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Area forecast discussion 
National Weather Service northern Indiana
1221 am EST Friday Dec 19 2014

issued at 1220 am EST Friday Dec 19 2014

A weak trough will bring light scattered snow showers and patchy
drizzle to far northern Indiana and southern Michigan early this
morning. Otherwise...a ridge of high pressure will bring dry
conditions to the region through the weekend with near seasonable


issued at 940 PM EST Thursday Dec 18 2014

Late evening update will be sent shortly to expand patchy freezing
drizzle mention southward across far northern Indiana during the
early overnight hours. Some reports of slick conditions have been
received just north of forecast area across Southern Lower
Michigan. Based on current observational trends and continued
profiles supportive of -fzdz have expanded mention across far
northern Indiana. Will hold off on advisory at this time with
still some lower confidence on extent of hazardous
conditions...but have issued Special Weather Statement to cover -fzdz threat over the next
few hours.


Short term...(this evening through friday)
issued at 314 PM EST Thursday Dec 18 2014

Dry sub-cloud layer has thus far kept precipitation associated with weak Ohio
Valley shortwave all snow grains as opposed to freezing drizzle in
our area. Still some flurries being reported over portions of northern
Indiana but 88d returns waning this afternoon as appears weak uvm was
shifting eastward out of our area. Band of lake enhanced snow
associated with weak trough moving through southern Michigan/lm located from kbiv-
kgrr should drop south into northwestern portion of the County Warning Area this evening and
overnight. Winds veering to northerly by Friday morning may
support light snow showers past daybreak across LaPorte County
but lowering inversion should end any lake effect snow by midday.
Weak lake induced instability... fairly low inversion heights... and
limited moisture in the dgz through the event suggests little
potential for accumulate. Moisture depth expected to increase a bit as
trough moves through area so kept ptype just snow. Otrws cloud deck
trapped beneath inversion remains rather widespread across the southern
Great Lakes/Midwest this afternoon and with weak flow as surface ridge builds into
our area tonight and Friday... expect mostly cloudy skies to
persist. Appears best chance for some sunshine Friday is across southern
Michigan zones as drier air filters southward from the upper Great Lakes. Given
expected persistent low cloud deck... leaned toward smaller
diurnal range guidance with lows tonight in the l-m20s and highs
Friday in the l-m30s.


Long term...(friday night through thursday)
issued at 314 PM EST Thursday Dec 18 2014

Focus of the long term remains on potential storm next week with
little sensible weather concerns through the weekend given
persistent high pressure over the region. Here is what we know:

200 knots Pacific jet streak...currently still on the other side of the
international date line...will eventually work its way into the
central Continental U.S. And carve out a deep longwave trough. Digging trough
will become negatively tilted...and eventually closed
Christmas evening. Strong upper divergence on the nose of this
cyclonically curved jet streak will work in tandem with impressive
diffluence and midlevel cva to support a deep surface low somewhere
over the Great Lakes/northeast Continental U.S. Christmas evening into Christmas

What we don't know is the exact track and evolution of this trough
and associated surface low(s). Model accuracy in these finer scale
details is very low beyond 3-4 days...largely due to the fact that
the relevant synoptic drivers are still over the data-sparse North
Pacific. Latest 12z nwp suite continues to offer an inconsistent
picture regarding the specific details of this event. That being can be useful to note the trends and the trend over the
past few cycles has generally been a warmer track for our County Warning Area and
later phasing. This would result in the bulk of precipitation falling as
rain in our area. Notably lacking with this event is a source of
very cold air upstream. Deepening low will certainly pull in some
below freezing temperatures eventually but this may take some time
and with a surface low track directly overhead or just to our
northwest...may arrive after the bulk of the precipitation/forcing has
exited. This is the solution championed by the latest 12z GFS and
similarly by the European model (ecmwf)...suggesting just some light snow showers and
perhaps some gusty winds on the 24th. Though it should also be noted
the latest GFS and European model (ecmwf) now bring a secondary low through the
region on Friday the 26th with a better chance of accumulating

Bottomline...there will be a strong storm somewhere over the region
during the middle to end of next week but important details
regarding timing...precipitation types...and amounts in our local area
remain unclear. To echo the sentiments of the previous
forecaster...restraint should be exercised in forecasting exact snow
amounts and with placing much value in any one particular model
iteration. Suffice it to say...anyone with travel plans during this
time should stay tuned to the latest forecast and be prepared for
hazardous weather conditions.


Aviation...(for the 06z tafs through 06z Friday night)
issued at 1220 am EST Friday Dec 19 2014

Weak surface trough now across far Southern Lower Michigan will drop into
northern in this morning. This feature and some lake enhancement
will likely bring a few snow showers and potentially patchy
freezing drizzle to mainly ksbn early this morning. Mainly
dry/cloudy thereafter as trough becomes increasingly diffuse with
high pressure becoming better established. Otherwise...MVFR ceilings
expected to persist through much of the period (may see brief
improvement to low VFR toward midday/afternoon) given residual
moisture under lingering low level thermal inversion.


Iwx watches/warnings/advisories...


short term...jt
long term...agd

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