIGHT COOL
INTO THE UPPER 30'S/LOW 40'S TUE NIGHT AND UPPER 20'S/LOW 30'S WED
AND THURS NIGHTS. FURTHER COOLING WILL BRING LOW/MID 20'S FRI AND
SAT NIGHTS.
RG
AVIATION
18Z TAF DISCUSSION.
VFR CONDITIONS WILL CONTINUE THROUGHOUT THE MAJORITY OF THE TAF
CYCLE. A WARM FRONT WILL LIFT NORTHWARDS ACROSS THE LOWER
MISSISSIPPI RIVER VALLEY THROUGHOUT THE TAF PERIOD WITH CLOUDS
INCREASING. LIFT TO THE NORTH OF THIS FRONT WILL EVENTUALLY LEAD
TO MVFR/IFR CEILINGS AND -SHRA. THESE CONDITIONS ARE FORECAST
TOWARDS THE END OF THE TAF CYCLE AFTER 13Z.
MA
PRELIMINARY POINT TEMPS/POPS
CHATTANOOGA AIRPORT, TN 42 52 50 62 42 / 80 100 100 10 20
KNOXVILLE MCGHEE TYSON AIRPORT, TN 41 51 47 63 43 / 70 100 100 10 10
OAK RIDGE, TN 40 49 47 62 42 / 70 100 100 20 20
TRI CITIES AIRPORT, TN 35 47 44 62 42 / 60 100 100 20 10
MRX WATCHES/WARNINGS/ADVISORIES
NC...NONE.
TN...NONE.
VA...NONE.
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