Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/28/22

Area Forecast Discussion

National Weather Service Indianapolis IN

 1005 PM EDT Tue Sep 27 2022

.Forecast Update...
Issued at 1005 PM EDT Tue Sep 27 2022

No major updates to the forecast this evening. Some minor changes to
reflect cloud cover and resulting temperature impacts. Clouds have
largely dissipated over the region after sunset, and widespread
stratocumulus remains well to our north. Guidance continues to bring
this area of clouds southward into central Indiana. Trimmed back
cloud cover before 04Z based on recent satellite obs. Nudged
temperatures down a bit to reflect a few more hours of clear skies
and relatively light winds. Increased winds and temps slightly
underneath the advancing cloud layer beyond 04Z. Otherwise, forecast
remains on track and another chilly night is in store.

&&

.Short Term...(This evening through Wednesday)
Issued at 251 PM EDT Tue Sep 27 2022

* Seasonably cool temperatures through the week

* Breezy conditions this afternoon diminish after sunset

A deep upper level trough will continue to slowly make eastward
progress across the region tonight through Wednesday morning, with
at least one embedded shortwave noted in satellite imagery. At the
surface, high pressure will continue to build into the region from
the north while a broad surface low over southern Canada continues
to pull away.

ACARS soundings depict a fairly deep, well-mixed boundary layer this
afternoon along with convective temperatures being reached resulting
in blustery conditions across Central Indiana. 17z Observations
show gusts have reached up to 25kts at many sites so far this
afternoon. Gusty conditions should continue through around sunset
when mixing wanes. Due to a tight pressure gradient from the
departing surface low and incoming high, winds may remain slightly
elevated overnight around 3 to 7 kts regionwide. A similar diurnal
wind trend is expected Wednesday afternoon as the pattern remains
very similar to today. With high pressure sinking southward, the
pressure gradient will slightly weaker tomorrow and winds should be
out of the northeast instead of northwest. Still expect gusts of 15
to 20kts tomorrow afternoon as forecast soundings show a mixed layer
up to 6kft allowing stronger gusts to mix to the surface.

As flow veers and become northerly overnight, expect a fetch of
moisture off of Lake Michigan to enhance cloud cover locally.
Current satellite imagery shows a fetch of clouds extending from NW
to SE coming off of Lake Michigan into northern Indiana. Latest runs
of the RAP and HREF show this band becoming more N to S oriented and
making its way through Central Indiana overnight. Also, with
temperatures falling near dew points overnight, this band of clouds
may expand and contribute to areas of lower stratus clouds forming.
Expect clouds to break up and rise after sunrise tomorrow becoming a
scattered cu deck by Wednesday afternoon as the boundary layer warms
inducing mixing.

Temperature forecast tonight largely depends on how widespread cloud
cover is from the fetch coming off of Lake Michigan. A few sites
this past morning dipped just below 40 for the first time this
season. Conditions Wednesday morning however may not be optimal for
radiational cooling with increased clouds and elevated winds
overnight. Therefore keeping morning low temperatures almost the
same as last night. The only area of concern for temperatures
dropping below 40 is the SW portion of the area from Bloomington to
Bedford to Vincennes where winds may be lower and cloud cover should
be less. Not concerned with frost as the lowest temperatures in any
sheltered area or valley will be around 37 to 38 degrees, and even
then temperatures that low will not be widespread.

&&

.Long Term...(Wednesday night through Tuesday)
Issued at 251 PM EDT Tue Sep 27 2022

* Cool and dry through Friday.

* Chance for tropical remnants to impact portions of the area early
  in the weekend.

The beginning of the long term will be dictated by an amplified
ridge over the Midwest. This ridge will tap into cool Canadian
Plains air, and transplant it into the Ohio Valley through moderate
NW flow. By Thursday, relatively high pressure will encompass the
Ohio Valley through CAA enduced mid level height rises. This should,
creat broad subsidence over the region clearing skies. The pattern
will be fairly progressive though with central Indiana in the
upstream portion of the ridge this weekend. Temperatures will be in
the mid 60s Thursday, gradually increasing into the upper 60s and
low 70s Friday.

The main forecast problem for the early portion of the long term
will be the possibility of frost Wednesday night. High pressure and
the bulk of the cold air mass should lead to the coldest
temperatures of the week. The clear skies and light winds will allow
the near surface layer to decouple, dropping surface temperatures
near the dew point. Current expectation are for lows in the mid to
upper 30s, with a few SW locations staying above 40.

More uncertainty is added for the weekend forecast with the
possibility of tropical remnants from Hurricane Ian. As of this
issuance, rain is still not in the forecast for Saturday and slight
chances have been included for SE central IN Sunday. However this
could change depending on Ian`s track into the CONUS. A few ensemble
members have the parent upper level low tracking near central
Indiana, of which would significantly increase cloud cover and
introduce the possibility of rain, but with the upper level ridge
axis expected just east of central Indiana, this should limit
north/westward progression. The remnants could also have a large
influence on high temperatures this weekend; current expectations
are for highs in the low to mid 70s.

&&

.Aviation...(00Z TAF Issuance)
Issued at 746 PM EDT Tue Sep 27 2022

Impacts:

* Brief periods of MVFR ceilings possible overnight into the morning
  hours.

Discussion:

Gusty winds out of the west-northwest, with gusts around 25 kts,
will continue to diminish this evening. A light breeze around 5 to
10 kts is expected to persist overnight, given a weakening but still
tight pressure gradient across Indiana. Surface high pressure will
traverse the Great Lakes from west to east, turning our winds more
northerly as it passes by. This northerly flow may allow an
extensive stratocumulus deck to our north to move southward.
Ceilings should be mainly within VFR levels but could briefly dip to
MVFR. A few sprinkles may occur near LAF, though chances are too low
to include in the TAF. Breezy conditions could return after sunrise
on Wednesday, but not as strong as they were today due to the
approaching surface high. Peak gusts may reach 15 to 20 kts during
the afternoon.


&&

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

&&

$$

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