Last night at Constitution Hall, Weather Report laid to rest any doubts about its character as an improvising jazz band.

Though their studio records are often meticulously arranged, the same songs opened up last night into strong and constant soloing. The memorable compositions by Joe Zawinul, Wayne Shorter and Jaco Pastorius provided nourishment, not boundaries, for the improvisations.

In contrast to the recent performances dominated by Zawinul, the electric jazz quartet seemed more democratic last night. Saxophonist Shorter reemerged as a major force in the band. Last night he mostly stuck to the tenor sax, producing a full-bodied tone that shook down scales and digressed into fierce gowls.

Young bassist Pastorius has continued to mature at an astonishing rate and can now hold his own with the two older co-founders. Pastorius achieved the unlikley feat of sustaining an electric bass solo by combining soft harmonies, tape loop echoes and Hendrix-like roars. Recent addition Peter Erskine played the drums with shifting, flowing combinations. Guest percussionist Robert Thomas Jr. thickened the rhythms with Afro-Latin textures.

The show came to a climax on Zawinul's instantly recognizable "Birdland." Shorter rang out the theme on soprano sax; Pastorius added a delightful scat vocal, and Zawinul surrounded the theme with a multitude of textures from his battery of keyboards.

Earlier in the show, a computer light show was projected behind the band. Green and turquoise veils of light unfurled outward and twisted into new shapes, but always folded back into the center. This was the perfect visual analogy for a band that opened up its themes and shaped them into new forms but always returned to the melodic origin.