Area Forecast Discussion
Issued by NWS Nashville, TN

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FXUS64 KOHX 300142
AFDOHX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NASHVILLE TN
842 PM CDT FRI AUG 29 2014

.UPDATE...
SOME FINE TUNING OF THE POP/WX SEEMED WARRANTED TONIGHT AS THE
LONG ADVERTISED RAIN PATTERN CONTINUES TO BE INDICATED IN BOTH
MODELS. SOME SUBTLE DIFFERENCE IN THE ECMWF/GFS...MAINLY IN THE INTENSITY OF
A 850 MB LLJ...WILL CONTINUE TO MAKE PINPOINTING AREAS OF HIGHEST
RAINFALL POTENTIAL SOMEWHAT COMPLICATED. WHILE CONFIDENT THAT JUST
ABOUT EVERYWHERE IN THE MIDSTATE WILL BE SEEING RAINFALL BETWEEN
18Z SAT AND 12Z SUNDAY...18Z MODEL RUNS CONTINUE TO SHOW A WETTER
PATTERN FOR THE TN RIVER VALLEY AND DRIER DEPICTION FOR THE
CUMBERLAND PLATEAU. THIS IS LARGELY DUE TO THE MAIN DYNAMICAL
SUPPORT...500 MB JET AND 850 MB SHORTWAVE DISTURBANCE...BEING
CONFINED TO WEST TN AND BRUSHING OUR NW COUNTIES. THIS WOULD BE
BETWEEN 00Z AND 03Z IF THE 18Z MODEL RUNS ARE CORRECT.

CONVECTIVE PARAMETERS ARE NOT ENOUGH TO WARRANT MUCH ON THE SIDE
OF SEVERE POTENTIAL...ESPECIALLY WITHOUT MUCH SURFACE FORCING TO
LIFT PARCELS...BUT WITH PWATS WELL OVER 2 INCHES..THE DYNAMICS
ALONE SHOULD BE ENOUGH TO WARRANT LIGHTNING ACTIVITY. THE ADDED
CONVECTIVE ELEMENT OF ~1000 J/KG AND LIS AROUND -5 COULD RESULT IN
SOME HEAVY DOWNPOURS AND GUSTY WINDS UP TO 40 MPH.

TWEAKED THE UPDATED WPC QPF FORECAST TO MIRROR OUR POP CHANCES IN
THE GRIDS. THIS LEAVES A 48 HOUR TOTAL JUST ABOUT IN LINE WITH THE
WPC 48 HOUR TOTAL WITH MINOR DISCREPANCIES IN THE TIMING OF THE
HEAVIEST RAINS.

&&

.PREV DISCUSSION... /ISSUED 620 PM CDT FRI AUG 29 2014/

UPDATE...FOR 00Z AVIATION.

AVIATION...00Z TAF DISCUSSION.

SOLID SOUTHERLY FLOW DEVELOPING OVER THE MID-STATE TONIGHT AHEAD
OF SHOWERS AND THUNDERSTORMS THAT WILL LIKELY COVER ALL 3
TERMINALS BY THIS TIME TOMORROW. FLIGHT CATEGORIES SHOULD REMAIN
VFR UNTIL SATURDAY AFTERNOON WHEN RAINS AND TS PICK UP IN COVERAGE
AND INTENSITY. RAINS MAY BE HEAVY AT TIMES AT KCKV. WILL SHOW
DETERIORATING CONDITIONS STARTING BY 17Z WEST OF THE PLATEAU...
SPREADING EASTWARD TOWARDS KCSV BY THE END OF THIS CYCLE. IFR
CONDITIONS MAY NOT COME UNTIL AFTER 00Z SUNDAY. WINDS WILL BE
MANAGEABLE...SOUTHERLY TONIGHT WITH A SLIGHT VEER TO SW BY THE
END OF THIS CYCLE.

UNGER

PREV DISCUSSION... /ISSUED 303 PM CDT FRI AUG 29 2014/

DISCUSSION...

DRY AIRMASS IN PLACE ACROSS THE MID STATE TODAY WITH 12Z OHX
SOUNDING SHOWING A PWAT OF ONLY 1.13 INCHES...WHICH HAS KEPT
CLOUD COVER RELATIVELY LOW AND THE FORECAST AREA PRECIP-
FREE...ALTHOUGH ONE ISOLATED SHOWER FORMED EARLIER ACROSS WESTERN
STEWART COUNTY.

CHANGES BEGIN TONIGHT AS MODELS CONTINUE TO INDICATE A DEEP SLUG
OF TROPICAL MOISTURE CURRENTLY MOVING ONSHORE THE GULF COAST WILL
SPREAD NORTHWARD INTO OUR REGION...WITH 12Z GFS SHOWING PWATS
RISING DRAMATICALLY INTO THE 2-2.3 INCH RANGE BY SATURDAY MORNING.
WIDESPREAD SHOWERS AND THUNDERSTORMS ARE ANTICIPATED TO DEVELOP
TOMORROW MORNING ACROSS SOUTHWEST ZONES AND SPREAD NORTHEAST
THROUGH THE DAY...WITH A LIKELY LULL IN ACTIVITY SATURDAY EVENING
BEFORE ANOTHER ROUND OF SHOWERS AND STORMS MOVES ACROSS SATURDAY
NIGHT INTO SUNDAY. A BLEND OF THE 12Z GFS/ECMWF INDICATES LIKELY
POPS WILL BE WARRANTED THROUGHOUT THE SATURDAY/SUNDAY TIMEFRAME.
ALTHOUGH NO SURFACE BOUNDARY WILL BE IN PLACE OR NEARBY FOR A
MORE FOCUSED FLOOD THREAT...SUCH HIGH PWATS ALONG WITH LIFT
PROVIDED BY A SOUTHWESTERLY 40-45KT H5 JET SUGGEST LOCALLY HEAVY
RAINFALL WILL CERTAINLY BE POSSIBLE IN SOME AREAS. CLOUDS AND
PRECIP WILL ALSO ACT TO KEEP TEMPERATURES DOWN BOTH SATURDAY AND
SUNDAY WITH HIGHS ONLY IN THE 80S.

UPPER RIDGE WILL BEGIN TO REBUILD ALONG THE GULF COAST BY MONDAY
WITH DRIER AIR ALOFT AND LOWER PWATS SHIFTING INTO OUR
REGION...WITH PRECIP CHANCES LOWERING BACK TO SLIGHT AND TEMPS
WARMING BACK INTO THE 90S. H5 RIDGE SHIFTS NORTHWARD AND CENTERS
OVER THE TENNESSEE VALLEY AND STRENGTHENS FROM MIDWEEK ON PER 12Z
GFS/ECMWF...SO THE FIRST WEEK OF SEPTEMBER LOOKS LIKE A HOT ONE
WITH HIGHS IN THE MID 90S AND ONLY LOW CHANCES FOR RAIN.

&&

.OHX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

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