Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 230005
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
705 PM EST MON DEC 22 2014

.SYNOPSIS...
ISSUED AT 1127 AM EST MON DEC 22 2014

TWO LOW PRESSURE SYSTEMS WILL MOVE THROUGH THE AREA THIS
WEEK...BRINGING RAIN AND SNOW TO THE REGION. EXPECT RAIN AND
DRIZZLE OVERNIGHT TONIGHT AND TUESDAY. ON WEDNESDAY...EXPECT RAIN
TO CONTINUE BEFORE CHANGING OVER TO SNOW LATE IN THE AFTERNOON.
SNOW IS EXPECTED WEDNESDAY NIGHT. HIGHS WILL BE IN THE 40S.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 408 PM EST MON DEC 22 2014

AREA OF RAIN ASSOCIATED WITH LOW LEVEL THETA-E ADVECTION/ISENT
LIFT/MOISTURE CONVERGENCE AHEAD OF DEEPENING CENTRAL PLAINS LOW
SHOULD CONT TO OVERSPREAD OUR CWA FROM WEST-EAST LATE THIS AFTN/EVE.
ANOTHER BATCH OF WIDESPREAD RAIN EXPECTED OVERNIGHT AS VORT MAX
ROTATING AROUND THE UPR LOW LIFTS NE THROUGH NRN IL AND OCCLUDING
SFC FRONT APPROACHES FROM THE WEST. RAINFALL SHOULD BE LIFTING NE
OUT OF OUR CWA TUE MORNING AS DRY SLOT WRAPPING AROUND THE LOW
SPREADS NE INTO OUR AREA. LOW LEVELS WILL LIKELY REMAIN SATURATED
WITH SOME WK LIFT CONTG UNTIL OCCLUDED FRONT PASSES... SO EXPECT
SOME LIGHT RAIN OR DRIZZLE WILL PERSIST UNTIL MIDDAY...ESPECIALLY
ACROSS NRN/ERN PORTIONS OF CWA. WITH WARM FRONT MOVG THROUGH THE
AREA THIS PERIOD... TEMPS SHOULD CONT ON A SLOW CLIMB OVERNIGHT AND
TUE... REACHING HIGHS IN THE M-U40S TUE AFTN.

&&

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 408 PM EST MON DEC 22 2014

...MAIN FOCUS OF THE LONG TERM IS THE STORM SYSTEM EXPECTED
CHRISTMAS EVE...

UNFORTUNATELY NEW MODEL RUNS CONTINUE TO DISAGREE ON THE SECONDARY
SFC LOW TRACK FOR CHRISTMAS EVE/CHRISTMAS DAY. THE 12Z GFS/GEM HAVE
A STRONGER SYSTEM MOVING FROM KY AT 12Z WED...TO NE IN/NW OH BY 18Z
WED...AND THE THUMB REGION/LAKE HURON BY 00Z THU. THE 00Z ECMWF/12Z
NAM HAVE A WEAKER SURFACE LOW ALONG THE GULF 12Z WED WITH A TROUGH
ACROSS THE OHIO VALLEY...THEN DEVELOP THE SURFACE LOW AND LIFT IT
INTO KY BY 18Z WED...WITH THE ECMWF A BIT STRONGER WITH THE LOW. AT
00Z THU BOTH MODELS HAVE THE SURFACE LOW SITUATED OVER WESTERN
OHIO...WITH THE NAM A BIT FURTHER NORTH. ALL OF THE MODELS HAVE A
CLOSED/CUT OFF LOW AND NEGATIVELY TILTED TROUGH IN THE MID
LEVELS...THOUGH THE NAM IS THE OUTLIER KEEPING THE CUT OFF LOW OVER
SOUTHERN ILLINOIS VERSUS THE GEM/GFS/ECMWF HAVE IT OVER SW LOWER MI.
AS MENTIONED IN PREVIOUS DISCUSSIONS...WITH THE DEEPENING LOW AND
THE NEGATIVELY TILTED TROUGH WANT TO LEAN TOWARDS THE SLIGHTLY
WESTWARD SOLUTIONS OF THE GEM/GFS. OVERALL WENT WITH A GEM/GFS/ECMWF
COMPROMISE GIVEN THESE SIGNIFICANT DIFFERENCES.

TUESDAY NIGHT AS THE FIRST SYSTEM MOVES OUT CUT POPS FOR THE FIRST
SIX HOURS AS DRY SLOT MOVES OVER THE AREA. AFTER 6Z HAVE INCREASING
TRENDS AGAIN AS SECONDARY LOW APPROACHES THE AREA. EXPECT RAIN
THROUGH THE LATE AFTERNOON ACROSS A MAJORITY OF THE CWA BEFORE THE
CHANGE OVER TO SNOW OCCURS...STARTING IN THE NORTHWEST NEAR LAKE MI.
EXPECT A MAJORITY OF THE SNOW ACCUMULATION TO BE IN THE 00Z TO 6Z
TIME FRAME AS TEMPERATURES FALL AND THE DEFORMATION ZONE OF THE
DEEPENING LOW SWINGS OVERHEAD. GENERALLY THINK THE GOING FORECAST OF
1 TO 3 INCHES IS STILL ON TRACK...MAINLY IN THE WEST AND CENTRAL CWA
GIVEN MIXED PRECIP/WARM GROUND CONCERNS WHEN THE FORCING IS STRONGEST.
AGAIN THOUGH...UNCERTAINTY REMAINS AS TO WHERE THE STRONGEST FORCING
WILL BE. TAKING A QUICK PEEK AT THE 12Z ECMWF...IT HAS COME IN LINE
CLOSER TO THE GEM/GFS SOLUTIONS...WHICH MAY FORCE THE AXIS OF
HEAVIER PRECIP FURTHER TO THE NORTHWEST. THOSE TRAVELING ON
CHRISTMAS EVE SHOULD CONTINUE TO MONITOR THE LATEST FORECASTS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 659 PM EST MON DEC 22 2014

LARGE AREA OF RAIN ALG NOSE OF STG ISENTROPIC LIFT/LL MSTR SURGE
WAS OVERSPREADING CWA THIS EVENING W/SWWD EXPANSION NOTED IN
REGIONAL COMPOSITE IMAGERY. MVFR CONDS TO START WILL DETERIORATE
GOING FWD OVERNIGHT W/AT LEAST IFR CONDS REALIZED AFT MIDNIGHT AND
FURTHER REDUCTION TO LIFR LIKELY TWD DAYBREAK GIVEN UPSTREAM
OBSERVATIONAL TRENDS OVR SE MO/WRN IL.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

SYNOPSIS...MCD
SHORT TERM...JT
LONG TERM...MCD
AVIATION...T


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