Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 211942
AFDIND

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
242 PM EST SUN DEC 21 2014

.UPDATE...
THE SYNOPSIS...NEAR TERM AND SHORT TERM SECTIONS HAVE BEEN UPDATED BELOW.

&&

.SYNOPSIS...
ISSUED AT 240 PM EST SUN DEC 21 2014

HIGH PRESSURE WILL PUSH OFF TO THE EAST TONIGHT. A COMPLEX LOW
PRESSURE SYSTEM WILL AFFECT THE AREA TOWARDS THE MIDDLE OF THE WEEK.
ANOTHER FRONTAL SYSTEM MAY AFFECT THE AREA BY THE END OF THE WEEK.

&&

.NEAR TERM /TONIGHT/...
ISSUED AT 240 PM EST SUN DEC 21 2014

NO PRECIPITATION EXPECTED TONIGHT AS SURFACE HIGH PRESSURE RETREATS
OFF TO THE EAST...HOWEVER THERE SHOULD BE A GRADUAL INCREASE IN
CLOUD COVER WITH TIME AS NEXT SYSTEM BEGINS TO ORGANIZE IN THE
PLAINS.

DEVELOPING WARM ADVECTION AND INCREASING CLOUD COVER SHOULD HELP TO
LIMIT THE TEMPERATURE FALL TONIGHT. LOW LEVEL THICKNESSES SUGGEST
THE GFS MOS LOWS TONIGHT LOOK REASONABLE.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
ISSUED AT 240 PM EST SUN DEC 21 2014

MODEL DATA CONTINUE TO OFFER DIFFERING SOLUTIONS AS TO THE EVOLUTION
OF THE PATTERN DURING THIS PERIOD. THERE IS CONSIDERABLE SPREAD
AMONG THE OPERATIONAL AND ENSEMBLE DATA AS TO THE LOCATION AND
INTENSITY OF A SECONDARY WAVE ALONG A TRAILING FRONTAL SYSTEM
TOWARDS THE MIDDLE OF THE WEEK...SO FORECAST CONFIDENCE IS LOWER THAN
USUAL. THE TRACK OF THIS WAVE VARIES ANYWHERE FROM UP THROUGH
WESTERN ILLINOIS TO ALONG THE WEST SIDE OF APPALACHIAN
MOUNTAINS...WITH SEA LEVEL PRESSURES RANGING FROM 982 MB TO 1005 MB.
THE ENSEMBLES AT THIS TIME SEEM TO FAVOR A WARMER MORE WESTERLY
SOLUTION...SO WILL NUDGE THE FORECAST IN THAT DIRECTION IN THE LATER
PERIODS.

LIFT IS PROGGED BY THE MODELS TO BRUSH THROUGH THE WEST CENTRAL AND
NORTHWEST ZONES BY THE MIDDAY HOURS ON MONDAY AND ON INTO THE
AFTERNOON HOURS. WILL START TO BRING IN SOME POPS BY THAT
TIME...WITH THE HIGHEST POPS OVER WEST CENTRAL AND NORTHWEST ZONES
CLOSEST TO BETTER LIFT.

WILL GO WITH HIGH POPS FOR MONDAY NIGHT INTO WEDNESDAY AS THE
PRIMARY FRONTAL ZONE SLOWS DOWN AND THE SECONDARY WAVE MOVES UP FROM
THE SOUTH. MODEL DATA IN GENERAL SUGGEST AIR MASS WON/T BE COLD
ENOUGH FOR A CHANGEOVER TO SNOW UNTIL WEDNESDAY...WITH THE WARMER
SOLUTIONS SUGGESTING NOT UNTIL WEDNESDAY AFTERNOON OR EVEN LATER.
FOR NOW...BASED ON THE OVERALL TRENDS...WILL PUSH BACK THE
CHANGEOVER TO SNOW FROM THE PREVIOUS FORECAST MORE INTO THE
AFTERNOON HOURS. SOME ACCUMULATING SNOW STILL LOOKS POSSIBLE
WEDNESDAY AFTERNOON...ESPECIALLY OVER THE NORTHWEST ZONES.

GIVEN THE WARMER TREND IN THE MODEL DATA...WILL LEAN TOWARDS THE
WARMER SIDE OF THE MOS GUIDANCE. HIGHS ON WEDNESDAY WILL PROBABLY BE
REACHED EARLY IN THE DAY...WITH TEMPERATURES FALLING OFF LATER.

&&

.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 211800Z TAF ISSUANCE/...
ISSUED AT 1208 PM EST SUN DEC 21 2014

VFR CONDITIONS SHOULD CONTINUE THROUGH TONIGHT WITH MVFR CEILINGS
INCREASING AFTER 14Z MONDAY AS A WARM FRONT APPROACHES FROM THE
SOUTHWEST.

WINDS WILL BE SOUTHEAST TO NEAR 10 KNOTS THIS AFTERNOON...6 KNOTS OR
LESS AFTER 00Z TONIGHT AND 10 KNOTS OR MORE AFTER 14Z MONDAY.


&&

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

$$

SYNOPSIS...JAS
NEAR TERM...JAS
SHORT TERM...JAS
LONG TERM....RYAN
AVIATION...MK

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