AFTERNOON-EVENING: A stationary front is in place across Illinois. To the north of the front some isolated t’storms and patchy fog have developed. However, closer to the front rain and some thunderstorms are continuing to move to the northeast.
Through mid-day the storms will continue advancing across Illinois along the stationary front. By 12-1 PM rain and some storms will be possible across zones 6 and 7. However, I do think the latest HRRR may be a bit aggressive with the precipitation coverage.
Through the afternoon the rain will continue to work its way off to the east of the zone forecast area. As it does, some breaks in the cloud cover looks to occur. This will allow for some sunshine to get through and the atmosphere to destabilize once again. The latest models do show 1500-2500 J/Kg of CAPE across the forecast zones this afternoon and evening. While I do think this level of instability is achievable given strong daytime heating and impressive surface moisture, the question of exactly how much afternoon sunshine occurs still remains.
At the upper-levels of the atmosphere a 500 mb jet will be in place just to the southwest of Illinois. However, the nose of the jet, which can help produce storms, will be aimed right at the St. Louis area by 4-5 PM.
At low-levels winds will be coming in from the south at 30-40 knots. While this is low-end threshold for a better severe weather threat, I do think it will get the job done. So through the evening strong to severe storms will be possible across the zones after 3-4 PM. Main risks with these would be damaging winds, hail, and an isolated tornado or two.
By 4-5 PM more rain and storms will develop in the warm sector along and ahead of the cold front as they move northeast.
By 7-8 PM storms will be in place across eastern portions of zone 6 and 7 as the front continues across the state.
By 10-11 PM the storms will be exiting off to the east into Indiana.
Through the overnight another disturbance will make its way across Illinois. However, because the prior storms and frontal passage will help stabilize the atmosphere, I am not expecting much in the way of overnight precipitation.
New rainfall totals this evening into the overnight will average around .50-.85″ across the area. However, I do think places that get under some of the strong to severe storms will see locally higher amounts of 1.50-2.50″ with perhaps a few places seeing a little more.
Lows tonight will be in the low 50’s north to around 60 south.
THURSDAY: A frontal boundary will be in place to the north of the forecast area on Thursday. While this won’t be a serious concern to the weather across zones 6 and 7, it could help generate some afternoon showers across zone 7. However, these will be light in nature.
Thursday the front to the north will allow clouds to persist across northern Illinois perhaps as far south as northern zone 7. However, I do think sunshine gets through on Thursday across zone 6 and most likely zone 7 as well.
Highs on Thursday will be in the mid 60’s north to mid 70’s south. Winds will be from the west to northwest with gusts of 25-30 mph possible.
Thursday night into Friday skies will remain clear with the exception of some clouds working in across very western Illinois.
Lows Thursday night will be in the upper 40’s north to mid 50’s south.
FRIDAY: While we will start the day on Friday with a mix of clouds and sun across Illinois, clouds will be increasing throughout the day.
This will be thanks to a warm front that will be lifting closer to the region through the afternoon from the southwest. While most of the day looks to be dry on Friday, some rain and storms will develop along the front and move into southern Illinois around 7 PM or so.
Highs on Friday will be in the mid 60’s north to mid 70’s south.
Friday evening into the overnight rain and storms will continue lifting to the north across Illinois. This as the aforementioned warm front lifts north as well.
WEEKEND: On Saturday the warm front will be lingering across the forecast area as the low pressure system gets itself together across the southern Plains.
With the front in place across the forecast area, rain and storm chances will continue through the day on Saturday.
Highs on Saturday will be in the low 60’s to low 70’s. However, high temperatures will be greatly dependent on where the warm front is located. If it’s north of the zones the temperatures will be warmer. If it’s south then it will be a cooler day.
Sunday the area of low pressure that was across the Plains will move closer to the forecast region. Models are currently showing the low tracking south of the forecast area across Paducah, KY to eastern KY.
This track would greatly decrease severe weather chances across the forecast area Sunday that we had previously mentioned. However, rain and general thunderstorms would remain possible.
With that being said, that track is not written in stone yet, so we will watch models for any new data or trends.
Highs on Sunday will be in the upper 50’s to low 60’s north and along the front. South of the front upper 60’s to upper 70’s will be possible.
LONG-RANGE (NEXT WEEK): While some rain may stick around Monday as an upper-level trough moves through, next week looks calmer as a whole.
A northwesterly flow aloft will prevail for most of next week. While that will help ease any severe storm/heavy rain concerns, at least some rain chances will remain since the northwesterly flow usually proves to be an active one.