Thursday, October 16, 2014

U.S. Winter Outlook: A repeat of last year?

Mike Halpert, Acting Director of the Climate Prediction Center, says it's unlikely that we'll see the cold pattern take place this winter like we did last winter, but cold snaps are likely.  After all, it is winter and there will be cold.

He also says what made last winter so memorable was not the cold outbreaks, although those were extreme at times, but the persistent pattern through the entire winter.  Meaning once we got past the December/January time frame, there was no break down of the cold.  The cold continued into the middle of March!  And looking ahead to this winter there, at this time, appears to be no signals that suggest this type of persistent pattern taking hold once again.

Photo: NOAA
Photo: NOAA
El Nino, which is an ocean-atmospheric phenomenon in the Tropical Pacific that affects global weather patterns, could still develop this upcoming winter.  Right now, this has not taken place but Climate Prediction Center forecasters do expect a weaker El Nino episode to develop within the next month or two.  Unfortunately, unlike with stronger El Nino episodes, a weaker one offers little help in trying to determine the winter outlook.  So the current outlook is more consistent with an El Nino event, but the probabilities are just a bit lower.

While there are no strong signals as to whether temperatures over the three month winter period will swing above or below average, it does appear that there is a slightly higher probability of a drier than normal pattern across the Great Lakes.

Bottom line with this forecast is this, seasonal forecasts are a young and evolving science with many different tools, both new and old, forecasters use.  While El Nino and La Nina events are something that can influence the weather across the U.S., we also have to look at other atmospheric circulations and phenomena that, at this time, are still evolving in trying to understand.  Looking ahead, there will be cold and snow this winter - that's a given.  But the probability of having the extreme cold like we did last year is unlikely. 

Tuesday, October 14, 2014

Rainfall from Monday and expected rainfall for today

Rainfall totals ranged anywhere between half an inch to two inches Monday evening.  Today's rainfall won't be quite as much, but I wouldn't be surprised if another half an inch to three quarters inch of rain fell by this evening.

Showers have already begun to overspread early this morning and will remain scattered through Noon.  Low pressure moving out of west-central Illinois will pull closer to north-central Illinois by this afternoon.  As it does, a few breaks in the cloud cover could help fuel some isolated thunderstorms into the early afternoon.  Severe weather isn't anticipated, but if storms were to develop stronger wind gusts could be possible.

Spooky scenes from out of this world

NASA's Goddard Space Flight Center
Even the sun is getting into the Halloween spirit!  Back on the 8th of October, the sun showed its more 'spooky' side with brighter spots that look like a grinning pumpkin.  NASA says the active regions of the sun appear brighter because those are the areas that emit more light and energy.  They indicate an intense and complex set of magnetic fields around the sun's atmosphere, known as the corona.

Monday, October 13, 2014

Monday weather update: Severe weather stays south, heavy rainfall likely north

A significant severe weather event will likely unfold across Arkansas, Mississippi, Kentucky, Louisiana and southeast Missouri this morning and afternoon.  An ongoing line of severe thunderstorms has already produced at least one tornado in Arkansas this morning with one confirmed fatality.  Severe weather this afternoon will remain in the middle and lower Mississippi River Valley closer tied to a strong cold front and low pressure system.  Further north, heavy rainfall will become a concern this afternoon and evening for northern Illinois and southern Wisconsin. 

Skies will remain cloudy through the morning and early afternoon for the Stateline with the threat for rain increasing after 2pm.  Showers with embedded thunderstorms continue to lift north and will reach the Quad Cities between 11am and Noon, and the I-88 corridor around 2pm.  While these thunderstorms are not expected to be severe, heavy rainfall into the evening will be likely.  Drier air wrapping in on the backside of the low could cut off some of the rainfall overnight, but additional showers are likely through mid-day Tuesday.  Through Wednesday morning, one to two inches of rain will be possible.

Friday, October 10, 2014

Cool & rainy or dry and warm: What will next week bring

Other than a few showers here and there, it's been a pretty quiet couple of weeks in the weather department and that trend looks to continue through the weekend.  Next week, however, a big pattern change is in the works that will bring rain and even a few thunderstorms with it.  While the rain is for certain, it's what will happen in the days that follow that are a little more fuzzy.

Low pressure will move from the southern Plains through Illinois and into the eastern Great Lakes by Tuesday morning.  With the strength of the
system and dynamics from the jet stream, another round of heavier rain could be possible by Monday evening.  However, forecast models disagree as to just how fast the low shifts east.  The European forecast models want to hang on to the low a little longer and basically cut it off from the main jet stream.  If this were to happen low clouds, a cool east breeze and scattered showers would persist through at least next Wednesday.  The American GFS, however, quickly shifts the low to the east with a strong ridge of high pressure building in behind.  If that were to happen, skies would clear and temperatures would rise back into the middle and upper 60's.

Large scale systems, like the one expected Monday, are more likely during the spring and fall months because that's usually when we begin to see the greatest temperature contrasts from north to south.  With these types of systems, they also tend to move a little more slowly which makes me believe the low will hang around through at least Wednesday, if not Thursday, before moving east next week.

Thursday, October 9, 2014

The Science of Frost

With frost in the forecast both Thursday and Friday night, you might be wondering what kind of weather gives us these icy conditions. Here's a quick list of the ingredients needed:

Clear skies and calm winds allow temperatures to fall quickly, allowing us to get to the freezing conditions needed for frost. You also need a little bit of moisture in the air. Since ice is made of water, moisture is the obvious fuel you need if you want to scrape your car's windshield off in the morning.

As for Thursday night's frosty conditions, the National Weather Service has issued a Frost Advisory for all of southern Wisconsin through Friday morning. -BA

Winter woes: Could this winter be like last winter?

It's been the topic of discussion for many over the past few weeks.  Just what does winter 2014-2015 have in store for us?  Is it going to be like last winter - snowy and cold?  Or, are we going to have something completely opposite?  Time will tell, but there are some atmospheric signals we can look at that may give us a little bit of a clue as to what we can expect.

This past summer was just a littler cooler and wetter than average, although not by much.  El Nino occurred during the summer and the Climate Prediction Center gives roughly a 60% - 65% chance of El Nino emerging during the fall and winter months.  Forecasters are expecting a weak El Nino event to occur and last through Spring 2015.  What does that mean for our winter?  Well, according to Jim Angel, state Climatologist with the Illinois State Water Survey, El Nino events can vary in size, duration and intensity which can lead to variation from event to event.

Overall, the general trend of El Nino during the winter months include a warmer and drier winter with roughly 70% - 90% of average snowfall.  The Polar Jet Stream is shifted north and a little weaker than the Pacific Jet Stream which remains across the south.  This keeps the wet weather and active storm track to the south with slightly warmer than average temperatures in the northern Rockies, Plains and Midwest.  Remember, though that this is the 'average' trend and there can be exceptions.  While we'll likely have some pretty cold and snowy days, the overall three month average temperature & snowfall could be slightly warmer and near normal snowfall.