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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KILN 110236
AFDILN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON OH
936 PM EST TUE DEC 10 2013

.SYNOPSIS...
THE COLDEST AIR OF THE YOUNG WINTER SEASON IS ON TAP FOR THE OHIO
VALLEY OVER THE NEXT FEW DAYS AS AN ARCTIC COLD FRONT SWEEPS
THROUGH THE AREA ON WEDNESDAY. WITH PLENTY OF SNOW COVER OVER MUCH
OF THE AREA...TEMPERATURES WILL WITHOUT A DOUBT FALL TO THEIR
LOWEST LEVELS OF THE SEASON THE NEXT FEW MORNINGS...AND WIND
CHILLS MAY DIP BELOW ZERO AT TIMES. THE FRONT WILL USHER IN SMALL
THREAT OF SNOW OR SNOW SHOWERS ON WEDNESDAY INTO WEDNESDAY
EVENING...BUT ANY ACCUMULATIONS WILL BE VERY LIGHT. WARMER
TEMPERATURES ARE IN THE CARDS BEGINNING FRIDAY AND SATURDAY...BUT
WILL COME WITH THE RISK OF MORE WINTRY PRECIPITATION...WITH THE
POTENTIAL FOR ACCUMULATING SNOW OR WINTRY MIX FOR SATURDAY.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
-- Changed Discussion --
OVERALL FORECAST THINKING HAS CHANGED VERY LITTLE SINCE EARLIER
TODAY. UPSTREAM HIGH AND MID CLOUDS HAVE YET TO REACH THE ILN
CWA...SO RADIATIONAL COOLING (AIDED BY THE SNOW PACK) IS CERTAINLY
ONGOING. HOWEVER...WITH WINDS EXPECTED TO REMAIN IN PLACE
TONIGHT...CONDITIONS MAY NOT BE COMPLETELY IDEAL. WITH AN
EXTREMELY WIDE VARIANCE IN RAW MODEL TEMPERATURES OVER THE NEXT
6-12 HOURS...THE FORECAST UPDATED WAS BASED MAINLY ON CURRENT
TRENDS...WHICH LEADS TO MIN TEMPS A COUPLE DEGREES WARMER THAN THE
PREVIOUS ISSUANCE. IT IS ULTIMATELY A MINOR CHANGE THAT STILL
ALLOWS FOR WIND CHILLS NEAR ZERO...ESPECIALLY IN THE WEST-CENTRAL
PORTIONS OF THE ILN CWA.

PREVIOUS DISCUSSION >
LAST NIGHT/S FRONTOGENETICALLY FORCED BAND OF POWDERY SNOW HAS
ZIPPED WELL DOWNSTREAM AND OFF THE ATLANTIC COAST...WITH SURFACE
HIGH PRESSURE SET TO BUILD ACROSS THE BLUEGRASS OF KENTUCKY
TONIGHT. CURRENT GUSTY WINDS /OWING TO RATHER TIGHT GRADIENT AND
STEEP LAPSE RATES/ SHOULD RELAX AS THE HIGH BUILDS INTO KENTUCKY.
CURRENT VISIBLE SATELLITE LOOPS...AND FORECAST SYNTHETIC-WRF CLOUD
COVER FROM GOES-R PROVING GROUND DATA...SUGGESTS THE BULK OF THE
UPCOMING NIGHT WILL BE CLEAR...WITH ONLY A FEW TRANSIENT BANDS OF
MID/HIGH CLOUDS TO MOVE ACROSS THE AREA...PROBABLY MORE SO IN THE
FAR NORTH AND WELL AFTER MIDNIGHT. WHILE LOW LEVEL WARM ADVECTION
WILL BEGIN AS THE NIGHT WEARS ON DUE TO THE NEXT WEATHER SYSTEM
PROGRESSING ACROSS WIS/MICH...THERE SHOULD BE RATHER HEALTHY
BOUNDARY-LAYER DECOUPLING THAT KEEPS THIS WARMING ALOFT...THANKS
TO THE BUILDING SNOW PACK OVER MUCH OF THE AREA. WHEN TAKING INTO
CONSIDERATION THIS MORNING/S POWDER...NOHRSC SNOW DEPTH ANALYSIS
SUGGESTS A GOOD CHUNK OF THE WFO ILN FORECAST AREA HAS 2-4 INCHES
ON THE GROUND...WITH MUCH OF NORTHERN KENTUCKY AND SOUTHWEST/SOUTH
CENTRAL OHIO HAVING 4+" ON THE GROUND. THIS IS DEEP ENOUGH TO
ALLOW A SIGNIFICANT RADIATIONAL COOLING ELEMENT TO THE OVERNIGHT
FORECAST...AND AN ANALYSIS OF THE HI-RES/SHORT TERM MODELS IS
LATCHING ON TO THIS AREA WITH FORECAST 2M TEMPS LATER TONIGHT WELL
INTO THE SINGLE DIGITS. THESE NIGHTS /IF TRUE PBL DECOUPLING
INDEED OCCURS/ WITH FRESH SNOW COVER CAN REALLY DROP OFF IN A
HURRY...SO WILL BE VERY AGGRESSIVE WITH LOWS TONIGHT...SLICING
BELOW EVEN SEEMINGLY TOO COLD MAV MOS. THIS OPENS THE DOOR FOR A
COLD-PRONE SITE OR TWO TO APPROACH ZERO...AND HONORED THIS WITH A
FEW SPOTS GETTING LESS THAN 5F OVERNIGHT...DOWN AS LOW AS 2F IN
THE GRIDS OUTLYING THE DAYTON AREA. THIS WILL ALLOW WHAT WINDS
WILL REMAIN TO PUSH WIND CHILLS INTO THE SINGLE DIGITS BELOW ZERO
IN SOME AREAS.
-- End Changed Discussion --

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
THE SHORTWAVE TROUGH CURRENTLY OVER WISCONSIN INTO NEBRASKA IS MOVING
INTO THE BASAL PORTION OF THE COLD LONGWAVE TROUGH OVER THE
EASTERN CONUS...AND WILL PASS LARGELY JUST NORTH OF THE AREA
THROUGH THE DAY ON WEDNESDAY. BULK OF SYNOPTIC SCALE FORCING /PV
AND JET/ REMAIN ALONG AND NORTH OF OHIO BORDER THROUGH THE DAY.
HOWEVER...WEAK MID/UPPER Q/G FORCING AND INCREASING LOW LEVEL
MOISTURE ALONG THE ADVANCING ARCTIC FRONT MAY BRING A TRANSIENT
BAND OF LIGHT SNOW AND/OR SNOW SHOWERS EITHER ALONG OR IMMEDIATELY
BEHIND THE FRONT...FROM LATE TOMORROW MORNING /NORTHERNMOST AREAS/
INTO LATER WEDNESDAY AFTERNOON AND EVENING FOR CENTRAL/SOUTHWEST
OHIO. BETTER CHANCES DEFINITELY ALONG/NORTH OF I-70 WHERE 0-2KM
MOISTURE IS A LITTLE HIGHER...WHICH MAY SUPPORT SOME LIGHT PRECIP.
DON/T THINK THERE WILL BE ANY ACCUM GREATER THAN 0.5" SHOULD ANY
SNOW FALL.

WARM ADVECTION SWLY FLOW WILL BE BRISK AHEAD OF THE FRONT...AND
KEEP WIND CHILLS DOWN /TEENS/...DESPITE TEMPS WARMING THROUGH THE 20S
TOWARD 30 /FAR SOUTH/. BUT THE FRONT WILL BRING A NOTICEABLE
CHANGE IN AIRMASS...WITH A RAPID DROP IN 925MB TEMPS FROM -4C AT
18Z TO -16C AT 09Z WEDNESDAY NIGHT. GUSTY SWLY FLOW WILL TURN
NWLY...AND SFC TEMPS SHOULD FALL OFF RATHER DRAMATICALLY THROUGH
THE NIGHT ON WEDNESDAY NIGHT...AS 1040MB HIGH PRESSURE SYSTEM
BUILDS THROUGH THE MID-MISSISSIPPI VALLEY. THE 925MB TEMPS AT 12Z
THURSDAY FROM THE ILN SOUNDING CLIMATOLOGY ARE -2 SIGMA...WHICH
IS SIGNIFICANT.

WHILE WEDNESDAY NIGHT/S AIRMASS IS MUCH COLDER...AM NOT AS
CONVINCED WINDS WILL DROP OFF WITH HIGH PASSING TO OUR
SOUTH...THUS MY LOW TEMPS FOR WED NIGHT ARE ONLY A FEW DEGREES
COLDER THAN TONIGHT. BUT...WIND CHILLS MAY BECOME MORE OF A
PROBLEM AS THE CORE OF THE ARCTIC AIRMASS BUILDS IN LATER ON WED
NIGHT INTO THURS MORNING. CURRENT PROJECT APPARENT TEMPS ARE
AROUND -10F IN WEST CENTRAL OHIO...AND ITS POSSIBLE WE MAY NEED A
WIND CHILL ADVISORY FOR A PORTION OF WED NIGHT INTO THURSDAY
MORNING...MUCH OF THIS DEPENDS ON HOW WINDS BEHAVE.

THURS/FRI ARE LARGELY BENIGN WEATHER DAYS AS THE STRONG HIGH
PRESSURE BUILDS THROUGH THE MID SOUTH. WINDS SHOULD TURN BACK SWLY
AND A RATHER STOUT WAA PATTERN WILL DEVELOP IN TIME...AS USUAL FOR
WINTER FIRST ABOVE THE SURFACE...WITH WARMING TAKING BETTER SHAPE
ON FRIDAY. THURSDAY WILL STILL BE COLD AS THE SHALLOW ARCTIC
AIRMASS WILL BE SLOW TO BUDGE. PLAYED THE MEDIAN VALUES OF ECMWF
ENSEMBLE MOS AS A STARTING POINT...AND DRIFTED UP/DOWN FROM THERE
BASED ON SNOW COVER. SHOULD BE A FAIR AMOUNT OF SUNSHINE BOTH
DAYS...THOUGH A WEAK SYSTEM /WHICH RIGHT NOW LOOKS TO BE DRY/
DIVES THROUGH THE AREA ON THURSDAY AND MAY ADD A LITTLE MORE
CLOUDS TO THE AREA.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
A MID LEVEL SHORT WAVE MOVING OUT OF THE ROCKIES FRIDAY NIGHT WILL
COMBINE WITH A STRONGER SOUTHERN STREAM SYSTEM LIFTING OUT OF THE
GULF STATES SATURDAY INTO SATURDAY NIGHT. THIS WILL MAKE FOR A
COMPLICATED FORECAST ACROSS OUR AREA AS THERE IS SOME UNCERTAINTY AS
TO EXACTLY HOW THESE TWO SYSTEMS WILL PHASE TOGETHER. BOTH THE 12Z
GFS AND 12Z ECMWF ARE SUGGESTING A DEVELOPING SURFACE LOW/WAVE WILL
LIFT UP INTO THE MID OHIO VALLEY SATURDAY BEFORE BETTER ENERGY
BEGINS TO TRANSFER OFF TO THE EAST COAST SATURDAY NIGHT INTO SUNDAY.
IN A DEVELOPING WAA AHEAD OF THIS...EXPECT PCPN TO DEVELOP/SPREAD
INTO THE REGION FRIDAY NIGHT AND THEN CONTINUE THROUGH THE DAY ON
SATURDAY. HOW MUCH WARM AIR IS PULLED UP AHEAD OF THIS AND THE EXACT
TRACK/PLACEMENT OF THE SURFACE WAVE WILL ULTIMATELY DICTATE THE
PRECIPITATION TYPE. RIGHT NOW IT DOES APPEAR THAT WE WILL WARM UP
ENOUGH IN THE LOWER LEVELS TO ALLOW FOR AT LEAST A MIX ACROSS ABOUT
THE SOUTHEAST HALF OF OUR FA ON SATURDAY...POSSIBLY GOING OVER TO
ALL RAIN ACROSS OUR FAR SOUTH/SOUTHEAST. ACROSS OUR
NORTHWEST...THERE IS A BETTER CHANCE OF PCPN REMAINING PRIMARILY
SNOW AND IF THIS IS THE CASE...SOME ACCUMULATIONS WILL BE POSSIBLE
THROUGH SATURDAY. IN WAA PATTERN DO NOT EXPECT TEMPS TO DROP OFF ALL
THAT MUCH FRIDAY NIGHT...AND THEN THEY SHOULD WORK UP ABOVE FREEZING
ACROSS AT LEAST THE SOUTHEAST HALF OF OUR FA ON SATURDAY.

PCPN WILL CONTINUE INTO SATURDAY EVENING BEFORE TAPERING OFF FROM
THE WEST OVERNIGHT. GOOD CAA WILL DEVELOP ON THE BACKSIDE OF THE
SYSTEM AND WITH SOME LINGERING LOW LEVEL MOISTURE...EXPECT SCATTERED
SNOW SHOWERS ON SUNDAY...ESPECIALLY ACROSS OUR NORTHERN AREAS. HIGHS
ON SATURDAY WILL BE IN THE MID TO UPPER 20S AND ONLY THE LOW TO MID
20S FOR MONDAY. IT ALSO LOOKS LIKE WE COULD GET INTO A FETCH OFF OF
LAKE MICHIGAN WHICH WOULD POSSIBLY LINGER A FEW SNOW SHOWERS ACROSS
PARTS OF OUR NORTH SUNDAY NIGHT INTO MONDAY. THE 12Z ECMWF IS
STRONGER AND A LITTLE FASTER THAN THE THE 12Z GFS WITH THE SHORT
WAVE DROPPING DOWN ACROSS THE NORTHERN PLAINS ON TUESDAY. WILL GO
AHEAD AND BRING SOME SLIGHT CHANCE POPS IN THROUGH THE
AFTERNOON...BUT IT LOOKS LIKE THE BETTER CHANCE FOR ANY PCPN WOULD
BE TUESDAY NIGHT.

&&

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
AS WINDS CONTINUE TO DIMINISH THIS EVENING...CLEAR SKIES WILL
REMAIN OVER THE TAF SITES FOR MOST OF THE OVERNIGHT PERIOD. HIGH
AND MID CLOUDS WILL MAKE THEIR WAY INTO THE NORTHERN TAF SITES
BEFORE SUNRISE. ALTHOUGH WINDS WILL NOT GO COMPLETELY CALM
TONIGHT...THE SNOW ON THE GROUND WILL AID THE RADIATIONAL COOLING
CONDITIONS...WHICH COULD LEAD TO MVFR VISIBILITIES IN THE CLEAR
LOCATIONS (SUCH AS THE SOUTHERN TAF SITES).

CLOUDS WILL CONTINUE TO INCREASE ON WEDNESDAY...AS A FRONT MOVES
THROUGH THE SOUTHERN GREAT LAKES. THE NORTHERN TAF SITES WILL BE
THE MOST LIKELY TO EXPERIENCE MVFR CEILINGS AND EVEN SOME LIGHT
SNOW...AND THIS HAS BEEN INCLUDED AT KDAY. THIS FORECAST ALSO
APPEARS REASONABLE FOR KCMH/KLCK AS WELL...BUT JUST BEYOND THE END
OF THE TAF PERIOD.

OUTLOOK...MVFR CEILINGS ARE POSSIBLE WEDNESDAY NIGHT. MVFR/IFR
CONDITIONS ARE POSSIBLE FRIDAY NIGHT INTO SATURDAY.

&&

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

&&

$$
SYNOPSIS...BINAU
NEAR TERM...BINAU/HATZOS
SHORT TERM...BINAU
LONG TERM...JGL
AVIATION...HATZOS