Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 300957
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
457 AM EST FRI JAN 30 2015

.SYNOPSIS...
ISSUED AT 455 AM EST FRI JAN 30 2015

LAKE EFFECT SNOW SHOWERS WILL DIMINISH TODAY AS A RIDGE OF HIGH
PRESSURE BEGINS TO BUILD IN FROM THE WEST. THIS RIDGE OF HIGH
PRESSURE WILL DEPART TO THE EAST TONIGHT ALLOWING FOR A RETURN OF
SOUTHERLY WINDS AND MILDER CONDITIONS FOR SATURDAY. A STORM SYSTEM
WILL ORGANIZE ACROSS THE ROCKIES ON SATURDAY AND WILL BRING A GOOD
CHANCE OF ACCUMULATING SNOW TO THE REGION FROM SATURDAY NIGHT
THROUGH SUNDAY NIGHT. HIGH TEMPERATURES TODAY WILL RANGE FROM THE
UPPER TEENS ACROSS SOUTHEAST LOWER MICHIGAN TO THE UPPER 20S ACROSS
WEST CENTRAL INDIANA. LOW TEMPERATURES TONIGHT WILL DROP BACK INTO
THE TEENS.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 455 AM EST FRI JAN 30 2015

A VIGOROUS UPPER LEVEL TROUGH DROPPING ACROSS THE SOUTHERN GREAT
LAKES REGION PROVIDED SOME SYNOPTIC ENHANCEMENT TO PRECIP...BUT
STRONGER FORCING WITH THIS VORT MAX IS PROGRESSING EAST OF THE AREA
EARLY THIS MORNING. THIS WILL RESULT IN A CONTINUED TRANSITION TO
MORE OF PURE LAKE EFFECT SNOW SHOWER SCENARIO FOR THIS
MORNING...ALTHOUGH SETUP LOOKS TO BE ON THE MARGINAL SIDE.
REINFORCING LOW LEVEL CAA PUSH WITH SECONDARY SFC TROUGH PASSAGE
OVERNIGHT WILL KEEP SHALLOW BASED INSTABILITY IN PLACE FOR CONTINUED
LAKE EFFECT SNOW SHOWERS THIS MORNING...WITH INVERSION HEIGHTS
LOWERING THROUGH MID MORNING AS STRONGER SYNOPTIC SCALE SUBSIDENCE
IS ESTABLISHED IN THE WAKE OF DEPARTING UPPER LEVEL TROUGH. ANY
ACCUMULATIONS SHOULD GENERALLY BE LESS THAN AN INCH AND MAINLY
THROUGH MID TO LATE MORNING.

OTHERWISE FOR TODAY MAIN FORECAST CHALLENGE WILL BE RESOLVING SKY
COVER TRENDS. UPPER INFLECTION ZONE/LOW LEVEL ANTICYCLONE TO
OVERSPREAD THE REGION TODAY WITH EARLY MORNING GUSTY WINDS
DIMINISHING. MID LEVEL SYNOPTIC SUBSIDENCE TO CONTINUE THIS MORNING
AND ALREADY SEEING SOME DECENT EROSION OF LOW CLOUD DECK ACROSS
PORTIONS OF THE AREA. CONCERN IS THAT SHARPENING LOW LEVEL INVERSION
UNDER THE INFLUENCE OF THIS SUBSIDENCE MAY ALLOW STRATOCU TO PERSIST
THROUGH THE DAY...PARTICULARLY DOWNWIND OF LAKE MICHIGAN. RETREATING
LOW LEVEL THERMAL TROUGH WILL RESULT IN SOUTHWEST TO NORTHEAST
GRADIENT FOR MAX TEMPS TODAY RANGING FROM MID 20S SOUTHWEST TO
AROUND 20 FAR NORTHEAST. BACKING LOW LEVEL WINDS IN ASSOCIATION WITH
THE RIDGE OF HIGH PRESSURE SHOULD TAKE ANY RESIDUAL LAKE EFFECT
CLOUDINESS NORTHEASTWARD ACROSS FAR NORTHERN PORTIONS OF THE AREA
TONIGHT...WITH OVERALL TREND TO PARTLY CLOUDY/MOSTLY CLEAR SKIES AND
LIGHT WINDS ALLOWING FOR MINS TO DROP BACK INTO THE TEENS EARLY
SATURDAY MORNING.

&&

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 455 AM EST FRI JAN 30 2015

THE MAIN CHALLENGES THIS PERIOD INCLUDE THE TIMING AND TRACK OF A
SHORTWAVE TROF WELL UPSTREAM OVER ALASKA THAT WILL RACE SOUTHEAST
INTO THE WESTERN GREAT LAKES REGION. NCEP MODELS AND OTHERS HAVE
RECENTLY BEEN TRENDING NORTH WITH THIS SYSTEM. THE GARCIA/MIXING RAW
RATIO SNOWFALL FAVORS SNOWFALL AMOUNTS BETWEEN 8 AND 10 INCHES.
HOWEVER...ISSUES INCLUDING SATURATION TIME...LOW LEVEL DRY AIR
ENTRAINMENT AND CONVECTION ALONG AND SOUTH OF THE WARM FRONT MAY CUT
DEEPLY INTO SNOWFALL AMOUNTS. CURRENT THINKING IS EVENT SNOWFALL
TOTALS OF 4 TO 9 INCHES...WITH THE LOWER AMOUNTS NORTH OVER LOWER
MICHIGAN AND THE HIGHER AMOUNTS OVER NORTHERN INDIANA AND NORTHWEST
OHIO.  CIPS TOP 15 ANALOGS PAINT A SOLID 4 TO 6 INCHES OF SNOW
ACROSS THE AREA. AFTER COORDINATION WITH NEIGHBORING OFFICES...
HAVE ELECTED TO HOLD OFF ISSUING A WATCH DUE TO UNCERTAIN MODEL
HANDING OF THIS SYSTEM AMID LINGERING UNCERTAINTIES. WILL HIGHLIGHT
CONCERNS IN A SPECIAL WEATHER STATEMENT FOR NOW. OTHERWISE...MUCH
COLDER AIR WILL BE OVER THE AREA FOR THE UPCOMING WORK WEEK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 123 AM EST FRI JAN 30 2015

SCATTERED SNOW SHOWERS TO CONTINUE OVER THE NEXT SEVERAL
HOURS...WITH TRANSITION TO MORE PURE LAKE EFFECT SNOW SHOWERS
AFTER 09Z. A STRONG UPPER VORT MAX DROPPING ACROSS THE SOUTHERN
GREAT LAKES REGION HAS ENHANCED COVERAGE/INTENSITY OF SCATTERED
SNOW SHOWERS ACROSS THE REGION. STRONGEST FORCING WITH THIS SHORT
WAVE WILL SLIP EAST OF THE TERMINALS AFTER 09Z...WITH CONTINUED
SCATTERED SNOW SHOWERS EXPECTED TO AFFECT KSBN THROUGH FRIDAY
MORNING. WILL MAINTAIN PRIMARILY MVFR CONDITIONS WITH THE PERIODIC
SNOW SHOWERS AT KSBN...ALTHOUGH VERY BRIEF PERIODS OF IFR VSBYS
ARE POSSIBLE WITH THE HEAVIER SNOW SHOWERS. INTENSITY OF LAKE
EFFECT SNOW SHOWERS SHOULD DIMINISH AFTER 12Z AS INVERSION HEIGHTS
CONTINUE TO LOWER...WITH TOTAL ACCUMULATIONS AT KSBN GENERALLY
LESS THAN AN INCH EXPECTED. A REINFORCING SURFACE TROUGH
ACCOMPANYING THIS STRONGER UPPER VORT MAX WILL CONTINUE TO ALLOW
FOR A PERIOD OF NORTHWEST WIND GUSTS AROUND 25 KNOTS...WHICH
SHOULD SLOWLY DIMINISH TOWARD DAYBREAK. CIGS IN THE 2500-3500 FT
RANGE MAY PERSIST INTO MUCH OF FRIDAY AS SYNOPTIC SUBSIDENCE
STRENGTHENS LOW LEVEL INVERSION HELPING TO TRAP LOW CLOUDS.

&&

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

$$

SYNOPSIS...MARSILI
SHORT TERM...MARSILI
LONG TERM...SKIPPER
AVIATION...MARSILI


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