000
FXUS63 KIWX 250940
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
440 AM EST SUN JAN 25 2015

.SYNOPSIS...
ISSUED AT 430 AM EST SUN JAN 25 2015

AN AREA OF LOW PRESSURE WILL MOVE FROM SOUTHERN IOWA THIS MORNING
TO SOUTHWEST INDIANA BY MID AFTERNOON AND THEN THROUGH KENTUCKY
TONIGHT. THIS CLIPPER SYSTEM WILL SPREAD ACCUMULATING SNOW OVER
PARTS OF NORTH CENTRAL AND NORTHERN INDIANA AND NORTHWEST OHIO
TODAY WITH RAIN SOUTH OF THIS AREA. HIGH TEMPERATURES WILL
OCCUR THIS MORNING WITH READINGS RANGING FROM THE LOWER 20S NORTH
TO UPPER 30S SOUTH. EXPECT FALLING TEMPERATURES DURING THE DAY.
LOWS TONIGHT WILL BE VERY COLD WITH SINGLE DIGITS ACROSS THE NORTH
AND TEENS SOUTH.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 439 AM EST SUN JAN 25 2015

CHALLENGING SHORT TERM FORECAST AS PCPN TYPE IN QUESTION EARLY TODAY
AND SNOWFALL AMOUNTS WILL DEPEND ON TIMING OF CHANGEOVER TO ALL
SNOW. 00Z MODELS GENERALLY IN GOOD AGREEMENT SYNOPTICALLY WITH
ALMOST ALL SOLUTIONS TAKING SURFACE LOW SOUTHEAST FROM IA THIS
MORNING TO NEAR KEVV BY EARLY AFTERNOON...THEN EAST ACROSS NORTHERN
KENTUCKY TONIGHT. PRECIPITATION WILL SPREAD EAST ACROSS THE LOCAL
AREA TODAY AHEAD AND NORTH OF THE LOW.

STRONG MERIDIONAL JET DIVING SOUTH THROUGH THE PLAINS WILL DRIVE
CLIPPER SYSTEM SOUTHEAST TODAY. LOW LEVEL NORTHEAST FLOW WILL
INCREASE AND THIS WILL BRING COLDER AIR SOUTH HELPING ERODE WARM
LAYER ALOFT AND CHANGE PCPN OVER TO ALL SNOW FROM NORTH TO SOUTH.
THERE IS A BIT OF A CONCERN THOUGH AS MOST HIRES GUIDANCE HAS BEEN
ANYWHERE FROM 2 TO 5 DEGREES TOO WARM WITH SFC TEMPS EARLY THIS
MORNING ACROSS LOWER MICHIGAN. AS OF 08Z THOUGH WE ARE FINALLY
STARTING TO SEE A THERMAL RESPONSE IN SFC OBS WITH TEMPS DROPPING A
FEW DEGREES. THIS IS ENCOURAGING BUT STILL CONCERNED THAT MODELS ARE
A FEW HOURS TOO FAST BRINGING THE COLDER AIR SOUTH WHICH IN TURN
COULD DELAY CHANGEOVER IN FAR SOUTH UNTIL MID AFTERNOON.
HRRR...RUC AND LAMP GUIDANCE HAVE BEEN PLAYING CATCHUP ALL NIGHT.
HAVE MANUALLY ADJUSTED HOURLY SFC TEMPS WITH SLIGHTLY SLOWER COOLING
THAN RUC GUIDANCE SUGGESTS. DO EXPECT COLDER AIR TO QUICKLY MOVE SOUTH
ONCE CLIPPER GETS CLOSER AND PRESSURE GRADIENT TIGHTENS LATER THIS
MORNING.

MEANWHILE...LACK OF LOW CLOUDS ALONG WITH LIGHT WINDS IN THE WESTERN
CWA HAS ALLOWED SFC TEMPS THERE TO DROP TO AROUND FREEZING WITH SOME
FOG DEVELOPMENT. DO EXPECT TEMPS HERE TO RISE ABOVE FREEZING AHEAD
OF PCPN ARRIVAL WITH SFC TEMPS ACROSS CENTRAL ILLINOIS IN THE MID TO
UPPER 30S EARLY THIS MORNING. THIS COMBINED WITH 1000-850MB WARM
TONGUE OF 2 TO 4C DEPICTED BY HIRES GUIDANCE SUGGEST A MIX OF RAIN
AND SNOW UNTIL WARM LAYER IS FULLY ERODED. TOP DOWN METHOD ACTUALLY
DEPICTS A FEW HOURS OF JUST RAIN ACROSS THE EXTREME SOUTHERN CWA
LATE MORNING INTO EARLY AFTERNOON BEFORE FULLY CHANGING OVER TO
SNOW.

THE FARTHER SOUTH TRACK OF CLIPPER HAS ALSO MEANT A SOUTHWARD SHIFT
IN STRONGEST FORCING AND HEAVIEST PCPN AXIS. STRONGEST FGEN FORCING
AND BANDING POTENTIAL NOW LOOKS TO BE JUST SOUTH OF OUR AREA. THIS
COMBINED WITH MIXED PCPN AND DELAYED CHANGEOVER TO SNOW HAS LED TO
DECREASED SNOW AMOUNTS OVER THE ENTIRE AREA. MODEL QPF NOW GENERALLY
AROUND A QUARTER INCH SOUTH OF THE US24 CORRIDOR. MIXING RATIOS OF 3
TO 4 G/KG AND PWATS AROUND 0.5 INCHES STILL A CONCERN...ESPECIALLY
IF ANY BANDING DEVELOPS. STILL EXPECT A SWATH OF 2 TO 4 INCHES
ACROSS THE FAR SOUTH AND THE HIGHER END AMOUNTS SOUTHEAST WHERE
PIVOT POINT AND SNOW THIS EVENING TAKE ADVANTAGE OF SLIGHTLY BETTER
RATIOS. ISOLATED AMOUNTS OF 5 INCHES NOT OUT OF QUESTION IF BANDING
CLIPS THIS AREA. WITH THIS BEING MID WINTER AND EXPECTATION OF A WET
2 TO 4 INCHES WITH LOW IMPACTS FOR TRAVEL HAVE OPTED TO NOT ISSUE
ANY ADVISORY AT THIS TIME. WILL HIGHLIGHT SNOWFALL IN AN SPS AND
HWO.

&&

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 439 AM EST SUN JAN 25 2015

NEXT CLIPPER-TYPE SYSTEM TO POTENTIALLY IMPACT THE AREA WILL ARRIVE
ON MONDAY NIGHT. FORCING MECHANISM IS REALLY MORE ACCURATELY
DESCRIBED AS JUST A THIN RIBBON OF CYCLONIC SHEAR VORTICITY ON THE
UPWIND SIDE OF DEEPENING EAST COAST TROUGH. AS SUCH...FORCING FOR
ASCENT IS PRETTY MINUSCULE AND RESIDENT AIRMASS...AT LEAST IN THE
MIDLEVELS...IS VERY DRY. WEAK 285K ISENTROPIC ASCENT AND SUBTLE LOW
LEVEL MOISTURE ADVECTION MAY GENERATE SOME VERY LIGHT SNOW BUT
LITTLE TO NO ACCUMULATION IS EXPECTED. PREFERENCE STILL LIES WITH
THE DRIER/FURTHER SOUTHWEST CANADIAN AND EUROPEAN SOLUTIONS.
ACTUALLY AM A LITTLE CONCERNED ABOUT POTENTIAL FOR FREEZING DRIZZLE.
NAM AND GFS FORECAST SOUNDINGS INDICATE DEEP ENOUGH SATURATION TO
SUPPORT ICE NUCLEATION BUT JUST BARELY AND AM CONCERNED THEY ARE
OVERDOING THE EXTENT OF LOW LEVEL MOISTURE AND ASCENT. WILL HOLD OFF
ON INCLUDING IN THE FORECAST FOR NOW GIVEN THE HIGHER PROBABILITY
THAT ANY PRECIPITATION THAT DOES MANAGE TO OCCUR WILL DO SO IN AN
ENVIRONMENT ADEQUATELY SATURATED TO SUPPORT ICE NUCLEI AND OTHER
LOCATIONS WILL SIMPLY REMAIN DRY. SOMETHING TO KEEP AN EYE ON THOUGH.

MORE IMPRESSIVE WAVE IS SET TO PLOW OVER THE WEST COAST RIDGE ON
WEDNESDAY. THIS ACTUALLY FORCES DOWNSTREAM HEIGHT RISES LOCALLY WITH
A BRIEF RETURN TO SOUTHWEST FLOW AND WARMER TEMPERATURES. SHORTWAVE
WILL THEN ENTER OUR REGION ON THURSDAY WITH THE NEXT DECENT CHANCE
OF PRECIP. NEEDLESS TO SAY....FORECAST CONFIDENCE IN EXACT TRACK IS
LOW AND THIS WILL HAVE A LARGE IMPACT ON THERMAL PROFILES AND QPF
TOTALS. CURRENTLY APPEARS THE BEST CHANCE FOR SIGNIFICANT SNOW WILL
REMAIN OVER CENTRAL MICHIGAN WITH MORE OF A MIX ACROSS NORTHERN
INDIANA AND OHIO. THIS WILL UNDOUBTEDLY CHANGE AS WE GET CLOSER
THOUGH.

AFTER A COLD START ON MONDAY...TEMPERATURES WILL QUICKLY RETURN TO
VALUES AT OR ABOVE NORMAL FOR THE MIDWEEK PERIOD. COOLER TEMPS
EXPECTED AFTER THURSDAY`S WAVE BUT MUCH COLDER CONDITIONS STILL
APPEAR POSSIBLE EARLY NEXT WEEK AFTER A THIRD WAVE/ARCTIC FRONT
PASSES OVER THE WEEKEND.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1236 AM EST SUN JAN 25 2015

MVFR CIGS WERE ACROSS THE TAF SITES AT ISSUANCE BUT CONDITIONS
WERE HIGHLY VARIABLE WITH MUCH OF WEST CENTRAL AND NORTHWEST
INDIANA BEING VFR. AN AREA OF LOCAL VIS BELOW 1SM BR WAS
DEVELOPING AROUND KVPZ. HIRES GUIDANCE ACTUALLY CAPTURES THIS
SMALL AREA AND EXPANDS IT EAST TOWARD KSBN OVERNIGHT. WILL HAVE TO
MONITOR BUT DID INTRODUCE MVFR VIS TO KSBN. CLIPPER SYSTEM TO
DIVE EVEN FURTHER SOUTH NOW WITH SFC LOW MOVING OVER KEVV TODAY.
HEAVIER SNOWFALL WILL BE SOUTH OF TERMINALS BUT STILL EXPECT TO
SEE LIGHT SNOW FROM LATE MORNING TO EARLY EVENING WITH IFR AT KSBN
AND LIFR STILL POSSIBLE AT KFWA.


&&

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

$$

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


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