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Area forecast discussion 
National Weather Service northern Indiana
951 PM EDT Monday Mar 30 2015

issued at 340 PM EDT Monday Mar 30 2015

Low pressure moving through the Great Lakes will spread light rain
to areas north of Highway 30 overnight with lows in the upper 30s
to lower 40s. Dry conditions will return tomorrow with highs
generally in the 50s.


issued at 942 PM EDT Monday Mar 30 2015

Evening update sent mainly to account for pop trends. Lead
isentropic lift(fgen)/low level thetae surge has been sufficient for
light rain across far northern Indiana this evening despite fairly
dry lowest 4k feet. NAM isentropic forecasts suggest rising cpds after
midnight in the wake of this leading isentropic lift/fgen
forcing...and have generally followed previous forecast idea of
decreasing probability of precipitation from southwest to northeast. Only other tweak was
to modify winds for a slightly southward adjusted low track based
on current trends...but otherwise no significant changes to
forecast elements.


Short term...(this evening through tuesday)
issued at 340 PM EDT Monday Mar 30 2015

Upper level jet streak will transition into the Great Lakes
tonight and send a strengthening midlevel vorticity maximum through the
region. Tight baroclinic zone is already in place over the Great
Lakes and this wave will incite a good 850mb frontogenetic
response...especially given reduced stability above this layer.
Track is not favorable for most of our County Warning Area though. Active frontal
zone will be draped across central Michigan and only clips our far
northeast counties. Still some disagreement among latest nwp with
respect to exact track and this will have a large effect on how
much of our County Warning Area sees precipitation given very sharp cutoff to forced
ascent. Kept overall spirit of previous forecast but did increase
probability of precipitation over our northeast half based on latest hi-res guidance.
Areas south of US-30 may remain completely dry. Forecast soundings
show lowest 2 kft is warm enough to support an entirely rain
event in areas that do see precipitation. Not impossible that our far
northeast could see a brief mix due to wet bulb effects but
chances and impacts are too low for inclusion in the forecast.
Rain should exit by tomorrow morning with drier air returning to
the region.

Lows tonight will probably stay on the warm side given increasing
southwest gradient with passing surface low. Nudged inherited
forecast up just a bit. Highs tomorrow will be slightly cooler than
today given brief return to north-northwest flow/caa. Decent mixing depths under
increasing sun will at least partially offset cold air advection though and highs
in our southwest could still reach the upper 50s.


Long term...(tuesday night through monday)
issued at 340 PM EDT Monday Mar 30 2015

Transition to a more Bona-fide Spring pattn expected this period west/longer
term suggestions of general weakening of negative height anomalies up across eastern
Canada and more troughing across the western US both of which have been
lagging for several months.

Beginning of period looks stellar west/sig ll thermal moderation ahead of
potent northern stream SW sweeping through southern Canada. Southwestward trailing frontal
boundary associated/west this system looks active Thursday afternoon timed west/northward reach of
ll Gomex moisture rtn and perhaps some risk for thunder. However will await
later guidance as frontal timing may be poor west/limited surface based
destabilization and extent of northward moistening.

Tail end of upper level disturbance ejects eastward Friday west/surface wave expected to
develop in vicinity of the Ohio River valley. Northward reach of potential overrunning
precipitation shield associated/west this system still quite uncertain and kept
west/subdued north-S pop gradient.

Unsettled pattn looks to increase through next week west/temperatures
moderating to at or above normal.


Aviation...(for the 00z tafs through 00z Tuesday evening)
issued at 805 PM EDT Monday Mar 30 2015

Westerly low level flow will increase this evening in advance of
a clipper system that will drop into the Great Lakes region. Low
level warm front pushing across Southern Lower Michigan/far
northern Indiana will continue to lead to some light rain at ksbn
over the next few hours. The chance of rain will decrease after
03z as low level front surges eastward. Will maintain dry
conditions at kfwa where low level dew point depressions are
expected to remain more substantial. Have also made no change to
previous low level wind shear mention due to aforementioned 50 knot westerly flow
at 2k feet preceding the clipper. A brief window may
exist...especially at ksbn...for higher end MVFR ceilings with passage
of surface wave Tuesday morning. Winds should back southwest in
advance of approaching surface wave this evening...and then veer
northwest for Tuesday behind this wave with speeds of 10 to 15 knots.


Iwx watches/warnings/advisories...


short term...agd
long term...T

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