May market meltdown is not out-of-the-question. It's not simply what's already concerning about the 'credit markets' heavy Auction Calendar; at the same time certainly that's a major factor to suppress equity interest in a seasonal time when available funds will need to absorb that supply (as that presses rates higher organically, besides any economic impacts).
 

Bottom line:  the market was and is extended. Month-end action was just a bit limited due to the news of the day. Techs were generally quite heavy. Regardless since the 2700's I've said look for the S&P to be 100 handles or more lower from April highs to the end of May. 

There is no change in my overall outlook for it working lower. Incidentally, a good while back one of my warnings related to reduced 'human' control of algorithmic trading. At the time I focused on trading desk reductions by 2/3 at UBS, once the largest trading room in New York.

Today Bloomberg reports that at one Goldman Sachs group it's already sort of happened; with 15 years ago 500 people working 'making markets' in stocks, and now there are 3 people. That's not a typo; machines have replaced them. Yes we all know about electronic execution; but problem is the absence of 'true' market makers is the kind of 'trap door' risk such as I've outlined before (and early February was an example of); when the 'maintenance of orderly markets', historically the role of market makers or specialists (such as exist mostly for photo-op's on the NYSE these days), diminishes.

What happens is the takeover by algorithmic guidelines; and vacuums as we have seen can ensue. Hence with a key reversal day like Monday, it behooves one to remember what can happen when the 'keyhole exits' do close; and especially if they close for a period of days or weeks.