704
FXUS63 KIND 021658
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1258 PM EDT Thu May 2 2024

.KEY MESSAGES...

- Warm and more humid today and tonight with chances for showers and
  thunderstorms.

- Multiple chances for showers and storms throughout much of the
  forecast period, with continued above normal temperatures.

- Repeated rounds of rainfall may lead to redevelopment of
  river flooding.

&&

.MESOSCALE UPDATE...
Issued at 1257 PM EDT Thu May 2 2024

Latest surface observations show a warm front lifting northward
across Indiana. Here in Indianapolis, surface dew points rose from
49 to 65 quickly after frontal passage. Concurrently, temperatures
have risen into the lower 80s. Satellite imagery shows a cumulus
field developing from the front southward, with the greatest
concentration of cumulus developing over the more forested/elevated
parts of central Indiana. ACARS soundings out of IND corroborate
this, showing a substantial amount of low-level moistening and
erosion of a weak capping inversion.

However, this weak capping inversion remains as of 17z...located
around 850mb. It can be seen in the characterization of the cumulus
field, which is relatively flat at the moment. As the boundary layer
warms, it is expected that this cap gradually dissipates over the
next several hours. It`s at this point that we`ll begin to see the
threat for isolated showers and storms, since lapse rates are quite
a bit steeper above just above the cap.

Model hodographs show a lack of shear through the depth of the
column (some faster flow exists above the CAPE profile but storms
may not reach high enough to feel the effects). With modest dry air
in the soundings above 850mb it is possible that a few of the more
robust updrafts produce gusty winds upon their collapse.
Additionally, an isolated instance of hail is possible, but may be
limited in size due to poor storm top venting and modest updraft
strength.

There are a few factors that should act to limit convection this
afternoon. These include a lack of large-scale lift and advection of
slightly drier air around the backside of a surface high to our
east. As this process occurs, higher-res models tend to concentrate
available buoyancy along and just south of the warm front. As such,
any showers and storms would likely be nearer to this boundary
compared to places further south. Overall, convective coverage will
likely remain isolated and spread northward with time.

&&

.FORECAST UPDATE...
Issued at 1011 AM EDT Thu May 2 2024

No changes needed to the forecast this morning. Latest satellite
shows diminishing cloud cover, which will set us up for a very warm
day today. A northward moving warm front will lift across the region
through morning and into the afternoon. An isolated shower or storm
is possible, but probabilities remain low. We reduced the dew point
a bit with the anticipation that mixing will be rather deep today.
Expect near record highs in the mid to upper 80s.

&&

.SHORT TERM (This afternoon through Friday)...
Issued at 748 AM EDT Thu May 2 2024

Synopsis:

Surface analysis early this morning shows two high pressure systems,
one over the western Great Lakes, and a second over the Carolina`s.
A cusp like feature was found across Central Indiana between these
two highs, with light northeast winds in place mainly north of I-70,
and light to calm winds across southern Central Indiana. Dew points
on the north side of this cusp were dry, in the mid to upper 40s and
low 50s. Across southern Central Indiana dew points were in the
lower 60s.  Deep and strong low pressure was found over the TX/OK
panhandle and SW Kansas, along with a warm front that stretched
north toward NB and IA. Abundant convection was found near these
features. GOES16 shows mainly clear skies across Central Indiana. A
dying thunderstorm/shower was found over southern IL and was
drifting NW.

Today...

Models today show the low pressure system over the western plains
pushing northeast toward IA through the day. This will result in the
previously mentioned cusp like boundary to push to northern Indiana
by this afternoon and allow the warmer and more humid air mass found
across southern Indiana to return to Central Indiana.  Aloft,
ridging over the Appalachians is expected to strengthen, and this
enhancement will allow for the development of southwest flow aloft
into Central Indiana and weak broad lift.  Little in the way of
lower level forcing is available this afternoon, although our area
will be within the warm sector. Forecast soundings show attainable
convective temperatures this afternoon, with CAPE around 1400 J/KG
and pwats around 1.15 inches. A cap does not appear to be in place.
HRRR hints at some shower/storm development late this afternoon
which given the warm and humid air mass in place seems reasonable.
Will use a dry forecast until 18Z-20Z, there after include chance
pops for precipitation given the diurnal heating and favorable air
mass in place. Low confidence in specific timing and location.

Given the expected time in the warm and humid air mass today, highs
in the middle 80s appear on the mark.

Tonight...

Showers and storms will once again be possible tonight. Models
suggest that as the IA surface low continues to progress northeast
toward Ontario, an associated cold front will be dragged toward
Indiana late overnight. Aloft ahead of the front, southwest flow is
noted in place across Indiana and upper forcing appears present
within that flow amid a shallow associated upper trough. Best timing
appears to be from the late evening through the overnight hours.
Forecast soundings trend toward saturation overnight with pwats near
1.50. HRRR suggests scattered showers/isolated thunderstorms passing
across our forecast area overnight as these features pass. Thus
given the upper forcing and the favorable air mass in place,
confidence for precipitation tonight is high. After diurnal
convection from the afternoon and early evening wanes, this more
organized precipitation with upper forcing available will arrive.
Thus a few hours in mid evening with no pops appear possible between
these two types of forcing.

Overall, will use high pops, mainly focused overnight when then
upper forcing is expected to pass. Given the rain and the lack of
wind shift through the night, lows only in the middle 60s are
expected.

&&

.LONG TERM (Friday night through Wednesday)...
Issued at 748 AM EDT Thu May 2 2024

Friday and Friday Night...

Look for the extended to remain warm with unsettled weather as daily
rain/storm chances are in the forecast. Widespread convection will
likely be ongoing to start the period on Friday due to increasing
large scale ascent and moisture advection from an upper shortwave
traversing the region. Organized convection is unlikely because of
weak deep-layer shear, but sufficient instability should be in place
for isolated to scattered storms. Latest guidance shows the best
forcing for ascent will shift east late in the day leading to lower
POPs heading into the overnight hours.

Saturday through Sunday night...

Uncertainty increases over the weekend with no substantial synoptic
systems expected to impact central Indiana. While precipitation
chances persist, the best chance for precipitation appears to be
late Saturday as a weak cold front approaches. Most guidance suggest
this frontal boundary will struggle to make much progress before
stalling out over portions of the area. Abundant PBL moisture is
likely to remain in place for this reason which supports keeping at
least low POPs in the forecast through the weekend, especially
during the afternoon hours when diurnal heating allows for better
destabilization. POPs for Sunday may be lowered across the north in
future updates depending on how far the front is expected to
progress. Severe weather is unlikely due to weak deep-layer shear.

Monday onward...

Confidence in the forecast for this period remains relatively low
due to diverging model solutions. However, ensemble guidance
generally shows an unsettled weather pattern continuing with broad
troughing over much of the CONUS. There is a signal for increasing
instability/deep-layer shear which could lead to some severe weather
threat materializing, primarily Tuesday into the middle of next
week. CSU machine learning and CIPS analogs are both still
suggesting the potential for strong to severe storms. While there is
a signal, predictability is low this far out due to the large spread
between models. Expect confidence to improve over the weekend into
early next week once models become better aligned.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 618 AM EDT Thu May 2 2024

Impacts:

- VFR Conditions expected for much of the forecast period.

- Convection possible on Thursday afternoon and evening.

- MVFR/IFR conditions possible in any convection that strikes a TAF
site.

- Confidence for afternoon showers/storms is low.

- Confidence for overnight showers is high.

Discussion:

Isolated convection has once again redeveloped over southern IL, but
these features will fail to make progress toward the TAF sites this
morning. GOES16 shows mainly clear skies across Central Indiana.

Overall, little change has been made since the previous forecast.

The high pressure system will drift east of the TAF sites on
Thursday, allowing the return of a warmer and a more humid air mass
across Central Indiana. Winds will become southerly by the
afternoon. Forecast soundings by afternoon suggest attainable
convective temperatures with CAPE near 1500 J/KG. Thus VFR CU
development will be expected during the afternoon and evening and
TSRA should be possible. However confidence for specific timing and
locations is low. Thus a large window of VCTS will be used.

On Thursday Night, the HRRR suggests continued sct showers and
storms across the area, arriving from the middle Mississippi valley.
For now, have used VCSH to account for these passing showers with
lower VFR Cigs. These showers appear to have some upper support
associated with them as a cold front advances toward Indiana. Thus
confidence here for rain is higher.


&&

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

&&

$$

MESOSCALE...Eckhoff
UPDATE...Eckhoff
SHORT TERM...Puma
LONG TERM...Melo
AVIATION...Puma