788
FXUS64 KMRX 140725
AFDMRX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MORRISTOWN TN
325 AM EDT FRI AUG 14 2020
SHORT TERM...(TODAY AND TONIGHT)
UPPER TROUGH REMAINS ACROSS THE TENNESSEE VALLEY AND SOUTHERN
APPALACHIANS. THIS IS PRODUCING SW FLOW ACROSS THE REGION WITH A
VERY MOIST AIRMASS IN PLACE. A 300MB 40KT JET WILL PRODUCE UPPER-
LEVEL DIVERGENCE ACROSS THE FORECAST AREA DURING THE AFTERNOON AND
ASSIST WITH WEAK SYNOPTIC ASCENT. IN RESPONSE, A WEAK SURFACE LOW
IS FORECAST TO FORM ACROSS NORTHERN AL WITH BOUNDARY LAYER
CONVERGENCE ACROSS SOUTHEAST TN. WHILE SCATTERED SHOWERS AND
THUNDERSTORMS ARE FORECAST ACROSS THE ENTIRE AREA ON FRIDAY, MOST
WIDESPREAD COVERAGE IS FORECAST ACROSS THE HIGHER ELEVATIONS AS
WELL AS SOUTHEAST TN.
THE RISK OF SEVERE WEATHER WILL BE LOW ON FRIDAY WITH RAP FORECAST
SOUNDINGS INDICATING VERY SATURATED THERMODYNAMIC PROFILES.
INSTABILITY IS EXPECTED TO BE MARGINAL WITH MLCAPE BETWEEN 1000
TO 2000 J/KG, BUT WITH THE VERY MOIST ATMOSPHERE AND HIGH FREEZING
LEVELS, RISKS OF DAMAGING WINDS AND HAIL WILL BE LOW. THE MAIN
RISK WITH THUNDERSTORMS ON FRIDAY WILL BE HEAVY RAINFALL AND
LOCALIZED FLOODING. THE 0Z SOUNDING AT OHX OBSERVED PW NEAR 1.9
INCHES, AND MODEL CONSENSUS IS PLACING PW VALUES OF 1.9 TO 2.1
INCHES ACROSS THE REGION ON FRIDAY AFTERNOON. THESE PW VALUES WILL
BE NEAR THE MAXIMA OF CLIMATOLOGY, AND WHEN COMBINED WITH THE
FAVORABLE SYNOPTIC LIFT, DEEP WARM CLOUD LAYER OF 12K TO 14K FT,
AND NEAR UNIDIRECTIONAL FLOW, SOME TRAINING AND FLASH FLOODING
WILL BE POSSIBLE.
CONVECTIVE ACTIVITY WILL DECREASE IN COVERAGE FRIDAY NIGHT, BUT
SOME SCATTERED SHOWERS OR THUNDERSTORMS WILL CONTINUE WITH LOCALLY
HEAVY RAINFALL, PRIMARILY EAST OF INTERSTATE 75. IN AREAS THAT
HAVE A CLEARING SKY, WINDS WILL BE LIGHT AND FOG DEVELOPMENT WILL
BE LIKELY.
JB
LONG TERM...(SATURDAY THROUGH THURSDAY)
MODELS IN DECENT AGREEMENT THAT THE AXIS OF A MID/UPPER LEVEL
TROUGH WILL BE TRAVERSING THE AREA ON SATURDAY WITH A COLD FRONT
PUSHING ACROSS AT THE SURFACE. WHILE SOME UNCERTAINTY ABOUT THE
EXACT POSITIONING OF THESE FEATURES AT THE START OF THE PERIOD, IT
DOES APPEAR BETTER CHANCES FOR PRECIP WILL BE EAST SO WILL CARRY
CHANCE POPS WEST AND LIKELY TO EVEN CATEGORICAL NORTH AND EAST.
WHILE A FEW STRONGER STORMS WITH STRONG GUSTY WINDS CANNOT BE
RULED OUT SATURDAY, THE MAIN THREAT SHOULD BE LOCALLY HEAVY
RAINFALL WHICH MAY LEAD TO FLOODING. WILL KEEP THIS IN THE HWO.
BY MONDAY THE TROUGH AXIS AND INITIAL FRONT WILL BE TO OUR EAST, WITH
DRYER AIR OVER OUR AREA. HOWEVER, MODELS HINT AT ANOTHER WEAKENING
FRONTAL BOUNDARY THAT WILL BE PUSHING THROUGH, SO DESPITE THE DRYING
WILL KEEP LOW POPS FOR CONVECTION MONDAY AS WELL. THE DRIER AIR WILL
REMAIN IN PLACE ON TUESDAY, ALTHOUGH MODELS SHOW ANOTHER MID/UPPER
LEVEL SHORT WAVE TROUGH APPROACHING, SO AGAIN WILL CARRY LOW POPS
FOR CONVECTION. THE TROUGH AXIS ALOFT WILL BE SET UP TO OUR WEST FOR
THE LATTER PART OF THE PERIOD. BETTER CHANCES FOR CONVECTION CAN BE
EXPECTED BOTH WEDNESDAY AND THURSDAY AS FLOW GAINS A MORE SOUTHERLY
COMPONENT AND MOISTURE INCREASES. TEMPERATURES DURING THE LONG TERM
PERIOD WILL GENERALLY BE NEAR TO SLIGHTLY BELOW SEASONAL NORMALS.
LW
AVIATION
06Z TAF DISCUSSION.
SHOWERS AND THUNDERSTORMS NEAR CHA WILL PERSIST FOR THE NEXT FEW
HOURS WITH VCTS AND TEMPO REDUCTIONS IN VIS WITH SHRA. SOME FOG IS
EXPECTED ACROSS THE AREA WHERE CLOUD COVER IS LOWER, AND AT THIS
TIME, HIGHEST CONFIDENCE IN LOW FOG IS NEAR RIVER VALLEYS ACROSS
THE NORTHERN AND EASTERN PORTIONS OF THE CWA NEAR TRI, AND
POSSIBLY TYS. WIDESPREAD SCATTERED SHOWERS AND THUNDERSTORMS ARE
EXPECTED LATE FRIDAY AFTERNOON AND FRIDAY EVENING ASSOCIATED WITH
AN UPPER LOW IMPACTING EACH TAF SITE. AS CONVECTION DECREASES IN
COVERAGE FRIDAY NIGHT, PATCHY FOG IS ONCE AGAIN EXPECTED TO
DEVELOP WITH CALM WINDS AND A CLEARING SKY.
JB
PRELIMINARY POINT TEMPS/POPS
CHATTANOOGA AIRPORT, TN 87 73 87 70 90 / 80 70 40 10 20
KNOXVILLE MCGHEE TYSON AIRPORT, TN 86 71 84 69 87 / 70 60 70 10 20
OAK RIDGE, TN 85 71 85 68 88 / 70 60 60 10 20
TRI CITIES AIRPORT, TN 84 69 82 65 83 / 70 50 70 30 20
MRX WATCHES/WARNINGS/ADVISORIES
NC...NONE.
TN...NONE.
VA...NONE.
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