288 
FXUS63 KIND 032250
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
650 PM EDT Mon May 3 2021

.Mesoscale Update...
Issued at 650 PM EDT Mon May 3 2021

Convective allowing models and radar trends support thunderstorms 
moving into northwestern parts of central Indiana after 02z. This 
upstream activity is currently moving east and approaching Rockford, 
Peoria and the northern St. Louis suburbs and has recently produced 
large hail and a tornado. Along and ahead of the convection, 
moderate instability with a surface base CAPE axis extended from 
south central Missouri to northeastern Illinois, and a 50 knot mid 
level jet streak was just north of St. Louis. This combo of 
instability, shear and moisture will keep these storms going through 
the late night as they move towards the Wabash River.

&&

.Short Term...(This evening through Tuesday night)
Issued at 328 PM EDT Mon May 3 2021

...HIGHLY CONDITIONAL SEVERE WEATHER THREAT OVERNIGHT...

Surface analysis this afternoon shows an area of low pressure to our 
northwest over NE Iowa/SE Wisconsin/NW Illinois, with a 
quasistationary front extending eastward through the Great Lakes, 
and a cold front extending south/southwestward into western Missouri 
to a second developing low over southern Oklahoma. These lows and 
baroclinic zone will be the focus for a conditional severe weather 
threat overnight that remains uncertain.

Latest synoptic guidance has coalesced somewhat around the slower 
solution advocated by the Euro in recent days with the development 
of the aforementioned secondary low as the more substantial upper 
level trough swings through the Four Corners region this afternoon.

It continues to appear that regional severe weather potential, if it 
occurs, will be in separate waves late this evening into the 
overnight, and then late tonight to just after daybreak Tuesday.

Supporting factors for severe weather are as follows: 1) Ample deep 
layer shear, instability, and moisture. 2) Support of an upstream 
MCV for the first wave, and support of the broader frontal 
zone/secondary low for the second. 3) Steep midlevel lapse rates. 4) 
Presence of a 30KT southwesterly low level jet feeding into the 
region later tonight.

Inhibiting factors for severe weather are as follows: 1) Widespread 
cloud cover has suppressed insolation throughout the day, although 
some clearing may be able to sneak into our west/southwest late this 
afternoon. 2) Timing is diurnally poor, particularly for the second 
wave which now looks most likely to arrive around daybreak Tuesday, 
and stabilizing boundary layer will limit surface-based instability 
and may result in elevated storms with perhaps a marginal hail 
threat at best. 3) Presence, albeit transient in some forecast 
soundings, of an elevated warm layer/cap between roughly 850-700mb. 
4) Potential for first wave of convection to move a bit further 
south through the area and fully exhaust available instability prior 
to arrival of second wave.

Many, but not all, of the 12Z CAMs coalesced around a solution 
whereby convection, currently developing over western Iowa and 
northeast Missouri ahead of the aforementioned MCV, consolidates 
into a QLCS and pushes southeastward along the instability gradient, 
perhaps brushing our west/southwest late this evening into the early 
overnight, with a lengthy gap afterwards before consolidated showers 
and storms ahead of the secondary low over the southern Plains into 
the Mississippi Valley arrive late in the night/around daybreak 
Tuesday.

The HRRR continues to suggest, albeit not as robustly as earlier 
runs, that the first wave of convection will push more 
east/southeastward into the forecast area, perhaps posing a severe 
threat as it weakens with eastward extent, with the second wave 
again arriving on a more west/northwesterly course from the central 
Mississippi Valley around daybreak. Cannot totally discount this 
with the potential for the MCV to continue to push eastward along 
the broader baroclinic zone, but the tendency should be for 
convection to move more east/southeastward in the open warm 
sector, such as it is.

The preponderance of the evidence, along with current orientation of 
the developing instability axis, although it should translate 
eastward with time (but erode later in typical diurnal fashion), 
suggests that the non-HRRR solutions are a bit more likely, although 
given the competing factors, confidence remains a bit lower than 
would ordinarily be the case this close to the potential events.

Agree with the rescission of the enhanced risk from the area and the 
pullback of the slight further to the west in the most recent SWO 
day 1 update.

One final complicating factor is speed of the front moving through 
the area. A thunderstorm threat and at least a very marginal severe 
threat, will likely linger into Tuesday ahead of the front, 
particularly south/southeast, depending on the evolution of features 
overnight.

As far as Tuesday night is concerned, guidance suggests a secondary 
vort lobe in the overall cyclonic flow will allow showers to linger, 
but the thunder threat, and particularly the severe threat, will 
likely be long over by then.

Preferred Consshort max/min temps to NBM given the continued slowing 
trend of the overall synoptic setup.

&&

.Long Term...(Wednesday through Monday)
Issued at 328 PM EDT Mon May 3 2021

Continued...changeable spring weather will continue to be the theme 
for Wednesday through Monday.

The lingering cold front is expected to exit the area on 
Wednesday...allowing dry high pressure to build through the Ohio 
Valley on Wednesday. Thus will trend toward a dry forecast at that 
time.

Aloft through Friday...strong ridging looks to remain in place over 
the Rockies while a deep cyclone over Hudson Bay provides broad 
cyclonic flow aloft for Indiana...the Great Lakes and the Northeast. 
A few embedded short waves are depicted to push across Indiana on 
Thursday and Friday afternoon...but deep moisture remains 
unavailable and lower levels are not organized. Thus will trend 
toward low chc pops on each afternoon as these wave pass as forecast 
soundings show attainable convective temperatures but shallow 
instability.

On Saturday through Monday a more zonal flow appears in place aloft 
as a surface low pressure system develops over the Plains. An 
associated surface warm front looks to be parked over southern 
Indiana on Saturday and lingers across the area through Monday. 
Models then suggest a few low pressure systems pushing along the 
front and across Central Indiana through the weekend. Thus chances 
for showers and storms through the weekend look reasonable.

&&

.Aviation...(00Z TAF Issuance)
Issued at 627 PM EDT Mon May 3 2021

IMPACTS: 

* MVFR or VFR ceilings through 04z-06z.

* Showers and thunderstorms and MVFR and worse flying conditions, 
  potentially strong to severe, after 04z.

* Winds 210-240 10 knots or less shifting to the northwest after 08z 
  as a cold front drops southeast over the terminals. Higher wind 
  gusts in thunderstorms. 

DISCUSSION: A cold front will drop southeast across central Indiana 
overnight. The front will interact with a moderately unstable 
airmass and veering wind with height and trigger scattered to 
numerous thunderstorms late tonight into Tuesday morning. The first 
concern will be the strong to severe storms moving in from Illinois. 
The most likely impact window for the terminals with this batch 
would be from 04z-09z. Then, more convection will likely be moving 
in from the southwest. This activity may be more widespread.

Modest southwest winds will shift to the northwest and north on 
Tuesday in the wake of the cold front.


&&

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

$$

Mesoscale...MK
Short Term...Nield 
Long Term...Puma 
Aviation...MK