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Area forecast discussion 
National Weather Service northern Indiana
415 PM EDT Friday Aug 28 2015

issued at 413 PM EDT Friday Aug 28 2015

Low pressure will move through the area this weekend...bringing
chances for showers and thunderstorms. By Monday...high pressure
moving into the region will bring above normal temperatures. Highs
today and Saturday will be in the upper 70s and 80s. Lows tonight
will be in the 60s.


Short term...(this evening through saturday)
issued at 413 PM EDT Friday Aug 28 2015

Low pressure system will bring rain to the area tonight and

Moderate to heavy precipitation observed over Iowa/southeast Minnesota/Wisconsin
this afternoon is associated with upper level divergence in the
right entrance region of a jet streak passing through the Great
Lakes. In the middle levels...there is a potent 500mb vorticity maximum/pv
anomaly and broad region of warm air advection/strong isentropic ascent.
Precipitation is mainly ahead of the warm front...with the surface
low over Iowa. This system will drift eastward through the short
term...and lead to precipitation chances over the County Warning Area tonight and

However...the 500mb vorticity maximum weakens and lifts northward into lower
Michigan tonight and Saturday as it encounters the high pressure ridge
anchored over the Atlantic...and forcing from the jet streak/upper
level divergence shifts northward. The area will be under weak warm air advection
tonight...with the warm front shifting northward into lower Michigan by
21z Sunday...but as forcing aloft dwindles best warm air advection dies off to the
northwest. Moisture is also limited...with precipitable waters around 1.2
inches/right around normal. With forcing moving north and dry air in
place earlier on...think the precipitation will be limited to the
far northwestern portions of the County Warning Area tonight. Kept a majority of the
County Warning Area dry for now with the exception of isolated showers near Lake
Michigan. Would not be surprised to see some patchy fog develop
later with increasing moisture and nearly calm winds expected.

Stronger moisture transport from the Gulf/Atlantic states develops
with south-southeast flow around the surface high to the southeast and
with the approaching surface low to the west. By Saturday afternoon
precipitable waters climb to 120-140 percent of normal and dewpoints rise into the
low to middle 60s. The surface cold front is forecast to move into Illinois/Northwest
Indiana towards late Sat afternoon evening...though forcing aloft by
this time is waning and the surface low/now over Lake Michigan/ is
weakening. Instability is decent in our area...and ranges from 1500-
2500 j/kg MUCAPE by late afternoon...depending on the model used. 0-
6 km shear is lacking however...only around 15-20 knots in the
afternoon. Thunderstorms are definitely possible...but unlikely to
be severe. Since models vary quite a bit in regards to exact
timing/placement of precipitation-and given weaker forcing/weakening
trend...have left high-end chance probability of precipitation for now on
Saturday...especially towards the afternoon. Kept thunderstorms
confined to the afternoon when instability is greatest.

Otherwise...high temperatures will range from the upper 70s to the
80s Saturday. Lows tonight will dip into the upper 50s and low 60s.

Long term...(saturday night through friday)
issued at 413 PM EDT Friday Aug 28 2015

At the beginning of the upper level short wave trough will
move across the lower Great Lakes region bringing a moderate chance
for precipitation Sat night into sun. The precipitation will end west to
east during the day. At the beginning of next week...heights will
increase as upper ridging builds into the region allowing for higher
humidity levels and warmer temperatures. Monday is expected to be dry
with passage of the upper level short wave. The effects from Erika
could be felt next week so have introduced low end probability of precipitation for
primarily afternoon hours Wednesday-Friday due with an expected return of
higher dewpoints during the week. Temperatures during the period will warm
from the upper 70/lower 80s sun to upper 80s by the end of the

Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 152 PM EDT Friday Aug 28 2015

A quiet evening in store for the forecast area before the next low
pressure system moves into the region. High clouds ahead of the
system have overspread both sites this afternoon...and will remain
through the taf period. Precipitation ahead of a low centered over
Iowa/WI will shift northeast of the area with better forcing tonight.
It is possible that ksbn sees a stray shower...but was not confident
enough to include in the taf.

Otherwise...a warm front will move in late tonight/Saturday
morning...but winds at the surface and aloft remain fairly light. Given
light winds and increasing moisture...there is potential for lower
visibilities at kfwa. Right now thinking this will play out similar
to this morning...with visibilities around 3-4 miles. Chances for
precipitation with this system are pretty low until after 18z
Saturday. Some guidance suggests a few showers with the warm front
near FWA/sbn earlier Saturday...but left out for now given low


Iwx watches/warnings/advisories...


Synopsis...mesoscale discussion
short term...mesoscale discussion
long term...Frazier
aviation...mesoscale discussion

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