# [gradsusr] Interpolating HRRR 15 minute GRIB to 5 minute

Jeff Duda jeffduda319 at gmail.com
Sat Dec 17 21:54:29 EST 2016

```Brandon,
lterp isn't going to help you with this. You want to perform a temporal
interpolation. lterp only does horizontal interpolation.

I've done stuff like this before. There's a few ways you can go. One of
them is far more complicated than the other and probably not worth it.

Method 1:
-Use linear interpolation in time. Simple and quick, but if you're looking
small scale features like precipitation or reflectivity, it's not going to
give you accurate results.

Method 2:
-Estimate the temporal derivatives at the initial time, then integrate
those forward to your sub-time steps. You can calculate things like
advection, the Coriolis force, and vertical motion easy enough. Source and
sinks for water vapor and heat will remain impossible, though. I'd have to
"do the math" to be sure, but this method may end up giving you the same
solution as method 1 would. In either case, I would recommend using method
1.

Good luck.

Jeff Duda

On Sat, Dec 17, 2016 at 2:32 PM, Brandon Schmidt <admin at wilmingtonwx.com>
wrote:

> Hello all,
>
> I'm currently looking for a solution to take an HRRR Sub-Hourly GRIB2 file
> with 4 time steps and interpolate it to have 12 time steps. I know this
> somehow involves the 'iterp' function but I can't seem to get it working.
> I'm barely even sure where to start...what must the destination control
> file contain to make this work? I imagine this can be done fairly easily,
> I'm just not sure how to do it myself. Any help would be greatly
> appreciated...thanks!
>
> _______________________________________________
>
>

--
Jeff Duda
Post-doctoral research fellow
University of Oklahoma School of Meteorology
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