Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/05/23
Area Forecast Discussion
National Weather Service Indianapolis IN
958 PM EDT Tue Jul 4 2023
.Forecast Update...
Issued at 958 PM EDT Tue Jul 4 2023
No changes to the forecast as everything remains on track. Isolated
showers that developed earlier this afternoon have been diminishing
quickly since sunset. This trend is expected to continue, with some
lingering low to mid-level cloud cover persisting into the night.
Winds should decrease as well now that boundary layer decoupling is
ongoing. A few places may see some patchy fog develop by morning,
especially across the southern portion of our CWA. Most likely
places to see fog are near rivers and in open areas / fields.
&&
.Short Term...(This evening through Wednesday)
Issued at 244 PM EDT Tue Jul 4 2023
* Isolated storms during the afternoon/evening today & tomorrow
* Seasonably hot and humid
.This evening and tonight...
Typical summertime weather pattern is in place today across Indiana
with weak, relatively zonal flow aloft and surface high pressure
just south of the region. Latest satellite and radar imagery shows a
cu-field over most of the area as afternoon heating has resulted in
low level mixing. Subtle lift ahead of a weak upper disturbance
within the upper level flow combined with a very warm and humid
airmass has resulted in isolated thunderstorm develop this
afternoon. Latest IND ACARS soundings does show steep low level
lapse rates and upwards of 2000+ j/kg CAPE across the area
supporting thunderstorm development. However, weak flow and
significant dry air through the column and weak forcing will keep
thunderstorms widely scattered and short lived. Most locations will
remain dry; however any storm does have the potential to produce
brief heavy rain and lightning. Outside of any convection,
temperatures this afternoon will make a run for the 90 degree mark.
Another mild and humid night is expected across the area tonight,
with dewpoints and lows remaining in the 60s to near 70 and
additional patchy fog possible in areas that received rainfall
recently.
.Wednesday...
Hot and humid summertime pattern continues into the middle of the
week with storm chances increasing Wednesday night.
Broad troughing over the Northern Plains shifts eastward Wednesday
with a surface cold front approaching from the west after sunset
tomorrow night. High pressure shifts eastward as well placing
Indiana in a region of southerly flow and continued warm and moist
air advection ahead of the front. Expect another hot day with highs
climbing into the upper 80s to lower 90s with dew points in the
upper 60s to lower 70s.
With an approaching upper trough and surface front, chances for
storms increasing Wednesday afternoon and evening. See the long term
section for more information on the potential severe weather threat
Wednesday night. The short term section will focus on the
thunderstorm threat Wednesday afternoon and evening before sunset.
During the day tomorrow, the cold front and greatest forcing will
remain well to the west towards IL, MO, and IA with Indiana in the
broad warm sector. Forecast soundings for tomorrow afternoon
indicate steep low level lapse rates with mixing heights above 5
kft, increasing moisture in the low and upper levels through the
day, and SBCAPE ranging from around 1200 j/kg in the east to over
3000 j/kg along the IL/IN border. Even with afternoon mixing, expect
dew points in the upper 60s to low 70s across the region. The hot,
humid airmass will be sufficient for isolated thunderstorm
development tomorrow afternoon; however very weak flow through the
column within a weakly forced environment will likely limit storm
coverage and longevity. Keeping 20-30 PoPs for the 18-00z timeframe
as afternoon convection is expected in such a hot, humid, and
unstable environment. Currently not expecting severe weather during
this time frame, however a brief strong wind gust could be possible
as storms become top heavy and collapse. Overall, most locations
should stay mainly dry through the daytime hours tomorrow.
&&
.Long Term...(Wednesday night through Tuesday)
Issued at 244 PM EDT Tue Jul 4 2023
* Storms possible Wednesday night into Thursday...then again from
Saturday evening into early next week
* Seasonably cool through much of the period
A deep upper low tracking across central Canada will serve as a
prominent feature through the beginning of the extended. First in
aiding in increased chances for convection late Wednesday into
Thursday, and second in keeping temperatures largely pleasant and
slightly cooler than normal beginning Thursday and continuing into
next week.
As mentioned in the short term, central Indiana will be squarely in
the warm sector of a weak mid latitude cyclone. Modest elongated CVA
upstream of the trough should help initiate a more organized line of
convection Wednesday afternoon to our west, progressing towards
central Indiana in the evening. Current CAMs have the line reaching
the Wabash Valley around 10PM. Looking at the dynamic profile of the
environment ahead of the convection, low to mid flow will be near
non-existent. This along with a fairly saturated column should limit
cold pool strength and eventually lead to a cold pool/shear
imbalance as the system reaches central Indiana. For this reason,
any severe risk will be marginal, with the outlying wet-microburst
induced damaging wind gust as the main threat. Regardless of
severity, it looks likely that most of central Indiana will witness
light rainfall within showers and thunderstorms after sunset
tomorrow with rainfall totals up to around 0.25".
This system wont be quite as progressive as MCSs last week, but
should still move out well in front of the parent cold front. Where
this cold front ends up Thursday will determine where and for how
long rain chances can be expected over central Indiana. In general,
expect most areas west of I-69 to be mainly dry in the afternoon,
with areas east of I-69 slowly reducing rain chances through the
afternoon. Deep instability will once again be present out ahead of
the cold front and therefor high topped convection and subsequently
a few strong thunderstorms could be possible in far E/SE central
Indiana in the afternoon; although, the current expectation is for
thunderstorms to remain sub-severe.
Behind the cold front, temperatures, as expected, will fall with
highs continuously in the low to mid 80s for Thursday through
Saturday. Surface high pressure will build behind the front through
height rises beneath CAA, leading to dry conditions Thursday evening
through portions of Saturday.
SW flow returns Saturday, but there is still lots of uncertainty as
to the magnitude and timing of return flow. This creates some
uncertainty for rain chances, of which begin as early as Saturday
afternoon. Trends are tipping towards a mostly dry forecast on
Saturday with subsidence induced dry air limiting moisture
progression until Saturday night, but this could still change in the
coming days.
By Sunday, low to mid level moisture should be enough for scattered
diurnal convection. The main synoptic forcing looks to be delayed
until Sunday night/Monday, where coverage of showers/thunderstorms
is likely to increases. The overall airmass will likely be slightly
warmer and more humid Sunday and Monday, but given uncertainty of
cloud cover and rainfall coverage high temperatures could vary
significantly.
&&
.Aviation...(00Z TAF Issuance)
Issued at 736 PM EDT Tue Jul 4 2023
Impacts:
* VFR flying conditions through 00z.
* Slight chance of showers and storms after 00z.
Discussion:
VFR flying conditions are expected this evening through tonight.
Very isolated showers formed this afternoon, near IND for instance,
and these are in the process of dissipating. Lingering low to mid-
level clouds could persist on and off into the night, however. Winds
are already diminishing across the region, and should remain under
5kts through 12z. There is a very slight chance of patchy ground fog
by morning that could briefly lead to reduced visibilities. Any fog
will quickly dissipate after sunrise.
After sunrise, daytime heating should allow the winds to pick back
up a bit to around 5-8kts. Direction should be southerly for the
most part, beginning out of the south southeast before settling to
either southerly or slightly south southwesterly. Additionally,
heating will allow for the formation and expansion of low-level
cumulus which may attain SCT coverage at times.
A slight chance of showers and thunderstorms returns late tomorrow,
after about 00z, from the northwest due to an approaching cold
front. All terminals may see a shower or storm after sunset, but due
to uncertainties with timing and intensity these will not be
explicitly mentioned in the TAFs for now. Guidance generally shows a
weakening trend as the convective activity advances into Indiana.
&&
.IND WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
Update...Eckhoff
Short Term...CM
Long Term...Updike
Aviation...Eckhoff
Area Forecast Discussion
National Weather Service Louisville KY
944 PM EDT Tue Jul 4 2023
.Forecast Update...
Issued 944 PM EDT Tue Jul 4 2023
Current forecast remains in good shape this evening. Satellite
imagery reveals partly cloudy skies with temperatures in the middle
to upper 70s. Very isolated convection has continued to diminish
this evening and much of the overnight continues to look dry. We`ll
see some patchy fog in the eastern river valleys. The PBL looks to
become quite stable overnight and we`re going to continue to carry
some smoke in the grids due to all the firework festivities this
evening. Visibility may be reduced in spots for a time this evening.
Otherwise, dry conditions are expected across the vast majority of
the region. Can`t rule out a stray shower or two across the far
south toward dawn Wednesday.
&&
.Short Term...(This evening through Wednesday)
Issued at 240 PM EDT Tue Jul 4 2023
The atmosphere has become modestly unstable this afternoon (1000-
1500 J/KG ML CAPE), and showers and storms have popped in two
separate areas. The first is roughly along and north of the I-64
corridor, with the second area across south central KY. These areas
are associated with slightly higher PWAT airmasses, with a relative
minimum across the rest of central KY. Overall, there isn`t much of
a trigger, however new convection will continue to fire off remnant
outflow from showers that have already developed through the
afternoon and early evening. Weak pressure pattern will remain in
place with light winds through quite a deep layer. Boundary layer is
still warm and moist, but PWAT values are fairly modest for this
time of year due to relatively dry mid-level air. Can`t rule out a
stray pop-up in the heat of the afternoon, but south-central
Kentucky is the only area with probabilities high enough to mention
even a slight chance. Otherwise expect a warm and muggy holiday,
pretty well in line with seasonal normals. Best chance of touching
90 this afternoon will be in south-central Kentucky, and in the
urban heat island of Metro Louisville.
Forecast soundings have been verified by recent AMDAR soundings into
and out of SDF that show a notable subsidence inversion around 600
mb. Outside of that, the sounding has a fairly dry and unstable
look, however this inversion will keep any updrafts from getting too
frisky above 15-20 K feet. Despite the inversion, DCAPE values are
sitting around 1000 J/KG in the drier airmass, and this is yielding
some notable gusty signatures both evident in t-storm outflow, and
in velocity signatures off TSDF/TCVG TDWRs. Don`t think we are
getting much of 30 mph out of any collapsing storm, but again this
is enough to trigger new development. Most of the convection will
stay in shower form due to the inversion limiting vertical depth,
but can`t rule out a few thunderstorms either.
Convection should diminish with the loss of heating, but still can`t
rule out a few cells overnight. We`ll likely see some patches of fog
once again, especially in eastern River Valleys, but added lingering
smoke from fireworks may cause the fog to be a bit worse in spots.
Wednesday should be mostly dry during the daylight hours with the
lack of a notable trigger in the area. As a result, temperatures
should warm in the upper 80s to around 90. Much like today, can`t
rule out an isolated to widely scattered shower or storm in the
afternoon, but overall the better activity isn`t expected to arrive
until later Wednesday night or Thursday morning.
.Long Term...(Wednesday night through Tuesday)
Issued at 305 PM EDT Tue Jul 4 2023
Summary:
- Seasonably warm and muggy with varying daily shower and
thunderstorm chances Thursday through the weekend
Discussion:
On the synoptic scale, medium-range model guidance is in relatively
good agreement over the next 3-7 days. Upper ridging extending from
north central Mexico into the Four Corners regions will gradually
slide westward over the weekend into the first half of next week
while an upper low descends from its current position north of
Hudson Bay into northern Ontario. As the upper low shifts southward,
shortwave troughs will intermittently swing along the southern flank
of the large-scale low, bringing attendant sfc frontal systems
through the north central and northeastern United States.
Even though the overall pattern will amplify as we head into early
next week with deeper troughing over the eastern one-third of the
CONUS, stronger flow aloft will remain confined to the Upper Midwest
and central/eastern Canada, which is typical for this time of year.
As a result, the pattern should be fairly cyclical, with decaying
frontal boundaries bringing increased chances for afternoon
showers/thunderstorms every 2-3 days as an upper shortwave swings
through. In between these passing systems, daily precipitation
chances will be reduced; however, no system looks resilient enough
(at this time) to clear out what will be a typically muggy
summertime air mass. As a result, at least low-end PoPs will need to
be continued through much of the extended forecast period as
instability should be sufficient for at least an isolated
shower/storm despite weak deep layer shear.
Additionally, given greater uncertainties associated with shortwave
disturbances, forecast confidence on timing with any one disturbance
is relatively low. Generally speaking, better chances for showers
and storms are expected on Thursday, with a relative lull Friday and
most of Saturday. Subsequently, guidance is hinting at another
disturbance for Saturday night through Monday, with different model
families varying by 12-24 hours on timing. As a result, think
current broad-brush chance to likely PoPs may be too high for
several of these days, but it will take additional refinement from
subsequent model runs to be able to key in on the most likely
windows for rain next weekend. Temperatures will remain seasonably
warm and muggy, with highs in the 80s and lows ranging from the mid
60s to the lower 70s.
&&
.Aviation...(00Z TAF Issuance)
Issued at 708 PM EDT Tue Jul 4 2023
IMPACTS:
- Fireworks likely to produce restrictions to vis at KSDF tonight
DISCUSSION:
Widely scattered convection continues to diminish across
northeastern KY this evening. Current thinking is that this
activity will not affect the KLEX terminal. Main forecast issue
this evening will be a likely reduction in visibilities at KSDF due
to expected fireworks across the metro area. Elsewhere, MVFR vsbys
will be possible at the terminals late tonight into Wednesday
morning with light and variable winds. The outlook for Wednesday
calls for VFR conditions across the region.
CONFIDENCE:
Medium to high on all elements.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&
$$
Update.......MJ
Short Term...BJS
Long Term....CSG
Aviation.....MJ