Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 182023
AFDIWX

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

.SYNOPSIS...
ISSUED AT 314 PM EST THU DEC 18 2014

HIGH PRESSURE OVER THE UPPER MIDWEST WILL MOVE SLOWLY EAST
PROVIDING FAIR WEATHER WITH SEASONABLE TEMPERATURES THROUGH THE
WEEKEND. THE ONLY EXCEPTION WILL BE A CHANCE OF LAKE EFFECT SNOW
SHOWERS NEAR LAKE MICHIGAN INTO EARLY FRIDAY. LOWS TONIGHT WILL BE
IN THE LOWER AND MIDDLE 20S AND HIGHS FRIDAY WILL BE IN THE LOWER
AND MIDDLE 30S.

&&

.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 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.
&&

$$

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


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