Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 210829
AFDIND

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
329 AM EST SUN DEC 21 2014

.UPDATE...
THE LONG TERM AND AVIATION SECTIONS HAVE BEEN UPDATED BELOW.

&&

.SYNOPSIS...
ISSUED AT 301 AM EST SUN DEC 21 2014

A LOW PRESSURE SYSTEM WILL BRING PRECIPITATION TO CENTRAL INDIANA
MONDAY THROUGH WEDNESDAY. AFTER A DRY CHRISTMAS...CHANCES FOR
PRECIPITATION WILL RETURN FRIDAY WITH A WEAKER SYSTEM. WARM AIR
AHEAD OF THE FIRST SYSTEM COULD BRING THE WARMEST READINGS OF
DECEMBER ON TUESDAY...THEN TEMPERATURES WILL RETURN TO CLOSER TO
AVERAGE BY CHRISTMAS.

&&

.NEAR TERM.../TODAY/
ISSUED AT 301 AM EST SUN DEC 21 2014

SKIES HAVE CLEARED ACROSS A GOOD PORTION OF CENTRAL INDIANA EARLY
THIS MORNING...BUT ADDITIONAL LOW CLOUDS WERE NEAR THE
ILLINOIS/INDIANA BORDER AND MOVING SLOWLY EAST.

CLOUD COVER WILL BE TOUGH TO PIN DOWN TODAY AND ONCE AGAIN
CONFIDENCE IS LOW IN THE DETAILS. LOW CLOUDS WILL MARCH INTO WESTERN
AND NORTHWESTERN SECTIONS OF THE AREA THIS MORNING. HOWEVER DRIER
AIR WILL FLOW INTO THE AREA AS WINDS INCREASE OUT OF THE SOUTHEAST.

FOR NOW WILL GO MOSTLY CLOUDY ACROSS THE NORTHWEST FORECAST
AREA...WITH SKIES REMAINING/BECOMING PARTLY CLOUDY ELSEWHERE.
ADJUSTMENTS WILL LIKELY HAVE TO BE MADE LATER THIS MORNING AS THE
EVOLUTION OF THE CLOUDS BECOMES CLEARER.

TEMPERATURES HAVE COOLED MORE THAN EXPECTED EARLY THIS MORNING DUE
TO THE PARTIAL CLEARING. THIS COLD START WILL HELP KEEP TEMPERATURES
BELOW MAV MOS AND CLOSER TO THE MET MOS TODAY.

&&

.SHORT TERM.../TONIGHT THROUGH TUESDAY NIGHT/
ISSUED AT 301 AM EST SUN DEC 21 2014

FOCUS IS ON CHANCES FOR PRECIPITATION THROUGH THE PERIOD. MODELS ARE
SHOWING DIFFERENCES AS WOULD BE EXPECTED WITH THE INCOMING SYSTEM
NOT FULLY SAMPLED YET. CANADIAN LOOKS TOO STRONG WITH THE
SYSTEM...WHILE THE LARGER CHANGE IN SOLUTIONS BETWEEN THE 12Z/00Z
ECMWF LEADS TO LOWER CONFIDENCE IN ITS SOLUTION THIS RUN. WILL USE A
BLEND OF REMAINING MODELS.

CLOUDS WILL INCREASE TONIGHT AS THE SYSTEM APPROACHES FROM THE WEST.
WILL GO A LITTLE WARMER THAN MAV MOS MOST AREAS.

ON MONDAY ISENTROPIC LIFT INCREASES DURING THE AFTERNOON. HOWEVER
DEEPER MOISTURE WILL BE SLOWER TO RETURN THANKS IN PART TO SOUTHEAST
WINDS IN THE LOWER LEVELS. WILL KEEP THE MORNING DRY AND GO WITH
SLIGHT CHANCE TO CHANCE POPS IN THE AFTERNOON. WITH THE CLOUDS AND
SOUTHEAST FLOW...MOS LOOKS TOO WARM FOR HIGHS. WILL CUT SOME.

MONDAY NIGHT AND TUESDAY FORCING RAMPS UP WITH SURFACE FRONT MOVING
INTO THE AREA...850MB WINDS APPROACHING 50KT...AND AN UPPER JET
MOVING IN. THUS WENT LIKELY POPS MOST AREAS BY LATE MONDAY NIGHT AND
LIKELY TO CATEGORICAL POPS ON TUESDAY.

CONTINUED LIKELY TO CATEGORICAL POPS TUESDAY NIGHT AS A SURFACE LOW
RIDES ALONG THE FRONT TOWARD CENTRAL INDIANA. LOOKS LIKE COLDER AIR
WILL BE SLOWER TO ARRIVE THAN PREVIOUSLY THOUGHT...SO WENT ALL RAIN
THROUGH TUESDAY NIGHT.

THE SYSTEM LOOKS TO BRING ENOUGH WARM UP INTO THE AREA ON TUESDAY
FOR HIGHS IN THE LOWER TO MIDDLE 50S...WHICH WILL BE THE WARMEST AIR
THIS MONTH ACROSS THE AREA.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
ISSUED AT 328 AM EST SUN DEC 21 2014

FOCUS FOR THE EXTENDED REMAINS ON POTENTIAL IMPACTS FROM A
STRENGTHENING LOW PRESSURE FOR CHRISTMAS EVE...FOLLOWED BY ANOTHER
STORM SYSTEM BRINGING PRECIPITATION TO THE OHIO VALLEY FRIDAY AND
FRIDAY NIGHT.

LEAD PORTION OF THE POWERFUL UPPER JET APPROACHING THE PACIFIC
NORTHWEST IS STARTING TO BE SAMPLED BY THE RAOB NETWORK.
HOWEVER...THAT HAS DONE LITTLE TO AID IN DEVELOPING A STRONGER
CONSENSUS FOR THE PHASED LOW PRESSURE SYSTEM TO IMPACT THE REGION
WEDNESDAY AS 00Z MODEL SUITE FRANKLY INTRODUCING MORE QUESTIONS THAN
ANSWERS. THE ECMWF AND OP GFS ARE BOTH SLOWER WITH PHASING THE
POLAR AND SUBTROPICAL JETS ALOFT...WITH THE STRENGTHENING UPPER
TROUGH NOT TAKING ON A NEGATIVE TILT UNTIL LATER ON WEDNESDAY AS THE
FEATURE PASSES CENTRAL INDIANA. CONSEQUENTLY THE DEEPENING SURFACE
LOW IS ALSO SLOWER TO TAKE PLACE...OCCURRING OVER THE EASTERN GREAT
LAKES BY EARLY CHRISTMAS MORNING. GFS ENSEMBLE MEMBERS STILL HAVE
QUITE A BIT OF SPREAD AND IT SHOULD BE NOTED THAT A COUPLE MEMBERS
REMAIN DEEPER AND FURTHER WEST WITH THE SURFACE WAVE TRACK.

TAKING INTO CONSIDERATION THAT MODEL SPREAD REMAINS LARGER THAN
DESIRED AND WITH BOTH THE OP GFS AND ECMWF SHIFTING THE LOW TRACK
FURTHER EAST WITH A SLOWER ENERGY PHASE...IT REMAINS PREMATURE TO
LATCH ONTO A SPECIFIC SOLUTION. 12Z RUNS TODAY AND DEFINITELY THE
00Z RUNS TONIGHT SHOULD GET FULL SAMPLING OF THE STRONG UPPER JET
ENERGY COMING INTO THE PACIFIC NORTHWEST. WITH THIS FEATURE SET TO
BE A MAJOR PLAYER INT HE EVOLUTION OF THE STORM SYSTEM...MAY
FINALLY START TO SEE A SLOW INCREASE IN MODEL CONSENSUS.

DO PLAN TO SLOW THE ARRIVAL OF THE COLDER AIR ON WEDNESDAY WITH RAIN
GRADUALLY CHANGING TO SNOW ON WEDNESDAY AFTERNOON AND EVENING.
CANNOT RULE OUT LIGHT ACCUMS BUT ATTEMPT TO EMPLOY ANY MORE DETAIL
WOULD BE FUTILE WITH SUCH TRACK UNCERTAINTY TO THE SURFACE WAVE. IF
THE WAVE TRACKS CLOSER TO THE FORECAST AREA VERSUS FURTHER
EAST...POTENTIAL FOR LIGHT ACCUMS WOULD BE GREATER WITH THE MID
LEVEL DEFORMATION BAND ALIGNING IN SOME MANNER OVER THE FORECAST
AREA. AS IT STANDS...WILL MAINTAIN CHANCE POPS THROUGH WEDNESDAY
NIGHT WITH STRONG WIND GUSTS BEING THE PRIMARY IMPACT...AND
POTENTIAL LIGHT ACCUMS AS A SECONDARY IMPACT. THE THREAT FOR TRAVEL
DISRUPTIONS REMAINS GREATEST DURING THIS TIME PERIOD...AND THOSE
WITH TRAVEL PLANS ARE ENCOURAGED TO MONITOR FORECASTS OVER THE NEXT
FEW DAYS.

CHRISTMAS DAY LOOKS TO BE QUIET AS THE SURFACE WAVE QUICKLY LIFTS
AWAY FROM THE REGION WITH SURFACE RIDGING DEVELOPING OVER THE OHIO
VALLEY. HIGHLY AMPLIFIED FLOW ALOFT WILL MAINTAIN AN ACTIVE
PATTERN...WITH ANOTHER SURFACE LOW TRACKING OUT OF THE CENTRAL
PLAINS AND INTO THE GREAT LAKES ON FRIDAY. STILL A LOT OF MODEL
VARIANCE WITH THIS SYSTEM...AND THAT IS NOT LIKELY TO CHANGE UNTIL
MODELS CAN GAIN A BETTER CONSENSUS ON THE CHRISTMAS EVE STORM. WILL
CARRY CHANCE POPS FOR FRIDAY AND FRIDAY NIGHT...WITH RAIN ON FRIDAY
TRANSITIONING TO LIGHT SNOW FRIDAY NIGHT BEFORE ENDING. SURFACE HIGH
PRESSURE WILL RETURN FOR THE WEEKEND...WITH CHILLY AND MAINLY DRY
CONDITIONS AS A SHARP UPPER TROUGH ESTABLISHES OVER THE GREAT
LAKES.

&&

.AVIATION /DISCUSSION FOR THE 210900Z TAF UPDATE/...
ISSUED AT 328 AM EST SUN DEC 21 2014

SKIES REMAIN RELATIVELY CLEAR OVER THE FORECAST AREA AT 08Z...WITH
STRATUS ATTEMPTING TO EXPAND BACK INTO THE STATE FROM THE WEST.
MADE SOME ADJUSTMENTS TO CLOUD FORECASTS AT ALL BUT KLAF...KEEPING
ONLY SCATTERED CLOUDS THROUGH DAYBREAK WITH MORE CLOUDS RETURNING
THEREAFTER.

06Z DISCUSSION FOLLOWS.

MODELS HAVE ABSOLUTELY NO HANDLE ON CEILINGS/CLOUD COVER FOR EARLY
THIS MORNING. THEY ARE DOING THE EXACT OPPOSITE OF WHAT THEY HAVE
DONE FOR THE PAST 5-6 DAYS...THEY ARE INDICATING CURRENT MVFR
VIS/S AND CEILING WHILE CENTRAL INDIANA HAS CLEARED OUT (IS VFR!)
AND WILL REMAIN THIS WAY AT LEAST UNTIL MUCH LATER THIS MORNING.
THEN /POSSIBLY/ ANOTHER INVERSION DEVELOPS AND BOTH
VISIBILITIES/CEILINGS WILL DROP TO MVFR WHICH WAS INDICATED IN ALL
OF THE TAFS SAVE FOR KHUF WHICH APPEARS TO REMAIN ON THE FRINGE OF
THE CLEARING SIDE.

SO THE REST OF THE TERMINALS KIND/LAF/BMG SHOULD EXPERIENCE
ANOTHER PERIOD OF MVFR FLIGHT CONDITIONS LATER THIS MORNING UNTIL
ABOUT NOON...THEN VFR CONDITIONS LOOK TO PREVAIL THERE AFTER FOR
ALL THE TAFS SITES. CONFIDENCE IS ON LOW-MEDIUM END THAT THESE
MVFR CONDITIONS WILL REDEVELOP...BUT WILL CONTINUE TO MONITOR
TRENDS AND IF OBSERVATIONS REMAIN OPTIMISTIC FOR THE NEXT SEVERAL
HOURS HERE AND UPSTREAM...MVFR CONDITIONS MAY BE PUSHED BACK OR
EVEN OMITTED WITH SUBSEQUENT TAF UPDATES.

WINDS WILL BE LIGHT AND VARIABLE THROUGH EARLY THIS MORNING...THEN
PICK UP TO AROUND 5KT FROM THE SE LATE THIS MORNING AND CONTINUE
INTO THE EVENING HOURS.

&&

.IND WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SYNOPSIS...50
NEAR TERM...50
SHORT TERM...50
LONG TERM....RYAN
AVIATION...SMF/RYAN

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