Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 310615
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
115 AM EST SAT JAN 31 2015

.SYNOPSIS...
ISSUED AT 405 PM EST FRI JAN 30 2015

HIGH PRESSURE WILL MOVE SOUTHEAST ACROSS THE OHIO VALLEY TONIGHT
AND SATURDAY PROVIDING FAIR WEATHER ACROSS OUR AREA. LOWS TONIGHT
WILL RANGE FROM 11 TO 17... WITH HIGHS SATURDAY IN THE LOWER TO
MIDDLE 30S. LOW PRESSURE IS EXPECTED MOVE FROM THE THE PLAINS
SATURDAY NIGHT TO THE UPPER OHIO VALLEY SUNDAY NIGHT. THIS SYSTEM
WILL CAUSE SNOW... POSSIBLY HEAVY... IN OUR AREA SATURDAY NIGHT
THROUGH SUNDAY NIGHT.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 405 PM EST FRI JAN 30 2015

BENIGN WEATHER EXPECTED THROUGH SATURDAY AS HIGH PRESSURE DRIFTS
ACROSS THE REGION. BANDS OF LAKE EFFECT CLOUDS AND FLURRIES HAVE
BEEN STEADILY CONTRACTING PAST COUPLE OF HOURS WITH THIS TREND
LIKELY TO INCREASE AS WE CLOSE IN ON THE EARLY EVENING HOURS. THE
CLEAR SKIES AND DIMINISHING WINDS WILL ALLOW LOWS TO DROP INTO
THE TEENS AS THE HIGH DRIFTS OVERHEAD.

THE REGION WILL BE ON THE WARM SIDE OF THE HIGH ON SATURDAY
ALLOWING AFTERNOON HIGHS TO CLIMB TO NEAR OR ABOVE
FREEZING...ALLOWING FOR TEMPORARILY IMPROVING ROAD CONDITIONS
PRIOR TO THE ARRIVAL OF THE SNOW SATURDAY EVENING.

&&

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 405 PM EST FRI JAN 30 2015

12 UTC MODELS/COBB OUTPUT ALONG WITH 09/15 UTC SREF ENSEMBLE
PLUMES LENDING INCREASED CONFIDENCE FOR SIG EVENT SAT NIGHT
THROUGH SUN NIGHT...LEADING TO PRIOR MIDDAY ISSUANCE OF WINTER
STORM WATCH FOLLOWING WPC/INTEROFFICE COORD. SW/BAJA VORTEX
PUMPING EXTREME MOISTURE TRANSPORT NWD. 4-6 G/KG PLUS WITHIN
850-500 MB EXTRUDED NWD FM SWRN MEXICO INTO INTMTN/CENTRAL ROCKIES
TO HARMONIOUSLY MELD WITH HIGH MOISTURE LADEN WRN VANCOUVER WAVE
INTO SAT. PRESENCE OF HUDSON BAY AND SWRN VORTEX TO AID IN PHASING
TO SHARPLY HEWN SEWD DIVING SHORTWAVE THROUGH NRN PLAINS INTO MID
MS VLY. INCREASINGLY RAMPED HGHT FALLS WITH LONG DURATION TO AID
IN LARGE SCALE ASCENT. PROLONGED EWD REACH OF HGHT ADJUSTMENTS
NOTED AS HFC IN EXCESS OF 100M/12HR SUN AM INTENSIFIES UPWARDS OF
180M/12 HR AS IT INTO SWRN OH/NRN KY BY 12 UTC MON.
EXTREME/PROLONGED MFLUX CONVERGENCE IN E-W FASHION THROUGH NRN IL
INTO NWRN OH PER I285/I290K NAM ISENTROPIC SFCS. 50 KT SWRLY
JETLET ORTHOGONAL TO ISENT SFCS MOVES EWD FM SERN MO UP OHIO BASIN
SUN AM TO NEAR KCVG BY 00 UTC MON. 7H TRACK IN LARGELY
OPEN/POSITIVE TILT TO WEAKLY CLOSED ALONG ROUTE 6 CORRIDOR AND
HINT OF TROWAL AT I285K JUST SOUTH...ALONG WITH TIGHTER ENSEMBLE
SPREAD LENDS HIR CONFIDENCE TO FARTHER NWD SWATH OF HEAVIEST
SNOWFALL. WHILE CONFIDENCE OF SIG EVENT/6 PLUS INCHES IS VERY
HIGH...EVENTUAL PLACEMENT AND DETAILS ALONG N/S GRADIENT EDGES
STILL EVOKE HESITANCE/UNCERTAINTY. THEREFORE ENTIRE CWA UNDER WSW
FOR 6 TO 12 INCHES POSSIBLE...WITH LATER RUNS PROVIDING SUFFICIENT
CONFIDENCE FOR UPG WARNING/ADV DECISIONS...LIKELY EARLY AM SUN AND
CERTAINLY BY NOON SHOULD DEFERENCE BE MADE TO 12 UTC SUN MODEL
OUTPUT. WHAT COULD GO WRONG...INCLUSION OF PLATES/NEEDLES IN DEEP
SUPERSATURATION ABOVE THE DGZ COULD LEAD TO MORE GRANULAR FLAKES
AND ANY FARTHER NWD TREND WOULD BEGIN TO GREATLY LESSEN FAR SRN
CWA SLR AS COLUMN WARMS...THOUGH SRN CWA NAM BUFKIT SITES FIRM IN
FROZEN/SNOW PTYPE PER ENERGY NOMOGRAM. RAMPED GRADIENT FLOW TO
BRING PD OF BLSN ESP LATE SUN AFTN/EVE AS OH VLY SFC LOW DEEPENS
ALONG TRACK THROUGH MID INTO UPR OH VLY.

BRIEF LES IN WAKE OF SYSTEM...THOUGH INITIAL BAND MAY SET WEST OF
CWA UNTIL BACKING FLOW BY DAYBREAK MON. THEREAFTER DRY AIR
INTRUSION ALONG WITH LOWERING/STRENGTHENING SUBSIDENCE INVERSION
SHOULD GREATLY MITIGATE NWRN CWA ACCUMS. WEAK CLIPPER SYSTEM INTO
GRTLKS TUE NIGHT/WED...FOLLOWED AGAIN BY AT LEAST WEAK LES
RESPONSE AS PRIMARY TROF AXIS SHARPENS FM HUDSON BAY INTO LWR
GRTLKS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1239 AM EST SAT JAN 31 2015

LIGHT SOUTHWEST FLOW THROUGH THIS AFTERNOON AS LOW LEVEL RIDGE
AXIS CONTINUES TO DROP SOUTHEAST ACROSS THE MID ATLANTIC STATES.
SOME INCREASE IN MID LEVEL WAA CLOUDS EXPECTED THIS MORNING...AND
SCT-BKN HIGH CLOUDINESS...BUT MVFR CIGS SHOULD HOLD OFF UNTIL
TONIGHT. LEAD UPPER VORT MAX ASSOCIATED WITH NEXT SIGNIFICANT
SYSTEM TO IMPACT THE AREA COMBINED WITH ISENTROPIC UPGLIDE WILL
ALLOW SNOW TO OVERSPREAD TERMINALS IN THE EVENING AND HAVE
INTRODUCED IFR VSBYS TOWARD THE END OF THIS PERIOD. SNOWFALL
INTENSITY/CIGS/VSBYS TO DETERIORATE MORE SIGNIFICANTLY AFTER THIS
FORECAST VALID PERIOD AND ESPECIALLY AFTER 12Z SUNDAY AS PRIMARY
UPPER LEVEL TROUGH APPROACHES FROM THE WEST.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...WINTER STORM WATCH FROM THIS EVENING THROUGH SUNDAY EVENING FOR
     INZ003>009-012>018-020-022>027-032>034.

MI...WINTER STORM WATCH FROM THIS EVENING THROUGH SUNDAY EVENING FOR
     MIZ077>081.

OH...WINTER STORM WATCH FROM THIS EVENING THROUGH SUNDAY EVENING FOR
     OHZ001-002-004-005-015-016-024-025.

LM...NONE.
&&

$$

SYNOPSIS...JT
SHORT TERM...FISHER
LONG TERM...MURPHY
AVIATION...MARSILI


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