Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 160641
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
141 AM EST TUE DEC 16 2014

.SYNOPSIS...
ISSUED AT 125 AM EST TUE DEC 15 2014

AN UPPER LEVEL DISTURBANCE AND LOW PRESSURE AREA WILL MOVE ACROSS
THE REGION ACCOMPANIED BY PERIODS OF RAIN THROUGH THIS MORNING.
SCATTERED RAIN SHOWERS WILL PERSIST INTO THIS AFTERNOON...WITH
LINGERING PRECIPITATION MIXING WITH SNOW AND THEN CHANGING TO ALL
SNOW TONIGHT. SOME LIGHT SNOW ACCUMULATIONS ARE POSSIBLE TONIGHT.
COLDER WEATHER WILL BE IN STORE FOR MID WEEK BEHIND THIS SYSTEM.
TEMPERATURES THROUGH EARLY THIS MORNING WILL REMAIN STEADY IN THE
LOW TO MID 40S. HIGHS TODAY SHOULD REACH THE MID AND UPPER 40S.

&&

.UPDATE...
ISSUED AT 730 PM EST MON DEC 15 2014

NEAR TERM UPDATES THIS EVENING HAVE BEEN MAINLY TO FOCUS ON POP
EVOLUTION. THE COMBINATION OF LEAD VORT MAX EJECTING AHEAD OF
PARENT UPPER CIRCULATION ACROSS SOUTHERN IOWA AND NARROW CORRIDOR
OF ENHANCED LOW LEVEL MOISTURE CONVERGENCE HAS LED TO BAND OF RAIN
PROGRESSING ACROSS THE AREA. MAIN TWEAKS TO POPS WERE FOCUSED ON
RESOLVING PROGRESSION OF THIS BAND OVER THE NEXT FEW HOURS ACROSS
EASTERN PORTIONS OF THE FORECAST AREA. DID LOWER POPS TO CHANCE
CATEGORY FOR A TIME LATER THIS EVENING INTO THE EARLY PORTION OF
THE OVERNIGHT HOURS BEFORE ANOTHER VORT MAX ASSOCIATED WITH UPPER
SPEED MAX NOSING INTO THE MID MS VALLEY BEGINS TO WRAP
CYCLONICALLY INTO THE OHIO RIVER VALLEY/SOUTHERN GREAT LAKES
REGION. LOW LEVEL MOISTURE AXIS ALSO SHOULD REMAIN ANCHORED ACROSS
THE REGION INTO TUESDAY MORNING...AND HAVE NOT MADE SIGNIFICANT
CHANGES TO LIKELY/CATEGORICAL POPS AFTER 09Z. OTHERWISE...PREVIOUS
GRIDS REMAIN ON TRACK...AND MAY JUST MAKE SLIGHT DOWNWARD
ADJUSTMENT TO MINS BASED ON CURRENT OBSERVATIONAL TRENDS.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 315 PM EST MON DEC 15 2014

BLOCKY PATTN ALOFT IN CONCERT W/HEADACHE INDUCING DIRTY RIDGE
FINALLY ON THE WAY OUT THIS PD AS POTENT CYCLONE OVR NW MO EJECTS
OUT ACRS THE SRN LAKES. BAND OF -RA ALG LEADING EDGE OF UPR
TROUGH/VERTICAL ASCENT PLUME HAD DECAYED OUT EWD W/TIME INTO WRN IN
AS FOCUS REDVLPD BACK WWD N-S THROUGH ERN IL. XPCD THIS BAND TO
DOMINATE GOING INTO THIS EVENING W/A GENERAL NEWD EXPANSION FVRD AS
NOTED IN ALL HIGHRES GUIDANCE. OTRWS HEAVIER RAIN POTENTIAL STILL
INDICATED FOR LT TONIGHT AS IMPRESSIVE MID LVL DRY SLOT WRAPS
OVERHEAD. SOME THUNDER NOTED EARLIER OVR NE KS/SE NE HWVR CIRC
INDICATED TO OPEN UP TUE AM W/WKNG WCB AND SUBDUED NWD THETA-E WRAP.
REGARDLESS DECENT AREA OF RAINFALL SHLD MATERIALIZE OVR NRN/ERN
AREAS TWD DAYBREAK.

ON TUE...OPENING CIRC ALOFT WILL PASS OVERHEAD MIDDAY AS MOIST
CYCLONIC FLW ENVELOPES CWA AND XPC OCCASIONAL SHRA TO PERSIST. HWVR
FOCUS FOR GREATER IMPLIED COVERAGE/INTENSITIES SHLD REMAIN GENERALLY
REMAIN ALG/NORTH OF HIGHWAY 6 IN PROXIMITY TO DECAYING MID LVL
DEFORMATION ZONE. TEMPS THROUGH THE PD LTL CHGD UNTIL CAA WING WRAPS
UNDERNEATH DEPARTING CYCLONE TUE NIGHT.

&&

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 315 PM EST MON DEC 15 2014

...LIGHT LAKE EFFECT SNOW SHOWERS EXPECTED WEDNESDAY AND
THURSDAY...THEN DEVELOPING LOW PRESSURE MAY BRING LIGHT SNOW FOR THE
WEEKEND....

A VERTICALLY STACKED LOW PRESSURE SYSTEM CENTERED OVER LAKE HURON
WILL GRADUALLY SHIFT EASTWARD INTO SOUTHERN ONTARIO TUESDAY NIGHT.
MEANWHILE...SFC HIGH PRESSURE WILL GRADUALLY DRIFT INTO THE WESTERN
GREAT LAKES THROUGH FRIDAY WITH ANOTHER SHORTWAVE/UPPER LEVEL LOW
LINGERING ALOFT. IN THE WAKE OF THE LOW...CAA ON WEST-NORTHWEST
WINDS WILL INTRODUCE THE POSSIBILITY OF LAKE EFFECT SNOW/RAIN
SHOWERS IN WNW WIND FAVORED AREAS...MAINLY FAR SW LOWER MI/NW
INDIANA. NOT EXPECTING ANYTHING SIGNIFICANT HOWEVER...AS MOISTURE
AND INSTABILITY ARE LACKING. WITH LAKE TEMPS AROUND 4-5C...700MB
DELTA TS STRUGGLE TO REACH 15C BY 12Z WEDNESDAY...AND THETA E LAPSE
RATES ARE FAIRLY PALTRY. SUBSIDENCE FROM THE INCOMING HIGH PRESSURE
WILL ALSO LIMIT CONVECTIVE DEPTH...WITH THE SUBSEQUENT INVERSION
DROPPING TO AROUND 875MB BY WEDNESDAY AM. THE INCOMING DRIER AIRMASS
WILL ALSO LEAVE US WITH A RATHER UNHEALTHY DGZ...WITH RH LESS THAN
20 PERCENT WITHIN THE -12 TO -18C LAYER. EARLY IN THE
EVENING...EXPECT A BIT OF MIXED PRECIPITATION...AS SFC TEMPS ARE
ABOVE FREEZING. AS DRYING TREND INCREASES ALOFT...WE COULD EVEN SEE
A BRIEF PERIOD OF FREEZING DRIZZLE. BY 6Z HOWEVER...ALL
PRECIPITATION SHOULD TRANSITION TO SNOW AS SFC TEMPS DROP BELOW
FREEZING. KEPT MARGINAL POPS IN WNW WIND FAVORED AREAS...GENERALLY
FLURRIES TO LIGHT SNOW SHOWERS.

THOUGH HIGH PRESSURE IS INCOMING...EXPECT PARTLY TO MOSTLY CLOUDY
SKIES TO LINGER WEDNESDAY AS MOISTURE IS ONCE AGAIN TRAPPED BENEATH
THE SUBSIDENCE INVERSION. LIGHT SNOW SHOWERS IN THE NORTHWEST ARE
EXPECTED TO CONTINUE THROUGHOUT THE DAY. CYCLONIC FLOW ALOFT WILL
ALSO BRING A FEW WEAK SHORTWAVES ACROSS THE CWA...WHICH WILL SERVE
TO LIFT INVERSION HEIGHTS TO NEAR 800 MB AT TIMES. HIGH TEMPERATURES
RETURN TO NEAR NORMAL FOR DECEMBER...PRIMARILY IN THE 30S.

SNOW SHOWERS WILL PERSIST NEAR LAKE MI INTO THURSDAY AFTERNOON WITH
THE 500MB FLOW BECOMING RELATIVELY ZONAL...BUT AS THE UPPER LEVEL
RIDGE BEGINS TO BUILD IN OVERHEAD...TEMPERATURES ALOFT BEGIN TO
WARM. ENDED ALL POPS BY 00Z FRIDAY AS A RESULT.

SFC LOW PRESSURE DEVELOPING IN THE GULF STATES WITH A DEEP UPPER
LEVEL TROUGH CENTERED OVER THE PLAINS WILL BEGIN TO LIFT
NORTHEASTWARD SATURDAY. BOTH THE ECMWF/GFS BRING THE CENTER OF THE
LOW INTO VIRGINIA/WEST VIRGINIA BY 00Z SUNDAY...HOWEVER THEY DIFFER
WITH RESPECT TO THE UPPER LEVEL TROUGH DEVELOPING INTO A CLOSED LOW.
THIS SYSTEM WILL BRING CHANCES FOR SNOW OVER THE WEEKEND. GFS IS
MORE PROGRESSIVE AND BRINGS THE PRECIPITATION INTO OUR CWA BY
SATURDAY 12Z...BUT THE ECMWF LINGERS BACK BY ABOUT 6-12 HOURS. KEPT
CONSENSUS POPS FOR NOW. TEMPERATURES WILL BE SOMETHING TO WATCH...AS
WE COULD SEE A RAIN/SNOW MIX DURING THIS PERIOD. WITH THE LATEST
MODEL TRENDS KEEPING US IN THE COLDER AIR BEHIND THE SYSTEM...KEPT
TEMPS RIGHT AROUND FREEZING FOR NOW...AND KEPT SNOW AS THE P-TYPE.
MONDAY WILL BE RELATIVELY QUIET AS HIGH PRESSURE RETURNS TO THE AREA.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 121 AM EST TUE DEC 16 2014

THE CORE OF THE UPPER LOW WAS OVER NW IL AND WILL TRACK EAST
ACROSS SOUTHERN LOWER MICHIGAN LATER TODAY. ANOTHER AREA OF RAIN
ASSOCIATED WITH AN UPPER LEVEL SHORT WAVE AND ACCOMPANIED BY LOW
CIGS AND VSBYS WILL SPREAD OVER THE TERMINALS EARLY IN THE TAF
PERIOD. EXPECT LOW TO VERY LOW IFR CONDITIONS EARLY THIS MORNING
AS THE UPPER LEVEL SYSTEM MOVES OVER THE AREA. SOME IMPROVEMENT IS
LIKELY AS THE LOW MOVES EAST FOLLOWED BY DRIER AIR SPREADING
ACROSS THE AREA NEAR THE END OF THE TAF PERIOD. HOWEVER...CIGS
MAY STILL BE IFR AT THE END OF THE TAF PERIOD.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 5 AM EST
     THURSDAY FOR LMZ043-046.

&&

$$

UPDATE...MARSILI
SYNOPSIS...MARSILI/SKIPPER
SHORT TERM...T
LONG TERM...MCD
AVIATION...SKIPPER


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