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Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
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FXUS64 KMRX 221906
AFDMRX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MORRISTOWN TN
306 PM EDT WED MAY 22 2013

.SHORT TERM...(TONIGHT AND THURSDAY)...CURRENT SURFACE ANALYSIS SHOWS
A WEAK COLD FRONT OVER THE MS RIVER VALLEY...WITH AN OUTFLOW
BOUNDARY BISECTING THE FORECAST AREA FROM LAST NIGHT`S CONVECTION
OVER MIDDLE TN. BOTH THE GFS AND NAM MODELS REVEAL A MODERATELY
UNSTABLE AIR MASS DEVELOPING THIS AFTERNOON AND EVENING...AS AN
UPPER-LEVEL TROUGH SWINGS EASTWARD ACROSS THE TN RIVER VALLEY. MODEL
SOUNDINGS ALSO INDICATE A DECENT MID LEVEL WIND FLOW BETWEEN 20 AND
40 KT...SO IT APPEARS THERE WILL BE A GOOD CHANCE FOR SEVERE WEATHER
INTO THIS EVENING. PRECIPITABLE WATER VALUES REMAIN HIGH THIS
AFTERNOON AND EVENING (BETWEEN 1.5 AND 1.75 INCHES)...SO THINK THAT
LOCALLY HEAVY RAINFALL WILL BE A POSSIBILITY WITH SOME STORMS.
MODELS ALSO INDICATE 0-1 KM HELICITY VALUES INCREASING AND LCL
HEIGHTS LOWERING THIS EVENING...ESPECIALLY OVER NORTHEAST TN AND
SOUTHWEST VA...SO IT APPEARS THAT THERE COULD BE AN ISOLATED TORNADO
OR TWO. THE COLD FRONT IS PROGGED TO MOVE THROUGH THE FORECAST AREA
ON THURSDAY...WITH WINDS INCREASING AND SCATTERED CONVECTION AGAIN
POSSIBLE. AS FOR TEMPS...GFS AND NAM GUIDANCE NUMBERS ARE IN GENERAL
AGREEMENT FOR TONIGHT AND THURSDAY...BUT WILL COMPROMISE WHERE SOME
SLIGHT DIFFERENCES ARE NOTED.

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)...DEEP UPPER
TROUGH FOR THIS TIME OF YEAR PUSHING A SECONDARY COLD FRONT
THROUGH THE FORECAST AREA THURSDAY NIGHT INTO FRIDAY MORNING. AIR
MASS NOT AS UNSTABLE BY THURSDAY EVENING WITH MAINLY SHOWERS AHEAD
OF SECONDARY FRONT. BEST CHANCE OF RAIN ACROSS NORTHEAST SECTIONS.
LOWS SEVERAL DEGREES COOLER IN THE 50S TO POSSIBLY UPPER 40S HIGHER
ELEVATIONS. HIGH PRESSURE FROM THE NW BUILDS IN FRIDAY WITH
TEMPERATURES AS MUCH AS 10 DEGREES BELOW NORMAL AND NORTH TO
NORTHWEST WINDS 10 TO 15 MPH. LOWS FRIDAY NIGHT DROPPING TO THE 40S
WITH UPPER 30S HIGHER ELEVATIONS AND HIGHER NE VALLEYS. FROST MAY
BE POSSIBLE IN ISOLATED LOCATIONS THERE. NORTHWEST FLOW WITH COOLER
TEMPERATURES TO CONTINUE SATURDAY THROUGH THE WEEKEND WITH
TEMPERATURES SLOWLY WARMING EACH DAY. MOISTURE TO INCREASE BY
SUNDAY AS FLOW AROUND RIDGE OVER THE CENTRAL STATES BRINGS A FRONT
INTO THE OHIO VALLEY. FROM SUNDAY EVENING THROUGH MID WEEK SHOWERS
AND THUNDERSTORMS POSSIBLE AGAIN. ACTIVITY SHOULD BE HIGHEST DURING
PEAK HEATING HOURS OF THE AFTERNOON AND EARLY EVENING.

&&

.PRELIMINARY POINT TEMPS/POPS...
CHATTANOOGA AIRPORT, TN             87  63  81  56  73 /  70  70  20  20   0
KNOXVILLE MCGHEE TYSON AIRPORT, TN  87  62  80  56  70 /  70  70  30  30  10
OAK RIDGE, TN                       87  62  80  55  71 /  70  70  30  30  10
TRI CITIES AIRPORT, TN              86  60  78  52  67 /  70  70  50  40  10

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.

&&

$$

DMG/TD
National Weather Service Weather Forecast Office
