Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 312234
AFDIND

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
532 PM EST SAT JAN 31 2015

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

&&

.SYNOPSIS...
ISSUED AT 435 PM EST SAT JAN 31 2015

A SIGNIFICANT STORM SYSTEM WILL IMPACT CENTRAL INDIANA STARTING
TONIGHT...AND CONTINUING THROUGH SUNDAY BEFORE FINALLY COMING TO AN
END EARLY MONDAY MORNING. AS THIS SYSTEM PUSHES AWAY FROM THE AREA
ON MONDAY...FRIGID TEMPERATURES WILL FILTER BACK INTO THE REGION.
THEN AFTER A RETURN TO NORMAL TEMPERATURES BY MID-WEEK...THE BITTER
COLD CONDITIONS WILL RETURN ONCE AGAIN FOR THE END OF THE WORK WEEK
IN THE WAKE OF A COLD FRONT MOVING THROUGH ON WEDNESDAY. THIS COLD
FRONT WILL ALSO BE RESPONSIBLE FOR WINTER PRECIPITATION FROM TUESDAY
NIGHT THROUGH WEDNESDAY NIGHT. COLD HIGH PRESSURE WILL BUILD BACK
OVER THE REGION FOR NEXT THURSDAY AND FRIDAY.

&&

.NEAR TERM /TONIGHT THROUGH SUNDAY NIGHT/...

ISSUED AT 435 PM EST SAT JAN 31 2015

FOCUS FOR THE NEXT 24 TO 36 HOURS IS THE STRONG LOW PRESSURE SYSTEM
DEVELOPING IN THE SOUTHERN PLAINS TONIGHT AND MOVING NORTHEAST INTO
THE OHIO VALLEY BY SUNDAY. FOR THE MOST PART...ALL THE 12Z MODELS
HAVE CONTINUED THE TREND OF PREVIOUS RUNS...WHICH TAKES THE LOW A
LITTLE FARTHER NORTHWARD. THIS IN TURN PULLS MORE WARM AIR INTO THE
REGION. AS STATED IN PREVIOUS FORECAST DISCUSSIONS...THERE WILL BE A
VERY SIGNIFICANT GRADIENT WITH REGARD TO SNOWFALL AMOUNTS ACROSS
CENTRAL INDIANA RANGING FROM LESS THAN AN INCH...POSSIBLY EVEN ZERO
TO A TRACE ACROSS THE FAR SOUTHERN COUNTIES...TO 9-12 INCHES ACROSS
THE NORTH IN CARROLL AND HOWARD COUNTY!

AHEAD OF THE LOW...ISENTROPIC LIFT DEVELOPS TONIGHT ALLOWING FOR A
MIXTURE OF SNOW AND POSSIBLY SOME RAIN TO OVERSPREAD THE AREA. A
COUPLE OF INCHES OF SNOW ACCUMULATION WILL BE POSSIBLE ACROSS THE
NRN COUNTIES TONIGHT...WITH VERY LITTLE IF ANY ACCUMULATION WELL TO
THE SOUTH OF THE I-70 CORRIDOR.

TEMPERATURES WILL WARM AHEAD OF THE LOW SUNDAY...ALLOWING FOR RAIN
TO MIX IN WITH SNOW...OR EVEN BECOME THE PREDOMINANT PRECIPITATION
TYPE FOR THE SOUTHERN HALF OF THE FORECAST AREA...ESPECIALLY DURING
A PERIOD SUNDAY AFTERNOON.

THE LOW BEGIN TO MOVE EAST OF THE REGION BY SUNDAY EVENING AND
COLDER AIR WILL THEN QUICKLY WORK IN ON THE BACKSIDE OF THE
SYSTEM...THUS CHANGING ALL THE PRECIPITATION BACK TO SNOW BY SUNDAY
NIGHT. IN ADDITION TO THE PRECIPITATION...THE WINDS WILL PICK UP
STARTING LATE SUNDAY AFTERNOON THANKS TO A STRENGTHENING TIGHT
PRESSURE GRADIENT WITH THIS SYSTEM AND WINDS WILL GUST UPWARDS OF 30
MPH. THIS WILL HAVE A NEGATIVE IMPACT ON TRAVEL...AT LEAST FOR THE
NORTHERN COUNTIES IN THE WINTER STORM WARNING AND ADVISORY AS
BLOWING SNOW BECOMES AN ISSUE WHICH CAN REDUCE VISIBILITIES AND ALSO
DRIFTING SNOW.

AS FOR TEMPERATURE DURING THIS PERIOD...GENERALLY STUCK WITH MOS BUT
WENT SLIGHTLY WARMER AT NIGHT TO ACCOUNT FOR ALL THE PRECIPITATION
AND CLOUD COVER AND WAS MORE CONSERVATIVE WITH HIGHS AND KNOCKED
DOWN HIGHS TEMPERATURES A NOTCH OR TWO FOR SAME REASONING.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY/...

ISSUED AT 435 PM EST SAT JAN 31 2015

THE WINTER STORM WILL BE COMING TO AN END ON MONDAY MORNING...WITH
SOME LIGHT ADDITIONAL SNOW ACCUMULATIONS POSSIBLE BETWEEN 12 TO 18Z
MAINLY ACROSS THE EASTERN COUNTIES OF THE FORECAST AREA AS THE LOW
ACCELERATES AWAY FROM THE REGION. ON THE BACK SIDE OF THE
STRENGTHENING SURFACE LOW...GUSTY NNW FLOW WILL LEAD TO STRONG COLD
ADVECTION AND HIGH TEMPERATURES FOR MONDAY WILL BE WELL BELOW NORMAL
RANGING FROM THE LOW TEENS (NORTH) TO LOW 20S (SOUTH). STRONG
NORTHERLY WINDS WILL ALLOW WIND CHILLS TO DROP TO BELOW ZERO ON
MONDAY AND TUESDAY MORNINGS. HIGH PRESSURE IS QUICK TO REESTABLISH
ITSELF ACROSS THE AREA FOR THE BEGINNING OF THE WORK WEEK AND BY
TUESDAY HIGHS WILL BE BACK IN THE 30S WHICH IS NORMAL FOR THIS TIME
OF YEAR.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...

ISSUED AT 251 PM EST SAT JAN 31 2015

THE EXTENDED TIMEFRAME IS CHARACTERIZED BY A COUPLE OF LIGHT SNOW
PRODUCING UPPER WAVES AND A COUPLE OF WELL BELOW NORMAL TEMPERATURE
DAYS BRACKETED BY A COUPLE SEASONAL DAYS.

A QUICK MOVING WEAK UPPER WAVE WILL MOVE ACROSS THE OHIO RIVER
VALLEY TUESDAY AFTERNOON THROUGH TUESDAY NIGHT...BRINGING LIGHT
SNOW CHANCES TO THE NORTHERN HALF OF CENTRAL INDIANA MAINLY ON
TUESDAY NIGHT. AFTER A COLD FRONT SLIDES SOUTHEAST THROUGH THE
FORECAST AREA WEDNESDAY...TEMPERATURES SOME 10 TO 15 DEGREES
BELOW NORMAL ARE EXPECTED INTO FRIDAY INCLUDING A RETURN OF
SINGLE DIGIT LOWS OVER PORTIONS OF CENTRAL INDIANA. ACCORDING TO
THE 12Z GFS...THE SECOND UPPER WAVE BEGINS TO AFFECT THE OHIO
RIVER VALLEY WEDNESDAY NIGHT WIPING A SWATH OF LIGHT SNOW ACROSS
PORTIONS OF SOUTHERN INDIANA. THERE IS SOME AMBIGUITY AS TO THE
EVOLUTION OF THIS SYSTEM...AS THE 12Z ECMWF SENDS THIS WEAK TROUGH
ACROSS THE NORTHERN PLAINS AND INTO THE AREA WEDNESDAY NIGHT AND
THURSDAY...PRODUCING VERY LITTLE ACROSS THE AREA. THIS STANDS IN
CONTRAST TO THE 12Z GFS DIGGING A MORE AMPLIFIED TROUGH ACROSS THE
CENTRAL AND SOUTHERN PLAINS DURING THE SAME TIMEFRAME. ACCOUNTED
FOR THIS LIGHT SNOW POSSIBILITY WITH SLIGHT CHANCE POP GENERALLY
ACROSS OUR SOUTHERN TWO TIER OF COUNTIES.

&&

.AVIATION /DISCUSSION FOR THE 010000Z TAFS/...
ISSUED AT 532 PM EST SAT JAN 31 2015

LOWER CONFIDENCE THAN USUAL TONIGHT AS MODEL DATA SUGGEST CRITICAL
THICKNESSES FOR PRECIPITATION TYPE WILL BE STRADDLING THE FORECAST
AREA. DIFFERENT PRECIPITATION TYPES WILL HAVE AN IMPACT ON
VISIBILITY RESTRICTIONS.

INITIAL BAND OF LIFT EXPECTED TO MOVE NORTHEAST ACROSS THE AREA
THROUGH ABOUT 010600Z OR SO. APPEARS KBMG WILL BE PREDOMINATELY
RAIN...WHILE KLAF WILL BE MOSTLY SNOW. KIND/KHUF LOOKS TO BE NEAR
THE TRANSITION ZONE...SO EXPECTING MIXED PRECIPITATION IN THOSE
AREAS. FOR THE MOST PART...THE RAIN OR RAIN/SNOW MIX WILL BE LIGHT
ENOUGH TO KEEP VISIBILITY RESTRICTIONS ABOVE IFR AT KBMG/KHUF/KIND.
A PERIOD OF IFR/LIFR VISIBILITY RESTRICTIONS MORE LIKELY IN KLAF
WHERE MOSTLY SNOW IS EXPECTED.

PRECIPITATION THREAT SHOULD DIMINISH TOWARDS/AFTER 010600Z AT THE
MORE SOUTHERN TAF SITES AS LIFT MOVES OFF TO THE NORTH. MORE
QUESTIONABLE WHETHER THERE WILL BE A BREAK IN KLAF LATER TONIGHT AS
BAND OF LIFT WILL EVENTUALLY SLOW DOWN AND BEGIN TO PIVOT BACK TO
THE SOUTH. NOT SURE AT THIS TIME WHETHER THAT POINT WILL BE OVER OR
NORTH OF KLAF. FOR NOW...WILL KEEP PERIODS OF IFR/LIFR IN KLAF
THROUGHOUT THE NIGHT...WITH A TENDENCY TOWARDS LOWER CONDITIONS AS
SUNRISE APPROACHES.

SURFACE WINDS EXPECTED TO GRADUALLY BACK AROUND TO 120-140 DEGREES
BY THE PRE DAWN HOURS AS LOW PRESSURE APPROACHES...BUT SPEEDS SHOULD
GENERALLY BE AT OR BELOW 7 KTS TONIGHT.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 7 AM EST MONDAY FOR INZ021-028>031-
035>042.

WINTER WEATHER ADVISORY UNTIL 7 AM EST MONDAY FOR INZ043>049.

&&

$$

SYNOPSIS...SMF
NEAR TERM...SMF
SHORT TERM...SMF
LONG TERM....MRD
AVIATION...JAS

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