Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 200937
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
437 AM EST THU NOV 20 2014

.SYNOPSIS...
ISSUED AT 437 AM EST THU NOV 20 2014

A SERIES OF UPPER LEVEL DISTURBANCES WILL CONTINUE TO BRING COLDER
AIR INTO THE REGION. THIS WILL FAVOR THE INTENSIFICATION OF LAKE
EFFECT SNOW SHOWERS TODAY INTO THIS EVENING BEFORE DIMINISHING LATER
TONIGHT. MUCH BELOW NORMAL TEMPERATURES WILL CONTINUE INTO FRIDAY
WITH MODERATING TEMPERATURES BY THE WEEKEND. ANOTHER STORM SYSTEM
WILL BRING A LIKELIHOOD OF RAIN FOR THE WEEKEND. THERE IS A
POTENTIAL OF SOME SLEET OR FREEZING RAIN LATE FRIDAY NIGHT OR EARLY
SATURDAY IN ADVANCE OF THIS SYSTEM. HIGH TEMPERATURES TODAY WILL
REACH INTO THE MID 20S. LOW TEMPERATURES TONIGHT WILL RANGE FROM THE
UPPER SINGLE DIGITS ABOVE ZERO TO THE LOWER TEENS.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 437 AM EST THU NOV 20 2014

LAKE EFFECT SNOW SHOWER EVOLUTION TODAY WILL CONTINUE TO BE THE
FORECAST FOCUS THROUGH LATE TONIGHT. CURRENTLY NO IMMEDIATE PLANS
EARLY THIS MORNING TO CHANGE ONGOING WINTER WEATHER ADVISORY/WINTER
STORM WARNING HEADLINES.

LAKE EFFECT SNOW SHOWERS HAVE BEEN SOMEWHAT SLOW TO ORGANIZE THROUGH
MUCH OF LAST EVENING INTO THE OVERNIGHT HOURS. SHORT TERM NAM/RAP
BUFFER SOUNDINGS DO DEPICT RISING LAKE INDUCED EQUILIBRIUM HEIGHTS
OVER THE NEXT SEVERAL HOURS HOWEVER AS LOW/MID LEVEL COLD ADVECTION
CONTINUES ACROSS THE SOUTHERN GREAT LAKES REGION. WATER VAPOR
IMAGERY AT 07Z DOES DEPICTS A SHEARED UPPER LEVEL SHORT WAVE NOSING
INTO EAST CENTRAL WISCONSIN...WHICH WILL BE SHIFTING ACROSS THE
SOUTHERN GREAT LAKES REGION THROUGH MID MORNING. CHANNELED DPVA WITH
THIS FEATURE MAY ENHANCE LAKE EFFECT SNOW SHOWERS THIS
MORNING...ESPECIALLY CONSIDERING DEPTH OF LAKE INDUCED INSTABILITY
INCREASING. WITH SOME VERY SUBTLE BACKING OF LOW LEVEL WIND FIELD IN
ADVANCE OF THIS FEATURE...BULK OF SNOW SHOWER ACTIVITY THROUGH MID
MORNING MAY NOT MAKE SUBSTANTIAL SOUTHWARD PROGRESS FROM CURRENT
POSITIONING. MAIN TWEAK TO FORECAST THROUGH MID MORNING WAS TO
REDUCE POPS SOMEWHAT ACROSS SOUTHWEST PORTIONS OF THE ADVISORY AREA.

BY MIDDAY...A SECONDARY UPPER VORT MAX DROPPING ACROSS THE NORTHERN
GREAT LAKES THIS MORNING SHOULD DIG ACROSS SOUTHERN LOWER MICHIGAN.
PASSAGE OF THIS UPPER VORT MAX SHOULD YIELD A MORE FAVORABLE
TRAJECTORY FOR THE INDIANA PORTION OF THE WINTER WEATHER ADVISORY.
IT STILL APPEARS AS THOUGH FETCH CONSIDERATIONS SHOULD FAVOR
NORTHERN BERRIEN...CASS COUNTY MICHIGAN....AND POSSIBLY INTO ST.
JOSEPH COUNTY MICHIGAN FOR THE GREATER ACCUMULATION POTENTIAL. SOME
COMPETING FACTORS PERSIST IN TERMS OF ATTEMPTING TO RESOLVE EXACT
MAGNITUDES OF SNOW ACCUMULATION AND WILL COMPLICATE THE FORECAST
TODAY. DENDRITIC GROWTH ZONE DOES APPEAR TO MAINTAIN SATURATION IN
THE 950-850 HPA LAYER THIS AFTERNOON WITH GOOD CO-LOCATION TO
SHALLOW BASED UPWARD VERTICAL MOTION FIELDS. LAKE-700 THERMAL
DIFFERENTIALS ALSO SHOULD HOVER INTO THE 25 TO 30 DEGREE CELSIUS
RANGE THROUGH MOST OF THE DAY...WITH MAXIMUM LAKE INDUCED
EQUILIBRIUM HEIGHTS IN THE LATE MORNING TO MIDDAY TIMEFRAME.
HOWEVER...A RELATIVELY DRY LAYER ABOVE THE LOW LEVEL INVERSION WOULD
FALL INLINE MORE WITH WEAKER MULTIBAND EVENTS PER LOCAL CLIMATOLOGY
STUDIES. WILDCARD IN THIS SETUP DOES APPEAR TO BE POTENTIAL POTENCY
OF SYNOPTIC ENHANCEMENT ASSOCIATED WITH AFOREMENTIONED CHANNELED
VORTICITY ADVECTION LATER THIS MORNING/AFTERNOON. GIVEN THE
PROLONGED SETUP INTO EARLY THIS EVENING...HAVE OPTED TO NOT DEVIATE
SUBSTANTIALLY FROM PREVIOUS FORECAST WITH PERHAPS THE GREATEST
PERIOD OF CONCERN FOR MORE SIGNIFICANT LAKE EFFECT ACCUMULATIONS
CENTERED IN THE 18Z-00Z TIMEFRAME GIVEN SYNOPTIC FORCING/IMPROVING
FETCH. WILL CARRY 4 TO 7 INCH/LOCALLY HIGHER ACCUMS FOR BERRIEN/CASS
IN THE WINTER STORM WARNING WITH SOME INCREASING CONCERNS OF THE
ROLE OF LOW/MID LEVEL DRY AIR CUTTING TOTAL ACCUMULATIONS. FOR THE
INDIANA WINTER WEATHER ADVISORY COUNTIES...WILL CARRY 2 TO 4 INCH
ACCUMULATIONS...FOCUSED MAINLY ALONG AND NORTH OF INDIANA TOLL
ROAD...WITH 2 TO 5 INCHES/LOCALLY HIGHER AMOUNTS FOR MICHIGAN WINTER
WEATHER ADVISORY AREA (GREATER POTENTIAL FOR HIGHER ACCUMS WEST OF
INTERSTATE 69).

LAKE EFFECT SNOW SHOWERS TO CONTINUE THIS EVENING...BUT SHOULD BE
DIMINISHING IN INTENSITY AS SYNOPTIC SUBSIDENCE
STRENGTHENS/INVERSION HEIGHTS LOWER. WIND SPEEDS SHOULD ALSO
DIMINISH THIS EVENING WITH BLOWING/DRIFTING CONCERNS SLACKENING
DURING THE OVERNIGHT HOURS.

&&

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 437 AM EST THU NOV 20 2014

LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO WEAKEN FRIDAY AND END
DURING THE AFTERNOON AS INVERSION HEIGHTS FALL AND AS WINDS BACK TO
THE SOUTH. LITTLE ADDITIONAL SNOW ACCUMULATION IS EXPECTED. WEAK
UPPER LEVEL RIDGING WILL BE OVER THE AREA SATURDAY AHEAD OF AN
EJECTING SHORTWAVE TROF OVER THE SOUTHERN PLAINS. MOISTURE FLUX
CONVERGENCE WILL INCREASE ESPECIALLY IN THE 925/850 LAYER AND SHOULD
SUPPORT LIGHT PRECIPITATION. THERMAL PROFILES SUPPORT MAINLY
FREEZING RAIN EARLY SATURDAY...ALTHOUGH SOME SLEET IS POSSIBLE
ESPECIALLY OVER NORTHEAST AREAS WHERE THE COLD AIR IS DEEPER. THE
MAX TEMPERATURE IN WARM LAYER SHOULD BE AT LEAST 3C WHERE
PRECIPITATION OCCURS AND SHOULD LIMIT THE CHANCE FOR SNOW. A
RELATIVELY BRIEF WINTER WEATHER ADVISORY MAY BE NEEDED EARLY
SATURDAY MORNING GIVEN SUBFREEZING GROUND TEMPS AND SURFACE TEMPS.
OTHERWISE...THE EJECTING SHORTWAVE WILL BECOME NEGATIVELY TILTED AS
IT LIFTS NORTHEAST INTO THE WESTERN GREAT LAKES REGION. UP TO AN
INCH OF RAINFALL IS POSSIBLE SUNDAY INTO SUNDAY NIGHT AS
PRECIPITABLE WATER VALUES RISE TO OVER AN INCH. SOME CONCERN FOR
LOCAL FLOODING GIVEN FROZEN GROUND...MELTING SNOW COVER AND
ADDITIONAL RAINFALL.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1255 AM EST THU NOV 20 2014

LAKE INDUCED INSTABILITY TO INCREASE OVERNIGHT AS LOW/MID LEVEL
COLD ADVECTION CONTINUES ACROSS THE SOUTHERN GREAT LAKES REGION.
SHEARED UPPER LEVEL WAVES WILL ALSO BE DIVING SOUTHEASTWARD INTO
THE REGION AIDING IN LAKE EFFECT SNOW. WESTERLY FETCH SHOULD KEEP
BULK OF SNOW SHOWERS NORTH OF KSBN...ALTHOUGH TOWARD MIDDAY...SOME
VEERING OF FLOW IS EXPECTED THAT COULD BE MORE FAVORABLE FOR LAKE
EFFECT SNOW SHOWERS AT KSBN. NOT MUCH CHANGE MADE TO PREVIOUS
TAFS...WITH IFR CONDITIONS AT KSBN IN THE 19Z-23Z TIMEFRAME.
SLOWING BUILDING MID LEVEL HEIGHTS TOWARD THE END OF THE PERIOD
SHOULD GRADUALLY SUBSIDE LAKE EFFECT SNOW THREAT. OUTSIDE OF LAKE
EFFECT SNOW SHOWERS...MVFR CIGS OF 2-3K FT ARE EXPECTED TO IMPACT
KSBN FOR MUCH OF THE PERIOD...WHILE GENERALLY VFR CONDITIONS ARE
ANTICIPATED AT KFWA WHERE ONLY SCATTERED FLURRIES ARE EXPECTED.
WEST WINDS TO REMAIN GUSTY TO 20 TO 25 KNOTS THROUGH THE PERIOD.


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...WINTER WEATHER ADVISORY UNTIL 4 AM EST /3 AM CST/ FRIDAY FOR
     INZ003>006.

MI...WINTER WEATHER ADVISORY UNTIL 4 AM EST FRIDAY FOR MIZ079-080.

     WINTER STORM WARNING UNTIL 4 AM EST FRIDAY FOR MIZ077-078.

OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 10 AM EST FRIDAY FOR LMZ043-046.

&&

$$

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


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