Area Forecast Discussion
Issued by NWS Nashville, TN

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FXUS64 KOHX 221736
AFDOHX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NASHVILLE TN
1136 AM CST MON DEC 22 2014

.AVIATION 18Z DISCUSSION...TROUGH AXIAL ROTATION IS RATHER STRONG
ACROSS THE CENTRAL PLAINS THIS TAF CYCLE. AS IT ROTATES FROM
NEGATIVE TO POSITIVE...THE PRELIMINARY FRONTAL BOUNDARY NEAR THE
MS RIVER THIS MORNING WILL WEAKEN AND LIFT OFF TO THE NORTH.
MOISTURE IS STILL ON THE INCREASE SO WE WILL STILL ENCOUNTER SOME
RAINFALL WITH THE LOW LEVEL FORCING THAT WILL BE AT WORK. THIS
WILL TRANSLATE TO A GOOD CHANCE OF SHOWERS UNTIL AROUND 02Z TO
07Z. A BRIEF BREAK FROM THE PRECIP IS THEN EXPECTED WHILE A SFC
LOW DEVELOPS IN THE NORTHWESTERN GULF TOWARD THE END OF THE TAF
PD. THE ASSOCIATED INVERTED TROUGH INVERSION...EXTENDING NE FROM
THE LOW...WILL BE TAKING AIM ON THE MID STATE BETWEEN 12Z- 18Z
TUESDAY. THUS...APPRECIABLE ISENTROPIC LIFTING WILL YIELD MORE
WIDESPREAD RAINFALL AFT 12Z.

AS FOR CIGS AND VSBYS...CIGS AOB 1 KFT SHOULD BE COMMON PLACE BY
00Z THIS EVENING. VSBYS WILL GENERALLY HOLD IN THE 3-5 MI RANGE.

&&

.PREV DISCUSSION... /ISSUED 643 AM CST MON DEC 22 2014/

UPDATE...FOR 12Z TAFS.

AVIATION...

CIGS ARE IN THE MVFR CATEGORY ACROSS ALL SITES THIS MORNING. THEY
WILL LIKELY REMAIN THERE OR DROP TO IFR LEVELS THIS EVENING AND
OVERNIGHT AS PRECIP MOVES INTO MIDDLE TENNESSEE. A TIGHT PRESSURE
GRADIENT WILL BRING GUSTY SOUTHERLY WINDS DURING THE
AFTERNOON...GUSTS TO 22 KNOTS WILL BE LIKELY. RAIN IS EXPECTED TO
CONTINUE DURING THE OVERNIGHT HOURS...WITH WINDS CALMING AFTER
MIDNIGHT. CIGS AND VIS WILL BE REDUCED TO IFR CONDITIONS AT ALL
SITES BY TUESDAY MORNING.

PREV DISCUSSION... /ISSUED 410 AM CST MON DEC 22 2014/

SHORT TERM...A SHIELD OF STRATUS AND WARMER MOIST AIR HAS BEEN
ADVANCING INTO MIDDLE TENNESSEE FROM THE SOUTH THIS MORNING.
TEMPERATURES HAVE ACTUALLY BEGUN TO INCREASE OVER THE PAST COUPLE
OF HOURS...THIS TREND IS EXPECTED TO CONTINUE TODAY AS MOIST
SOUTHERLY FLOW INCREASES ACROSS THE TENNESSEE VALLEY. TEMPERATURES ARE
EXPECTED TO SURGE INTO THE UPPER 50S WITH LIGHT SHOWERS DEVELOPING
OVER THE WESTERN HALF OF MIDDLE TENNESSEE BY THIS AFTERNOON. A
DEEPENING UPPER LOW OVER THE CENTRAL PLAINS WILL MOVE EAST TOWARD
THE MISSISSIPPI VALLEY MONDAY NIGHT WHICH WILL ALLOW PWATS TO
GRADUALLY INCREASE AND MAX OUT NEAR 1.2 INCHES OVER MIDDLE
TENNESSEE...THEREFORE SOME MODERATE SHOWERS WILL BE POSSIBLE
OVERNIGHT. A SURFACE LOW WILL RIDE UP THE EASTERN SIDE OF THE
UPPER TROUGH TUESDAY AFTERNOON AND INTO WEDNESDAY NIGHT PROVIDING
ENOUGH INSTABILITY TO MENTION AT LEAST A CHANCE OF THUNDERSTORMS
DURING THIS PERIOD. NO SEVERE STORMS ARE EXPECTED...AND ANY CHANCE
OF THUNDER WILL DISSIPATE AFTER THE LOW PASSES TO THE NORTH
WEDNESDAY MORNING AND COOLER AIR MOVES INTO OUR AREA. PRECIP WILL
GRADUALLY MOVE EAST WEDNESDAY AFTERNOON AND EVENING.

LONG TERM...AS COLDER AIR PUSHES IN BEHIND OUR DEPARTING FRONT
WEDNESDAY NIGHT, WE COULD BE LOOKING AT A BRIEF PERIOD OF A LIGHT
WINTRY MIX. HOWEVER, THE AIR MASS IS PACIFIC IN NATURE, AND THE
GOOD NEWS IS THAT LOWS WEDNESDAY NIGHT ARE ONLY EXPECTED TO DROP
INTO THE MIDDLE 30S. AFTER A DRY DAY ON THURSDAY, OUR
PROGRESSIVE UPPER LEVEL PATTERN, SWINGS ANOTHER FRONT IN OUR
DIRECTION FOR THE WEEKEND, WITH RAIN CHANCES INCREASING AGAIN BY
SATURDAY. RIGHT NOW, IT LOOKS LIKE THIS FRONT SHOULD PUSH STEADILY
EASTWARD AND BRING SOME DRIER WEATHER BEHIND IT FOR SUNDAY. THE
LATEST ECMWF SOLUTION LOOKS A BIT SQUIRRELY, AS IT DEEPENS THE
UPPER LEVEL SHORTWAVE A BIT AND SLOWS IT DOWN AS IF IT`S TRYING TO
CUT IT OFF. HOWEVER, THE PROBLEM IS, IT KEEPS AN OPEN WAVE THE
ENTIRE TIME. THEREFORE, WILL VEER AWAY FROM LATEST ECMWF SOLUTION,
KEEP A PROGRESSIVE PATTERN IN PLACE AND LIMIT THE WINDOW FOR
PRECIPITATION IN MIDDLE TENNESSEE. HAVE KEPT THINGS DRY DURING THE
LATEST PERIODS, AS THE TIMING OF ANY UPSTREAM SHORTWAVES IS
DIFFICULT TO DETERMINE.

&&

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

&&

$$

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