Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 251030
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
530 AM EST WED FEB 25 2015

.SYNOPSIS...
ISSUED AT 405 AM EST WED FEB 25 2015

DRY CONDITIONS EXPECTED TODAY...AHEAD OF ANOTHER WEAK SYSTEM
CROSSING THE REGION TONIGHT. THIS SYSTEM WILL GENERATE SOME LIGHT
SNOW LATE TONIGHT INTO TOMORROW BUT ACCUMULATIONS WILL BE LESS
THAN AN INCH. HIGHS TODAY WILL BE IN THE LOWER 20S WITH LOWS
TONIGHT AROUND 10 DEGREES.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 529 AM EST WED FEB 25 2015

QUIET WEATHER ANTICIPATED TODAY WITH JUST SOME VERY LIGHT SNOW
ARRIVING LATER TONIGHT. SURFACE RIDGE CURRENTLY BUILDING IN BEHIND
EXITING COLD FRONT. A FEW POSTFRONTAL LAKE EFFECT FLURRIES IN OUR
NORTHWEST COUNTIES EARLY THIS MORNING BUT NO ACCUMULATION/IMPACT
EXPECTED GIVEN VERY STRONG DRY AIR ADVECTION (SEE 00Z KGRB
SOUNDING) AND LIMITED INSTABILITY. SURFACE WINDS VEER TO MORE
NORTHEASTERLY DIRECTION BY LATE MORNING AND WILL SHUT OFF ANY
REMAINING FLURRIES. CALENDAR DAY HIGHS HAVE ALREADY BEEN REACHED
WITH DAYTIME TEMPS REMAINING IN THE UPPER TEENS TO LOWER 20S UNDER
STRONG PUSH OF LOW LEVEL CAA AND INCREASING MIDLEVEL CLOUDS.

NEXT SHORTWAVE TO IMPACT OUR AREA IS CURRENTLY ENTERING THE NORTHERN
PLAINS AND WILL SWING THROUGH OUR REGION BY LATE TONIGHT.
HOWEVER...CONFLUENT MID/UPPER LEVEL FLOW WILL SHEAR OUT THIS ALREADY
LACKLUSTER WAVE BY THE TIME IT REACHES US. 285K ISENTROPIC ASCENT
WASHES OUT WEST OF OUR AREA AND THE ACTUAL SURFACE LOW IS ABSORBED
BY SOUTHEAST CONUS SYSTEM. JUST SOME WEAK CVA AND ELEVATED
DEFORMATION/FGEN TO SPREAD LIGHT SNOW OVER OUR CWA. LOW LEVEL
MOISTURE ADVECTION IS ALSO LIMITED GIVEN N/NE FLOW. FORECAST
SOUNDINGS DO SHOW A VERY DEEP DENDRITIC GROWTH ZONE AND RELATIVELY
LIGHT WINDS THAT COULD LEAD TO SOME DECENT SIZED FLAKES AND HIGHER
SNOW RATIOS BUT BEST OMEGA/SUPERSATURATION WRT ICE IS MAINLY ABOVE
THE DGZ AND WILL INTRODUCE A FAIR AMOUNT OF PLATES AND COLUMNS. DID
RAISE POPS SLIGHTLY OUT OF RESPECT FOR THE 700MB FORCING BUT ANY
ACCUMULATIONS WILL BE LESS THAN A HALF INCH. OVERNIGHT TEMPS
EXPECTED TO HOLD AROUND 10F GIVEN INCREASING CLOUDS/PRECIP.

&&

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 529 AM EST WED FEB 25 2015

WEAK AND SHEARED SHORT WAVE WILL BE CROSSING THE AREA THURSDAY
WITH LITTLE MOISTURE TO WORK WITH. COLD AIR ADVECTION ALONG WITH
SAGGING BAROCLINIC ZONE MAY BE ENOUGH TO SQUEEZE OUT A HUNDREDTH
OR TWO OF PCPN AND A FLUFFY HALF INCH OF ACCUMULATION. RAISED POPS
TO MID CHANCE BUT LIGHT QPF AND DRY LOWER LEVELS PRECLUDE
ADDITIONAL BUMP.

HIGH PRESSURE TO BE OVER THE AREA THU NIGHT INTO SAT WITH ARCTIC
COLD AIR IN PLACE. LOWS DROPPING BACK BELOW ZERO THU NIGHT AND FRI
NIGHT WITH SOME AREAS LIKELY IN DOUBLE DIGITS BELOW
ZERO...ESPECIALLY EAST WHERE GRADIENT WILL BE WEAKEST.

UPPER LOW LOOKS TO DIG INTO WESTERN CONUS THIS WEEKEND AND ALLOW
SOUTHWEST FLOW ALOFT TO DEVELOP OVER CENTRAL CONUS. SPLIT FLOW WILL
COMPLICATE THINGS IN OUR REGION AS WE HAVE SEEN MOST OF WINTER WITH
A LEAD SHORT WAVE EJECTING OUT OF THE SOUTHWEST WHILE NORTHERN
STREAM WAVE RACES ACROSS THE GREAT LAKES. INTERACTION AND TIMING
STILL A QUESTION BUT MEDIUM RANGE MODELS IN GOOD AGREEMENT ON
SPREADING MOISTURE INTO THE AREA WITH LIGHT SNOW SUNDAY AND A FEW
INCHES OF ACCUM POSSIBLE. HAVE INCREASED POPS TO LIKELY CATEGORY IN
LINE WITH LATEST GUIDANCE AND MATCHING SURROUNDING OFFICES.

FOCUS THEN SHIFTS TO POSSIBLE STRONGER SOUTHERN STREAM WAVE FOR
SOMETIME IN THE DAY 6 TO 7 TIMEFRAME. GFS AS USUAL FASTEST MODEL TO
EJECT STRONG SHORT WAVE OUT OF SOUTHWEST AND THROUGH THE GREAT
LAKES. ECMWF ABOUT 12 TO 18 HOURS SLOWER WITH PCPN ARRIVAL TUESDAY.
OF CONCERN WITH THIS POTENTIAL SYSTEM WILL BE FREEZING RAIN AND
SLEET AS DEPARTING 1030MB HIGH WILL BE SLOW TO MOVE EAST AND WILL
AID IN LOCKING NEAR SURFACE COLD WEDGE INTO PLACE. WARM AIR
ADVECTION ALOFT LOOKS STRONG AND THUS A PERIOD OF FREEZING RAIN AND
SLEET BEING SHOWN IN MODEL SOUNDINGS. STILL VERY EARLY AND MANY
QUESTIONS REMAIN ON TIMING...STRENGTH...AND LOW LEVEL THERMAL
PROFILES FOR PCPN TYPE. HAVE KEPT PCPN AS SNOW MON NIGHT WITH RAIN
OR SNOW MIX FOR TUESDAY AT THIS TIME. WILL BE WATCHING THIS SYSTEM
CLOSELY AND SEE HOW MODEL TRENDS PLAY OUT NEXT FEW DAYS. QUITE
CONFIDENT SOLUTIONS WILL FLUCTUATE AS THEY HAVE ALL WINTER WITH THE
STRONGER SYSTEMS IN SPLIT FLOW PATTERN.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1238 AM EST WED FEB 25 2015

DRY SURFACE COLD FRONT WILL CROSS THE AREA DURING THE NEXT FEW
HOURS. FORECAST SOUNDINGS AND MOS GUIDANCE STILL SUGGEST A BRIEF
PERIOD OF HIGH END MVFR CEILINGS POSSIBLE AT KSBN IMMEDIATELY
BEHIND THE FRONT GIVEN QUICK SHOT OF BOUNDARY LAYER COOLING AND
MOISTURE FLUX FROM LAKE MICHIGAN. DRY AIR ADVECTION SHOULD
SCATTER LOW CLOUDS BY LATE MORNING THOUGH AND VFR CONDITIONS
EXPECTED THROUGH THE REST OF THE DAY. NEXT CHANCE OF LIGHT SNOW
AND REDUCTION IN FLIGHT CATEGORY LOOKS TO BE JUST OUTSIDE THIS TAF
FORECAST PERIOD...AS A WEAK AND MOISTURE STARVED SHORTWAVE SWINGS
THROUGH THE REGION.


&&

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

$$

SYNOPSIS...AGD
SHORT TERM...AGD
LONG TERM...LASHLEY
AVIATION...AGD


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