Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/14/23

Area Forecast Discussion

National Weather Service Indianapolis IN

 1156 PM EDT Thu Apr 13 2023

...Updated Aviation Discussion...

.Forecast Update...
Issued at 959 PM EDT Thu Apr 13 2023

Forecast is in decent shape this evening. High and some mid clouds
are increasing from the south from the low pressure system in the
southern states. Adjusted cloud cover as needed based on latest obs.

Radar has some weakening echoes moving into the far south from
weaker forcing on the periphery of the low pressure system. Fort
Knox, Kentucky did report some light rain from these echoes even
with large dewpoint depressions at the surface. However, at this
time, given the weakening nature of the echoes as they move into
central Indiana, feel that coverage of drops reaching the ground
will be too low to mention.

Made some tweaks to low temperatures based on latest trends, but no
significant changes were made.

&&

.Short Term...(This evening through Friday)
Issued at 257 PM EDT Thu Apr 13 2023

* Well above normal temperatures continue into Friday
* Increasing high clouds ahead of approaching weather systems

.This Evening and Tonight...

Forecast for this afternoon is on track, therefore little changes
made with today`s forecast package. High pressure is centered off
the coast of the Mid Atlantic states with a tropical low pressure
over Mississippi and another moving into Western Nebraska. This
pattern has resulted in weak southerly flow across the state with
subsidence under the high keeping skies clear. 18z IND ACARS
sounding shows a mixing height up to 1 km agl into a very dry layer
aloft. The forecast for falling RH values and steady dew points in
the 30s today has verified quite nicely. While RH values have
dropped significantly, winds have remained fairly light resulting in
little fire weather concerns today.

Overnight, conditions will remain similar, with no gusts as the PBL
decouples. Winds speeds staying around 5-8MPH throughout the night
and steady WSW advection will limit diurnal cooling some. However
increased cloud cover this evening into tonight, especially in the
upper levels as downstream moisture from the tropical low reaches
the region could have a more profound impact on temperatures. Kept
low temperatures in the mid 50s for tonight (around NBM75th
percentile) to account for increasing cloud cover and winds staying
slightly elevated.

.Tomorrow...

The tropical low across the Gulf Coast states Thursday continues its
weakening trend and slowly pushes north northeast within the weak
mean flow. The system erodes from the bottom up as it tracks towards
the Ohio and Tennessee Valleys with little to no surface reflection
as it makes its way this far north. The upper low reaches Kentucky
then turns northeastward toward West Virginia by tomorrow night.
Little impacts expected from this system across Indiana tomorrow,
however it will feel noticeably more humid than the past few days.
Moisture advection increases ahead of the system with dew points
rising from the 30s to the 50s by Friday afternoon. High clouds
associated with the expansive cloud shield push northward overnight
and into tomorrow across Indiana. RAP forecast soundings and cross
sections suggest high clouds increase and thicken through the day
keeping temperatures a few degrees cooler than today. With such a
warm airmass in place, expecting temperatures to still reach the mid
to upper 70s tomorrow, with the warmest temperatures along and north
of I-70 where clouds will be thinner.

&&

.Long Term...(Friday night through Thursday)
Issued at 257 PM EDT Thu Apr 13 2023

* Slight chance of rain on Friday
* Scattered showers and thunderstorms late Saturday into Sunday
* Cooler conditions on Monday
* Dry weather along with warming trend beginning Tuesday

Synoptic Pattern Overview

Currently, a large upper-level ridge resides over the Midwestern
United States. This has provided us with abundant sunshine and
above-average temperatures. To our south, a cut-off low pressure
system has developed in the Gulf of Mexico and moved inland. Out
west, a trough is beginning to dig into the intermountain west and
will progress eastward with time. The cut-off low to our south will
then open up and move northeastward ahead of the advancing trough.
Finally, the west coast trough is modeled to make its way into the
Plains and then the midwest, amplifying significantly as it does so.
By the time it reaches Indiana, it may already be in the occlusion
process. Afterward, broad ridging returns to the Plains and upper
Midwest.

Friday Night

The southern cut-off low, originating from the Gulf, will begin
lifting northward tonight. As it does so, moisture will begin
spreading northward as well. It is not out of the question that an
isolated shower or even a thunderstorm works its way into the area
during the day tomorrow. Chances of this appear quite low, however,
as the parent cyclone passes to our south and east. Upper-level
forcing seems almost nonexistent, as flow between the low and trough
to our west largely cancels out...leaving very little air flow
through the column. CAMs suggest that the best chance of any
shower/storm activity will be late in the afternoon, as surface
heating drives some meager amounts of CAPE around 500 J/kg. Given
the weak flow aloft, buoyancy-driven precip threat, will taper PoPs
downward after sunset as the PBL cools and instability is lost. Will
not remove PoPs entirely, however, as some hi-res members show
lingering showers into the night.

Saturday and Sunday

Any lingering showers from the cut-off low should be ending by
Saturday morning. Most the day thereafter should be dry, as weak
subsidence between the trough and low acts to inhibit shower
activity. Things change as the western trough makes its approach,
however. The nose of potent jet at the base of the trough begins to
edge into Illinois and Indiana by 00z. Diffluence aloft and PVA will
lead to some increased environmental lift, which may promote a few
isolated showers and thunderstorms late in the day.

The greatest threat for rain and storms looks to be overnight
Saturday and into Sunday, as the highly-amplified trough tilts into
the negative and swings into Indiana. Strong diffluent flow aloft,
strong PVA, and increasing low-level moisture all point towards
increasing precip potential after sunset as a potent cold front
makes its way eastward. Given the impressive dynamics aloft and
continued moisture advection, the nocturnal timing of the event
should not inhibit convective development.

In terms of severe potential, a few things stand out that point
towards a lower threat. First, the trough itself becomes highly
amplified, leading to generally southerly flow at all altitudes.
While speed shear is high, roughly over 50 kts, directional shear is
quite low. Boundary-parallel flow favors a linear storm mode.
Second, the nocturnal / early timing of the event. As mentioned
before, given the strong environmental forcing above and along the
front, the timing may not be enough to inhibit convective
development...it is enough to inhibit CAPE. Smaller CAPE and lapse
rates will lead to weaker thunderstorms less capable of strong
updrafts and downdrafts. Furthermore, BUFKIT soundings show a
shallow but potent surface inversion developing overnight. These two
factors work against a tornado threat. Thirdly, a rather weak LLJ
will limit downward momentum transfer in any storm that fires up, as
there will be rather weak flow to transfer downward. So while an
occasional wind gust is possible, mainly after the surface inversion
begins to weaken, the potential is not too impressive. To summarize,
while numerous showers and storms are likely, severe potential
appears low due to poor lapse rates, limited instability, and a weak
LLJ. Will need to monitor model trends, however, in case the arrival
of the trough / front is slower which would place the convective
activity more into Sunday afternoon. Recent model trends have slowed
down a bit with latest runs.

Once the showers and storms end Sunday morning, a strong cold front
will sweep through bringing an unfortunate end to our above-average
warmth. Temperatures will follow a non-diurnal curve, reaching their
max early before dropping into the low 50s during the afternoon.
Winds could be on the gusty side as well, as a surface low deepens
to our north. Guidance suggests gusts ranging from 25 to 30 kts at
times.

Monday

On Monday we will find ourselves in the broad cyclonic northwesterly
flow on the backside of the departing trough and surface low. BUFKIT
soundings show an optimal sounding for widespread stratocumulus with
possible showers and flurries. Therefore, expect a cold dreary day
on Monday compared to what we have seen recently. Model blends may
be a bit warm, given the robust CAA and signal for persistent
stratocu. Residual breeziness should contribute to the overall
unpleasantness of the colder air.

Tuesday through Thursday

Ensemble guidance shows the big cold upper-level trough departing
completely by Tuesday. Strong surface high pressure, passing to our
south, will provide large scale subsidence allowing for clearing
skies. While the day may begin with some lingering stratocu, it
should end mainly clear. Some high clouds may become apparent by
sunset in part from ridge-building out west.

Surface low pressure in the northern plains should work in tandem
with the high to our south to tighten the MSLP gradient, driving a
potent 850mb LLJ which will accelerate WAA. By Wednesday, as ridging
builds eastward, high temps look to return back into the 60s.
Further WAA may allow temperatures to jump into the 70s again by
Thursday.

&&

.Aviation...(06Z TAF Issuance)
Issued at 1156 PM EDT Thu Apr 13 2023

Impacts:

- VFR flying conditions with good confidence through the TAF period

Discussion:

Upper low will move across the Tennessee Valley today and
Appalachians tonight. This will bring some mid and high clouds to
the terminals. A brief very light shower or two are possible at
KBMG, but chances are too low to mention. Otherwise, high confidence
in VFR flying conditions.

Winds will be SE and then S less than 10 knots.

&&

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

$$

Update...50
Short Term...CM
Long Term...Eckhoff
Aviation...MK