663 
FXUS63 KIND 301852
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
252 PM EDT Sun Apr 30 2023

.Short Term...(This evening through Monday)
Issued at 252 PM EDT Sun Apr 30 2023

...Wet and windy and cool conditions persist into May...

* Scattered showers and t-storms with small hail this evening
* Winds increase tonight into tomorrow with gusts to 40 mph
* Well below normal temperatures in the 40s to begin the new month 

.This evening and tonight...

A strong upper low and associated surface low will slowly meander 
through the Great Lakes region over the next 24 to 36 hours keeping 
dreary, wet, and windy conditions across much of Indiana. Latest 
satellite and radar imagery shows low pressure located near Green 
Bay, WI with deep moisture and clouds rotating about it, engulfing 
the entire northeast quarter of the US and most of Southern Canada. 
Abundant lift and moisture under the cyclonic flow in addition to 
upper vort maxes rotating into the region will lead to the 
development of showers and storms through the rest of this evening. 
Surface heating, cold air advection aloft, and an increasing 30-40 
kt low level jet have resulted in an very steep low level lapse 
rates, CAPE up to 500 j/kg, and speed shear... an environment 
conducive for strong convective showers and t-storms. With freezing 
levels very low for this time of year, any shower or storm has the 
potential to produce copious amounts of small hail, as has been 
reported already throughout Indiana today. Increase winds aloft and 
steep lapse rates have lead to higher gusts to 40 kts mixing down to 
the ground, especially in convective showers. These conditions will 
persist through around sunset when instability begins to wane.

For tonight, the boundary layer begins to stabilize as surface 
temperatures slowly cool into the upper 30s and low 40s. A tight 
pressure gradient and a strong low level jet aloft should keep winds 
elevated through the night with sustained winds of 10-20 mph 
expected in most locations. A few gusts to 30-35 mph still possible 
overnight. Clouds and winds will keep surface temperatures from 
falling much overnight, despite temperatures aloft at 850 mb falling 
to -4C by tomorrow morning. 

.Monday...

Same weather pattern continues into the first day of March... I mean 
May! It certainly will not feel like May across Indiana as 
temperatures struggle to get out of the 40s north of I-70 with 
widespread rain chances and blustery conditions.  

Another upper shortwave rotates into Central Indiana bringing 
another round of rain to much of Central and North Central Indiana. 
Despite steep lapse rates Monday, the environment looks a little bit 
more stable than on Saturday and Sunday. With low freezing levels, 
graupel and/or small hail is possible, but currently thinking there 
will not be as much convective activity than the previous few days. 

Main concern Monday will be the potential for strong winds to 40 mph 
to mix down to the surface. Strong 40-50 kt low level jet persists 
over the area the entire day along with a strong pressure gradient 
will lead to breezy conditions all day. Clouds and rain will keep 
mixing heights lower and limit boundary layer heating; however lapse 
rates will be steep enough to bring down some higher gusts aloft. 
Thinking gusts to 40 mph will be common, but gusts over 45-50 mph 
will be more infrequent. Therefore, issuing a Special Weather 
Statement for gusty winds tomorrow. Areas across South Central 
Indiana that receive more breaks in the clouds and more boundary 
layer heating could reach Wind Advisory criteria for winds; however 
confidence is still low on frequent gusts over 45 mph so will opt to 
not issue an advisory at the moment.

&&

.Long Term...(Monday night through Sunday)
Issued at 252 PM EDT Sun Apr 30 2023

Monday Night Through Thursday.

A persistent pattern will be in place for much of the early week as 
a broad and strong upper level low low continues to spin across the 
Eastern Great Lakes.  This will keep flow both at the surface and 
aloft northwesterly flow in place through Thursday.  A weaker 
shortwave within the more broad cyclonic flow will enhance the 
precipitation Monday with lingering showers into the overnight hours 
along with cloudy skies.

The strong CAA will be enough to overpower the poor radiational 
cooling conditions during the overnight hours and will lead to a 
drop in temperatures into the upper 30s Monday night and then into 
the mid 30s Tuesday night.  Winds to 15 mph will limit frost 
formation Tuesday night, but will need to monitor the strength of 
the CAA for any potential freeze. Conditions are more favorable for 
at least patchy frost Wednesday night with weaker winds and clear 
skies.

Conditions will gradually warm Wednesday into Thursday as the 
aforementioned low pushes off the east coast, but weak northwesterly 
flow will continue through Thursday keeping conditions near to 
slightly below normal.

Friday Through Sunday.

A weak ridge will develop across the High Plains Friday with a weak 
storm complex expected across the northern periphery of the ridge. 
The expected flow pattern will keep any convection to the southwest 
of Indiana but there could be a few showers on the northern edge of 
the complex Friday night into early Saturday. 

Confidence in the forecast begins to decrease with much of the 
weather dependent on how the storm complex develops in the earlier 
portions of the weekend, but think that conditions should remain 
warmer than they will have been in the previous week.  The next 
upper level system will also be strengthening over the Rockies, but 
don't expect any local impacts until later in the week.

&&

.Aviation...(18Z TAF Issuance)
Issued at 139 PM EDT Sun Apr 30 2023

Impacts:

* Numerous showers and isolated t-storms through this evening 
* Brief periods of heavy rain, low vis and cigs, wind gusts to 40 
  kts, and small hail with strongest convection 
* Winds shifting to WNW with gusts over 30 kts at times this evening 
  through tomorrow 
* Lowering ceilings to IFR/MVFR levels overnight tonight 

Discussion: 

Latest satellite and radar imagery shows numerous showers and 
isolated thunderstorms across Central Indiana this afternoon 
impacting flying conditions. Steep low level lapse rates, cold air 
advection aloft, and low freezing levels have resulted in strong 
convection capable of producing wind gusts in excess of 40 mph and 
copious amounts of small hail. As with any storm, brief periods of 
lower ceilings and vis are expected, in addition to erratic wind 
directions. Greatest coverage of showers and storms will be from 18z 
through around 23z, then diminish after sunset. Ceilings will go 
back and forth between VFR and MVFR today, then lower to MVFR to IFR 
overnight tonight as the atmosphere stabilizes near the surface. Vis 
will be up and down as well, with vis as low as 4sm at times under 
the strongest convection. 

The overall wind direction will remain around 240-270 this afternoon 
becoming 260-290 later this evening as Central Indiana remains under 
cyclonic flow from low pressure to the north. Low level jet 
increases to 30-40kts this evening and persists into tomorrow. Steep 
low level lapse rates and a tight pressure gradient will lead to 
surface winds sustained between 10-20 kts with gusts over 35 kts at 
time.


&&

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

$$

Short Term...CM
Long Term...White
Aviation...CM