Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 251838

Area Forecast Discussion
National Weather Service Northern Indiana
238 PM EDT Tue Apr 25 2017

Issued at 404 AM EDT Tue Apr 25 2017

Expect a couple more days of dry and warm weather for the region.
As a frontal system approaches midweek, the chances for showers
and thunderstorms will increase, with the best chance Wednesday
night into Thursday. Highs this afternoon will be in the 70s and
in the upper 70s to lower 80s on Wednesday.


.SHORT TERM...(This Evening through Wednesday)
Issued at 234 PM EDT Tue Apr 25 2017

Quiet weather continues in the short term with continued warm and
dry. Surface ridge axis extending down from expansive Canadian
high will retreat northward in response to a pair of low pressure moving up along the eastern seaboard the other
developing/deepening in the plains. Plains cyclone will have
continued gradual veering of winds from SE to S and low levels
will respond with modest warm air advection...although thermal
ridge axis and associated mid-trop height rises will focus to the
east of our area. Despite more southerly flow...expect little
response in boundary layer moisture as dewpoints only gradually
respond up into the low to mid 50s. This will allow for
comfortable overnight lows of 55-60 followed by well above normal
on Wednesday with highs reaching near 80.


.LONG TERM...(Wednesday Night through Tuesday)
Issued at 234 PM EDT Tue Apr 25 2017

Strong upper jet dynamics coming onshore in the western US
represents the leading edge of an impressive trans-Pacific wave
train that will lead to a very active pattern in the long term.
Upper trof over the Rockies will amplify as jet dynamics impinge
on the backside. This will slow eastward progress of lead surface
wave and result in arrival of frontal boundary out of phase with
diurnal heating cycle and significantly limit instability. Still a
marginal severe threat late Wednesday night in the presence of a
strongly sheared profile with a 50kt LLJ and 80kt mid level speed
max. Slight backing of the surface wind ahead of the front is
indicating good turning in the 0-1km layer then primarily
unidirectional above. Front works thru the forecast area on
Thursday with similar limited severe potential in eastern CWA.
Break between systems Thursday night into Friday as weak surface
ridging builds in behind first system as frontal boundary stalls
out in E/W orientation down along TN valley. Next Pacific wave
slams more strong jet dynamics onshore in the west and re-
amplifies upper trof over the Rockies for the weekend system. From
here models offer a wide array of solns with respect to
timing/placement/intensity...with the unfortunate result of
blending these solns into an unrealistically long duration of
likely POPs for 4 forecast periods...and a total of 8+ consecutive
periods of precip chances. Will work to trim away at the
beginning and ending edges otherwise wait for future runs to
hopefully lead to a better consensus. Thru the haze of all those
precip chances lies a powerfully dynamic system that bears keeping
an eye on for severe and heavy rain potential toward the end of
the weekend as all models suggesting a well developed surface low
that will be supported by a closed negatively tilted upper
trof...a coupled upper jet...and low and mid level jets of 70 and
90kts respectively. Seasonable to above normal temps thru Sunday
then trending back toward near to slightly below normal beginning
of next week.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 100 PM EDT Tue Apr 25 2017

Prevailing SE flow and VFR conditions to continue through much of
this TAF cycle. Developing low pressure in the plains will veer
winds to more southerly direction nearing the end of the period and
daytime heating will mix down gusts to 25kts.





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