October's Temperature Flip Flop

From A/C to cranking up the heat and firing up the wood stove for the first time, all in the same week. Welcome to October folks! In southern Illinois, September may mark the official start to fall on the calendar, but the month often features a lot of summer-like weather. October and November are the two big transition months in the later half of the year, where the battle between summer and winter occurs. So far, October 2018 has featured one of the more epic battles I can remember with record breaking heat and humidity through the first ten days, but then turning to patchy frost just two days later.

Temperature Rankings Through First 11 Days of October
Paducah, Evansville, and Cape Girardeau all with the warmest starts to October on record

The change between summer and fall has been swift here in the middle of October. The 71º for a morning low on October 10th ties an all-time October record for warmest low temperature.
Fast forward to October 12th, the mercury dipped into the 30s for the first time this season. That's a 35º difference in morning lows in just two days.

Now, for the burning question, what's the rest of the month hold? Are we done with the heat and stuck with the cold? Get ready for one BIG flip flop. In weather, there's always a pairing, and we call these "couplets". Where there's a ying, there's a yang. If there's extreme heat, there's extreme cold somewhere.

First 10 days of October vs. Normal

The pattern that has brought the heat to the east, is now shifting out west. Cool weather has arrived for the first time this season east of the Rockies, and it's here to stick around the rest of the month. 

Rest of October: Projected Temperatures vs. Normal

Summer Not Ready to Give Up as We Turn to September

OUTLOOK

September is a month of transition as the days get shorter and the temperatures start to become noticeably cooler throughout the month. High temperatures cool by more than 10º over the course of the month, and low temperatures drop nearly 15º as the high humidity of the Summer finally starts to subside.

Summer tends to hold on through the first half of September though, and that will be the case in 2018. A pattern that sends a big area of high pressure along the East Coast westward into the Southeast will keep the heat and humidity lingering around through the first half of the month. In southern Illinois, those needing rainfall may be hoping for a break down in the setup, with widespread storms becoming tough to come by in this pattern.

 Along the outer edges of the high, moisture will pump into the Missouri Valley and Upper Midwest with potential for flooding rainfall over these areas of the Corn Belt. The resulting downstream rises along the rivers will be something to watch on the Mississippi River over the next few weeks.

LAST 30 DAYS RAINFALL OVERVIEW
Quite a bit of progression in relation to rainfall over the last 30 days across the region. Counties along the Ohio River and parts of the Missouri Bootheel have been dealing with a lot of dry weather over the course of the Summer, but finally, these areas, especially Missouri, have seen a little relief.

Rainfall compared to normal over the last 30 days (August 1-August 30th)

Radar estimated rainfall over the last 30 days (August 1-August 30th)

Further north, it's a completely different story. Several large storm complexes have brought very heavy rainfall across southwest Illinois and the St. Francois Mountains of southeast Missouri.

July is in the books, but heat & humidity set to make a return

A LOOK BACK AT JULY 2018

Many will remember July for the heat, but also the humidity through the first half of the month. 14 of the first 20 days of the month had afternoon temperatures in the 90s with heat index values often well into the triple digits. The heat and the humidity was consistent with isolated storms on a daily basis. Miss out on those storms, and it was tough to find much relief. The pattern shift in the last 10 days allowed for a welcomed break and beneficial rains through the last few days of the month. The two hottest days of July came back in the 4th and 5th with 94º and 95º respectively. The two coolest days came the last two days of the month with 75º on the 30th and 81º on the 31st. The last ten days of the month didn't feature a single 90º reading which helped bring the overall month much closer to average.

July 2018 at WSIL-TV (Carterville, Illinois)

Rainfall through the month was generally reliant on spotty storms, but the last few days of the month brought beneficial rains to much of southern Illinois. It didn't make up for the lack of rain through the first 29 days, but Jefferson, Franklin, Jackson, Williamson, and Union counties did quite well.

Rainfall estimates based on radar July 29th - July 31st

LOOKING AHEAD

While I suspect the break from the heat has been welcomed for most, there's still a lot of Summer left. The pattern is already looking to change and usher in more seasonable warmth, at the very least. Ridge of high pressure over the Atlantic will expand westward and kick the heat up a notch into the weekend. 

High pressure along the East Coast shifts westward through the weekend

Looking into the first full week of August, the big persistent ridge in the West remains strong while the high pressure along the East Coast gets shoved into the Caribbean. Cooler air will spill into the Northeast, but Mid-Mississippi Valley (and southern Illinois) will be firmly in the "battle zone" between that cool air to the east and big time heat in the west. The heat and humidity will generally win out in this scenario, but upper-level waves moving from the northwest to the southeast will kick off better chances for scattered storms almost daily. 

Northwest flow overhead will bring better chances for storms into the Mid-Mississippi Valley

SUMMMARY

Heat turns up for the weekend, but an active pattern overall will bring more storm chances next week.

July 18th: Late Week Storms, Cooler End to July

FRIDAY SEVERE POTENTIAL

First things first, let's talk about storm potential on Friday (July 20th). A large storm system is set to move into the Midwest with multiple shortwaves, or areas of energy, diving southeast down the Mississippi River Thursday and Friday. While storms are possible as early as Thursday afternoon, it's Friday's storm potential that raises some eyebrows. As is often the case with severe weather in southern Illinois, it's a conditional risk with plenty of uncertainty. Some forecast guidance suggests high instability and high amounts of shear possible, both would be easily capable of sustaining severe storms. Questions arise with storms late Thursday night into Friday morning and how this impacts the instability, or fuel for storms. The best shear for storms is in the evening, while some of the best timing for instability is earlier in the day. Still a lot of questions, but it's something we're keeping an eye on.

Instability Friday Evening

Shear Friday Evening

LONG RANGE OUTLOOK

Breaks from the heat and humidity have been short-lived through June and July thus far. The pattern has been consistent and stubborn, but FINALLY, a prolonged break is on the way. The stubborn upper-level ridge centered over the Plains and Southeast is set to shift west for the last two weeks of July. It's a pattern shift that signals cool and wet for southern Illinois. The switch to “northwest flow” is not only cool, but active. The concerns of drought as we headed into the Summer are all but gone as this pattern supports continued wet weather with multiple chances for storms. Below, image 1, shows the ridge shifting west while the trough takes hold over the eastern U.S. through the last week of July.

Image 2, is what we call an analog. Analogs look back at similar scenarios and use historical context to indicate what may happen in the future. Through the first few days of August, the image below is a strong signal for the prolonged period of cooler weather on the way.

Image 1

Image 2

July 5th: A break from the heat is coming up, but for how long?

HEAT AND HUMIDITY

Whew. We're in the midst of an impressive heat wave gripping the Midwest, but a break is on the way. The actual temperatures have generally remained in the low to mid 90s, but it's been the humidity that has been high to extreme for an extended time. In the summer, we use a dew point of 70 as the benchmark for high humidity. Dating back to the first week of June, there's only been one afternoon with dew points below 70. By Saturday morning, dew points will be back in the 50s for the first time in nearly a month! Enjoy!

Big dome of high pressure responsible for the heat remains in control through Thursday

By Saturday, dome of high pressure is shifted west

RAINFALL

Despite the heat, rainfall has drastically improved over the last two weeks across southern Illinois. A series of gully-washer rains packed with multiple rounds of severe storms have helped many across the region. Looking at southern Illinois in particular, huge improvement is noted across Franklin, Perry, Jefferson, and Wayne counties. One of the driest spots in southern Illinois continues to be Hamilton County, but no one is in drought at this point in the Summer.

Last 60 Days of Rainfall Compared to Normal (Ending Morning of July 5th)

Last 60 Days of Rainfall Compared to Normal (Ending Morning of June 18th)

The question is,  how long does the heat stay away? The upper-level high pressure has been the key for to the heat this Summer. When it goes west, we cool down and also enjoy a more favorable storm track for rainfall. When it shifts east, we get hot and rain chances resort to pop ups. 

LONG RANGE OUTLOOK

The big dome of high pressure will likely remain the key through the rest of the Summer. While it roars back east for the week of July 9th-14th, there are signs it will shift west in the third week of the month allowing a big trough. It spell a more active pattern with better rain chances that needs to be monitored. As for the heat, the trough looks more focused in the Plains, meaning we could be on the warmer side of it. Our expected summer drought has not taken hold as of right now, and I'm not sure I see if through the end of July. Just remember, it's still the first week of July, so we're far from the end of heat and humidity. 

June 19th: A break from the heat, better rain chances on the way

A LOOK BACK
Heat and humidity have gripped the area in mid-June with five (and likely six after Tuesday) straight days with temperatures 90º. The average high temperature so far for the month of June is just shy of 90º with only two afternoons cooler than normal.

Daily Afternoon Temperatures Through June 18th

Through June 18th, the month has been one of the top 3 warmest on record. Following on the heels of the warmest May on record across southern Illinois, the growing season has been extremely warm thus far.

I've had some questions regarding this year's hot weather in comparison to the brutal summer of 2012, but there are some BIG differences. In 2012, we recorded around 3" of rainfall from April through June. 2018? We've recorded 10"+ of rainfall from April through June 18th. The dry weather also led to an abnormally low amount of humidity in 2012 with the only year we didn't muster a single 70º dew point.


LONG RANGE OUTLOOK
A major pattern shift is set to occur this week finally breaking the heat and humidity and increasing rain chances. To this point, the month of June has been very dry for much of southern Illinois, especially areas that have missed on some of the afternoon t-storms.

THIS WEEK

Storm Moves in Later in the Week

As the big ridge that's gripped the region moves southeast, a seasonably strong storm system will enter the picture from the northwest. A big surge of moisture from the western Gulf of Mexico will aid in the development of more widespread showers and storms as the storm system drops through the Plains. Biggest risk for any type of heavy rain is on Thursday, but scattered to even possibly widespread showers and storms will stick around through Friday.

NEXT WEEK

Ridge Gets Push West, Pattern Remains Active

The big dome of high pressure remains one of the nearly permanent features we have kept an eye on this spring and now into summer. Ridge appears to shift to the West which keeps the middle of the country active. It's a similar pattern we saw at the beginning of June.

Last 60 Days Rainfall Compared to Normal
Much of Southern Illinois 2-4" Drier Than Normal

BELOW: Models indicating next 10 days wetter than normal

Thursday brings brief break (kind of), then heat and humidity roar back

Good Wednesday morning! Almost everyone in southern Illinois picking up at least some rain on Tuesday afternoon as storms finally moved south of I-64 a bit. Upper-level high pressure over South Texas continues to be the driving force for weather across the middle of the country. This is a pretty typical Summer-time pattern.

On this Wednesday, we're watching a cold front moving through the Midwest with some slight temperature and humidity relief behind it. Surface high pressure is set to move in behind the front and shift eastward into the Great Lakes over the next 24 hours.

Wednesday morning dew point map highlighting the drier air moving in from the north.

It doesn't appear we're going to get a huge break from the humidity, but the north winds should be enough to take dew points from the low to mid 70s back into the low to mid 60s by Thursday afternoon with the front becoming nearly stationary running parallel to the Mississippi River.

High dew points are evident Thursday afternoon west of the front, while drier air takes over southern Illinois

Once high pressure moves eastward Friday morning, heat and humidity quickly roar back, with an oppressive combination we haven't quite seen yet this year. The upper-level high pressure is set to move from South Texas right into the Mid-South towards the end of the week. While daily chances for storms have become the norm, the big dome of high pressure moving overhead will essentially cut off storms.

Upper-level high pressure location Wednesday

Upper-level high pressure location Friday

Under the dome, it's going to be hot, dry, humid. The weekend will likely bring temperatures in the low 90s with heat indices cracking the century mark.

This big upper-level ridge looks to be a staple in weather for the middle U.S. through at least the remainder of the month. A shift westward would allow some relief and possibly the return of storms, but many of the longer range forecast models continue to hold onto this idea of hot and dry through the next 10 days.

Rainfall projection over the next 10 days. Notice the rain seems to circulate around the position of the dome of high pressure