Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 03/22/23
Area Forecast Discussion
National Weather Service Indianapolis IN
1025 PM EDT Tue Mar 21 2023
.Forecast Update...
Issued at 1025 PM EDT Tue Mar 21 2023
A few changes made to the forecast with this evening`s update.
Latest IND ACARS soundings shows that the atmosphere has fully
saturated down to the surface as light rain spreads across Central
Indiana. The antecedent environment was much drier than what
guidance suggested it would be this evening as dew points remained
in the teens for many locations up until the past couple hours. This
will likely result in rainfall totals through the night being a bit
lower than anticipated; however the rainfall tonight is almost
negligible compared to what is in the forecast Thursday - Saturday.
See the Long Term and Hydrology sections of the discussion for more
details on the heavy rain threat for the end of the week.
Nudged winds down a bit for the overnight hours as the low levels
stabilize with rainfall and nocturnal cooling. Despite an increasing
low level jet, mixing has shut off since sunset and the gradient
remains relatively weak with the main area of low pressure still
back in the Plains. Depending on how much heating occurs tomorrow,
winds may need to be lowered even more for that time period.
Moisture and low clouds trapped under the inversion may limit the
amount of heating that takes place in the boundary layer, resulting
in lighter winds and lower temperatures. Nudged high temps down a
few degrees to account for low stratus likely persisting through
tomorrow.
&&
.Short Term...(This evening through Wednesday)
Issued at 220 PM EDT Tue Mar 21 2023
* Breezy conditions with gusts to around 20kts this afternoon
* Rain arrives this evening
Rain Potential
High clouds have been gradually increasing throughout the night so
far, and will continue to do so going forward as additional moisture
streams in aloft. The moisture stream is rather deep, with high-
level moisture originating out of the eastern Pacific and low-level
flow out of the Gulf of Mexico. As such, cloud cover should increase
in coverage and thicken with time. Isentropic ascent associated with
ongoing warm air advection should allow rain to develop by late in
the day.
Rainfall should be light, despite the deep moisture. Dry air remains
in place below 850mb. Developing rain showers will eventually be
able to overcome the dry air, but it will take time, and should cut
back on amounts somewhat. Additionally, favorable dynamics remain
far to the north and west, thus limiting lifting to primarily the
warm advective processes. Model soundings show lingering low-level
moisture after the first batch of rain exits off to the east. The
NAM soundings in particular shows the classic drizzle profile after
about 10-12z Wednesday morning. Therefore, one can expect damp and
dreary conditions to persist through the end of the short range.
Winds
Besides the rain, breezy southerly winds may also be present at
times today with a fairly tight MSLP gradient over the region. The
gradient should relax a bit today, but enough sunshine should make
it through the increasing cloud cover early on to promote some low-
level mixing. Winds aloft are not terribly strong, and so am not
expecting gusts over 25kts today. However, gusts around 20kt are
certainly possible. Gusts should diminish as the rain arrives and
the low-levels quickly stabilize. The MSLP re-tightens after about
02-04z allowing a southerly wind around 10kts to persist.
Temperatures
The efficient mixing should allow temperatures to easily exceed 50
degrees today. Temperatures should then drop rather quickly as the
rain sets in, due to the substantial low-level dry air and
evaporative cooling. Based on model soundings, a quick dip to around
40 degrees is possible upon rainfall onset. This should be followed
by a gradual rise during the overnight hours as the southerly winds
allow warm air advection to continue. Therefore, lows should occur
early in the night.
&&
.Long Term...(Wednesday night through Tuesday)
Issued at 220 PM EDT Tue Mar 21 2023
*Heavy rain and flooding Thursday into Saturday
Wednesday Night Through Saturday.
An active weather pattern will be in place for much of the long term
period with scattered showers ongoing Wednesday night. Synoptically
things look fairly innocuous initially with a slow moving frontal
boundary across southern Wisconsin and northern Illinois early
Wednesday night. Storms are likely along the frontal boundary with
the potential for some elevated hail, but think the majority of the
storms will remain north and west of the forecast area. Flow aloft
is fairly zonal with a more pronounced trough across southern
Canada. Strong southerly flow will feed into the sinking frontal
boundary late Wednesday night through Thursday night which will be
the catalyst for the first round of heavy rain Thursday night into
Friday.
The aforementioned flow will push PWATs well over an inch with a warm
and saturated temperature profile. A long but narrow axis of heavy
rain will then dump 2-3 inches of rain from central Oklahoma through
Indiana and into Pennsylvania by Friday morning. A few rumbles of
thunder are expected, but models have pretty consistently kept the
lapse rates very marginal with only slightly favorable dynamics in
the wind field. Any severe threat would be mid to late afternoon and
across southern Indiana. This potential is also dependent on the
front remaining to the north in this timeframe which isn`t certain.
Focus then shifts to the potential for a second round of heavy rain
which confidence is gradually increasing may impact the southern
counties. Models have come closer into alignment on the development
of a trough that will eject from eastern Colorado Friday evening and
deepen close to 1mb/hr over the next 24 hours as it pushes into the
Upper Midwest. The heavier axis of precipitation will likely be
south of the forecast area, but the general trend has been northward
of late with the TROWAL axis possibly impacting the northwestern
counties as well. Temperatures will be too warm for snow, but
another lesser axis of rain looks probable across Illinois and
northwestern Indiana by Saturday morning. Cyclonic flow in the
aftermath of this system isn`t quite as robust, so not expecting as
long of a period of lingering light rain in the aftermath of the
heavier precipitation.
Details on the QPF forecast and impacts will be covered in the
hydrology section at the bottom.
Sunday Through Tuesday.
Conditions look generally dry and seasonable for Sunday before the
next potential rain producing system arrives early next week. Models
remain all over the place with the development of another potential
robust low while other models are not showing as robust cyclogenesis
with lesser amounts of rain. Light snow may mix in Monday night
into Tuesday as the surface flow becomes more northwesterly, but
questions remain on how cold the air will be and how the warmer
weekend weather may impact snow accumulations.
&&
.Aviation...(00Z TAF Issuance)
Issued at 735 PM EDT Tue Mar 21 2023
Impacts:
* Wind gusts around 15-25 kts this evening, diminishing late
* Rain and MVFR conditions arriving around 03z
* IFR ceilings expected from late tonight through much of the
period tomorrow with drizzle
Discussion:
Deteriorating conditions expected this evening through tomorrow as
rain and lower clouds move into Central Indiana.
Wind gusts of 15 to 25 kts expected to continue over the next few
hours as low level lapse rate remain steep resulting in stronger
winds aloft mixing down to the surface. While sustained winds may
remain elevated around 10 kts overnight, gusts should diminish late.
Light rain has already pushed into Indiana from the southwest and
has reached KHUF and KBMG. Light rain will slowly push northeastward
over the next few hours. Ceilings have been slow to fall as the
environment still remains drier than what guidance shows. Expecting
VFR ceilings to persist over the next couple hours; however expect
MVFR ceilings after 03-05z, then IFR ceilings towards sunrise
tomorrow. MVFR to IFR ceilings expected to persist into the day
tomorrow as a low level inversion keeps low stratus and moisture
trapped near the surface. Visibility expected to drop to 5-6SM with
light rain this evening. Lower vis likely late tonight into tomorrow
morning due to lower stratus and areas of drizzle.
&&
.Hydrology...
Issued at 220 PM EDT Tue Mar 21 2023
* Flooding expected Thursday night into the weekend
Potential for flooding arrives Thursday evening into the overnight
hours with very heavy rain expected as a frontal boundary drifts
south through central Indiana. While model differences remain
regarding the specific location of the axis of heaviest rainfall,
confidence is high on impactful rain amounts across south central
Indiana. Probabilistic output puts the potential for at least 2
inches of rain nearly 100 percent across southern Indiana
The heaviest rainfall with the second portion of the event is likely
to focus to the south and east of central Indiana Friday into Friday
night, but models continue to trend the low pressure system and
leftover front further north which puts the southern counties within
axis for a potential second round of heavy rain.
Probabilistic output puts the potential for at least 2 inches of
rain nearly 100 percent across southern Indiana between the two
events and a 40-50% chance for amounts in excess of 4 inches. This
looks reasonable with the 2 impactful systems, but think that the
bigger threat and more widespread rain will come from the first
event.
MMEFS ensembles show that widespread minor river flooding is likely
across most of central Indiana with the potential for moderate
flooding across the lower Wabash Valley where the heaviest rainfall
is currently progged. In addition to river/stream flooding, flash
flooding is possible along with more widespread flooding of low
lying and flood prone areas.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Update...CM
Short Term...Updike
Long Term...White
Aviation...CM
Hydrology...White