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Area forecast discussion 
National Weather Service northern Indiana
656 PM EST Sat Jan 31 2015

Synopsis...
issued at 427 PM EST Sat Jan 31 2015

A cold front will move south from the Great Lakes to the Ohio
Valley tonight. A strengthening low pressure system will move east
along the front through the Ohio Valley Sunday and Sunday night.
Snow will overspread our area tonight and become heavy on Sunday.
Winds will increase Sunday and Sunday night causing blowing and
drifting snow making travel difficult...if not impossible. Lows
tonight will primarily be in the 20s..with little if any
temperature rise on Sunday. Much colder temperatures are in store
for Sunday night and Monday.

&&

Update...
issued at 645 PM EST Sat Jan 31 2015

No significant changes to earlier zones at this time. Precipitation lifting NE toward
the area being forced by weak lead shortwave moving into the upper MS
valley/Midwest. All rain upstream across Illinois at this time but amdar
soundings east of Chicago suggest a profile supportive of snow.
Maintained going mixed precipitation weather grids across southwestern portion of the
County Warning Area this evening... with just snow across the rest of the area. 18z
models continue to support forecast of a major winter storm impacting the
County Warning Area late tonight through Sunday night as main upper trough digs southeast
into the Midwest preceded by strong moisture transport from the SW
and accompanied by a deepening surface low moving east from Kansas through
the Ohio Valley resulting in increasing winds and significant drifting
snow for the latter half of the event.

&&

Short term...(this evening through Sunday night)
issued at 418 PM EST Sat Jan 31 2015

Increased confidence throughout the day with respect to quite significant
winter weather event targeting County Warning Area. WV imagery and upstream
preconditioning sets stage for deep wall of moisture
advection/mflux convergnece for prolonged period into County Warning Area. Precipitable water
values over cntl plains on order of 200-300 percent of normal.
Expansive breadth of bulk moisture with consistent 0.5 to 0.65
inch precipitable water pivoting slowly through southern two thirds County Warning Area through the
event...with culminating 0.9 inch precipitable water tap across southwestern Ohio sun
evening...on order of 2 South Dakota above climatological
mean...implicating this event with high potential for being sig
outlier to climatology. Highly confluent/ramping i285/i290k isent
upglide over southeastern Missouri this evening...to 50-55kt low level
jet entering far southern in by Sun afternoon. Strong trailing middle level
deformation with prolonged period of system relative isent
upglide persisting through 06 UTC Monday...lending to ext in time
to eastern County Warning Area until 12 UTC. Blsn to impact highly...espcly across east-west
roads across northern County Warning Area where event slr to be hiest. 7h closed low
track along with trowal/deformation axis portends to axis of
heaviest snow from about Knox to Toledo...with a fairly broad
20-30 miles either side...before sig snow total gradients found.
Extreme deepening with sensational middle tropopheric height falls
ramping in excess of 200m/12 hour through as it tracks eastward through
middle/Ohio Valley Sun night...and more strongly closed 7h track and
presence of decreased static static stability Sun afternoon into
early evening gives concern for possible mesobanding leading to
amounts upwards of 15 inches through far northern in along north of
Route 30...to scntl lower Michigan/extreme northwestern Ohio. 18 UTC NAM even
generating pockets of 30-80 j/kg MUCAPE across northern two thirds County Warning Area
Sunday into early Sun night...perhaps pointing to convective
elements...commensurate snowfall rates would then likely peak at
2-4 inches per hour...albeit briefly.

From 03/09 UTC sref with its increased clustering over northern/cntl
County Warning Area to 12/18 UTC model suite consistent message appears.
Remarkably even the lowest outlier in 09 UTC sref members across
northern County Warning Area pegged at 8-10 inches...with consensus means about 6-8
inches hir. Idyllic deep dgz along north of Route 30...with
NAM/arw depicting 7-9kft dgz layer. Still minor concern with
supersaturation above to introduce plates/Needles for finer sized
flakes...but concede quantitative precipitation forecast/dynamics of system to offset. Ksbn to
kjym most consternation across far southwestern/southern Indian counties where
initial warm 0-2km wet bulb intrusion lending possible mix at
onset and lessened slr thereafter with partial melt.

&&

Long term...(monday through saturday)
issued at 418 PM EST Sat Jan 31 2015

One or More Lake effect snow bands will reside near or just west
of the forecast area across lake and Porter counties. Hi res
models trend this feature slowly east through the morning and
then dissipate as it shifts across northern Indiana. Despite what
should be a well formed band that may extend the long axis of Lake
Michigan...inversion heights will be lowering and moisture will be somewhat
limited. Also exact evolution of the band will be determined by
any potential intensification of the surface low and its final track.
As a result have not made many changes other than to increase
probability of precipitation slightly in far northwest areas and try to bring the band somewhat
east before weakening.

Although no big systems are during the period...a weak system
will drop southeast towards the region Tuesday into early Wednesday.
Light snow will be possible with this feature followed by another
brief shot of cold air before some moderation again late week
into the weekend.

&&

Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 633 PM EST Sat Jan 31 2015

Cold front dropping south across the Great Lakes will move through the
terminals tonight. Weak shortwave lifting into the upper Midwest ahead of
main system will spread a band of snow with IFR conditions to the
terminals by late evening. Deepening low pressure system will track from
eastern Kansas Sunday morning to southern Indiana Sunday evening. Snow will
become heavier and east-NE winds stronger during the day as the low
approaches resulting in LIFR aviation conditions with accumulating
snow and blsn.



&&

Iwx watches/warnings/advisories...
in...Winter Storm Warning until 4 am EST /3 am CST/ Monday for
inz003>009-012>018-020-022>027-032>034.

Michigan...Winter Storm Warning from 10 PM this evening to 7 am EST Monday
for miz081.

Winter Storm Warning until 4 am EST Monday for miz077>080.

Ohio...Winter Storm Warning from 10 PM this evening to 7 am EST Monday
for ohz001-002-004-005-015-016-024-025.

Lm...none.
&&

$$

Update...jt
synopsis...jt
short term...Murphy
long term...Fisher
aviation...jt



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