000
FXUS63 KIWX 010905
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
405 AM EST SUN DEC 1 2013

.SYNOPSIS...
ISSUED AT 405 AM EST SUN DEC 1 2013

A WEAK COLD FRONT WILL CROSS THE AREA LATER TODAY BUT MOISTURE IS
VERY LIMITED AND EXPECT JUST A GRADUAL INCREASE IN CLOUD COVER
THROUGH TONIGHT. THIS FRONT WILL THEN STALL OVER THE AREA AND
PRODUCE A SLIGHT CHANCE OF RAIN AND SNOW TOMORROW BEFORE LIFTING
BACK NORTH AS A WARM FRONT ON TUESDAY.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 405 AM EST SUN DEC 1 2013

LATEST SURFACE ANALYSIS SHOWS RATHER DIFFUSE PRESSURE TROUGH IS
FINALLY ENTERING THE SOUTHERN GREAT LAKES...ASSOCIATED WITH AN
INCREASINGLY ILL-DEFINED UPPER PV ANOMALY BEING STRETCHED ACROSS THE
NORTHERN LAKES. THIS FEATURE WILL CONTINUE TO SLOWLY PUSH SOUTHEAST
DURING THE DAY TODAY WITH LITTLE...IF ANY...IMPACTS. MODELS CONTINUE
TO BE TOO AGGRESSIVE IN SATURATING THE LOW LEVELS. REGIONAL AND
UPSTREAM 00Z SOUNDINGS INDICATE A VERY DRY AIRMASS REMAINS IN PLACE
AND MOISTURE ADVECTION POTENTIAL IS LIMITED. UPPER LEVEL FORCING IS
ALSO VERY WEAK WITH THE MAIN NORTHERN STREAM JET STREAK...SUCH AS IT
IS...EXITING RAPIDLY EASTWARD. NOT SURPRISINGLY...ONLY SOME MIDLEVEL
CLOUDINESS ALONG AND IMMEDIATELY BEHIND THE FRONT. ONE HAS TO GO
INTO NORTHERN WI/MI TO REACH THE LOW STRATUS DECK AND HAVE YET TO
SEE ANY PRECIP REPORTS UP THERE. IT IS AN EXPANSIVE STRATUS SHIELD
THOUGH...ONE THAT WILL ARRIVE HERE EVENTUALLY. LACK OF STRONG
UPSTREAM SURFACE HIGH/DRY AIR ADVECTION IS ALLOWING WHAT LITTLE COLD
ADVECTION THERE IS TO SATURATE THE LOWER LEVELS. THERE ARE ACTUALLY
SEVERAL LOW AMPLITUDE WAVES IMMEDIATELY UPSTREAM IN CENTRAL CANADA
THAT ARE PREVENTING ANY NOTABLE SUBSIDENCE OVER THE REGION. THESE
LOW CLOUDS WILL GRADUALLY ENVELOPE THE AREA THROUGH THE DAY TODAY
BUT EXPECT WE WILL REMAIN DRY GIVEN VERY LIMITED MOISTURE DEPTH SEEN
ON FORECAST SOUNDINGS. THIS MAY CHANGE OVERNIGHT AS MOISTURE FLUX
FROM THE LAKES...COMBINED WITH BETTER MIDLEVEL MOISTURE FROM TROUGH
AXIS APPROACHING THE OHIO VALLEY...ALLOWS FOR A LITTLE BETTER RH
PROFILES. STILL NOT CONVINCED IT IS WORTHY OF A MENTIONABLE POP
THOUGH AS ANY ACTIVITY THAT DOES MANAGE TO DEVELOP WILL STRUGGLE TO
PRODUCE ANYTHING MORE THAN A TRACE. IF PRECIP DOES OCCUR BY EARLY
TOMORROW MORNING...NARROWING DOWN A TYPE WILL BE EXCEPTIONALLY
DIFFICULT. NOT ONLY WILL SURFACE TEMPS BE HOVERING RIGHT AROUND THE
FREEZING MARK...BUT SEEDER/FEEDER PROCESSES FROM MIDLEVEL SATURATION
COULD PROVIDE NECESSARY ICE NUCLEI TO ALLOW LIGHT SNOW DESPITE DRY
LAYER AROUND 850MB. HOWEVER THIS BETTER MIDLEVEL SATURATION DOES NOT
ARRIVE UNTIL VERY LATE AND SOME PATCHY DRIZZLE/FREEZING DRIZZLE
REMAINS POSSIBLE. PREFER TO LEAVE THE TONIGHT PERIOD DRY FOR NOW
GIVEN MODELS OVERLY AGGRESSIVE LOW LEVEL SATURATION WITH THIS FRONT
AND STILL FAIRLY UNIMPRESSIVE FORECAST SOUNDINGS...BUT LATER SHIFTS
MAY NEED TO ADJUST WITH THE BENEFIT OF MORE OBSERVATIONAL DATA AND
NEAR TERM MODEL GUIDANCE.

TRICKY TEMP FORECAST FOR TODAY WITH THE SLOWLY APPROACHING COLD
FRONT. COULD EASILY SURGE INTO THE LOW TO MID 40S BY LATE MORNING
BEFORE THE COOLER AIR AND LOW CLOUDS ARRIVE. ECMWF RAW AND
STATISTICAL GUIDANCE EVEN SUGGEST UPPER 40S IN OUR SOUTH...WHICH
MAY NOT BE TOO FAR OFF GIVEN YESTERDAYS STELLAR THERMAL RECOVERY.
MIDLEVEL CLOUDS WILL BE INCREASING BY LATER THIS MORNING BUT STILL
FEEL LOW/MID 40S EASILY ATTAINABLE...ESPECIALLY IN OUR SOUTHEAST
GIVEN LATE ARRIVAL OF COOLER 925MB TEMPS. HAVE THEREFORE BUMPED
HIGHS UP BY SEVERAL DEGREES. ALSO INCREASED OVERNIGHT LOWS A BIT.
POSTFRONTAL CAA IS VERY WEAK AND EXPECT BLANKET OF LOW CLOUDS TO
KEEP TEMPS FROM DROPPING MUCH BELOW UPPER 20S/LOWER 30S.

&&

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 405 AM EST SUN DEC 1 2013

A VERY COMPLICATED UPPER AIR PATTEN EVOLVING DURING THE LONG TERM
PERIOD WITH TRANSITION TO A HIGHLY AMPLIFIED PATTERN. MEDIUM RANGE
MODELS ARE STRUGGLING TO HANDLE THE HIGHLY ENERGETIC AND CHAOTIC
PATTERN WITH A LOT OF UNCERTAINTY REMAINING IN LATEST FORECAST
ITERATIONS. CONFIDENCE IN DETAILS REMAINS LOW FOR MID TO LATE WEEK
PATTERN AND TIMING OF ARCTIC FRONT AND PCPN TYPE ACROSS THE AREA.
RELUCTANT TO MAKE TOO MANY SIGNIFICANT CHANGES GIVEN MUCH OF THE
ENERGY REMAINS OUTSIDE OF GOOD UPPER AIR NETWORK AND THE STRONG JET
STREAKS BEING INDICATED IN LATEST MODELS WILL SURELY BE HANDLED
DIFFERENTLY OVER NEXT SEVERAL MODEL RUNS.

WEAK FRONTAL BOUNDARY WILL BE JUST SOUTH OF AREA ON MONDAY WITH
SHALLOW MOISTURE IN ITS WAKE AND A COUPLE WEAK SHORT WAVES MOVING
THROUGH. MODELS NOT AS STRONG WITH FGEN FORCING AND OVERALL OMEGA AS
PREVIOUS RUNS BUT STILL INDICATE SOME VERY LIGHT QPF POSSIBLE. WILL
MAINTAIN SLIGHT CHANCE POPS WITH PCPN TYPE STILL IN QUESTION WITH
LIGHT SNOW MOST PROBABLE FAR NORTH AND A MIX CENTRAL AND SOUTH WITH
CHANGE TO MAINLY RAIN LATE MORNING TO AFTERNOON. AGAIN...FORCING
WEAK AND AMOUNTS WOULD BE LIGHT IF EVEN MEASURABLE MOST AREAS.

WARM AIR ADVECTION DEVELOPS MONDAY NIGHT INTO TUESDAY AS WARM FRONT
BEGINS TO LIFT NORTH IN RESPONSE TO RISING HEIGHTS AS COLD UPPER LOW
DROPS SOUTH INTO WESTERN CONUS. THIS IN RESPONSE TO IMPRESSIVE RIDGE
DEVELOPMENT OVER EASTERN PACIFIC WHICH LOOKS TO BECOME CROSS POLAR
BY THURSDAY. THIS WILL LEAD TO STRONG DOWNSTREAM ARCTIC COLD AIR
INTRUSION INTO MUCH OF CONUS. THIS IS WHERE DETAILS REMAIN MUDDLED
FOR MID TO LATE WEEK WITH OVERALL EVOLUTION OF SYNOPTIC FEATURES.

MODELS HAVE BEGUN TO AGREE ON UPPER LOW DROPPING INTO NORTHERN CONUS
EARLY MONDAY BUT RATHER THAN DIGGING SOUTH AS WE NORMALLY WOULD
EXPECT...UPPER LOW BECOMES FRACTURED WITH JET ENERGY ROUNDING BASE
OF LONG WAVE TROUGH. THE DEGREE OF FRACTURING AND STRENGTH OF LEAD
LOW THAT BREAKS OFF SEEMS TO BE WHAT IS MOST PROBLEMATIC IN MODELS
EVOLUTION. GFS HAS BEEN CONSISTENT WITH THIS OCCURRENCE WHILE GEM
AND ECMWF HAVE PLAYED CATCH UP. GFS REMAINS STRONGEST SOLUTION WITH
THIS LEAD LOW TRACKING EAST ACROSS THE NORTHERN TIER OF STATES.
MEANWHILE...ENERGY IS LEFT IN BASE OF TROUGH FURTHER SOUTH WHILE
ENERGY FROM MEANDERING LOW OFF THE CA COAST GETS INGESTED INTO LONG
WAVE TROUGH. THE RESULT IN THE GFS IS A MUCH DEEPER SURFACE LOW OVER
THE UPPER MS VALLEY WHICH LIFTS NORTH AND SWINGS AN OCCLUDED FRONT
THROUGH OUR AREA TUE NIGHT AND WED...MUCH QUICKER THAN GEM AND
ECMWF. THE QUESTION HAS BECOME WHETHER THE SLOWER MODELS WILL
CONTINUE TO PLAY CATCH UP OR IF GFS IS DISPLAYING A COMMON BIAS WITH
THESE TYPE SYSTEMS. HAVE OPTED TO REMAIN IN MIDDLE OF PACK WITH A
MORE ENSEMBLE APPROACH...FAVORING THE SLOWER MODELS. THIS REQUIRED A
SLIGHT ADJUSTMENT TO FORECAST GRIDS TO ACCOUNT FOR A FASTER
INTRUSION OF INITIAL SURGE OF COLDER AIR COMING LATER WEDNESDAY
NIGHT AND THURSDAY BUT NOT AS FAST AS GFS. A MASSAGE OF WEATHER TYPE
GRIDS AND POPS WERE MADE BUT CONFIDENCE IN ANY OF THESE CURRENT
MODEL ITERATIONS FOR F72-F120 REMAINS VERY LOW SO GRIDS REMAIN VOID
OF TOO MANY DETAILS. 00Z GEFS ENSEMBLES SHOW A LARGE VARIANCE AND LATEST
ENSEMBLE MOS FOR WED AND THU SHOWS DIFFERENCES OF 20 DEGREES BETWEEN
WARMEST AND COLDEST ENSEMBLE MEMBERS. THUS MORE EVIDENCE FOR
ADDITIONAL MODEL CHANGES IN THE COMING DAYS AND A CAUTIOUS APPROACH
TO CURRENT FORECAST.

THE CERTAINTY IS THAT VERY COLD ARCTIC AIR WILL MOVE IN BY FRIDAY
AND DEEPEN FOR THE WEEKEND AND LAST INTO EARLY NEXT WEEK.
HIGHS IN THE LOW TO MID 20S AND LOWS IN THE SINGLE DIGITS TO TEENS
LOOK LIKELY OVER THE WEEKEND. LAKE EFFECT SNOW SHOWERS ALSO EXPECTED
BUT CURRENT MODEL SOLUTIONS...FOR WHAT THEY ARE WORTH AT THIS TIME
RANGE...SUGGEST A MORE WNW FETCH WHICH WOULD LIMIT ACCUMS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1238 AM EST SUN DEC 1 2013

A WEAK COLD FRONT WILL SLOWLY CROSS THE AREA LATER THIS MORNING.
INITIALLY VERY DRY AIR WILL KEEP CONDITIONS IN VFR CATEGORY BUT
DECREASING WINDS AND MOISTURE POOLING ALONG THE FRONT COULD LEAD
TO SOME PATCHY FOG OR LOW STRATUS AROUND 12Z...ESPECIALLY AT KSBN.
SOME MARGINAL IMPROVEMENT EXPECTED WITH DAYTIME HEATING BUT
MVFR CEILINGS WILL BECOME INCREASINGLY LIKELY THROUGH THE DAY AS
COLDER AIR FILTERS INTO THE REGION AND LOWER LEVELS BECOME
SATURATED. IFR CONDITIONS MAY BE POSSIBLE BY THE END OF THE PERIOD
BUT EXPECT THEY WILL HOLD OFF UNTIL AFTER 06Z.

&&

.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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