Understanding severe weather: frequency and preparedness tips

Severe Weather Frequency:

It's that time of the year once again - when we pause to review the key components of severe weather and discuss how to stay safe when strong to severe storms are threatening your area. 

Of course, severe weather can occur at any point in the year if the atmospheric setup is right. That being said, there are two periods on the calendar when the threat for severe weather is typically highest across northern Illinois. Our primary severe season occurs in the spring - typically April, May, and June followed by a secondary season in the fall. 

Time of Day:

Severe thunderstorms can also happen at any point in the day, but the most favored window is between 3PM-10PM. But once we move into the evening and overnight hours, things can get even more dangerous. Nighttime severe weather is harder to spot, people are settling in or already asleep, and threats like strong winds, tornadoes, and flash flooding become a lot more hazardous as visibility and awareness is much lower. It's a big reason why we emphasize staying weather aware and have multiple ways to receive watches and warnings, even when the sun goes down.

P.P.M.A - Plan, Practice, Monitor, Act:

That is why it is important to remember the four key steps: plan, practice, monitor, and act. Before any threat for severe weather arrives, make sure you've created a safety plan and practice it - whether that be at home, school, or at work. Make sure your severe weather kit is up to date as well, stocked with things like snacks, water bottles, flashlights, extra batteries, and clothes like closed-toed shoes. 

 

Once the threat for severe weather arises, keep up with the latest updates through the First Warn Weather App, through Eyewitness News broadcasts, and a NOAA weather radio. Staying informed gives you valuable time to reach. And when a warning is issued or strong to severe storms are moving in, don't wait- act immediately and get to your shelter.

Mild, but unsettled for the first week of meteorological spring

Mild, but Unsettled:  

After a weekend that brought slightly chilly highs in the upper 30s, milder weather is set to take over as we head meteorological spring. With it however will come several opportunities for rainfall. 

Today will be dry and pleasant, with highs climbing into the mid to possibly upper 40s.  

Overnight Mix:

Clouds will gather up this evening into tonight as the first of many systems pushes in. Dry conditions will hold tight until about midnight, possibly into the early stage of Tuesday morning. After about 2AM-3AM, isolated light showers are expected to filter in from the west. At first, a shallow layer of cold air may allow for a few brief patches of freezing rain, though the expectation is for any mix to quickly turn to plain rain before mid-morning Tuesday. 

Shower coverage will increase slightly late Tuesday morning into Tuesday afternoon with a few pockets of steadier rain being a possibility. With that being said, several dry periods can also be expected with high temperatures peaking in the low 40s. 

 

  

Late-Week Chances:

Several more storm systems are on the table between Wednesday and early Saturday, resulting in the higher potential for rainfall locally. Next highest chance will arrive Wednesday evening into Wednesday night as a weak surface low wobbles in from the southwest. A better chance for more widespread rainfall will accompany a slightly stronger low and it's associated warm front Friday into Friday night.  

Forecast models continue to show the axis of heavier rainfall ending up to our south. Areas from southeast Oklahoma to central Illinois/Indiana could wind up with 2"-4" of rain during this stretch. 

This of course would be where the highest chance for flash flooding would end up. 

Warmer and wetter pattern begins Monday night

 The first week of meteorological spring will start out with some sunshine, but clouds and more widespread rain potential will fill in over the course of the week. We will not see much cloud cover Sunday night into Monday morning, allowing temperatures to quickly warm from the low 20s to the mid-40s by Monday afternoon. Thicker clouds filter in by evening ahead of the first of several weather systems.

We will remain dry through about 12AM-3AM Tuesday morning, but isolated and light rain will begin to develop before daybreak Tuesday. Initially, there may still be just enough cold air in place to cause a few patches of freezing rain, but this will quickly flip over to just liquid rain by morning.

Coverage of showers will be a bit higher late Tuesday morning into the afternoon, with a few pockets of steadier rain. There will be several dry hours Tuesday afternoon and evening, but it will remain damp with some spotty drizzle mixed in. Temperatures will struggle to reach as warm as they were Monday considering the added cloud cover and spotty rain.

More widespread potential for rain arrives Wednesday and again Friday with stronger passing waves overhead. Each of these could bring some pockets of steady to heavy rain with a few embedded rumbles of thunder. Some drier windows between systems will be centered around Wednesday morning and Thursday afternoon. In total through Saturday morning, rainfall may amount to around an inch for most in Northern Illinois. There may be a sharp cutoff with under a half inch for some in Wisconsin and the most abundant rain remaining across Central Illinois. Temperatures will continue to rise, particularly with Friday's passing system bringing afternoon highs up near 60°!

Warming trend with periods of steady rain next week

 A warmer and wetter pattern change is on the way for much of next week. The upper level flow will turn to come out of the Southwest, pushing a much warmer and moisture-filled air mass our direction. The most abundant moisture begins to set in Monday night into Tuesday, when our potential for steady rain showers will begin. The map below shows our "precipitable water" values, which is a measure of how much water vapor there is in a vertical column of air. When PW values reach an inch or higher, that indicates some very rich moisture, especially for early March standards.

Even meager forcing will be able to shake out some of that moisture in the form of scattered rain showers beginning Monday night or Tuesday morning. With a little bit of cold air still in place, there is a low-end chance for some of this precipitation early Tuesday to fall in the form of light wintry mix. But the bulk of it will come down as rain with temperatures steadily climbing at the surface and in the low/mid levels of the atmosphere. Surface temperatures will reach the upper 40s to 50s starting Wednesday.

The coverage of rain shown above for Tuesday afternoon is fairly scattered, with around 40-60% of the area seeing rain at any given time. We will see similar coverage of rain continue into the middle of the week, including Wednesday and Thursday. There will still be many dry hours through the week, but the main window for steady rain in the near-term looks to be Monday night into Tuesday. Two more systems will pass later in the week, with lesser confidence on timing between Wednesday-Thursday then Friday-Saturday.

Several of these systems could bring some broad soaking rainfalls over the Midwest and Ohio River Valley through the course of the week. Heaviest rain looks to be displaced mainly across Missouri into Central and Southern Illinois/Indiana, with some locations possibly seeing 2-4" of rain next week! Locally in Northern Illinois, projections give us around a 50/50 chance to see around an inch through the course of the week.

Brief cooldown into the weekend transitions into active pattern next week

 

Well yesterday sure did feel nice as consistent sunshine and a southerly wind through the day allowed for temperatures to reach up into the mid 60's! Unfortunately, though, a cold front overnight did sweep through the region which has caused a dramatic change in temperature as we're in the mid 20's to start the weekend. Today will have a bit of chilly feel as we'll be right near freezing which will be accompanied by the chances of a few snow showers.

Through the morning and afternoon, a weak clipper system will pass just to our north which will allow for some snow chances throughout the day. As of now, most snow showers look to remain north of the state line however a few minor accumulation totals in Southern Wisconsin may be possible today. Across Northern Illinois, snow shower chances will be a bit lower however, intermittent snow showers will be possible into the afternoon today, but accumulation totals will remain near zero or very minimal. 
 

Shifting the focus into next week, we'll see consistent southwesterly flow starting late Monday night and into Tuesday which will allow for warmer temperatures along with higher atmospheric moisture content. Combining that with a stronger and more active jet stream, precipitation chances look to be higher heading into the middle of the week. 

Sharp cool-down with few snow showers this weekend

 After reaching the mid-60s Friday, it will be a much more winter-like weekend with highs in the 30s and scattered chances for snow showers. As a broad area of cooler air spreads Southward from the Northern Plains, a narrow axis of moisture will intersect it, developing some snow showers.

The steadiest of these snow showers will be centered along and North of highway 20 in far Northern Illinois up through Southern Wisconsin, but a few light snow showers may be possible as far South as I-88 or even I-80. The timing of snow will be mainly between late morning and early evening.

In total, up to 1-2" may come down across parts of Southern Wisconsin and far Northern Illinois, with a sharp gradient to little/no accumulation further South of Highway 20 and I-88. Impacts to roadways will be somewhat limited due to the warm ground from the 60-degree highs the day before. However, a few slick spots will be possible as temperatures drop into the low 20s and teens Sunday morning.

Another passing system will keep the chill going through Sunday and bring another narrow axis snow showers Sunday night into Monday. Strong high pressure over the Great Lakes will likely limit how much snow may reach this far North, keeping the majority if not all of the snow South of I-80 and into Central Illinois. The large majority of the Stateline will remain dry between Sunday and Monday afternoon.

A pattern change is on the way toward the middle and end of next week. A more Southwesterly flow aloft will force more moisture and warmth our direction, leading to increasing rain chances the later and later into next week you go. While it will not be raining the entire time, pockets of soaking rains with over 1-2" of rain may be possible across parts of Central and Southern Illinois. The Northward extent of the beneficial rainfall is still uncertain this far out. It also comes with a subtle warm up, as temperatures return to the 40s and 50s by Wednesday and Thursday.

Elevated brush fire risk with strong winds Friday afternoon

 A much milder air mass has pushed temperatures into the 50s and 60s across the Stateline as of 2PM, very warm for late February standards! But this has not come with much moisture, as dew point temperatures are still sitting below 30° across the area. As a result, relative humidity is around 20-30% for many.

Wind gusts have not been all that strong but may still push 25+ mph at times this afternoon, mostly from the West-Southwest then West-Northwest. While not strong enough for substantial fire danger, this will be strong enough to promote an elevated brush fire risk. Be sure to avoid outdoor burning this afternoon!