Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/19/23

Area Forecast Discussion...UPDATED

National Weather Service Indianapolis IN

 906 PM EDT Tue Apr 18 2023

.Forecast Update...
Issued at 906 PM EDT Tue Apr 18 2023

No changes to the Frost Advisory configuration across northeast
portions of our area. Gradient may be enough for winds to pick up
slightly toward dawn, but prior to that calm winds and good
radiative conditions are expected to support a shallow radiative
inversion and temperatures cold enough for some frost.

Tomorrow`s forecast temperatures appear too low (typical bias of a
shift toward strong southwesterly winds and adequate PBL mixing in
models). We raised temperatures a degree or two.

&&

.Short Term...(This evening through Wednesday)
Issued at 300 PM EDT Tue Apr 18 2023

* Frost Advisory for portions of North Central Indiana tonight

* Much warmer and windier tomorrow with highs nearing 80 degrees

.This evening and Tonight...

Current surface analysis late this afternoon shows clear skies across
Central Indiana as an elongated area of high pressure is directly
overhead. Latest IND ACARS sounding shows a strong subsidence
inversion around 1 km agl with a mixed layer below it. This
inversion has kept a strong 40+ kt low level jet from mixing down to
the surface this afternoon. Mixing within the PBL has lead to some
stronger gusts of 15 to 20 mph at the surface mainly along and north
of the I-70 corridor.

For tonight, elongated area of high pressure begins to push eastward
as a developing system in the Plains pushes a warm front into SW
Indiana. This will result in a sharp SW-NE temperature gradient
across the state with lows ranging from near freezing in Randolph
County to near 50 in Knox County. Have issued a Frost Advisory from
Carrol County to Henry County and points north and eastward from 1
AM to 9 AM EDT for the potential for frost tonight. This area will
be closest to the center of the surface high with optimal conditions
for radiation cooling overnight. Further south and west, higher
clouds will begin to advect northward ahead of the warm front and a
tightening easterly pressure gradient may keep winds slightly
elevated overnight. This will keep low temperatures quite a bit
warmer, especially across SW Indiana. Lower confidence does exist in
the southward extent of the frost potential. Lows last night went
quite a bit below guidance as optimal radiational cooling conditions
lead to many areas dropping to or below freezing. Potential is there
for some counties north and east of the I-74 corridor and south of
the current Frost Advisory to dip into the mid and upper 30s before
winds and higher clouds move in, but confidence in frost is not high
enough there to warrant an advisory. Thinking much of Marion County
will be safe from frost as the urban heat island effect and light
easterly winds will keep temperatures elevated enough.

.Wednesday...

Warm front pushes north of the region tomorrow with strong warm air
advection leading to temperatures quickly rising into the 70s by the
afternoon hours. Best moisture and forcing for ascent remains west
of the region in Illinois, so not concerned with thunderstorm
potential as the front moves northward. Expect high clouds overhead
through the day, especially if storms form in Illinois and their
anvils drift into the region. Southerly winds pick up as well during
the afternoon as deep mixing occurs into a strengthening 40 kt low
level jet. Expect gusts around 20 to 30 mph during the afternoon
hours, with the strongest winds west of the I 65 corridor, where the
strongest pressure gradient and higher winds aloft are located.

&&

.Long Term...(Wednesday night through Tuesday)
Issued at 300 PM EDT Tue Apr 18 2023

* Warm up through Thursday

* Showers and storms return late Thursday into Friday

* Cooler weather returns this weekend into early next week

Wednesday Night through Friday...

Warm dry conditions are expected early in the period as upper
ridging and S/SW surface flow remains. A more active pattern is
expected late week with a deep trough across the Rockies ejecting
eastward. Increasing S/SW surface flow ahead of an approaching
surface low associated with the trough will advect moisture
northward and help warm temperatures into the low 80s Thursday.
Moisture will increase to some extent, but not as broadly as the
previous warm up. Models suggest subsidence induced dry air will
advect northward towards Indiana. The dry air should enhance diurnal
mixing. With a strong LLJ moving overhead and a tightening pressure
gradient, windy conditions are likely. Winds could gust up to 40 mph
from late morning to the early evening hours. In addition, daytime
mixing will likely drop RH values to around 20-30%. 10-hour fuel
moistures are high across central Indiana, but dry weather over the
next few days could lead to elevated fire conditions.

By Thursday evening, a cold front associated with the aforementioned
system will begin to push into far western portions of the area. A
narrow zone of moisture advection ahead of the boundary combined
with low-level convergence and increasing large-scale ascent will
allow for a line of showers and thunderstorms to develop. Forecast
soundings show very weak instability across central Indiana which
should limit severe weather potential. However, strong low-mid level
flow combined with 30-35 kts of effective bulk wind shear could
produce isolated damaging wind gusts. This front is expected to
begin slowing down Thursday night and potentially stall near
southeastern portions of the area on Friday as mean flow flow
becomes parallel to it. Confidence is lower late week and into the
weekend as model ambiguity increases. Due to the front stalling,
precip chances will remain through Saturday, especially across far
southeastern counties. Guidance generally show another wave of low
pressure forming across Texas which may help to push the boundary
out by Saturday night.

Precipitation chances aside, confidence remains okay regarding
temperature trends. Regardless of the above scenarios, colder air is
expected to advect in behind the front late week. Ensemble means
show prolonged troughing over the eastern half of the US this
weekend and perhaps into next week. Therefore, a cool-down longer in
duration than the one we are seeing now is becoming increasingly
likely. Lows by Sunday morning could be down into the low to mid
30s, which would prompt some concern for frost potential as
surface high pressure looks to be overhead by then. Winds may
remain high enough to prevent frost Sunday morning but the better
chance for frost appears to be Monday morning as surface high
pressure develops.

&&

.Aviation...(00Z TAF Issuance)
Issued at 739 PM EDT Tue Apr 18 2023

Impacts:

* Winds veering from west-northwesterly to northeasterly and
  eventually southerly.

* Southerly gusts Wednesday afternoon as high as 25-30 knots

Discussion:

Winds will shift to northeasterly/easterly this evening and tonight
and then southerly tomorrow. Gradient and mixing will result in
stronger winds and gusts during the afternoon tomorrow (Wednesday).
Otherwise, VFR conditions will prevail.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
Frost Advisory from 1 AM to 9 AM EDT Wednesday for INZ021-031-
038-040>042-049.

&&

$$

Update...BRB
Short Term...CM
Long Term...Melo
Aviation...BRB