Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 241530
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1030 AM EST WED DEC 24 2014

.SYNOPSIS...
ISSUED AT 1017 AM EST WED DEC 24 2014

THE LOW HAS MOVED UP FROM THE SOUTH AND IS CURRENTLY IN THE
EASTERN PORTION OF THE REGION. THIS LOW WILL CONTINUE TO MOVE
NORTHWARD AND BE NORTH OF THE GREAT LAKES BY EARLY CHRISTMAS
MORNING. AS THE LOW PULLS AWAY AND TEMPERATURES DROP...THE RAIN
WILL CHANGE OVER TO SNOW...WHICH WILL END CHRISTMAS MORNING. HIGH
TEMPERATURES TODAY WILL RANGE FROM THE LOWER 40S IN THE WESTERN
PORTION OF THE REGION TO THE UPPER 50S IN THE EASTERN PORTION.
LOWS TONIGHT WILL BE IN THE LOWER 30S.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 358 AM EST WED DEC 24 2014

COMPLICATED FCST TODAY INTO THIS EVENING AS RAPIDLY DEEPENING MID
LAT CYCLONE TRACKING NNE INTO THE LOWER LAKES BRINGS WIDESPREAD
RAIN, GUSTY WINDS, NON ZERO THUNDER CHANCES, AND A CHANGEOVER TO
SNOW LATER THIS AFTERNOON/EVENING...

SYNOPTICALLY SPEAKING...A 170 KT 300MB JET AXIS ROUNDING THE BASE OF
TROUGH INTO THE TN/EASTERN OH VALLEYS WILL ACT TO SHARPEN THE
SOUTHERN FLANK OF AN ANONYMOUSLY DEEP CENTRAL CONUS UPPER TROUGH
TODAY...WITH A SOUTHERN PLAINS SHORTWAVE AND IMPRESSIVE 200 METER 5H
HEIGHT FALL CENTROID TRACK NORTHEAST INTO CENTRAL/NORTHERN INDIANA
BY LATER THIS AFTERNOON AND LOWER MI BY THIS EVENING. THIS DEEP
LAYER UVM RESPONSE AUGMENTED BY REDUCTION IN MID LVL STABILITY
(LAPSE RATES 7C/KM PLUS IN DEEP LAYER ABOVE TIGHTENING FRONTAL CIRC)
AND NICE PV COUPLING WITH LOW LEVELS WILL SUPPORT SFC CYCLOGENESIS
AND A RATHER SUBSTANTIAL DEFORMATION AXIS/TROWAL. AMPLE MOISTURE
(PWATS NEARING 1`) INTO CIRCULATION GIVEN GULF/SUBTROPICAL MOISTURE
CONNECTION INTO STRONG AGEOSTROPHIC RESPONSE UNDER THE ASCENDING
BRANCH OF JET WILL LEAD TO THIS STRONG MID LVL DEFORMATION/DYNAMIC
FORCING/FGEN...WHICH WILL NO DOUBT LEAD TO A RATHER SIGNIFICANT
PRECIPITATION EVENT...ESPECIALLY ALONG/WEST OF THE I-69 CORRIDOR.

TRACK AND IMPACTS...LATEST GUIDANCE AND OBSERVATIONAL TRENDS HAVE
SURPRISINGLY TRENDED EAST TOWARD PREVIOUS ECMWF GUIDANCE WITH
CONSENSUS SFC LOW TRACK TO THE IN/OH BORDER 18Z (990-995 MB)...TO
FAR SE LOWER MI 00Z (SUB 990 MB)...AND NEAR OR JUST NORTHEAST OF
LAKE HURON BY 06Z (SUB 980 MB). THIS RAPID DEEPENING AND EASTWARD
ADJUSTMENT POSSIBLY DUE TO SOUTHEAST CONUS CONVECTION/LRH FOCUSING
PV COUPLING FARTHER EAST AND LATER CLOSE OFF AT 700/500 MB. LUCKILY
NO REAL HAZARDOUS WEATHER OUTSIDE OF WIDESPREAD RAIN AND INCREASING
WINDS IN DEVELOPING TROWAL EXPECTED THROUGH MID AFTERNOON. THIS
CHANGES LATE THIS AFTERNOON INTO THIS EVENING...RANGING FROM
POTENTIAL FOR HEADLINE WORTHY WINDS/THUNDER TO CHANGEOVER TO
SNOW/ACCUMS WEST OF I-69.

EAST OF I-69...NICE ISALLOBARIC COUPLET (6-8MB/3HR PRESSURE RISES)
IN TANDEM WITH STEEPENING LOW LEVEL LAPSE RATES MAY BE ENOUGH TO TAP
INTO LLJ AND PRODUCE SOME ADVISORY LEVEL WIND GUSTS ACROSS FAR
EASTERN ZONES BY THIS AFTERNOON/EVENING. ISO CONVECTION/STRONGER
SHOWERS ALSO A SLIGHT CONCERN FOR HIGHER GUSTS. OPTED TO ISSUE A
WIND ADVISORY FOR GUSTS TO 45 MPH DURING THIS TIME FOR MOST OUR OF NW
OH COUNTIES. OTHERWISE...LOWERED POPS FOR RAIN A BIT THIS
MORNING/EARLY AFTN ACROSS THE SOUTHEAST WITH DRY SLOT WORKING IN.
DEFORMATION AXIS/COOLING DOES PIVOT THROUGH LATER IN THE
AFTERNOON/TONIGHT. HOWEVER...BULK OF LIFT/MOISTURE WITHIN IN
DENDRITIC GROWTH ZONE WILL HAVE SHIFTED NORTH OF THE LOCAL AREA BY
THIS TIME HINTING AT LITTLE IN THE WAY OF ACCUMULATIONS WITH SNOW
SHOWERS/DRIZZLE/MARGINAL TEMPS EAST OF I-69.

SNOW POTENTIAL ALONG/WEST OF I-69 ON WESTERN FRINGE OF SYSTEM...THIS
REMAINS THE PRIMARY ITEM OF CONSTERNATION GIVEN MARGINAL BOUNDARY
LAYER TEMPS AND LINGERING MODEL SPREAD IN TRACK/TIMING. JUST A 20-30
MILE SHIFT WEST OF EAST WILL MAKE ALL THE DIFFERENCE. AS MENTIONED
IN PREV DISCUSSIONS RAIN IS EXPECTED TO CHANGE OVER TO A NARROW BAND
OF WET SNOW (POSSIBLY HEAVY DUE TO STRONG FORCING/REDUCED STABILITY
MENTIONED ABOVE) WITHIN DEFORMATION AXIS AS STRONG UPWARD
MOTION/DYNAMICS OVERWHELMS. THE MILLION DOLLAR QUESTION IS WHEN DOES
THIS OCCUR...WHICH WILL LIKELY DEPEND ON HOW RAPIDLY THE CYCLONE
DEEPENS AND STRENGTH/WARMTH OF TROWAL. GIVEN THE UNCERTAINTY KEPT
SNOW AMOUNTS/TIMING SIMILAR TO THE INHERITED FCST...GENERALLY 1-3"
LATE THIS AFTN/EVE. PER COLLABORATION DID INCLUDE OUR FAR WEST IN AN
ADVISORY DURING THIS TIME GIVEN POTENTIAL FOR 1" PER HOUR SNOWFALL
RATES/REDUCED VISIBILITIES...WITH A LOWER CONFIDENCE SPECIAL
WEATHER STATEMENT SE OF THE ADVISORY AREA.

&&

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 355 AM EST WED DEC 24 2014

SYNOPTIC SCALE SUBSIDENCE AND LOW/MID LEVEL DRYING TO OCCUR EARLY
THURSDAY AS STORM SYSTEM EXITS THE AREA. DID MAINTAIN SOME SLIGHT
CHANCE SNOW SHOWER POPS FOR THE EARLY MORNING HOURS THURSDAY. MID
LEVEL RIDGING TO BUILD INTO THE REGION FOR THE AFTERNOON WHICH
SHOULD EVENTUALLY DIMINISH CLOUD COVER LATER IN THE DAY...ALTHOUGH
LOW BASED INVERSION MAY ALLOW SCT-BKN LOW CLOUDS TO PERSIST INTO THE
AFTERNOON. MODERATE LOW LEVEL WAA VIA WESTERLY LOW LEVEL FLOW FOR
THE AFTERNOON HOURS...ALTHOUGH GIVEN AFOREMENTIONED
SUBSIDENCE-ENHANCED INVERSION SOME QUESTION AS TO EXTENT OF SFC
WARMING. THUS...HAVE OPTED TO MAINTAIN HIGHS STEERED TOWARD THE
COOLER MET GUIDANCE...PARTICULARLY ACROSS THE WEST WHERE SOME NEW
SNOWCOVER IS POSSIBLE DEPENDING ON EXTENT OF WEDNESDAY ACCUMS.
LIMITED DIURNAL RANGES EXPECTED FOR THURSDAY NIGHT WITH STRONG LOW
LEVEL HEIGHT GRADIENT IN PLACE AND BROAD LOW LEVEL THERMAL RIDGING
HELPING TO MAINTAIN LOWS IN THE LOWER 30S.

LOW/MID LEVEL FRONTAL BOUNDARY WILL RE-FOCUS ACROSS THE
SOUTHERN/CENTRAL PLAINS BY FRIDAY MORNING AS A MORE AMPLIFIED UPPER
TROUGH IS DIGS ACROSS SOUTHWEST CONUS. INITIALLY ON FRIDAY BETTER
LOW LEVEL MOISTURE TRANSPORT WILL CIRCUMNAVIGATE LOCAL AREA DUE TO
PRESENCE OF SOUTHEAST CONUS LOW LEVEL ANTICYCLONE...WITH A PERIOD
(ALBEIT SHORT IN DURATION)...OF MORE SIGNIFICANT MOISTURE TRANSPORT
LATE FRIDAY AFTERNOON/FRIDAY NIGHT. A PORTION OF SOUTHWEST CONUS
UPPER PV ANOMALY IS EXPECTED TO LIFT THROUGH DOWNSTREAM PORTION OF
THE TROUGH ACROSS CENTRAL CONUS ON FRIDAY...BRINGING INCREASES
CHANCES OF RAIN BY FRIDAY AND SATURDAY WITH ASSOCIATED FRONTAL
BOUNDARY. THERE COULD BE ENOUGH LINGERING MID/UPPER LEVEL
FRONTOGENESIS FORCING LATE SATURDAY AFTERNOON/SATURDAY NIGHT FOR
SOME LIGHT SNOW BEHIND THE SFC COLD FRONT...AND WILL MAINTAIN LOW
CHANCES FOR THIS PERIOD.

FORECAST CONFIDENCE BEGINS TO DWINDLE FOR THE SUNDAY-TUESDAY
TIMEFRAME AS DETERMINISTIC SOLUTIONS REMAIN QUITE VARIED IN HOW TO
HANDLE ADDITIONAL SHORT WAVES DROPPING ACROSS WESTERN CONUS. MOST
NOTABLE OF THESE SYSTEMS IS ONE THE EC HAS BEEN ADVERTISING FOR THE
MONDAY/MONDAY NIGHT TIMEFRAME...ALTHOUGH LATEST 00Z EC HAS COME A
BIT MORE INLINE WITH MORE SUPPRESSED SOLUTIONS OF GFS/GEM KEEPING
BULK OF PRECIP JUST SOUTHEAST OF LOCAL AREA. THERE COULD BE SOME
MERIT TO THIS MORE SUPPRESSED IDEA GIVEN SUCH STRONG ANTICYCLONE
BUILDING ACROSS THE PLAINS...BUT THIS CERTAINLY WILL NEED TO BE
WATCHED IN UPCOMING CYCLES. DID HAVE TO MAINTAIN BROADBRUSH
SLIGHT/LOW CHANCE POPS -SN THROUGH MUCH OF THIS PERIOD. OF SLIGHTLY
HIGHER CONFIDENCE IN DAYS 5 TO 7 IS A TREND TO MUCH COLDER
TEMPERATURES LOOKING LIKE A STRONGER POSSIBILITY BY NEW YEARS WITH
MEDIUM RANGE MODELS STILL DEPICTING HIGHLY AMPLIFIED WESTERN
CONUS/CANADIAN RIDGING.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 638 AM EST WED DEC 24 2014

RAIN WILL CONTINUE TO EXPAND THIS MORNING AS LARGE SCALE SYNOPTIC
SUPPORT INCREASES IN ASSOCIATION WITH MID MS VALLEY UPPER
TROUGH. CONDITIONS WILL DETERIORATE TO IFR OR POSSIBLY LIFR THIS
MORNING...WITH LITTLE OR NO IMPROVEMENT EXPECTED THROUGH THE DAY.
SFC LOW PRESSURE ACROSS NORTHERN KENTUCKY WILL RAPIDLY STRENGTHEN
TODAY AS IT TRACKS INTO NORTHWEST OHIO...AND THEN TO SOUTHEAST
LOWER MICHIGAN THIS EVENING. COLDER AIR BEING DRAWN SOUTHWARD
SHOULD ALLOW FOR A RAIN CHANGING TO SNOW SCENARIO AT BOTH
TERMINALS IN ASSOCIATION WITH DEFORMATION FORCING. LITTLE CHANGE
MADE TO THE 06Z TAFS WITH BRUNT OF THIS ACCUMULATION AT KSBN IN
THE 00Z-06Z TIMEFRAME. CONFIDENCE IN SNOW ACCUMULATION AT KFWA
REMAINS SOMEWHAT LOWER WITH LATER CHANGEOVER TIMING FROM RAIN TO
SNOW...ALTHOUGH PROBABILITY OF AT LEAST A 3 HOUR WINDOW OF MORE
SOLID SNOW DOES APPEAR TO BE INCREASING AT KFWA THIS EVENING.
GUSTY WEST WINDS OF 30 TO 35 KNOTS ARE ALSO EXPECTED AT KFWA WHICH
WILL BE INLINE FOR THE STRONGER WINDS BASED ON FORECASTED TRACK OF
THE LOW PRESSURE AREA.


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...WINTER WEATHER ADVISORY FROM 4 PM EST /3 PM CST/ THIS AFTERNOON
     TO MIDNIGHT EST /11 PM CST/ TONIGHT FOR INZ003-004-012-013-
     020.

MI...WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO MIDNIGHT EST
     TONIGHT FOR MIZ077-078.

OH...WIND ADVISORY FROM 4 PM THIS AFTERNOON TO 3 AM EST THURSDAY FOR
     OHZ002-004-005-015-016-024-025.

LM...SMALL CRAFT ADVISORY UNTIL 4 PM EST THURSDAY FOR LMZ043-046.

&&

$$

SYNOPSIS...LOTHAMER
SHORT TERM...STEINWEDEL
LONG TERM...MARSILI
AVIATION...MARSILI


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