static void CheckCertificateExpiry(string CertificateSubject)
{
    X509Store store = new X509Store(StoreName.My, StoreLocation.LocalMachine);
    X509Certificate2Collection storecollection;
    X509Certificate2 x509;
    TimeSpan timespan;

    store.Open(OpenFlags.ReadOnly);
    storecollection = (X509Certificate2Collection)store.Certificates;
    storecollection = storecollection.Find(X509FindType.FindBySubjectName, CertificateSubject, true);

    if (storecollection.Count == 0) 
    {
        Notify("Certificate for `" + CertificateSubject + "' not found", EventLogEntryType.Information);
    }
    else
    {
        x509 = storecollection[0];
        timespan = Convert.ToDateTime(x509.GetExpirationDateString()) - DateTime.Now;
        Notify("[" + CertificateSubject + "] certificate will expire in [" + timespan.Days + " days] issued by " 
                                                                + x509.GetNameInfo( X509NameType.SimpleName,true), 
            (timespan.Days > 30)?EventLogEntryType.Warning:EventLogEntryType.Error);
    }
}

static void Notify(string strComment,EventLogEntryType eventType)
{ 
    //implement different notification options here
    switch (cmdArg)
    { 
        case "CON": Console.WriteLine(strComment);
                    break;
        case "EVT": EventLog evtlog = new EventLog("System", ".");
                    evtlog.Source = "CertExpiryCheck";
                    evtlog.WriteEntry(strComment, eventType);
                    break;
    }
}