National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS64 KOHX 091843
AFDOHX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NASHVILLE TN
1243 PM CST MON DEC 9 2013

.UPDATE...FOR 18Z AVIATION FORECASTS.

&&

.AVIATION...IFR AND MVFR CONDITIONS SHOULD PERSIST AT BNA...CKV
AND CSV FROM THIS AFTERNOON UNTIL AT LEAST AFTER DAYBREAK
TUESDAY. NO PRECIP EXPECTED TODAY BUT A LIGHT MIX SHOULD DEVELOP
OVERNIGHT...MORE SO AT BNA AND CSV BUT LESS AT CKV. IF IT PRECIPS
IN CKV...IT SHOULD BE IN THE FORM OF SNOW. AT BNA...COULD START AS
A MIX BUT FORECAST SOUNDINGS SUPPORT FAIRLY QUICK CHANGE TO ALL
SNOW WITH LIGHT ACCUMULATIONS BY 12Z. FURTHER EAST AT CSV...PRECIP
LIKELY TO BEGIN AS RAIN AND FREEZING RAIN...POSSIBLY CHANGING TO
SNOW BEFORE IT ENDS. PRECIP SHOULD END QUICKLY TUESDAY MORNING AS
SYSTEM EXITS BUT EXPECT LOW CLOUDS TO PERSIST.

&&

.PREV DISCUSSION... /ISSUED 555 AM CST MON DEC 9 2013/

UPDATE...FOR AVIATION.

AVIATION...
12Z TAFS...DEPARTING SYSTEM WILL PRODUCE A FEW EARLY MORNING -SHRA
AT CSV. OTHERWISE...IFR CIGS WILL LIFT TO MVFR EARLY THIS
MORNING WHERE THEY WILL STAY MUCH OF THE DAY WITH NW WINDS 5-10KT.
SOME VFR IS POSSIBLE LATER TODAY. TONIGHT...CONDITIONS WILL GO
DOWN AGAIN AS ANOTHER SYSTEM BRINGS LIGHT WINTRY PRECIPITATION
ACROSS THE AREA. CSV IS MOST LIKELY TO BE IMPACTED WITH ICE FROM
FZRA AND SOME PLSN PRODUCING SOME ACCUMULATIONS LATE IN THE NIGHT.
GENERALLY LIGHTER AMOUNTS OF MIXED WINTRY PRECIP WITH MVFR WX
EXPECTED FOR CKV AND BNA.

13

PREV DISCUSSION... /ISSUED 414 AM CST MON DEC 9 2013/

DISCUSSION...

SHORT TERM...TODAY AND TOMORROW.

LIGHT RAIN AND DRIZZLE OVER THE EASTERN HALF OF THE AREA IS WHAT
REMAINS OF LAST NIGHT`S SYSTEM.  TEMPERATURES REMAIN WELL ABOVE THE
FREEZING MARK SO ALL OF THIS IS LIQUID HITTING THE GROUND.  NOT FAR
BEHIND ARE TEMPERATURES FALLING NEAR FREEZING.  CKV IS RINGING IN AT
33 AT FORECAST TIME.  THE GOOD NEWS IS...EVEN AS MORE COLD AIR
FILTERS INTO THE NORTHWEST THIS MORNING...THIS SHOULD NOT POSE ANY
PROBLEMS AS THE SPIGOT HAS ALL BUT BEEN TURNED OFF FOR THE TIME
BEING.  TEMPERATURES TODAY WILL BE TRICKY WITH THE CAA MOVING IN
DURING THE DAYTIME.  WILL MAINTAIN HIGHS NEAR MOS BUT THE
TEMPERATURE CURVE THROUGHOUT THE DAY WILL LIKELY NOT BE NORMAL.
AREAS IN THE EAST ARE PROBABLY ABOUT AS WARM AS THEY WILL GET ALL
DAY.

THIS EVENING...ANOTHER SLUG OF MOISTURE IS EXPECTED TO START MOVING
IN FROM THE SOUTH. ONSET OF PRECIPITATION FOR OUR SOUTHERN
COUNTIES BETWEEN 9 PM AND MIDNIGHT WILL LIKELY BE RAIN AS
TEMPERATURES WILL REMAIN A BIT WARMER. AT THE SAME TIME...
TEMPERATURES WILL HAVE FALLEN NEAR OR JUST BELOW THE FREEZING MARK
OVER THE NORTHERN TWO THIRDS OF MIDDLE TENNESSEE BECAUSE OF
TODAY`S CAA. AS IS VERY TYPICAL OF WINTER WEATHER EVENTS HERE IN
THE MID-SOUTH...AND SIMILARLY TO WHAT WE HAVE SEEN OVER THE LAST
COUPLE OF DAYS...EVEN WITH SURFACE TEMPERATURES BELOW FREEZING...A
NOSE OF 5-6 DEGREES CELSIUS AROUND 850MB WILL LIKELY MELT ANY ICE
CRYSTAL FORMATION ABOVE IT...RESULTING IN FREEZING RAIN. AS WE GO
THROUGH THE NIGHT...THAT WARM NOSE SHOULD ERODE...AND A CHANGEOVER
TO SNOW AND SLEET IS LIKELY. EITHER WAY...QPF VALUES THROUGHOUT
THE OVERNIGHT PERIOD ARE LOW. THE HIGHEST VALUES ARE 0.25" AT MOST
OVER THE EASTERN HALF OF THE AREA...WHICH MEANS A POSSIBILITY OF
SOME VERY LIGHT ICE ACCUMULATIONS FOR AREAS EAST OF INTERSTATE 65
AFTER MIDNIGHT. BECAUSE OF TODAY`S TEMPERATURES IN THE LOW TO
MIDDLE 40S AND THIS MORNING`S RAINFALL...I DON`T EXPECT ANY MORE
THAN 0.10" OF ICE TO ACCUMULATE ANYWHERE. HERE`S THE PROBLEM:
INCONSISTENT MODEL DATA OVER THE LAST FEW DAYS CONCERNING
TONIGHT`S PRECIPITATION TYPE HAS LEFT THIS FORECAST IN THE LOW TO
MEDIUM RANGE AS FAR AS CONFIDENCE. I AM GOING TO REFRAIN FROM
ISSUING ANY WINTER WEATHER ADVISORIES AT THIS TIME...AND TAKE A
LOOK AT THE NEXT SET OF FORECAST SOUNDINGS. IF WE CAN GET SOME
CONSISTENCY...I MAY CONSIDER A WW ADVISORY FOR THOSE EASTERN
COUNTIES LATE TONIGHT.

AS THE MOISTURE PULLS OFF TO THE EAST TUESDAY MORNING...SOME
FLURRIES ALONG AND EAST OF I-65 MAY BE POSSIBLE THROUGH 15Z...BUT
THIS SHOULD BE OF NO CONSEQUENCE.

LONG TERM...WEDNESDAY THROUGH THE WEEKEND.

WHILE THE MOISTURE WILL FINALLY COME TO AN END BY TUESDAY AFTERNOON
AND THE SUN WILL RETURN TO THE STATE...OVERNIGHT TEMPERATURES ARE
GOING TO FALL INTO THE TEENS BY THURSDAY MORNING.  OUR SAVING GRACE
LOOKS TO BE THE ORIGINATING LOCATION OF THE AIR MASS THAT WILL
INVADE THE MID-SOUTH DURING THE MIDDLE OF THE WEEK.  IT SEEMS TO BE
COMING FROM THE PACIFIC NW...WHICH WOULD SUGGEST A MUCH MORE
MARITIME POLAR AIR MASS...VERSUS ONE THAT COMES DOWN FROM CANADA AND
CAN BE MUCH COLDER.

MID-WEEK HIGH PRESSURE WILL MOVE OFF TO THE EAST BY FRIDAY AHEAD OF
A SOUTHERN STREAM SYSTEM THAT IS PROGGED TO MOVE INTO THE REGION
FRIDAY NIGHT.  LONG RANGE GUIDANCE IS IN PRETTY GOOD AGREEMENT ABOUT
TIMING SO FAR WITH THIS EVENT...SO I WILL BUMP POPS FRIDAY NIGHT AND
SATURDAY...AND WHILE THIS LOOKS TO BE MOSTLY A COLD RAIN
EVENT...THERE IS A DECENT AMOUNT OF ENERGY ASSOCIATED WITH THE
SHORTWAVE AS IT MOVES OVER THE STATE.  SOME ELEVATED THUNDER IS
POSSIBLE FRIDAY NIGHT...BUT WILL STICK WITH JUST RAIN RIGHT NOW AS
GUIDANCE MIGHT BE AGREEING ON TIMING...BUT DEFINITELY IS NOT
AGREEING ON THE OVERALL EVOLUTION.  THE SATURDAY AFTERNOON AND NIGHT
WRAP-AROUND MOISTURE IS WHAT WILL HAVE TO BE MONITORED FOR MORE
POSSIBLE FROZEN PRECIP.

UNGER

&&

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

$$

49