256
FXUS64 KMRX 190709
AFDMRX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MORRISTOWN TN
254 AM EDT THU SEP 19 2019
SHORT TERM...(TODAY AND TONIGHT)
A BACKDOOR COLD FRONT IS SLIDING THROUGH THE AREA, AND APPEARS TO
BE LOCATED BETWEEN TYS AND CHA AT THE MOMENT. AS IT CONTINUES TO
PUSH WESTWARD, BROKEN TO OVERCAST CLOUD COVER WILL EXPAND WESTWARD
AS WELL, SO THAT MUCH OF THE AREA MAY START THE DAY WITH MOSTLY
CLOUDY SKIES. HOWEVER, MODELS INDICATE THAT THIS CLOUD LAYER IS
FAIRLY THIN, AND WE WILL HAVE DRIER AIR PUSHING IN FROM THE NE AT
850 MB THIS AFTERNOON. SO THE EXPECTATION IS THAT WE WILL SEE
CLOUDS ERODING THROUGH THE AFTERNOON. THIS WILL MAKE FOR A TRICKY
TEMPERATURE FORECAST, BUT THE BOTTOM LINE IS THAT BEHIND THE
FRONT, TEMPERATURES WILL BE QUITE A BIT COOLER THAN WE HAVE SEEN
OVER THE PAST FEW DAYS, WITH HIGHS IN THE UPPER 70S TO LOWER 80S
IN MOST SPOTS. DEWPOINTS WILL DROP AS WELL, ALLOWING OVERNIGHT
LOWS IN THE 50S IN THE VALLEY.
LONG TERM...(FRIDAY THROUGH WEDNESDAY)
THE NICE BREAK FROM THE HIGH HEAT AND HUMIDITY WILL UNFORTUNATELY
COME TO AN END FRIDAY THROUGH THE WEEKEND AS LONGWAVE TROUGHING
AMPLIFYING OVER THE WESTERN U.S. RESULTS IN A STRONG AMPLIFYING
RIDGE OVER THE TN AND OH VALLEYS. H5 HEIGHTS WILL EXCEED 592 DAM
CENTERED OVER THE SOUTHEAST STATES BY SATURDAY AND SUNDAY. AT THE
SURFACE, HIGH PRESSURE OVER THE SOUTHERN APPALACHIANS FRIDAY WILL
SLOWLY MOVE TO THE MID ATLANTIC COAST BY SUNDAY RESULTING IN
STRENGTHENING SOUTHWESTERLY WAA. SUBSIDENCE FROM THE ABOVE
MENTIONED SURFACE AND UPPER LEVEL RIDGING WILL KEEP ALL AREAS DRY
THROUGH THE WEEKEND WITH HIGH TEMPS INCREASING A FEW DEGREES EACH
DAY. WENT SLIGHTLY ABOVE GUIDANCE FOR HIGHS AND SLIGHTLY BELOW
GUIDANCE FOR LOWS AS THE DRY CONDITIONS WILL LEAD TO LOWER OVERALL
TD'S. SUSPECT THAT TD'S WILL STRUGGLE TO RISE ABOVE THE UPPER
50'S DESPITE THE DEEP LAYER WAA UNTIL THE NEXT SHORTWAVE AND COLD
FRONT APPROACHES MONDAY. THIS HOT AND RELATIVELY DRY AIRMASS WILL
START TO INCREASE FIRE DANGER THIS WEEKEND.
BY MONDAY A SHORTWAVE TROUGH AND ATTENDANT COLD FRONT WILL BE MOVING
ACROSS THE GREAT LAKES AND OH VALLEY. THE ECMWF CONTINUES TO BE
SOMEWHAT MORE AMPLIFIED WITH THIS SYSTEM THAN THE GFS, BUT EITHER
WAY, THE STRONG SOUTHEAST RIDGE WILL BE FLATTENING, AND THIS WILL
ALLOW THE COLD FRONT TO SETTLE TO AT LEAST NORTHEAST TN AND
SOUTHWEST VA BY MONDAY EVENING. THERE IS NOT STRONG MOISTURE
TRANSPORT FROM THE GULF AHEAD OF THIS FRONT, SO WITH THE DROUGHT
CONDITIONS IN PLACE, HAVE CONTINUED TO KEEP POPS IN THE SLIGHT
CHANCE RANGE MONDAY AND MONDAY NIGHT WITH ANOTHER HOT DAY EXPECTED.
MODEL SPREAD INCREASES TUESDAY THROUGH WEDNESDAY WITH THE GFS
LINGERING THE OLD FRONT IN THE VICINITY OF THE SOUTHERN APPALACHIANS
AS A SECOND AND STRONGER MID LEVEL SHORTWAVE DIVES INTO OUR REGION
FROM THE MISSISSIPPI VALLEY, WHILE THE ECMWF MAINTAINS ITS MORE
AMPLIFIED SOLUTION OF BROAD LONGWAVE TROUGHING DEVELOPING OVER THE
EASTERN U.S. TUESDAY AND WEDNESDAY CAUSING THE FRONT TO PUSH WELL
SOUTH AND SURFACE HIGH PRESSURE TO SETTLE INTO THE TN VALLEY. HAVE
SLIGHT CHANCE POPS TUESDAY AND WEDNESDAY FOR VERY LIGHT SHOWERS OR
SPRINKLES TO ACCOUNT FOR THIS UNCERTAINTY, BUT ANYTHING WILL REMAIN
WIDELY SCATTERED DUE TO FEEDBACK OF THE DRY GROUND. TEMPS WILL BE
COOLER TUESDAY AND WEDNESDAY, BUT STILL ABOVE THE NORMAL LATE
SEPTEMBER VALUES.
PRELIMINARY POINT TEMPS/POPS
CHATTANOOGA AIRPORT, TN 83 60 87 59 / 0 0 0 0
KNOXVILLE MCGHEE TYSON AIRPORT, TN 81 58 87 59 / 10 0 0 0
OAK RIDGE, TN 83 59 87 58 / 0 0 0 0
TRI CITIES AIRPORT, TN 79 51 84 54 / 10 0 0 0
MRX WATCHES/WARNINGS/ADVISORIES
NC...NONE.
TN...NONE.
VA...NONE.
DGS/RG
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