When you run fpressure=figure, it creates the figure object handle fpressure. But after you clear the workspace, the figure object handle is gone although the figure window still exists. You can "find" those figure obejct handles but won't be able to match by figure object handle name. I suggest you add some keywords to be able to find it later.
close all; clear all;
fpressure=figure;ftemperature=figure;
clear;
f=findall(0,'type','figure')
close all; clear all;
fpressure=figure('name','pressure');
ftemperature=figure('name','temperature')
clear
fpressure=findall(0,'type','figure','name','pressure')
