-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KILN 060552
AFDILN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON OH
1252 AM EST FRI DEC 6 2013

.SYNOPSIS...
WINTER STORM WILL IMPACT THE OHIO VALLEY BEGINNING THIS EVENING
AND CONTINUING THROUGH FRIDAY EVENING. HEAVY MIXED WINTER
PRECIPITATION WILL SLOWLY TRANSITION TO ALL SNOW BEFORE ENDING
FRIDAY EVENING. SIGNIFICANT SNOW ACCUMULATIONS ARE LIKELY FROM
SOUTHERN INDIANA INTO CENTRAL OHIO...AND A BAND OF GLAZE ICE
ACCUMULATION TOPPED BY A FEW INCHES OF SNOW WILL BE LIKELY ALONG
AND SOUTH OF THE OHIO RIVER IN KENTUCKY INTO PARTS OF SOUTH
CENTRAL OHIO. HEAVY...POTENTIALLY FLOODING RAIN...WILL IMPACT
PARTS OF EASTERN KENTUCKY INTO SOUTHEAST OHIO. IT WILL MOST
CERTAINLY BE A SIGNIFICANT CHANGE FROM THE 60 DEGREE TEMPERATURES
SEEN OVER PARTS OF THE AREA IN THE PAST FEW DAYS. YET ANOTHER
WINTER SYSTEM WILL BRING MORE POTENTIAL FOR MIXED-PHASE
PRECIPITATION BEGINNING SUNDAY AND LINGERING INTO MONDAY ACROSS
MUCH OF THE AREA. THAT SYSTEM LOOKS TO HAVE LESS MOISTURE
AVAILABLE TO WORK WITH...BUT MAY STILL HAMPER TRAVEL OVER THE OHIO
VALLEY.

&&

.NEAR TERM /THROUGH TODAY/...
LIKE WITH MANY SIGNIFICANT WINTER SYSTEMS IN THE OHIO VALLEY...THE
BOTTOM LINE IS A HIGH-CONFIDENCE HEAVY PRECIPITATION EVENT FOR THE
AREA...BUT LOW CONFIDENCE IN THE WAVY/WAFFLING TRANSITION ZONE AS
ARCTIC AIR SEEPS INTO THE AREA AND IMPINGES ON A VERY ATYPICALLY
WARM AIRMASS. SO WHILE WE FEEL CERTAIN ON MANY AREAS SEEING A GOOD
AMOUNT OF WINTRY PRECIPITATION...THE AMOUNTS OF EACH INDIVIDUAL
TYPE ARE PARTICULARLY LOW CONFIDENCE...AND FOR THIS STORM...THAT
LOW CONFIDENCE ZONE IS CENTERED SQUARELY ON THE I-71 CORRIDOR
INCLUDING CINCINNATI...WILMINGTON...AND COLUMBUS.

LATEST OBSERVATIONAL TRENDS INDICATE COLD FRONT HAS EXITED THE WFO
ILN FORECAST AREA TO THE EAST. BAND OF RAIN/STORMS ACCOMPANYING
THIS HAS SHIFTED EAST...AND ALREADY BEGINNING TO SEE IMPACT OF
INCREASING DEEP-LAYERED FRONTOGENESIS /FGEN/ AS RAIN/MIX IS
DEVELOPING TO OUR WEST/SOUTHWEST AND SPREADING DOWNSTREAM TOWARD
THE AREA. SFC TEMPS HAVE DROPPED BELOW FREEZING ACROSS WRN IND
WHERE FZRA HAS RECENTLY BEEN REPORTED. WHILE MUCH OF THIS UPCOMING
EVENT WILL BE DRIVEN BY THERMODYNAMICS /FGEN FORCING IN RIGHT
ENTRANCE REGION OF INCREASING UPPER LEVEL JET/...THERE IS A SUBTLE
MID LEVEL WAVE SEEN IN WV/IR LOOPS THIS AFTERNOON OVER OK/KS
SPREADING QUICKLY DOWNSTREAM TOWARD THE AREA. BUT UNLIKE MOST
SIGNIFICANT WINTER WEATHER SYSTEMS...THIS SYSTEM DOES NOT HAVE A
DEEPENING/CLOSING OFF 700-500MB CYCLONE OR PV-DRIVEN FORCING...BUT
IT DOES HAVE AN EXTREMELY IMPRESSIVE MID/UPPER LEVEL JET /UP TO
180KTS AT 250MB BY 18Z FRIDAY OVER ONTARIO/ AS THE MASSIVE/COLD
LONGWAVE TROUGH WHICH HAS BEEN CENTERED TO OUR WEST IMPINGES ON
THE STOUT/STUBBORN/WARM SUBTROPICAL RIDGE OVER THE FAR SOUTHEAST.
THE HEIGHT GRADIENT COMPRESSION IS HELPING DRIVE THE INTENSIFYING
JET...AND FGEN FIELDS OVER A DEEP LAYER REALLY RESPOND THIS
EVENING THROUGH FRIDAY AHEAD/DOWNSTREAM OF THE WEAK FEATURE
EJECTING OUT OF THE PLAINS. THUS...EXPECT WAVES/BANDS OF
PRECIPITATION TO CONTINUE TO DEVELOP AND PUSH ACROSS THE AREA
TONIGHT THROUGH FRIDAY EVENING...WITH DEFINITE PERIODS OF MORE
INTENSE PRECIPITATION AS THE INDIVIDUAL FGEN REGIONS TRANSLATE
THROUGH THE FLOW.

OF COURSE ALL OF THIS PRECIPITATION FORCING IS OCCURRING AS THE
AIRMASS COOLS SLOWLY WITH MODIFIED ARCTIC AIR SEEPING IN. NOT
SURPRISINGLY...A LITTLE FASTER AT THE SURFACE DUE TO THE DENSITY
OF THE LOW LEVEL AIRMASS...AND THUS THE LIKELIHOOD OF A NARROW
RIBBON OF SLEET/FREEZING RAIN. AND UNFORTUNATELY...AS THAT WEAK
WAVE TO OUR SOUTHWEST MOVES IN...THIS TRANSITION ZONE SLOWS/STALLS
AND WAFFLES RIGHT OVER THE AREA...AND LENDS TO A MUCH LOWERED
CONFIDENCE IN DETERMINISTIC WINTER PRECIPITATION AMOUNTS.

THE BIGGEST CHANGE SEEN IN DETERMINISTIC NWP ON 05.12Z RUNS WAS A
SHIFT IN NCEP GUIDANCE /NAM AND GFS/ TO A SLOWER SEEP OF COLDER
AIR ALOFT /OR IN OTHER WORDS A LONGER DURATION OF FREEZING RAIN
POTENTIAL/. NON-NCEP GUIDANCE /ECMWF...CMCREG...CMCGLB/ HAVE NOT
WAVERED IN ALLOWING COLDER AIR TO SEEP IN A SHIFT THIS ALL TO
SNOW. SO CHANGES IN TODAY/S FORECAST WERE A NOD TOWARD NCEP
GUIDANCE AND ALLOW MORE POTENTIAL FOR GLAZE-ICE ACCUMULATION VIA
FREEZING RAIN...ESPECIALLY ALONG AND JUST EAST OF I-71 INCLUDING
CINCINNATI...WILMINGTON...AND AREAS SOUTH OF COLUMBUS. IN
FACT...TAKEN VERBATIM...THE 05.12Z NAM WOULD ARGUE FOR SIGNIFICANT
/HIGH-IMPACT ICING IN THIS CORRIDOR. POSSIBLE...YES...BUT THIS WAS
A SHIFT IN CONTINUITY FOR THE NAM...AND REALLY HAS VERY LITTLE
SUPPORT FROM THE OTHER GUIDANCE. THE 05.12Z GFS SITS AT A VERY
NICE MIDDLE-ROAD...BETWEEN THE NAM AND MUCH COLDER NON-NCEP
GUIDANCE. THUS USED GFS THERMAL PROFILES TWEAKED A BIT COLDER TO
FIT IT SQUARELY IN THE MIDDLE OF THE 05.12Z DETERMINISTIC NWP
ENVELOPE...NOT NEARLY AS "ICE STORM" LOOKING AS THE NAM...BUT NOT
NEARLY AS "ALL SNOW" AS THE CMC/ECMWF. PERHAPS NOT
SURPRISINGLY...THE THERMAL FIELDS OF THE GFS ALIGN CLOSELY WITH THE
05.09Z SREF MEAN. TOUGH FORECAST...WHEN THE GAMUT FROM SIGNIFICANT
SNOW (6-10") OR SIGNIFICANT ICE (0.25"-0.50") ROUGHLY ARE
JUXTAPOSED ON TOP OF EACH OTHER AMONG GUIDANCE...AND SEPARATION OF
SAID DISCREPANCIES IS NO MORE THAN A TIER OR TWO OF COUNTIES. COBB
TECHNIQUES RUN AT CINCINNATI BEAR THIS OUT...FORECASTING 0.75" ICE
ACCUMULATION AND 3" SNOW /NAM/ TO 0.50" ICE AND 9" OF SNOW
/GFS/...TO VERY LITTLE ICE AND 6"+ SNOW /ECMWF/. THUS...IT GOES
WITHOUT SAYING THAT GRADIENTS IN MY FORECAST TODAY ARE LIKELY
OFF...BUT REPRESENT THE CONSENSUS OF SFC AND LOW LEVEL THERMAL
FIELDS. FORECAST DETAILS STILL APT TO SHIFT.

THE 05.12Z GFS FORECAST SOUNDINGS SUGGEST PRECIPITATION SPREADING
IN THIS EVENING WILL MIX/CHANGE TO SLEET/FREEZING RAIN IN THE WEST
BY MID EVENING AND SPREAD INTO THE I-71 CORRIDOR NEAR OR JUST
AFTER MIDNIGHT. A FAIRLY RAPID CHANGE TO SNOW IS EXPECTED FAR WEST
INCLUDING SERN IND/WCNTL OH AS COLD AIR DRIVES IN...BUT SOUNDINGS
"STALL" THE EROSION OF WARM AIR ALOFT THROUGH ABOUT 18Z IN THE
I-71 CORRIDOR LATE TONIGHT INTO MUCH OF FRIDAY MORNING...EVEN
CONSIDERING WET BULB PROCESSES...MAINTAINING A PARTIALLY MELTING
ELEVATED WARM LAYER UP TO 1.5C...LIKELY NOT WARM ENOUGH FOR
COMPLETE MELTING /AND THUS A HIGHER FZRA THREAT/. CROSS SECTIONS
NORMAL TO THICKNESSES IN THE RIGHT ENTRANCE REGION OF THE JET
SUGGEST A SLOPED REGION OF STRONG FGEN ACROSS THE AREA TONIGHT
THROUGH FRIDAY...INDICATING TRANSIENT BANDS OF HEAVIER PCPN...AND
SOME QUITE HEAVY LIKELY FRIDAY CONSIDERING AMPLE/DEEP NEGATIVE
SATURATED GEOSTROPHIC POTENTIAL VORTICITY ATOP THE FGEN FORCING
REGION AND VERTICAL MOTION MAXIMUM. THIS SUGGESTS THE POTENTIAL
RELEASE OF SLANTWISE INSTBY BY FGEN CIRCULATIONS. STILL SEEING TWO
DISTINCT PERIODS OF HEAVIER PRECIPITATION POTENTIAL...ONE
TONIGHT...AND ONE LATE FRIDAY MORNING INTO TOMORROW AFTERNOON...THE
LATTER OF WHICH WILL DRIVE MOST OF THE WINTRY ACCUMS...AND MAY
INCLUDE 1"/HR SNOW RATES FM SERN IND UP THROUGH THE DAYTON AREA TO
WEST OF CMH.

SO THE POTENTIAL IS THERE FOR BOTH A BAND OF HEAVY SNOWFALL /6-10"/
FROM SRN IND INTO WCNTL OH...AND A BAND OF HEAVY MIXED
SLEET/FREEZING RAIN/SNOW ALONG THE I-71 CORRIDOR. SOUNDINGS LOOK
AWFULLY SLEETY IN THIS CORRIDOR...BUT WE/RE IN THE NOISE LEVEL OF
MODEL ACCURACY IN TERMS OF THE ELEVATED WARM LAYER WHERE A DEGREE
EITHER DIRECTION COULD CHANGE THE NAME OF THE GAME...SO THERE COULD
BE SIGNIFICANT SNOW OR SIGNIFICANT GLAZE ICE IN THIS REGION TOO.
JUST TOO TOUGH TO TELL. FURTHER EAST IT APPEARS THE WAVERING NATURE
OF THE THERMAL ZONE WILL ALLOW MUCH OF THE PRECIP TO FALL AS
RAIN...AND THIS AREA MAY NEED SOME FLOOD HEADLINES AS WE SEE THIS
EVOLVE. THERE IS LIKELY TO BE A STRONG GRADIENT OF WINTER ACCUMS
ACROSS NERN KY INTO SCNTL OH...AND HAVE TRIED TO GRADIENT THIS AS
BEST AS POSSIBLE IN GRIDDED FORECAST.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM SATURDAY/...
SYSTEM SHIFTS OUT QUICKLY FRIDAY NIGHT WITH RAPIDLY IMPROVING
CONDITIONS BUT COLD TEMPS BURROWING IN OVER FRESH SNOW FIELD. HAVE
TAKEN SAT MAX TEMPS DOWN A FEW DEGREES...WITH SKIES BECOMING
MOSTLY SUNNY. AHEAD OF NEXT WINTER SYSTEM DISCUSSED BELOW.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
THE ILN CWA WILL RECEIVE ONLY A BRIEF REPRIEVE FROM WINTER WEATHER
ON SATURDAY...BEFORE ANOTHER STORM SYSTEM AFFECTS THE REGION LATE
SATURDAY NIGHT THROUGH EARLY MONDAY.

THE OVERALL WEATHER PATTERN IS BEING MODELED WITH A GOOD DEGREE OF
CONSISTENCY THROUGH TUESDAY...PROVIDING CONFIDENCE IN THE LARGE
SCALE FORECAST FEATURES WELL BEYOND THE END OF THE SUNDAY-TO-MONDAY
STORM SYSTEM. AFTER THIS SYSTEM MOVES AWAY...SURFACE HIGH PRESSURE
IS FORECAST TO SETTLE OVER THE OHIO VALLEY. AS THE HIGH MOVES AWAY
AND WEAKENS...SIGNIFICANT DISAGREEMENTS DEVELOP WITH REGARDS TO
UPSTREAM JET ENERGY AND TROUGHING IN THE SOUTHERN STATES...TWO
FACTORS THAT MAY POTENTIALLY PROVIDE SOME WEATHER IMPACTS TO THE
AREA LATER IN THE WEEK.

OBVIOUSLY...THE FORECAST FOCUS WILL BE ON THE SECOND HALF OF THE
WEEKEND...WITH THE POTENTIAL FOR ANOTHER SET OF CHALLENGING MIXED
PRECIPITATION FORECASTS. WEAK HIGH PRESSURE OVER THE OHIO VALLEY AND
SOUTHERN GREAT LAKES IS FORECAST TO MOVE NORTHEAST OF THE REGION
SATURDAY NIGHT...AS TROUGHING OVER THE PLAINS AMPLIFIES AS IT
LUMBERS TO THE EAST. BROAD AMBIENT SURFACE LOW PRESSURE OVER THE
SOUTHEASTERN STATES WILL EVENTUALLY MAKE ITS WAY NORTHWARD AS A
TROUGH...COMBINING SOMEWHAT WITH A DEVELOPING SURFACE LOW DEVELOPING
AHEAD OF THE MID-LEVEL TROUGH AXIS. MOST OF THE MODEL QPF RESPONSE
AND ENHANCED RH THAT IS FORECAST TO ENVELOP THE OHIO VALLEY WILL BE
THE RESULT OF THE SOUTHERN STREAM OF MOISTURE. HOWEVER...CAUGHT
SOMEWHAT BETWEEN THE TWO STREAMS...THE ILN CWA IS FORECAST TO ONLY
BRIEFLY ENTER A REGIME OF PARTICULARLY DEEP MOISTURE...AND MODEL QPF
OUTPUT IS NOT SIGNIFICANT (STORM TOTAL QPF RANGES FROM ABOUT AN INCH
IN THE SOUTHEAST TO ONLY ONE OR TWO TENTHS IN THE NORTHWEST).
DESPITE THIS...CONFIDENCE HAS INCREASED ENOUGH IN THE OVERALL
SCENARIO TO USE 100-POPS FOR MUCH OF THE ILN CWA...DROPPING TO
LIKELY IN THE FAR NORTHWEST.

UNTIL THE EVENT GETS A LITTLE CLOSER AND MESOSCALE MODELS CAN PICK
UP ON SOME OF THE SPECIFICS OF THE FORCING (SUCH AS FRONTOGENESIS OR
DEFORMATION PLACEMENT)...IT APPEARS (IN GENERAL) THAT THE
LIQUID-EQUIVALENT PRECIPITATION OUTPUT MAY NOT BE ENOUGH TO TURN
THIS EVENT INTO ONE WITH SIGNIFICANT WIDESPREAD IMPACTS. THAT WILL
END UP BEING A CRUCIAL FACTOR...BECAUSE THERMAL PROFILES ARE
DEFINITELY GOING TO BE SUPPORTIVE OF A WIDE RANGE OF WINTER
PRECIPITATION TYPES. COMING OUT OF A SNOW EVENT AND A VERY COLD
PERIOD ON SATURDAY...AMBIENT TEMPERATURES (GROUND AND AIR) WILL BE
QUITE LOW. AT THE TIME OF PRECIPITATION ONSET EARLY SUNDAY
MORNING...SNOW WILL BE THE FAVORED PRECIPITATION TYPE. AS AN
ELEVATED WARM FRONT MOVES NORTH INTO THE REGION THROUGH SUNDAY
MORNING AND INTO THE AFTERNOON...CONDITIONS WILL EVENTUALLY SUPPORT
PRECIPITATION TYPES CHANGING FROM SNOW TO A MIX OF FREEZING RAIN AND
SLEET. AS CONDITIONS CONTINUE TO WARM...THE SURFACE TEMPERATURES
WILL WALK A VERY FINE LINE ON SUNDAY AND SUNDAY NIGHT...MAKING THE
EVENTUAL FORECAST BETWEEN RAIN AND FREEZING RAIN CHALLENGING AND
PIVOTAL. AS THE SYSTEM MOVES AWAY EARLY ON MONDAY...A BRIEF PERIOD
OF MIXED PRECIPITATION WILL BE POSSIBLE AS COLDER AIR MOVES IN
AGAIN...BEFORE DRY CONDITIONS TAKE OVER LATE MONDAY INTO MONDAY
NIGHT.

THOUGH FAR TOO EARLY TO SPECULATE ON NUMBERS...THE EARLY INDICATIONS
SUGGEST THAT THIS MAY END UP AS A MULTI-FACETED HIGHER-END
ADVISORY-LEVEL EVENT (BASED ON BOTH SNOW AND ICE
ACCUMULATIONS)...IMPACTING MOST (IF NOT ALL) OF THE ILN CWA.
MESOSCALE FEATURES WOULD HAVE TO BE PINPOINTED IN ORDER TO DETERMINE
IF WATCHES OR WARNINGS COULD EVENTUALLY BECOME NECESSARY...BUT IF
FUTURE MODEL RUNS INDICATE AN INCREASE IN MOISTURE CONTENT FROM THE
CURRENT FORECAST...THAT WOULD ALSO BE OF CONCERN. RIGHT NOW...THE
HEAVIEST QPF RESPONSE IS IN THE SOUTHEASTERN CWA...WHERE A
SIGNIFICANT PERCENTAGE OF THE PRECIPITATION IS FORECAST TO FALL AS
RAIN.

BEYOND MONDAY...BEHIND ANOTHER COLD FRONT...MOST OF NEXT WEEK
APPEARS DRY BUT FRIGID. RAW MODEL TEMPERATURES APPEAR TO BE TOO
HEAVILY INFLUENCED BY AN EXPECTED SNOWPACK (WITH MIN TEMP BULLSEYES
WELL INTO NEGATIVE NUMBERS ON SEVERAL DIFFERENT MODELS).
HOWEVER...THE TREND IS CLEAR...AND BOTH MAX AND MIN TEMPS HAVE BEEN
LOWERED FOR MUCH OF THE WEEK. WHILE TEMPERATURES SHOULD EVENTUALLY
GET (BARELY) ABOVE FREEZING FOR MOST OF THE ILN CWA EARLY ON
MONDAY...SUB-FREEZING TEMPS ARE FORECAST FOR THE NEXT FOUR DAYS
STRAIGHT...EVEN FOR MAXES. NON-DIURNAL TEMPERATURES WERE DRAWN IN
FOR THE ENTIRE PERIOD FROM SATURDAY NIGHT THROUGH MONDAY.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
WIDESPREAD SNOW WILL RESULT IN MVFR CONDITIONS AT BEST FOR THE
NEXT 24 HOURS WITH THE TAIL END OF THE SNOW OCCURRING TOWARDS THE
END OF THE FORECAST. MODELS ARE SUGGESTING A HEAVIER BAND OF SNOW
OCCURRING THIS AFTERNOON AND VLIFR CONDITIONS ARE POSSIBLE BETWEEN
18Z AND 2Z WITH A HEIGHTENED CHANCE ALONG THE I-71 CORRIDOR FROM
19-23Z.

OUTLOOK...MVFR TO IFR CIGS AND VSBYS LIKELY SUNDAY INTO MONDAY
WITH EXCEPTION OF DAYTON. SIGNIFICANT ICE POSSIBLE SUNDAY ALL
LOCATIONS.
-- End Changed Discussion --

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
OH...WINTER STORM WARNING UNTIL 1 AM EST SATURDAY FOR OHZ042>044-
     051>053-060>062.
     WINTER WEATHER ADVISORY UNTIL 1 AM EST SATURDAY FOR OHZ026-034-
     035.
     WINTER STORM WARNING UNTIL 1 AM EST SATURDAY FOR OHZ045-046-
     054>056-063>065-070>073-077>080.
     WINTER WEATHER ADVISORY FROM 7 AM THIS MORNING TO 1 AM EST
     SATURDAY FOR OHZ074-081-082-088.
KY...WINTER STORM WARNING UNTIL 1 AM EST SATURDAY FOR KYZ089>097.
     WINTER WEATHER ADVISORY FROM 7 AM THIS MORNING TO 1 AM EST
     SATURDAY FOR KYZ098>100.
IN...WINTER STORM WARNING UNTIL 1 AM EST SATURDAY FOR INZ050-058-
     059.
     WINTER STORM WARNING UNTIL 1 AM EST SATURDAY FOR INZ066-
     073>075-080.
-- End Changed Discussion --

&&

$$
SYNOPSIS...BINAU
NEAR TERM...BINAU
SHORT TERM...BINAU
LONG TERM...HATZOS
AVIATION...FRANKS