Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 kiwx 201052 
afdiwx

Area forecast discussion
National Weather Service northern Indiana
652 am EDT Thu Jul 20 2017

Synopsis...
issued at 415 am EDT Thu Jul 20 2017

There is a chance for thunderstorms from today through Sunday
before cooler and drier air arrives for next week. Severe weather
will remain possible with damaging winds and heavy rainfall as
the primary concerns. Meanwhile it will also be very hot and humid
through Saturday. Heat indices today could reach 100 to 105 for a
brief period in the afternoon if clouds dissipate. Actual high
temperatures today will generally be in the upper 80s to around 90
and lows tonight will be in the upper 60s to lower 70s.

&&

Short term...(today and tonight)
issued at 415 am EDT Thu Jul 20 2017

Complex forecast unfolding in the short term period with respect to
both convection and potential heat this afternoon. Initial mesoscale convective system that
moved in late last evening has left behind an impressive mesoscale convective vortex that
was rotating through the area early this morning. Bulk of associated
pcpn has ended but this feature did push a composite outflow south
of the local area. This complicates remainder of forecast given
expected upstream mesoscale convective system remnants which will approach near or after
12z.

Surface ts/tds have dropped into the upper 60s behind initial
outflow early this morning and not handled well by short term
consensus blends. Expecting light winds to recover through
daybreak coming back to southwest which will aid in recovering of
tds this morning. Upstream convection will be making a push
southeast from WI to northwest in this morning but likely weakening after
daybreak. Cams have struggled with first mesoscale convective system but have been rather
consistent on this next wave making it into northwest County Warning Area after 12z.
Latest 06z hrrr has a decent handle on ongoing convection and
basically followed this run for pops with some blending of
neighbors given uncertainty further south and East. Cape has been
scoured behind initial wave and with nocturnal cooling but deep
layer shear has increased with stronger winds aloft pushing in.
Overall severe threat looks low with this morning decaying mesoscale convective system but
locally heavy rainfall possible with precipitable waters near 2 inches and deep
warm layer.

Cloud cover and delayed recovering of tds should keep temps in the
upper 70s to low 80s through mid morning. Expecting a spike in both
once mesoscale convective system begins to fall apart and cloud cover thins by afternoon.
Highs will be very dependent on how fast cloud cover dissipates
but still looks like most areas will reach the upper 80s and
southwest could reach 90 with sun this afternoon and a quick
recovery. Dew points will be well into the 70s and heat indices
could reach 100f to 105f if the higher Max ts are reached. With
the uncertainty from cloud cover and pcpn and only a short window
for heat advisory criteria this afternoon, have held off on any
advisories but will defer to day shift for monitoring and possible
late morning issuance if needed. Will continue to highlight in
severe weather potential statement.

Another round of convection and possible severe weather cannot be
ruled out for later this afternoon and evening. Various model
solutions indicate another convectively enhanced short wave
possible with surface boundary bisecting the area. Best chances
look to be near or south of US 30 corridor anywhere from late
afternoon into mid evening but again dependent on recovery and
destabilization this afternoon along with upstream wave. Heavy
rainfall continues to be a concern with high moisture content and
isolated damaging winds will be the primary severe hazard.

&&

Long term...(friday through wednesday)
issued at 415 am EDT Thu Jul 20 2017

The general trend of models is to meander a surface boundary
across the local area through late Saturday before finally
pushing this feature south with relatively cooler and drier air
invading for late in the weekend and next week. The problems are
before that with how convection and severe chances will play out
along with heavy rainfall potential.

As has been the case this season yet another boundary will become
quasistationary over the region and numerous convectively enhanced
short waves will ride stronger flow aloft along this boundary.
Questions on exact location of this front and where stronger and
deeper convection will develop remain but models have maintained
some continuity with large scale features so inclined to stay close
to previous forecast and latest blends. Best chances still look to
be Friday night into Saturday morning across the north with a
strong wave and another good low level jet. High Theta east air looks
to be advected into the area over boundary with pwats around 2"
so it really is not a question of if it will develop but where.
Latest blends push northern half of area into likely pop category
and think this is reasonable given the rather persistent signals
with front hanging over the central or southern forecast area.
Damaging winds and heavy rainfall/flooding remain the primary
concerns with little change in synoptic conditions. Of course any
composite outflow boundaries or mcvs could throw a wrench in
entire forecast and will need to be monitored. Will keep a severe
mention in severe weather potential statement along with heavy rainfall and local flooding
potential given antecedent wet conditions. The high dew point air
will remain in place near and south of the large scale boundary
and temps will be dependent on this front and clouds as well. Very
muggy conditions expected but apparent temps will be difficult
given convective cloud debris. Mid to upper 80s likely with run
at 90 still possible Friday and Saturday for afternoon apparent
temps near 100f through this period.

Primary front to push south of area late Sat night or early Sunday
morning. Secondary front and mid level trough will bring a small
chance for thunderstorms Sunday afternoon with steepening lapse
rates. Cooler and drier air then expected next week with another
wave possible late.

&&

Aviation...(for the 12z tafs through 12z Friday morning)
issued at 646 am EDT Thu Jul 20 2017

More storms were racing southeast across northeast Illinois and should
reach Northwest Indiana/sbn terminal near the start of the taf
period. This activity should weaken later this morning before more
storms eventually redevelop later today. The timing of these
afternoon storms was still quite uncertain, so just placed a thunderstorms in the vicinity
in both terminals for now.



&&

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

$$

Synopsis...Lashley
short term...Lashley
long term...Lashley
aviation...skipper



Visit US at www.Weather.Gov/iwx

National Weather Service Glossary of Abbreviations