Why Did We See 70's Last Week?

We had a beautiful stretch of weather last week to start off the month of November as highs exceeded 70 degrees four straight times. It was unusual, and record high temperatures were threatened during the stretch of warmer weather. So why did we see that warmth?

Well, surprisingly enough, it starts all the way in the Gulf of Alaska. Due to the dynamics of the atmospheric circulation pattern of the Northern Hemisphere, this low pressure system is semi-permanent. With that low being there---and being strong enough--a dominant high pressure system was located right off of the Pacific Northwest coast, causing ridging--or warmer weather--to form adjacent to the West Coast.

Then, due to the properties of ridges and troughs, a trough was located immediately downstream of that high pressure system and ridge over the western half of the United States. That trough brought a period of colder weather and rainy/snowy weather to the West. And, as you would probably expect, a ridge was located over the eastern United States as the jet stream lifted north. As a result, locations from Nebraska to New Jersey witnessed temperatures well-above normal, in addition to plentiful sunshine.

The strength of that ridge allowed it to remain in place for nearly five days before a strong low pressure system was finally able to break the ridge down and bring a return to normal temperatures to the Stateline.

Potential Storm System Next Week

As we enter an extended period of dry and cool weather, it is easy to look ahead at when the next storm system will affect the region. So, looking ahead at the next seven days, that system will move in on Wednesday and Thursday in the form of rain, strong winds, and potentially some thunderstorms. Over the past few days, forecast models have continued to suggest a low pressure develop in Oklahoma and move northeast towards the Stateline while deepening and strengthening at the same time.

In association with a deepening low pressure system is moderate to even heavy rain and possibly some thunderstorms for the area and surrounding states. The two main long range forecast models were in disagreement regarding the placement and movement of that low, but the most recent runs of those models have shown a better agreement between them, which is a good sign for forecasters because it allows us to create forecasts with better accuracy and reliability. Therefore, as opposed to being "unsure" of the timing of the rain for next week, it appears pretty likely that the rain and possibly even thunderstorms will move in Wednesday afternoon and last through Thursday late morning before leaving a few scattered showers behind on Friday.

The area in darker green is the concentrated region of heaviest rainfall for this system, an area that could see well over an inch of rainfall before all is said and done. Not only will the rain be heavy, but the winds will pick up Thursday as the low pressure deepens and moves overhead.

This type of pattern is very typical for this time of the year. Having a streak of nice, dry, and mild days followed by a strong storm system that brings a decent rainfall and colder air is not abnormal for October and November as the wintertime cold tries to win the battle against the remaining warm air in place.

Back to Reality

We had a very warm week across the Stateline with temperatures topping out in the 70's on four straight afternoons with plenty of sun to be had for the region. With that extended stretch of warmth, we can officially say we have experienced an Indian Summer because we saw our first freeze event of the season followed by several days spent well above average.

These are the official high temperatures from Thursday. Most of the region basking in the lower 70's before the afternoon cloud cover rolled in. And, following that cloudiness was a cold front that pushed through on Thursday night bringing rain with it. The rain ended rather quickly as it raced off to the east, but the bigger story is the much cooler air settling into the Stateline. Winds ahead of the cold front were out of the south throughout the week, which is why we soared into the lower 70's. Those winds have shifted to west northwest, and that means cooler air is filtering into the region from Canada. So, if you enjoy the warmer temperatures, the latest forecast may not be what you want to see as we return to normal.

Here is that outlook featuring much cooler weather for the weekend. High temperatures will be near 50 degrees, a good 20-25 degrees cooler than those high temperatures we saw from Monday through Thursday. While these temperatures may seem cold, they are actually seasonal for the first half of November.

Thursday Evening Weather Update

We've had a few wind-whipped showers this evening, but the main rain/thunder event remains to the west.  However, showers are beginning to become a little more widespread in eastern Iowa and those are now moving into far northwest Illinois.

There have been a couple lightning strikes ahead of the main cold front, but we're not expecting a widespread thunderstorm event.  Rain coverage will continue to increase and spread east through Midnight, with rain ending by daybreak Friday.

Other than an occasional wind gusts nearing 40 mph, there haven't been many reports of strong thunderstorms.  Those have been further west and south.

Rainfall totals will add up to half an inch in many spots by Friday morning.

Rain Thursday - Thunder Possible, Too

Not only could Thursday bring rain, but it may also bring a few thunderstorms into the night.  We typically don't think of thunderstorms in November, but it's possible.  Especially after several warm days in a row.

A change in the jet stream pattern that is currently bringing snow to the west will take us from the 70's back down to the 50's, more typical for this time of year, by the end of this week.  In between, rain will fall Thursday night.  But it's not only the drops of rain we could hear Thursday.  There is a possibility of thunderstorms Thursday evening into Thursday night.

Most of Thursday will remain dry, but clouds will be on the increase during the afternoon.  Dew point temperatures Wednesday reached the upper 50's to near 60 degrees.  That's pretty high for this late in the season.

As a cold front moves in from the west, showers/storms will occur west of the Mississippi River.  Very strong winds in the jet stream will help drive storms possibly from Iowa down south through Texas during the afternoon.

The actual cold front doesn't pull through until Thursday night in Northern Illinois and Southern Wisconsin, which is a limiting factor for our thunderstorm potential.  However, those strong winds in the jet stream continue into the night.  That may be just enough to sustain a few stronger storms in the area late Thursday evening.  Even though the probability is low, should thunderstorms develop strong winds would be a very good possibility.  A scenario we often refer to as a 'high shear, low CAPE' environment.  The wind shear in the atmosphere, or changing of wind speed and/or direction from the surface above, will be very high.  But the CAPE, or available energy needed for strong storms, will be low.  It's often set ups like this we have to pay close attention to because we're not expecting any severe weather. 

Soggy Thursday Night

After a beautiful past week with temperatures making it into the 70's, changes will occur for the end of the week. An incoming cold front and low pressure, currently tracking across the western plains, will bring rain and cooler temperatures to northern Illinois and southern Wisconsin Thursday night and Friday morning. Overall, we'll mainly see rain showers though a few thunderstorms are possible. In any of the storms, higher rain totals will be observed, which is good, since rain totals are down about 2" since the start of the year. Rain totals look to accumulate to about a half inch of rain, with more accumulating rain to the north and in the southern plains.

Another Foggy Morning

More fog for you this morning - impacting visibilities across the Stateline. There is a Dense Fog Advisory in place for Winnebago, Boone, McHenry, Ogle, Lee, and DeKalb counties. Fog is area wide, but locally dense in some places. The fog will thicken the farther east you travel, DeKalb's visibilities are down to a quarter of a mile. The Advisories for Jo Daviess, Carroll, Whiteside, and Stephenson counties have expired early, while the Advisory for eastern areas will last until 10am.
As mentioned in the post below, the cloud cover and fog will impact temperatures this afternoon. Where the fog and low level clouds linger, temperatures will be in the low to mid 60's, while those that see the fog dissipate quicker and see more sun will warm into the upper 60's and possibly low 70's.