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000
FXUS61 KILN 010015
AFDILN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON OH
715 PM EST SAT FEB 28 2015

.SYNOPSIS...
A WARM FRONT WILL MOVE THROUGH THE OHIO VALLEY ON SUNDAY...WITH
SNOW AND RAIN EXPECTED ACROSS THE REGION. A STRONGER WEATHER
SYSTEM WILL MOVE THROUGH THE AREA ON TUESDAY AND
WEDNESDAY...BRINGING A SIGNIFICANT AMOUNT OF RAINFALL. HIGH
PRESSURE WILL BRING DRY CONDITIONS FOR THE END OF THE WEEK.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
A SIGNIFICANT AMOUNT OF WARM ADVECTION ALOFT IS ALREADY ONGOING
OVER THE OHIO VALLEY...ESPECIALLY AT 850MB AND ABOVE. HIGH AND MID
LEVEL CLOUDS ARE ALSO STREAMING INTO THE REGION. OVERALL...THE
SURFACE PRESSURE PATTERN IS QUITE WEAK...AND THIS WILL REMAIN THE
CASE THROUGHOUT THE NEXT COUPLE DAYS OF THE FORECAST.

LATER THIS EVENING...A LOW-LEVEL JET IN THE 925MB-850MB WILL
INCREASE IN INTENSITY...BEGINNING A MORE SIGNIFICANT TRANSPORT OF
MOISTURE INTO THE REGION. IN AN AREA OF WEAK CONVERGENCE ALONG AND
NORTH OF A SURFACE WARM FRONT...PRECIPITATION WILL OVERSPREAD THE
REGION DURING THE OVERNIGHT HOURS...BECOMING WIDESPREAD ACROSS THE
ILN FORECAST AREA BY SUNDAY MORNING. THE IMPACTS FROM THIS
PRECIPITATION WILL BE DISCUSSED IN THE SHORT TERM FORECAST
DISCUSSION.

ALTHOUGH TEMPERATURES MAY FALL AFTER SUNRISE TONIGHT...THE
INCREASING WARM ADVECTION IN THE LOW LEVELS WILL LEAD TO A REBOUND
AFTER 06Z. THUS...MIN TEMPS SHOULD OCCUR NEAR OR JUST AFTER
MIDNIGHT...AND MAY NOT BE MUCH LOWER THAN TEMPS CURRENTLY OBSERVED
THIS AFTERNOON.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY/...
A WARM FRONT IS EXPECTED TO MOVE NORTH THROUGH THE ILN FORECAST
AREA ON SUNDAY MORNING. AS THIS OCCURS...THETA-E ADVECTION WILL BE
STEADY ACROSS THE AREA...WITH THE ENVIRONMENT BECOMING FAIRLY
MOIST. ON SUNDAY MORNING AND EARLY AFTERNOON...MODEL SOUNDINGS
INDICATE SATURATION OR NEAR-SATURATION FROM THE SURFACE ALL THE
WAY THROUGH 10KFT. PRECIPITABLE WATER VALUES WILL RANGE FROM 0.5
TO 0.8 INCHES ACROSS THE FORECAST AREA...AND YET IT IS SNOW THAT
REMAINS THE BIGGEST CONCERN FOR THE SHORT TERM OF THE FORECAST.

THOUGH THE MOISTURE CONTENT WILL BE HIGH...OVERALL THE FORCING
INVOLVED WITH THIS WEATHER SYSTEM WILL BE FAIRLY WEAK AND
UNFOCUSED. IT IS CLEAR THAT THE GREATEST PRECIPITATION AMOUNTS
WILL SET UP THROUGH (OR JUST NORTH OF) THE MIDDLE OF THE ILN
FORECAST AREA...AND THAT THE EVENTUAL NORTHERNMOST EXTENT OF THE
RAIN-TO-SNOW TRANSITION WILL ALSO EXIST SOMEWHERE IN THIS
VICINITY. THE MODEL SPREAD IN THIS AREA OF TEMPERATURE TRANSITION
IS ACTUALLY NOT ALL THAT LARGE...AND THE NORTHERNMOST EXTREMES
AMONG THE SOLUTIONS ARE NOT AS FAR NORTH AS MIGHT BE EXPECTED WHEN
CONSIDERING OTHER WEATHER EVENTS OF THIS NATURE. THUS...THERE IS
CONFIDENCE THAT MIXED RAIN AND SNOW WILL BE ABLE TO MAKE IT NO
FURTHER NORTH THAN A LINE FROM ABOUT FRANKLIN COUNTY IN TO LICKING
COUNTY OH...AND THAT ANYWHERE NEAR THAT LINE WILL EXPERIENCE
MAINLY SNOW. THUS...THE HIGHEST SNOWFALL ACCUMULATIONS ARE
FORECAST JUST NORTH OF THAT LINE...ROUGHLY FROM RICHMOND IN TO
DELAWARE OH...WITH A SOLID SWATH OF 5 INCHES IN THE GRIDS.
ALTHOUGH MOISTURE IS PLENTIFUL...AND THUS QPF AMOUNTS ARE SOMEWHAT
HEAVY GIVEN THE WEAK FORCING...SNOW RATIOS WILL BE TOWARD THE LOW
END OF THE SCALE. IN FACT...GUIDANCE NUMBERS FROM WPC (12:1 TO
14:1) MAY WELL BE TOO HIGH. THERE WILL BE LITTLE CONTRIBUTION FROM
THE DENDRITIC GROWTH ZONE...WHICH WILL BE RESIDING SOMEWHERE
AROUND 15KFT AND ABOVE THE MAJORITY OF THE MOISTURE. WHAT THIS
EVENT HAS GOING FOR IT IS DURATION...WITH SNOW EXPECTED TO FALL
ACROSS A PERIOD OF AROUND 18 HOURS. IN ADDITION...THERE MAY BE
SOME ISOTHERM COMPACTION OCCURRING ACROSS THE NORTHERN ILN CWA ON
SUNDAY MORNING (ESPECIALLY IN THE 925MB-850MB LAYER)...WITH WEAK
FRONTOGENETIC SIGNATURES ON A FEW OF THE MODELS. THUS...SOME 6
INCH AMOUNTS WILL BE POSSIBLE...BUT WITH A LONG ENOUGH DURATION
THAT HAZARDS WORTHY OF A WARNING DO NOT SEEM LIKELY.

THE TRANSITION BETWEEN SNOW AND RAIN WILL UNDOUBTEDLY LEAD TO A
LITTLE LESS CERTAINTY IN THE FORECAST FURTHER TO THE SOUTH...WHERE
SNOW FORECAST TOTALS RANGE FROM 4 INCHES TO 1 INCH ACROSS A
STRETCH OF ONLY 30 MILES. OF ADDITIONAL CONCERN IS THE POTENTIAL
FOR ICE DURING THE MORNING HOURS. THERE IS A CLEAR SIGNAL FOR A
WARM LAYER NEAR 900MB PUSHING ABOVE THE COLDER AIR AT THE
SURFACE...GENERALLY ACROSS THE SOUTHERN THIRD OF THE FORECAST AREA
BETWEEN 07Z AND 13Z. HOWEVER...BUFKIT SOUNDINGS SHOW THIS LAYER TO
BE OF A FAIRLY SMALL MAGNITUDE...AND UNSATURATED. THIS IS NOT
TERRIBLY SUPPORTIVE OF A WHOLE LOT OF FULL HYDROMETEOR
MELTING...FAVORING A MIX OF FREEZING RAIN AND SLEET. THIS SEEMS
MOST LIKELY TO OCCUR IN THE SOUTHWESTERN PART OF THE CWA...WHERE A
TIER OF COUNTIES WAS ADDED TO THE WINTER WEATHER ADVISORY. THIS
ADDITION WAS BASED ON A COMBINATION OF SNOW AMOUNTS (AROUND AN
INCH) AND ICE POTENTIAL (PERHAPS UP TO FIVE HUNDREDTHS).5

TEMPERATURES SHOULD PEAK OUT IN THE 18Z-21Z TIME FRAME...MATCHING
THE NORTHERNMOST EXTENT OF THE RAIN-SNOW LINE. AFTER THIS...WINDS
WILL SHIFT TO THE WNW AND ALLOW COLD ADVECTION TO TAKE
OVER...QUICKLY CHANGING THE PRECIPITATION TYPE TO SNOW ACROSS THE
ENTIRE CWA. ADDITIONAL ACCUMULATIONS OF A FEW TENTHS (WITH PERHAPS
ANOTHER INCH IN CENTRAL OHIO) WILL BE POSSIBLE BEFORE SNOW COMES
TO AN END ON SUNDAY EVENING. TEMPERATURES ON SUNDAY NIGHT WILL
COOL FROM NW TO SE...AS SKIES ALSO BEGIN TO CLEAR OUT. IGNORING
THE RAW GFS NUMBERS...SHOULD RANGE FROM THE UPPER TEENS TO UPPER
20S.

ON MONDAY...DRY HIGH PRESSURE WILL BUILD INTO THE REGION...WITH
LIGHT WINDS AND MOSTLY SUNNY CONDITIONS.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
HIGH PRESSURE WILL QUICKLY MOVE OFF TO THE EAST MONDAY NIGHT AS
RETURN FLOW DEVELOPS ON THE BACK SIDE. WARM...MOIST ASCENT WILL
INCREASE TO OUR WEST DURING THE EVENING AND WILL SHIFT
EAST/NORTHEAST INTO THE REGION LATE MONDAY NIGHT INTO TUESDAY
MORNING. COLD AIR WILL BE IN PLACE AT THE SURFACE. THUS...AS PCPN
INITIALLY BEGINS AND BEFORE SATURATION...SNOW/SLEET/FREEZING RAIN
WILL OCCUR. AS SATURATION INCREASES...AND MAX TEMPS ALOFT
INCREASE...MORE AND MORE OF THE REGION WILL TRANSITION OVER TO A
PERIOD OF FREEZING RAIN. TEMPERATURES WILL CONTINUE TO WARM ALOFT
AND IN THE LOW LEVELS THROUGH TUESDAY MORNING WHICH SHOULD CHANGE
THE WINTRY PCPN TO RAIN FROM SOUTH TO NORTH. PRELIMINARY AMOUNTS
LOOK LIKE A TENTH OF AN INCH OR LESS OF ICING AND LESS THAN AN INCH
OF SNOW/SLEET.

MODELS CONTINUE TO INDICATE THAT A MID LEVEL S/WV WILL EJECT NE FROM
THE CENTRAL PLAINS TO THE WESTERN GREAT LAKES MONDAY AFTERNOON INTO
MONDAY EVENING. AS THIS OCCURS...A FAIRLY STRONG LLJ OF 60 TO 70
KNOTS ALONG WITH A DEEPENING SFC LOW WILL PUMP ANOMALOUSLY HIGH
PWATS INTO THE LOWER GREAT LAKES AND THE OHIO VALLEY.  THESE VALUES
ARE FORECAST TO BE BETWEEN 1.20 TO 1.40 INCHES...WHICH IS ABOUT 300
PERCENT ABOVE NORMAL FOR EARLY MARCH. THIS SCENARIO WILL BRING RAIN
TO THE REGION...MODERATE TO LOCALLY HEAVY. THERE WILL BE A CONCERN
FOR FLOODING GIVEN MOIST CONDITIONS AND SNOW PACK/STORED SNOW WATER
EQUIVALENT FROM SUNDAYS SYSTEM. ALTHOUGH MOST STREAMS/RIVERS ARE
RUNNING LOW ATTM...SNOW MELT AND MODERATE/HEAVY RAIN WILL RESULT IN
RAPID RISES. IN ADDITION...THE PROLONGED COLD HAS ALLOWED ICE TO
FORM ON MANY RIVERS...CREEKS AND STREAMS...SOME THICK IN SPOTS.
WATER FLOWING INTO FAIRLY ICE COVERED BASINS WILL HAVE A HARD TIME
DRAINING WHICH MAY LEAD TO FLOODING AND/OR ICE JAMS. ANOTHER
CONCERN...BUT WITH LOW CONFIDENCE ATTM...WILL BE WHETHER A LOW
TOPPED QLCS (MAYBE A LINE OF FOCUSED SHOWERS WITH LITTLE TO NO
THUNDER) GETS GOING ALONG THE FRONT IN A REGIME OF HIGH SHEAR/LOW
CAPE ALONG WITH STRONG LOW LEVEL FRONTAL CONVERGENCE. TO ADD TO THE
COMPLEXITY...WHERE SNOW COVER CAN HOLD ON...IT MAY ADD A SHALLOW
STABLE LAYER TO ANY QLCS DEVELOPMENT. ATTM...THE BEST CHANCE FOR A
POTENTIAL QLCS TO HAVE AN AFFECT SEEMS MORE POSSIBLE ALONG AND SOUTH
OF THE OHIO RIVER. THE WARMEST TEMPERATURES OF THE WEEK WILL OCCUR
TUESDAY NIGHT AHEAD OF FRONT AS TEMPERATURES WARM INTO THE 40S AND
50S. A FEW LOWER 60S MAY OCCUR IN OUR FAR SE COUNTIES. WILL CONTINUE
TO MENTION THE WINTRY AND FLOOD THREATS IN THE HWO. WILL HOLD OFF ON
THE MENTION OF THE QLCS POTENTIAL ATTM. WOULD LIKE TO SEE A FEW MORE
RUNS AND SOME HIGH RESOLUTION MODELS.

A COLD FRONT IN ASSOCIATION WITH THE MID LEVEL ENERGY/SFC LOW WILL
PUSH SOUTHEAST THROUGH THE REGION LATE TUESDAY NIGHT INTO WEDNESDAY
MORNING. THIS WILL BE FOLLOWED EVENTUALLY BY AN ARCTIC FRONT. MODELS
ARE NOW HEDGING ON WHETHER OR NOT ADDITIONAL ENERGY MOVING THROUGH
THE SOUTHWEST FLOW ALOFT WILL ALLOW FOR A SECONDARY SURGE OF
PRECIPITATION NORTH INTO OUR REGION LATER ON WEDNESDAY. HAVE KEPT
SOME CONTINUITY WITH THE PREVIOUS FORECAST TO ALLOW FOR A HIGHER
CHANCE FOR PCPN FOR POINTS ALONG AND SOUTH OF THE OHIO RIVER. PCPN
IN THE CAA WILL TRANSITION FROM RAIN TO SNOW. GIVEN LOW CONFIDENCE
ON SECONDARY SURGE...PINPOINTING POTENTIAL SNOW AMOUNTS ATTM WOULD NOT
BE PRUDENT.

THE ENTIRE SYSTEM FINALLY GETS SHUNTED FAR ENOUGH EAST FOR
PRECIPITATION TO END WEDNESDAY NIGHT. HIGH PRESSURE WILL BUILD IN
THURSDAY AND FRIDAY BRINGING DRY CONDITIONS BUT A RETURN TO BELOW
NORMAL TEMPERATURES. A WEAK FRONT IS FORECAST TO DROP THROUGH THE
REGION ON SATURDAY. THIS FRONT APPEARS MOISTURE STARVED.
TEMPERATURES WILL MODERATE SOME AHEAD OF THE FRONT ON SATURDAY BUT
WILL STILL AVERAGE BELOW NORMAL.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
LATEST RUNS OF THE HIRES MODELS ARE INDICATING THAT THE INITIAL
SHOT OF SNOW THAT IS WORKING UP THE OHIO VALLEY WILL ONLY GRAZE
CVG/LUK...SO ADJUSTED THE FORECAST FOR SOME MVFR CIGS AND VSBYS
FROM 04-06Z DUE TO THE SNOW. ADDITIONAL LIFT COMES IN TOWARDS 12Z
CAUSING PCPN TO REDEVELOP. SOUNDINGS ARE INDICATING THAT PCPN MIGHT
FALL AS FZRA/PL BY THAT TIME...BEFORE TRANSITIONING TO RAIN AFTER
SUNRISE.

FARTHER N INTO ILN...THE SNOW SHOULD LAST LONGER BEFORE THE WARMER
AIR BEGINS TO MIX IN AFTER 12Z. KEPT A RA/SN MIX FOR MUCH OF THE
DAYLIGHT HOURS AFTER 14Z AS THE RAIN/SNOW JUST SEEMS TO HANG OVER ILN.

KDAY SHOULD REMAIN ALL SNOW THROUGH THE EVENT...WITH THE HEAVIEST
SNOW 10-14Z. A COUPLE OF THE MODELS ARE SUGGESTING A BRIEF
BREAK/DECREASE IN INTENSITY IN THE PCPN AROUND 18Z...SO TRIED TO
SHOW THAT IN THE TAFS.

COLDER AIR BEGIN TO WORK BACK IN LATE SUNDAY AFTERNOON GRADUALLY
CHANGING THE PCPN BACK TO SNOW FOR ALL LOCATIONS.


OUTLOOK...MVFR/IFR CEILINGS LIKELY INTO SUNDAY NIGHT. MVFR/IFR
CEILINGS AND VISIBILITIES ARE POSSIBLE TUESDAY INTO WEDNESDAY WITH
RAIN AND SNOW.

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
OH...WINTER WEATHER ADVISORY UNTIL 10 PM EST SUNDAY FOR OHZ026-034-
     035-042>046-051>056-060>062.
     WINTER WEATHER ADVISORY UNTIL 3 PM EST SUNDAY FOR OHZ063>065-
     070>072-077.
     WINTER WEATHER ADVISORY UNTIL 10 AM EST SUNDAY FOR OHZ078.
KY...WINTER WEATHER ADVISORY UNTIL 10 AM EST SUNDAY FOR KYZ089>093.
IN...WINTER WEATHER ADVISORY UNTIL 10 PM EST SUNDAY FOR INZ050-058-
     059.
     WINTER WEATHER ADVISORY UNTIL 3 PM EST SUNDAY FOR INZ066-073-
     074.
     WINTER WEATHER ADVISORY UNTIL 10 AM EST SUNDAY FOR INZ075-080.

&&

$$
SYNOPSIS...HATZOS
NEAR TERM...HATZOS
SHORT TERM...HATZOS
LONG TERM...HICKMAN
AVIATION...SITES