River Flood Advisory 57, NWS Nashville, TN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NASHVILLE TN
638 PM CST SUN NOV 27 2011

.UPDATE...FOR 00Z AVIATION FORECAST

&&

.AVIATION...
POOR FLYING CONDITIONS WILL CONTINUE WITH WIDESPREAD RAIN ACROSS
THE TENNESSEE VALLEY THROUGH THIS FORECAST CYCLE. LOOK FOR IFR
CONDITIONS WITH LIFR AT TIMES. THIS EVENING THE WEATHER MAP IS
SHOWING AN ELONGATED SURFACE LOW ORIENTED NORTH TO SOUTH DOWN
THROUGH EASTERN TENNESSEE WITH CLOSED UPPER LOW OVER LOWER
MISSISSIPPI VALLEY. UPPER LOW WILL MOVE INTO THE TENNESSEE VALLEY
MONDAY NIGHT AND TUESDAY WITH A POSSIBLE MIX OF SNOW AND RAIN
ACROSS THE AREA LATE MONDAY NIGHT AND TUESDAY.

BOYD
&&

.PREV DISCUSSION... /ISSUED 307 PM CST SUN NOV 27 2011/

DISCUSSION...HIGH AMPLITUDE PATTERN OVER THE US WITH A STRONG H5
RIDGE OVER THE WRN ATLANTIC A DEEP TROUGH OVER THE MS VALLEY AND A
LARGE H5 RIDGE OVER THE WEST. BOTTOM OF THE UPPER TROUGH TO OUR
WEST IS EXPECT TO CLOSE OFF AND BRING A STRONG H5 LOW OVER THE MIDSTATE
ON MON NGT AND TUE. THE LOW MOVES QUICKLY NEWD TUE NGT AND WED...BEING
POSITIONED OVER WRN NY BY WED AM.

THIS PRESENT AN INTERESTING SITUATION FOR OUR AREA. WITH EXTENSIVE
COLUMN MOISTURE OVER THE AREA AND A STRONG DYNAMICS MOVING INTO
THE MIDSTATE...HEAVY RAINFALL IS A DEFINITE POSSIBILITY.
HOWEVER...THE SFC LOW...THAT FORMS IN RESPONSE TO THE UPPER LOW
CLOSING OFF OVER THE DEEP SOUTH...MOVES NORTH INTO KY MON EVE
SHUTTING OFF THE HEAVY RAINFALL POSSIBILITIES FOR THIS AREA. THUS
HAVE SHORTENED THE END OF THE FLOOD WATCH FROM TUE AM TO MON EVE
AT 6 PM.

HOWEVER...THERE REMAINS ANOTHER QUESTION. THAT IS THE POSSIBILITY
OF FREEZING/FROZEN PRECIP. THE 1000-850MB LAYER TEMP HAS ALWAYS
BEEN A GOOD DEMARCATION LINE BETWEEN LIQUID AND FREEZING PRECIP.
THERE SEEMS TO BE PLENTY OF AGREEMENT THAT THE PERCIP WILL FORM AS
SNOW ALOFT BUT THE QUESTION IS WHAT HAPPENS AS IT FALLS THROUGH
THE LOWER LAYERS. THERE IS SOME ADHERENCE TO THE IDEA THAT DYNAMIC
COOLING WILL OCCUR AND LOWER FREEZING TEMPS ALOFT DOWN TOWARD THE
SFC...IF SUFFICIENT PRECIP IS OCCURRING FOR THAT TO HAPPEN.
WHETHER OR NOT THIS WILL HAPPEN...IF AM UNSURE. SO THE BEST POLICY
FOR NOW IS TO GO WITH A RAIN/SNOW MIX ON MON NGT AND TUE AM. AS WE
GET CLOSER TO THIS TIME PERIOD MORE PRECISION IS POSSIBLE. GIVEN
THE ABOVE UNCERTAINTIES HAVE OMITTED ANY HINT OF SNOW ACCUMULATIONS.

THE SFC LOW PULLS NEWD INTO OK/NRN KY BY TUE AM AND THEN INTO THE
ERIE PA AREA BY TUE EVE. ANY CHANCE OF PRECIP OVER THE AREA SHUTS
OFF LATE TUE NGT WITH ONLY A HINT OF SNOW SHOWERS OVER THE NRN
PLATEAU WED AM.

SFC HIGH CROSSES THE AREA WED NGT AND THU WITH A DRY FRONTAL PASSAGE
ON FRI. OTHERWISE...NO SGFNT WX IN THIS PERIOD.

&&

.OHX WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH MONDAY AFTERNOON FOR TNZ007>011-
026>034-059>066-075-077>080-095.

&&

01

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE NASHVILLE TN
231 PM CST SUN NOV 27 2011

TNZ007>011-026>034-059>066-075-077>080-095-281130-
ROBERTSON-SUMNER-MACON-CLAY-PICKETT-CHEATHAM-DAVIDSON-WILSON-
TROUSDALE-SMITH-JACKSON-PUTNAM-OVERTON-FENTRESS-WILLIAMSON-MAURY-
MARSHALL-RUTHERFORD-CANNON-DE KALB-WHITE-CUMBERLAND-BEDFORD-
COFFEE-WARREN-GRUNDY-VAN BUREN-GILES-
231 PM CST SUN NOV 27 2011

...FLASH FLOOD WATCH IN EFFECT THROUGH MONDAY AFTERNOON...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR MIDDLE TENNESSEE.

.DAY ONE...TODAY AND TONIGHT

A COLD FRONT WILL MOVE ACROSS THE AREA TODAY AND THIS EVENING AND
BRING RAIN SHOWERS...SOME WITH LOCALLY HEAVY RAINFALL. PONDING OF
WATER IN LOW LYING AREAS IS LIKELY...AND FLOODING IS POSSIBLE. A
SLOW MOVING LOW PRESSURE AREA WILL MOVE NORTHWARD OUT OF THE GULF
COASTAL REGION AND UP ACROSS THE TENNESSEE VALLEY LATE
TONIGHT...KEEPING THE RAIN FALLING...SOME OF WHICH WILL BE LOCALLY
HEAVY.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

LOCALLY HEAVY RAINS ARE FORECAST TO CONTINUE...MAINLY OVER THE
EAST...THROUGH MONDAY AFTERNOON. FLASH FLOODING WILL REMAIN A
POSSIBILITY.

A TURN TO COLDER WEATHER WILL OCCUR LATE MONDAY NIGHT INTO TUESDAY...
WITH RAIN SHOWERS BECOMING MIXED WITH OR CHANGING TO SNOW SHOWERS.
MINOR SNOW ACCUMULATIONS ARE POSSIBLE...ESPECIALLY ON GRASSY AREAS...
MAINLY ACROSS SOUTHERN COUNTIES AND ALONG THE CUMBERLAND PLATEAU.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS AND LOCAL EMERGENCY MANAGEMENT OFFICIALS ARE ENCOURAGED TO
REPORT HEAVY RAINFALL AMOUNTS AND FLOODING TO THE NATIONAL WEATHER
SERVICE IN NASHVILLE.

TNZ005-006-022>025-056>058-093-094-281130-
STEWART-MONTGOMERY-BENTON-HOUSTON-HUMPHREYS-DICKSON-PERRY-HICKMAN-
LEWIS-WAYNE-LAWRENCE-
231 PM CST SUN NOV 27 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR MIDDLE TENNESSEE.

.DAY ONE...TODAY AND TONIGHT

A COLD FRONT WILL MOVE ACROSS THE AREA TODAY AND PRODUCE
WIDESPREAD SHOWERS...SOME OF WHICH MAY PRODUCE LOCALLY HEAVY
RAINFALL. PONDING OF WATER IN LOW LYING AREAS IS LIKELY. A SLOW
MOVING LOW PRESSURE AREA WILL MOVE NORTHWARD OUT OF THE GULF
COASTAL REGION AND UP ACROSS THE TENNESSEE VALLEY LATE
TONIGHT...KEEPING THE RAIN FALLING.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

A TURN TO COLDER WEATHER WILL OCCUR LATE MONDAY NIGHT INTO
TUESDAY... WITH RAIN SHOWERS BECOMING MIXED WITH OR CHANGING TO
SNOW SHOWERS. MINOR SNOW ACCUMULATIONS ARE POSSIBLE...ESPECIALLY
ON GRASSY AREAS.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS AND LOCAL EMERGENCY MANAGEMENT OFFICIALS ARE ENCOURAGED
TO REPORT HEAVY RAINFALL AMOUNTS AND FLOODING TO THE NATIONAL WEATHER
SERVICE IN NASHVILLE.

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