Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 190055
AFDIWX

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

.SYNOPSIS...
ISSUED AT 750 PM EST THU DEC 18 2014

A WEAK UPPER LEVEL DISTURBANCE DROPPING ACROSS THE SOUTHERN GREAT
LAKES WILL BRING SOME SCATTERED LIGHT SNOW SHOWERS TO SOUTHERN
LOWER MICHIGAN AND NORTHWEST INDIANA TONIGHT. OTHERWISE...A RIDGE
OF HIGH PRESSURE WILL BRING DRY CONDITIONS TO THE REGION THROUGH
THE WEEKEND WITH NEAR SEASONABLE TEMPERATURES. LOW TEMPERATURES
TONIGHT WILL DROP INTO THE LOWER TO MID 20S WITH HIGHS ON FRIDAY
REACHING INTO THE LOWER TO MID 30S.

&&

.UPDATE...
ISSUED AT 750 PM EST THU DEC 18 2014

A WEAK SFC TROUGH WILL DROP INTO SOUTHWEST LOWER MICHIGAN LATE
THIS EVENING ALLOWING FOR SCATTERED SNOW SHOWERS TO CONTINUE
SOUTHWARD PROGRESSION INTO NORTHWEST PORTIONS OF THE AREA. UPPER
LEVEL SHORT WAVE TROUGH DROPPING ACROSS SOUTHEAST ONTARIO/NORTHERN
LAKE HURON NOT LIKELY TO MAKE MUCH SOUTHWARD PROGRESS OVERNIGHT
WITH WEAK SHORT WAVE RIDGING BUILDING INTO THE WESTERN GREAT LAKES
TOWARD MORNING. LAKE EFFECT PARAMETERS STILL LOOK ON THE MEAGER
SIDE WITH LOW INVERSION HEIGHTS/DRY MID LEVEL AIR. WITH UPSTREAM
TROUGH CONTINUING TO SHEAR OUT AND LOSE SOUTHWARD PROGRESSION
OVERNIGHT...LIMITED DEPTH OF MOISTURE APPEARS TO SUPPORT AT LEAST
SOME THREAT OF LIGHT FREEZING DRIZZLE...WHICH HAS ALSO BEEN NOTED
IN RECENT UPSTREAM SFC OBS ACROSS SRN LOWER MICHIGAN. HAVE
MAINTAINED PREVIOUS LOW TO MID RANGE SCT -SHSN POPS TONIGHT IN
VICINITY OF LAKE MICHIGAN AND ADDED CHANCE -FZDZ ACROSS SOUTHWEST
LOWER MICHIGAN. CURRENTLY NOT EXPECTING ANY PATCHY FREEZING DRIZZLE
TO BE SIGNIFICANTLY IMPACTFUL GIVEN RELATIVELY DRY SUBCLOUD LAYER.
HAVE HELD OFF ON -FZDZ INCLUSION FOR NW INDIANA AND WILL MONITOR
UPSTREAM TRENDS TO DETERMINE IF THIS MENTION NEEDS TO EXPANDED
SOUTHWARD OVERNIGHT FOLLOWING PROGRESSION OF THE TROUGH. HAVE
MAINTAINED PREVIOUS ACCUMULATIONS OF A TENTH OF AN INCH OR
TWO...WITH BEST CHANCE OF THIS DUSTING IN VICINITY OF SFC TROUGH
AS IT PROGRESSES SOUTHWARD OVERNIGHT.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 314 PM EST THU DEC 18 2014

DRY SUB-CLOUD LAYER HAS THUS FAR KEPT PRECIP ASSOCIATED WITH WK OH
VALLEY SHRTWV ALL SNOW GRAINS AS OPPOSED TO FREEZING DRIZZLE IN
OUR AREA. STILL SOME FLURRIES BEING REPORTED OVER PORTIONS OF NRN
INDIANA BUT 88D RETURNS WANING THIS AFTN AS APPEARS WK UVM WAS
SHIFTING EASTWARD OUT OF OUR AREA. BAND OF LAKE ENHANCED SNOW
ASSOCIATED WITH WK TROF MOVG THROUGH SRN MI/LM LOCATED FM KBIV-
KGRR SHOULD DROP SOUTH INTO NWRN PORTION OF THE CWA THIS EVE AND
OVERNIGHT. WINDS VEERING TO NORTHERLY BY FRIDAY MORNING MAY
SUPPORT LIGHT SNOW SHOWERS PAST DAYBREAK ACROSS LAPORTE COUNTY
BUT LOWERING INVERSION SHOULD END ANY LAKE EFFECT SNOW BY MIDDAY.
WK LAKE INDUCED INSTABILITY... FAIRLY LOW INVERSION HEIGHTS... AND
LIMITED MOISTURE IN THE DGZ THROUGH THE EVENT SUGGESTS LITTLE
POTENTIAL FOR ACCUM. MOISTURE DEPTH EXPECTED TO INCREASE A BIT AS
TROF MOVES THROUGH AREA SO KEPT PTYPE JUST SNOW. OTRWS CLOUD DECK
TRAPPED BENEATH INVERSION REMAINS RATHER WIDESPREAD ACROSS THE SRN
GRTLKS/MIDWEST THIS AFTN AND WITH WK FLOW AS SFC RIDGE BUILDS INTO
OUR AREA TONIGHT AND FRIDAY... EXPECT MOSTLY CLOUDY SKIES TO
PERSIST. APPEARS BEST CHC FOR SOME SUNSHINE FRIDAY IS ACROSS SRN
MI ZONES AS DRIER AIR FILTERS SOUTHWARD FROM THE UPR GRTLKS. GIVEN
EXPECTED PERSISTENT LOW CLOUD DECK... LEANED TOWARD SMALLER
DIURNAL RANGE GUIDANCE WITH LOWS TONIGHT IN THE L-M20S AND HIGHS
FRI IN THE L-M30S.

&&

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 314 PM EST THU DEC 18 2014

FOCUS OF THE LONG TERM REMAINS ON POTENTIAL STORM NEXT WEEK WITH
LITTLE SENSIBLE WEATHER CONCERNS THROUGH THE WEEKEND GIVEN
PERSISTENT HIGH PRESSURE OVER THE REGION. HERE IS WHAT WE KNOW:

200 KT PACIFIC JET STREAK...CURRENTLY STILL ON THE OTHER SIDE OF THE
INTERNATIONAL DATE LINE...WILL EVENTUALLY WORK ITS WAY INTO THE
CENTRAL CONUS AND CARVE OUT A DEEP LONGWAVE TROUGH. DIGGING TROUGH
WILL BECOME NEGATIVELY TILTED...AND EVENTUALLY CLOSED OFF...BY
CHRISTMAS EVE. STRONG UPPER DIVERGENCE ON THE NOSE OF THIS
CYCLONICALLY CURVED JET STREAK WILL WORK IN TANDEM WITH IMPRESSIVE
DIFFLUENCE AND MIDLEVEL CVA TO SUPPORT A DEEP SURFACE LOW SOMEWHERE
OVER THE GREAT LAKES/NORTHEAST CONUS CHRISTMAS EVE INTO CHRISTMAS
DAY.

WHAT WE DON`T KNOW IS THE EXACT TRACK AND EVOLUTION OF THIS TROUGH
AND ASSOCIATED SURFACE LOW(S). MODEL ACCURACY IN THESE FINER SCALE
DETAILS IS VERY LOW BEYOND 3-4 DAYS...LARGELY DUE TO THE FACT THAT
THE RELEVANT SYNOPTIC DRIVERS ARE STILL OVER THE DATA-SPARSE NORTH
PACIFIC. LATEST 12Z NWP SUITE CONTINUES TO OFFER AN INCONSISTENT
PICTURE REGARDING THE SPECIFIC DETAILS OF THIS EVENT. THAT BEING
SAID...IT CAN BE USEFUL TO NOTE THE TRENDS AND THE TREND OVER THE
PAST FEW CYCLES HAS GENERALLY BEEN A WARMER TRACK FOR OUR CWA AND
LATER PHASING. THIS WOULD RESULT IN THE BULK OF PRECIP FALLING AS
RAIN IN OUR AREA. NOTABLY LACKING WITH THIS EVENT IS A SOURCE OF
VERY COLD AIR UPSTREAM. DEEPENING LOW WILL CERTAINLY PULL IN SOME
BELOW FREEZING TEMPERATURES EVENTUALLY BUT THIS MAY TAKE SOME TIME
AND WITH A SURFACE LOW TRACK DIRECTLY OVERHEAD OR JUST TO OUR
NORTHWEST...MAY ARRIVE AFTER THE BULK OF THE PRECIP/FORCING HAS
EXITED. THIS IS THE SOLUTION CHAMPIONED BY THE LATEST 12Z GFS AND
SIMILARLY BY THE ECMWF...SUGGESTING JUST SOME LIGHT SNOW SHOWERS AND
PERHAPS SOME GUSTY WINDS ON THE 24TH. THOUGH IT SHOULD ALSO BE NOTED
THE LATEST GFS AND ECMWF NOW BRING A SECONDARY LOW THROUGH THE
REGION ON FRIDAY THE 26TH WITH A BETTER CHANCE OF ACCUMULATING
SNOWFALL.

BOTTOMLINE...THERE WILL BE A STRONG STORM SOMEWHERE OVER THE REGION
DURING THE MIDDLE TO END OF NEXT WEEK BUT IMPORTANT DETAILS
REGARDING TIMING...PRECIP TYPES...AND AMOUNTS IN OUR LOCAL AREA
REMAIN UNCLEAR. TO ECHO THE SENTIMENTS OF THE PREVIOUS
FORECASTER...RESTRAINT SHOULD BE EXERCISED IN FORECASTING EXACT SNOW
AMOUNTS AND WITH PLACING MUCH VALUE IN ANY ONE PARTICULAR MODEL
ITERATION. SUFFICE IT TO SAY...ANYONE WITH TRAVEL PLANS DURING THIS
TIME SHOULD STAY TUNED TO THE LATEST FORECAST AND BE PREPARED FOR
HAZARDOUS WEATHER CONDITIONS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 750 PM EST THU DEC 18 2014

A WEAK SFC TROUGH DROPPING SOUTHWARD ACROSS SOUTHERN LOWER
MICHIGAN WILL EVENTUALLY REACH NORTHWEST/NORTH CENTRAL INDIANA
OVERNIGHT. SOME LAKE ENHANCEMENT WITH THIS TROUGH WILL LIKELY
PROVIDE A PERIOD OF SNOW SHOWERS AT KSBN PARTICULARLY IN THE 04Z-
08Z TIMEFRAME. HAVE MAINTAINED MVFR VSBYS RESTRICTIONS WITH THE
SNOW SHOWERS DURING THIS PERIOD...ALTHOUGH VERY BRIEF IFR VSBYS
ARE A POSSIBILITY. OTHERWISE...MVFR CIGS ARE EXPECTED TO HOLD
OVERNIGHT AT TERMINALS...GENERALLY AOA 2K FT. DID INCLUDE CIGS
BELOW 2K FT IN ASSOCIATION WITH SCATTERED SNOW SHOWERS AT KSBN IN
THAT 04Z-08Z PERIOD. SOME IMPROVEMENT TO HIGHER END MVFR OR VFR
CIGS BY MIDDAY FRIDAY...BUT GIVEN LINGERING LOW INVERSION HEIGHTS
WILL MAINTAIN MVFR CONDITIONS THROUGH THIS PERIOD.

&&

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

$$

UPDATE...MARSILI
SYNOPSIS...MARSILI
SHORT TERM...JT
LONG TERM...AGD
AVIATION...MARSILI


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