If the information Ian presented is correct, you are slightly in error, there have been days before '60 that had over 4 inches of rain. However, you will note that considerably *more* such days have happened in the past 50 years than happened over a similar span earlier in the record. And this is what is predicted as a result of global warming. Not necessarily entirely novel weather events, but increased frequency of previously rare events, and/or increased severity of "normal" dramatic weather events.

As to why it's happening? Higher heat means more evaporation, more evaporation means more water to become rain when the conditions are right. It's why scientists are predicting both droughts and floods as a result of global warming.

Really? That's not what the NOAA website says.

http://www.nws.noaa.gov/climate/xmacis.p...

Philadelphia Area (ThreadEx Station)

Extremes

Highest Daily Precipitation (inches)

Days: 1/1 - 12/31

Length of period: 1 day

Years: 1872-2013

Rank Value Ending Date

1 6.63 9/16/1999

2 5.63 8/3/1898

3 5.53 10/8/2005

4 5.21 8/13/1873

5 4.84 8/14/2011

6 4.77 8/27/1971

7 4.69 9/14/1966

8 4.68 7/12/2004

9 4.65 9/22/1882

10 4.62 6/29/1973

EDIT: The Chicago numbers were a bit harder to get but I did find this:

July

Day Record Precipitation Daily/Year

26 4.10/1878

August

Day Record Precipitation Daily/Year

2 5.63/1885

http://www.crh.noaa.gov/lot/?n=mayrec-or...

EDIT 2: 5 thumbs down from alarmists for linking to an NOAA website that showed that there were 3 days in Philly and 2 days in Chicago that contradict the questioners assertions?

Alarmists: "We don't want to see no stinkinnng facts. We want to scare people. We don't care if it's true or not."

Well this is one of the predictions of GW/climate change. As stated before the oceans are warming. This sends more moisture in the air and it has to come down somewhere. I forget if it was 09 or 10 but Nashville was predicted to get 5" of rain over the weekend and instead got 13" which pushed the river 12 feet over flood stage. They said it was a once in a millenium occurrence

There is suspicion that both Katrina and Sandy were do to climate change. This is speculation only at this point and difficult to prove

Higher temps in the oceans and atmosphere accelerate the water cycle and lead to larger and more frequent storms.

As most credible climate experts will tell you, 75 years is not even a blink of the eye in terms of climate trends/history.

Don't let anything bother you untill we have a more clear understanding of climate.....remember that climate science is in its infancy and there remains much to be discovered/learned.

According to "Inconvenience Truth" the world only had until 2008 to stop global warming. Now it is TOO LATE.

90% of humanity will die HORRIBLE deaths from floods, hurricanes, droughts, blizzards, tsunamis and earthquakes.

Only the Lear jet people like Michael Moore and Al Gore will survive the coming climate APOCALYPSE in their underground mansions.

I would ask for a second opinion. Your sources are suspect.

Knob

hy have extreme rain events increased so dramatically?

I have been looking at the top 10 largest rainfall for major cities across the country and using only those with a complete record - 1899 or before. What I have noticed is really odd. Philadelphia has seen 16 days in which 4 inches of rain or more has fallen in a single day. However, none of these occurred before 1960, when Hurricane Donna hit. You mean to tell me that for 75 years (1885-2013 period of record for Philly) there was not one single day with a 4 inch rain, and in the last 52 years they have had 16? That is mathematically impossible! Chicago is another city. From 1885 until 1956 there was not one day in which 4 inches of rain fell, now you have had over a dozen since then.

In some cases, 5 out of the 10 wettest days ever have occurred in the last 30 years!