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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
530 AM EST FRI DEC 19 2014

.SYNOPSIS...
ISSUED AT 1220 AM EST FRI DEC 19 2014

A WEAK TROUGH MAY BRING LIGHT SCATTERED SNOW SHOWERS AND PATCHY
DRIZZLE TO FAR NORTHERN INDIANA AND SOUTHERN MICHIGAN EARLY THIS
MORNING. OTHERWISE...A RIDGE OF HIGH PRESSURE WILL BRING DRY
CONDITIONS TO THE REGION THROUGH THE WEEKEND WITH NEAR SEASONABLE
TEMPERATURES.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 355 AM EST FRI DEC 19 2014

WEAK SFC-850 MB TROUGH ACROSS SOUTHERN LOWER MI WILL BECOME 
INCREASINGLY DIFFUSE INTO NRN IN/OH TODAY. THERE MAY BE JUST ENOUGH 
LAKE ENHANCEMENT AND LOW LEVEL CONVERGENCE/MOISTURE TO FOCUS A FEW 
FLURRIES OR PATCHY FREEZING DRIZZLE THROUGH MID MORNING (MAINLY
ALONG/NORTH OF US 30). THIS COULD LEAD TO A FEW SLICK SPOTS EARLY
THIS MORNING. DRY/SEASONABLE OTHERWISE AS LOW AMPLITUDE SHORTWAVE
RIDGING OVERSPREADS IN ADVANCE OF A DISJOINTED HIGH PLAINS UPPER
TROUGH AXIS. THIS AND HIGH STATIC STABILITY THROUGH THE COLUMN
WILL HELP SFC HIGH PRESSURE BECOME MORE FIRMLY ESTABLISHED ACROSS
THE REGION INTO TONIGHT...WITH A BKN/OVC LOW CLOUD DECK LIKELY
REMAINING TRAPPED BENEATH A STUBBORN INVERSION FOR MOST LOCATIONS.

&&

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 355 AM EST FRI DEC 19 2014

NOT A LOT OF CHANGE IN THINKING HERE WITH RESPECT TO WINTER STORM 
NEXT WEEK...BUT AS EXPECTED MODELS CONTINUE TO JUMP AROUND WITH 
POTENTIAL SOLUTIONS. CONFIDENCE REMAINS HIGH ON A STRONG WINTER 
STORM IN THE MIDWEST AND GREAT LAKES REGION BUT THE IMPORTANT 
DETAILS ON STORM TRACK...PCPN TYPE AND SNOW AMOUNTS REMAIN QUITE 
UNCERTAIN.

NORTHERN HEMISPHERIC WATER VAPOR LOOP FROM THE PAST WEEK TELLS THE 
STORY OF DEVELOPING PATTERN CHANGE AND ORIGIN OF ENERGY FOR UPCOMING 
WINTER STORM. POWERFUL 160-180KT JET ENERGY CURRENTLY OVER NORTHERN 
PACIFIC HANDLED FAIRLY WELL BY MODEL INITIATIONS PER GOES HIGH 
DENSITY WIND PLOTS. VAPOR LOOP SHOWS IMPRESSIVE MOISTURE PLUME 
STRETCHING BACK TO EAST ASIA AND THE SOUTH PACIFIC. THIS PLUME HAS 
BEEN ENERGIZED BY RECURVING TROPICAL DISTURBANCES FROM THE SOUTH 
PACIFIC AS WELL AS THE INDIAN OCEAN. THIS HAS HELPED STRENGTHEN 
NORTHERN PACIFIC JET WITH ENERGY SET TO RIDE INTO WESTERN CONUS THIS 
WEEKEND AND INTO NORTHERN PLAINS EARLY NEXT WEEK. BUILDING RIDGES IN 
BOTH THE WESTERN ATLANTIC AND ESPECIALLY EASTERN PACIFIC WILL HELP 
THIS JET ENERGY FORM A CLOSED LOW SOMEWHERE OVER THE MIDWEST TO 
GREAT LAKES REGION. THIS IS WHERE THE UNCERTAINTY IN DETAILS LIES AS 
MEDIUM RANGE MODELS CONTINUE TO DIVERGE ON HOW AND WHERE THIS LOW 
WILL FORM AND EVOLVE. 

THE GENERAL SYNOPTIC IDEA REMAINS SIMILAR AMONG THE MODELS WITH MID 
LEVEL LOW FORMING TO OUR WEST ACROSS THE PLAINS STATES SUNDAY INTO 
MONDAY. SOUTHERLY LOW LEVEL JET WILL INCREASE AHEAD OF THIS LOW 
MONDAY INTO TUESDAY ALLOWING DEEP MOISTURE TRANSPORT INTO OUR AREA. 
THERMAL PROFILES WARM ENOUGH FOR MAINLY RAIN THROUGH TUESDAY. PWATS 
AROUND THREE QUARTERS OF AN INCH BEING SHOWN BY MEDIUM RANGE MODELS 
WHICH IS CLOSE TO BEING 2 STANDARD DEVIATIONS ABOVE NORMAL. THUS 
SOME CONCERN GROWING WITH THIS LATEST MODEL RUN OF MODERATE TO HEAVY 
RAINFALL RELATIVE TO MID DECEMBER. FORTUNATELY NO SNOW PACK TO WORRY 
ABOUT AND RIVERS RUNNING NEAR NORMAL. 

AS STORM DEEPENS AND TAKES ON A NEGATIVE TILT TUESDAY...SECONDARY 
ENERGY IN BASE OF ELONGATED TROUGH BECOMES THE PROBLEMATIC FEATURE 
FOR MODELS AND THE DETERMINING FACTOR FOR HOW MUCH SNOW WE WILL SEE 
TUE NIGHT INTO WED. LATEST 00Z ECMWF AND GEM NOW REVERTING BACK TO 
PREVIOUS SOLUTIONS WITH SECONDARY LOW FORMING IN MID MS VALLEY AND 
MOVING NORTHEAST THROUGH WESTERN OH AS A PANHANDLE HOOK TYPE SCENARIO. 
BOTH OF THESE MODELS HAVE A SUB 990MB LOW NOW OVER WESTERN OH BY 12Z 
WED WITH POTENTIAL FOR DECENT SNOWFALL OVER PARTS OF THE CWA. 
OPERATIONAL GFS IS SIMILAR BUT MUCH WEAKER WITH THIS SFC LOW. 
MEANWHILE...PARALLEL GFS SHOWS A SIMILAR SOLUTION TO ECMWF/GEM BUT 
TAKES THE LOW NORTH ALONG THE IN/IL STATE LINE WITH A 979MB SFC LOW 
OVER LAKE MICHIGAN BY 12Z WED. OBVIOUSLY THIS WOULD GIVE US MUCH 
LESS SNOWFALL. CONFIDENCE REMAINS LOW IN DETAILS FOR CHANGEOVER TO 
SNOWFALL AND POTENTIAL AMOUNTS GIVEN THIS PLETHORA OF SOLUTIONS AND 
MAIN PLAYERS STILL OVER THE DATA SPARSE NORTH PACIFIC. PAST 
EXPERIENCE HAS SHOWN THAT THESE WINTER STORMS WITH A STRONG NEGATIVE 
TILT TEND TO FAVOR A MORE WESTWARD SOLUTION. 

WILL MAINTAIN CONSISTENCY WITH PREVIOUS FORECAST AND SURROUNDING 
SITES USING SUPERBLEND INIT BUT GIVEN DECENT AGREEMENT ON 
PRECIPITATION ACROSS THE AREA MONDAY NIGHT THROUGH TUESDAY NIGHT DID 
NUDGE ENTIRE AREA INTO LIKELY POP CATEGORY FOR THESE PERIODS. ALSO 
INCREASED SKY COVER AND WINDS. AS FOR PCPN TYPE...KEPT IT ALL RAIN 
THROUGH TUESDAY AND LEFT TUE NIGHT AS RAIN OR SNOW GIVEN 
UNCERTAINTY. BY WED THE STORM SHOULD BE OCCLUDING AND MOST LIKELY 
NORTH OF US SO COLD AIR SHOULD BE WRAPPED AROUND AND IN PLACE GIVEN 
ALL CURRENT SOLUTIONS. THUS HAVE ALL SNOW FOR WED AND WED NIGHT. 
LAKE RESPONSE THEN LIKELY INTO CHRISTMAS DAY WITH WINDY CONDITIONS 
OVER ENTIRE AREA. STRONG WINDS AND SHORT WNW FETCH OVER THE LAKE MAY 
ACTUALLY BE A DETRIMENT TO LAKE EFFECT BUT STILL WORTHY OF CHANCE 
POPS IN FAVORED NW AREAS.        

NOT TO FORGET THE EARLY PART OF THE LONG TERM PERIOD BUT WEATHER 
WILL BE BENIGN WITH A FEW SUBTLE SHORT WAVES. WEAK PV ANOMALY AND 
SHORT WAVE ON SATURDAY MAY SQUEEZE OUT A FEW FLURRIES BUT MOISTURE 
LACKING FOR ACCUMULATIONS. WARMING TREND INTO NEXT WEEK AHEAD OF 
DEVELOPING STORM. 

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 530 AM EST FRI DEC 19 2014

MVFR CIGS AND LIGHT WINDS THE HIGHLIGHT THIS PERIOD UNDER
LINGERING INVERSION/HIGH PRESSURE. WEAK SFC TROUGH MAY TOUCH OFF
SOME SPOTTY SHSN/FZDZ AND FUEL ALT CEILINGS THIS MORNING. DRY
CONDITIONS OTHERWISE WITH POTENTIAL FOR BRIEF IMPROVEMENT TO VFR
POSSIBLE MIDDAY/AFTERNOON.

&&

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

$$

SYNOPSIS...STEINWEDEL
SHORT TERM...STEINWEDEL
LONG TERM...LASHLEY
AVIATION...STEINWEDEL


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