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Area forecast discussion 
National Weather Service northern Indiana
555 am EDT sun Apr 19 2015

issued at 348 am EDT sun Apr 19 2015

A low pressure system approaching from the south will bring
widespread rain and a few embedded thunderstorms to the area late
this afternoon and into the evening. After a brief break late
tonight...another round of rain is expected on Monday. Rainfall
totals of up to an inch are possible. Highs today will be in the 60s
with lows tonight around 50 degrees.


Short term...(today and tonight)
issued at 348 am EDT sun Apr 19 2015

Morning water vapor shows southwest Continental U.S. Upper low finally
beginning to lift northeast and open as it is absorbed by digging
northern stream trough. Piecemeal ejection of pv anomaly will
bring two main batches of rainfall. The first will arrive this
afternoon with a secondary wave at the beginning of the long term
period. Pushed back and refined timing of precipitation onset this
afternoon based on latest guidance. Slow ejection of midlevel vorticity
maximum and exceptionally dry antecedent airmass (reference current
surface dewpoints over the area and 00z kdtx sounding) suggest
precipitation will probably not fully infiltrate our County Warning Area until late
afternoon. This idea is supported by nearly all of the latest hi-
res guidance which indicates precipitation not arriving in earnest until
around 20z. No doubt we will get a decent rain event by that time
though. Good cva/height falls will support deepening surface
cyclone directly overhead with a healthy slug of 295-300k
isentropic ascent. Most impressive aspect of this event is the
degree of moisture advection. Strong south-southwest subtropical jet will
allow northward expansion of pronounced Gulf moisture plume with
precipitable water values climbing to around 1.4 inches...near the 99th percentile
for this time of year. Heavier rain will not last particularly
long given orientation of forcing is orthogonal to the mean flow
but most locations should pick up around 0.5-0.75 inches. MUCAPE
is virtually nonexistent with moist adiabatic lapse rates
throughout the column. Contemplated pulling thunder mention
altogether but models suggest a few pockets of static instability
may be possible and an isolated embedded thunderstorm cant be
completely ruled out. Therefore held with inherited isolated
thunder mention. No severe threat.

Brief break in steady rain expected later tonight (after midnight)
as our area resides in between midlevel waves. Highs today may still
reach the middle to upper 60s given delayed arrival of low level
moisture plume and associated rainfall. Will still be ample
middle/upper level clouds during the early part of the day but did
adjust maximum temperatures up by a few degrees to be more in line with latest
consensus guidance. Lows tonight should hold around 50f under mostly
cloudy skies.


Long term...(monday through saturday)
issued at 348 am EDT sun Apr 19 2015

Sig scattered remains west/two pronged ejection of southern stream SW energy. Lead
SW will lift up through the southern lakes this afternoon while secondary
follows Monday am...inducing a likely vigorous frontal wave along southwestward
trailing cold front. However details associated/west this development differ
considerably both west/development along the cold front and midlvl deformation
evolution through the day. Broad consensus argues for bumping probability of precipitation
higher both Monday am and Monday afternoon.

Otrws this period and beyond will be dominated by deep northern stream cutoff
as it meanders slowly eastward from the northern lakes on Tuesday to southeast Canada/New
England Sat. Given County Warning Area remains positioned firmly within largely
subsident southwestern flank of upper trough axis again dropped allblend pop
Happy guidance in light of sig drying as modified polar air wraps
southward through the Ohio Valley. Sky forecasts at this range difficult to
ascertain however given the degree of ll cold air advection and building surface ridging
W/time...frost/freeze threat likely to be a major issue west/damage to
emerging fruit trees especially Thursday and Friday nights as ll thermal trough

After Monday...temperatures through the remainder of the period will be well below


Aviation...(for the 12z tafs through 12z Monday morning)
issued at 555 am EDT sun Apr 19 2015

Still expect VFR conditions to rapidly deteriorate later this
afternoon as midlevel shortwave...surface low pressure...and a strong
Theta-E surge move into the area. Latest hi-res models still show
precipitation beginning around 20z. IFR conditions are possible in the
00-06z timeframe but confidence is not high enough to include in
the taf at this juncture. There is also a slight chance of thunder
but probabilities are too low to mention in the taf. Marginal
improvement is possible after 06z as initial wave lifts northeast
but forecast soundings suggest at least high end MVFR will
continue through the overnight.


Iwx watches/warnings/advisories...


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

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