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.

Heavy Rain and Severe Storms in Areas Already Hard Hit

Deadly tornadoes and flooding occurred over the weekend from East Texas all the way through central Illinois.  Residents there have only had a few days to clean up and dry out before preparing for round number two coming up Wednesday and Thursday.

A developing low pressure over the pan-handle of Texas Tuesday night will move east through Oklahoma, Arkansas and into southern Indiana by Thursday night.  Strong to severe

thunderstorms are possible once again over East Texas, Louisiana and Mississippi late Wednesday into Thursday, while flooding rainfall is possible over most of central and southern Missouri and Illinois.  Rainfall totals there could reach between three to five inches of additional rainfall from what fell over the weekend.  Flash Flood Watches and Flood Watches have been issued in Missouri, Illinois and Arkansas. 

Frosty Nights Ahead

First it was the rain...and now we are talking frost tonight. A Frost Advisory will go into effect late tonight through early tomorrow morning. You'll want to make sure you bring inside or cover any sensitive plants this evening.

We have the perfect setup for widespread frost develop for the area. An incoming high pressure system will arrive late today and will settle overhead by tomorrow. This brings with it drier air which helps to clear out the cloud cover this evening. Dry air also means low dew points, this typically brings colder overnight lows as low temperatures fall close to dew point temperatures. You also need light winds for frost development, because when winds are stronger it helps to mix out the colder air. When you have clear skies, then you have nothing to insulate heat near the surface, again helping low temperatures to fall to their lowest potential, the dew point.

You'll want to either bring in or cover any sensitive plants before you head to bed tonight. This evening isn't the only chilly night in the forecast, frost is possible again Saturday night into Sunday morning.

Small Hail with a Few of the Stronger Showers Monday Afternoon

It wasn't severe, but there were a few reports of pea sized hail that fell with some of the stronger showers Monday afternoon.  Today was actually a pretty good set up for not only an increase in shower activity, but also for the development of small hail or graupel.

It wasn't overly warm at the surface, but definitely a lot warmer than what it was roughly 10,000ft up into the atmosphere.  Temperatures there fell between -11 and -13 degrees!  Pretty cold for the start of May.  As low pressure moved into southern Wisconsin surrounding air was forced upwards, due to a decrease in pressure.  As the air was pulled up, it quickly cooled causing just enough instability in the atmosphere to form those bulky looking cumulus clouds we had earlier today and eventually leading to the bouts of heavy rainfall during the afternoon.  Since the air didn't have far to travel aloft before running into an air mass where temperatures were below freezing, the liquid droplets were quick to freeze into tiny hail stones.  The showers that developed were not strong enough to maintain the now heavier frozen droplets, or hail, in the atmosphere causing them to fall with the stronger showers.   

There will still be a few showers from time to time Monday night, but as the low pulls even further away from the western Great Lakes the rain will become less and less.  Cloud cover does stick around, but at least our skies will begin to dry out.

April Showers...

...bring May flowers. After the April we just had, our flowers will be beautiful!

It was a soggy April with the month's total exceeding seven inches! The average is 3.35" which means we doubled April's average! The official surplus tops at 3.78"! In the past five days alone, Rockford received 3.02", which is about a quarter of an inch below the month's average. Here's a daily breakdown of the past fast five days:

Wednesday, April 26th: 0.56"
Thursday, April 27th: 0.65"
Friday, April 28th: 0.03"
Saturday, April 29th: 1.01"
Sunday, April 30th: 0.74"

 Though all of this rain is not good for area farmers, who want to continue with spring planting. This week will feature small rain chances and temperatures that trend below average.