119 
FXUS63 KIND 051545
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1145 AM EDT Tue Sep 5 2023

...Updated Aviation Discussion...

.Forecast Update...
Issued at 832 AM EDT Tue Sep 5 2023

Previous forecast remains valid. So, we only have a few minor points 
to add for this update. 

1. CIRA satellite layered moisture products show extensive mid-high 
level subtropical moisture, and this should increase rainfall 
efficiency with any convection that forms today. Brief heavy 
downpours may occur. 

2. Midlevel lapse rates aren't particularly steep and absence of dry 
air in the midlevels is resulting in fairly small theta-e difference 
in the vertical. Thus, intense/damaging downbursts are less likely. 

3. Midlevel moisture advection is driving initial weak convection 
across southern Illinois, but heating of moist PBL should result in 
isolated/scattered deeper convective cells across the area later 
this afternoon. 

Increase cu/stratocu field and midlevel deck may tend to hold 
temperatures down a couple of degrees compared to yesterday. Some 
locations could reach 90 but most will peak in the upper 80s.

&&

.Short Term...(Today and tonight)
Issued at 252 AM EDT Tue Sep 5 2023

Active weather expected today and tonight as two systems impact the 
area. First, and upper-level low currently located over Arkansas is 
accelerating northward. Second, a trough located over the Dakotas 
will swing eastward today gradually phasing with the aforementioned 
upper-low. The two systems will combine roughly over Indiana leading 
to a few rounds of showers and thunderstorms.

The first round of showers will occur this afternoon as the upper-
level low swings northward and weakens. Forcing is weak, as little 
in the way of flow exists aloft and only meager vorticity advection 
is shown by the models. Nevertheless, plenty of moisture exists in 
the lower atmosphere...and even meager forcing should be enough. 
Model soundings show decent CAPE (up to 2000 J/kg MLCAPE), high 
moisture content through the column (PWATs over 1.70" which is 90th 
percentile for this time of year), and next to no shear (10kts 0-
6km). Given little in the way of shear, pulse storms are the most 
likely storm mode today. Coverage will be isolated to scattered in 
nature, and cell lifespan should be short. The primary convective 
hazard is brief downbursts containing gusty winds.

The second round of showers and storms occurs late tonight into 
Wednesday. The trough and its associated cold front is the primary 
forcing mechanism this time around. Model soundings show modest 
lapse rates, deep CAPE (~2000 J/Kg MLCAPE to 10km agl), and a bit 
more shear (20-25kts 0-6km). Mid-levels appear a bit drier 
compared to the first round of showers/storms. Primary convective 
mode appears to be multicell clusters or line segments (focused 
along the front). Primary convective hazard is strong to severe 
wind gusts given the deep CAPE and dry mid-levels. An isolated 
instance of large hail is not out of the question but this appears
unlikely.

Temperatures today should be a bit cooler than yesterday as cloud 
cover thickens and limits solar insolation. Nevertheless, highs in 
the mid to upper 80s are still likely. High dew points should lead 
to a rather high heat indices for September, but these should remain 
below advisory level. Heat indices between 95 to 100 are possible. 
Temps are not expected to drop quickly after sunset, given thick 
cloud cover and ample low-level moisture. Lows in the low 70s are 
likely.

&&

.Long Term...(Wednesday through Monday)
Issued at 252 AM EDT Tue Sep 5 2023

Wednesday through Thursday.

An upper trough will pivot east across the upper Midwest and Lake 
Superior on Wednesday pushing an associated cold front southeast 
across central Indiana late Wednesday and Wednesday night. The cold 
front will interact with a broad ribbon of weak to moderate 
instability and deep moisture to produce scattered to numerous 
thunderstorms on Wednesday. Modest deep shear of 20-25 knots and 
uncertainty involving the evolution of overnight convection support 
nothing more than the SPC DAY2 Marginal Risk for severe storms. If 
the overnight convection dies off early enough, the atmosphere 
should have time to retool to the tune of moderate instability as 
opposed to weak, and potential present more of a threat for strong 
to severe storms. The lack of shear supports more of a downburst 
threat with any line or cluster. Temperatures will also be highly 
dependent on how long the morning convection/debris hangs around but 
with the cold front to the west, stuck with the seasonable or higher 
highs, mostly in the mid 80s. 

Thursday night Through Tuesday.

Upper troughing will be slow to exit the Ohio Valley late this week, 
which will keep some clouds around, but with the cold front well to 
the southeast and broad surface high pressure settling in, look for 
dry, cool and less humid weather this weekend with afternoon highs 
only in the 70s, except for perhaps lower 80s at times in the 
Vincennes and Loogootee areas. The nighttime will be refreshing as 
well with lows mostly in the 50s. Showery weather looks like it will 
return around Tuesday as although they have spatial and temporal 
differences, models and ensembles suggest a Canadian trough will 
pivot down across the upper Midwest and Great Lakes.

&&

.Aviation...(18Z TAF Issuance)
Issued at 1145 AM EDT Tue Sep 5 2023

Impacts:

* Mainly VFR conditions, brief MVFR possible early morning

* Scattered showers and isolated storms this afternoon

* Some wind gusts to 20kts possible this afternoon and again 
  Wednesday afternoon

Discussion: 

Timing of showers and storms is somewhat uncertain and may require 
amendments. It appears the probability of thunder is low to moderate 
peaking this afternoon and again tomorrow afternoon. Near the core 
of the midlevel low, thunderstorms are ongoing in southern Illinois 
at these should move northeast toward KHUF and KLAF toward late 
afternoon. Additional isolated thunderstorms could form on the 
flanks of the upper low and impact other TAF sites mid-late 
afternoon. Additional showers should weaken as they move into 
western Indiana late tonight and continue eastward through the 
morning. Redevelopment of thunderstorms is expected tomorrow along 
the front possibly impacting KIND and KBMG, likely east of KHUF and 
KLAF. 

MVFR stratus could develop late tonight through early Thursday per 
model forecast soundings. 

Wind gusts to 20 knots during peak mixing today and again tomorrow, 
and of course gusty near thunderstorms.

&&

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

$$

Update...BRB
Short Term...Eckhoff
Long Term...MK
Aviation...BRB