Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 231925
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
225 PM EST TUE DEC 23 2014

.SYNOPSIS...
ISSUED AT 1038 AM EST TUE DEC 23 2014

A LOW PRESSURE MOVING BY JUST TO THE NORTHWEST IS MOVING LIGHT
RAIN TO DRIZZLE ACROSS THE AREA. HIGH TEMPERATURES TODAY WILL BE
ON THE MILD SIDE RANGING FROM AROUND 50 IN SOUTHERN MICHIGAN TO
THE LOWER 50S NEAR THE OHIO RIVER. TONIGHT RAIN SHOWERS ARE
EXPECTED TO MOVE BACK IN FROM A LOW MOVING NORTHWARD UP FROM THE
GULF OF MEXICO. LOW TEMPERATURES TONIGHT WILL RANGE FROM AROUND 40
IN SOUTHERN MICHIGAN TO AROUND 50 NEAR THE OHIO RIVER. THIS LOW
WILL CONTINUE RAIN CHANCES FOR TOMORROW. THE RAIN IS THEN EXPECTED
TO CHANGE OVER TO SNOW TOMORROW NIGHT.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 412 AM EST TUE DEC 23 2014

UPPER LOW AND ATTENDANT 997 MB SFC REFLECTION OVER CENTRAL IA WILL
SHEAR/WEAKEN NE INTO WI TODAY. THIS FEATURE AND DEEPENING SSW FLOW
IN ADVANCE OF A HIGHLY AMPLIFIED CENTRAL CONUS LONGWAVE TROUGH WILL
HELP LIFT A WARM FRONT/OCCLUSION THROUGH THE LOCAL AREA THIS
MORNING RESULTING IN AN UNSEASONABLY MILD PERIOD. RAIN SHOWER
COVERAGE WILL RAPIDLY DIMINISH FROM SW TO NE EARLY THIS MORNING
(BEFORE DAYBREAK) AS INITIAL PV/THETA-E ADVECTION SURGE LIFTS OFF
TO THE NORTH AND PRONOUNCED MID LVL DRY SLOT OVERSPREADS. STILL
EXPECT LOW CLOUDS AND PATCHY LIGHT SHOWERS/DRIZZLE ALONG AND IN
ADVANCE OF THE SFC BOUNDARY INTO THIS AFTERNOON GIVEN MOIST LOW
LEVELS (6-7 G/KG WITHIN 1000-850 MB LAYER) AND WEAK CYCLONIC FLOW
(CHANCES SHIFTING MORE INTO EASTERN ZONES WITH LITTLE IN THE WAY
OF PCPN WESTERN AND NORTHERN ZONES BY AFTERNOON). HELD ONTO LOW
RAIN CHANCES THIS EVENING (HIGHEST SOUTHEAST) AS THE NEXT SLUG OF
DEEPER MOISTURE LIFTS NORTH IN ADVANCE OF A DEVELOPING LOWER MS/TN
VALLEY CYCLONE TO BE DISCUSSED IN THE LONG TERM SECTION.


&&

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 412 AM EST TUE DEC 23 2014

WHILE THE FORECAST PROJECTION TIME TO THE CHRISTMAS EVE STORM
NARROWS THE RANGE OF SOLUTIONS WITH REGARDS TO STORM TRACK REMAINS A
BIT WIDER THAN ONE WOULD LIKE TO SEE AT THIS TIME. NO DRASTIC
CHANGES MADE TO WX/POP GRIDS AS LARGE SCALE EVOLUTION STILL ON TRACK
BUT THE DETAILS WITH WHERE ANY ACCUMULATING SNOWFALL WILL DEVELOP
REMAIN IN QUESTION.

AS EXPECTED AND DISCUSSED HERE IN DEPTH OVER THE PAST SEVERAL
DAYS...00Z MODEL SUITE HAS IN GENERAL SHIFTED SLIGHTLY WESTWARD
COMPARED TO 24 HOURS AGO BUT A SIGNIFICANT SPREAD STILL REMAINS
AMONG THE MOST TRUSTED AND RELIABLE MODELS. PARALLEL GFS CONTINUES
TO BE ON THE WESTERN ENVELOPE OF SOLUTIONS TAKING THE SURFACE LOW
FROM NEAR KLWV AT 12Z WED TO JUST NORTH OF KSBN BY 18Z. GEFS
ENSEMBLES ARE CLUSTERED AROUND A SIMILAR TRACK BUT A BIT SLOWER WITH
MEAN SFC LOW CLOSER TO KLAF BY 18Z. OPERATIONAL GFS...GEM AND ECMWF ARE
A BIT FURTHER EAST TAKING LOW NORTH THROUGH EASTERN INDIANA...WITH
OPERATIONAL GFS FASTER BUT DEEPER THAN ECMWF. 00Z AND 06Z NAM
REMAINS FURTHEST EAST TAKING LOW TO NEAR KTOL BY 00Z THU. THUS QUITE
A BIT OF UNCERTAINTY CONTINUES IN THE IMPORTANT THERMAL AND
MESOSCALE DETAILS WITH LOCATION AND TIMING OF WHERE RAIN WILL CHANGE
TO SNOW. GIVEN THESE LATEST MODEL SOLUTIONS...CHANGEOVER TO SNOW
VARIES FROM NORTH CENTRAL INDIANA AND EXTREME SOUTHWEST LOWER
MICHIGAN WITH THE EASTERN MODELS TO NORTHEAST ILLINOIS WITH THE
WESTERN MODELS.

WATER VAPOR IMPRESSIVE EARLY THIS MORNING SHOWING JET ENERGY DIGGING
DEEP INTO WEST TEXAS AND NORTHERN MEXICO. ENERGY LOOKS TO BE FINALLY
ROUNDING BASE OF TROUGH AROUND 08Z WITH IMPRESSIVE TROPICAL MOISTURE
STREAMING NORTH OUT OF THE EAST CENTRAL PACIFIC AND GULF OF MEXICO.
CYCLOGENESIS JUST GETTING UNDERWAY WITH WHAT APPEARS TO BE A COUPLE
WEAK LOWS FORMING IN THE WESTERN GOMEX AND SOUTHERN TIP OF TX. THE
ULTIMATE TRACK OF THIS SYSTEM WILL DEPEND ON HOW FAST MID LEVEL
DYNAMICS COME TOGETHER AND WHEN/WHERE UPPER LOW CLOSES OFF. WE
CONTINUE TO HEDGE TOWARD THE WESTERN SOLUTIONS GIVEN EXPECTED RAPID
INTENSIFICATION...NEGATIVE TILT AND DEEPENING OF SFC LOW. WOULD
FAVOR SURFACE LOW DEVELOPMENT AND TRACK TO BE CLOSER TO MID LEVEL
CLOSED LOW GIVEN THIS SCENARIO. THUS LEANED SLIGHTLY TOWARD THE GEFS
AND PARALLEL GFS SOLUTIONS BUT DID BLEND A BIT OF THE ECMWF AND GEM
GIVEN THE UNCERTAINTY. RESULT REMAINS CLOSE TO PREVIOUS FORECASTS
WITH SLIGHT ADJUSTMENTS MADE TO QPF AND SNOW GRIDS. THERE IS STILL A
LOW CHANCE FOR A NARROW BAND OF MODERATE TO HEAVY SNOW ON THE BACK
SIDE OF THIS SYSTEM BUT THE INHIBITING FACTORS CONTINUE TO BE THE
WARM AIR BEING WRAPPED AROUND THE DEEPENING LOW AND THE INITIALLY
WARM AND WET LOWER LEVELS. THE DEBATE AND UNKNOWN QUESTION IS IF THE
INTENSIFICATION WILL RESULT IN STRONG ENOUGH DYNAMICAL COOLING TO
OFFSET THIS WARM NEAR SURFACE LAYER AND ALLOW SIGNIFICANT ACCUMS TO
MATERIALIZE. AFTER MUCH COLLABORATION BETWEEN OFFICES AND WPC HAVE
ALL AGREED TO TREAD CAUTIOUSLY WITH ACCUMS FOR NOW AND GENERALLY
KEPT AMOUNTS IN THE 1 TO 3 INCH RANGE OVER OUR NW COUNTIES AND SEE
IF BETTER AGREEMENT DEVELOPS TODAY BETWEEN MODELS.

THE WARM SECTOR EAST OF THE LOW TRACK COULD ALSO BECOME QUITE MILD
ON WED AS WARM AIR IS DRAWN NORTHWARD. WOULD NOT BE SURPRISED TO SEE
MAX TEMPS REACH THE 60S IN THE FAR SOUTHEAST. THERE IS ALSO A LOW
CHANCE FOR THUNDER...ESPECIALLY WITH THE MORE WESTWARD TRACK. FOR
NOW OPTED TO LEAVE MENTION OUT OF FORECAST BUT COULD NEED TO BE
ADDED IN NEXT FEW FORECASTS. WE CONTINUE TO STRESS THE UNCERTAINTY
AND NEED FOR PEOPLE TRAVELING TO CONTINUE MONITORING FORECASTS AND
REMAIN AWARE.

REMAINDER OF LONG TERM BASICALLY RELEGATED TO SUPERBLEND WITH
SEVERAL WEAKER SYSTEMS LOOKING TO SKIRT THE AREA.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 153 PM EST TUE DEC 23 2014

SLIGHTLY DRIER AIR HAD SPREAD INTO NORTHWEST INDIANA...HELPING TO
SCATTER OUT THE LOWER SC LAYER AT THE START OF THE PERIOD.
HOWEVER...CLOUDS WILL RAPIDLY SPREAD BACK INTO THE FORECAST AREA
TONIGHT AS A 998 MB SURFACE LOW OVER EAST LA RACES NORTH.
CONDITIONS SHOULD BECOME IFR OR LOW IFR AS THE LOW MOVES NORTH
AND AS WIDESPREAD RAIN DEVELOPS. BUFKIT/THERMAL PROFILES INDICATE
THE PRECIPITATION WILL BE ALL RAIN THROUGH 18Z.

&&

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

$$

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


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