Show Values For Temperatures Not Equal To Or Above Threshold?

The below stored procedure is used to create a vertical benchmark line on the X-Axis which has a hour scale. I use the stored procedure to find out which temperature crosses or equals the threshold temperature (340), then plot the vertical benchmark line at the hour the first temperature is equal to or greater than 340 degrees and less than 1000 degrees.

The logic below works if the temperature is equal to or greater than 340 degrees and less than 1000 degrees. THE ISSUE is I have 8 temperatures if they don't cross the threshold of 340 degrees I need to set a default value for my vertical line. In other words if the temperature is 180 and my threshold is 340 then set my vertical line on the highest temperature close to 340.

I tried removing my Where clause (but then it breaks the logic for those temperatures that are equal to or greater than 340). I tried using Case When but this didn't give me what I want either. I tried UNION as well. All giving me results I don't want.

Here is what I am looking for:

This first example is one where there was a temperature that was equal to or greater than the threshold of 340 degrees. This is CORRECT

Code:
first_to_cross_thresholdAgeSampleDateDiffAgeovenStartTimestampAgeovenCompleteTimestamp
2014-02-04 19:24:003.3500002014-02-04 16:02:13.0002014-02-05 05:02:13.000

If 8 temperatures did not equal or cross the threshold then give me the hour of the highest temperature close to the threshold but do not return 0.

For Example:

temp1 92
temp2 108
temp3 0
temp4 284 <<< this is the closest to the threshold so give me the hour when this occurred.
temp5 2192 *Remember I can only count temperatures less than 1000 degrees. Anything above 1000 degrees mean there is nothing in the oven. So it is false/positive.
temp6 102
temp7 0
temp8 12

Code:

first_to_cross_thresholdAgeSampleDateDiffAgeovenStartTimestampAgeovenCompleteTimestamp
2014-02-05 00:30:001.3000002014-02-05 02:00:13.0002014-02-05 02:00:13.000

Code:
CREATE PROCEDURE [dbo].[AgeScoreCardThreshold_JJ_12232013]
-- Add the parameters for the stored procedure here
@LicenseNumber int = NULL,
@Lot varchar(50) = NULL

[code].....