Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/19/23

Area Forecast Discussion

National Weather Service Indianapolis IN

 1000 PM EST Wed Jan 18 2023

.Forecast Update...
Issued at 1000 PM EST Wed Jan 18 2023

A deepening surface low is nearing SW portions of central Indiana.
Associated with this low is a strong frontogenetical zone and LLJ,
of which is creating widespread vertical ascent and rain showers
over the region. ACARs soundings show a nearly moist adiabatic
troposphere leading to efficient rain development in some of these
showers. Some of the higher rain rates are due to the development of
gravity waves along the LLJ, and can be seen by transverse wave
increases in reflectivity moving NNE within the widespread rain.
Although lightning cannot be ruled out, the lack of any conditional
instability will limit cloud tops and charge separation. Best
chances for lighting will be over SW portions of the region where a
little dry air influence may increase low to mid level lapse rates
slightly.

Temperature and wind forecasts for tonight are similar with lows
around 40 and wind gusts up to 30mph.

&&

.Short Term...(This evening through Thursday)
Issued at 316 PM EST Wed Jan 18 2023

* Widespread rain...locally heavy at times...expands across central
  Indiana this afternoon into tonight. Isolated thunderstorms
  possible mainly south of I-70

* Isolated strong storms cannot be ruled out over far southern
  portions of central Indiana this evening with damaging winds the
  primary threat.

* A brief risk for scattered severe storms over eastern portions of
  central Indiana Thursday afternoon

* Strong...gusty winds at times tonight and Thursday

Rain is quickly overspreading the forecast area from the southwest
this afternoon right on schedule. 20Z temperatures were chilly and
had been held down by the clouds all day and the onset of
rainfall...generally holding in the upper 30s and lower 40s.

An upper low across the High Plains this afternoon will be the
primary feature of interest over the next 24-30 hours as it lifts
E/NE into the Great Lakes by Thursday night. A stronger surface wave
over central Kansas will track in tandem with the upper low while a
second wave organizes along the warm front over the lower Ohio
Valley this evening. The double barreled surface low will then lift
into the lower Great Lakes by late Thursday enabling a cold front to
pivot across the region during the afternoon. The focus remains on
the widespread and locally heavy rainfall expected over the next 12
hours or so...and a conditional risk for stronger storms over far
southern portions of the forecast area this evening. That being
said...a sneaky secondary setup for low topped and isolated severe
convection is in play along the cold front Thursday afternoon
focused mainly across northern and central Ohio but perhaps as far
west as our eastern forecast area.

First...the primary impacts into the overnight will be locally heavy
rainfall and a small risk for stronger storms later this evening
across southern counties. Expect the rainfall ongoing across the
southwest half of the forecast area this afternoon to continue
expanding northeast across the rest of central Indiana into the
early evening. The arrival and deepening of a 60kt 850mb jet later
this evening on the lee side of the developing surface wave over
southern Illinois will only further infuse moisture advection into
the region as isentropic lift intensifies. Overall precip efficiency
progs are solid with convergence in the 925-850mb and 850-700mb
layers aligned across the southern half of the region into the early
overnight as the lead surface wave shifts N/NE through the Wabash
Valley with an arcing trough moving across the forecast area through
the predawn hours.

With excellent diffluence present in the mid and upper levels to
enhance rainfall rates above the parameters present mentioned
above...widespread totals of an inch or greater appear plausible
along and south of I-70 with slightly lower amounts further north.
The highest totals potentially in excess of 1.5 inches will focus
across the Wabash Valley where the deepest moisture and lift will
align the longest. The dry conditions experienced throughout the
Fall continue to aid in keeping flooding concerns largely in check.
That being said...these amounts in tandem with recent rainfall
across the region has brought soil moisture levels back closer to
normal. While mainstem rivers should have no issue with this amount
of rainfall...could see brief localized flooding develop along
smaller tributaries across south central Indiana by Thursday
morning.

The other aspect for this evening into the overnight is the isolated
severe potential. Trends have pulled back on the conditional risk
throughout the day today with the primary focus for storms producing
damaging winds focused more over the lower Ohio Valley and
especially points S/SW from there. A closer analysis of model
soundings however...do suggest a narrow window for perhaps a
stronger gust or two out of any embedded storm that track across far
southern portions of the forecast area...especially if the low level
inversion can weaken just enough. Outside of the rain and convection
tonight...a tight pressure gradient and the presence of the low
level jet overhead will produce increasingly gusty winds overnight.

The surface trough and deeper moisture will shift east of the
forecast area by daybreak Thursday as a notable dry slot with
subsidence overspreads the region ahead of the trailing surface wave
across the mid Mississippi Valley. Initially...skies will remain
cloudy with moisture trapped beneath a shallow inversion but as the
drier air expands down through the column...skies will clear across
the southeast half of the forecast area late morning into the first
half of the afternoon immediately ahead of the approaching cold
front. The boundary layer will quickly become well mixed with a
renewed surge of gusty winds perhaps peaking at 40-45mph in spots.

An intense piece of energy aloft will pivot around the base of the
upper low and across the region Thursday afternoon with the frontal
boundary moving west to east across the forecast area. The
combination of steepening lapse rates with weak but efficient
instability...a secondary 850mb jet and the strong forcing aloft
will create a favorable setup for scattered low topped convection to
quickly organize by mid afternoon across the eastern half of the
forecast area. Any stronger cell will have no issue pulling 40+kt
winds at 3-4kft to the surface with a risk for damaging winds.
Strong 0-1km helicity could also offer a threat for rotating
convection as well. Timing of the frontal passage will be critical
in determining how much of an impact this will be across the
forecast area. As it stands...conditions are most favorable just to
the E/NE of the forecast area across central and northern Ohio but
any subtle slowdown would pull the risk back west into the forecast
area for an hour or two Thursday afternoon. Will continue to monitor
this evolving threat,

Once the front passes...much colder air will advect into the region
with a return of thick stratus. Any lingering precip should remain
rain with any potential for snowflakes holding off until Thursday
evening.

Temps...despite the cooler temps this afternoon...should see
steadily rising temperatures through much of the overnight as the
warm front lifts into the area. Highs will peak in the mid to upper
50s over a good chunk of the forecast area Thursday afternoon ahead
of the front before falling late.

The front will swing through the area

&&

.Long Term...(Thursday night through Wednesday)
Issued at 316 PM EST Wed Jan 18 2023

The long term period will start off with some lingering
precipitation Thursday night with the exiting system. Winds will
still be moderate with gusts up to about 35 kts for the overnight
hours, but will weaken through the day Friday. CAMs are hinting at
the potential for some isolated snow or rain showers even into the
day Friday which easily form over the area in these type of set ups,
but confidence is low at the moment so keeping with guidance for now
which has near zero PoPs. Otherwise, ridging and surface high
pressure will settle in Friday through Saturday night leading to dry
weather and a chance for clouds to thin out.

Another system will move in around daybreak Sunday as a surface low
tracks from out of the ArkLaTex region and through the Ohio and
Tennessee Vallies. The question for Sunday will be the temperatures
and precipitation type. For now, it looks as though there is some
agreement that temperatures will warm above freezing through the
day. So while precip may start as snow, it should become almost all
rain by the afternoon. Could see a transition back to snow before
precip ends Sunday night.

After a brief break from precipitation on Monday, another system
looks to move in around mid next week. There is currently quite a
spread between models so low confidence in any details for the
system at the end of the period.

Temperatures will finally return to near, to slightly above, normal
throughout the long term.

&&

.Aviation...(00Z TAF Issuance)
Issued at 633 PM EST Wed Jan 18 2023

Impacts:
-MVFR cigs through 00Z, IFR afterwards.
-MVFR to IFR vsbys during showers 21Z to 09Z.
-Wind shift from 090 to 180 around 08Z, gusts to 30kts tonight.
-LLWS from 04Z to 09Z tonight.

Discussion:
MVFR cigs will drop to IFR late this evening with the
arrival of heavier rain across central Indiana. This will continue
through the night as winds shift from the east to south and become
gusty.  LLWS will be a concern from 04Z to 09Z, especially in any
periods where the surface winds weaken. MVFR vsbys may persist past
the end of the rain with cigs gradually lifting after 12Z tomorrow.
Stronger winds will continue into the daytime hours with a continued
wind shift from south to eventually northwest.


&&

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

$$

Update...Updike
Short Term...Ryan
Long Term...KH
Aviation...Updike