Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 182332

Area Forecast Discussion
National Weather Service Northern Indiana
732 PM EDT Tue Apr 18 2017

Issued at 724 PM EDT Tue Apr 18 2017

A cold front over the upper Midwest this evening will move into
northern Indiana by Wednesday morning. The front will become
stationary across our area Wednesday afternoon, then lift north
Wednesday night as low pressure moves northeast from the central
Plains. Scattered thunderstorms are expected to develop along this
frontal boundary Wednesday afternoon and night. As the low lifts
northeast across the upper Great Lakes Thursday, the accompanying
cold front will move across our area, likely causing
thunderstorms. Isolated severe storms are possible Wednesday and
Thursday, mainly in the afternoon and evening. Temperatures will
remain well above normal through Thursday, cooling off to a bit
below normal behind the cold front on Friday.


.SHORT TERM...(This Evening through Wednesday)
Issued at 154 PM EDT Tue Apr 18 2017

Forecast period to begin with the first in a series of
disturbances that will impact the region. Water vapor imagery
depicting well- defined short wave trof over central MN...models
are in good agreement with this feature shearing out in
predominately zonal flow as it moves into the northern great lakes
region tonight. Latest surface analysis has low pressure also
centered over central MN with cold front extending S/SW down
through the plains. As this feature tracks E/NE into eastern
Ontario by 12Z Wednesday cold front will take on a more E/W
orientation...diminishing low level mass convergence. Dry easterly
flow will veer tonight and become more southerly...but still
lacking in deep layer moisture return...the combination of these
factors will limit precip chances tonight as front approaches.
Frontal boundary stalls over the area Wednesday and will get a
modest increase in precip chances with time with increase in low
level moisture as thetae ridge nudges further east into our area
and airmass south of stalled front destabilizes with afternoon
heating with over 1500J/kg of CAPE. Marginal severe potential in a
weak flow/shear environment...primary threat would be hail in
elevated convection along/north of the front. With flow becoming
more southerly along with increase in clouds will have mild
temperatures tonight with lows 55-60. Mild again Wednesday as most
of the area will find itself south of stalled front...exception
may be NW CWA with possible lake shadow in W/NW flow behind front.


.LONG TERM...(Wednesday Night through Tuesday)
Issued at 154 PM EDT Tue Apr 18 2017

Frontal boundary will lift north of the area Wednesday night as
short wave energy will activate surface frontal wave in the
plains. Low pressure will then track NE into the great lakes
region Thursday and drag a cold front through the area. Latest
model guidance suggests timing of front may be favorable for
destabilizing eastern portion of CWA Thursday afternoon and with a
stronger and predominately unidirectional wind profile...a linear
convective mode along the cold front will have potential for some
strong storms with a marginal damaging wind threat. A much cooler
pattern taking shape for Friday into the weekend as weak surface
riding builds into the great lakes region. Also in play this
weekend will be a southern stream system that will move eastward
out of the southern plains into the Tennessee valley this
weekend...alot of uncertainty on the northern extent of precip
shield with this system but models seem to be trending a little
further south as latest blend has significantly lower POP`s from
previous run. Cool and dry weather to begin next week as southern
periphery of Canadian high pressure builds into the area.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday Evening)
Issued at 724 PM EDT Tue Apr 18 2017

Dry low level sely flow will veer sswly tonight as a cdfnt currently
located from nw WI to nw IA moves to a wrn MI-ne IL line by 12z. As
winds veer, moist low levels over the OH valley will advect north
across nrn IN overnight and Wed resulting in conditions at or near
mvfr. Front will become stnry Wed across nrn IN as a low pressure
system moves ne from the central Plains. Diurnal heating should
destabilize airmass sufficiently to allow sct tstms to develop in
the aftn. Given combination of expectation of small coverage of
TS and potential impacts confined to last 6hrs of the taf period,
held off adding tsra mention attm.





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