Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 06/21/23

Area Forecast Discussion

National Weather Service Indianapolis IN

 959 PM EDT Tue Jun 20 2023

.Forecast Update...
Issued at 959 PM EDT Tue Jun 20 2023

The weak low pressure system and associated deeper moisture which
helped produce scattered showers and storms this afternoon has
gradually pushed south of the area this evening. This along with the
loss of daytime heating has allowed showers to diminish across the
area. Expect a quiet night with breezy conditions early. Winds will
continue to weaken overnight as the PBL decouples and the pressure
gradient relaxes with the aforementioned surface low moving further
south. Diurnal cooling will be limited some by these winds and
clouds. Expects lows generally in the mid 60s tonight.

&&

.Short Term...(This evening through Wednesday)
Issued at 254 PM EDT Tue Jun 20 2023

The synoptic scale pattern across the CONUS can be characterized by
broad ridging over the upper-midwest with a cut off low centered
over Tennessee. This is a Rex Block pattern, and no significant
changes are expected synoptically within the next 1 to 3 days. The
upper-level low to our south will be the primary factor in our
weather through the short term.

A southwest to northeast gradient in cloud cover currently exists
across the region, as seen on satellite. Drier air and greater
subsidence associated with the midwest ridging has allowed for the
clear skies generally northwest of Indianapolis. To the southeast,
deeper moisture and weak lifting from the low has contributed to
increased cloud cover and therefore cooler temperatures. In between,
enough moisture remains that a diurnal cumulus field has developed.
These clouds are flat in appearance, signifying a capping inversion
that remains, which is verified by recent ACARS soundings out of
IND. Some CAPE exists, roughly 1000 J/kg, and should the capping
inversion be overcome, a few showers or even a thunderstorm are
possible this afternoon. Given the cap, and a rather dry column
above it...chances of this are quite low and most places should
remain dry.

At the surface, the now well-mixed boundary layer has allowed for
some downward momentum transfer from about 850mb resulting in wind
gusts around 25 kts. These gusts will continue through sunset,
before diminishing as radiative cooling processes stabilize the
lower atmosphere. BUFKIT soundings hint at a sharp low-level
inversion forming overnight. This will act to stabilize the
atmosphere and allow any lingering rain showers to diminish as well.
Quiet conditions should then continue overnight, with perhaps some
mid-level clouds associated with a weak vort max rotating around the
broader upper low. Low temperatures tonight are expected to drop
into the 60s, assuming optimal radiative cooling. Warmer overnight
lows in locations that experience persistent cloud cover.

The weather on Wednesday will not be significantly different than
today. In fact, the upper low and ridge will be in essentially the
same locations respectively...and as such, we will experience a
repeat of today. Solar insolation will act to rapidly steepen low-
level lapse rates, allowing for diurnal cumulus formation and
enhanced downward momentum transfer. This will allow wind gusts to
develop by late morning. Soundings only indicate 30-35kts at the top
of the boundary layer, corresponding to 20-25kts at the surface.

Rain chances are tricky, as the aforementioned vort max may enhance
lift a bit compared to today. A few more showers may be possible at
times, especially in the afternoon when available energy is
maximized. Nevertheless, will plan on carrying only chance PoPs for
now between 10 to 30 percent, with the highest likelihoods being
across our southern counties. Poor lapse rates and substantial mid-
level dry air should limit convective potential. A few thunderstorms
are possible, however, especially in our southern counties where
greater moisture exists. No convective hazards are anticipated as
limited shear exists for storm organization. Any cells that fire up
will move with the mean flow and collapse upon themselves fairly
quickly. A few wind gusts to 30-35kts are possible with the more
robust cells, should any manage to develop. Temperatures should top
out in the upper 80s across our northwest under relatively sunnier
skies, with lower 80 under the cloud deck across our southeast.

&&

.Long Term...(Wednesday night through Tuesday)
Issued at 254 PM EDT Tue Jun 20 2023

* Sharp gradients in clouds/precip/temperatures this week
* Greater chances for showers E of I-65, warmer and sunnier to the NW
* Pattern shifts into the weekend for drier and warmer conditions

.Thursday into Friday...

Unusual weather pattern continues into the latter half of the week
across Indiana as a cut off upper low meanders around the Ohio and
Tennessee Valleys while ridging builds to the north. With Central
Indiana right in between these synoptic features, expect both a
temperature, cloud cover, and precipitation gradient from northwest
to southeast across the region through at least Friday.
Deterministic and ensemble runs are in good agreement with this
upper low meandering around the Ohio Valley through the end of the
week with multiple vort maxes rotating about it. Lower confidence
exists in the timing and placement of these smaller scale features
as lower resolution mid range guidance does not handle this pattern
well. Keeping 20-30 PoPs in the forecast through Friday with the
highest chances across Southern and Eastern Indiana. Finer scale
details for timing of convection and coverage will likely become
clearer in the coming days as higher resolution guidance may be able
to resolve those features better. Overall, most locations in the
region will remain dry through the week.

Despite lower confidence with some details, higher confidence exists
in partly to mostly cloudy skies sticking around through the period,
with thickest and most widespread clouds in southern and eastern
Indiana. GFS and NAM time-height cross sections reveal ample mid and
upper level saturated layers as persistent moist, easterly flow off
the Atlantic advects into the region Thursday and Friday. Lowered
high temperatures towards the NBM 25th percentile as well to account
for increased clouds. Warmest locations with highs closer to normal
in the mid 80s will be across northern and western portions of
Indiana, furthest from the upper low with greater influence from
high pressure to the north. Keeping highs in the upper 70s to around
80 for the southern and eastern 2/3 of the region due to clouds and
showers around.

.The Weekend through Early Next Week...

Signs of a pattern change are on the horizon as longer range
guidance shows the stalled out upper low finally weakening and
pushing northeastward Saturday and Sunday. Brief, yet weak ridging
sets up over the area before another front approaches from the
northwest by the beginning of next week. Skies should be generally
clear, but diurnal warming processes could result in pulse-type
summertime convection. This warrants chance PoPs for the weekend,
but any precip this weekend will be localized and spotty in nature.
Max afternoon temperatures will warm into the upper 80s to lower 90s
by Sunday, with the hottest locations likely across Western Indiana.

Longer range ensembles are signaling at different pattern setting up
for much of next week as ridging within the subtropical jet builds
over the Southern and Central Plains. This pattern typically places
Indiana in a region of northwesterly flow aloft and warmer, more
moist westerly/southwesterly flow at the surface. The northwesterly
flow pattern does support fronts and smaller mesoscale features to
be directed into the Ohio Valley leading to sporadic thunderstorm
chances. Confidence is low this far out on any severe weather
potential or timing of showers/storms. However confidence is rising
in this type of pattern setting up with normal to slightly above
normal temperatures and increases chances for precipitation.

&&

.Aviation...(00Z TAF Issuance)
Issued at 720 PM EDT Tue Jun 20 2023

Impacts:

* East-northeasterly wind gusts around 20-28 kts diminishing over
  the next few hours

* VFR conditions expected through the period

* East-northeasterly wind gusts around 18-24 kts return Wed PM

Discussion:

VFR conditions are expected through the period. Central Indiana
will be situated between a rather weak mid-level trough and
Canadian high pressure. The gradient between these two features
has produced wind gusts around 20-28 kts this evening. Expect
these gusts to diminish shortly after sunset.

A few isolated showers have moved near the KIND/KBMG sites at times
this afternoon. These diurnally driven showers should also diminish
over the next few hours. Daytime heating on Wednesday should result
in wind gusts around 18-24 kts during the afternoon. Wind direction
will remain predominately easterly through the period.


&&

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

$$

Update...Melo
Short Term...Eckhoff
Long Term...CM
Aviation...Melo