653
FXUS63 KIWX 191021
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
621 AM EDT Sun May 19 2024

.KEY MESSAGES...

- Warm temperatures in the 80s through Tuesday. 70 degree
  temperatures take over for the late week.

- Chance of storms for Monday and Monday night. Widespread
  severe weather is not expected, but an isolated storm may have
  a hail threat.

- Strong to possibly severe thunderstorms still appear possible
  late Tuesday night and possibly again on Wednesday. Both of
  these periods are marked by low confidence in severe weather.

- Lull in precip chances for Thursday, but additional chances
  of showers and thunderstorms Friday into next weekend.

&&

.DISCUSSION...
Issued at 400 AM EDT Sun May 19 2024

A strong upper vort max lifting across northern Great
Lakes/southwest Ontario will continue to allow a weak surface trough
to settle across the southern Great Lakes region this afternoon. As
this trough becomes more divorced from stronger forcing aloft, it
will slow down across the local area today and may serve as a
focus for isolated-scattered afternoon showers and
thunderstorms. A modest low level moisture axis is shifting
across the local area this morning, and will settle across the
Ohio River Valley this afternoon. Near term guidance is
indicating some differences in mixing depths and low level
moisture magnitude this afternoon which will have a large effect
on convective temperatures. Have largely kept idea from
previous forecast intact with a band of 20-30 PoPs along
expected position of this weak sfc trough this afternoon.
Steering flow will continue to be weak today with flow up to 500
mb of less than 20 knots. Any isolated stronger showers or
storms could produce a highly localized heavier rain amount
along with a few sub-severe wind gusts of 30+ mph given large
low level dew point depressions and steep low level lapse rates.
Depending on actual instability magnitudes this afternoon and
some potential outflow interactions, isolated showers could
persist into this evening before diminishing late evening/early
overnight hours. The much above normal temperatures will
continue today as some weak low level warm advection
accompanying the aforementioned sfc trough axis should add a
degree or two on from yesterday`s highs with possible exception
for areas receiving any isolated/scattered showers and storms
this afternoon and better convective cloud cover.

For Monday into early Tuesday morning, attention will turn to an
upper level short wave expected to emanate from Central Plains
convection today. Predictability in exact strength and track of this
short wave is on the low side, given upstream convective evolution
today will go a long way in modulating this disturbance. A zone of
stronger southerlies downstream of this disturbance will allow
better low level moisture transport to shift across Mid MS Rvr
Valley midday Monday and likely into the western Great Lakes/Lower
Michigan by Monday night. Some steeper mid level lapse rates should
also advect into the region Monday/Monday night preceding this wave.
Have maintained some broadbrush chance PoPs particularly across
western/northern portions of the forecast area given expected track
of convectively enhanced vort max. While shear profiles should not
be supportive of highly organized convection, cannot rule out
potential of some hail Monday afternoon into early Tuesday
morning with any stronger showers and thunderstorms. Very warm
conditions will continue Monday and Tuesday, with better low
level mixing also aiding in realizing high temps into the mid
80s to locally 90.

The later Tuesday period is still likely the main time period of
concern for this forecast as stronger upper level wave ejects
northeast out of Baja of California region and acquires slight
negative tilt across the Upper Midwest by Tuesday evening. The
GFS remains a fast outlier compared to bulk of other guidance
and a little more aggressive in dampening Great Lakes upper
ridging. This could allow band of showers and thunderstorms to
reach far western areas by late evening Tuesday with a severe
potential. However, guidance consensus is to maintain stronger
initial upper ridging across the Great Lakes with a more delayed
arrival of pre-frontal forcing. This would result in a likely
decaying line of storms progressing across western areas late
Tuesday night. The challenge in this scenario will be similar to
Monday`s system in that the evolution of Central Plains into
Upper Midwest convection late Monday night into early Tuesday
will impact mid/upper height structure. Will still support
consensus solution in greater severe potential impacting areas
across Mid Ms Rvr Valley late Tuesday afternoon into Tuesday
evening, with some low-confidence risk of severe storms possibly
affecting far western areas overnight Tuesday into early
Wednesday morning. Have also continued trend in lowering PoPs
late Tuesday afternoon/early Tuesday evening as a cap may
temporarily affect the area until late night.

Secondary upper wave digging across central CONUS will allow cold
front to progress across the area on Wednesday, but how this
secondary wave phases or not phases with initial upper PV anomaly
should dictate frontal progression. It does appear the synoptic
setup should favor a more veered low level flow by Wednesday.
Instability remains somewhat of a wildcard on Wednesday, but some
fairly steep mid level lapse rates should yield some moderate
afternoon instability across the southeast depending on low level
temp/dew point trends. Depending on how things play out, some
hail/wind threat could accompany storms with cold frontal
progression Wednesday, but this is a highly conditional and low
confidence scenario at this time.

Cooler conditions settle in for late work week, with a lull in
precip chances expected Thursday into early Friday.  Predictability
with large scale pattern is somewhat low for Friday into early next
week, but some signal exists for another fropa some time next
weekend with additional precip chances.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 619 AM EDT Sun May 19 2024

VFR conditions are expected to persist through the afternoon.
The only change made to the TAFs was to slightly adjust wind
direction/speeds. A weak cold front will move through the area
this evening after 21Z and may spark a few isolated showers. Chances
for impacts are too low to mention in the TAF. A mention of a
shower or storm may be needed at KFWA in later TAF forecasts,
should confidence increase.


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Marsili
AVIATION...Johnson