In brief - the CRJ manual(s) don't give data (e.g. runway length required, etc.) for a takeoff in temperatures above 48°C (at 1100 feet elevation). Therefore it is not legal to do so, and the plane is grounded.
C'mon people.
The 48°C is a cert based on a multitude of factors, but really it is MTOW. ie at MTOW, with ALL of the other factors in a cert, there is a temp limit (based on sea level pressure.)
When the temp gets higher, you need to limit MTOW to the point where you cannot meet the DEP climb rate/obstacle clearance for the SID. It is a simple if/then, but the reality is that MTOW gets limited before max temp.
Cert assumes the worst case scenario, ie MTOW, max bleeds, min engine perf, and a host of other variables. (even icing on at max temp ?!?!) The airline performance people are the ones who decide if the ac can DEP given the cert and the parameters.
Some airlines that operate at airports with higher temps, go above and beyond the cert parameters, and have custom DEP procedures that provide the required obstacle clearance.
Regarding the article,
The various 737s, 747s and 777s made by Boeing can stay in operation until temperatures hit 52 C, an American Airlines spokesman told the National Post. French-made Airbus products, meanwhile, can operate until 53 C.