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Area forecast discussion
National Weather Service northern Indiana
402 PM EDT Fri Sep 20 2019

Synopsis...
issued at 351 PM EDT Fri Sep 20 2019

The above normal temperatures will continue into the weekend.
Mainly dry conditions are expected tonight, although isolated
showers will be possible through early evening south of Route 30,
with another possibility of isolated showers across Northeast
Indiana and Northwest Ohio late tonight into Saturday. Otherwise,
a storm system will bring increasing chances of showers and
thunderstorms, especially Sunday afternoon and Sunday night.
Locally heavy rainfall will be possible across Northwest Indiana
into southwest lower Michigan. Low temperatures tonight will drop
into the mid 60s. High temperatures on Saturday will reach into
the mid 80s.

&&

Short term...(this evening through saturday)
issued at 351 PM EDT Fri Sep 20 2019

Challenging forecast in the short term with respect to low precip
chances.

While upper level ridging remains the dominant feature across the
region, small scale perturbations very slowly progressing through
this ridge along with weak surface based instability have allowed
for the development a few isolated showers from Northwest Indiana
into Northwest Ohio. This trend should continue for the remainder
of the afternoon hours with likely downward trend after sunset.
These showers are also developing along a low/mid level moisture
gradient that will slowly be progressing eastward tonight.

By later tonight, modest increases in low level southwest flow
will allow for eastward progression of aforementioned low/mid
level moisture boundary. Some signal in near term guidance that
above factors will be sufficient for additional isolated-scattered
shower development across Northeast Indiana/Northwest Ohio
generally south of Route 30. If these showers do develop, cannot
rule out an isolated storm, but will hold off on thunder inclusion
at this time with only weak instability expected.

On Saturday, isolated-scattered showers may be ongoing across
eastern portions of the area, but should gradually shift off to
the east during the afternoon as the stronger mid/level moisture
advection shifts east of the area. It still appears as though a
lull in deeper moisture profiles may occur locally during the day
Saturday between initial moisture gradient shifting east, and axis
of deeper pre-frontal moisture across the mid MS valley to the
western Great Lakes in advance of next system. This should provide
most locations with mainly dry conditions during the day, and have
kept just low chance pops from Northwest Indiana to SW lower Michigan.
Another warm day is in store Saturday with highs in the mid 80s.

&&

Long term...(saturday night through friday)
issued at 351 PM EDT Fri Sep 20 2019

By Sunday night, lead short wave will be lifting northeast across
the northern plains and eventually into western Ontario. This
will keep better moisture transport focused across northern
Illinois into Northwest Indiana/southwest lower Michigan. Subtle
veering of low level flow as this wave lifts northeast should
shift highly anomalous moisture axis eastward (1.75 to 2 inch
pwats). It does appear as though a lull in better forcing may set
up early Sunday as initial lead wave dampens and exits the region,
while next strong upper wave begins to emerge from central/northern
plains.

Forcing in the form of more favorable jet dynamics and stronger
frontal response is expected late Sunday afternoon into Sunday night
as this next wave approaches. Concern persists for some locally
heavy rainfall during this period given generally weak cape
profiles, warm cloud depths approaching 12k feet, and highly
anomalous pwats. Still expecting northwest locations to be favored
for the heaviest rainfall amounts of 1 to 2 inches, but ultimate
storm total will depend on how much rain the northwest receives in
association with initial lead wave later Saturday into early
Sunday. With dry antecedent conditions, still not expecting high impact
flood concerns at this point, but minor flooding will at least be
a possibility Sunday night.

The biggest item of uncertainty in this forecast continues to be
the exact timing of the heaviest precipitation, whether it will be
Sunday afternoon into the night, or holding off until Sunday
evening. Consensus guidance does seem to be creeping to slower
idea hinted at by the sref means the past few days and have
steered slightly toward that direction with this issuance. Will
need to watch Sunday afternoon for the potential of bands of
showers and storms forming across the area southeast of the main
forcing with some differential heating forcing a possibility in
this setup. Despite strengthening wind fields, severe setup still
looks meager with instability the main limiting factor.

Some showers may continue late Sunday night into early Monday as
stronger upper forcing moves across the area, but Monday will
feature transition to drier and cooler conditions.

Looking ahead, medium range models now in general agreement in
southern stream cut off remaining across baja of California region middle
of next week, with progressive northern stream giving additional
chances of showers midweek.

&&

Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 117 PM EDT Fri Sep 20 2019

Isolated showers across northeast Illinois/Northwest Indiana
earlier this morning have dissipated over the last few hours for
the most part. While northern Indiana will remain entrenched in
large scale synoptic upper ridging through this valid forecast
period, small scale disturbances moving through the ridge and the
slow eastward progression of a low and mid level moisture gradient
could give rise to some renewed isolated to scattered shower
development, particularly during the overnight hours across
Northeast Indiana. This activity may tend to increase after 06z as
modest low level jet develops and interacts with this moisture
gradient. Still not enough confidence to include shower mention at
terminals at this forecast distance however. Otherwise, mainly
VFR conditions expected with the only exception being the
possibility of a brief period of MVFR vsbys once again early
Saturday morning with patchy shallow fog.

&&

Iwx watches/warnings/advisories...
in...none.
Michigan...none.
Ohio...none.
Lm...none.
&&

$$

Synopsis...marsili
short term...marsili
long term...marsili
aviation...marsili



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