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Area forecast discussion 
National Weather Service northern Indiana
359 PM EST Wednesday Jan 28 2015

Synopsis...
issued at 401 am EST Wednesday Jan 28 2015

Clouds will increase this evening as a ridge of high pressure
shifts off to the east. An upper level disturbance across The
Rockies will track into the Great Lakes and Ohio Valley regions
tonight bringing a wintry mix late tonight into Thursday. Some
minor ice and snow accumulations are possible...particularly
across far northern Indiana...much of lower Michigan...and
Northwest Ohio.

&&

Short term...(this evening through thursday)
issued at 359 PM EST Wednesday Jan 28 2015

Quiet/dry weather continues into this evening with attention
turning to light wintry mix later tonight/tomorrow...

Middle level tropopause undulation just entering western NE/northeast Colorado will
translate east with 120-140 meter height fall track at 500 mb
into the Northern Ohio valley by Thursday morning...while a separate
northern stream wave drops out of south-central Canada into the
western lakes by Thursday afternoon. Precipitation tied to strong
isentropic lift/moisture convergence within downstream low level jet/Theta-E
ridge (ample moisture as precipitable waters surge to 0.80 inches and 1000-850
mb mixing ratios to 4-5 g/kg within moisture channel) should break
out shortly after midnight in northwest in/SW lower Michigan...and then spread
east-southeast into the rest of the forecast area through middle morning in advance of an
elongated surface trough. Precipitation may be more spotty/showery during this
time given overspread of steep middle level lapse rates and slight lag
of deeper moisture/mid-upper level ascent. Should see light precipitation
fill in along and behind the surface trough late morning through middle
afternoon across mainly northern/eastern portions of the forecast area
as weak deformation forcing shifts through. This forcing/deeper
moisture then exits east by late afternoon..although should see
some drizzle/light snow showers linger given some lake
enhancement.

Ptype initially still expected to be a sleet/freezing rain mix
later tonight/early Thursday morning as saturation/wet bulbing
occurs and warm layer centered around 800 mb overspreads. Sub
freezing surface ambient temperatures in the north and east likely with light
icing expected toward daybreak/morning commute hints at the
potential for difficult travel from light ice accretions. Per
collaboration and poor timing will issue a headline for these
areas...with confidence in duration/measurable precipitation too low across
southwest zones for a headline at this time. Surface temperatures and any icing
concerns should abate by late morning as warm/moist advection in
southerly flow allows surface wet bulb temperatures to warm above freezing.
Ptype continues to be messy into the afternoon...more light
snow/sleet than rain in Southern Lower Michigan and rain changing to
light snow southern half. Deep layer of temperatures warmer than -10c and
marginal boundary layer temperatures will significantly reduce snow
ratios with little to no snow/sleet accumulation expected.

&&

Long term...(thursday night through wednesday)
issued at 359 PM EST Wednesday Jan 28 2015

Steady course this forecast cycle. Assured though modest/shallow les
convection culminating late Thursday night...with lake induced cape at or below
300 j/kg and eql below 6kft. Dry air entrainment/backing steering flow
and increased turbidity within cbl to sharply degrade response by
midday Friday. Most focus on possible Sat night/Sunday snow event.
Increased model spread lending to low confidence for any sig event.
Latest European model (ecmwf) quells moisture farther southward than prior and even prior
all in Gem has backed off considerably but still slow/strong with
GFS weak and decisively fast. Best course of action at this time to
continue/though slightly lower msrbl probability of precipitation for light snow event sun as
upstream attempt to congeal notable shortwave energies currently
located across northern Canada/Gulf of Alaska/siberian straits. At least
80-100m/12 hour height fall centroid per latest middle of Road
European model (ecmwf)...on order of 50m/12 hour weaker than prior iteration... drops
east-southeastward from northern plains into middle Ohio should illicit sufficient deep
layer ascent for at least a light event. Later forecasts allowed to
fine tune as potential outcomes hopefully hone.

&&

Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1213 PM EST Wednesday Jan 28 2015

VFR with a gradual increase in southerly winds and middle-high level
clouds can be expected this afternoon as warm advection commences.
Moisture channel within ramping low level jet will drift east over
northern Indiana later tonight into early Thursday morning in
advance of an approaching middle level disturbance and elongated surface
trough. The result will be deteriorating flight conditions and
increasing chances for rain showers (freezing rain possible at
onset) during this time.

&&

Iwx watches/warnings/advisories...
in...Freezing Rain Advisory from 6 am to 10 am EST Thursday for
inz007-009-018-026-027.

Freezing Rain Advisory from 4 am to 9 am EST Thursday for
inz004>006-008-016-017.

Michigan...Freezing Rain Advisory from 6 am to 10 am EST Thursday for
miz080-081.

Freezing Rain Advisory from 4 am to 9 am EST Thursday for
miz077>079.

Ohio...Freezing Rain Advisory from 6 am to 10 am EST Thursday for
ohz001-002-004-005-015-016-024-025.

Lm...none.
&&

$$

Synopsis...marsili
short term...steinwedel
long term...Murphy
aviation...steinwedel



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