Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 03/17/23

Area Forecast Discussion...UPDATED

National Weather Service Indianapolis IN

 810 PM EDT Thu Mar 16 2023

.Forecast Update...
Issued at 810 PM EDT Thu Mar 16 2023

Periods of light rain within warm advection isentropic ascent regime
preceding the next shortwave trough will continue through the
evening. Many locations have already received up to around 0.10"
across central Indiana, with locally 0.25" particularly across west-
central and southwest portions of the area where more moderate
embedded showers have occurred. Several more hours of periodic rain
is expected. We increased amounts slightly, commensurate with HREF
mean QPF, which brings west-central and southwest portions of the
area up to around or slightly over 0.50" by morning when the rain
ends.

This is occurring ahead of a deepening closed low over the northern
Plains and phasing southern stream shortwave trough. This will force
a cold front through in the predawn hours ending precipitation.
Preceding this will be tightening MSLP gradient and increasing low-
level jet (i.e., fairly strong ageostrophic response). Wind
speeds/gusts are somewhat in question later tonight. The gradient
would support a noteworthy increase, but a deep isothermal layer,
high-centered low-level jet core, and limited mixing will probably
limit more substantial gusts. The newest version of the model blend
starting point is ironically higher than all other models, due to
overzealous bias correction. So, we have cut wind speeds back
slightly more in line with the consensus of all other guidance for
the overnight period.

Hourly temperatures were adjusted slightly. Over-performing rain and
associated evaporative cooling had countered warm advection. There
may be a rise of a degree or two later this evening as low-level
flow strengthens and upstream temperatures closer to the Ohio river
are about 5-7 degrees warmer.

&&

.Short Term...(This evening through Friday)
Issued at 304 PM EDT Thu Mar 16 2023

...COLD FRONT APPROACHES CENTRAL INDIANA TONIGHT. WIDESPREAD SHOWERS
AND WIND GUSTS UP TO 40MPH LIKELY, ESPECIALLY NEAR AND AFTER FRONTAL
PASSAGE TONIGHT...

Ahead of a quickly-progressing cold front`s overnight arrival, cloud
coverage has begun to spread across Central Indiana this afternoon.
Temperatures have been steadily climbing throughout the afternoon as
mixing brings both dry air and breezy winds down from aloft. Recent
IND ACARS soundings depict the moistening of the column above a
weakened inversion based around 900mb. This hints that the
atmosphere has not fully mixed out yet, and temperatures may rise a
few additional degrees before the sun sets later this evening.
However, the increasing cloud coverage in the middle portions of the
troposphere may serve as a limiting factor for this warming, meaning
that it is unlikely that maximum temperatures today will rise above
the 60 degree mark.

Forecast guidance continues to converge towards a fast-moving front,
meaning that the highest precipitation chances will exist between
02Z-08Z. As dry air wraps around the parent low throughout the day
on Friday and winds shift to westerly and then northwesterly
components throughout the day tomorrow, expect the forecast area to
dry out and for cloud coverage to slowly thin out heading into
tomorrow evening. Wind are anticipated to be quite gusty overnight
into tomorrow, with gusts up to 40mph plausible. Pops after daybreak
tomorrow were lowered to chance levels in accordance with the
increased confidence in a faster-moving front. QPF hovers around
half an inch of rain for the forecast area, meaning that this
rainfall is unlikely to produce any significant hydrological
impacts. While a few snowflakes cannot be entirely ruled out of the
picture at the tail end of the precipitation due to strong cold air
advection, chances of this appear low, and no significant winter
weather appears likely from the passage of this first boundary.

Perhaps the most interesting aspect of the short term forecast is
the non-traditional diurnal curve in which temperatures will follow.
As cold air seeps in from the northwest while the front pushes
through the area tomorrow, only marginal levels of heating can be
expected, and this should be limited to southeastern portions of the
forecast area. Areas in the NW are unlikely to see high temperatures
above 40, and most of the area will remain below 45 degrees
tomorrow.

In short, expect Friday to be a rather gloomy day, with blustery
winds and clouds expected for the majority of the day.

&&

.Long Term...(Friday night through Thursday)
Issued at 304 PM EDT Thu Mar 16 2023

* Winter-like temperatures and the chance for light snow this weekend
* Warming trend beginning early next week

.Friday night - Sunday...

Long term begins with another cold snap incoming for the weekend
across Central Indiana. Area of low pressure late Friday night into
Saturday pulls northward into Quebec while the mid and upper level
trough hangs back around the northern Great Lakes. A mid and upper
level wave on the backside of the trough pushes south early Saturday
morning in the form of an arctic front at the leading edge of a
frigid incoming airmass. Potential is there for scattered snow
showers to develop as this boundary pushes through from the north
and latest guidance has come in a bit more aggressive with the snow
shower potential. Hi-res RAP guidance shows a 150 kt upper jet
streak developing in Southern Indiana placing much of the state in
an area of enhanced lift in the left exit region. RAP forecast
soundings and cross sections show a saturated layer near the surface
up to around 5,000 ft, including the dendritic growth zone. Guidance
also shows 0-3km CAPE around 30-70 j/kg and 0-3 km shear upwards of
40-50 kts. All of these parameters coming together may create a
conducive environment for snow showers and squalls 06z Saturday
through early Saturday afternoon. While any accumulations would be
spotty, it is not out of the question a few of the stronger showers
could produce rates high enough to quickly coat the ground with a
dusting.

Dry air advection and subsidence under an approaching area of high
pressure dry much of the column out by Saturday night and into
Sunday. Guidance does show the upper trough hanging back over the
region into Sunday, so will have to watch the possibility of left
over moisture becoming trapped in the boundary layer keeping clouds
around through Saturday night. If this happens, low temperatures
Saturday night may remain elevated. By Sunday, expect a much drier
and clear day across the region with high pressure located just to
the south and west.

Temperatures this weekend are expected to be well below average as a
deep trough and arctic airmass settle in over the Midwest and Great
Lakes. Temperatures aloft at 850mb fall as low as -15C with
continued cold air advection and northerly flow as surface high
pressure remains just west of the region. Highs will likely struggle
to reach freezing Saturday with overnight lows dropping into the
upper teens to low 20s. Once again, new vegetation growth and buds
will likely be damaged from prolonged exposure to sub-freezing
temperatures.

Along with the cold temperatures and snow showers, winds should
remain elevated much of the weekend, being the strongest on Saturday
and weakening some on Sunday. A 30 kt low level jet remains over the
area Saturday with steep low level lapse rates during peak heating
of the day. Expect gusts to 30-35 mph Saturday afternoon diminishing
some during the overnight hours. These winds may also be enhanced
Saturday by convective snow showers developing. Windy conditions
along with brief periods of heavier snowfall in the strongest
showers may lower visibility briefly. Low level jet weakens for
Sunday however gusts to 15 to 20 mph are still possible. Wind chill
this weekend will drop down into the single digits during the
morning hours and may keep daytime hours feeling like its in the
teens rather than 20s-30s!

.Next Week...

The weather pattern almost repeats itself going into next week as
high pressure pushes east and yet another system develops in the
Plains. Ensemble guidance suggest below normal temperature anomalies
on Monday with a warming trend through the week as warm air
advection increases ahead of the developing system. Highs in the 50s
to possibly 60 degrees likely with little chances for rain the first
half of the week. No surprise that there is quite a bit of model
spread with that next system; however confidence is still somewhat
high in dry weather with a warming trend. Both GFS and EC ensembles
show an increase in moisture and pw late next Thursday into Friday
indicating the next possibility of rain for Central Indiana.

&&

.Aviation...(00Z TAF Issuance)
Issued at 606 PM EDT Thu Mar 16 2023

Impacts:

* Wind speeds and gusts increasing late evening through dawn

* Low ceilings (at least MVFR and probably IFR) through early morning

* Winds trending westerly Friday morning

* Lingering MVFR through much of Friday; uncertain ending time

Discussion:

We are in the warm advection preceding rain shield of the
approaching mid-latitude system. Ceilings will continue to lower
reaching MVFR later this evening, and IFR overnight. Preceding the
cold front, gradient tightens enough to cause an increase in wind.
Low-level wind shear thresholds may be minimally met, specially if
surface winds aren`t as strong as expected, given the position and
magnitude of the low-level jet.

Once the front comes through during the predawn hours, winds will
veer to westerly. MVFR ceilings will linger in moist cyclonic low-
level flow likely through much of the day. This is the most
uncertain part of the forecast and we`ll have to refine the end time
once confidence increases.


&&

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

$$

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