(at around 34 mins) When the crew arrives at April's house, the water gushes in from the window, beginning the indoor shark fight scene. Immediately after this, when the characters leave the house to look for Matt, the water level outside is almost nonexistent.
Dry streets are repeatedly visible in the background of shots when they're supposed to be flooded with several feet of water.
(at around 27 mins) During the tunnel scene the cars are stopped for no reason. Then, after driving through the tunnel, Fin looks in the rear view mirror and it shows a flooded area with lots of sharks directly behind the vehicle. This same shot is shown a couple of times. However, when they leave the vehicle there is no water or sharks.
(at around 19 mins) As the waterspout destroys the Santa Monica Pier, an aerial cutaway shot shows the pier on a clear, sunny day with calm surf.
(at around 31 mins) During the trip to the Hollywood mansion there are several shots where a piece of paper on the left wiper appears and disappears from shot to shot.
(at around 1h 18 mins) The pilot of the helicopter is shown flying the helicopter with both hands held forward, as one might do with a conventional yoke on an airplane. In a helicopter. the left hand would be down at his side handling the collective, which contains the throttle and is used to set the pitch of the main rotor blades. This is extremely evident during the crash, when he has both hands on the cyclic (the stick(, which determines the rotor disc's direction, but has a minimal effect on the rate of descent.
According to physics, if you shot a shark caught in a tornado, it would still fly around in the tornado versus falling straight down to the ground.
(at around 1h 1 min) When Nova shoots the doorknob of the surplus supply hangar, the knob comes popping outward, not going inward.
(at around 1h 9 mins) In the helicopter take-off scene, a close-up of the vertical speed indicator clearly shows the aircraft is descending at almost 900 ft/min.
(at around 1h 21 mins) Closer to the end of the movie Fin starts his chainsaw on one pull. However it is highly improbable that a two-cycle chainsaw would start on one pull unless previously warmed up.
(at around 41 mins) After deciding to save the children on the school bus and when the film first cuts to the bridge, the film is played in reverse as noted by all the vehicles driving backwards.
(at around 51 mins) At one point, the girl with the shotgun "fires" the shotgun in the middle of cocking the gun to load a new round.
When Fin is saving the kids you can see a safety line that is going off to the side of the road.
(at around 1 min) Near the opening we see a group of shark finners and on the same boat the captain offers his financier what is supposed to be a bowl of shark fin soup. The financier proclaims it's "good, not great". Shark fin is made of cartilage and has no flavor of it's own. The broth is usually chicken or pork based and the shark fin is used as a texture component only. So the financier would simply be commenting on the quality of the broth, not the actual shark fins.
At minute 55:00, despite all of the rain, water spouts and tornado, during the chase scene the pavement is bone dry.
Earlier in the movie, when waves hit the shark fishing boat where Palmer and Captain Carlos are bargaining, everything starts toppling up and down except the soup bowl kept on the table.
There are several scenes showing patrol cars marked "State Police." The California State Police was a very small force that primarily operated around the state capitol in Sacramento. They merged with the California Highway Patrol in 1995.
(at around 31 mins) After Fin turns on the radio broadcast about "unsubtantiated reports of sharks swimming in the streets", the sound of the wipers doesn't match the rhythm of the wipers on screen.
You can not see the LA skyline from Van Nuys. The Hollywood Hills are in between.
(at around 49 mins) When Fin and April first see the waterspouts from the bridge, they are looking directly towards the L.A. skyline (featuring the distinctive, circular US Bank building). In the very next shot of them on the bridge, they're still staring at the waterspouts, but the skyline is now behind them.
During the rain scene , it goes back and forth between raining quiet heavily to barely raining at all .