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Area forecast discussion 
National Weather Service northern Indiana
710 am EST Thursday Jan 29 2015

issued at 421 am EST Thursday Jan 29 2015

A series of upper level disturbances will track across the region
today. After a period of light freezing rain this morning across
Southern Lower Michigan...Northeast Indiana...and Northwest
Ohio...a mix of light rain and light snow is then expected this
afternoon with little or no snow accumulation. Colder air will
filter into the region later this afternoon into tonight behind a
frontal boundary. This will provide the potential of light snow
accumulations with lake effect snow showers tonight into early Friday.
High temperatures this afternoon will range from the middle 30s to
around 40. Low temperatures tonight will range from the middle teens
to lower 20s.


Short term...(today and tonight)
issued at 421 am EST Thursday Jan 29 2015

Forecast concern for the short term will continue to center on
freezing rain chances this morning...followed by potential of
continued light precipitation through the day and lake effect snow

Primary forcing mechanism through much of the overnight hours has
been a relatively narrow zone of moderate to strong low/middle level
moisture convergence. This axis is shifting across extreme
Northeast Indiana and south central lower Michigan as of 09z. A
light glaze of ice accumulation was received at weather forecast office iwx this morning
with this axis of precipitation. Currently expecting the biggest concerns
will persist across extreme Northeast Indiana...far Northwest
Ohio...and south central lower Michigan this morning where near surface
warm advection is weaker...and not able to fully offset evaporative
cooling effects. Up to 0.05 inches of ice accumulation is possible
across especially northeast portions of the Freezing Rain Advisory
area. Aforementioned axis of low/middle level moisture convergence
should be fairly progressive through Northwest Ohio through 14z
which should mark an end to any additional ice accumulation. Only
wildcard for this forecast is the potential of upstream pv anomaly
across middle MS River Valley to impinge on this axis of stronger
moisture convergence forcing across Northwest Ohio...which could
yield an increase in precipitation coverage/intensity...especially
considering the approach of a plume of very steep middle level lapse
rates. For this reason...have continued to hold the eastern Freezing
Rain Advisory segment in effect until 10 am EST...although will
likely be able to clear at least Northeast Indiana counties over the
next few hours. Did remove a St. Joseph Indiana/Wells/Adams County
from the advisory with surface temperatures having risen above freezing.

For the remainder of the day...guidance still suggests potential of
precipitation redeveloping in weak deformation/fgen axis across northwest
portions of the area later this morning...and shifting across the
remainder of the area this afternoon. It does appear as through
local area may be situated between the more pronounced middle/upper
level waves through most of the afternoon...lending to some question
as to extent of measurable precipitation in this weak deformation axis.
Have made some slight downward adjustments to probability of precipitation but have kept
general idea of previous forecast intact. Thermal profiles should
support mainly liquid from middle to late morning across most of the
forecast area...with possible exception across the far
north/northwest where some light snow/sleet may mix in. Surface low
pressure reaching far Southern Lake Huron this afternoon will allow
for onset of more significant cold advection across especially
western/northern locations where a brief period of mainly light snow
is possible on western periphery of light deformation precipitation.
Marginal Thermo profiles/low level wet bulbs suggest little or no
snow accumulation however. Pressure rise bubble working across
southern Iowa is expected to enter the area this afternoon...which
should yield some west northwest gusts to 20 to 30 miles per hour accompanying
the low level cold air advection.

For tonight...lake effect/enhanced snow showers should develop early
this evening as weak synoptic upper wave tracks across the southern
Great Lakes. A more vigorous wave dropping out of south central
Canada will bring more pronounced low level cold air advection and increasing lake
effect chances during the overnight hours. Relatively dry middle levels
and shallow instability profiles continue to suggest minor snow
accums of an inch or two possible for northwest fetch lake effect


Long term...(friday through wednesday)
issued at 421 am EST Thursday Jan 29 2015

Lake effect snow will gradually wind down during the day Friday.
Increasing subsidence/lowering inversion...backing winds...and dry
air entrainment will take an increasing toll on lake induced
convection. Accumulating snow will probably end by midday with just
some residual flurries possible across Berrien and Cass counties
during the afternoon as low level winds back to a more westerly
direction. High temperatures will be on the cool side with thermal trough
still in place but nothing out of the Ordinary for late January.
Expect highs generally in the middle 20s. West/SW low level flow develops
by Friday night and Saturday...advecting slightly warmer air into
the region ahead of next approaching trough. Raised highs a bit to
be more in line with latest MOS guidance. Should make a run at lower
30s in most locations after overnight lows in the middle to upper teens.

Attention then turns to potential snow on Sunday. As expected...
deterministic models have struggled immensely with the evolution of
this system. Run to run variability and intermodel disagreement has
been very high. This is not surprising given the event is predicated
on a rather complex interaction between multiple jet streaks and
shortwaves that have not even developed yet. GFS ensemble members
still show a high degree of spread and confidence remains very low.
00z operational GFS trended a bit further north but still keeps bulk
of the precipitation south of our County Warning Area. Latest Gem and NAM extrapolation
suggest a stronger and further north solution while the European model (ecmwf)
remains the most subdued. Will largely stay the course with this
forecast package. Still maintain a better than 50/50 shot of
measurable snow based on strength and placement of upper level jet
seen in all of the latest deterministic models...especially the
further south you go. Confidence in exact amounts and location
remain very low however. Stay tuned to the latest forecasts over the
next day or two as the solution space should gradually narrow.

Much colder air still expected early next week as 850mb temperatures drop
to around -20c. This should keep monday's highs in the teens with
lows Sunday and Monday night in the single digits. Brief warm up
seen on Tuesday in warm air advection regime ahead of another clipper system but
another...possibly colder...Arctic surge is possible for the middle
and end of next week. Very high amplitude ridge is shown to develop
over western noam with persistent troughing over eastern Canada
yielding very cold north/northwest flow for the Great Lakes.


Aviation...(for the 12z tafs through 12z Friday morning)
issued at 658 am EST Thursday Jan 29 2015

No substantial changes made from previous forecast for the 12z
tafs. Zone of low/middle level moisture convergence has now exited
into Northwest Ohio taking most of the freezing rain east of the
terminals. Light rain may redevelop later this morning as a fairly
strong upper vorticity maximum tracks into the area from northern Illinois.
Weak deformation zone should allow for rain/snow to develop early
this afternoon...eventually changing to primarily snow later this
afternoon as colder air advects southward. Surface low pressure will
work across Southern Lake Huron this afternoon which will drag a
frontal boundary eastward across the area. Ceilings are expected to
deteriorate by middle to late morning as low level reflection
approaches the area...with lower end MVFR or IFR ceilings persisting
through much of the Day. Lake effect snow showers will develop
tonight...with a period of IFR visibilities possible at ksbn late in the
period. Northwest winds will develop behind the front this
afternoon...with gusts to around 25 knots expected.


Iwx watches/warnings/advisories...
Michigan...Freezing Rain Advisory until 10 am EST this morning for miz081.

Ohio...Freezing Rain Advisory until 10 am EST this morning for ohz001-



short term...marsili
long term...agd

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