Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 200511
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1211 AM EST SAT DEC 20 2014

.SYNOPSIS...
ISSUED AT 1210 AM EST SAT DEC 20 2014

HIGH PRESSURE WILL CONTINUE TO PROVIDE THE REGION WITH DRY
CONDITIONS...LIGHT WINDS...AND MOSTLY CLOUDY SKIES THIS WEEKEND.
HIGHS ARE FORECAST TO REACH THE LOW TO MID 30S TODAY AND THE MID
TO UPPER 30S ON SUNDAY. CHANCES FOR RAIN RETURN MONDAY INTO
TUESDAY AS AN UPPER LEVEL TROUGH DIGS INTO THE PLAINS AND GULF
MOISTURE STREAMS NORTH INTO THE REGION.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 353 PM EST FRI DEC 19 2014

SFC RIDGE FROM SE CANADA TO THE SRN PLAINS WILL MOVE SLOWLY EAST
THROUGH THIS PERIOD. ALTHOUGH THERE WAS SOME CLEARING TODAY OVER
NRN PORTIONS OF THE AREA... CONSIDERABLE LOW LEVEL MOISTURE WILL
REMAIN TRAPPED IN WK FLOW BENEATH A SUBSIDENCE INVERSION BASED
AROUND 3KFT WHICH SHOULD PROMOTE LOW CLOUDINESS OVER THE AREA
THROUGH SATURDAY. IN ADDITION... A SHRTWV DROPPING SE THROUGH SD
THIS AFTN IS EXPECTED TO MOVE ACROSS OUR AREA SATURDAY. MID/UPR
LEVEL MOISTURE/LIFT ASSOCIATED WITH THIS SYSTEM MAY BE SUFFICIENT
TO CAUSE SOME FLURRIES IN THE AREA... THOUGH A PERSISTENT 3-5KFT
DRY LAYER ABOVE THE LOW LEVEL INVERSION SUGGESTS MEASURABLE PRECIP
IS UNLIKELY. LITTLE CHANGE EXPECTED FROM RECENT TEMPERATURES WITH
LOWS GENERALLY IN M20S AND HIGHS IN THE M30S... THOUGH WITH
LIGHT/VARIABLE WINDS TONIGHT... LOCALLY COOLER MINS LIKELY IF ANY
AREAS CLEAR OUT FOR A FEW HOURS.

&&

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 353 PM EST FRI DEC 19 2014

INCONSISTENCIES AMONG THE VARIOUS DETERMINISTIC NWP MEMBERS CONTINUE
WITH RESPECT TO POTENTIAL WINTER STORM DURING THE MIDDLE OF NEXT
WEEK. WILL CONTINUE TO TRY TO NARROW DOWN THE SCOPE OF THE EVENT IN
A MEANINGFUL YET JUDICIOUS WAY. NO IMPACTFUL WEATHER EXPECTED DURING
THE LATTER HALF OF THE WEEKEND SO WILL FOCUS ATTENTION ON POSSIBLE
HOLIDAY STORM NEXT WEEK.

THE LARGE SCALE PICTURE REMAINS UNCHANGED. LATEST WATER VAPOR
IMAGERY SHOWS IMPRESSIVE NORTH PACIFIC JET THAT WILL DRIVE THIS
EVENT. THIS JET STREAK WILL EVENTUALLY CARVE OUT A DEEP LONGWAVE
TROUGH OVER THE CENTRAL CONUS THAT WILL FORCE RAPID CYCLOGENESIS AS
IT ROUNDS THE BASE OF AN INCREASINGLY NEGATIVELY TILTED TROUGH. THE
DIFFICULTIES REVOLVE AROUND THE FACT THAT THE JET ENERGY WILL ARRIVE
IN TWO PIECES. THE LEAD WAVE/SURFACE LOW WILL MOVE INTO THE UPPER
MIDWEST ON MONDAY. THE MAIN JET CORE WILL THEN DIG SOUTHEAST AND
DEVELOP A SECONDARY/STRONGER LOW THAT WILL ABSORB THE NORTHERN WAVE
SOMEWHERE OVER THE OHIO VALLEY/GREAT LAKES. IT IS THE EXACT
TIMING/TRACK OF THIS MAIN JET STREAK THAT WILL DETERMINE SENSIBLE
WEATHER IMPACTS FOR OUR LOCAL AREA AND THIS IS WHAT MODELS CONTINUE
TO STRUGGLE WITH. 12Z GFS INDICATES A QUICKER ARRIVAL THAT FORCES
EARLIER PHASING AND A MORE NORTHWEST TRACK OF THE SURFACE LOW
COMPARED TO THE ECMWF AND GEM. THIS WOULD RESULT IN PRIMARILY A RAIN
EVENT FOR OUR AREA WITH JUST SOME LIGHT SNOW AND GUSTY WINDS LATE
WED/EARLY THURS. 12Z ECMWF AND GEM TRACK THIS LOW FURTHER EAST WITH
BETTER CHANCES FOR ACCUMULATING SNOWFALL. HOWEVER...WITH NO GOOD
SOURCE OF COLD AIR UPSTREAM...WILL TAKE TIME FOR PRECIP TO
CHANGEOVER REGARDLESS. SUCH FINER SCALE DETAILS ARE DIFFICULT TO PIN
DOWN THIS FAR OUT BUT WILL HAVE A LARGE IMPACT ON SNOWFALL
AMOUNTS...TIMING...AND LOCATION.

TO SUMMARIZE...STILL EXPECT A STRONG LOW PRESSURE SYSTEM SOMEWHERE
IN THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY BUT
IMPORTANT DETAILS ARE STILL UNCLEAR. ALL OF THE PRECIP LATE MONDAY
THROUGH TUESDAY WILL BE IN THE FORM OF RAIN. CHANGEOVER TO SNOW
EXPECTED SOMETIME WEDNESDAY BUT EXACT TIMING AND AMOUNTS REMAIN
UNCERTAIN. SYSTEM WILL EXIT THE AREA ON THURSDAY. AGAIN...ANYONE
WITH CHRISTMAS EVE TRAVEL PLANS SHOULD STAY TUNED TO THE LATEST
FORECASTS AND BE PREPARED FOR HAZARDOUS CONDITIONS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1210 AM EST SAT DEC 20 2014

HIGH MVFR TO LOW VFR MVFR CIGS ARE EXPECTED TO PERSIST THROUGH THE
TAF CYCLE AS MOISTURE REMAINS TRAPPED UNDER INVERSION/DIRTY HIGH.
DRY/LIGHT WINDS OTHERWISE WITH LOW LEVEL RIDGE IN PLACE.

&&

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

$$

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


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