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Area forecast discussion 
National Weather Service northern Indiana
1238 am EST Tuesday Mar 3 2015

Synopsis...
issued at 253 PM EST Monday Mar 2 2015

Clouds will increase overnight...leading to a return of wintry
weather on Tuesday. Under cloudy skies tonight...temperatures drop
quickly before rising to near freezing Tuesday morning. A wintry
mix of precipitation will spread north late tonight and
Tuesday...starting as snow...changing to sleet and freezing rain
Tuesday morning. Most areas will see light rain by afternoon.

Lows tonight will be in the upper teens after midnight...rising
to near freezing by daybreak Tuesday. Highs Tuesday will be in the
lower 30s.

&&

Short term...(this evening through tuesday)
issued at 253 PM EST Monday Mar 2 2015

Complex and challenging forecast beginning overnight into Tuesday
morning. Models in general agreement on the track and depth of the
surface low driving into the Central Plains and northern Great
Lakes during the day Tuesday. Isentropic ascent over the Ohio
River valley will help build a pronounced warm layer by daybreak
Tuesday and this will allow light precipitation to form. There is
potential for freezing rain...mixed with sleet at the onset...with
models suggesting warm air to mix down by mid-day...ending the
frozen/freezing precipitation.

It is the interim period from daybreak through noon that is causing
the greatest difficulty. Insolation has increased dramatically over
the last few weeks and we are experiencing a lot of snowmelt this
afternoon. Not sure if the Road surface temperatures will be cold
enough to support significant accumulation of ice...but as we have
seen here...a light glaze of ice can be very dangerous.

The other concern is that some of the model soundings hint that the
surface temperatures...especially in the northeast may remain below
freezing. With enough uncertainty...have opted to cover the entire
warning area with a Winter Weather Advisory for the period of 11z to
18z on Tuesday. As we get closer to onset of the event...the
advisory will need to be adjusted to reflect the changing
environment.

On top of all that...as the rain falls on the Snow Field a favorable
boundary layer environment will be set up for fog formation. Winds
may be enough to keep the visibility from dropping too much...but
with the Snow Field and recent cold...expect to see at least some
advective fog formation as the precipitation falls.

&&

Long term...(tuesday night through monday)
issued at 253 PM EST Monday Mar 2 2015

Forecast period begins with cold front passage associated with
exiting system. Front expected to be entering the forecast area at
the start of the period and be south of the County Warning Area by 12z Wednesday. High
pressure center moves into the Dakotas and places our region in a
prolonged cold air advection pattern which will result in continued
falling temperatures Wednesday morning and little diurnal recovery in the
afternoon.

Cold air mass then continues to build into the region and will
have lows near zero both Thursday and Friday morning with highs
only in the teens Thursday. Light lake effect snow showers
expected in the northwest County Warning Area with fairly unidirectional west/northwest flow below
4kft inversion heights. Initial Arctic intrusion will be rather
shallow and surface based which should keep les light on
Wednesday.

Thermal trough then arrives Wednesday night and northwest winds gain a little
more of a northerly component which has potential to bring a
single band over the area...but winds begin to back to more
westerly flow during the day Thursday and increase shear below
inversion to disrupt banding and bring it to an end Thursday
afternoon/evening.

Quiet and warmer weather remainder of extended...surface high
pressure shifts off to the east bringing return flow to the
region. Upper trough axis also shifts east with 160m height rises in
its wake. Temperatures will warm from the 20s on Friday into the 30s for
the weekend. Weak systems will traverse the northern Great Lakes
region and bring small chances for precipitation primarily north of our
forecast area...so will continue with dry forecast in this time
period pending a stronger signal from models.

&&

Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1232 am EST Tuesday Mar 3 2015

Prior taf forecasts on track and continued trend with this
package. Slight adjustments made to precipitation timing based on latest
00z models and 03z hires models which continue to slow onset of
precipitation. This in large part due to very dry wedge in the lower levels
which will aid in evaporation of falling precipitation until deeper
moisture surge arrives around 12-15z. This dry wedge also under
deep layer of supercooled water. This suggest evap cooling
processes may also allow some of this water to freeze and fall as
sleet along with snow at onset. Moved up timing of sleet given
this possible scenario. Precipitation becomes freezing rain for a few hours middle
morning with warm air aloft. This deepens to near surface around
18-19z with surface temperatures just barely above freezing for just rain in
afternoon. Change back to light snow with cold front passage early
evening. A slight chance for fzdz this evening with drying aloft
but few models show some cloud seeding so will not introduce any
mention into tafs at this time given small probability.

&&

Iwx watches/warnings/advisories...
in...Winter Weather Advisory from 6 am EST /5 am CST/ this morning to
1 PM EST /noon CST/ this afternoon for inz003>009-012>018-
020-022>027-032>034.

Michigan...Winter Weather Advisory from 6 am this morning to 1 PM EST this
afternoon for miz077>081.

Ohio...Winter Weather Advisory from 6 am this morning to 1 PM EST this
afternoon for ohz001-002-004-005-015-016-024-025.

Lm...none.
&&

$$

Synopsis...Lewis
short term...Lewis
long term...Jal
aviation...Lashley



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