Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/14/22

Area Forecast Discussion

National Weather Service Indianapolis IN

 1022 PM EST Tue Dec 13 2022

.Forecast Update...
Issued at 1022 PM EST Tue Dec 13 2022

* Evening Update

Numerous showers are pushing into the western periphery of central
Indiana. This should continue within strong isentropic lift over the
region. PoPs have been updated based off current observations. A
deep saturated profile could lead to moderate rain rates at times,
with around 0.5" possible over western central Indiana by tomorrow
morning. ACARs soundings are showing minimal to zero elevated
instability with this precipitation. Mostly due to a robust warm
nose north of 2000 feet, and the lack of significant cold air in the
mid levels (trapped further west). However, thunder will be possible
tomorrow evening/night as 700-500mb cold air begins to interact with
a narrow warm sector. Any convection should be elevated limiting the
possibility of a high wind threat tomorrow.

Temperatures will not follow a typical diurnal curve overnight with
deep cloud cover and strong WAA. Eastern portions of central Indiana
did cool slightly faster than expected this evening resulting in a
few readings less than 40 degrees. This should increase throughout
the night though with temperatures in the mid 40s tomorrow morning.

Grid updates are out.

&&

.Short Term...(This evening through Wednesday)
Issued at 250 PM EST Tue Dec 13 2022

*Widespread rain tonight, amounts around an inch
*Breaks in the rain tomorrow with low clouds and fog

Tonight.

A strong upper level closed low currently situated over southwestern
Nebraska will continue to progress to the northeast during the
evening and overnight hours with rapidly increasing surface pressure
gradients over central Indiana.  Efficient moisture transfer from
the Gulf continues to saturate the low to mid levels across central
Indiana with dense upper level clouds continuing to advect into the
area from the southwest.

Current thoughts are that precipitation will arrive between 12 AM
and 2 AM across the southwestern counties with a rain progressing
through the rest of central Indiana between 2 AM and 4 AM. Rain
amounts of around an inch are expected through the morning hours
with additional light amounts through the day.  A few rumbles of
thunder are possible across the far southern counties where a small
amount of elevated instability is expected, but coverage and
frequency of thunder will be minimal

Model soundings show a modest inversion in the lowest 3000ft which
will help limit the mixing down of the 30-35kt LLJ, but think that
the winds will occasionally be able to gust to 30kts with the rain
and strong dynamics of the system.

The near surface flow will be more easterly than southerly through
the overnight hours but with a more southerly component closer to
850mb, a non-diurnal temperature curve is expected for tonight with
lows likely around the onset of rain at midnight.  Temperatures
towards sunrise will likely be in the mid 40s to near 50 while
overnight lows will be closer to 40.

Wednesday.

The initial surge of moisture with this system will exit the area by
mid morning with only a few lingering showers through the mid to
late afternoon hours.  That being said, the low level moisture
remains locked in place even as the upper level dynamics and
moisture wane, so expect thick and low clouds to persist through the
day with periods of drizzle.

Surface winds are expected to be strong enough to limit fog, but
wouldn`t be shocked to see patchy spots even into the afternoon
hours. The second round of this system will be covered in the long
term section below.  WAA will allow for some temperature increase
into the afternoon with highs in the low 50s.

&&

.Long Term...(Wednesday night through Tuesday)
Issued at 250 PM EST Tue Dec 13 2022

* Widespread rainfall early in the long term.

* Much colder conditions arrive early in the period and continue
  through and beyond the long term.

* Occasional flurries possible at times much of the long term, light
  snow showers possible with a weak disturbance early next week.

The long-awaited major pattern change is upcoming in the long term
portion of the forecast.

Wednesday night, a secondary area of low pressure associated with a
shortwave trough pivoting around the much larger closed upper level
low will move through the area, bringing an additional period of
widespread rain to central Indiana, especially during the evening
hours. The surface boundary looks to finally make its passage
through the area during the overnight hours, with the onset of
strong cold advection shortly thereafter. There is a high likelihood
of a non-diurnal temperature progression Wednesday night into
Thursday and have made adjustments to the grids to depict this as
much as is practical. Temperatures may rise a little or simply
continue to fall during the day on Thursday, but a dry punch
immediately following the secondary low should put an end to
precipitation by daybreak.

That said, a few additional shortwave troughs pinwheeling around the
broader upper low may have an impact on portions of the area late in
the week and into the weekend, with occasional flurries possible at
times - primarily Thursday night into Saturday. Moisture will be
lacking to say the least in the Arctic airmass, but it is
surprisingly frequently observed here during the cool season that
cyclonic flow/CVA aloft needs very little in order to spit flurries
off and on for an extended period of time - will keep the flurry
mention out for now to avoid plastering 48 hours of non-measurable
phenomena across the forecast 3-5 days out, but as the week goes on
and more becomes clear, would not be at all surprised to see some
flurries enter the forecast.

The next question turns to early next week, when significant model
disagreement exists upon a very weak upper level wave and possible
inverted surface trough which could bring some light snow showers to
the area as early as Monday or slightly beyond. Will carry some 20-
30 pops but cannot justify more given major differences in guidance
members - but this will bear close watching as these mid/upper level
weakly forced setups can sometimes overperform if a little
frontogenetic forcing is thrown into the mix, which appears possible
in some models.

Again, temperatures will turn much colder during the long term
period, with the first shot of cold air likely to be followed by a
reinforcing burst of Arctic air late in the period. Highs late in
the period and beyond will likely be cooler, and at times
significantly so, than the low temperatures observed over the past
week or so. Blend appears to have a solid handle on this and aside
from the non-diurnal expectation early in the period, significant
adjustments were not required.

&&

.Aviation...(00Z TAF Issuance)
Issued at 649 PM EST Tue Dec 13 2022

Impacts:
-Easterly wind gusts to 30kts this afternoon tonight and tomorrow.
-MVFR to IFR ceilings and vsbys due to rain tonight.
-Slight improvement in conditions tomorrow before more rain tomorrow
night

Discussion: A line of moderate rain showers will move through
central Indiana overnight. MVFR ceilings and vsbys will be the
predominant condition, however IFR conditions are possible at times.
Winds will gust within these showers, with peak gusts around 30kts.

Tomorrow, there will be a break in rain, and some mixing should
erode the low level clouds enough for a few hours of VFR and within
gusts up to 30kts. Rain returns in the evening along with IFR
ceilings.


&&

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

$$

Update...Updike
Short Term...White
Long Term...Nield
Aviation...Updike