IND issues Area Forecast Discussion (AFD) at Aug 5, 5:52 AM EDT276
FXUS63 KIND 050952
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
552 AM EDT Mon Aug 5 2024
.KEY MESSAGES...
- Isolated thunderstorms across northern portions of central Indiana
this afternoon and evening
- Mostly sunny and hot today
- Chance of thunderstorms Tuesday and Tuesday Night; severe storms
possible
- Not as hot and less humid Wednesday through next weekend
&&
.SHORT TERM (Today and tonight)...
Issued at 303 AM EDT Mon Aug 5 2024
A subtle low-amplitude midlevel perturbation is seen in water vapor
channel imagery over the Dakotas early this morning. This is modeled
to move east-southeastward toward Indiana today and provide a very
small amount of ascent. This, coupled with surface convergence along
a weak front that will be nudged into northern portions of the area
late in the day, and a moist PBL, will result in isolated
convection. Forcing is better than yesterday which saw roughly ~10%
coverage across the same area, so we think ~20% coverage seems
reasonable from late afternoon through early evening.
There are some questions on the position of the surface convergence.
A few CAMs are too aggressive with upstream convection that augments
the boundary somewhat (i.e., the 3-km NAMnest). The most likely
scenario appears to be isolated single cells will develop by late
afternoon or early evening near or just north of Lafayette and
Kokomo, and move east-southeast at around 20 mph. The surface
boundary and convection will be south of stronger westerlies aloft,
and thus shear values will be quiet weak. Convection should be
weakly organized at best and the potential for severe storms is low,
though given the degree of instability and theta-e differential, a
strong/severe wind episode cannot be ruled out. Warm cloud depth
will support heavy rain although cell coverage and motion should
limit this threat.
Most locations across central Indiana will peak in the "high"
category for wet bulb globe temperatures, given light winds and
strong radiative component. Heat index values are expected to be
around 100F at most locations.
The MSLP pattern and PBL moisture characteristics will be similar to
the last few nights tonight, so patchy fog is once again expected.
Limiting factors may be convective debris clouds in some areas
tempering radiative cooling. Most locations will see a repeat of the
previous few nights, however.
&&
.LONG TERM (Tuesday through Sunday)...
Issued at 303 AM EDT Mon Aug 5 2024
Generally quiet weather expected through the long range with the
exception of Tuesday/Tuesday night. Ridging out west with troughing
over the east coast will place Indiana under northwesterly flow
aloft. A potent wave embedded in the flow is expected to drop
southward Tuesday afternoon. Enough instability is present for
convection, but the bulk of the synoptic-scale forcing will pass to
the northeast of the Indy metro area. Guidance has trended a bit
towards the idea of at least scattered convection across most of the
area. We will include the highest PoPs across our northern and
northeastern counties, closest to the forcing.
Regarding severe weather potential, model soundings show deep CAPE
profiles along with strong effective shear (over 45kt). Lapse rates
are at least modestly steep (6.5-7.0 C/Km), but very dry air is
found above 700mb. Given rather weak synoptic-scale forcing,
updrafts may have a difficult time with dry-air entrainment across
the southwestern portions of the CWA. Given the amount of dry air,
large DCAPE (over 1500 J/Kg) may lead to strong downbursts/wind
gusts at times. Additionally, an isolated large hail threat may
occur within the strongest updrafts given steep lapse rates and high
ELs...especially in any supercells/transient mesocyclones. Given
broadly curved hodographs...cannot rule out tornadoes, but at least
within the various CAMS, convection tends to be north of a rapidly
southward propagating boundary/cold front. This in turn may limit
the favorability of the near-surface environment.
After that boundary/cold front passes through, a return to near-
normal to below-normal temperatures is expected. Broad troughing
with generally northerly flow then looks to persist through the
remainder of the period. Continued near to below normal temperatures
are favored, along with dry conditions, through the coming weekend.
&&
.AVIATION (12Z TAF Issuance)...
Issued at 552 AM EDT Mon Aug 5 2024
Impacts:
- Patchy fog possible again tonight
Discussion:
The pattern remain similar. MSLP gradient may favor winds staying up
for at least part of the night. One difference may be convective
outflow and/or cloud debris that might slightly alter the air mass
at northern TAF sites making visibility reductions a little more in
question. Patchy fog is possible at/near TAF sites, but probability
of sub-VFR visibility is low.
Otherwise VFR conditions are expected to prevail with a light
southwesterly wind.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...BRB
LONG TERM...Eckhoff
AVIATION...BRB
Source:
IND issues Area Forecast Discussion (AFD) at Aug 5, 5:52 AM EDT---------------
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