Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 230912
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
412 AM EST TUE DEC 23 2014

.SYNOPSIS...
ISSUED AT 1244 AM EST TUE DEC 23 2014

A WARM FRONT WILL LIFT NORTH THROUGH THE AREA EARLY THIS MORNING
BRINGING SCATTERED SHOWERS. DRIER AND MUCH MILDER AIR WILL FILTER
IN BY THIS AFTERNOON WITH LOW CLOUDS AND SOME PATCHY LIGHT RAIN OR
DRIZZLE POSSIBLE. HIGHS THIS AFTERNOON WILL BE UNSEASONABLY MILD
INTO THE UPPER 40S TO MID 50S. A STRENGTHENING LOW PRESSURE
SYSTEM WILL THEN TRACK DUE NORTH INTO INDIANA ON WEDNESDAY.
TEMPERATURES WILL LIKELY BE WARM ENOUGH FOR PRECIPITATION TO FALL
AS MAINLY RAIN ACROSS THE LOCAL AREA. CHRISTMAS DAY WILL FEATURE
DRIER AND COOLER CONDITIONS AS HIGH PRESSURE BUILDS IN.

&&

.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 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1244 AM EST TUE DEC 23 2014

AREA OF MORE ORGANIZED RAIN TIED TO STRONG MOISTURE/PV SURGE
WILL LIFT NE THROUGH NRN IN EARLY THIS MORNING. HIGH END MVFR TO
VFR CONDITIONS AT ISSUANCE WILL DETERIOTE TO IFR BY DAYBREAK GIVEN
THE LOW LEVEL MOISTURE SURGE AND UPSTREAM OBSERVATIONS. LOW IFR
STRATUS/HAZE WILL LIKELY LINGER AT THE TERMINALS THROUGH LATE
MORNING/EARLY AFTERNOON AS SFC OCCLUSION LIFTS THROUGH...WITH
POCKETS OF DRIZZLE/LIGHT RAIN POSSIBLE. IMPROVEMENT TO MVFR-VFR
POSSIBLE BY THIS AFTN/EVE AS DRY SLOT OVERSPREADS.

&&

.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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