Good afternoon, before we go into details with the severe weather potential for Sunday, we will take a brief look at the current conditions as of this write up. Warm front as of 11 am is now in southwest Indiana and this front will continue to push northward. Showers on radar across northern Indiana, with heavy rainfall from near South Bend to Walkerton. Temperatures are ranging from a cool 43 in South Bend and Elkhart, to a mild 64 in Evansville, Washington, and Jasper.
Looking ahead to Sunday, a strong cold front will continue to march east and southeastward across the Central Plains and will be in a position from central Wisconsin to eastern Iowa to northwest Missouri by Sunday morning. Showers and thunderstorms could be ongoing as FutureCast will show below. As of the 1:30 pm Convective Outlook from the Storm Prediction Center, an enhanced risk of severe weather is for all of central Indiana and a small portion of northern and southern Indiana. A marginal risk of severe weather for extreme northern extreme southern Indiana, with a slight risk in between these area. It is of a quick note that the threats have been pushed southward a bit, and the southward push could continue depending largely on which areas will be in the warm sector.
Now what is causing the severe weather potential is a strong cold front that will sweep through the area on Sunday afternoon through early Monday morning. Bulk shear by Sunday evening will range from 35 kts in southwest Indiana to an incredible 80 kts in northwest Indiana, that is plenty of shear to maintain thunderstorms. Winds at 5,000 feet will range from 20 kts in northwest Indiana to around 45 kts in southern Indiana. Lapse rates in excess of 7.5 also suggest the potential for very large hail. However, the exact location of the warm front, and extensive cloud cover and the possibility of a cap being in place can also limit the overall severe weather potential. Supercell thunderstorms, some semi-discrete could develop during the afternoon hours, and some of those storms will produce all severe weather modes, including a few tornadoes, especially near the location of the warm front, then the storms will congeal into one or more lines of strong to severe storms, where damaging winds, and a brief spin up tornado or two will be possible. The main threat for those in the enhanced risk area will be large hail and damaging winds, but again a few tornadoes will be possible and the hail may exceed 2″ in diameter. For the slight risk area, large hail and damaging winds will be the main threats, but can not rule out an isolated tornado. In the marginal area, large hail and damaging winds are the main threats, but there is also a non-zero risk of an isolated tornado.
Finally looking at FutureCast radar from 4 am Sunday through 4 am Monday morning, showers and thunderstorms may be ongoing near the vicinity of the warm front, some small hail and brief heavy rain may be possible with these storms. Some of these storms may also play a role in the overall severe weather potential as well. Stronger rounds of thunderstorms will begin during the early to mid afternoon hours, first starting in Illinois, then moving into Indiana. It will be some of these storms that will have the potential to become severe. As we head into the evening hours, showers and thunderstorms, some still could be severe will continue to move ahead of the cold front and with the loss of any daytime heating, these storms will eventually begin to wane slowly after sunset, moving into southern Indiana after midnight.
Even if the severe weather do not play out as we are expecting it to and that is still entirely possible, heavy rainfall will still be possible with any thunderstorm, and to prove that point, here’s two model solutions of possible rainfall through 7 am Monday. The GFS is a bit conservative, but still suggesting 1 to 2″ across much of the state. The NAM 3km model I think might be a little too aggressive at least in the rainfall totals, but as FutureCast showed, most of the heaviest rain will focus on central Indiana, where the model suggests anywhere from 1.5 to 5.25″ of rainfall. Even the conventional NAM is suggesting over 4″ in east-central Indiana. Localized flooding will be possible in any of these scenarios.
So to conclude, we are still looking at the potential for severe weather on Sunday, there still remain a few uncertainties that will be answered over the next 12 to 18 hours. Right now, the area that could see the greatest impacts will be central Illinois and central Indiana, as things have trended a bit more southward. Heavy rainfall will be possible, even if severe weather do not occur and localized flooding will be possible. Finally, even though I haven’t mentioned it above, even outside of thunderstorms, winds could gust up to 30 mph ahead of the front that could knock down some branches. Stay weather aware for Sunday and be sure to keep tuned to the latest information on the Equinox Weather Facebook page.