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Tracing the transition between the diffuse atomic interstellar medium (ISM)and cold, dense gas is crucial for deciphering the star formation cycle ingalaxies. Here we present MACH, a new survey of cold neutral hydrogen (HI)absorption at $21\rm\,cm$ by the Karl G. Jansky Very Large Array. We target 42bright background sources with $60<l<110^{\circ}$, $30<b<62^{\circ}$,significantly expanding the sample of publicly-available, sensitive $21\rm\,cm$absorption outside the Galactic plane. With matching $21\rm\,cm$ emission datafrom the EBHIS survey, we measure the total column density and cold HIfraction, and quantify the properties of individual HI structures along eachsightline via autonomous Gaussian decomposition. Combining the MACH sample withresults from recent HI absorption surveys, we produce a robust characterizationof the cool atomic medium at high and intermediate Galactic latitudes. We findthat MACH HI has significantly smaller column density relative to samples atsimilar latitudes, and the detected cold HI structures have smaller linewidths, temperatures and turbulent Mach numbers, suggesting that MACH probes aparticularly quiescent region. Using all available observations, we compute thecumulative covering fraction ($c$) of cold HI at local velocities outside thedisk: structures with $\tau>0.001$ are ubiquitous ($c\sim100\%$), whereas highoptical depths ($\tau>1$) are extremely rare ($c\sim0\%$).

The MACH HI absorption survey I: Physical conditions of cold atomic gas outside of the Galactic plane