  We report on an exact solution of the nearly antiferromagnetic Fermi liquid
spin fermion model in the limit \pi T << \omega_{sf}, which demonstrates that
the broad high energy features found in ARPES measurements of the spectral
density of the underdoped cuprate superconductors are determined by strong
antiferromagnetic (AF) correlations and precursor effects of an SDW state. We
show that the onset temperature, T^{cr}, of weak pseudo-gap (pseudoscaling)
behavior is determined by the strength, \xi, of the AF correlations, and obtain
the generic changes in low frequency magnetic behavior seen in NMR experiments
with \xi(T^{cr}) \approx 2, confirming the Barzykin and Pines crossover
criterion.
