471 
FXUS63 KIND 201339
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
939 AM EDT Fri Aug 20 2021

.Forecast Update...
Issued at 938 AM EDT Fri Aug 20 2021

With localized weak high pressure still just to the NE of central 
Indiana, precipitation chances have been removed from the forecast.
If an isoalted shower/thunderstorm does develop is would be over SW 
portions of the area, but confidence in this occuring is low at this 
time. Otherwise, forecast is on track, with no significant changes 
made. Diurnal cu should develop over the next few hours with highs 
in the upper 80s. 

Zone and grid updates out.

&&

.Short Term...(Today through Saturday)
Issued at 255 AM EDT Fri Aug 20 2021

Surface analysis early this morning shows strong high pressure in 
place over Michigan...with light easterly flow in place across 
Central Indiana. Surface low pressure was found over Colorado and 
the Dakotas. Aloft...water vapor was showing strong ridging in place 
over the Mississippi valley and a trough over the eastern Great 
Lakes. NW flow aloft along with subsidence was in place across 
Indiana. GOES16 show mainly clear skies across the area...however 
with recent rains today and dew points in the mid 60s...patchy 
dense fog development is expected.

Today...Any morning fog due to earlier rain should burn off quickly 
with the return of daytime heating by mid morning. Models suggest 
the strong ridging aloft will build east today...reaching the 
eastern Great lakes by this evening. Given the strong subsidence 
seen on water vapor with this ridge...mainly dry weather should be 
in play. Time heights show subsidence through the day and soundings 
show dry air within the mid levels. However forecast soundings do 
shows attainable convective temperatures and CAPE around 1000 
j/kg...which is low for this time of year. HRRR shows some isolated 
TSRA/SHRA development as convective temps are reached. Thus will 
keep much of the area dry today...with only an isolated mention for 
pops during the 20Z-24Z time frame. Given the expected sun...will 
trend highs at or above persistence.

Tonight...the upper ridge axis is suggested to still be to the west 
of Indiana and subsidence should still be in play. Time heights and 
forecast soundings again show a dry column through the night. 
Surface high pressure is suggested to have moves east to NY/PA...but 
Indiana will still be largely under its influence. Thus with no 
triggering available...will trend toward mostly clear skies and lows 
at or slightly above expected dew points.

Models suggest the ridge axis aloft will pass across Indiana on 
Saturday afternoon. Some weak forcing dynamics appear to be 
associated with this crossing. Forecast soundings show some trending 
toward saturation within the column with attainable convective 
temperatures. Furthermore...pwats surge toward 1.8 inches late in 
the day as max heating is reached. Thus once again will use small 
chances for afternoon and early evening showers and storms as the 
weak forcing aloft and peak heating arrive at a favorable time. 
Again will trend highs at or above the expected persistence.

&&

.Long Term...(Saturday night through Thursday)
Issued at 255 AM EDT Fri Aug 20 2021

Ensemble means indicate upper ridging can be expected across the 
Ohio Valley over the upcoming weekend, and into early next week. 
After that, the ridge will tend to flatten out, as a short wave 
trough moves through southern Canada and the northern Great Lakes.

Ensembles suggest a weakening frontal system may pass through the 
area near the beginning of the period. Will hold onto chance PoPs 
from Saturday night into Sunday to cover this front.

Otherwise, the ensembles suggest a better precipitation threat 
towards the middle of next week, as the upper flow flattens out, 
allowing for potential disturbances to move through the area from 
the west or northwest. As a result, will bring chance PoPs back into 
the forecast from Tuesday through Thursday.

&&

.Aviation...(201200Z TAF Issuance)
Issued at 638 AM EDT Fri Aug 20 2021

IMPACTS:
- Areas of IFR/LIFR visibility due to fog expected to dissipate by 
201400Z.
- Isolated convection possible after 201900Z.
- Surface winds 150-180 degrees at 5-7 kts from late morning through 
the afternoon hours.

DISCUSSION: 

Areas of IFR/LIFR conditions due to fog expected to burn off by the 
late morning hours, as the moisture layer is very shallow and restricted
to near ground level.

Attainable convective temperatures this afternoon, coupled with a 
generally uncapped air mass, will lead to the potential for isolated 
to widely scattered convection by mid afternoon. A lack of a focus 
for convection today should keep activity sparse enough to keep direct
impact threats low.


&&

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

$$

Update...Updike
Short Term...Puma
Long Term...JAS
Aviation...JAS