692
FXUS64 KMRX 191934
AFDMRX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MORRISTOWN TN
334 PM EDT FRI JUL 19 2019
SHORT TERM...(TONIGHT AND SATURDAY)
MAIN WEATHER STORY FOR THE SHORT TERM PERIOD WILL BE THE HOT AND HUMID
CONDITIONS THROUGH SATURDAY. CURRENTLY ACROSS THE AREA, SKIES
WERE PARTLY TO MOSTLY CLOUDY WITH TEMPERATURES IN THE MID TO UPPER
80S ATOP DEWPOINTS IN THE LOW TO MID 70S. LATEST RADAR IMAGERY
DEPICTS AN AREA OF SHOWERS AND THUNDERSTORMS MAINLY WEST OF I-75
AND SOUTH OF I-40. WATER VAPOR IMAGERY IS INDICATING DRIER AIR
ALOFT ADVECTING FROM THE NORTH THAT HAS LIKELY KEPT MOST AREAS
DRY TODAY. THE UPPER LEVELS FEATURE RIDGING ALOFT THROUGH MUCH OF
THE REGION WHICH IS HELPING TO KEEP CONDITIONS WARM. WITH HIGHS
EXPECTED IN THE UPPER 80S TO LOW 90S AND DEWPOINTS NEAR THE LOW
70S, THIS WILL CREATE VERY HUMID CONDITIONS WITH HEAT INDICES IN
THE UPPER 90S TO NEAR 100. NOT ANTICIPATING NEEDING ANY HEAT
ADVISORIES FOR THIS AFTERNOON AS MOST LOCATIONS SHOULD STAY BELOW
ADVISORY CRITERIA.
THE CURRENT CONVECTION SHOULD DISSIPATE AFTER SUNSET AS THE BOUNDARY
LAYER BEGINS TO STABILIZE. WARM AND HUMID CONDITIONS WILL PERSIST
INTO TONIGHT AS THE RIDGE HOLDS OVER THE AREA. LOWS TONIGHT
SHOULD BOTTOM OUT INTO THE LOW TO MID 70S. SATURDAY SHOULD
CONTINUE TO BE WARM AND HUMID AS TEMPERATURES QUICKLY INCREASE
UNDER RIDGING ALOFT. GUIDANCE SUGGESTS MOST LOCATIONS WILL REACH
OR SURPASS THE 90 DEGREE MARK, ESPECIALLY ACROSS THE VALLEY. THIS
SEEMS PLAUSIBLE AS 925MB TEMPERATURES INCREASE UPWARDS OF 28-30
DEGREE C.THIS COMBINED WITH A MOIST AIRMASS WITH DEWPOINTS NEAR
70-75 DEGREES WILL PRODUCE HEAT INDEX VALUES INTO THE UPPER 90S
TO LOW 100S. DECIDED TO HOLD OFF ON ISSUING ANY HEAT ADVISORIES
FOR SATURDAY AS CONFIDENCE ON HOW MUCH OF THE AREA REACHES
ADVISORY CRITERIA REMAINS LOW. NONETHELESS, THE DANGEROUS HEAT
INDEX VALUES WILL PERSIST AND SHOULD CONTINUE TO BE MONITORED.
INSTABILITY WILL INCREASE ON SATURDAY WITH CAPE VALUES IN THE
2,000-3,000 J/KG RANGE. AS A RESULT, CONVECTION IS EXPECTED
MAINLY DURING THE AFTERNOON HOURS. COVERAGE IS EXPECTED TO BE
GREATER THAN TODAY AS THERE ARE SOME INDICATIONS THAT THE RIDGE
BEGINS TO BREAK DOWN. DCAPES OF 800-1200 J/KG MEANS THAT ANY OF
THE STRONGER STORMS COULD PRODUCE STRONG/GUSTY WINDS. PW VALUES
NEAR 2.0 INCHES SUGGEST THAT LOCALLY HEAVY RAINFALL WILL ALSO BE
POSSIBLE.
LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
GUIDANCE CONTINUES TO BE IN GOOD AGREEMENT THROUGH THE EXTENDED WITH
THE MAIN STORY BEING A SIGNIFICANT PATTERN CHANGE ACROSS THE REGION
EARLY THIS UPCOMING WEEK.
THE EXTENDED BEGINS WITH A SHORTWAVE TROUGH DIVING SOUTHEASTWARD
ACROSS THE NORTHERN GREAT PLAINS AND UPPER MISSISSIPPI VALLEY LATE
SUNDAY INTO SUNDAY NIGHT. THIS WILL BRING HEIGHT FALLS ACROSS THE
REGION WITH INCREASING POPS FOR SCATTERED CONVECTION ON SUNDAY AND
MONDAY. MLCAPE EACH AFTERNOON WILL BE IN THE 1000 TO 2000 J/KG RANGE
ACROSS THE AREA WITH EFFECTIVE DEEP LAYER SHEAR GENERALLY BETWEEN 10
TO 20 KT AND INCREASING TO 20 TO 25 KT LATE MONDAY AS STRONGER
DYNAMICS ASSOCIATED WITH THE UPPER TROUGH APPROACHES THE REGION.
WHILE WIDESPREAD SEVERE WEATHER IS NOT FORECAST WITH THIS SYSTEM,
THE SETUP FAVORS THE POTENTIAL FOR A FEW STRONG TO POSSIBLY SEVERE
THUNDERSTORMS, ESPECIALLY LATER MONDAY AS THE FRONT APPROACHES AND
MID-LEVEL LAPSE RATES INCREASE WITH PVA ACROSS THE AREA.
THE SHORTWAVE WILL AMPLIFY LONGWAVE TROUGHING ACROSS THE EASTERN
CONUS MONDAY NIGHT WITH AN ASSOCIATED SURFACE COLD FRONT MOVING
THROUGH THE REGION. LIKELY WIDESPREAD CONVECTION WILL BE ASSOCIATED
WITH THIS FRONT, AND WITH STRONG BOUNDARY LAYER FORCING AND PW
BETWEEN 1.8 AND 2.0 INCHES, EXPECT SOME HEAVY RAINFALL AT TIMES.
THE COLD FRONT SHIFTS EAST ON TUESDAY WITH A FEW LINGERING SHOWERS
OR ISOLATED THUNDERSTORMS ACROSS THE FAR EASTERN MOUNTAINS CLOSER TO
THE FRONT AND WHERE SOME WEAK OROGRAPHIC LIFT MAY ENHANCE SHOWERY
COVERAGE. HOWEVER, EXPECT OROGRAPHIC LIFT TO BE MINIMAL WITH WINDS
FROM THE N/NNE BEHIND THE FRONT WHICH IS NOT NORMAL TO THE AVERAGE
TERRAIN AXIS. SURFACE HIGH PRESSURE BUILDS IN WITH MUCH LOWER
DEWPOINT IN THE MID 50S TO LOWER 60S BY WEDNESDAY MORNING. IN FACT,
BOTH NAEFS AND ECMWF OUTPUT SHOW 850MB TEMPERATURES BEING BETWEEN
THE 3RD AND 10TH PERCENTILE COMPARED TO CLIMATOLOGY. IN ADDITION,
CIPS ANALOG DATA SHOWS HIGH PROBABILITIES OF BELOW NORMAL
TEMPERATURES WITH SURFACE TEMPERATURES BEING ABOUT 10 DEGREES BELOW
NORMAL. THIS ANOMALOUS COLD AND DRY AIRMASS WILL RESULT IN MUCH
COOLER TEMPERATURES WITH AN ALMOST FALL-LIKE FEEL MID TO LATE WEEK
WITH VERY LOW TO NO CHANCES OF PRECIPITATION IN THE FORECAST.
PRELIMINARY POINT TEMPS/POPS
CHATTANOOGA AIRPORT, TN 75 91 74 89 / 30 60 40 60
KNOXVILLE MCGHEE TYSON AIRPORT, TN 74 92 72 88 / 20 40 30 50
OAK RIDGE, TN 74 92 73 88 / 20 30 30 50
TRI CITIES AIRPORT, TN 70 92 70 87 / 20 20 30 60
MRX WATCHES/WARNINGS/ADVISORIES
NC...NONE.
TN...NONE.
VA...NONE.
AD/JB
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