Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 02/19/23

Area Forecast Discussion

National Weather Service Indianapolis IN

 548 PM EST Sat Feb 18 2023

...Updated Aviation Discussion...

.Short Term...(This evening through Sunday)
Issued at 257 PM EST Sat Feb 18 2023

Both increasing cirrus and particularly expansive/long-lasting
contrails were observed early this afternoon. This signals
increasing moisture within westerlies aloft. Satellite moisture
channel products show cirrus being augmented via terrain forcing in
the central Rockies region, merging with a plume of subtropical
moisture that has now overspread the southern/central Plains.

All of this is occurring downstream of a compact southern stream
shortwave trough that will pass over Indiana late tonight through
early Sunday. Increasing ascent and moisture will be sufficient for
thickening cirrus and lowering to a midlevel stratus deck later
tonight. However, the sub-cloud layer is particularly dry per latest
ACARS and model soundings. Precipitable water anomalies rise only to
near neutral/normal, which is driven almost entirely by midlevel
moistening since anomalous low-level moisture is currently confined
to the lower Gulf of Mexico due to recent equatorward cP air mass
intrusion. We will likely see sufficient midlevel moistening and
ascent for virga on radar late tonight, but we don`t expect
measurable precipitation. A brief period of sprinkles is possible in
the pre-dawn or early morning hours Sunday, but even that is in
question given the magnitude of the dry sub-cloud layer.

There is slightly more spread than average among the deterministic
and ensemble model suite for temperatures Sunday, capping our
forecast confidence at moderate. The nature of the lifting low-
amplitude southern stream shortwave and subsequent zonal flow
suggests limited equatorward movement of the cold front and higher
latitude cold air mass. So, models do confine cold advection to our
north through the end of the day. We accepted the deterministic
NBM/blend which falls roughly at the 75th percentile, since the
greater adiabatic warm plume holding to our south. We would consider
higher percentile guidance if this plume were more centered over our
area to account for model deficiencies in PBL/mixing process, which
is a common bias. Regardless, we should still reach the low-mid 50s
for maximum temperatures with some potential error of a couple of
degrees.

Gradient will continue to be enhanced between surface high/subsident
regime to the east and negative MSLP anomalies to our west forced by
a northern stream wave. This, coupled with deeper mixing, should
make for slightly windier conditions Sunday (i.e., gusts up to
around 30 mph during peak mixing).

&&

.Long Term...(Sunday night through Saturday)
Issued at 257 PM EST Sat Feb 18 2023

* Mild start to next week with warming trend through Thursday
* Chances for Rain Next Week; Best chances Wednesday through Thursday

Active weather pattern sets up next week with numerous systems
passing through the region increasing clouds and the chances for
rain, but also keeping temperatures above average for this time of
year.

.Sunday night and Tuesday...

First in a series of weather systems passes through Sunday night
into Monday. High pressure is centered across the Southeast CONUS
while a moisture starved frontal boundary slowly sags southward
through the Midwest and Great Lakes. The weak front slides through
Indiana early Monday morning at the same time a strong west to east
oriented upper level jet streak develops over the Ohio Valley. While
the column is fairly dry, there may be just enough moisture present
within the boundary layer for sprinkles and isolated rain showers to
develop during the early morning hours. Added this into the
forecast; however thinking most places will remain dry.

Weak westerly flow sets up behind the front with little to no change
in airmass; there expect similar temperatures as Sunday with highs
generally in the upper 40s to lower 50s.

Another quick moving system moves across the Upper Great Lakes early
Tuesday swinging a weak, moisture starved front through region
again. Very little forcing and moisture are associated with this
system, so mainly expect an increase in clouds. The main concern
with this Tuesday system is where it potentially stalls out just
south of the region. Models typically struggle to resolve very weak
features and this one is no exception. Guidance is struggling
whether to hold the front up around Kentucky or further south
towards the Tennessee Valley. Due to the uncertainty, keeping partly
to mostly cloudy skies for Tuesday as weak southwesterly flow aloft
transports moisture up and over the boundary and into Indiana. Put
20 PoPs for the Southern 1/3 of the forecast area as the possibility
is there for a few isolated showers or sprinkles if the front stalls
out closer the the Ohio River. Still no real major changes in
airmass or temperatures so keeping with the status quo for Tuesday
with highs ranging from the upper 40s to mid 50s.

.Wednesday through Friday...

Mid to late next week becomes more active as multiple strong storm
systems develop in the Plains and track towards the region. The
aforementioned stalled out front from Tuesday lifts northward early
Wednesday as a warm front bringing the next chances for rain,
thunderstorms, and much warmer air.

Since the energy that will eventually lead to the development of
these systems is still a ways out in the Pacific and has not been
sampled by the models, there is still quite a bit of spread on the
evolution and track of the mid to late week systems. Confidence is
increasing that low pressure develops on the lee side of the Rockies
early Wednesday with its associated warm front extends eastward and
lifts north through the Ohio Valley. This front could be the focus
for heavy rain and thunderstorms to develop as a strong low level
jet pumps warm, moist Gulf air northward over the boundary.
Increasing temperatures and PoPs Wednesday to account for this
pattern setting up. While finer details may still not be clear,
confidence is increasing in wet weather Wednesday and Thursday.

Deterministic and ensemble members still mostly show this system
tracking northeastward Thursday, keeping Central Indiana in the warm
sector with southerly flow and warm, moist conditions. Not too
concerned with severe weather at the moment as much of the upper jet
energy and strongest temperature gradient remains displaced well
north and west of the convection. However with guidance still in
disagreement on the finer details, expect things to change over
the next few days. While severe weather potential for now may seem
low, cannot completely rule it out.

Thursday and Friday`s weather will also heavily depend on the
potential development of the mid week system. With the system
potentially being more positively tilted, CAA will be minimized,
limiting the extend of a potential cool down in its wake. A brief
cool down is expected Friday as the system departs, but expect
another warming trend into the next weekend.

&&

.Aviation...(00Z TAF Issuance)
Issued at 547 PM EST Sat Feb 18 2023

Impacts:

* VFR Conditions expected
* Brief LLWS possible near sunrise.

Discussion:

A quick moving tropical plume of moisture will push across Indiana
overnight before exiting on Sunday. A weak short wave within the
plume may result in some virga or sprinkles, but very dry air within
the lower levels should prevent any precip from reaching the ground.

Aloft a LLJ of near 40knts is expected to push across Indiana
overnight. This may result in some LLWS due to speed at the diurnal
minimums.

A moderate pressure gradient along with mixing may cause winds to
gust to around 25 knots Sunday afternoon. Forecast confidence is
high.

&&

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

$$

Short Term...BRB
Long Term...CM
Aviation...Puma