Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 180900
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
400 AM EST THU DEC 18 2014

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

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

&&

.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 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1209 AM EST THU DEC 18 2014

KEPT MVFR CIGS THE ENTIRE TAF PERIOD AT BOTH SBN AND FWA WITH WEST
WINDS 7-10 KTS. EARLY EVENING UPPER AIR SOUNDINGS AND OVERNIGHT
AIRCRAFT OBSERVATIONS SHOW AN INCREASING DEPTH TO THE FRONTAL
INVERSION FROM SOUTHWEST TO NORTHEAST. AN AIRCRAFT SOUNDING AT FWA
AT 0316Z SHOWED THE BASE OF THE SUBSIDENCE INVERSION AROUND 850
MB...OR ABOUT 4000 FT ABOVE THE SFC. GIVEN UPSTREAM MOISTURE BELOW
THE INVERSION...A CONTINUED NORTHWEST TO NORTH FETCH AND THE
ADDITIONAL OF SOME LAKE MOISTURE...BELIEVE IT WILL BE DIFFICULT TO
BREAK OUT OF THE MVFR SC DECK FOR THE NEXT 24 HOURS. THEREFORE...
HAVE KEPT MVFR CIGS THE ENTIRE PERIOD.


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 11 AM EST THIS MORNING FOR LMZ043-046.

&&

$$

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


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