River Flood Warning 60, NWS Northern Indiana

Area Forecast Discussion
National Weather Service Northern Indiana
744 PM EDT Thu May 16 2019

.SYNOPSIS...
Issued at 730 PM EDT Thu May 16 2019

Scattered showers and perhaps an isolated thunderstorm will
continue to be a possibility through the early evening. A much
better chance for widespread storms will arrive late this evening
and overnight. Some of these storms may be severe with hail and
heavy rain the primary threats. Additional strong storms are then
possible again on Friday afternoon. Saturday appears warm and
primarily dry but additional storms are then expected on Sunday.

&&

.UPDATE...
Issued at 730 PM EDT Thu May 16 2019

An old mesoscale convective vortex originating from last night's
upper MS Valley convection allowed renewed MCS and even a few
supercells to form across northeast Illinois into central Indiana
earlier this afternoon. This MCS has rapidly shifted south across
southern Indiana early this evening. Northern Indiana/southern
Lower Michigan remain situated along a very strong west to east
instability gradient. A strengthening westerly low level jet
tonight will shift this instability axis across the region later
this evening. Next forcing mechanism to focus on will be sagging
low level frontal boundary later this evening into the overnight.
By the time this frontal forcing drops into the area, instability
should be slightly more elevated in nature. MUCAPES on the order
of 2000-2500 J/kg along with steepening mid level lapse rates
could yield isolated large hail potential, especially in the 03Z-
07Z timeframe. Better elevated CAPE should gradually sag south of
Route 30 later during the overnight with attention during later in
overnight hours possibly turning to some hydro concerns with a
potential of training cells. Best chance of heaviest rain fall may
be across central portions of forecast area roughly in vicinity
of Route 30 corridor where low level boundary may tend to stall
tonight, and where near term guidance indicates weakness in
Corfidi vectors for a time late evening/overnight. Thinking from
previous forecast still remains in intact with greatest severe
potential (mainly in form of hail) from about 03Z-07Z. Updated
forecast to be sent shortly with just minor tweaks to PoPs to
account for current convective evolution.

&&

.SHORT TERM...(This Evening through Tonight)
Issued at 115 PM EDT Thu May 16 2019

Hi-res models and 12Z NAM have struggled to initialize ongoing
convection which keeps a high level of complexity in downstream
evolution. However, a window for severe weather and heavy rain
exist this afternoon and overnight.

Stationary boundary that was stretched across the NW zones this
morning has slowly shifted just north of the area, but expanding
anvil blow-off has helped to combat significant warming. With the
muted heating, the cap presented in forecast soundings may hold
until break around 20Z for the far SW to closer to 00Z for the NW.
This afternoon into the early evening, forecast MLCAPE has been
forecast in the 2000-3000 J/kg range primarily along and west of
HWY 31 with lowering values as you go east. Curved hodographs
present a potential window this afternoon for discrete storms west
of HWY 31. One note is some of the morning CAMs were showing
potential for discrete storms after the MCS diminished. As is
evident on RADAR, the MCS has contracted in areal extent but is
persisting with a linear/bowing structure. Given the factors
listed above, severe storms are possible this afternoon primarily
west of HWY 31 this afternoon and early evening. These storms will
be capable of producing hail and damaging wind gusts. The
possibility of the brief tornado cannot be ruled out as low-level
helicity is in the 150-200 m^s/s^2.

As we move into the late evening into the overnight hours, the
front north of the area is expected to drop southwards back into
the area. Isentropic upglide will allow for storms to develop
along and just north of the front. There is disagreement on the
western extent of this convection mainly due to the possible
lingering effects of the MCS. Models show that MLCAPE will still
be in the 2000-2500 J/kg range at the onset before gradually
decreasing into the overnight hours. Isolated strong to severe
storms can't be ruled out, but the primary threat through the
overnight hours is likely heavy rain. MBE velocities drop into
the 5 to 10kt range after midnight and into the morning hours with
near parallel storm motions. PWATs continue to be forecast around
1.5" which is on the higher end of mid-May. This could easily
result in flooding issues as the ground is still fairly saturated,
and rivers continue to be at elevated heights. The location of
these higher precip amounts remains difficult to pinpoint given
the influences of the ongoing MCS and drastically different
frontal progressions between models.

&&

.LONG TERM...(Friday through Thursday)
Issued at 302 PM EDT Thu May 16 2019

Location of the undulating front continues to be a challenge for
the forecast Friday through Sunday. Convection will likely be
ongoing to start out Friday morning as the front should be
situated near Route 24. Embedded perturbations in the upper flow
should help to prolong convection along and north of the front
through the better part of the day. Primary concern is for locally
heavy rain as elevated instability is forecast to be meager.
Front Looks to push northwards across the area late Friday night
into Saturday to help clear convection, but models continue to
surge the front too far north given the cool lake surface.

There remains a chance for strong to severe storms on Sunday as a
vigorous Plains low lifts into the Midwest. Medium range models
have sped the system up slightly which would bring storms into the
area between 12Z and 15Z vs. the 15-18Z timing from the 00Z
models. Will have to see if a faster timing is an actual trend
with time as is would limit storm strength given a less favorable
timing.

Mostly dry conditions expected for the start of next week before
yet another lifting plains low moves in for mid-week.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
Issued at 730 PM EDT Thu May 16 2019

Lull in greater coverage of showers and thunderstorms to begin the
period across northern Indiana should give way to increasing
showers and storms after 03Z or 04Z into the overnight. Passage
of a short wave earlier today has kept better instability anchored
just to the west of the area this evening. A westerly low level
jet will advect moderate to strong elevated instability eastward
this evening. The combination of this increased elevated
instability and frontal boundary sagging into northern Indiana
should provide an uptick in showers and thunderstorms in the 03Z-
05Z period. Have maintained thunder mention at terminals in the
04Z-08Z timeframe with earlier timing at KSBN, and slightly later
timing at KFWA following the frontal forcing. It is possible
thunder mention may need to be extended a little later into the
early morning hours of Friday at KFWA depending on how things
evolve with frontal progression. MVFR cigs will be possible behind
this front late tonight into Tuesday, although have kept cigs at
or above 2k feet at this time.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

UPDATE...Marsili
SYNOPSIS...Marsili/CM
SHORT TERM...CM
LONG TERM...CM
AVIATION...Marsili

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