Frost/Freeze Warnings in Place

A Frost Advisory has been issued once again for Green, Rock, Winnebago, Boone, McHenry and DeKalb counties late Sunday night through early Monday morning.  Freeze Warnings have been issued for southeast Wisconsin, nearly all of Michigan, northern Indiana and Ohio.  High pressure centered over Ontario, Canada will keep temperatures in the mid, and possibly low, 30's over parts of the Great Lakes Sunday night.

Counties west of Rockford are not included in the advisory as of yet because temperatures are expected to warm slightly, with the possibility of a little more cloud cover, during the overnight.  However, to be on the safe side it may be a good idea to cover or bring in any plants that may be sensitive to the cold.  This should hopefully be the last frost/freeze of the season.

Warming Back Up

We've had a beautiful start to the weekend with temperatures hitting the low to mid 60°s here in the stateline.  Along with that, we've gotten plenty of sunshine! This will continue for the rest of the weekend, so be sure to make plans to go outside and enjoy the amazing weather.  This weekend has been a complete 180 from last weekend, and the reason for that is high pressure.  A high pressure system is making its approach from the north, which has helped to clear the skies and allow the sun to make its presence.  High pressure keeps air from rising, and thus keeping storms and rain showers from forming.  This high lingers around through Sunday afternoon, which is why the weather tomorrow will be just like today.

However, we do have to deal with a chilly overnight tonight as temperatures will drop into the mid 30°s.  As that high clears the skies during the overnight, the lack of clouds will allow temperatures to drop fairly fast.  This can lead to frost formation, and we do have a chance for some patchy frost up north tomorrow morning.  Green, Rock, Walworth, Stephenson, Winnebago, and Boone counties all have a chance for from patchy frost occurring early tomorrow morning.  Our southern counties will be slightly warmer, just enough to keep frost formation unlikely. 

After the weekend, temperatures will warm up a little more for the work week into the mid 60°s, but a low pressure system will bring us some cloud cover for the work week as well.  We'll still see a good amount of sunshine, but this low will help to keep our temperatures on the warmer side for the entire week.  A warm front will move near our area Monday night, but it doesn't look strong enough to form any rain showers.  That low will dissipate on Tuesday when a ridge of high pressure moves in, creating a blocking pattern known as an Omega Block.  This will help to keep the weather calm for the rest of the week, allowing us to enjoy the 60° temperatures in peace

Warm and Sunny Weekend with a Cooler Week Ahead

We have an amazing end to the work week here in the stateline, with warm temperatures in the mid to upper 60°s and lots of sunshine! You can't ask for better weather on a Friday, and one of the reasons for it is that we have a low pressure system out east tracking away from us.  This has allowed for air pressure to increase, which helps to keep plenty of clouds out of our area and bring us more sunshine.  That sunshine helped to warm our temperatures near average, but unfortunately we couldn't break that barrier today, although a few places came close with highs at 67°.  As that low tracks east, our wind speeds will die down for the overnight, but that low will also pull some light rain showers near our area around 7am tomorrow morning.  They will skim the eastern part of our viewing area, moving through Boone, McHenry, DeKalb, and the eastern portion of Winnebago county.  However, the heavier rain showers will be pulled eastward, so we'll only see some drizzle.

The drizzle will move out between 9-10am, and after that we have a beautiful weekend to look forward to.  60° temperatures and plenty of sunshine; that's what this weekend has in store for us.  You'll want to make plans for the outdoors because it's going to be great! Another low will move in to start the work week, bringing clouds for Monday and a chance for thunderstorms late Tuesday night.  That low will stall in the plains afterwards, leaving clouds to stall in our area for Wednesday and Thursday, but drier air moves in on Friday to clear the skies and give us more sunshine.  Temperatures will be in the low 60°s for Monday, but once the clouds continue to pour in our temperatures will stay in the upper 50°s for the rest of the week.

More Frosty Nights Ahead

Well we finally made it back into the 60's yesterday, and we'll do it again today! There is even a day where we climb into the low 70's, but before we get there we have some frosty nights ahead.

A combination of a few things will bring chilly overnight temperatures this weekend. First, we remain under the influence of northerly flow in the upper levels of the atmosphere, which typically supports cooler temperatures overall. We'll also be watching for an incoming cold front that will arrive late tonight or early tomorrow. While it brings a few light showers this evening, by Saturday evening low temperatures will be dropping into the mid 30's. You'll want to bring in or cover any sensitive plants with frost looking more and more likely. By Sunday night the atmosphere will be primed for optimal radiational cooling, which will again bring temperatures into the mid 30's. We will have mainly clear skies and light winds into Monday morning.

At least there is a light at the end of the tunnel, with a forecast high of 72° on Tuesday.

It's Been A While Since We Had a 60 Degree Day

Temperatures Thursday were in the 50's under cloudy skies early in the day, but warmed into the low to mid 60's once the sun came out.  It's been a little while since we had a 60 degree day in the Stateline.  The last time the mercury climbed to 60 degrees, or beyond, was back on April 26th when the high reached 69 degrees.  Since then temperatures have been in the 40's and 50's - unseasonably cool for the end of April and beginning of May.

Look for another 60 degree day Friday with just a slight cool down for the start of the weekend.

Roller Coaster Temperatures through May

April was an above average month, with our monthly temperature and rain total topping out above the average mark. But so far, May has been trending below average.

The past several days, along with forecast highs through the weekend remain below average. The average for the beginning of May is in the upper 60's, but we've been stuck in the 50's so far. We'll make it into the low 60's Thursday and Friday, but we fall back into the 50's behind a weak cool front early Saturday. Frost will also once again be possible Saturday night into Sunday as low temperatures drop into the mid and upper 30's.

We'll be on the up swing by Sunday, making it into the low 60's before upper 60's arrive Monday. I even went ahead and added a couple 70's to the forecast for Tuesday and Wednesday, but a chance for rain could keep temperatures a touch cooler. It will be nice to finally reach the 70's again, though that is about average for this time of year. The Climate Prediction Center keeps the probability of warmer than average temperatures just west of the Mississippi by next week, and then a higher probability of cooler temperatures to the east.

While we're forecast to make it into the upper 60's and low 70's by the middle of next week, it won't last. The Climate Prediction Center outlooks the Midwest and the Stateline area to see a higher probability to below average temperatures through the middle of the month.

Blocking Pattern Keeps Us Cool Through the Weekend, Could Warm Us Next Week

The forecast for the beginning of May is definitely cooler than what it should be.  Highs struggled to make it out of the 40's the past couple of days with persistent cloud cover and rain showers.  And while temperatures will be warming from where they have been, the numbers will still fall short of where they should be.

High pressure developing over Greenland will cause the jet stream to buckle heading into the upcoming weekend.  This will cause low pressure, currently forming over the south-central Plains (see previous post), to 'sit and spin' over the East Coast.  Meanwhile, a strong ridge of high pressure will build over the inter-mountain west with temperatures climbing near 80 degrees as far north as Montana.  Temperatures closer to home will not make it much past the low 60's for the weekend as cool north winds keep the chilly air around the Great Lakes and Midwest a little longer.


This pattern, however, breaks down late in the weekend with a second blocking pattern developing.  This jet stream block, known as an Omega Block, keeps low pressure over the East Coast and low pressure in the Southwest, while high pressure builds over the middle of the country.  If the low over the East Coast isn't quite as strong as some models suggest and doesn't push too far westward, temperatures locally could warm back into the low to mid 70's.  However, if the low out East is a little stronger it may push the warmth to the west keeping the continued chill over the Stateline.

So, what's the cause for this shift in our weather?  Part of it has to do with the NAO, or North Atlantic Oscillation.  'The what' you may be asking yourself.  The NAO is a essentially a fluctuation in pressures in the mid-levels of the atmosphere between the central Atlantic Ocean and Greenland.  There are two phases to the NAO, a positive and negative phase.  During the positive phase lower pressure develops near Greenland allowing the jet stream to position itself more from west to east.  During the negative phase of the NAO, the jet stream becomes a little more blocky with high pressure developing over Greenland.  This causes the jet stream to 'back up' so to speak, causing storm systems further west to slow down - like what's soon to develop over the East Coast. 

Now, going back to the potential warm up into next week...
Notice how the forecast (in red) for the NAO keeps it negative through the middle of the month.  If that were to hold true, it wouldn't hold much promise for our temperatures warming early next week.