Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 171241
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
ISSUED BY NATIONAL WEATHER SERVICE INDIANAPOLIS IN
741 AM EST WED DEC 17 2014

.SYNOPSIS...
ISSUED AT 424 AM EST WED DEC 17 2014

COLDER CONDITIONS CAN BE EXPECTED TODAY. A FEW AREAS OF LIGHT
SNOW ALONG WITH PATCHY FREEZING DRIZZLE WILL CHANGE TO ALL SNOW
BEFORE ENDING EARLY TODAY. LIGHT LAKE EFFECT SNOW SHOWERS ACROSS
SOUTHERN LOWER MICHIGAN AND FAR NORTHERN INDIANA WILL LINGER
THROUGH TONIGHT WITH LIGHT SNOW ACCUMULATIONS POSSIBLE. HIGHS
TODAY WILL BE ONLY FROM 30 TO 35. LOWS TONIGHT WILL DIP INTO THE
UPPER TEENS TO MID 20S.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 735 AM EST WED DEC 17 2014

NO SIGNIFICANT CHANGES MADE OTHER THAN REMOVAL OF PRE DAWN DATA AS
IT APPEARS LIGHT POST FRONTAL PRECIPITATION HAS ENDED. STILL
REMAINS A LOW THREAT FOR PRECIPITATION OFF THE LAKE BUT PRIMARILY
CONFINED TO LOCATIONS IN MICHIGAN OR NEARBY.

PREVIOUS DISCUSSION ISSUED AT 422 AM EST WED DEC 17 2014...

LIGHT POST FRONTAL PRECIPITATION HAD FORMED IN THE AREA OF COLD AIR
ADVECTION OVERNIGHT. NCEP MODELS WERE NOT HANDLING THIS LIGHT
PRECIPITATION VERY WELL. DEEPER LIFT HAD DIMINISHED...SO ONLY LIGHT
PRECIPITATION IS EXPECTED. HOWEVER... WHERE THE DENDRITIC GROWTH
ZONE WAS ABOVE THE CLOUD LAYER...PATCHY FREEZING DRIZZLE WAS BEING
REPORTED. COLD AIR ADVECTION EARLY THIS MORNING SHOULD HELP DEEPEN
THE COLD LAYER AND HELP TURN ANY REMAINING PRECIPITATION TO JUST
SNOW. FOR NOW...DUE TO THE PATCHY AND BRIEF NATURE OF THE FREEZING
DRIZZLE...HAVE ISSUED A SPECIAL WEATHER STATEMENT FOR NORTHERN
INDIANA AND NW OHIO. OTHERWISE...LIGHT LAKE EFFECT SNOW SHOWERS
SHOULD PERSIST. GIVEN DELTA T VALUES RISING TO AROUND 11C AND
RELATIVELY LOW INVERSION HEIGHTS...MINOR SNOW ACCUMULATIONS OVER THE
FAR SOUTHWEST CORNER OF LOWER MICHIGAN INTO ADJACENT AREAS OF
NORTHWEST INDIANA ARE POSSIBLE TODAY AND TONIGHT.

&&

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 422 AM EST WED DEC 17 2014

MOST OF THIS LONG TERM PERIOD WILL BE RELATIVELY QUIET WITH A
TRANSITION TO A MORE ACTIVE PATTERN BY END OF PERIOD AND INTO
CHRISTMAS.

LONG TERM PERIOD BEGINS ON THURSDAY WITH A LOW END LAKE ENHANCED
RESPONSE EXPECTED TO SEASONABLY COLD AIR AND SOME WEAK SYNOPTIC
FEATURES. SINGULARLY NOTHING REALLY STANDS OUT FOR LAKE EFFECT OR
SYNOPTIC PCPN BUT COLLECTIVELY THERE MAY BE A WINDOW FOR SOME LIGHT
SNOW SHOWERS OR DRIZZLE/FREEZING DRIZZLE. NAM12 SHOWS ELONGATED MID
LEVEL TROUGH AND AREA OF SHEARED VORTICITY SINKING SOUTHWARD THROUGH
THE LAKES REGION LATE TONIGHT. ASSOCIATED SURFACE TROUGH TO FOLLOW
BUT BECOMES STATIONARY OVER THE WESTERN LAKES AND INTERIOR MICHIGAN
THURSDAY AS DIABATIC HEATING FROM THE WARMER LAKES LEADS TO RESIDUAL
LAKE AGGREGATE TROUGHING. THIS TROUGH TO PROVIDE A CYCLONICALLY
CURVED FETCH DOWN THE LONG AXIS OF LAKE MICHIGAN. DELTA T VALUES WILL
ONLY BE MARGINAL IN THE 11 TO 13C RANGE AND MOISTURE WILL BE
CONFINED TO LOWEST 3KFT. THE DGZ IS NOT EVEN CLOSE TO SATURATED WITH
ONLY THE VERY TOP OF THE SATURATED LAYER NEARING THE -10C THRESHOLD.
WHAT MAKES THIS INTERESTING IS THE POSSIBILITY OF A FEW MESOVORTICES
DEVELOPING WITHIN AXIS OF SURFACE TROUGH NEAR THE LAKESHORE WHERE
DIFFERENTIAL HEATING AND CONVERGENCE WILL BE MAXIMIZED. THESE
PARAMETERS ARE SIMILAR TO THE LOCALLY STUDIED TYPE VI LAKE EFFECT
EVENTS BUT PARAMETERS ARE MUCH WEAKER THAN TYPICALLY EXPECTED.
HOWEVER...A SIMILAR CASE THIS FALL DID PRODUCE SEVERAL VORTICES
WHICH BRIEFLY ENHANCED PCPN NEAR THE LAKESHORE...THOUGH DELTA T
VALUES WERE SLIGHTLY HIGHER. NAM12 IS PICKING UP ON THIS POTENTIAL
WITH A RATHER STRONG 925MB VORTICITY SIGNATURE IN THE EXPECTED
LOCATION. THE LIMITING FACTORS ARE QUITE STRONG BUT BELIEVE THIS
SIGNATURE AND COMBINATION OF FEATURES WARRANT LOW TO MID CHANCE POPS
WITH SCATTERED WORDING. PCPN TYPE REMAINS A QUANDARY GIVEN THE LACK
OF ICE INTRODUCTION. WITH THE SMALL PROBABILITY OF THIS EVENT HAVE
OPTED TO STICK WITH SNOW SHOWERS FOR NOW AND EVALUATE HIGHER RES
GUIDANCE AS TIME NEARS AND SEE IF CONDITIONS COME TOGETHER. ANY SNOW
ACCUMULATIONS WILL BE LIGHT AND GENERALLY AN INCH OR LESS BUT ALSO
CONDITIONAL ON THIS ENHANCED DEVELOPMENT.

A WEAK SHORT WAVE TO PASS BY TO OUR SOUTH LATER THURSDAY WHICH
SHOULD HELP LOCK CLOUDS IN ACROSS THE REGION. WILL KEEP FORECAST DRY
BUT A FEW FLURRIES NOT OUT OF QUESTION. SEVERAL MORE WEAK SHORT
WAVES TO MOVE THROUGH BUT SHOULD STAY DRY THROUGH THE WEEKEND. A
STRONGER SYSTEM TO OUR SOUTH THIS WEEKEND STILL LOOKS TO STAY SOUTH
BUT WILL ALSO HELP TO KEEP SKIES CLOUDY.

THE END OF THIS PERIOD STILL LOOKS TO BE A CHALLENGE WITH A LOT OF
DIFFERENCES AMONG MODELS AND LACK OF CONFIDENCE IN ANY SPECIFIC
OUTCOME. MODELS ARE ALL IN AGREEMENT ON A DECENT STORM SYSTEM MOVING
THROUGH THE MIDWEST NEXT WEEK BUT SPECIFIC AND IMPORTANT DETAILS
VARY SIGNIFICANTLY IN THESE LONGER TIME PERIODS OF DAY 6 TO 9. FOR
NOW HAVE STAYED WITH THE CONSENSUS BLENDS OF MID CHANCE POP CATEGORY
TUESDAY. THERMAL PROFILES ALL OVER THE SPECTRUM BUT ACCUMULATING SNOWFALL
IS PLAUSIBLE BY CHRISTMAS EVE. THOSE WITH TRAVEL PLANS SHOULD STAY
TUNED AND STAY INFORMED AS DETAILS BECOME MORE CLEAR OVER THE NEXT
WEEK.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 549 AM EST WED DEC 17 2014

COLD AIR ADVECTION WILL CONTINUE TODAY. DRIER AIR WAS SPREADING
ACROSS NORTHERN INDIANA...SO EXPECT CLOUDY CONDITIONS WITH LAKE
EFFECT SNOW SHOWERS REMAINING MAINLY NORTHWEST AND NORTH OF SBN.
MVFR CIGS SHOULD IMPROVE BY LATE IN THE TAF PERIOD. WENT
OPTIMISTIC WITH VFR CONDITIONS AT BOTH SITES BY 00Z.


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 5 PM EST THURSDAY FOR LMZ043-046.

&&

$$

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


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