300 
FXUS63 KIND 041328
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
928 AM EDT Mon Sep 4 2023

.Forecast Update...
Issued at 928 AM EDT Mon Sep 4 2023

Clouds have expanded north into the western half of the forecast 
signaling the expansion of the plume of moisture lifting into the 
lower Ohio Valley between the ridge to our east and the upper low 
currently over eastern Oklahoma. Skies remained mostly sunny over 
the eastern half of central Indiana. 13Z temperatures were in the 
70s.

The overall forecast for the rest of the day is in decent shape but 
a few adjustments are needed. The moisture plume...nicely noted on 
the water vapor imagery...will continue to lift into the region from 
the south through the day...keeping cloud coverage higher across the 
western half of the forecast area. Potential remains for a few stray 
showers this afternoon to focus primarily in the vicinity of the 
Wabash Valley as well...but poor lapse rates and drier air aloft 
should minimize convective depth and keep any lightning from 
occurring. Have pulled the mention of thunder as a result.

The arrival of the deeper moisture may serve to increase dewpoints 
subtly but the increase in clouds conversely may end up keeping 
temps down slightly from original thoughts. Pulled back on highs by 
a couple degrees but still anticipating a very warm and humid day 
with highs peaking in the upper 80s and lower 90s.

Zone and grid updates out.

&&

.Short Term...(Today and tonight)
Issued at 252 AM EDT Mon Sep 4 2023

As with the last couple of nights, near surface moisture beneath a 
shallow inversion along with clear skies and light to calm winds 
will drum up some brief occasional fog over the Wabash Valley and 
other sheltered locales and near streams and corn fields. Again any 
fog will lift quickly after sunrise. 

Otherwise, broad surface high pressure, anchored over the Smoky 
Mountains, an upper ridge building across the Great Lakes, Ohio 
Valley and the South and a 750 millibar CAP will lead to hot and dry 
weather. The exception may be over the Wabash Valley this afternoon 
as instability and moisture increase within the SSW flow around the 
Smoky Mountains high and impulses are ejected NNE around the base of 
an Ozarks and lower Mississippi Valley trough. Models suggest a 
ribbon of CAPE will build in over the Wabash Valley this afternoon. 
So, despite the negative influences of the broad surface high and 
upper ridge, the Wabash Valley, being closer to the trough and its 
inflow of more moist and unstable air could lead to at least some 
isolated PM thunderstorms. Lack of shear should limit these to non-
severe. Steep lapse rates beneath the CAP will allow for deep 
mixing, although winds aloft are not that impressive, so only modest 
gusts to less than 20 knots are expected. Attainable convective 
temperatures support scattered diurnal cu. Still plenty sunshine and 
the SSW winds will make for another hot and humid day, similar to 
yesterday, with afternoon highs in the upper 80s and lower 90s.  

With lack of synoptic support, convection will end by sunset with 
just some increase in high clouds ahead of the upper trough. The 
trough will swing further east to the Mississippi Valley by 12z 
Tuesday with better chances of convection expected just past the 
tonight period. The increase in high clouds may keep temperatures up 
and help deter more of the patchy fog overnight tonight compared to 
the last few nights. As such, slightly warmer overnight lows in the 
upper 60s to lower 70s look reasonable going into Tuesday.

&&

.Long Term...(Tuesday through Sunday)
Issued at 252 AM EDT Mon Sep 4 2023

A pattern change can be expected in the long range as anomalous 
ridging breaks down and is replaced by more quasi-zonal flow. Before 
this happens, an upper-level low over eastern Texas will phase back 
into the mid-latitude jet stream and head northeastward. Guidance 
tracks the feature towards Indiana but weakens it significantly as 
it nears. Nevertheless, enough forcing and instability remains 
present to generate some scattered convection Tuesday afternoon.

Model soundings show a rather deep CAPE profile (roughly 2500 J/Kg) 
with abundant moisture (PWATS in the 90th percentile, 1.80 inches), 
and very weak flow through the column (less than 20 kts 0-6km 
shear). Given the upper-level nature of the system, little in the 
way of surface forcing exists. Convection will likely initiate 
randomly, and be pulse-like in nature given the weak flow aloft. 
Severe weather is not expected. However, a quick downburst or an 
isolated instance of sub-severe hail is possible.

A separate upper-level feature, namely a potent mid-latitude 
trough, is expected to arrive later Tuesday night. The majority of 
guidance depicts this feature deamplifying as it approaches. The 
trough's associated surface low should pass well north through the 
Great Lakes region, with the attendant cold front sweeping through 
Indiana on Wednesday. Despite the weakening upper-level support, 
enough surface forcing may exist for showers and thunderstorms again 
Wednesday afternoon.

Model soundings for Wednesday show less overall CAPE (~1500 J/kg), 
drier mid-levels, and a bit more shear (25 kts 0-6km). The lack of 
shear should limit storm-scale organization and thus severe 
potential. Storm mode looks to be multicell clusters or line 
segments, focused primarily along the approaching cold front. Given 
the mid-level dry air and weak shear...storms could quickly become 
outflow dominant, reducing their longevity. Primary hazard appears 
to be quick downbursts with strong gusty winds.

Once the cold front clears the area, we'll be left with much more 
seasonable weather as troughing and sustained northerly flow takes 
hold. Some lingering stratus or stratocumulus may persist into 
Thursday or Friday given the northerly flow. Forecast highs range 
from the upper 70s to low 80s, which is right around average for 
this time of the year. Cool and crisp lows in the upper 50s are 
likely. Conditions may become optimal for some patchy morning fog 
over the weekend. Precip-wise, Thursday through Monday looks mainly 
dry.

&&

.Aviation...(06Z TAF Issuance)
Issued at 554 AM EDT Mon Sep 4 2023

Impacts:

- Any linger visibility restrictions at KBMG will improve
  no later than 12-13z

- Very small chance for brief MVFR flying conditions in  a 
thunderstorm at KHUF this afternoon 

Discussion: 

Broad surface high pressure over the Appalachians will continue to 
be the main influence on the weather across the terminals today and 
tonight. However, increased moisture and instability in the 
southwest flow around the high along and ahead of an Ozarks upper 
trough could be enough to trigger a thunderstorm or two over the 
Wabash Valley this afternoon. Still, chances are too low to put in 
the KHUF TAF. Otherwise, with the upper ridge over the area and deep 
moisture lacking, scattered diurnal cu and high clouds ahead of the 
aforementioned trough will be only cloud cover. 

Winds will be from the southwest and increase to up to 10 knots this 
afternoon. Any lingering fog at KBMG will lift around or shortly 
after issuance time.

&&

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

&&

$$

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