IND issues Area Forecast Discussion (AFD) at Jul 24, 1:37 AM EDT466
FXUS63 KIND 240537
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
137 AM EDT Wed Jul 24 2024
.KEY MESSAGES...
- Isolated afternoon showers and a few storms are possible today
with better chances Wednesday PM
- Locally heavy rainfall will be the main threat from storms
- Wildfire smoke at times which may reduce visibility and air
quality
- Seasonable temperatures in the 80s through this weekend gradually
warming into early next week
&&
.FORECAST UPDATE...
Issued at 930 PM EDT Tue Jul 23 2024
Despite a lack of any significant focusing mechanism or shear,
isolated airmass convection continues to pop up across portions of
central Indiana, with somewhat of an axis apparent regionally along
and north of the I-70 corridor in a zone of very weak surface
convergence. This convection should not linger too much longer as
the boundary layer begins to stabilize, though have extended slight
chances through about midnight northwest, as an outflow boundary
from upstream convection over northern Illinois may impinge upon
that area in the next couple of hours and possibly spark a few more
showers and storms. As the night wears on, expect convection to die
out as low level stabilization continues.
Patchy fog may develop overnight in preferential areas, primarily in
the Wabash and White river valleys, and have added some fog to the
grids as a result. This should be a bit more limited than last night
and dense fog is not expected, though a few patches here and there
cannot be ruled out.
Dewpoints will remain fairly high as low level moisture continues to
pool along a stationary boundary to the south and the approaching
weak cold front to the north. Forecast lows generally in the mid 60s
continue to look good and only minor tweaks were made.
&&
.SHORT TERM (This evening through Wednesday)...
Issued at 258 PM EDT Tue Jul 23 2024
Latest IND ACARS soundings and SPC Mesoanalysis show a modestly
unstable air mass over central Indiana. This is also evident on
satellite, as diurnal cumulus have quickly developed upon reaching
our convective temperature (low to mid 80s). A few shallow rain
showers have developed, but these are far and few between. Soundings
and model data indicate that broad subsidence exists over the
region. This, combined with dry air aloft, will limit shower
development during the afternoon hours.
Overnight, we can expect any lingering cumulus to diminish after
sunset. Mainly clear skies along with light surface winds may lead
to some patchy fog by morning. The best chance of this is in our
typically fog-prone locations (along rivers, valleys, open fields,
corn fields).
A cold front is likely to trigger convection this evening over
southern Wisconsin or northern Illinois. Some CAMS have this
activity congealing into a cluster or broken line and propagating
southward towards Indiana. There is a low probability that this
activity reaches our northwestern counties early in the morning
hours. This will depend on the strength and orientation of the low-
level jet that is likely to develop overnight.
Aside from convection, increasing wildfire smoke may lead to reduced
air quality at times. High resolution smoke models indicate that a
plume of denser smoke may arrive Wednesday morning. While smoke
currently in the air is mainly aloft, models are showing a greater
component of near-surface smoke that may begin to reduce visibility
at times, especially north of Indianapolis.
CONVECTIVE POTENTIAL AND HAZARDS
Convection looks to redevelop Wednesday afternoon along the front,
where ever it ends up. There exists some spatial and temporal
uncertainty within guidance regarding the location of the front by
early afternoon. Despite this uncertainty, the front is most likely
to reside over the northern half of Indiana. Best timing for storm
development is after 16-18z or so.
Taking a deeper dive into Wednesday's convective potential, we see
some variability within CAM guidance. The bulk of this variability
arises from differences in cold front timing/location. CAMs seem to
be in good agreement that convection will fire up in the afternoon
and trek southeastward with time. Model soundings show steep low-
level lapse rates that become more modest with height. Despite the
meager mid-level lapse rates, MLCAPE values are quite decent (over
2000 J/Kg). Some mid-level dry air exists as well, leading to about
1000 J/Kg DCAPE. Hodographs show very little shear below 300mb, and
storms may behave more like single-cell/pulse storms or multicell
clusters. The strongest of these may promote a brief downburst or
hail threat.
&&
.LONG TERM (Wednesday night through Tuesday)...
Issued at 258 PM EDT Tue Jul 23 2024
The long term period will start off with chances for thunderstorms
as an upper low pushes off to the NE. Convection is expected to stay
below severe levels but a few cells could produce locally heavy rain
and brief gusty downbursts. The line of storms will be concentrated
to the southern half of the forecast area by midday Thursday,
finally exiting to the SE by the evening. Meanwhile, upper ridging
will be centered over the SW states, stretching towards the Great
Lakes through the weekend. At the surface, high pressure will settle
in behind the exiting system, allowing for dry weather over the
weekend and warming temperatures for the remainder of the long term.
Looking towards next week is a bit more uncertain as models are
showing a variety of solutions. There is a possibility that there
could be a stalled system and return southerly flow over the region
that could lead to a conveyor belt of scattered showers and
thunderstorms throughout early next week which could start as early
as Sunday. For now, keeping with the slight chance and chance PoPs
throughout the latter half of the period.
Temperatures will start out with low to mid 80s, warming to upper
80s for the rest of the period. The latter half of the period will
also see overnight lows near 70 degrees.
&&
.AVIATION (06Z TAF Issuance)...
Issued at 137 AM EDT Wed Jul 24 2024
Impacts
- Patchy fog possible this morning, mainly near HUF/LAF.
- Scattered showers and storms possible as a front sags into the
area after 18z. Brief MVFR restrictions possible.
- Potential for transient visibility reductions from smoke transport
into the region.
Discussion:
Predominantly VFR conditions through the period.
Winds will be light to occasionally calm before daybreak as a weak
surface pressure gradient exists. These light winds may promote some
patchy fog. Have carried 6SM at the outlying sites as a nod to this
potential. There is also a chance for lower visibility reductions
near HUF/LAF, but confidence is low.
A cold front will sag into the area later today, allowing winds to
become more west/northwesterly in nature with time, and increasing
shower/storm chances. Winds may become light and variable behind the
boundary after 00Z. Will carry VCSH during the PM hours as a
suggestion of this potential due to uncertainty in timing and impact
at any one point. Potential will exist for MVFR restrictions
wherever showers/storms develop.
Additionally, satellite obs and HRRR smoke progs suggest an increase
in transport of upstream wildfire smoke into the area. There will be
at least some potential for transient visibility reductions in smoke
or haze as a result of this, and will carry 6SM in HZ all sites
tomorrow.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Nield
SHORT TERM...Eckhoff
LONG TERM...KF
AVIATION...Melo
Source:
IND issues Area Forecast Discussion (AFD) at Jul 24, 1:37 AM EDT---------------
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