200
FXUS63 KIND 171233 AAA
AFDIND

Area Forecast Discussion...UPDATED
National Weather Service Indianapolis IN
833 AM EDT Fri May 17 2024

.KEY MESSAGES...

- Dense fog across northwest portions of central Indiana
  diminishing this morning

- Scattered showers and storms will continue into the evening hours

- More fog possible tonight

- Very warm Sunday-Tuesday with highs in mid to upper 80s...before
increasing threat of strong/severe t-storms next Tuesday-Wednesday

&&

.FORECAST UPDATE...
Issued at 833 AM EDT Fri May 17 2024

Dense fog is ongoing across northwest portions of central Indiana
this morning, generally northeast of a Paris, IL to Rockville to
Delphi line. This should lessen over the next couple of hours.
Further southeast, some visibility reductions have been observed,
but to a lesser magnitude.

The northern delineation of rain is just south of I-70. There`s a
subtle shortwave perturbation that has enhanced rainfall coverage
and magnitude. MRMS QPE of locally one inch or more over the last
6 hours has resulted in some minor flooding across southern
portions of the area (re: ongoing flood advisories).

As the shortwave moves east, coverage and intensity of rain should
decrease. Despite cloud cover that will likely persist, even a small
amount of diabatic surface heating today will result in isolated to
scattered convective cells, given the moist low-level environment
and upstream positively tilted shortwave trough. Midlevel flow is
weak and so cell motion will be slow. Given recent rain, saturated
ground and low flash flood guidance values, isolated areas of
flooding will be possible today with slow-moving convective cells.

Aside from some needed refinements based on observational data, the
forecast is in good shape.

&&

.SHORT TERM (Today and tonight)...
Issued at 255 AM EDT Fri May 17 2024

Early this morning, showers with some embedded thunder were across
much of the southeastern half of the forecast area. Forcing for
these was coming from upper energy in a broad upper trough along
with some influence a couple of upper jet streaks.

Much of this forcing will gradually shift east during the predawn
hours, but some will linger across the south. By 12Z, will only have
likely PoPs across the far south with PoPs diminishing farther
northwest. Will continue to watch hi-res hourly guidance as some of
these hint at another band developing near the I-70 corridor, which
would warrant higher PoPs there at 12Z.

Will have to watch for any fog development, mainly northwest where
cloud cover will be thinnest.

Forcing during the day today will weaker. While the area will remain
in broad upper troughing, heights will be on the rise, and the jet
streaks will have less influence having moved east. At the surface,
no strong boundaries will be around. However, smaller boundaries,
some from previous convection, will linger. Moisture will continue
to be available, and even with clouds around, heating will add
instability.

Thus, expect scattered convection to continue throughout the day.
Will go chance PoPs most areas, with lower confidence on specific
timing and location of highest PoPs. Instability and shear won`t be
enough for a severe storm threat.

With some breaks in the clouds expected this afternoon, temperatures
will rebound into the middle and upper 70s.

Tonight...

Any lingering forcing will remain weak with not much change in the
synoptic setup. Will keep some lower PoPs around, mainly during the
evening when instability is highest. Similar to this afternoon,
instability/shear will be weak enough so that severe storms are not
expected.

Lingering low level moisture could lead to some fog overnight
tonight. Will add a mention to the forecast and continue to monitor.

Low temperatures will be around 60 degrees.

&&

.LONG TERM (Saturday through Thursday)...
Issued at 255 AM EDT Fri May 17 2024

Saturday through Monday Night...

The long term will start out with chances for scattered, mainly
light rain across central Indiana...from the northern portions of a
rather weak southern wave lifting from the Lower Mississippi Valley
to near Kentucky.  Around 500-1000 J/kg of CAPE and 0.90-1.20 inches
of precipitable water could promote a few t-storms with more
impressive rainfall rates, especially over southeastern counties,
yet appears lack of wind shear and next to no low-level
convergence...will lead to less than 0.25 inches of precipitation
for most locations.  Dry conditions should be the rule by pre-dawn
Sunday as rather weak yet broad surface high pressure builds in from
the Great Lakes to the Mid-Atlantic under an arriving upper ridge.

A late spring transitional-type pattern will then feature broad
troughiness across much of southern Canada, whose occasionally-
plunging short waves over western North America will likely direct
increasing heights into the Midwest.  There has not been the best
run-to-run model consistency with placement/tilt of both the overall
trough as well as embedded vorts, yet latest trends are for
disturbed weather to hang well to the north/west and the upper ridge
axis to build near Indiana.  Overall light northeasterly surface
winds from the passing, weak surface ridge will likely veer to
southerly breezes Monday ahead of strengthening surface low pressure
over the central Plains.  Moderation through the weekend will yield
an unseasonably warm and rather humid early week more indicative of
early summer, with mid to upper 80s likely Sunday and Monday.

Tuesday through Thursday...

The middle of next week should see an increasingly active mid-level
pattern with at least two vort maxs spinning around the overall
deepening western North America trough...before ejecting to the
Upper Midwest and/or Central Plains.  Surface cyclogenesis would
result along a strengthening cold frontal zone from the Upper
Mississippi Valley to the southern Plains...while the antecedent
surface ridge departs to the Atlantic coast.

Rain chances are expected to cross the region around the Tuesday-
Wednesday timeframe, although there is so far low confidence in when
the front, connecting what may be multiple areas of low pressure
from the various vort maxs, will actually pass the CWA.  Multiple
rounds of convection are certainly possible ahead of this eventual
passage...with ample instability fueled by dewpoints into the 60s,
as well as probably a third day in the 80s Tuesday...and what should
be increasing wind shear under the eastern extents of the trough
arriving from the west. Greater confidence for Thursday following
the cold frontal passage which would return dry conditions and drop
readings back closer to seasonal.  The normal max/min at
Indianapolis through the short term is 75/55.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 642 AM EDT Fri May 17 2024

Impacts:

- IFR/MVFR this morning and likely again late tonight.
- Scattered light rain showers much of the period. Isolated thunder.

Discussion:

IFR has expanded more than expected, and these conditions will be
around to start the period. Gradual improvement to MVFR and then VFR
will occur into early afternoon (VFR approximately 18Z). Additional
MVFR and worse conditions are likely late tonight, but will add
these with later issuances due to the already busy TAF.

Area of showers with embedded thunder will impact mainly KBMG early.
Additional scattered showers and isolated storms will pop up mainly
this afternoon and then diminish this evening.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...BRB
SHORT TERM...50
LONG TERM...AGM
AVIATION...50