River Flood Warning 70, NWS Indianapolis, IN

Area Forecast Discussion
National Weather Service Indianapolis IN
1118 AM EDT Fri Mar 24 2023

...Updated Aviation Discussion...

.Forecast Update...
Issued at 827 AM EDT Fri Mar 24 2023

Minor update to refine northern edge of precipitation, expremize
precipitation probabilities to 100 percent where it is currently
raining, and a small area of light fog through late morning just
north of the precipitation.

The deepest tropical moisture connection from the western Gulf
northeastward into our region has shifted slightly southward per
latest low-layer CIRA ALPW. A renewed meridional surge of moisture
ahead of the eastward migrating mid-latitude system, isentropic
ascent, and associated rain is expected later today. This is
expected to exacerbate river flooding over the next few days. If
deeper convection and heavier rates are able to occur this far
north, overland flooding and/or flash flooding will be more of a
concern given recent rain and saturated ground. We'll review new
model data for these concerns and the evening/overnight time
period and add more detail later today.

&&

.Short Term...(Today and tonight)
Issued at 258 AM EDT Fri Mar 24 2023

* Flood Watch Remains in Effect Through Saturday Morning

* A lull in rain coverage will occur later this morning into the
  afternoon

* Another round of heavy rain will occur this evening into the
  overnight, especially south.

Early this morning...

Cold front has settled south of central Indiana early this morning,
taking the strongest convection with it. Training thunderstorms with
heavy rain were just south of the forecast area, with widespread
moderate rain across much of the southern half of central Indiana.
Lighter rain to dry conditions were across the north.

The above setup will continue for the predawn hours, with the rain
slowly shifting south with the surface front. Severe weather is not
expected with the front to the south, but a flooding threat will
continue across the southern forecast area (especially far south
closer to the training heavier convection early).

This morning into mid-afternoon...

Light rain will continue across the south early in the period, but
with loss of forcing from the initial upper wave exiting the area,
coverage will decrease. Many places will only have chance PoPs or
lower by 18Z. Temperatures will only be in the 40s to lower 50s.

Later this afternoon into this evening...

A deepening upper trough approaching from the west will allow a
surface low to deepen and move toward the area later this afternoon
and into the area tonight. An 850mb jet over 50kt will return,
pumping more moisture to the area, with precipitable water values
returning into the 1 to 1.5 inch range.

Lift and moisture from the aforementioned features will spread rain
from south to north once again during the later afternoon through
the evening. Heavy rain will be possible again, especially south
where the best moisture will be. Frontogenetical forcing will
increase the locally heavy rain threat.

Will go with categorical PoPs by 00Z across the southern half of the
area, with lower PoPs north. During the evening, will go near 100
PoP all areas.

Overnight...

Uncertainty remains on the track of the deepening surface low as it
moves into the area. This will have an impact on how far north the
warm sector gets and any severe weather threat.

As the surface low moves into the area overnight, coverage of rain
will diminish some. The warm sector will move at least into the far
southern forecast area, if not the southeast third or more. With
strong winds not far off the surface, this could allow for a few
severe wind gusts to reach the surface. The Storm Prediction Center
has placed the southern third of the area in a Marginal Risk, and
this looks reasonable.

Behind the low very late tonight, winds will increase with a tight
pressure gradient. Locations of stronger gusts will depend on
surface low track and timing, but at the moment believe stronger
gusts will likely not arrive until after 12Z Saturday.

Temperatures will rise overnight, especially in the south where the
warm sector is able to move in.

&&

.Long Term...(Saturday through Thursday)
Issued at 258 AM EDT Fri Mar 24 2023

* Windy Saturday with falling temperatures
* Seasonable Temperatures and Light Rain Chances through Next Week
* Potential for More Significant Rainfall Again Late Next Week

.Saturday...

Long term period begins with a deepening area of low pressure
tracking from around St. Louis to South Bend and swinging a strong
cold front through the state. While the heavy rain threat will be
ending early Saturday morning, the passage of the strong cold front
will bring rapidly changing weather conditions throughout the day.

Main area of concern for Saturday is the strong wind threat before
and after the frontal passage mid morning. Strong 60+ kt low level
jet pushes into Central Indiana ahead of the front, bringing much
warmer air northward into the region. Highs will likely be reached
during the early morning hours ahead of the front where a few
locations in Eastern Indiana could spike into the 60s briefly. Low
level warning with cold air advection aloft will lead to steepening
lapse rates and the potential for higher gusts to mix to the
surface. Latest guidance indicates the potential for gusts over 45
mph before and after FROPA Saturday morning through the afternoon
hours. With such saturated grounds from recent heavy rainfall,
strong winds and sharp wind shift could easily down trees with
shallower root systems. Will go ahead and issue an SPS for strong
wind gusts Saturday; however a Wind Advisory may be needed in future
forecast updates as guidance continues to show strong wind potential
for that time period.

Another potential concern would be any convection developing in the
warm sector as it briefly pushes into Central Indiana. While dry air
will be pushing in aloft, there may be just a deep enough saturated
level near the surface combined with sufficient lift from the
passing low and modest CAPE for the development of a few convective
showers or thunderstorms. With such strong wind energy just above
the surface, 0-1 km shear near 35 kts, EBWD around 50-60 kts, and 0-
3 km SRH over 200 m^2/s^2, it will not take much to transfer that
wind energy to the surface. Southerly winds will already be strong
ahead of the front with gusts over 40 mph. Any shower or
thunderstorm develop could easily produce a damaging wind threat.
This will be something to watch as well Saturday morning.

Saturday afternoon, the strong wind threat continues on the backside
of the front as much colder air wraps around the low and into the
region. Expect quite the temperature different from the early
morning hours with temperatures likely falling from the 50s-60s into
the 30s-40s by the evening hours.

.Sunday - Early Next Week...

Expect a relatively quiet long term through about mid week but yet
another potent storm system looms for the latter half of the week
that could bring another round of moderate rainfall and renewed
flooding to portions of the Ohio Valley or Great Lakes regions.

Pattern going into next week favors a broad long wave trough over
much of the CONUS with occasional subtle short waves moving through
the mean flow. Medium range models handling timing and strength of
these weaker waves differently so broad brush low chance pops best
course of action for now until better model consistency develops.
First of these waves arrives later Sunday into Monday. With deeper
moisture cut off, current expectations through mid week are for
light precipitation amounts with these fast moving waves. Thermal
profiles do suggest enough cold air aloft that with right timing,
some precipitation could be mixed or frozen across northern areas.
Low confidence at this time step to get that detailed with forecast.

Broad CONUS trough begins to amplify again toward Thursday as more
Pacific energy moves onshore along West Coast. This should allow for
a good moisture return with warmer temperatures by end of the week
across the Ohio Valley. The signal is evident in most medium range
guidance but timing and degree of amplification remain in question.
Will side toward ensemble guidance and blends for PoPs with HWO
messaging of rain potential with uncertainty. Guidance suggest
another 1 to 2" rainfall event possible but location highly
uncertain.

&&

.Aviation...(12Z TAF Issuance)
Issued at 1118 AM EDT Fri Mar 24 2023

Impacts:

* IFR to LIFR visibility and ceilings may briefly improve this
  afternoon

* Drizzle or light showers, with more steady rain this
  evening/overnight

* Strong winds begin early Saturday.

Discussion:

Cool/moist northeasterly surface flow north of the front is
contributing to IFR or LIFR ceilings and visibility at midday.
Surface heating may be enough for conditions to briefly improve (but
likely still be IFR or worse) through the afternoon, then continued
poor flying conditions tonight.

More widespread steady rain will move in this evening and continue
tonight followed by strong winds beginning early Saturday and
persisting through much of the day. Ceilings should gradually
improve through the day.

&&

.Hydrology...
Issued at 258 AM EDT Fri Mar 24 2023

* Heavy rainfall will produce flooding into the weekend

Six hour rain amounts through 06Z were up to around 1 inch across
the southern half of central Indiana, with lower amounts north. Some
streams/creeks are already responding to this rain. Rain will
continue for the remainder of the night which may cause some of
these to exceed flood stage, as well as cause minor flooding of
typical low lying areas. Will continue to monitor closely.

The second portion of the flooding concerns will come tonight
into Saturday morning, bringing another axis of heavy rainfall with
the expectation for an 0.75 to 1.50 inches of rain across all of
central Indiana. Locally higher amounts are possible far south if
enough of the warm sector of the system can get into the area.

MMEFS ensembles show that widespread minor to moderate river
flooding likely across most of central Indiana with a lower
potential even for a few spots to approach major flood levels should
the higher amounts be realized. In addition to river/stream
flooding, flash flooding is possible along with more widespread
flooding of low lying and flood prone areas. Flooding of mainstem
rivers is expected to continue through the weekend and into next
week.

Although focus for the heaviest rain has shifted south, will not
make any changes to the Flood Watch at this time. Depending on the
path of the surface low and warm sector, heavier rain could still
get farther north, even if the odds are lower of this occurring.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Saturday morning for INZ040>042-045>049-
051>057-060>065-067>072.

&&

Update...BRB
Short Term...50
Long Term...CM/Lashley
Aviation...BRB
Hydrology...Team IND

Hazardous Weather Outlook...UPDATED
National Weather Service Indianapolis IN
927 AM EDT Fri Mar 24 2023

INZ021-028>031-035>049-051>057-060>065-067>072-251330-
Carroll-Warren-Tippecanoe-Clinton-Howard-Fountain-Montgomery-Boone-
Tipton-Hamilton-Madison-Delaware-Randolph-Vermillion-Parke-Putnam-
Hendricks-Marion-Hancock-Henry-Vigo-Clay-Owen-Morgan-Johnson-Shelby-
Rush-Sullivan-Greene-Monroe-Brown-Bartholomew-Decatur-Knox-Daviess-
Martin-Lawrence-Jackson-Jennings-
Including the cities of Delphi, Flora, Williamsport, West Lebanon,
Lafayette, West Lafayette, Frankfort, Kokomo, Attica, Covington,
Veedersburg, Crawfordsville, Lebanon, Zionsville, Tipton, Fishers,
Carmel, Noblesville, Anderson, Muncie, Winchester, Union City,
Farmland, Parker City, Clinton, Fairview Park, Rockville, Montezuma,
Rosedale, Greencastle, Plainfield, Brownsburg, Danville,
Indianapolis, Greenfield, New Castle, Terre Haute, Brazil, Spencer,
Gosport, Martinsville, Mooresville, Greenwood, Franklin,
Shelbyville, Rushville, Sullivan, Carlisle, Shelburn, Farmersburg,
Linton, Bloomfield, Jasonville, Worthington, Bloomington, Nashville,
Columbus, Greensburg, Vincennes, Washington, Loogootee, Shoals,
Bedford, Mitchell, Seymour, and North Vernon
927 AM EDT Fri Mar 24 2023

This hazardous weather outlook is for central Indiana.

.DAY ONE...Today and Tonight.

Heavy rainfall is expected across portions of the area this evening
and tonight. Localized flooding is likely to develop, especially
across southern Indiana.

Isolated to scattered thunderstorms are possible tonight. Some
storms may produce strong wind gusts.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Wind gusts over 40 mph are possible on Saturday.

There is the potential for moderate river flooding to develop along
some rivers into next week.

.SPOTTER INFORMATION STATEMENT...

Formal spotter activation is not anticipated. However, with the
Indianapolis radar out of service, spotter reports of rainfall and
wind gusts will be important.

&&

More information, along with other weather, hydrological and climate
information can be found at http://weather.gov/ind