Saturday, March 28, 2015

Windy Sunday afternoon

Temperatures Saturday topped out in the upper 30's and low 40's.  Not bad even if it was below average.  That's all about to change Sunday as strong southwest winds will bring in somewhat of a warmer air mass, but it's not necessarily going to feel all that warmer on Sunday.

Strong low pressure will remain tied to the U.S/Canadian border Sunday afternoon.  A warm front will lift through southern Wisconsin and northern Illinois, followed then by a cold front Sunday evening.

Moisture will increase some Sunday morning ahead of the warm front and this could lead to a quick burst of a wintry mix - sleet, freezing rain & snow - between 6am and 9am, before switching over to all rain mid-morning Sunday.  Heads up if you're going to be traveling early on Sunday. 

Wind gusts by Sunday morning will already be approaching 30 mph and will increase through the afternoon with gusts close to 40 mph.  The wind will ease a little once the cold front passes Sunday evening, but there will still be an occasional wind gust near 20 mph through 8pm Sunday night.

While the surface low pressure will be far away from the Stateline, there may be just enough energy in the atmosphere to generate a thunderstorm or two midday Sunday.  So, keep your ears open for that.  The start of next week won't be nearly as windy, and temperatures will warm into the low to middle 50s - closer to average for this time of year.

Friday, March 27, 2015

Thunderstorm 101: How storms form and when tornadoes are most frequent in Illinois

It may not seem like it, but soon we'll be trading in the recent snow for springtime showers and thunderstorms.  And with the recent severe weather in the Plains the past couple of days, I wanted to discuss a little more on how thunderstorms form, and the frequency of tornadoes in Illinois.

Just like the interstate you drive on to get you where you need to go, the jet stream acts like an interstate for storm systems.  Since the jet stream flows from west to east, storms typically track from west to east.  While there are a lot of factors that contribute to the development and strength of thunderstorms - like lift in the atmosphere, moisture and instability - the strength of the wind within the jet stream is a major factor.

Higher wind speeds within the jet stream are called 'jet streaks'.  And it's those jet streaks that can help enhance thunderstorm development.  Going back to the interstate thought, when you come up to a construction zone on the highway, you slow down.  When you get out of the construction zone, you speed up.  Winds do pretty much the same as they round the ridges and troughs in the jet stream.  As winds get closer to the dip, or trough, in the jet stream they tend to slow down.  As winds round the base of the trough and come out on the other side, they speed up and spread out.  This causes 'divergence' in the atmosphere, which causes lift throughout the atmosphere.  Where that lift occurs, is where low pressure systems develop and thunderstorms form, and intensify, at the surface.  Now, there also needs to be moisture (higher dew points) and instability, but if all comes together just at the right moment, severe weather can develop.

Since we're getting closer to severe weather season in northern Illinois and southern Wisconsin, I thought we should take a look at the frequency of tornadoes by month, as well as time of day.  Tornadoes can occur any month of the year - remember the January 2008 and November 2011 tornadoes?  But, the months that experience the highest frequency of tornadoes throughout Illinois are April, May and June.  This is as the jet stream shifts north, pulling warmer air with it.


Tornadoes can also occur any time of the day,
but most frequently we see them late in the afternoon and early evening.  The reason:  by that time we've maximized the amount of heating and instability (two ingredients needed for thunderstorms).  However, tornadoes can occur any time of day and it's the ones that form during the 'off hours' of the early morning or overnight, that tend to be the most dangerous because people are either not aware that severe weather is occurring, or they're fast asleep and don't hear the warning.  That's why it's so important to have a safety place in your house, know what to do when severe weather occurs and most importantly, have a way to receive warnings.  Something that will wake you up in the middle of the night.

Warmer weather will come, I promise you this.  And as we transition into the warmer months, let's work to become better prepared for when severe weather occurs!

Click here for the complete report from the Illinois State Climatologist Office, Illinois State Water Survey

Near record cold, once again

It's a phrase we've become used to this winter season:  Temperatures today will be near record cold.

Unseasonably cold air continues to spill down through the Great Lakes as a very strong ridge of high pressure builds out west.  Record highs are possible through the west, while record cold highs are possible closer to home.

The record cold high for today is 31 degrees, set back in 1965.  Today, I'm forecasting a high of 35 degrees.  Below average weather will last through the weekend before temperatures climb into the low 60's by next week.

Thursday, March 26, 2015

Pattern change coming to welcome the first of April

We've had a few cold days this week, and that chill will last through the weekend.  A strong ridge of high pressure will build out west with temperatures running nearly 15 to 25 degrees above average.  Unfortunately, this will do nothing to help the drought situation that continues to worsen out west. 

Just the opposite will happen through the Great Lakes and out east where highs will run almost 15 to 25 degrees below average.  This pattern will stick around into the weekend, which will keep temperatures below average.

A strong low pressure system will help to break down the ridge out west on Sunday.  This low will also pull a cold front through, but the air mass behind the front will have come from the Pacific, rather than the north.  This means temperatures into next week will begin to warm into the 50's, possibly breaking the 60 degree mark for the first of April.  Hopefully this isn't an April Fool's joke by Mother Nature.

As we head a little further into April, the jet stream will take on a more active, spring-like pattern with systems coming through every few days.

Wednesday, March 25, 2015

Earthquake Near the Stateline

The US Geological Survey confirmed that a small earthquake, 2.9 magnitude, was recorded near Lake in the Hills this evening. The quake occurred just after 6:00pm tonight in southern McHenry county. Lake in the Hills is about 40 miles to the south east from the Rockford area. There haven't been reports of any damage, but there are reports of some people feeling light shaking, and hearing rumbles in Rockford. While earthquakes in Illinois aren't common they do happen from time to time. In the past 100 years there have been at least 20 earthquakes in varying magnitudes. The USGS haven't noted a cause, but normally when there is an earthquake east of the Rockies, it's due to faulting in the bedrock miles deep.
Did anyone hear or feel the earthquake this evening? 

Tuesday, March 24, 2015

Rain, Freezing Rain, and Thunder

A little bit of everything is possible with our next system Tuesday evening.  As winds increase with the low level jet tonight, this could bring a few rumbles of thunder to Illinois overnight.

The first round of showers moved through northern Illinois around dinner time, next round will come around 10pm and 11pm. The rain continues overnight and lasts through daybreak Wednesday morning, clearing out from west to east.

Temperatures are hoovering close to the freezing mark, so along with the rain, freezing rain and sleet is also possible. Temperatures will warm after midnight though, and will help to decrease that threat. Looks like we could pick up about a half to three quarters of an inch of rain by tomorrow morning. There is a slight chance for another passing shower tomorrow afternoon. Clouds will clear for a bit early afternoon before increasing again a little later on. High temperatures will warm to either side of 50°.

First round of spring severe weather possible

Don't worry, it's not for us!  But, areas to the south could experience their first bout of severe weather later today and tomorrow.

A fairly strong spring jet stream pattern has taken shape over the southern Rockies this morning.  This will allow low pressure to develop in Oklahoma and pull northeast reaching northern Illinois tonight.

Winds are currently from the east, but will increase from the southeast today ahead of a warm front.  That front will pull a warm, moist air mass northward later today.  Rain will overspread from south to north through the overnight, and with that could come a few rumbles of thunder.  Further south in central & southern Illinois, Missouri and parts of Arkansas and Oklahoma are in for possible severe weather with hail, gusty winds and isolated tornadoes. 

Rainfall amounts could add up, as the biggest rainfall is expected since the end of last year.  Totals between a quarter inch to half inch will be likely by Wednesday morning.  Temperatures today and tonight will be key in determining just what type of precipitation will fall.  Most of northern Illinois should experience rain, however, just over the border and further north in Wisconsin may experience more of a wintry mix through Wednesday morning.