Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 251804

Area Forecast Discussion
National Weather Service Northern Indiana
204 PM EDT Tue Jul 25 2017

Issued at 409 AM EDT TUE Jul 25 2017

High pressure will provide another comfortable day with relatively
low humidity and high temperatures near 80. A brief warmup will
occur Wednesday prior to the arrival of a cold front. Highs will
reach the middle 80s with slightly higher humidity. Showers and
thunderstorms are likely late Wednesday night into Thursday. Some
storms could be severe along with heavy rainfall, especially over
north central Indiana. Drier and cooler conditions will return
Friday and continue into the weekend.


.SHORT TERM...(This Evening through Wednesday)
Issued at 201 PM EDT Tue Jul 25 2017

Sunny skies and low humidities across the area this afternoon as
latest surface analysis has high pressure extending from SW Quebec
down through the great lakes region. Upstream convective complex
over SE corner of MN struggling to make eastward progress as it
moves away from instability axis extending up through the northern
plains. Surface ridge will slide eastward through the period
bringing southerly return flow to the area on Wednesday. So after
another comfortable night with lows near 60...expect to see a
gradual increase in humidity Wednesday as dewpoints climb toward
70 by late in the day in SW CWA with highs warming into the mid


.LONG TERM...(Wednesday Night through Tuesday)
Issued at 201 PM EDT Tue Jul 25 2017

Water vapor imagery depicting 2 upper level systems of note
across Canada that will impact the forecast area early on in the
long term period. Closed low over Manitoba will continue eastward
across northern Ontario and into western Quebec by Wednesday
night. This will drag associated surface cold front toward the
area and provide the focus for a nocturnal MCS Wednesday night and
convective redevelopment along the front Thursday. Easterly track
of the lead upper low will have mid and upper level flow/forcing
becoming more detached to the north of our area with time...but
ensemble means still indicating around 30kts of effective shear as
frontal wave moving up from the mid MS valley will enhance low
level shear profiles. Severe potential will be limited by weak
instability as CAPEs struggle to reach 1000J/kg Wednesday night.
This environment would however be supportive of a heavy rain
threat as lack of instability will favor low centroid storms with
greater precip efficiency in a moisture rich environment as low
level moisture return ahead of approaching front will have PW
values exceeding 2 inches. Varying models solutions wrt timing of
frontal wave and subsequent frontal passage on Thursday. If slower
trend is realized...may see enough recovery in SE CWA to
destabilize ahead of the front in support of convective
redevelopment. Second short wave currently over Alberta will dig
SE into the great lakes region Thursday night into Friday which
will re-enforce cooler drier NW flow pattern as surface high
pressure builds into the area over the weekend. Low chances for
precip return toward the end of the forecast period as a weak
disturbance drops down in NW flow.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
Issued at 142 PM EDT Tue Jul 25 2017

High pressure over the region will slowly shift east overnight
causing winds to veer to a southerly component by Wednesday
morning. With a more southerly trajectory, expect moisture to
increase in the lower layers but do not think it will be enough
to justify mention of what should result in sporadic BR
development tonight.





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