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Area forecast discussion 
National Weather Service northern Indiana
755 PM EDT Sat Apr 18 2015

issued at 755 PM EDT Sat Apr 18 2015

Clouds will gradually increase overnight as a frontal system
races northward from the lower Mississippi Valley and into
northern Indiana by Sunday afternoon. A more steady rain will
move in Sunday afternoon and continue into Sunday night. A few
isolated embedded thunderstorms are also possible Sunday
afternoon. Lows tonight will range from the middle 40s to lower 50s.
Sunday will mark the start of a cooling trend with highs in the


Short term...(this evening through sunday)
issued at 435 PM EDT Sat Apr 18 2015

Moisture has pooled along the southern third of the forecast area
and surface trough / frontal boundary has pushed out of
Michigan...evident on radar. Instability and convergence along
and south of this boundary has triggered isolated thunderstorms
south of US-30. Expect to see additional development as the
easterly flow and convergence increase over the next few hours.

Convection will end as the insolation decreases and should have a
quick decrease in coverage.

High pressure gradually retreating through Sunday morning.
Approaching system with abundant cirrus shield will continue to
overspread the region and with deepening easterly flow...boundary
layer moisture will be shifted south and west overnight...and
expect this to be slow to return to the northern two-thirds of
the area until Sunday morning.

Much cooler day Sunday as the clouds and precipitation overspread
the region.


Long term...(sunday night through saturday)
issued at 435 PM EDT Sat Apr 18 2015

A second system immediately following the ejecting southwestern
shortwave will move across the area early Monday. Followed a GFS
solution which has trended this system slower. This trend appears
reasonable with a deep digging upper trough and a 90 knot upper jet
on the back side of this system. Therefore...have adjusted the
timing of rain chances Sunday night and Monday. Isentropic 300k
surface supports the best rain chances Monday morning. A Little
Break in the showers is possible after midnight Sunday night.

After this system...much cooler air will move into the area for
the rest of the week as a cold core upper low becomes quasi
stationary near or just north of Lake Superior. Temperatures will
be below normal from Tuesday through the end of the week as much
colder and drier air spreads into the area. Continued to cut
superblend rain chances. Although very chilly air aloft with
allow impressive lapse rates of 9 to 10c/km from the surface to
750 mb...very dry air in the low levels with dew points in the
middle 20s to lower 30s will probably be too dry to support much
more than isolated showers. Expect highs during this period in
the low to middle 50s with lows in the low to middle 30s. Kept the
mention of frost out for now given uncertainty of the timing and
location of lingering clouds.


Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 755 PM EDT Sat Apr 18 2015

Sig changes/detail to latest tafs for northern Indiana. Ramped Erly
flow at kfwa with Lake Erie breeze passage likely to make inroads
into ksbn site next hour or so...before eastward push tied to diurnal
heating cycle slows/washes out. Other concern with respect to ramping 40kt
east-eserly flow overnight above stable near surface layer warranting low level wind shear
mention until greater mixing/veering of surface winds by middle morning.
Sig dlay in timing of rain shield for northern line with
latest ruc13/18 UTC NAM analysis. Advance of deep saturated
layer/Theta-E wall to likely support rapid downward spiral of ceilings
to at least fueling/alternate criteria...if not IFR/LIFR in
latter hours of valid timeframe.


Iwx watches/warnings/advisories...


Synopsis...mesoscale discussion
short term...Lewis
long term...skipper

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