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Area forecast discussion 
National Weather Service northern Indiana
826 am EST Sat Jan 31 2015

Synopsis...
issued at 501 am EST Sat Jan 31 2015

A winter storm will impact the region beginning tonight and
continuing into Sunday night. The heaviest snow with this system
is expected Sunday morning through early Sunday evening...with
blowing and drifting snow also becoming a concern Sunday afternoon
and evening. After milder conditions today into the 30s...much
colder temperatures are in store for Sunday night and Monday.

&&

Update...
issued at 825 am EST Sat Jan 31 2015

Discontent with Michigan counties under watch especially given 03
UTC sref/06 UTC NAM along with wpc continuing to peg northern third
with hiest snow swath. Degree of isent moisture flux
convergence/advection into Southern Lower Michigan to easily overwhelm/shunt
northward any dry air entrainment issues. Revert to broad 6 to 12 inch
accums and await 12 UTC model suite/09 UTC sref output before fine
tuning with application of greater mesoscale detail/warning
segmentation. Actually right now am more concerned with diminished
amounts far southwestern/southern in counties owing to magnitude of warm wet
bulb wedge extruded northward through Indiana. 1kft plus 1c wet bulb per
kgus 06 UTC NAM profile...would suggest at least a partial melt
overnight...lending to lower slr for first 6-9 hours of event.

&&

Short term...(today and tonight)
issued at 501 am EST Sat Jan 31 2015

Forecast concerns for the short term will center on snow overspread
the area tonight which will lead into potentially high impact snow
event for the area into Sunday night covered in the long term
section below. A Winter Storm Warning will be in effect from 00z
this evening through 09z Monday morning with a Winter Storm Watch in
effect for Southern Lower Michigan counties for the same times.

Quiet weather expected to continue through most of the day with some
middle level warm air advection induced cloudiness across northern Illinois this
morning expected to shift across northern Indiana over the next few
hours. An upper level short wave tracking across the northern Great
Lakes may allow some low clouds to push across the far north...but
most locations should be partly cloudy at least through early
afternoon. An increase in middle and high level clouds is expected
later this afternoon as primary short of interest for upcoming snow
event begins to dig across the central rockies. High temperatures
this afternoon should be 3 to 6 degrees warmer than yesterday into
the lower and middle 30s.

For tonight a sheared upper level short wave will lift into the
southern Great Lakes region downstream of primary vorticity maximum. Broad
synoptic support for uvm will also increase as local area becomes
positioned in favorable right entrance of upper jet. Isentropic
ascent per 290k surface also to significantly ramp up toward daybreak
Sunday. Overall expecting light snowfall amounts in the 1 to 3 inch
range for tonight...which will lead into period of greatest impacts
with this winter storm on Sunday/Sunday night discussed in long term
section below as stronger middle/upper level forcing approaches the
region.

&&

Long term...(sunday through friday)
issued at 501 am EST Sat Jan 31 2015

Heavy snow is expected early Sunday...continuing through Sunday
evening before ending early Monday. Several favorable factors coming
together for a winter storm with heavy snow and blowing snow. Moisture
laden subtropical moisture in the middle to upper levels will arrive in
tandem as the northern stream system and the southern stream phase.
Precipitation efficiency with this setup should be very good. For
this event...favored a GFS solution. The GFS has been trending
toward a slower and more northern track and a relatively long
duration event. Also...this GFS seems to be handling all of the
significant parameters for this winter storm reasonably well. The
290k Garcia/mixing ratio method renders 8 to 12 inches of
snow...with lesser amounts over far Southern Lower Michigan. Still
some uncertainty over this far northern portion of the area given
lower mixing ratios and a greater chance for dry air entrainment
with low level/drier northeast flow during the second half of the
event. Therefore... after coordination with surrounding offices...
kept lower Michigan in a Winter Storm Watch for now and deferred to
the next shift the option to update. Was hesitant to raise high end
snowfall amounts in light of climate data...although GFS...European model (ecmwf) and
NAM all support snowfall totals of 12 to 15 inches across northern
Indiana and Northwest Ohio. Climate percentages at both feet Wayne and
Lafayette indicate a two day snowfall total of 8 inches or more is
rare...it only happens on average of once every 5 to 6.5 years.
Furthermore...a snowfall of 12 inches or more happens only once in
every 15 to 25 years. Given these factors...and considering the
above...kept ongoing snowfall amounts close to the ongoing/inherited
amounts...with the latest thinking that total snowfall amounts from
this storm should range from 7 to 11 inches. Significant travel
impacts will be mounting Sunday night as winds increase with blowing
and drifting snow. Raised wind speeds considerably Sunday evening
given the new and farther north and deeper GFS low with a tight
surface pressure gradient over the area. Otherwise...snowfall should
end from west to east late Sunday night. Snow drifts on unplowed
roads will likely make some roads impassible. Wind chills dropping
well below zero early Monday morning are expected.

&&

Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 641 am EST Sat Jan 31 2015

VFR conditions are expected to persist through the day...with the
possibility of some VFR low clouds moving into northern Indiana
later this morning in association with upper wave tracking across
the Great Lakes. Conditions to deteriorate tonight as lead short
wave and isentropic lift increase with light snow overspreading
the terminals. Have continued trend from 06z tafs with transition
to IFR visibilities by late evening...with intensity of snow increasing
toward daybreak Sunday. Further deterioration is expected just
after this forecast valid period as the primary upper level system
approaches the region with significant snow accumulations for
Sunday.

&&

Iwx watches/warnings/advisories...
in...Winter Storm Warning from 7 PM EST /6 PM CST/ this evening to 4
am EST /3 am CST/ Monday for inz003>009-012>018-020-022>027-
032>034.

Michigan...Winter Storm Warning from 7 PM this evening to 4 am EST Monday
for miz077>081.

Ohio...Winter Storm Warning from 7 PM this evening to 4 am EST Monday
for ohz001-002-004-005-015-016-024-025.

Lm...none.
&&

$$

Update...Murphy
synopsis...marsili
short term...marsili
long term...skipper
aviation...marsili



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