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Area forecast discussion
National Weather Service northern Indiana
410 am EDT Sat Sep 21 2019

issued at 1234 am EDT Sat Sep 21 2019

Above normal temperatures will remain the story this weekend in
advance of a cold front that will eventually bring increasing
chances for showers and thunderstorms from northwest to southeast
tonight through Sunday night. Highs today will reach the mid to
upper 80s, with highs ranging from the upper 70s in southwest
Michigan to the mid 80s along and east of Interstate 69 on Sunday.
Cooler and drier conditions will follow into early next week.


Short term...(today and tonight)
issued at 331 am EDT Sat Sep 21 2019

Increasing low level moisture has allowed patchy ground fog to
develop once again overnight. This fog is expected diminish
through sunrise as low level mixing increases.

There is a slight chance for a few showers this morning through
midday across eastern in and Northwest Ohio. These chances are in
response to weak perturbations in the upper flow and an 850mb
f-gen band lifting to the northeast with time. Forecast soundings
show some instability across the east during this time frame so
a few rumbles of thunder aren't out of the question. The f-gen
band is forecast to move northeast of the area by the early
afternoon which will allow chances to drop off as well across the

As the eastern precip chances drop this afternoon, precip chances
across far northwest in and SW lower Michigan will be on the rise. An
embedded shortwave trough axis and associated exit region of a
phasing upper jet moves across northern Illinois and Southern Lake
Michigan this afternoon and evening. Convection is expected to
develop in a SW to NE orientation across Illinois and lower Michigan
which will persist through the overnight hours. This convection
is expected to persist into the overnight hours. The far northwest zones
are likely the only areas to be impacted by convection through the
overnight hours. Pwats increasing to near 2" and potential for
storm training will keep the potential for locally heavy rainfall
possible for the far northwest.

High temperatures are expected to rise back into the mid-80s once
again this afternoon, but should be a few degrees lower than
yesterday given the anticipated increased cloud coverage.
Overnight lows will hold in the upper 60s.


Long term...(sunday through friday)
issued at 331 am EDT Sat Sep 21 2019

By Sunday morning the embedded shortwave mentioned above will be
well north of the area while the longwave trough axis over the
central US starts to lift northeastwards. The previous track of
the trough had a greater easterly component which helped to
spread precip chances much quicker on Sunday, but the new
northeasterly track will cause convection to struggle to expand
eastwards. It now appears the area wide pops will be delayed until
Sunday evening/night and be tied more with the passage of the
surface cold front. While this won't have a significant impact on
storm total amounts for northwest in and SW lower Michigan, amounts east
of Highway 31 will likely be reduced. Have started trending the
forecast in that direction, but amounts could come down further.
Highest storm total amounts of 1.5 to 2" remain possible for northwest in
and SW lower Michigan. Instability is still expected to be
severely limited however, heavy precip loading of the downdrafts
could result in isolated gusty winds along the cold front. The
front moves east of the County Warning Area just after the Monday morning commute.

Monday afternoon through Tuesday are anticipated to be dry with
cooler Post-frontal air filtering into the western Great Lakes.

Models have come into better agreement over the past 24 hours
with the evolution of the upper air pattern Wednesday through
Friday. A shortwave is forecast to dive southwards across the
southwestern US and become a closed low over Arizona by Wednesday
morning. Closer to home, a secondary trough within the westerlies
will sweep across the northern plains and upper Midwest. This
will bring another cold front into the area Wednesday afternoon.
Convection is anticipated to develop in advance of this front.
There is some timing differences in regards to the onset of
precip chances, but agreement exists with chances spreading area
wide Wednesday night into early Thursday morning as the front
advances eastwards. Dry conditions return by midday Thursday.


Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1234 am EDT Sat Sep 21 2019

A stray shower will remain possible this morning into the early
afternoon at mainly kfwa as weak moisture advection sets up on
the leading edge of increasing low-mid level flow. However, point
chances and expected coverage remain too low for a vcsh/rain showers
mention in the tafs at this time. Mainly VFR and dry with light
winds otherwise this morning, though there does remain some slight
concern for shallow br/fog formation toward daybreak.

Southerly winds will increase later this morning and afternoon,
especially at ksbn where winds may gust in excess of 20 knots. A
pre-frontal disturbance and eastward fold of deeper moisture may
allow for rain showers to survive into ksbn late afternoon and
evening, though confidence is low. Conditions should remain mainly
VFR otherwise this afternoon and evening.


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