093 
FXUS63 KIND 280817
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
417 AM EDT Sat Mar 28 2020

.UPDATE...
Aviation section updated

&&

.SYNOPSIS...
Issued at 309 AM EDT Sat Mar 28 2020

Two rounds of thunderstorms will progress through the region 
today. The first round, this morning, will bring a threat of 
heavy rain and flash flooding to north central Indiana. The 
second, this evening into the overnight hours, will produce 
numerous thunderstorms with a slight risk of some reaching severe 
criteria. All modes of severe weather are possible tonight 
including isolated tornadoes. After this system passes through 
late tonight, high winds will be a concern over most of central 
Indiana with the largest threat to the north. Calmer and drier 
conditions are expected for the start of next week. 

&&

.NEAR TERM /Today and Tonight/...

Issued at 351 AM EDT Sat Mar 28 2020

As of 07Z, a stationary boundary is positioned over south central
Indiana. A significant temperature gradient is situated along 
this boundary with temperatures in the upper 60s towards the south
and upper 40s in our northern counties. Cloud cover and scattered
rain showers remain north of the boundary, slowing its 
progression northward. 

Ongoing convection over central Illinois will move over this 
boundary and become elevated as is approaches the Indiana border. 
WSW winds within the low-level jet and a west to east oriented 
boundary will position the northern portions of our CWA in an area 
of continuous convective initiation over the morning hours. 
Multiple rounds of precipitation with rain rates between 1 to 1.5 
in/hr are possible within the strongest bands. This will cause a 
narrow swath of rainfall totals greater than 1 inch over a short 
period of time. With this in mind, flash flooding is a possibility
and a Flash Flood Watch has been issued over north central 
Indiana to depict this threat. Some thunderstorms this morning 
could become severe if they can maintain themselves north of the 
boundary. Lapse rates near 8C/km in the mid-levels will provide 
plenty of instability for strong updrafts within long-lived 
cells, allowing for the possibility of large hail growth. However,
storms with hail greater than or equal to 1 inch should be 
isolated. 

As the low pressure system over Kansas moves eastward, the LLJ will 
shift more southerly, pushing the boundary north and placing most of 
central Indiana in the warm sector. Temperatures within the warm 
sector should reach the mid to upper 70s by late afternoon. 
Convective allowing models have had a difficult time 
understanding the extent of this morning's convection, which will 
have a large impact on the northward progression of the boundary. 
Increases in cloud cover and rain would cool surface temperatures 
and suppress the boundary farther south. Monitoring this 
progression will be impeccable in understanding the convective 
event later today.

Within the warm sector, cloud cover should break slightly as 
dewpoint depressions within the mid-levels increase towards 10C. 
This should help destabilize the boundary layer. Mid-level 
instability will be sufficient for convective development during 
the afternoon, but without a significant source of lift convective
initiation could be limited. However, continued monitoring of 
developing convection this afternoon and evening will be needed 
as the main ingredients are present for the possibility of 
severe thunderstorms and isolated tornadoes. For now, expect 
broken cloud decks throughout the afternoon, with the occasional 
thunderstorm if air parcels are able to reach the LFC. 

As the low pressure system approaches Indiana, the LLJ will 
increase, and along with a cold front, will provide the proper lift 
for convection. Significant wind shear exists within the enhanced
LLJ, and any convective cells could produce a mesocyclone. 
Current CAMs show supercell like structures over central Illinois 
tomorrow afternoon. How quickly this front and enhanced LLJ 
approaches central Indiana will have a large impact of the extent 
of severe weather today and if these potential supercells can 
prosper over the CWA. As the day progresses, instability and 
upper-level support weakens ahead of the front and could impede 
convective growth and limit severe outcomes, helping explain the 
reduced risk over central Indiana, compared to central Illinois. 
All severe weather outcomes are possible this afternoon and 
tonight, including isolated tornadoes. The greatest risk for 
tornadoes will be towards the north, near the boundary, where low 
level SRH is enhanced due to backing of the surface winds. 

&&

.SHORT TERM /Sunday through Monday Night/...

Issued at 309 AM EDT Sat Mar 28 2020

Within the short term, the main threat will be an increase of winds 
and wind gusts throughout the day on Sunday. A wrapped-up surface 
low with steep pressure gradients will pass north of central 
Indiana sunday afternoon and evening. Sustained winds up to 25 mph
with gusts between 35 and 40 mph are possible. Strongest winds 
will be towards the north where the pressure gradients are 
steeper. 

In the wake of the previous day's cold front, temperatures will 
drop with afternoon highs in the mid 50s. Some lingering showers 
are possible, however they will be limited and weak. Any rain on 
Sunday after 12z shouldn't exceed 1/10 an inch over any specific 
area. Overnight lows Sunday night should be in the low 40s. 

For Monday, a surface ridge will move in, clearing out skies and
reducing surface winds. Sunny conditions will allow for diurnal
heating and afternoon temperatures in the upper 50s. High pressure
through all levels will keep conditions clear and calm Monday 
night with lows in the upper 30s. 

&&

.LONG TERM /Tuesday through Friday Night/...

Issued at 302 AM EDT Sat Mar 28 2020

ECMWF suggests low pressure moving through the deep south on
Tuesday...providing wrap around cyclonic flow to Central Indiana.
Pops will be needed for light precip chances early in the day and
mainly south as the low exits for the Carolinas late in the day. 
Meanwhile surface high pressure is suggested to build across the 
plains states and across Indiana and the Ohio valley for the 
middle of the work week. Thus will trend toward dry weather then.

ECMWF pushes a low from the Northern plains across the Great Lakes
on Thursday pushing a cold front across Indiana on Thursday. At
this point moisture looks to be a problem for this system as high
pressure to the south effectively block gulf moisture. Will trend
toward a dry forecast for now...but would not be surprised to see
at least some small chance pops later with the frontal passage.

High pressure and dry weather is then expected to build across the
area on Friday in the wake of the front.

&&

.AVIATION /Discussion for the 280900Z IND Taf Update/...

VFR conditions are expected to continue the next several hours. As
precip has diminished across the area overnight...have removed
much of the ongoing VCSH mention. Look for precip to return later
this morning as heating returns. Any shower/storm that does strike
a TAF Site will result in brief MVFR/IFR conditions.

Previous Discussion below

/Discussion for the 28/06Z TAF Issuance/...

Issued at 1144 PM EDT Fri Mar 27 2020

As showers and thunderstorms move in over the next several hours,
there will be vast fluctuation from VFR to IFR at times. Some of 
the storms could become severe at times, and the threat will 
linger through the TAF period. In addition, low level wind shear 
will be a threat at times throughout Saturday morning, ramping up
again Saturday evening and into Saturday night. Meanwhile, at the
surface, winds will start out southeasterly, becoming more 
south/southwesterly through the course of the period. Sustained 
speeds will reach the 12 kt mark late morning Saturday with gusts 
up to 22 kts in the afternoon and gusting up to 30 kts by Saturday
night.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch until noon EDT today for INZ021-029>031-038-
040>042.

&&

$$

SYNOPSIS...Updike
NEAR TERM...TDUD
SHORT TERM...Updike
LONG TERM....Puma
AVIATION...TDUD/JP