Area Forecast Discussion
Issued by NWS Wilmington, OH

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553
FXUS61 KILN 141533
AFDILN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON OH
1033 AM EST SUN FEB 14 2016

.SYNOPSIS...
SNOW WILL OCCUR NORTH OF A WARM FRONT THAT WILL APPROACH FROM THE
SOUTHWEST TODAY AND LIFT THROUGH THE AREA TONIGHT. AN AREA OF LOW
PRESSURE WILL PASS JUST SOUTHEAST OF THE REGION MONDAY AFTERNOON
AND NIGHT. ANOTHER LOW PRESSURE SYSTEM WILL CROSS THE AREA TUESDAY
AFTERNOON AND EVENING.

&&

.NEAR TERM /THROUGH TONIGHT/...
ADJUSTMENTS FOR THE NEAR TERM OF THE FORECAST WERE FOCUSED ON THE
SNOW POTENTIAL THIS AFTERNOON...WITH SOME SLIGHT ADJUSTMENTS TO
FORECAST NUMBERS REQUIRED. SOME MINOR CHANGES WERE ALSO MADE
OVERNIGHT AND GOING INTO MONDAY...BUT THE FORECAST THINKING FOR
THE SETUP FROM OVERNIGHT INTO TOMORROW HAS NOT CHANGED MUCH.

WATER VAPOR SATELLITE IMAGERY SHOWS A WELL-DEFINED SPIN IN
IOWA...ASSOCIATED WITH THE SHORTWAVE THAT IS MOVING TOWARD THE
REGION TODAY. AS THIS SHORTWAVE MOVES EAST...FORCING IS BEGINNING
TO INCREASE IN THE LOWER OHIO VALLEY...DRIVEN JUST AS MUCH BY
FORCING A LITTLE LOWER IN THE ATMOSPHERE. WITH HIGH PRESSURE
MOVING EAST OF THE OHIO VALLEY...A SWITCH TO SOUTHERLY FLOW HAS
OCCURRED...AND WARM FRONTAL PROCESSES ARE UNDERWAY. CONVERGENCE
AND ISENTROPIC ASCENT IS GRADUALLY INCREASING IN STRENGTH AHEAD OF
THE INCREASED SOUTHERLY FLOW...AND PRECIPITATION IN ILLINOIS /
WESTERN KENTUCKY / EASTERN MISSOURI HAS BECOME WIDESPREAD.

ALTHOUGH MODELS ARE IN STRONG AGREEMENT ON THIS OVERALL
SETUP...THERE ARE STILL SOME CONFLICTING FACTORS PREVENTING A
HIGH-CONFIDENCE FORECAST FOR THE EVENTUAL SNOWFALL NUMBERS. RECENT
HIGH-RESOLUTION MODEL RUNS AND SOME OF THE 06Z OPERATIONAL RUNS
HAVE DEFINITELY INDICATED A LITTLE STRONGER FORCING THAN PERHAPS
PREVIOUSLY INDICATED. CONSEQUENTLY...QPF AMOUNTS (ESPECIALLY OVER
THE FAR SOUTHWESTERN CWA) HAVE INCREASED AS WELL. OF COURSE...QPF
SHOULD ONLY BE USED AS ONE FACTOR IN THE FORECAST PROCESS...AND
NEEDS TO BE SCRUTINIZED. THE LOCATION AND STRENGTH OF THE FORCING
AND MOISTURE ARE OF GREATER CONCERN TO LOOK INTO. FOR
EXAMPLE...BOTH THE RECENT HRRR AND RAP RUNS HAVE AROUND A TENTH OF
AN INCH OF LIQUID EQUIVALENT IN THE SOUTHWESTERN ILN COUNTIES
BEFORE 18Z...VALUES THAT ARE SIMPLY NOT OCCURRING RIGHT NOW (WITH
JUST ONE OR TWO REPORTS OF SOME LIGHT SNOW FROM THE MOSTLY-VIRGA
ECHOES CURRENTLY MOVING THROUGH CENTRAL AND EASTERN KENTUCKY).
FURTHERMORE...SNOW RATIOS MUST BE CONSIDERED THROUGH THE DEPTH OF
THE THERMAL PROFILE...AND CANNOT BE BASED SOLELY ON SURFACE
TEMPERATURES. IN FACT...IT IS THE STRENGTH OF THE WARMING ALOFT
(LEADING TO THE ISENTROPIC ASCENT) THAT WILL HELP LIMIT SNOW
RATIOS...BY DEVELOPING A DEEP ISOTHERMAL LAYER OF ROUGHLY -8C TO
-10C FROM THE SURFACE THROUGH 700MB. THIS IS NOT ESPECIALLY
FAVORABLE FOR EFFICIENT SNOW PRODUCTION...AND WILL LIKELY KEEP
RATIOS AT OR BELOW 15:1. HOWEVER...THERE WILL BE A PERIOD WHERE
THE CONTRIBUTION OF FORCING FROM THE SHORTWAVE ALLOWS FOR ASCENT
THROUGH AN EVEN DEEPER LAYER...PERHAPS ALLOWING FOR A PERIOD OF AN
HOUR OR TWO WITH SOME HEAVIER SNOW RATES.

WITH ALL THE FACTORS CONSIDERED TOGETHER...SNOW NUMBERS WERE
INCREASED BY ABOUT A HALF INCH THROUGH THE CENTER OF THE ILN
FORECAST AREA...AND BY ALMOST AN INCH IN THE FAR SOUTH AND
SOUTHWEST. THE WSW PRODUCT WAS BROKEN OUT INTO TWO GROUPS TO
ALLOW FOR A 2-3 INCH FORECAST AND A 3-4 INCH FORECAST.

THE FORECAST THINKING DID NOT CHANGE MUCH WITH REGARDS TO THE
POTENTIAL FOR FREEZING DRIZZLE EARLY MONDAY MORNING. ONCE THE
DEEP-LAYER MOISTURE HAS DEPARTED...AND SATURATION IS LIMITED TO
BELOW -10C...ICE CRYSTALS ARE UNLIKELY TO BE INTRODUCED INTO THE
ATMOSPHERE. THOUGH STRONG FORCING WILL ALSO BE DEPARTED...WEAK
ISENTROPIC ASCENT WILL CONTINUE IN THE LOW-LEVELS...ALLOWING FOR
THE POTENTIAL FOR FREEZING DRIZZLE. THOUGH TEMPERATURES WILL BE
RISING GOING INTO MONDAY MORNING...THE COLD GROUND CONDITIONS
WILL BE VERY SLUGGISH IN THEIR RESPONSE...WITH SOME POTENTIAL FOR
LIGHT DEPOSITION OF ICE IF DRIZZLE IS ABLE TO DEVELOP.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
SHORT WAVE TRACKING OUT OF THE SOUTHERN PLAINS WILL HEAD INTO THE
CENTRAL APPALACHIANS MONDAY INTO MONDAY NIGHT. GUIDANCE IS COMING
INTO PRETTY GOOD AGREEMENT THAT THE ASSOCIATED SURFACE LOW WILL
MOVE FROM MIDDLE TENNESSEE INTO EASTERN KENTUCKY AND THEN WEST
VIRGINIA. SHIELD OF PRECIPITATION NORTH OF THE LOW WILL SPREAD
INTO THE SOUTHERN AND EASTERN ZONES MONDAY AFTERNOON THROUGH
MONDAY NIGHT. WARMER TEMPERATURES SHOULD RESULT IN MUCH OF THE
PRECIPITATION WILL BE IN THE FORM OF RAIN EXCEPT PERHAPS ON THE
NORTHWEST EDGE.

A NARROW SURFACE RIDGE WILL MOVE ACROSS THE REGION TUESDAY
MORNING PROVIDING A BRIEF RESPITE FROM PRECIPITATION. BUT THEN A
WELL DEVELOPED CLIPPER WILL MOVE ACROSS THE AREA TUESDAY AFTERNOON
AND NIGHT. 00Z NAM AND GFS ARE IN EXCELLENT AGREEMENT BUT WITH THE
ECMWF BEING A BIT SLOWER THERE IS SOME TIMING UNCERTAINTY.
CURRENTLY APPEARS THAT THIS WILL BRING SNOW IN THE NORTHERN PART
OF THE FORECAST AREA WITH RAIN OR SNOW IN THE SOUTH DEPENDING ON
THE LOW LEVEL TEMPERATURES.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
ON WEDNESDAY...WILL GO WITH A DRY FORECAST...ALTHOUGH CONSIDERABLE
CAA STRATOCUMULUS IS EXPECTED.

FOR WEDNESDAY NIGHT INTO THURSDAY...HIGH PRESSURE WILL BUILD SOUTH
INTO THE OHIO VALLEY. SKIES ARE EXPECTED TO BECOME PARTLY CLOUDY.
MODELS DIFFERENT ON THE EXTENT OF COLD AIR FILTERING IN THE
REGION...SO HAVE SIDED WITH A WPC BLENDED APPROACH.

AS THE HIGH MOVES EAST THURSDAY NIGHT...A WARM FRONT IS FORECAST TO
APPROACH FROM THE WEST. WE SHOULD SEE AN INCREASE IN WAA INDUCED
CLOUDS. AS OF NOW...ANY PCPN GENERATED WITH THE WARM FRONT IS
EXPECTED TO STAY NORTHWEST OF THE AREA. OVERNIGHT LOWS WILL BE EARLY
FOLLOWED BY SLOWLY RISING TEMPERATURES AS WINDS INCREASE FROM THE
SOUTH.

FOR FRIDAY INTO FRIDAY NIGHT...LOW PRESSURE WILL TRAVERSE THE GREAT
LAKES AS A COLD FRONT PUSHES IN FROM THE NORTHWEST. MODELS VARY ON
HOW MUCH MOISTURE WILL BE PULLED NORTHWARD ALONG AND AHEAD OF THE
FRONT SYSTEM...ALONG WITH THE TIMING...SO HAVE GONE WITH A CHANCE OF
RAIN. FRIDAY CERTAINLY LOOKS TO BE THE WARMEST DAY OF THE EXTENDED
WITH TEMPERATURES RISING INTO THE 50S AREA WIDE.

ON SATURDAY...FRONT EXITS TO THE EAST...BUT CAA STRATOCUMULUS MOVES
INTO THE REGION. PCPN WILL MOVE EAST AS WELL. TEMPERATURES WILL COOL
INTO THE MID 40S TO LOWER 50S FOR HIGHS.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
VFR AND DRY CONDITIONS WILL START OUT THE TAF PERIOD. ALTHOUGH A
FEW FLURRIES CANNOT BE RULED OUT AT KCVG THIS MORNING MOST OF THE SNOW
WILL MOVE INTO THE TAF SITES THIS AFTERNOON INTO TONIGHT. CIGS
WILL LOWER AND VSBYS WILL BE REDUCED WITH THE SNOWFALL.

THE DEEPER MOISTURE WILL MOVE OUT TONIGHT. THERE IS SOME QUESTION
AS TO WHETHER ICE WILL BE IN THE CLOUDS OVERNIGHT TONIGHT INTO
EARLY MONDAY MORNING. WHETHER OR NOT THERE IS OR NOT WILL
DETERMINE WHETHER OR NOT LIGHT SNOW WILL CONTINUE OVERNIGHT
TONIGHT OR WHETHER FREEZING DRIZZLE WILL BE PRESENT. THERE ARE
ENOUGH INDICATIONS TO SUGGEST THAT SNOW WILL TRANSITION TO
FREEZING DRIZZLE AND THEREFORE HAVE FREEZING DRIZZLE IN TOWARDS
THE END OF THE TAF PERIOD. CIGS WILL BE LOWER IN THE IFR CATEGORY
DURING THIS TIME AND POTENTIALLY EVEN LIFR.

OUTLOOK...MVFR/IFR CONDITIONS ARE POSSIBLE WITH PRECIPITATION
FROM MONDAY THROUGH TUESDAY NIGHT.

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
OH...WINTER WEATHER ADVISORY UNTIL 10 AM EST MONDAY FOR OHZ063>065-
     070>074-077>082-088.
KY...WINTER WEATHER ADVISORY UNTIL 10 AM EST MONDAY FOR KYZ089>100.
IN...WINTER WEATHER ADVISORY UNTIL 10 AM EST MONDAY FOR INZ066-
     073>075-080.

&&

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



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