AFTERNOON – OVERNIGHT: Calm conditions have started the day across zones 6 and 7. While many places are already seeing some sunshine, some patchy fog and mist are still impacting some areas.
Clouds will thicken up across forecast area today, especially later this morning into the afternoon. This will be thanks to a front to the south of the zones that starts to lift northward.
Through the afternoon rain chances will be increasing from south to north across the forecast area. By 1-2 PM rain will be starting to move into southern portions of zone 6.
Through the evening isolated to scattered rain and storms will make their way north across northern zone 6 into southern zone 7 by 5-6 PM.
Through the evening into the overnight rain and storms will continue to spread northward. By 10-11 PM scattered chances of rain will be possible across all zones.
Rain and perhaps a few storms will continue to spread across the forecast area through the overnight hours. Pretty widespread rain coverage looks possible through most of the overnight, by 2-3 AM rain and some storms will be ongoing across the forecast zones.
Lows overnight will be in the upper 40’s north to upper 50’s south.
SATURDAY: Through the morning hours on Saturday a warm front will be in place south of the region. As this starts to lift northward the heavier concentration of rain will lift northward as well. By 7-8 AM more scattered areas of rain look to be in place across zones 6 and 7.
Through the morning hours on Saturday the warm front will lift northward through zone 6 into zone 7. While isolated to scattered areas of rain/storms will persist through most of the morning hours, by 12-1 pm some drier conditions are expected.
With the warm front to the north of the forecast area would allow for a warmer day, with highs in the mid 60’s to mid 70’s. However, if the front should remain farther south, highs would only be in the upper 50’s to mid 60’s north of the front. Winds on Saturday will be strong at times with gusts of 35-45 mph possible.
While a more northerly warm front would allow for those warmer temperatures and perhaps some sunshine, it would also cause the environment to become unstable in the afternoon.
If the warm front does go far enough north and some sunshine can get through during the afternoon hours on Saturday, the environment would have the potential to become moderately unstable. The latest NAM model suggests the potential of 2000-3000 J/Kg of CAPE from the I-70 corridor southward by 4-7 PM Saturday.
While winds at mid-levels of the atmosphere are less than stellar, the higher wind max at 850 mb could help support a more organized strong to severe storm threat across southern portions of Illinois. However, the 850 mb winds are a bit displaced to the east of the strongest instability. So, any storms that do form would likely have a relatively short window of time (5 pm- 9 pm?) to become better organized severe storms.
With that being said, strong to severe storms do look possible across southern Illinois Saturday evening. Main threats will be damaging winds and hail. However, a few isolated tornadoes could occur as well.
By 4-5 PM storms look to be developing along the warm front across northern zone 7.
Through the evening hours the NAM does show a few more storms developing to the south, but these look to quickly merge into more of a line by 7-8 PM.
Through the evening the initial storms will move off to the east of the forecast area. As they do, a cold front will move southward. Along this front more isolated scattered areas of rain and some storms will develop by 12-1 AM.
Through the overnight the front will continue through Illinois as a cold front. While some isolated areas of rain and some storms will continue ahead of it, these will start to fade through Sunday morning.
Lows Saturday night into Sunday will be in the low 50’s to low 60’s.
SUNDAY: While the front will be out of the state by Sunday morning there will be an upper-level trough lagging behind that will be moving into the region. With this disturbance aloft, isolated to scattered rain showers chances will remain by 7-8 AM Sunday morning.
Through the day one Sunday isolated to widely scattered rain showers look to persist. However, by late afternoon into the evening an upper-level vorticity max will move across the state.
As the vorticity max moves through the area this will allow for more scattered rain to develop across both zones 6 and 7. I do think the best chances would be located just under the vorticity Sunday evening.
By 6-7 PM the NAM shows some of those more widespread rain showers.
Highs on Sunday will be low 60’s north to low 70’s far south.
Sunday night the upper-level disturbance will move out taking most of the rain chances with it. While a few light rain showers will remain possible, they will be hit and miss.
New rainfall totals through the end of the weekend look to average out around .75-1.15”. However, there will be areas that get under the heavier rain and storms that see 2-3” of rainfall!
MONDAY- TUESDAY: A large are of high pressure will build into the central U.S. to start next week. This will ridge into the region allowing for mostly dry conditions Monday into Tuesday.
However, by Tuesday we will return to a more northwesterly flow aloft. While no significant systems usually occur in the flow (in the warm months), a piece of energy looks to break off on Tuesday and move through the region.
Although high pressure will remain in place some rain looks possible Tuesday afternoon.
Highs to start next week will be cooler, with temperatures topping out in the 60’s to perhaps around 70 across southern Illinois.
LONG-RANGE: With an upper-level ridge building to the west, an upper-level trough and northwesterly flow looks to remain in control of the weather across the forecast zones through next week.
As some energy moves through the 500 mb flow there will be chances of rain showers next week. Although, I’m not expecting any major rain events.
With the rough building in it will keep temperatures below average for most of next week.