Temperatures hit 90 degrees for the first time this season Wednesday afternoon

 

Phew! It was a toasty one this afternoon with temperatures warming into the upper 80s and low 90s. Rockford reached its warmest temperature so far this season with a high of 91 degrees! The record high for May 27th is 99, which was set back in 2012. The low this morning fell to 52.

Skies have been mostly sunny for much of the afternoon with only a few cumulus clouds bubbling up over the last few hours. Those clouds have formed with the little instability we have overhead but are beginning to quickly fade this evening. Temperatures will remain in the 80s through sunset but are expected to quickly drop following the passage of a back-door cold front this evening. Overnight lows will once again drop into the low to mid 50s.

Thunderstorms have developed along the cold front to our north in Wisconsin but will really lose steam as they travel closer to southern Wisconsin after 7pm/8pm. There is a small chance for an isolated shower or storm in southern Wisconsin, but the vast majority of the viewing area is expected to remain dry.

On average, our first 90 degree day is usually reached around June 4th. Last year the mercury reached 90 degrees on May 15th. Our earliest recorded 90 degree day occurred on April 10th back in 1930, and our latest was in 2008 when we didn't reach 90 degrees until September 1st. This will likely be our only 90 degree day through the rest of May as temperatures are expected to remain in the 70s and 80s through the weekend and into the beginning of June.

Dry weather to persist, a few slight chances of rain

 Written by: First Warn Weather Intern Patrick Murray

Overall, dry weather will continue to dominate the forecast to end the month of May, and the beginning of June doesn't look to tell much of a different story. An Omega block has settled in across the central US, with high pressure in place preventing any storm system from reaching the area.

High pressure is expected to be in place across the Great Lakes region next week. As this area of high pressure slowly pushes off to the east, and we find ourselves on the western edge of a disturbance centered over the northeast, multiple back-door cold fronts will make their way through the Stateline.

The first looks to arrive Thursday afternoon/evening, with weak forcing and upper-level winds in place, rain looks unlikely, though temperatures will cool nicely into the end of the week.

Another cold front approaches the area Saturday night into Sunday, with high pressure in place over the area, limited moisture will be in place, meaning most, if not all of the area, stays dry.

The final of this parade of back-door cold fronts moves in Monday evening. Slightly better dynamics will be in place for this one. Despite this, rain chances still remain very slim. Most of us will stay dry, though a few of us could see an isolated shower and perhaps even a rumble of thunder thanks to some instability aloft.

So, what exactly is a back-door cold front? Typically, cold fronts move in from the west/northwest and are associated with an area of surface low pressure. Back-door cold fronts, on the other hand, come from the east/northeast (or the "back-door" if you will) and are often associated with breezes off of Lake Michigan. Usually, we monitor these back-door fronts for the potential for some shower and thunderstorm activity, but the dynamics in place over the next week, and strong high pressure will likely prevent most of us from seeing any rain, meaning the end of May and beginning of June promise to be drier than what we are accustomed to.

Summer like conditions to round out the month

 

May has certainly been on the warmer side with temperatures as we've already seen more than half the days this month with temperatures above average! This doesn't look to change as we head towards the month as high pressure will looks to keep us above average through the rest of May!

Starting with today with high pressure moving to our east today, winds will gradually shift southward allowing for warmer temperatures to creep up into the region. Today as well as tomorrow could be the warmest days not only of the month, but the entire year so far as plenty of sunshine both days should bring us into the upper 80's.

Through the evening tomorrow a weak cold front is expected to move through the state line which may bring an isolated sprinkle or two to some of us. However, the biggest impact will be sending our temperatures down into the 70's towards the end of the week. Thankfully, our upper-level pattern will continue our very warm pattern with upper-level ridging developing, on the flip side though this will also keep us very dry heading into June. As we round out the month, precipitation probabilities may need to be monitored quite heavily as this year's May might be one for the record books in terms of record low precipitation. 

What is an upper-level blocking pattern?

 The last week of May will feel more summer-like as temperatures climb into the mid and upper 80s Tuesday and Wednesday, and then in the upper 70s/80s for the rest of the week. The warmup, the result of an upper-level blocking pattern that'll hold strong through the weekend. You've likely heard us talk about blocking patterns, but what exactly are they?

An upper-level blocking pattern occurs when either high pressure or low pressure develop over an area, preventing other weather systems from moving through - hence a block. Blocking patterns can last for several days which can often result in a persistent weather pattern for those locations that end up under the block. For example, blocking high pressure in the summer months can lead to warm -or hot- and dry conditions for many days in a row. There are several blocking patterns that can occur, but the two meteorologists often reference the most are the omega block and rex block.

Omega Block:

An omega block often occurs in the summer and is responsible for hot and dry conditions that tend to lead to heat waves as precipitation usually occurs around the outer edges of the blocking high. This blocking pattern gets its name because it resembles the Greek letter Ω.

The higher pressure aloft will cause the air to sink, warming temperatures near the surface. The sinking motion also prevents any air from rising, limiting the chance for any precipitation to develop underneath the ridge. This is why these types of blocking patterns can worsen drought conditions, while at the same time cause temperatures to soar. Often times heat and drought will go hand-in-hand. Overtime, the blocking pattern will start to break down as smaller scale disturbances move over top of the ridge, causing it to weaken and eventually breaking it down.

Rex Block:

Rex blocks occur when high-pressure becomes locked in place from low-pressure to the south. The cut-off nature of the low prevents the high from moving and typically the jet stream winds to the west are not strong enough to initially move the high itself. These types of patterns will hold until one of the pressure systems changes intensity, causing the high and low to become unbalanced.

Dry conditions can be found near the blocking high while an unsettled pattern will occur near the low. 

Memorial Day forecast: Morning clouds give way to afternoon sunshine

 Radar may look a little daunting early this morning, but showers will dissipate by the time they arrive. There is a very small chance (10%) for a stray shower Northwest of Rockford through 11AM, but sunshine is expected by the afternoon.

That sunshine will result in a jump in temperatures. Afternoon highs will push into the mid-80s for most. Game on for any outdoor plans, including any parades, cookouts, and other festivities. Remember to apply sunscreen and hydrate today as it will be a warm day!

Summer-like week with rain chances few and far between

 While some locations got a bit of rainfall last night into the early hours of this morning, it wasn't for everyone. A few spots across Lee/DeKalb Counties saw between 0.5-1.0" of rain, but the Rockford airport only picked up 0.19", bringing the monthly total to 0.47", the 3rd driest May to date.

No rain expected for your Memorial Day plans, but a few clouds will pass by midday. Those clouds will not limit the degree of warming whatsoever, as afternoon highs still push into the mid-80s. A+ for any outdoor plans!

Unfortunately, it does not look like we have much rain on the way with a blocking high pressure that will set up near the Great Lakes, limiting rainfall potential locally through the week ahead. Soaking rain may be likely as close as Southern Illinois, but the dry air from Great Lakes high pressure will severely limit Northward extend of that moisture, resulting in very little if any widespread rainfall over the next 5-7 days.

On the bright side, that drier weather will lead to a few more days in the mid-80s for afternoon highs. A backdoor cold front Wednesday may produce our only isolated rain chance, but also will work to bring a "cooler" Easterly wind with highs back to the upper 70s to close out the week.

Warm and dry to close out Memorial Day weekend

 After a few light showers Saturday night, the remainder of the holiday weekend will be dry with a continually warmer trend. The overnight rain will be exiting to the East by early Sunday morning. Southeastern parts of the Stateline such as Rochelle and DeKalb may hold onto a slim chance for light rain through 7AM, but mid-morning into afternoon will bring a decrease in clouds, drying things out.

Temperatures Sunday afternoon will approach or surpass the 80-degree mark with more abundant sunshine after midday. Evening and overnight will not be very cool, only seeing lows drop into the mid-50s. Monday will bring another step up in the temperature department, despite some afternoon cloud cover. Mid-80s appear likely, and without any rain, Monday will be a picture-perfect unofficial start to the summer season for any outdoor activities that may be in the plans.

Radar Monday morning may look a little daunting with some showers to the Northwest, but we should see those decay as they approach by midday, resulting in only a few passing clouds locally. The chance for any rain is under 10%. Once the clouds pass by 5PM, the evening and nighttime will be clear once again.