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000
FXUS63 KIWX 021830
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
130 PM EST MON DEC 2 2013

.SYNOPSIS...
ISSUED AT 1218 PM EST MON DEC 2 2013

A WARM FRONT WILL LIFT NORTH TODAY INTO TUESDAY AS WARM MOIST AIR
CONTINUES TO SPREAD NORTH OVER THE WESTERN GREAT LAKES REGION. THE
COMBINATION OF WARM MOIST AIR AND THE PASSAGE OF WEAK UPPER LEVEL
SYSTEMS WILL CAUSE CHANCES FOR LIGHT PRECIPITATION. RAIN IS
POSSIBLE... WITH A WINTRY MIX OR JUST SNOW FURTHER NORTH OVER
MAINLY LOWER MICHIGAN TONIGHT INTO EARLY TUESDAY. THE PRECIPITATION
WILL BECOME JUST RAIN AS TEMPERATURES WARM TUESDAY...AND CLIMB
WELL INTO THE 50S WEDNESDAY.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 435 AM EST MON DEC 2 2013

QUIET WEATHER WILL CONTINUE FOR MUCH OF THE DAY TODAY BEFORE WEAK
WARM FRONT LIFTS NORTH OVERNIGHT AND BRINGS LOW CHANCE FOR SOME
LIGHT PRECIP. SUBTLE SHORTWAVE RIDGING WILL BUILD OVER THE GREAT
LAKES REGION LATER THIS MORNING AS CURRENT MIDLEVEL TROUGH AXIS
SHIFTS EASTWARD. THIS TROUGH IS GENERATING PLENTY OF MIDLEVEL
CLOUDS...ALONG WITH SOME VIRGA...BUT MUCH DRIER LOWER LEVELS WILL
PREVENT ANY PRECIP THIS MORNING. CHANCES FOR PRECIP WILL THEN
INCREASE BY LATE AFTERNOON AS LEE CYCLOGENESIS ASSOCIATED WITH DEEP
PV ANOMALY CURRENTLY OVER BRITISH COLUMBIA CAUSES SOUTHWEST FLOW TO
INCREASE LOCALLY AND SEND OLD STATIONARY FRONT BACK NORTH AS A WARM
FRONT. FORCING FOR UVM WILL BE VERY WEAK OVER OUR AREA THOUGH. WEAK
SHORTWAVE WILL GET SHEARED OFF THE MAIN TROUGH AND PASS THROUGH THE
NORTHERN GREAT LAKES BUT THE BEST CVA WILL BE FOCUSED WELL TO OUR
NORTHWEST. MODELS ALSO INDICATE A FAIR AMOUNT OF 290K ISENTROPIC
ASCENT BUT SYSTEM RELATIVE FLOW VECTORS ARE NOT FAVORABLY ALIGNED
WITH THE ISOBARS OVER OUR AREA AND AGAIN THE BEST FORCING LOOKS TO
PASS TO OUR NORTHWEST. FOR THIS REASON PREFER THE QPF OFFERED BY THE
06 NAM AND 00Z GEM WHICH GENERATES A FEW HUNDREDTHS AT BEST AND
MAINLY OVER OUR NORTHWEST COUNTIES. HAVE THEREFORE MAINTAINED JUST
LOW CHANCE POPS FOR OUR CWA. ALSO PUSHED BACK START TIME BY SEVERAL
HOURS. CANT COMPLETELY RULE OUT SOME LIGHT PRECIP IN OUR SOUTHWEST
COUNTIES JUST BEFORE 00Z BUT EXPECT MOST OF THE ACTIVITY WILL BE
CONFINED TO THE TONIGHT PERIOD. IF PRECIP DOES OCCUR...TYPES WILL BE
MESSY IN OUR NORTHEAST COUNTIES (NORTH OF US-30 AND EAST OF US-31).
HERE...EVAPORATIONAL COOLING AND A COOL EASTERLY WIND WILL BE ENOUGH
TO CAUSE SURFACE TEMPS TO DROP TO AROUND FREEZING BY THIS EVENING.
WITH WAA ALOFT...THIS COULD RESULT IN A BRIEF PERIOD OF SLEET AND
FREEZING RAIN AT THE ONSET OF PRECIP...EVEN PERHAPS A LITTLE SNOW IN
OUR FAR NORTHEAST COUNTIES. CONTINUED WAA AND VEERING SURFACE WINDS
WILL FORCE A CHANGEOVER TO ALL RAIN BY LATER TONIGHT THOUGH. IT
SHOULD BE STRONGLY EMPHASIZED THAT ANY NON-LIQUID PRECIP WILL BE
BRIEF AND WITH SURFACE TEMPS BARELY FLIRTING WITH THE FREEZING
MARK...IMPACTS WILL BE VERY LIMITED...IF ANY.

HIGH TEMPS TODAY WILL BE SLIGHTLY COOLER THAN YESTERDAY GIVEN
CURRENT TEMPS IN THE MID TO UPPER 20S AND PLENTY OF CLOUD COVER
THROUGH THE DAY. LATEST MOS GUIDANCE SHOWS MID 40S IN OUR SOUTH WITH
UPPER 30S IN THE NORTH. SEE LITTLE REASON TO ARGUE WITH THAT AND
HAVE ADJUSTED ACCORDINGLY. LOWS TONIGHT WILL NOT DROP VERY FAR FROM
AFTERNOON HIGHS GIVEN INCREASING WAA AND ABUNDANT CLOUDS FROM
LIFTING WARM FRONT. EXPECT LOW 30S IN THE NORTHEAST AND UPPER 30S IN
THE SOUTHWEST.

&&

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 436 AM EST MON DEC 2 2013

MODEL DISPARITY CONTINUES IN THE LONG TERM WITH RESPECT TO HOW FAST
INITIAL ARCTIC FRONT WILL PUSH THROUGH OUR LOCAL AREA. MODELS HAVE
AT LEAST CONVERGED INTO TWO CAMPS...THE UNITED STATES AND THE REST
OF THE WORLD. NAM12...GFS...SREF AND GEFS ARE ALL IN ON A FASTER
ARCTIC FRONT ARRIVAL WEDNESDAY WHILE ECMWF...GEM...UKMET ARE ABOUT
12 TO 18 HOURS SLOWER. THIS LEADS TO SIGNIFICANT DIFFERENCES IN THE
WED-THU TIME PERIODS WITH RESPECT TO TEMPERATURES...PCPN TYPE AND
CHANGEOVER. WHILE MY ALLEGIANCE LIES TO THE UNITED
STATES...PREFERENCE FOR THIS FORECAST LIES WITH THE REST OF THE
WORLD. OUR OWN LITTLE RIDER CUP MATCH SO TO SPEAK.

WATER VAPOR CLEARLY SHOWS THE SOURCE OF ISSUES AMONGST MODELS WITH
DEEP UPPER LOW DROPPING SOUTH ALONG THE BC COAST EARLY THIS MORNING.
THE MODEL DIFFERENCES STILL LIE IN HOW THIS ENERGY WILL SPLIT AND
EVOLVE INTO MID WEEK. THE US MODELS REMAIN PERSISTENT ON SPLITTING
OFF ENERGY ACROSS THE NORTHERN CONUS WITH A DEEPENING UPPER LOW INTO
MN TUE NIGHT AND WI BY WED WITH. THIS ALLOWS FOR STRONG CYCLOGENESIS
ACROSS THE PLAINS WITH A DEEPENING SURFACE LOW LIFTING INTO WI TUE
NIGHT. THIS HELPS PUSH THE ARCTIC FRONT EASTWARD FASTER AND ACROSS
OUR AREA EARLY WED MORNING. THE AGREEMENT BETWEEN THE US MODELS IS
QUITE GOOD WITH GFS THE DEEPEST AND SLIGHTLY FASTER MODEL. THE
ECMWF...UKMET AND GEM SPLIT THE UPPER LOW ENERGY BUT KEEP THE FOCUS
OF THE MAIN LOW CLOSER TO BASE OF LONG WAVE TROUGH ACROSS THE
INTERMOUNTAIN WEST. THIS LEADS TO A BROADER SOUTHWESTERLY UPPER
LEVEL FLOW AND A WEAKER AND SLOWER SURFACE REFLECTION. THESE MODELS
BRING THE ARCTIC FRONT ACROSS OUR AREA WED NIGHT. OTHER THAN THIS
MAJOR DIFFERENCE...THE MODELS TEND TO AGREE WELL ON THE LARGE SCALE
PATTERN FOR THE REMAINDER OF THE PERIOD AS DEEP LONG WAVE TROUGH
SLOWLY MOVES INTO THE CENTRAL CONUS AND VERY COLD ARCTIC AIR SPREADS
ACROSS A LARGE PART OF THE CONUS BY THE WEEKEND.

SO WHAT MODEL CAMP DO WE GO WITH. BASED ON GFS BIAS OF BEING TOO
STRONG AND FAST WITH CLOSED UPPER LOWS AND SEEING THESE TYPE OF
SYSTEMS GENERALLY DIG INTO THE WESTERN CONUS HAVE OPTED TO USE THIS
REASONING FOR DISCOUNTING THE FASTER CAMP. EVEN THE GEFS ENSEMBLES
MINUS THE OPERATIONAL RUN SHOW A LITTLE MORE CONTINUITY AND
AGREEMENT WITH THE SLOWER CAMP MODELS. ENSEMBLE MOS STILL SHOWING A
BIG DISPARITY IN HIGHS ON WED WITH STANDARD DEVIATION OF 3 AND HIGHS
RANGING FROM 50 TO 37 BETWEEN MEMBERS. THE SLOWER CAMP ALSO MAKES
FOR GOOD CONTINUITY BETWEEN FORECASTS AND OFFICES AND SEEMS TO BE A
PREFERENCE OF WPC AS WELL.

RESULT IS JUST SOME MINOR TWEAKING TO CURRENT FORECAST WITH
ADJUSTMENTS BASED ON LATEST CONSENSUS GUIDANCE. WITH WARM FRONT
LIFTING NORTH TUESDAY SHOULD SEE TEMPS REBOUND INTO UPPER 40S NORTH
TO MIDDLE 50S SOUTH. THIS COULD BE ON THE LOW SIDE IF WE SEE LESS
CLOUDS. CHANCES FOR RAINS SHOWERS WILL PERSIST TUE INTO WED AHEAD OF
THE MAIN FRONT WITH WEAK SHORT WAVES EMBEDDED IN MEAN FLOW. MOISTURE
DEPTH AND OMEGA NOT THAT IMPRESSIVE SO KEPT POPS IN LOW CHANCE RANGE
FOR NOW. TIMED FRONT THROUGH THE AREA WEDNESDAY NIGHT INTO THURSDAY.
WILL LIKELY SEE FALLING TEMPS ON THURSDAY AS COLD AIR ADVECTION
STRENGTHENS DURING THE DAY. CHANGEOVER IN PCPN LOOKS TO BE RATHER
QUICK SO NO INTRODUCTION OF FREEZING PCPN WITH THOSE DETAILS
RELEGATED TO LATER FORECASTS. SOME MEDIUM RANGE MODELS STILL SHOWING
A WAVE RIDING ALONG FRONT THU NIGHT BUT HOW FAR NORTH THE PCPN
SHIELD SPREADS REMAINS IN QUESTION. HELD ONTO THE LIKELY POPS IN THE
SOUTHEAST FOR NOW.

THIS ARCTIC AIR LOOKS TO BE AS COLD IF NOT COLDER THAN LAST
INTRUSION. GEMNH VERY COLD WITH -20C AT 850MB ACROSS OUR AREA BY
SATURDAY. MOST OTHER MODELS NOT QUITE THAT COLD BUT CERTAINLY IN THE
-12 TO -16C RANGE. THIS WILL RESULT IN HIGHS IN THE LOW TO MID 20S
AT BEST AND LOWS IN THE TEENS WITH SINGLE DIGITS VERY POSSIBLE. LAKE
EFFECT SNOW SHOWERS WILL BE ONGOING BUT SUCH A COLD AIRMASS WITH NW
FLOW TENDS TO LIMIT ACCUMS AND PRODUCE MUCH SMALLER FLAKE SIZES.
HAVE RAISED POPS IN FAVORABLE AREAS TO ACCOUNT FOR SNOW SHOWERS FROM
THE EXTREME INSTABILITY BUT ACCUMS REMAIN UNCERTAIN.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1230 PM EST MON DEC 2 2013

MVFR CONDITIONS LINGERING ACROSS MUCH OF THE AREA ATTM BUT
CIGS/VSBYS GRDLY IMPROVING AND EXPECT THAT TREND TO CONT THROUGH
THE AFTN. SCT SHRA OVER IA EXPECTED TO MOVE EAST ACROSS NRN
INDIANA TONIGHT AS A WK SHRTWV MOVES THROUGH AND STNRY FRONT OVER
THE LWR OH VALLEY LIFTS NORTH. THIS SHOULD AID LOWERING CIGS/VSBYS
OVERNIGHT WITH SOME IFR CONDITIONS LIKELY AROUND DAWN TUE. WARM
FRONT WILL LIFT NORTH OF THE AREA TUE MORNING ALLOWING FOR
IMPROVING CIGS/VSBYS.

&&

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

$$

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


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