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Area Forecast Discussion

521
FXUS64 KMRX 202022
AFDMRX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MORRISTOWN TN
322 PM EST SAT DEC 20 2014

.SHORT TERM...(TONIGHT THROUGH MONDAY)...CLOUDS ARE SLOWLY ERODING
FROM THE WEST THIS AFTERNOON...AND MOST OF THE TN VALLEY SHOULD BE
CLEAR BEFORE MIDNIGHT IF THE TREND CONTINUES AND IF THE HRRR IS
ACCURATE. WITH THE EXPECTED CLEARING AND CALM WINDS...CONDITIONS
APPEAR FAVORABLE FOR FOG TONIGHT. CROSSOVER TEMPERATURES ARE
ESPECIALLY FAVORABLE NORTH...SO WILL MENTION PATCHY/AREAS OF FOG
THERE AS WELL AS SW NC. FOG SHOULD BE SLOW TO DISSIPATE DUE TO THE
LOW SUN ANGLE AND WEAK MIXING TOMORROW MORNING. THE REST OF THE DAY
SHOULD BE MOSTLY SUNNY...WITH HIGH CLOUDS INCREASING LATE IN THE
DAY.

A WEAK SHORTWAVE TROUGH IN THE SOUTHERN STREAM NOW OVER TX WILL BE
LIFTING E-NE AND CROSSING OUR AREA SUNDAY NIGHT AND MONDAY. WITH THE
JET POSITIONED FROM SOUTHERN AL TO THE NC COAST...THE MAJORITY OF
LIFT AND DEEP MOISTURE APPEARS TO BE EAST OF OUR AREA. THE NAM
PULLS MORE MOISTURE INTO OUR AREA THAN THE GFS...BUT EVEN THE NAM
SHOWS THIS MOISTURE MAINLY BELOW THE -10C LEVEL...SUGGESTING THAT
DRIZZLE IS MORE LIKELY THAN MEASURABLE RAINFALL. AS A RESULT...WILL
CUT BACK POPS TO A CHANCE EAST TO NOTHING WEST...BUT MENTIONING
DRIZZLE EVERYWHERE. QPF WILL BE REDUCED AS WELL...TO NO MORE THAN A
TENTH IN THE MOUNTAINS. TEMPERATURE PROFILES IN ALL THE MODEL
SOUNDINGS INDICATE ALL LIQUID PRECIP. THE TROUGH PASSAGE SHOULD
BRING AN END TO ANY RAIN/DRIZZLE ON MONDAY AFTERNOON.

.LONG TERM...(MONDAY NIGHT THROUGH SATURDAY)...QUITE THE ACTIVE LONG
TERM PERIOD WITH A HIGHLY AMPLIFIED SYSTEM COMING IN FOR CHRISTMAS THAT
WILL BRING...RAIN...MAYBE A FEW STORMS...WIND...AND PERHAPS SNOW.

MONDAY NIGHT INTO TUESDAY HEIGHTS WILL BE QUICKLY BUILDING OUT AHEAD
OF A DEEP TROUGH MOVING ACROSS THE CENTRAL U.S. AND SOUTHERN PLAINS.
THIS WILL ALLOW FOR MONDAY NIGHT AND TUESDAY DAY TO BE UNSEASONABLE
WARM. LOWS MONDAY NIGHT WILL BE 10 TO 12 DEGREES ABOVE NORMAL. HIGHS
ON TUESDAY WILL BE IN THE MID TO UPPER 50S...5 TO 10 DEGREES ABOVE
NORMAL. RAIN CHANCES INCREASE ON TUESDAY AS THIS HIGHLY AMPLIFIED
AND DEEP TROUGH IS ON OUR DOORSTEP BY TUESDAY AFTERNOON. DID DECIDE
TO INTRODUCE SLIGHT CHANCE OF THUNDERSTORMS FROM KNOXVILLE SOUTH
TUESDAY AFTERNOON INTO TUESDAY NIGHT. CAPE IS VERY WEAK BUT SHEAR
AND HELICITY ARE ROBUST...IN LARGE PART DUE TO A STRONG 850MB JET OF
40 TO 50 KTS THAT WILL BE IN PLACE. BETTER INSTABILITY EXISTS
FURTHER TO OUR SOUTH AND SOUTHWEST BUT DID WANT TO MENTION A STORM
OR TWO POSSIBLE ACROSS OUR CENTRAL AND SOUTHERN AREAS. ABUNDANT
MOISTURE AND STRONG LIFT WILL LEAD TO SOME DECENT RAINFALL ACROSS
THE AREA FOR TUESDAY NIGHT INTO WEDNESDAY...MORE SO ACROSS THE
SOUTHERN AREAS. CURRENT GFS SOUNDINGS SHOW PW VALUES RANGING FROM
1.40 TO 1.20 INCHES FROM SOUTH TO NORTH. THIS PUTS US AT 2SD ABOVE
NORMAL FOR THIS TIME OF YEAR. I DON`T THINK FLOODING WILL BE A
CONCERN THOUGH BECAUSE OF HOW QUICKLY THIS SYSTEM IS MOVING. SO NOW
THAT WE HAVE TALKED ABOUT RAIN AND STORMS...LET`S TALK ABOUT SNOW.

CHRISTMAS EVE IS LOOKING TO BE RATHER NASTY WITH THE DEEP TROUGH AND
ASSOCIATED SURFACE LOW MOVING ACROSS. LIGHT TO MODERATE RAIN
CONTINUES WEDNESDAY MORNING WITH STRONG COLD FRONT MOVING THROUGH BY
LATE AFTERNOON INTO EARLY EVENING. AS THE FRONT MOVES THROUGH EXPECT
RAIN TO CHANGE TO SNOW ACROSS MUCH OF THE AREA ALONG WITH BREEZY
WINDS. THE MILLION DOLLAR QUESTION IS HOW MUCH MOISTURE WILL BE
LEFT. MODELS HAVE BEEN CONSISTENT IN SHOWING THE HIGHLY AMPLIFIED
SYSTEM FOR SEVERAL DAYS OUT BUT HAVE NOT BEEN WITH THE EXACT
PLACEMENT OF THE LOW. THE LATEST FEW MODEL RUNS OF THE ECMW AND THE
GFS ARE TRENDING THE LOW FURTHER TO OUR WEST. THIS MEANS THAT THE
BULK OF THE MOISTURE WILL HAVE PASSED OFF TO OUR EAST BEFORE IT GETS
COLD ENOUGH TO SNOW BACK BEHIND THE COLD FRONT. IT LOOKS LIKE OUR
SNOW WILL BE IN THE FORM OF WRAP AROUND MOISTURE. THE CHANGEOVER TO
SNOW LOOKS TO OCCUR SOMETIME ON WEDNESDAY EVENING WITH SNOW
LINGERING THROUGH EARLY CHRISTMAS MORNING. MOST OF THE PRECIP DURING
THIS TIME FRAME SHOULD BE IN THE FORM OF SCATTERED LIGHT SNOW
SHOWERS. LITTLE TO NO ACCUMULATION EXPECTED AT THIS TIME FOR LOWER
ELEVATIONS. HIGHER ELEVATIONS MAY GET AN INCH OR TWO. AGAIN...ALL OF
THE ABOVE DEPENDS ON THE TRACK OF THE LOW...BUT THIS IS HOW IT`S
LOOKING FOR NOW.

THIS SYSTEM QUICKLY EXITS ON THURSDAY...CHRISTMAS DAY...AS IT RACES
OFF TO THE NORTHEAST. ANOTHER QUICK MOVING WEAKER SYSTEM MOVES
THROUGH ON FRIDAY INTO SATURDAY THAT COULD BRING SOME LIGHT SHOWERS
TO THE AREA.




&&

.PRELIMINARY POINT TEMPS/POPS...
CHATTANOOGA AIRPORT, TN             33  53  41  56 /   0  10  20  10
KNOXVILLE MCGHEE TYSON AIRPORT, TN  31  50  38  55 /   0  10  20  10
OAK RIDGE, TN                       30  50  38  55 /   0   0  20  10
TRI CITIES AIRPORT, TN              30  48  35  51 /   0  10  30  40

&&

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

$$

DGS/SR



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