Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 10/21/23

Area Forecast Discussion

National Weather Service Indianapolis IN

 913 PM EDT Fri Oct 20 2023

.Forecast Update...
Issued at 913 PM EDT Fri Oct 20 2023

- Mostly Clear and cool overnight

Surface analysis this evening shows low pressure in place over
Ontario, providing broad cyclonic flow across the eastern Great
Lakes and northeast Indiana. High pressure was found centered over
the southern plains, with a ridge axis stretching northward across
Illinois to Central WI. This was resulting in cooler northwest
surface flow across Central Indiana. GOES16 shows the back edge of
the cloud shield associated with the surface low over the eastern
third of Indiana. This shield continued a slow departure eastward.
Flow aloft was from the northwest, due to a strong ridge over the
Rockies as seen on water vapor imagery. Dew points across Central
Indiana were in the lower to middle 40s.

Overall, the ongoing forecast remains in good shape and no large
adjustments will need to be made. Models suggest the cloud cover to
the east will continue to drift east, allowing clear skies to arrive
across the entirety of the forecast area. As the low departs the
pressure gradient will continue to lessen, allowing winds to fall to
around 5 knots through the night. Clear skies and light winds will
allow for good radiational cooling conditions overnight. However
models suggest most locations keep their dew point depressions
greater 1-2F. Thus some isolated fog will be possible, but not
worthy of a mention other than here. Given the dew points in the low
to middle 40s, ongoing lows in the lower 40 appear on the mark.

&&

.Short Term...(This evening through Saturday)
Issued at 303 PM EDT Fri Oct 20 2023

* Cloud Coverage Diminishing Into The Evening
* Gusty Winds Tomorrow

Rest of Today...

A deck of stratus clouds on the backside of an upper level trough
remains draped across most of Indiana this afternoon. While there
have been occasional breaks in the cloud coverage, clearing has been
a bit slower than originally anticipated, with only far SW portions
of the forecast area consistent seeing enough sunshine to warm up.
While afternoon highs in Knox and Daviess Counties may cross the 60
degree threshold, the majority of the forecast area will be
relegated to the 50s.

A few forecast models have picked up on the potential for a few
showers to develop within the forecast area this afternoon amidst
wraparound cyclonic flow and supportive 500mb vorticity fields. It
is plausible that these models are picking up on the addition of
moisture to the column from a NW wind blowing over Lake Michigan,
but observations discount the magnitude of such advection. While
Recent IND ACARS soundings have depicted surface based parcels,
marginal lapse rates and a subtle subsidence inversion aloft will
limit both potential and coverage. Chance PoPs were added for areas
north and east of the Indy Metro to account for this, and the recent
development of a few showers in a broken line from Muncie to
Shelbyville supports this thinking.

This intrusion of dry air in the column is contributing with the
gustiness this afternoon, particularly as mixing process take effect
in accordance with the diurnal cycle. These effects are particularly
noticeable on the edge of the cloud deck. Gusts of up to 25mph are
plausible this evening, but winds should decrease in intensity
overnight as the diurnal cycle takes effect.

Tonight...

It appears that the parent upper level responsible for the forecast
area has finally started moving, and clearing should progress
through the forecast area. However, the approach of another low
pressure system should reintroduce some clouds to the sky around
daybreak and shift winds to a southerly direction overnight. These
southerly winds will inhibit any potential patchy fog formation, as
they are likely to hover just around 5mph. However, dewpoint
depressions will remain on the edge of favorable fog formation
values, and observational trends will need to be monitored
overnight accordingly. Expect overnight minimum temperatures in the
lower 40s.

Tomorrow...

As this second upper level feature approaches the area tomorrow, a
few showers appear possible in far northeastern portions of the
forecast area. Not only is this feature less amplified than the
feature that caused today`s extensive cloud coverage, but it is also
comparatively starved for moisture. This system is still expected to
produce clouds northeast of the I-74 corridor, but anticyclonic
vorticity advection and dry air over the southern half of the
forecast area should limit the spatial extent of this. The most
interesting portion of Saturday`s forecast is the winds; it could be
quite gusty at times on Saturday afternoon amidst the diurnal mixing
process. Strengthening winds aloft on the backside of this feature
could work with this mixing process to produce gusts up to 30 MPH in
magnitude. Sustained winds will approach 15mph tomorrow evening in
accordance with the tightening pressure gradients, so interests with
outdoor activities planned for Saturday evening should take note of
this gustiness.

&&

.Long Term...(Saturday night through Friday)
Issued at 303 PM EDT Fri Oct 20 2023

All ensemble clusters generally agree on mean ridging and anomalous
midlevel heights next week across the eastern half of the country
next week. This will be a warm pattern for Indiana.

Preceding this will be a weak mid-upper shortwave trough that will
cross Saturday evening. The primary thermodynamic modification will
be northeast of our area, with dry/subsident layer over our area
peripheral to the trough. Furthermore, moisture will be limited
(PWAT generally ~75% of climo). Can`t rule out a passing shower
across the northeast third of the area Saturday evening and early
Saturday night, but the probability of measurable amounts at any one
location is quite low.

As this shortwave trough departs, midlevel heights will rise quickly
and a warming trend will start. The most anomalous temperatures
won`t arrive until Tuesday since the most pronounced lower
tropospheric warm plume will lag the Monday diurnal cycle slightly.
Temperatures Tuesday should be around 10 degrees above mid-late
October climatology.

Differences in medium-range deterministic and ensemble guidance
emerge for the latter portion of next week. Relative to the GFS, the
ECMWF/EPS camp is more suppressed with eastern ridge. GFS/GEFS shows
an entirely different synoptic signal upstream in the west and
eventually a seasonally strong mid-latitude system at least
approaching the area late next week. In contrast, ECMWF/EPS is lower
in latitude with frontal intrusion and shows a positively tilted
potentially anafrontal rain scenario Wednesday into Thursday. The
best course of action for now is to retain low-Mostly Clear and cool overnight

Surface analysis this evening shows low pressure in place over Ontario, providing broad cyclonic flow across the eastern Great Lakes and northeast Indiana. High pressure was found centered over the southern plains, with a ridge axis stretching northward across Illinois to Central WI. This was resulting in cooler northwest surface flow across Central Indiana. GOES16 shows the back edge of the cloud shield associated with the surface low over the eastern third of Indiana. This shield continued a slow departure eastward. Flow aloft was from the northwest, due to a strong ridge over the Rockies as seen on water vapor imagery. Dew points across Central Indiana were in the lower to middle 40s.

Overall, the ongoing forecast remains in good shape and no large adjustments will need to be made. Models suggest the cloud cover to the east will continue to drift east, allowing clear skies to arrive across the entirety of the forecast area. As the low departs the pressure gradient will continue to lessen, allowing winds to fall to around 5 knots through the night. Clear skies and light winds will allow for good radiational cooling conditions overnight. However models suggest most locations keep their dew point depressions greater 1-2F. Thus some isolated fog will be possible, but not worthy of a mention other than here. Given the dew points in the low to middle 40s, ongoing lows in the lower 40 appear on the mark.



hxgckj to mid-range precipitation probabilities for a broad time
period late next week, and refine in subsequent forecasts as
ensemble spread narrows.

The Day 8-14 period appears to by synoptically active. There`s some
signal for the first cold intrusion of the season, but also
conflicting signals of a continued warm pattern. Spread is just too
large to see a higher probability scenario to communicate at this
time.

&&

.Aviation...(00Z TAF Issuance)
Issued at 616 PM EDT Fri Oct 20 2023

Impacts:

* VFR Conditions expected this TAF Period.
* Gusty Winds expected Saturday afternoon.

Discussion:

Weak ridging across the region tonight will provide subsidence
across Central Indiana tonight and much of Saturday. GOES16 shows
the back edge of cloud cover stretching from a Chicago...IND to SDF
line, slowly sliding eastward as the large cyclone to east gradually
departs. This will lead to VFR Conditions and clearing skies this
evening. Forecast soundings tonight and Saturday show a dry column.

A quick moving surface low, almost clipper like,  is expected to
push to Central Indiana by Saturday afternoon. This will result in a
strengthening pressure gradient across the area and gusty winds. The
system appears moisture starved, thus VFR conditions are expected to
continue.


&&

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

$$

Update...Puma
Short Term...Marcus
Long Term...BRB
Aviation...Puma