flash flood watch

The whole area is under a Flash Flood Watch until tomorrow morning. Rain is approaching from the SW, and the heaviest rain will arrive after sunset into the early AM. Another 1-2" of rain can't be ruled out, with higher amounts in certain locations. After some places -- particularly in the northern suburbs -- saw 3" or more of rain last night the ground is already saturated and the flooding risk is elevated. 

The good news is that the rain should clear out tomorrow morning. The temps should climb into the 60s with a drier north wind and some sunshine. Sunday looks really nice with sun and temps near 70.

In other news, I've had more questions about El Niño -- or El Grande Niño as this one is being called -- and the effects on our weather. The answer remains that El Niño looks like to persist if not strengthen into the winter, and that usually correlates with a mild winter in Chicago. But the correlation is not perfect, and this year's El Niño is being affected by "The Blob" -- a massive layer of warm water in the North Pacific. See below if you want to read more. 

So, we're still favored for a much wilder winter this year than the prior two just based on reversion to the mean -- those were two pretty harsh winters. And the building El Niño gives us a further likelihood of a mild winter. But it's too early to write that in stone, and The Blob may well throw a monkey wrench into the system. 

http://www.nws.noaa.gov/com/weatherreadynation/elnino_article.html#.Vfx5r99VhBf

http://ww2.kqed.org/science/2015/08/09/possible-spoiler-for-el-nino-a-battle-of-the-blobs/

https://en.wikipedia.org/wiki/The_Blob_(Pacific_Ocean)

season recap and outlook

Summer 2015 in Chicago closed slightly on the cool side -- roughly the 35th percentile for warmth. June was certainly cool and wet but the rest the summer was unremarkable. We had a significant run of consecutive highs >80 but fewer than average highs >90. There has also been an abundance of tornadoes in the NWS Chicago region -- 29 confirmed so far -- which sets the all-time record. 

And now that summer is technically over, the first week of September goes down as the warmest of the year based on average temperature. 

Looking ahead, there is a likely resurgence of warmth next week. After temps peak in the 60s Friday and through the weekend we're likely to get in back to the 80s next week. 

And looking ahead to winter, there is a very strong El Nino in progress. The implications are significant, but it's also easy to over-extrapolate. For example, the North Pacific is also very warm, which could cause a "blocking pattern" similar to the one experienced at times in the prior two winters. That's not likely, but it's possible. So yes, the prior winters with a strong El Nino 1982-83 and 1997-98 -- were mild in Chicago, but that's not something to write in stone just yet. The odds are definitely in our favor to have a milder winter than the prior one (and certainly milder than 2013-14) but exactly how this plays out is TBD -- seasonal forecasts made a few months in advance are not especially good just yet. 

https://climateillinois.wordpress.com/2015/08/31/temperature-departures-in-illinois-during-the-1982-83-and-1997-98-el-nino/

https://climateillinois.wordpress.com/2015/08/26/last-two-big-el-nino-events-milder-winters-in-illinois/