Please follow http://www.wcc.nrcs.usda.gov/webmap/index.html#elements=A&networks=!&states=!&counties=!&hucs=&minElevation=&maxElevation=&elementSelectType=all&activeOnly=true&hucLabels=false&stationLabels=&overlays=&hucOverlays=&mode=stations&openSections=dataElement,parameter,date,elements,location,networks&controlsOpen=true&popup=&base=esriNgwm&lat=39.98&lon=-98.96&zoom=4&dataElement=PREC¶meter=PCTAVG&frequency=DAILY&duration=null&customDuration=&dayPart=E&year=2015&month=10&day=8&monthPart=E.