Area Forecast Discussion
Issued by NWS Wilmington, OH

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000
FXUS61 KILN 220211
AFDILN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON OH
911 PM EST SUN DEC 21 2014

.SYNOPSIS...
HIGH PRESSURE WILL CONTINUE MOVING EAST OF THE REGION TONIGHT...AS
A TROUGH OF LOW PRESSURE BEGINS TO MOVE INTO THE MISSISSIPPI
VALLEY. WITH SOUTHERLY WINDS BEGINNING TO INCREASE...WARMER
CONDITIONS ARE EXPECTED THROUGH WEDNESDAY. AS THE TROUGH AND A
COLD FRONT MOVE THROUGH THE REGION...CHANCES OF PRECIPITATION WILL
INCREASE FOR TUESDAY AND WEDNESDAY...WITH COOLER CONDITIONS FOR
THE END OF THE WEEK.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
UPDATES THIS EVENING HAVE CENTERED AROUND LOCALIZED CLEARING AND
QUICK POST-SUNSET TEMP DROP WHICH HAVE SOME LOCATIONS ALREADY IN
THE MID 20S. THIS WAS WELL DOCUMENTED BY PVS SHIFT IN DISCUSSION
BELOW. HAVE CONTINUED TO PLAY FOR TEMPS TO LARGELY STABILIZE
THROUGH LATE EVENING ACROSS THE NRN KY/SRN OH BUT CONTINUE TO
SLOWLY FALL IN CNTL OHIO.

22.00Z KILN SOUNDING SHOWS WEAK WAA CENTERED AROUND 900MB WHERE
WINDS BEGIN TO TURN MORE SOUTHERLY. SATELLITE LOOPS THIS EVENING
CAPTURE AN EXPANDING AREA OF STRATUS OVER TN/KY SURGING NWRD.
RECENT RAP/HRRR/NAM RUNS EXPAND THIS STRATUS /USING 925MB RH AS
PROXY/ NORTH TO THE OHIO RIVER AND INTO SRN OHIO BY SUNRISE ON
MONDAY. BUFR SOUNDINGS AT CVG FROM VARIOUS HRRR/RAP/NAM RUNS HAVE
SHOWN A PROPENSITY TO SATURATE AMIDST WEAK VERTICAL MOTION...WITH
POTENTIAL FOR A PATCH OR TWO OF LIGHT FREEZING RAIN OR RAIN
DEPENDING ON BOUNDARY LAYER TEMPS AS THE MOISTURE ARRIVES.
INTERESTINGLY...RECENT HRRR SIMULATED REFLECTIVITIES ARE QUITE
ROBUST BUT ACCUMULATED PRECIPITATION /QPF/ IS VERY SPARSE IN THE
MODEL...SUGGESTING NEAR SFC DRY LAYER /SOUTHEASTERLY FLOW/ MAY BE
ENOUGH TO KEEP MUCH FROM HITTING THE GROUND. VERY LOW CONFIDENCE
HERE...AND NOT ENOUGH FEEL FOR A HAZ WX THREAT TO PUT IN HAZ WX
OUTLOOK RIGHT NOW...BUT DID UPDATE FORECAST TO MENTION SMALL
THREAT OF LIGHT FREEZING RAIN IN NRN KY/SERN IND/FAR SRN OH
BETWEEN 08Z AND 13Z. GIVEN THE WEAK VERTICAL MOTION...THE MARGINAL
SATURATION...AND VERY LIGHT/SCATTERED QPF FOOTPRINT ON RECENT
RAP/HRRR/NAM RUNS...DON/T HAVE ENOUGH CONFIDENCE TO HIGHLIGHT IN
EITHER AN HWO OR SPECIAL WX STATEMENT. GOING FORECAST ONLY NEEDED
MINOR TEMPORAL/SPATIAL TWEAKS TO LATE NIGHT RA/FZRA CHANCES.

PREVIOUS DISCUSSION...
IT TOOK SOME TIME...BUT THE LOW CLOUDS HAVE ALL ERODED
FROM THE ILN FORECAST AREA...UNDER THE INFLUENCE OF WARMING
TEMPERATURES (ESPECIALLY AT AROUND 900MB). THE WEATHER PATTERN IS
GRADUALLY EVOLVING INTO ONE THAT IS FAVORABLE FOR DEEP SOUTHERLY
FLOW...BUT IT WILL STILL BE ANOTHER FORECAST PERIOD OR TWO BEFORE
THIS ALIGNMENT IS MAXIMIZED. FOR NOW...THE RIDGING OVER THE MID-
ATLANTIC IS RATHER FLAT...AND THE SURFACE HIGH IS STILL CLOSE
ENOUGH TO PROVIDE AN EASTERLY COMPONENT TO THE LOW-LEVEL FLOW.

AS THE 925MB/850MB GRADIENT BEGINS TO TIGHTEN OVERNIGHT...MOISTURE
WILL BEGIN TO BE TRANSPORTED NORTH...EVENTUALLY REACHING THE OHIO
VALLEY BEFORE MORNING. UNTIL THEN...IT APPEARS THAT SKIES WILL BE
COVERED ONLY IN CIRRUS...LEADING TO SOME FAIRLY FAVORABLE
RADIATIONAL COOLING CONDITIONS (AT LEAST DURING THE FIRST HALF OF
THE OVERNIGHT PERIOD). TEMPERATURES MAY BEGIN TO WARM SOMEWHAT
BEFORE 12Z...ESPECIALLY ONCE THE LOW CLOUDS MOVE IN. RAW MODEL
TEMPERATURES ALL INDICATED A SHARP DROP IN TEMPERATURES BETWEEN
21Z AND 03Z...FOLLOWED BY LITTLE CHANGE AFTER THAT.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/...
THE CHANGES IN THE WEATHER PATTERN OVER THE OHIO VALLEY WILL
BECOME MORE PRONOUNCED ON MONDAY. A SURFACE PRESSURE GRADIENT
WILL BEGIN TO INCREASE...BETWEEN A DEVELOPING SURFACE LOW IN
WESTERN IOWA AND A DEPARTING SURFACE HIGH OVER THE CANADIAN
MARITIME PROVINCES. A LARGE MID-LEVEL TROUGH OVER THE CENTRAL
STATES WILL DEVELOP INTO A CLOSED LOW...AND WITH RIDGING OFF THE
ATLANTIC COAST...A REGIME OF DEEP SOUTHWESTERLY FLOW WILL SET UP
OVER THE OHIO VALLEY. MOISTURE TRANSPORT FROM THE GULF WILL REACH
THE ILN FORECAST AREA EARLY MONDAY MORNING...WITH PRECIPITABLE
WATER VALUES GRADUALLY INCREASING THROUGH TUESDAY...LEADING
THROUGH THE FIRST OF TWO MAIN WAVES OF PRECIPITATION. THE SECOND
WAVE ON WEDNESDAY WILL BE COVERED IN THE LONG TERM SECTION OF THE
FORECAST DISCUSSION.

A WEAK LEAD SHORTWAVE IS FORECAST TO ROTATE NORTHEAST THROUGH THE
OHIO VALLEY ON MONDAY MORNING...COMBINING WITH THE FRONT EDGE OF
THE NORTHWARD-MOVING MOISTURE. THERE APPEARS TO BE JUST ENOUGH
ISENTROPIC LIFT TO SUPPORT SOME WEAK SHOWERS...MAINLY IN THE
SOUTHERN AND SOUTHEASTERN PORTIONS OF THE FORECAST AREA...WHERE A
20-POP HAS BEEN USED IN THE FORECAST. HOWEVER...THIS SHORTWAVE
WILL BE WEAKENING WITH TIME...AND WIDESPREAD PRECIPITATION IS NOT
LIKELY TO OCCUR. AS THIS LIGHT PRECIPITATION MOVES IN...THE REGION
WILL BE COMING OUT OF ANOTHER CHILLY MORNING...WITH TEMPERATURES
ONLY EXPECTED TO RISE ABOVE FREEZING JUST BEFORE THE PRECIPITATION
ARRIVES. A WORST-CASE SCENARIO COULD SUPPORT SOME LIGHT FZRA NEAR
THE OHIO RIVER AT AROUND 12Z...BUT IT APPEARS THAT THE
PRECIPITATION WILL BE LIGHT/SPARSE ENOUGH (AND TEMPERATURES
WARMING JUST SOON ENOUGH) TO MAKE THIS A LOW-PROBABILITY SCENARIO.

TEMPERATURES ON MONDAY WILL WARM SIGNIFICANTLY BEYOND VALUES ON
SUNDAY...THANKS TO WARM ADVECTION...AND EVEN IN THE ABSENCE OF
MUCH INSOLATION. TEMPERATURES ACROSS THE ILN FORECAST AREA SHOULD
RANGE FROM THE LOWER-TO- MID 40S IN THE NORTH TO THE LOWER 50S IN
THE SOUTH. THESE WARMING TEMPERATURES WILL BE AIDED BY A LACK OF
PRECIPITATION...AS THE FORWARD PROGRESSION OF THE DEVELOPING LOW
PRESSURE IS NOT PARTICULARLY FAST.

CHANCES FOR PRECIPITATION WILL INCREASE AHEAD OF THE PROGRESSION
OF THE MID-LEVEL LOW...WHICH WILL BE MOVING NORTHEAST INTO THE
GREAT LAKES ON TUESDAY MORNING. AS MOISTURE CONVERGENCE INCREASES
OVER THE LOWER OHIO VALLEY...A SWATH OF SHOWERY PRECIPITATION IS
EXPECTED TO TRANSLATE NORTHEASTWARD AS WELL. THIS ACTIVITY WILL
EVENTUALLY OUTRUN THE SLOWING COLD FRONT...BUT WILL BE AIDED BY
FAVORABLE DIFFLUENT FLOW AHEAD OF THE APPROACHING UPPER JET
STREAK. WHILE THE GREATEST CHANCES FOR PRECIPITATION (AND GREATEST
MODEL OUTPUT QPF) APPEAR TO BE IN THE NORTHWESTERN CWA...THE FOCUS
FOR ANY POTENTIAL FOR THUNDER WILL BE IN THE NORTHERN KENTUCKY AND
SOUTH CENTRAL OHIO. SURFACE-BASED INSTABILITY WILL BE VERY
UNLIKELY...WITH SOME LEVEL OF INVERSION STILL REMAINING IN
PLACE...AS ALSO EVIDENCED BY THE SLIGHTLY DECOUPLED WIND
DIRECTIONS BETWEEN THE SURFACE AND 850MB. HOWEVER...850MB PARCELS
WILL HAVE A ROUGHLY MOIST-ADIABATIC PROFILE ABOVE THEM...WITH 15Z
SPC SREF PARAMETERS INDICATING AT LEAST A CHANCE OF EQUILIBRIUM
LEVELS COLD ENOUGH TO SUPPORT SOME WEAK CONVECTION. THUS...A BRIEF
PERIOD WITH A SLIGHT CHANCE OF THUNDER WAS INCLUDED THURSDAY
MORNING AND AFTERNOON IN THE SOUTHERN/SOUTHEASTERN PORTIONS OF THE
FORECAST AREA.

POPS WILL DECREASE ON TUESDAY EVENING AS THE MID-LEVEL WAVE MOVES
OFF...AND UPPER SUPPORT IS LOST. CHANCES WILL INCREASE AGAIN EARLY
WEDNESDAY MORNING...AS LOW-LEVEL FORCING AND CONVERGENCE BEGINS
TO INCREASE AHEAD OF A DEVELOPING SURFACE LOW. THROUGHOUT THIS
PERIOD...TEMPERATURES WILL BE DOMINATED BY ADVECTION...WITH
NON-DIURNAL CURVES REQUIRED FOR THE FORECAST GRIDS. HIGHS ON
TUESDAY SHOULD RANGE FROM THE LOWER 50S TO UPPER 50S FROM NORTH TO
SOUTH...WITH LITTLE CHANGE IN TEMPERATURE EXPECTED TUESDAY NIGHT.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
LOW PRESSURE WILL DEEPEN ALONG A COLD FRONT AT THE BEGINNING OF THE
LONG TERM PERIOD. GFS/CMC ARE SIMILAR IN THE INTENSIFYING PROCESS AS
THE LOW MOVES NORTHEAST FROM THE MIDDLE OHIO VALLEY TO SOUTHEAST
ONTARIO INTO WEDNESDAY NIGHT. THE ECMWF IS A LITTLE STRONGER AND THE
NAM IS A WEAK OUTLIER. HAVE TAKEN A BLEND OF THE GFS/CMC. AS THE
DEEPENING PROCESS OCCURS...WIDESPREAD SHOWERS ARE EXPECTED WEDNESDAY
MORNING. BY WEDNESDAY AFTERNOON...THE COLD FRONT WILL PUSH NORTHEAST
THROUGH THE REGION. THE COVERAGE OF PCPN WILL DECREASE BEHIND
FRONTAL PASSAGE AS DRIER SLOT OF AIR ALOFT MOVES IN BRIEFLY. BY
WEDNESDAY NIGHT...SOME WRAP AROUND MOISTURE WILL OCCUR...BUT
COVERAGE LOOKS TO BE CHANCE AT BEST. IT WILL BE WARM AHEAD OF THE
FRONT WITH TEMPERATURES DROPPING WEDNESDAY AFTERNOON INTO THE NIGHT.
HIGHS ON WEDNESDAY WILL RANGE FROM THE 50S TO NEAR 60 WITH LOWS
BOTTOMING OUT INTO THE LOWER AND MID 30S BY CHRISTMAS MORNING. IT
SHOULD BECOME COLD ENOUGH FOR A CHANCE OF RAIN/SNOW SHOWERS AND THEN
A CHANCE OF SNOW SHOWERS CHRISTMAS EVE NIGHT. HOWEVER...LITTLE IS
EXPECTED IN THE WAY OF ACCUMULATIONS GIVEN RECENT WARM TEMPERATURES
AND NO REAL FOCUS/FORCING FOR APPRECIABLE SNOWFALL RATES. IT WILL
BECOME BRISK TO LOCALLY WINDY DURING THE PERIOD...BUT WINDS ARE
EXPECTED TO STAY BELOW ADVISORY CRITERIA ATTM.

ON CHRISTMAS DAY...DEEPENING LOW PRESSURE WILL CONTINUE TO MOVE
NORTHEAST AWAY FROM THE REGION. ANY THREAT FOR SNOW SHOWERS WILL
QUICKLY COME TO AN END DURING CHRISTMAS MORNING. BY
AFTERNOON...SKIES SHOULD BECOME PARTLY CLOUDY AS SURFACE RIDGING
QUICKLY BUILDS INTO THE AREA BEHIND DEPARTING SYSTEM. HIGHS ON
CHRISTMAS WILL RANGE FROM THE UPPER 30S TO THE LOWER 40S...NEAR
SEASONAL NORMALS.

FOR THURSDAY NIGHT...SURFACE RIDGE WILL MOVE EAST WITH RETURN
SOUTHWEST FLOW ENSUING ALONG WITH INCREASING CLOUDS AHEAD OF THE
NEXT SYSTEM.

FOR FRIDAY INTO SATURDAY...LOW PRESSURE AND A COLD FRONT WILL MOVE
ACROSS THE GREAT LAKES AND OHIO VALLEY. SYSTEM APPEARS TO BE
MOISTURE STARVED SO WILL CONTINUE WITH LOW CHANCE POPS. WE SHOULD
SEE A WARM UP ON FRIDAY FOLLOWED BY A COOL DOWN SATURDAY IN THE WAKE
OF THE SYSTEM.

BY SUNDAY...HIGH PRESSURE AND MUCH COLDER TEMPERATURES ARE EXPECTED.
HIGHS BY THEN WILL RANGE FROM THE UPPER 20S TO THE LOWER 30S.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
THE EVENING KILN RAOB CONFIRMS SOME DRIER AIR IN THE LOW LEVELS OF
THE ATMOSPHERE. OUR AREA WILL REMAIN UNDER BROKEN CIRRUS FOR THE
BULK OF THE OVERNIGHT HOURS. AS SURFACE HIGH PRESSURE DRIFTS
FURTHER EAST OF THE AREA...SOUTHERLY LOW LEVEL FLOW WILL DRAW
INCREASING MOISTURE UP FROM THE SOUTH LATE TONIGHT INTO MONDAY
MORNING. LATEST SATELLITE IMAGERY REVEALS LOW LEVEL CLOUDS ALREADY
WORKING THEIR WAY FROM TENNESSEE INTO SOUTHERN KENTUCKY. EXPECT AN
MVFR CLOUD DECK TO MOVE IN FROM SOUTH TO NORTH OVER THE TERMINALS
AROUND 10Z TO 13Z MONDAY. ALONG WITH THIS INCREASE IN LOW LEVEL
MOISTURE AND A WEAK UPPER DISTURBANCE WILL COME THE CHANCE FOR
PERHAPS SOME ISOLATED RAIN SHOWERS IN THE MORNING. LATEST HI-RES
MODELS ARE NOT OVERLY EXCITED ABOUT THIS POSSIBILITY BUT THEY DO
HINT AT IT. THUS...WENT WITH VCSH FOR NOW. IF THE RAIN DOES
MATERIALIZE...CANNOT RULE OUT PERHAPS A BRIEF PERIOD OF VERY LIGHT
FZRA AT THE CINCINNATI TERMINALS BEFORE 12Z WITH SURFACE TEMPERATURES
EXPECTED TO BE RIGHT AROUND FREEZING. THE MVFR CLOUD DECK SHOULD
MIX OUT A BIT IN THE AFTERNOON...THEN REDEVELOP BY THE END OF THE
KCVG TAF PERIOD WITH A CHANCE OF SHOWERS AS THE NEXT STORM SYSTEM
APPROACHES FROM THE WEST. WINDS WILL REMAIN LIGHT OUT OF THE
SOUTHEAST TONIGHT...PICKING UP TOWARDS THE END OF THE TAF PERIOD.

OUTLOOK...MVFR TO IFR CIGS AND VSBYS ARE POSSIBLE MONDAY NIGHT
INTO THURSDAY. WINDS WILL PICK UP SIGNIFICANTLY STARTING
WEDNESDAY.

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
OH...NONE.
KY...NONE.
IN...NONE.

&&

$$
SYNOPSIS...HATZOS
NEAR TERM...BINAU
SHORT TERM...HATZOS
LONG TERM...HICKMAN
AVIATION...KURZ







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