3 hr Pressure Change Contour - -4 hr
Contour plot of the change in pressure from the current hour to 3 hours previous for the contiguous US. This is a good indicator of the movement and intensification of pressure systems. If the pressure change is negative in the region of a low pressure system (see above chart), the low is deepening. If the negative pressure change is out in front of the low pressure system, it indicates movement. The location of the maximum pressure drops indicate the possible direction of the low pressure system.