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Area Forecast Discussion

556
FXUS64 KOHX 240904
AFDOHX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NASHVILLE TN
404 AM CDT THU APR 24 2014

SHORT TERM...

THE FOCUS OF THE SHORT TERM IS ON A PROGRESSIVE SHORTWAVE PROGGED TO
ENTER THE MIDDLE TN AREA LATE TONIGHT. BEFORE THAT A SFC HIGH WILL
STRENGTHEN OVER THE LEE OF THE APPALACHIANS WHILE THE SURFACE LOW
ASSOCIATED WITH THE SHORTWAVE MOVES NE THROUGH MISSOURI. THIS WILL
SHIFT WINDS TO THE SOUTHWEST BY MID DAY AND MOISTURE ADVECTION WILL
BEGIN. EURO MOS BRINGS OUR DEWPOINTS INTO THE MID 50S BY AROUND
06Z...JUST IN TIME FOR THE DYNAMICS OF THE UPPER LEVEL SYSTEM TO
MATURE. THE CONVECTIVE ENVIRONMENT IS MORE CONDUCIVE FOR A LOW END
SEVERE EVENT OUT TOWARDS THE TN RIVER AND FARTHER WEST...THE SLIGHT
RISK LOOKS VERY APPROPRIATE. DO BELIEVE THE ARRIVAL TIME OF THE
SYSTEM...BEING WELL AFTER DARK...WILL BE THE BIG DIFFERENCE BETWEEN
WHAT THEY SEE OUT IN WEST TENNESSEE VS MIDDLE. AGREE WITH SPCS
THINKING THAT THE SYSTEM WILL EVOLVE INTO A LINE...WHICH IS THE MODE
THAT IS BEING SUGGESTED BY THE 4 KM WRF. WHILE A LOW END TORNADO
THREAT IS POSSIBLE WITH THE BETTER DIURNAL HEATING AND CONVECTIVE
ENVIRONMENT ALONG THE MS RIVER...THE THREATS FOR MIDDLE
TENNESSEE...DUE TO INHERITING A MATURE LINE THAT WILL BE QUICKLY
LOSING ITS CONVECTIVE FUEL...WILL BE MAINLY STRAIGHT LINE WINDS.
THESE STORMS SHOULD EXIT THE PLATEAU NO LATER THAN 18Z TOMORROW AND
ANOTHER VERY NICE SUNNY AND WARM DAY WILL BE IN STORE ON FRIDAY.

LONG TERM...

A NICE WEEKEND OF WARM TEMPERATURES AND PRETTY DRY CONDITIONS BEFORE
SUNDAY AFTERNOON WHEN A WARM FROM RISES OUT OF THE NORTHERN AL AND
MS STATES. ITS AT THIS POINT THE WARM SECTOR BEGINS SETTING UP FOR A
POTENT DYNAMICAL AND CONVECTIVE SYSTEM TO DEVELOP MONDAY. AS STATED
IN PREVIOUS AFDS...A HIGHLY CONVECTIVE ENVIRONMENT CHARACTERIZED BY
SBCAPE VALUES IN THE 1500-2000 RANGE FOR THE TN VALLEY...LIS OVER -5
AND DEWPOINTS POSSIBLY REACHING THE MID 60S WILL BE DRAPED
EVERYWHERE SOUTH OF THE NORTHERN KY BORDER AND EAST OF THE MS RIVER.
THE HIGHEST DEWPOINTS AND CAPE VALUES WILL BE LOCATED IN LA AND MS
AND IT WILL BE IN THIS AREA THAT THE UPPER LEVEL DYNAMICS BEGIN TO
COINCIDE WITH THE WARM/MOIST SECTOR MONDAY AFTERNOON.

THE UPPER LEVEL DYNAMICS AND LOW ORIENTATION DIFFER FROM GFS TO
ECMWF SOLUTION WITH A MORE NEGATIVELY TILTED...ELONGATED 250 MB
HEIGHT ORIENTATION WITH THE ECMWF. THIS ORIENTATION WOULD YIELD
SIGNIFICANTLY MORE UPPER LEVEL DIVERGENCE ALLOWING ANY DEVELOPMENT
OF DISCRETE CELLS...WHICH SEEMS CERTAINLY POSSIBLE BEGINNING AFTER
18Z MONDAY IN THE ARKLAMISS AREA...TO GROW UPSCALE RAPIDLY. WITH
OVER 60 KTS OF DEEP LAYER SHEAR TO MAINTAIN MESOS THESE STORMS WOULD
BE ABLE TO PRODUCE STRONG TORNADOES...LARGE HAIL...AND DAMAGING
WINDS. AS THE AFTERNOON MOVES ON...THESE FEATURES WILL BEGIN TO
FILTER NE INTO THE TN VALLEY AOA THE 00Z-06Z RANGE. IT IS AT THIS
TIME THAT THE SYSTEM SHOULD BEGIN UNDERGOING OR HAVE UNDERGONE A
SHIFT FROM A HIGHLY CONVECTIVE SYSTEM...TO A MORE DYNAMICALLY DRIVEN
SYSTEM...WHICH WOULD HOPEFULLY MEAN A SEVERE QLCS TAKING ON MORE OF
A SEVERE STRAIGHT LINE WIND THREAT WITH LARGE HAIL STILL POSSIBLE.

THE COMPLICATION AT THIS RANGE WILL BE WHERE THIS TRANSITION WILL
TAKE PLACE...WHETHER THAT OCCURS DUE TO CONGLOMERATION OF DISCRETE
CELLS OR THE FRONT CATCHING UP TO THE ISOLATED DEVELOPMENT...IS
UNKNOWN AT THIS TIME. REASONABLY CONFIDENT AFTER NIGHTFALL...THAT
THIS TRANSITION WILL TAKE PLACE...JUST WHERE IT WILL IS THE
QUESTION. UNFORTUNATELY...THE TEMPORAL RESOLUTION OF THE MID RANGE
MODELS LIMITS THE ABILITY TO ADD MORE FINE TUNING TO THIS ANALYSIS.

BUT TO SUMMARIZE...A WINDOW OF DISCRETE SUPERCELL DEVELOPMENT
APPEARS POSSIBLE AOA THE 21Z RANGE UNTIL NIGHTFALL IN THE NORTHERN
HALF OF MS AND WESTERN TN POSSIBLY STRETCHING INTO NORTHERN ALABAMA
AND WESTERN MIDDLE TN. BY NIGHTFALL...A MORE LINEAR SYSTEM WILL
COMPLETE THE JOURNEY THROUGH THE MID STATE DECREASING THE TORNADIC
THREAT BUT KEEPING STRAIGHT LINE WINDS AND LARGE HAIL POSSIBLE. THIS
IS THE BEST SUMMARY OF EVENTS AND DETAILS THAT CAN BE PROVIDED FOR
MONDAY GIVEN THE CURRENT INFORMATION. HOPEFULLY MORE SPECIFICITY
WITH LATER MODEL RUNS.


&&

.PRELIMINARY POINT TEMPS/POPS...
NASHVILLE      81  60  75  50 /  10  80  20   0
CLARKSVILLE    80  60  75  49 /  10  70  10   0
CROSSVILLE     75  59  71  48 /  05  80  30   0
COLUMBIA       80  60  76  49 /  10  80  10   0
LAWRENCEBURG   80  59  77  50 /  10  80  10   0
WAVERLY        81  60  76  51 /  10  70  10   0

&&

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

$$

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