Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 181735
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1235 PM EST THU DEC 18 2014

.SYNOPSIS...
ISSUED AT 1240 AM EST THU DEC 18 2014

LIGHT LAKE EFFECT SNOW SHOWERS ARE POSSIBLE TODAY INTO THIS
EVENING AS A TROF MOVES SOUTH OVER LOWER MICHIGAN INTO NORTHERN
INDIANA. LITTLE IF ANY SNOW ACCUMULATION IS EXPECTED. HIGHS TODAY
AND FRIDAY WILL BE AROUND 30 TO 35. LOWS TONIGHT WILL BE IN THE
20S.

&&

.UPDATE...
ISSUED AT 950 AM EST THU DEC 18 2014

BAND OF LAKE EFFECT SNOW ASSOCIATED WITH SFC TROF MOVG SOUTH THROUGH
SRN MI/LM AND WK LAKE INDUCED INSTABILITY PASSED THROUGH MKG THIS
PAST HOUR WITH APPARENTLY SOME LIGHT ACCUM PER ASOS OB. THIS BAND IS
EXPECTED TO REMAIN NORTH OF OUR CWA THROUGH DAYLIGHT HOURS TODAY BUT
SHOULD REACH OUR SWRN MI COUNTIES EARLY THIS EVE. KEPT A CHC OF
PRECIP IN THE FCST ACROSS NRN PORTION OF THE CWA DUE TO WK LIFT
ASSOCIATED WITH WKNG UPR TROF MOVG EAST INTO THE OH VALLEY AND SOME
WK LAKE ENHANCEMENT. HWVR CHANGED PRECIP WORDING FOR THE DAYTIME
PERIOD TO FLURRIES/FREEZING DRIZZLE AS EXPECT A NON-MEASURABLE EVENT
THROUGH EARLY EVE AND MOISTURE ON MORNING DTX SOUNDING CONFINED TO
JUST BLO DGZ. GIVEN SFC TEMP-DWPT SPREADS AROUND 5F... DO NOT EXPECT
FREEZING DRIZZLE WILL BE HEAVY ENOUGH TO CAUSE GLAZED SURFACES...
JUST SOME SMALL LIQUID DROPLETS ON THE WINDSHIELD ALONG WITH THE
SNOW GRAINS.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 358 AM EST THU DEC 18 2014

UPPER AIR SOUNDINGS FROM YESTERDAY EVENING AND OVERNIGHT AIRCRAFT
OBSERVATIONS SHOWED AN INCREASING DEPTH TO THE INVERSION FROM
SOUTHWEST TO NORTHEAST. THE BASE OF THE INVERSION RANGED FROM LESS
THEN 2000 FEET AT LINCOLN IL/ILX...TO 4000 FEET AT FT WAYNE TO 5000
FEET NEAR DETROIT. OVERNIGHT SATELLITE SHOWED CLOUDS FILLING IN OVER
LAKE MICHIGAN WHERE THE INVERSION HEIGHT WAS ONLY 3000 FEET. THIS
LOW INVERSION HEIGHT WAS LIMITING LAKE EFFECT SNOW SHOWERS.  A
SURFACE TROF WILL MOVE SOUTH ACROSS LOWER MICHIGAN THIS AFTERNOON
AND INTO NORTHERN INDIANA THIS EVENING...AND HELP TO KEEP A SMALL
CHANCE FOR SNOW SHOWERS LATE TODAY AND EARLY TONIGHT. OTHERWISE...
KEPT LOW CHANCES FOR LIGHT LAKE EFFECT SNOW SHOWERS GIVEN A LOW
INVERSION HEIGHT AND A MARGINAL FETCH WITH MEAGER DELTA T VALUES
AROUND 11C. BELIEVE IT WILL BE DIFFICULT TO BREAK OUT OF THE LOW
CLOUDS WITH THIS PATTERN THROUGH TONIGHT. GIVEN ABUNDANT CLOUD
COVER...KEPT TEMPERATURES COLD TODAY WITH HIGHS ONLY IN THE LOWER
30S.

&&

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 358 AM EST THU DEC 18 2014

MOST IMPORTANT INFORMATION FIRST SO THIS LONG TERM WILL BEGIN WITH
DISCUSSION OF POSSIBLE WINTER STORM NEXT WEEK. HYPE ALREADY WELL
UNDERWAY BUT A LOT OF UNCERTAINTY REMAINS WITH RESPECT TO THE VERY
IMPORTANT AND CRITICAL DETAILS OF WHEN AND WHERE THIS STORM WILL
CREATE IMPACTS. CAUTIOUS BUT INFORMATIVE APPROACH WARRANTED GIVEN
THE DAY 6 TO 7 TIME FRAME AND A VERY ENERGETIC PACIFIC JET STREAM
WHICH IS POORLY SAMPLED. THUS NUMEROUS CRITICAL CHANGES AND
DEVIATIONS IN MODEL SOLUTIONS EXPECTED WITH EACH ITERATION OVER THE
NEXT SEVERAL DAYS. THE BROAD SYNOPTIC AGREEMENT AMONG MODELS DOES
GIVE HIGHER THAN NORMAL CONFIDENCE THAT A SUBSTANTIAL STORM SYSTEM WILL
IMPACT SOME PART OF THE EASTERN CONUS REGION BY CHRISTMAS.
HOWEVER...ALREADY SEEING MODEL ADJUSTMENTS IN POTENTIAL TIMING AND
TRACK OF SYSTEM AS WELL AS HOW FAST COLDER AIR WILL SWEEP IN.
CONFIDENCE REMAINS BELOW NORMAL ON IMPORTANT DETAILS SUCH AS
TRACK...PCPN TYPE AND AMOUNTS. LATEST 00Z MODELS TRENDING SYSTEM
WESTWARD AS THEY TEND TO DO WITH DYNAMICALLY STRONG AND NEGATIVELY
TILTED SYSTEMS. CURRENT MODEL RUNS DO BRING COLD AIR IN ON CHRISTMAS
EVE SO KEPT PCPN TYPE ALL SNOW IN THIS PERIOD FOR NOW. MODELS STILL
SHOWING A VERY STRONG LOW DEVELOPING WITH TIGHT GRADIENT AS BLOCKY
PATTERN STALLS SYSTEM OVER GREAT LAKES REGION. ANY SNOW THAT DOES
FALL BY CHRISTMAS WILL CERTAINLY CREATE TRAVEL ISSUES AND HAVE
SIGNIFICANT IMPACTS DUE TO BLOWING AND DRIFTING. THIS REMAINS WORTHY
OF MENTION IN HWO BUT RESTRAINT SHOULD BE EXERCISED FOR NOW IN THE
FORECASTS OF TRACK AND SNOW AMOUNTS GIVEN LITTLE SKILL AT THIS TIME
RANGE.

OTHERWISE A RATHER BENIGN LONG TERM PERIOD EXPECTED LEADING UP TO
THIS POTENTIAL STORM. SEASONABLE TEMPERATURES TO START THE PERIOD
FRIDAY WITH A SUBTLE WARMING TREND INTO EARLY NEXT WEEK. SEVERAL
WEAK SHORT WAVES AND TRAPPED LOW LEVEL MOISTURE BENEATH INVERSION TO
LIKELY KEEP SKIES AT LEAST PARTLY CLOUDY IF NOT MOSTLY CLOUDY
THROUGH THE PERIOD. INITIAL SHORT WAVE AND MOISTURE SURGE MONDAY
WILL BRING INITIAL CHANCES OF PCPN INTO THE REGION.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1229 PM EST THU DEC 18 2014

WKNG SHRTWV MOVG EAST THROUGH THE OH VALLEY TODAY PROVIDING WK LIFT
WHICH COMBINED WITH LINGERING LOW LEVEL MOISTURE WAS CAUSING SOME
LIGHT SNOW WITH OCNL MVFR VSBY RESTRICTIONS. LACK OF MID LEVEL
MOISTURE SUGGESTS SOME POTENTIAL FOR VERY LIGHT -FZDZ AS WELL BUT
GIVEN PREDOMINANTLY -SN SFC OBS ATTM OPTED TO KEEP THIS OUT OF THE
18Z TAF. A BAND OF LAKE ENHANCED -SHSN ALONG A WK TROF MOVG SOUTH
ACROSS SRN LAKE MICHIGAN IS EXPECTED TO IMPACT SBN TONIGHT WITH A
BRIEF PERIOD OF -SHSN WITH MVFR VSBY RESTRICTIONS AND PSBLY LIGHT
ACCUMS. OTRWS LOW CLOUDS SHOULD REMAIN TRAPPED BENEATH INVERSION
THROUGH TONIGHT... WITH DIMINISHING CLOUD TEND FRIDAY AS DRIER AIR
FILTERS IN.

&&

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

$$

UPDATE...JT
SYNOPSIS...SKIPPER
SHORT TERM...SKIPPER
LONG TERM...LASHLEY
AVIATION...JT


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