  We have used the first ~3 years of 3.4 micron (W1) and 4.6 micron (W2)
observations from the WISE and NEOWISE missions to create a full-sky set of
time-resolved coadds. As a result of the WISE survey strategy, a typical sky
location is visited every six months and is observed during 12 or more
exposures per visit, with these exposures spanning a ~1 day time interval. We
have stacked the exposures within such ~1 day intervals to produce one coadd
per band per visit -- that is, one coadd every six months at a given position
on the sky in each of W1 and W2. For most parts of the sky we have generated
six epochal coadds per band, with one visit during the fully cryogenic WISE
mission, one visit during NEOWISE, and then, after a 33 month gap, four more
visits during the NEOWISE-Reactivation mission phase. These coadds are suitable
for studying long-timescale mid-infrared variability and measuring motions to
~1.3 magnitudes fainter than the single-exposure detection limit. In most sky
regions, our coadds span a 5.5 year time period and therefore provide a >10x
enhancement in time baseline relative to that available for the AllWISE
catalog's apparent motion measurements. As such, the signature application of
these new coadds is expected to be motion-based identification of relatively
faint brown dwarfs, especially those cold enough to remain undetected by Gaia.
