293
FXUS63 KIND 190226
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1026 PM EDT Thu Jul 18 2024

.KEY MESSAGES...

- Clear and comfortable Tonight
- Mostly Sunny and Mild on Friday
- Seasonable warmth and moderate humidity to return early next week,
  with chances of rain/t-storms starting Monday

&&

.FORECAST UPDATE...
Issued at 1026 PM EDT Thu Jul 18 2024

Only minor changes made to the forecast with this evening`s update.

Surface high pressure will be the dominant weather influence over
the next several days bringing much drier and relatively "cooler"
air to the state. The high will become centered over the Southern
Great Lakes and Northern Indiana by early tomorrow morning resulting
in a very weak pressure gradient across much of the area. Expect
winds to go calm for most areas, especially north of I-70. Excellent
conditions for radiational cooling may lead to patchy fog
development tonight in North Central Indiana and also in the Wabash
River Valley, so have added that to the forecast. Any fog will
quickly lift and dissipate by the 8-9am timeframe tomorrow morning.

Other than some morning fog, no weather concerns for Friday and the
beginning of the weekend. Much cooler and drier air filtering in
will keep highs at or just below normal for this time of year in the
upper 70s to lower 80s in addition to noticeably lower humidity
values.

&&

.SHORT TERM (This evening through Friday)...
Issued at 306 PM EDT Thu Jul 18 2024

Surface analysis early this afternoon shows strong high pressure in
place over MN/WI/IA. This high was dominating the weather across the
upper Midwest and  spilling southeast across Indiana into the Ohio
Valley. This was resulting in cool northeast flow across Central
Indiana. Dew points across Central Indiana have fallen to the middle
50s as this cooler, Canadian, air mass begins to settle across
Indiana GOES16 shows a few CU clouds today.  Aloft, water vapor
showed strong ridging in place over the western CONUS. This was
resulting in cooler NW upper flow across the upper Midwest and into
the Ohio valley along with subsidence. This subsidence was allowing
our surface high pressure system to build.  Water vapor imagery
shows subsidence across Indiana and Illinois.

Tonight and Friday...

Models show the strong high pressure system to the northwest is
expected to expand and settle across IL/IN and OH through Friday.
This will be the result of the strong ridge in place over the
western CONUS providing continued lee side subsidence over the
northern plains and upper Midwest. Forecast soundings show a dry
column tonight and on Friday with a mid level inversion in place
which will also prevent cloud growth. Thus a mostly clear night and
mostly sunny Friday is expected.

Cold air advection is ongoing this afternoon and becomes more
neutral on Friday as the dome of coolest 850mb temperatures, near
12C, settles across Indiana. This should lead to pleasant
temperatures for lows tonight in the middle to lower 50s. Highs on
Friday should reach the upper 70s to around 80.

&&

.LONG TERM (Friday night through Thursday)...
Issued at 306 PM EDT Thu Jul 18 2024

A cold front yesterday has brought about a pattern change to cooler
and drier conditions. Additionally, an upper-level trough now
resides over the region. Upstream over the western US, anomalous
ridging should act to buckle the synoptic scale flow
...causing our trough to remain in place. This feature will be our
primary weather-maker through the weekend.

At the surface, high pressure has slid southward behind the front.
Much cooler temperatures, up to 10 degrees cooler, and drier
conditions now prevail. As mentioned above, the upper-level trough
and associated cooler air mass will remain in place. Even though it
is not expected to move much...it will slowly moderate in place as
the air mass stagnates. A slow warming trend is therefore expected
through the weekend.

By early next week, surface high pressure repositions itself to our
southeast. This should lead to a southerly return flow allowing for
muggy/humid conditions to return. With moisture comes instability,
and therefore the chance of scattered showers and thunderstorms.
Despite a lack of synoptic-scale forcing, enough instability may
become present to help generate "air mass" thunderstorms. These,
especially in weak flow atmospheres, likely will not move much and
be short-lived.

Guidance hints at a few waves / vort maxes dropping southward after
cresting the western ridge next week. These may locally enhance
rainfall chances Monday through Wednesday. Guidance is not yet in
close agreement regarding these features and their timing/location.
As such, confidence in the forecast decreases a bit by next week.
Temperatures will likely depend on how the convective situation
unfolds as well.

Overall, expect dry conditions and slightly below-average
temperatures now through the weekend. Next week, humidity increases
and daily rain/storm chances should be present. Forecast confidence
decreases because synoptic and mesoscale forcing looks to be
nebulous and ill-defined. Looking further at the 8-14 day period, no
strong signal for either cooler or warmer than normal temperatures
is present at this time.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 741 PM EDT Thu Jul 18 2024

Impacts

- Patchy fog possible near sunrise

Discussion:

Mostly VFR is expected through the TAF period as strong high
pressure over the midwest becomes centered over the state tomorrow.
This will keep winds relatively calm overnight tonight and then
under 10 kts out of the northeast during the day tomorrow.

Only forecast concern is the chance for patchy fog late tonight and
around sunrise which could result in brief periods of low cigs and
vis at KLAF, KHUF, and possibly KBMG. The Wabash River Valley has
the best chance at seeing patchy fog. Do not think it will be very
widespread, but the possibility of it happening is high enough to at
least mention it in the TAFs. Any fog that does develop should
quickly lift and dissipate within the 12-14z timeframe.


&&

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

$$

UPDATE...CM
SHORT TERM...Puma
LONG TERM...Eckhoff
AVIATION...CM