Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 02/08/24

Area Forecast Discussion

National Weather Service Indianapolis IN

 928 PM EST Wed Feb 7 2024

.Key Messages...

- Rain chances Late Thursday Afternoon and evening.

- River flooding along the Wabash ending by Wednesday night.

- Wind gusts over around 30 mph likely Thursday with a few gusts to
  40 mph possible Thursday night.

- Rain chances increase late Friday night into Saturday.

&&

.Forecast Update...
Issued at 927 PM EST Wed Feb 7 2024

Breaks in the thick cirrus, that was moving overtop the high
amplitude ridge, dry boundary layer and surface and very light to
calm winds, have allowed temperatures at a few locales to rapidly
drop to the upper 30s and lower 40s. So had to lower nighttime
temperatures a few degrees at some sheltered locations. That said,
as the surface low pressure gradient tightens overnight, ahead of
the northern Plains low pressure system, winds will become southerly
and increase in speed and should result in steady or slowly rising
temperatures. Daybreak temperatures will likely be in the upper 30s
to lower 40s, which will be a change from the previous frosty
mornings.

&&

.Short Term...(This evening through Thursday)
Issued at 255 PM EST Wed Feb 7 2024

Synopsis -

Surface analysis early this afternoon shows a broad area of high
pressure over the east coast. Influence of this high extended west
to the eastern Great Lakes, the Ohio Valley and the Gulf Coast.
Weak southerly flow was found across Central Indiana. Low Pressure
was found over WY. This was resulting in a moderate pressure
gradient across the plains states, which was slowly pushing eastward.
Aloft, water vapor showed a strong ridge in just east of the
Mississippi Valley. This was resulting in lee side subsidence across
the eastern third of the United States including Indiana.

GOES16 shows ridge riding cirrus flowing over the ridge and spilling
into Indiana from the northwest. Radar was quiet across the region.
ACARS soundings show a very dry column within the lower and middle
levels.

Tonight -

Partly cloudy and dry weather with mild temperatures are expected
tonight. Models suggest the ridge axis aloft will push to Indiana
this evening before exiting to the east overnight. This will keep
continued subsidence in play along with a lack of lower level
clouds. The controlling area of high pressure will also drift east,
allowing the pressure gradient to the west to advect into the Ohio
valley late tonight and Thursday. Models also depict late tonight
and on Thursday morning an moderate 50 knt LLJ streaming across
Central Indiana. However, overall deep moisture with this system is
lacking. Forecast soundings across the area continue to reveal very
dry lower and mid levels, due to the past few days of subsidence.
Thus we will only expect continued high clouds passing across
Indiana, advecting from the plains states. Clouds and increasing
winds allowing mixing overnight should result in mild low
temperatures with lows in the upper 30s and lower 40s.

Thursday -

The upper ridge axis will be well east of Indiana by Thursday
morning and will continue its eastward progression through the day.
Meanwhile an upper trough will be working through the northern
plains and upper Midwest. Much of the best upper forcing with this
feature looks to remain well north of Central Indiana over the
western Great Lakes before streaming farther away into Ontario.
However, the surface cold front with this feature is expected to
approach Central Indiana on Thursday before passing across the state
through the day. The previously mentioned LLJ will remain in play
through the day along with the passing cold front. However moisture
remains an issue. Forecast soundings fail to show deep saturation,
but lower and mid levels do show some saturation arriving by
afternoon. Pwats are suggested to reach near 0.77in. HRRR does
suggest some scattered precipitation across Central Indiana Thursday
afternoon...albeit light and quick moving. DESI suggests several
members pushing an area of scattered light rain across Central
Indiana from 20Z onward. The quick moving precip should be light, as
many of the hours of the day will be dry. Thus will trend toward a
dry morning and early afternoon before adding pops late in the
afternoon as the cold front and these very light shows may pass.
Given the good mixing and warm southerly flow ahead of the front,
highs in the middle and upper 50s should be reached.

&&

.Long Term...(Thursday night through Wednesday)
Issued at 255 PM EST Wed Feb 7 2024

SYNOPTIC OVERVIEW

Upper-level flow across the CONUS can be described as highly
amplified, with a ridge axis over the Plains bounded by deep
troughing on either side. Indiana resides downstream of the ridge as
of this writing. High clouds have increased today ahead of an
approaching trough, currently over the Intermountain west. This
trough will induce cyclogenesis in the lee of the Rockies today. The
resulting low pressure center then races off to the northeast.

The low should pass far enough to our north that any significant
dynamic forcing bypasses Indiana. As a result, confidence in rain
continues to decrease. A few showers or sprinkles may still be
possible, especially Thursday night into Friday morning...but
overall rain threat appears minimal with perhaps a trace to a few
hundredths at most. Guidance shows a tight MSLP gradient with this
system, which may bring some warm yet gusty southwesterly winds
Thursday night into Friday. Gusts over 30mph are likely at times,
with a few gusts exceeding 40mph not out of the question. Such
strong warm southwesterly winds look to bring our warmest day in a
while, with highs reaching into the low 60s Friday.

As the low pulls away, it will drag a weak cold front into the
region which looks to stall out north of us near Chicago. This
boundary will set up a baroclinic zone that another upstream wave
will traverse. Uncertainty remains regarding this wave, with some of
the global models keeping it a bit more compact and potent...while
the NAM for instance keeps it elongated and weaker. Nevertheless,
they all show precipitation developing ahead of the fast-moving
system. Timing-wise, precipitation onset late Friday night or early
Saturday morning is most probable. Thermal profiles suggest that
rain is easily the only realistic precipitation type.

As the second system exits, only a slight southward push of colder
air ensues. The aforementioned baroclinic zone shifts southward as a
result, but not by much. The west coast trough looks to send one
final wave our way, which should arrive on Monday. Given the
baroclinic zone stretching further south, model soundings indicate
precipitation type may be a concern with this system...especially
near and north of the system`s center. Greater uncertainty in
guidance exists with this system, both in run to run consistency and
in system magnitude and location.

Beyond that, ensembles show a return to northwesterly flow and
potentially colder weather.

FORECAST CONFIDENCE

Confidence is increasing regarding Thursday night`s rainfall
potential. Trends have been drier, and now the vast majority of
guidance shows little in the way of measurable precip across
Indiana. Confidence for wind gusts over 30mph is high. Per DESI,
probability for gusts reaching 30mph is near 100 percent, with gusts
over 40mph rather high across our northwest at over 75 percent.
Additionally, very little spread exists amongst the various ensemble
members which indicates greater certainty in a particular scenario.
DESI probability drops significantly when looking at potential for
45mph gusts, indicating a much lower probability of reaching this
threshold.

Regarding Saturday`s system, confidence is moderate in terms of its
timing but low regarding precipitation amounts. Much of the
variability in guidance primarily resides in system strength, which
in turn affects how much precipitation develops ahead of it.

Regarding Monday`s system, confidence is quite low. Much variability
remains in model guidance and until a consensus emerges it is too
soon to talk about potential affects. The only thing with this
system where at least some confidence exists is its Monday arrival
time.

&&

.Aviation...(00Z TAF Issuance)
Issued at 611 PM EST Wed Feb 7 2024

Impacts:

- Non-convective low level wind shear possible 08z-15z

- Winds 170-210 degrees to 20+ knots and gusts to 30+ knots
  after 15z Thursday

- MVFR ceilings and showers possible after 22z Thursday

Discussion:

Thick cirrus will stream in ahead of a departing high amplitude
ridge, that was extending from northern Ontario to the Gulf of
Mexico. Then, a low level jet will move overhead overnight and
Friday morning, ahead of a low pressure system. This will also
result in a strengthening surface pressure gradient and HI-Res model
soundings are suggesting 30+ knot winds may mix down aloft from the
2K foot inversion, Thursday afternoon. Otherwise, winds will be
southeast less than 10 knots tonight and south winds will sustain to
20+ knots Thursday afternoon. Finally, a few showers and maybe even
MVFR ceilings are possible late Thursday afternoon and evening.


&&

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

$$

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