Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 231429
AFDIND

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
930 AM EST TUE DEC 23 2014

.UPDATE...
AVIATION SECTION HAS BEEN UPDATED BELOW.

&&

.SYNOPSIS...
ISSUED AT 338 AM EST TUE DEC 23 2014

A COMPLEX AND INTENSIFYING LOW PRESSURE WILL BRING UNSETTLED WEATHER
TO CENTRAL INDIANA THROUGH EARLY CHRISTMAS DAY. RAIN WILL TRANSITION
TO LIGHT SNOW LATE WEDNESDAY AFTERNOON WITH SNOW CONTINUING INTO
THURSDAY MORNING. HIGH PRESSURE WILL BRING A BRIEF PERIOD OF DRY
WEATHER THROUGH FRIDAY...WITH ANOTHER COLD FRONT PROVIDING
PRECIPITATION CHANCES FOR THE OHIO VALLEY FRIDAY NIGHT THROUGH
SUNDAY. COOLER DRIER AIR WILL RETURN FOR EARLY NEXT WEEK.

&&

.NEAR TERM /TODAY/...
ISSUED AT 338 AM EST TUE DEC 23 2014

RAINFALL COVERAGE HAS DROPPED OFF CONSIDERABLY SINCE LATE EVENING AS
LOW PRESSURE OVER IOWA BEGINS THE OCCLUSION PROCESS. BULK OF THE
RAIN NOW WELL NORTH OF THE FORECAST AREA OVER THE LOWER GREAT LAKES
WITH SCATTERED LIGHT SHOWERS LINGERING IN ITS WAKE. MILD DECEMBER
NIGHT ONGOING WITH WARM FRONT CURRENTLY LIFTING INTO SOUTHERN
COUNTIES. TEMPS WERE IN THE MIDDLE AND UPPER 40S AS OF 08Z.

AFOREMENTIONED SURFACE LOW WILL GRADUALLY WEAKEN OVER THE WESTERN
GREAT LAKES TODAY AS ENERGY DIVES INTO THE RAPIDLY AMPLIFYING UPPER
TROUGH DEVELOPING OVER THE CENTRAL PLAINS. THIS FEATURE WILL BECOME
A BIGGER PLAYER IN WEATHER ACROSS THE REGION WEDNESDAY. FOR TODAY
HOWEVER...EXPECT LIMITED PRECIP COVERAGE AS DRIER AIR WRAPS AROUND
THE BASE OF THE WEAKENING SURFACE LOW. FORCING ALOFT WILL BE MINIMAL
FOR THE FIRST HALF OF THE DAY AS WELL AND KEPT POPS AT CHANCE OR
LOWER THROUGH 18Z.

AS A SECONDARY LOW BECOMES ORGANIZED OVER THE NORTHERN GULF LATER
TODAY...DEEPER MOISTURE WILL BEGIN LIFTING BACK NORTHEAST INTO THE
OHIO AND TENNESSEE VALLEYS IN RESPONSE TO THE SHARPENING UPPER
TROUGH. HI-RES MODEL GUIDANCE PICKING UP THIS THINKING WELL...WITH
RAIN INCREASING IN COVERAGE ACROSS THE SOUTHEASTERN HALF OF THE
FORECAST AREA BY LATE DAY. WILL SLOWLY START BUMPING POPS UP FOR THE
AFTERNOON...WITH POTENTIAL FOR LIKELY POPS OVER FAR SOUTHEASTERN
COUNTIES BY EARLY EVENING.

DESPITE THE DRIER AIR ALOFT...MODEL SOUNDINGS MAINTAIN SOME FORM OF
A LOW LEVEL INVERSION OVER MUCH OF THE REGION THROUGHOUT THE DAY.
COULD SEE SOME BREAKS IN THE LOW DECK OVER THE WABASH VALLEY...BUT
IN GENERAL ANTICIPATE SKIES REMAINING MOSTLY CLOUDY ALL DAY.

TEMPS...NEAR STEADY TEMPS THROUGH DAYBREAK WILL WARM INTO THE LOWER
AND MIDDLE 50S FROM NORTHWEST TO SOUTHEAST UNDER NEUTRAL TO SUBTLE
WARM ADVECTION. TOOK A MOS BLEND WITH A LEAN TOWARDS THE MAV AS MET
GUIDANCE SEEMED AGGRESSIVE WITH ITS WARMING.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...
ISSUED AT 338 AM EST TUE DEC 23 2014

FORECAST CHALLENGES FOCUS ON THE IMPACTS FROM THE STRENGTHENING
SECONDARY LOW AS IT LIFTS NORTH THROUGH THE REGION ON WEDNESDAY.
00Z MODEL GUIDANCE STILL EXHIBITING DIFFERENCES BUT OVERALL THE
WINDOW FINALLY APPEARS TO BE NARROWING WITH RESPECT TO SYSTEM TRACK
WITH GREATER CONFIDENCE IN WINTRY/WIND IMPACTS FOR CENTRAL INDIANA.

THE LOW WILL TRACK THROUGH THE TENNESSEE VALLEY TONIGHT...THEN
CONTINUE NORTH INTO THE GREAT LAKES BY WEDNESDAY EVENING. CONSENSUS
TRACK OF THE LOW LOOKS TO COME RIGHT UP THROUGH THE EASTERN HALF OF
THE FORECAST AREA. NAM AND ECMWF TRACK THE SYSTEM ALONG THE
INDIANA-OHIO BORDER WHILE THE GGEM/OP GFS/PARALLEL GFS/SREF/ARW-
WRF ALL TRACK THE LOW DUE NORTH THROUGH CENTRAL INDIANA.
INDIVIDUAL GFS ENSEMBLE MEMBERS ARE TIGHTLY CLUSTERED ON THE
CENTRAL INDIANA TRACK AS WELL. NMM-WRF IS FURTHER WEST WITH THE ONLY
TRACK ALONG THE INDIANA-ILLINOIS BORDER. CONFIDENCE IS GROWING IN
A TRACK THROUGH THE HOOSIER STATE AND CONSIDERING THE RAPID
STRENGTHENING TO THE SYSTEM AS THE UPPER LOW TAKES ON A NEGATIVE
TILT...COULD SEE THE CONSENSUS EVEN SHIFT A BIT WEST FROM ITS
CURRENT LOCATION.

EXPECT RAINFALL COVERAGE TO BECOME WIDESPREAD TONIGHT AS
PROGRESSIVELY DEEPER MOISTURE AND FORCING EXPAND INTO THE OHIO
VALLEY WITH THE APPROACHING SURFACE WAVE. SUPPORT EXISTS FOR
CONVECTIVE ELEMENTS TO PRECIPITATION LATE TONIGHT AND EARLY
WEDNESDAY WITH SOME HINTS OF A BRIEF PERIOD OF ELEVATED INSTABILITY
IMPACTING THE SOUTHEAST HALF OF THE FORECAST AREA. WOULD NOT BE
SHOCKED TO SEE A FEW RUMBLES OF THUNDER WEDNESDAY MORNING...BUT
CONFIDENCE JUST IS NOT HIGH ENOUGH TO MENTION IN THE FORECAST AT
THIS TIME. BETTER POTENTIAL FOR ISOLATED THUNDER WILL EXIST JUST
SOUTHEAST OF THE FORECAST AREA WHERE LOW LEVEL JET IS AIMED.

AS THE LOW LIFTS INTO THE REGION AND STRENGTHENS BY WEDNESDAY
AFTERNOON...A WELL DEFINED TROWAL AT 850MB WILL ARC ACROSS THE LOWER
GREAT LAKES BACK INTO NORTHERN ILLINOIS IN THE VICINITY OF THE UPPER
LOW. COLDER AIR WILL UNDERCUT THIS FEATURE AND SHIFT EAST INTO THE
FORECAST AREA DURING THE LATE AFTERNOON WITH RAIN GRADUALLY
TRANSITIONING TO A WET SNOW. HEAVIEST SNOWFALL IS ANTICIPATED ACROSS
CENTRAL AND NORTHERN ILLINOIS IN VICINITY OF THE TROWAL AND
UNDERNEATH A MID LEVEL DEFORMATION BAND.

WHILE THE GREATER IMPACTS FROM SNOW ARE LIKELY TO BE NORTHWEST OF
THE FORECAST AREA...HOPE IS NOT ENTIRELY LOST FOR THOSE STILL
LOOKING TO WAKE UP TO A WHITE CHRISTMAS. THE DEFORMATION BAND WILL
QUICKLY LIFT NORTHEAST INTO THE EVENING...CLIPPING THE NORTHERN
WABASH VALLEY IN THE PROCESS. THIS IS THE LOCATION WHERE THE
GREATEST CONFIDENCE IN LIGHT ACCUM SNOWS EXIST AS SNOWFALL RATES MAY
BE HEAVY ENOUGH FOR A PERIOD OF TIME TO OVERCOME THE MARGINAL LOW
LEVEL TEMP ISSUES THAT WILL BE PRESENT. RIGHT NOW...SEE THE
POSSIBILITY FOR 1-2 INCHES NORTHWEST OF A ROCKVILLE-CRAWFORDSVILLE-
KOKOMO LINE. RATHER SHARP GRADIENT FOR POINTS SOUTH AND EAST WITH
AMOUNTS DROPPING OFF TO JUST A DUSTING AT BEST OVER SOUTHEAST
COUNTIES. SNOW SHOWERS WILL DIMINISH IN COVERAGE AND INTENSITY EARLY
CHRISTMAS MORNING AND COMPLETELY END BY MIDDAY AS THE LOW ROCKETS
INTO WESTERN QUEBEC. LOW CLOUDS MAY LINGER FOR MUCH OF THE DAY WITH
CLEARING THURSDAY AFTERNOON AND EVENING AS DRIER AIR ADVECTS INTO
THE REGION.

WINDS WILL BECOME RATHER GUSTY WEDNESDAY INTO CHRISTMAS MORNING WITH
THE PASSAGE...BUT OVERALL IMPACTS FROM WIND NOT EXPECTED TO BE AS
GREAT AS PREVIOUSLY THOUGHT OVER THE LAST FEW DAYS. COULD SEE GUSTS
PEAK IN THE 35 TO 40MPH RANGE WEDNESDAY NIGHT...BUT THESE WILL
LIKELY DO LITTLE TO BLOW SNOW AROUND CONSIDERING ITS WET AND SLOPPY
NATURE WITH RATIOS ON THE ORDER OF 8/10-1 AT BEST AND SURFACE TEMPS
THAT WILL REMAIN AT OR ABOVE FREEZING DURING THE TIMEFRAME WHEN SNOW
IS GREATEST. STILL THOUGH...THOSE WITH TRAVEL INTERESTS LATE
WEDNESDAY NIGHT INTO EARLY CHRISTMAS DAY ARE ENCOURAGED TO REMAIN
ABREAST OF FORECAST UPDATES OVER THE NEXT COUPLE DAYS.

TEMPS...EXPECT WEDNESDAY HIGHS BY MIDDAY WITH FALLING TEMPS INTO THE
AFTERNOON AS COLD ADVECTION ARRIVES. AS MENTIONED ABOVE...TEMPS NOT
EXPECTED TO GO BELOW FREEZING UNTIL LATE WEDNESDAY NIGHT AND EARLY
THURSDAY IN THE 29-32 RANGE. SOUTHEAST COUNTIES MAY NOT DROP BELOW
FREEZING AT ALL WEDNESDAY NIGHT. GENERALLY TOOK A MOS BLEND ON TEMPS
THROUGH WEDNESDAY NIGHT...THEN UNDERCUT GUIDANCE THURSDAY/THURSDAY
NIGHT.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
ISSUED AT 248 AM EST TUE DEC 23 2014

FOR MUCH OF THE PERIOD MODELS ARE CLOSE ENOUGH TO ACCEPT THE
SUPERBLEND INITIALIZATION. HOWEVER THERE ARE SOME DIFFERENCES IN
HANDLING OF SYSTEM IMPACTING CENTRAL INDIANA AROUND SUNDAY. WITH
UNCERTAINTY IN TIMING AND LOCATION...STAYED CLOSE TO THE
INITIALIZATION HERE AS WELL.

FRIDAY WILL BE DRY AND MILD AS CENTRAL INDIANA GOES INTO A WARM
SECTOR OF AN APPROACHING LOW PRESSURE SYSTEM. PRECIPITATION WILL BE
POSSIBLE FRIDAY NIGHT AS A COLD FRONT MOVES INTO THE AREA. LATEST
MODEL RUNS INDICATE THAT CENTRAL INDIANA WILL REMAIN IN THE WARM AIR
DURING THE NIGHT...SO WENT JUST RAIN FOR PRECIPITATION TYPE.

THE FRONT WILL FINISH CROSSING THE AREA ON SATURDAY SO KEPT SOME
POPS IN. COLD ADVECTION WILL BEGIN...BUT FOR NOW IT LOOKS LIKE
TEMPERATURES WILL REMAIN JUST WARM ENOUGH FOR RAIN FOR MOST OF THE
AREA.

QUESTIONS THEN ARISE ON DEVELOPMENT OF A LOW PRESSURE SYSTEM ALONG
THE THE COLD FRONT SATURDAY NIGHT AND SUNDAY. ECMWF IS MUCH FARTHER
NORTH AND BRINGS MORE PRECIPITATION INTO THE AREA. GFS HAS NO
PRECIPITATION AND A MORE SUPPRESSED SYSTEM. WITH THE UNCERTAINTIES
INVOLVED STUCK WITH SUPERBLEND AND CHANCE POPS. IT SHOULD BE COLD
ENOUGH FOR SNOW.

WENT WITH SUPERBLEND/S DRY POPS SUNDAY NIGHT AND MONDAY...BUT IF
ECMWF IS RIGHT WOULD HAVE TO ADD SNOW CHANCES SUNDAY NIGHT.
CONFIDENCE IS LOW.

&&

.AVIATION /DISCUSSION FOR 231500Z KIND TAF UPDATE/...
ISSUED AT 531 AM EST TUE DEC 23 2014

MINOR TWEAKS MADE TO KIND TAF TO BETTER MATCH CURRENT CONDITIONS.
NO OTHER CHANGES ARE NEEDED AT THIS TIME.

PREVIOUS AVIATION DISCUSSION FOLLOWS...
VARIABLE FLYING CONDITIONS THROUGH THE DAYLIGHT HOURS...RETURNING TO
MVFR/IFR AFTER 00Z.

DRY SLOT FROM LOW PRESSURE SYSTEM IS WORKING INTO THE AREA AND
SCOURING OUT SOME OF THE LOWER CLOUDS QUICKLY ACROSS PORTIONS OF
ILLINOIS. SOME OF THIS WILL WORK INTO THE WESTERN TAF SITES EARLY IN
THE PERIOD...WITH EASTERN SITES SEEING SLOWER IMPROVEMENT.

BY 16-18Z EXPECT WESTERN SITES TO BE VFR WITH MVFR EXPECTED AT
EASTERN SITES. CONFIDENCE IS MEDIUM AT BEST WITH CEILINGS AT EASTERN
SITES SINCE IT IS UNCERTAIN ON HOW FAR EAST THE SCOURING WILL GET.
THESE CONDITIONS SHOULD PERSIST THROUGH THE AFTERNOON.

MODELS SUGGEST SOME RAIN IS POSSIBLE ACROSS EASTERN SITES AS EARLY
AS 19Z...BUT MAIN PUSH OF RAIN WILL NOT REACH SITES UNTIL AFTER 00Z.
WHEN THIS ARRIVES...CONDITIONS WILL DETERIORATE TO MVFR OR WORSE.

SOUTH/SOUTHWEST WINDS WILL SHIFT TO NORTHEAST AROUND 00-03Z AS LOW
PRESSURE APPROACHES.

&&

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

&&

$$

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

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