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RUC parallel

Geoff Manikin

I don't have the ability to post in the target area forum, so I thought I'd post this here; I encourage those who can post in that forum to note this information to those currently posting there about dew points and cape values in the RUC.

A new version of the RUC will be implemented at the end of June. I'll spare the many details of the changes right now, but one item of significant relevance is the much improved handling of soil moisture. The operational RUC tends to dry out sfc moisture way too quickly, and the new version has shown significant ability to generate a much more realistic evolution of it.

Graphics are available at http://www.emc.ncep.noaa.gov/mmb/ruc2/para

The problem today is that the machine on which I generate the graphics is unavailable today; I have, however, been able to produce a limited set of graphics for some of the fields.

I am posting this, as I have seen many comments in the target area forum about the model's handling of dew points and resultant cape over the SD/NE region late today. If you examine the 18z cycle on my page, you'll see that the new version of the model keeps much higher dew points and cape across this region this evening. The soil moisture availability field shows the differences that at least partly explain the discrepancy.

I apologize that the site is incomplete today, but I thought it worth pointing out with so many folks closely examining the parameters in NE/SD today. The site should be completely reliable tomorrow.
Ruc revamp

This is very interesting. I have always suspected that the RUC dries out the soil moisture too quickly. If anything, the NAM or ETA seems to do the reverse.

Another annoying thing about the RUC's CAPE calculations if I remember correctly, is that the RUC uses a lowest 30 mb mixed parcel, while the ETA or NAM uses a lowest 100 mb mixed parcel, making comparisons between the two models awkward.

This is good news.
not quite true regarding the capes. There is currently only 1 cape in the RUC. It is labeled as a "sfc-based" cape, but in reality, the lowest 300 mb is searched for the level with the highest theta-e. This parcel is lifted for the computation. This has been the source of much confusion, as users often see high values in situations with stable air at the ground.

There are 4 capes (and CINs) in the Eta (NAM). The "standard" value is the sfc-based one, for which the parcel in the lowest 70 mb with the highest theta-e is lifted. There is also a 180 mb "best" cape; for this, the average T and q are computed in 6 30mb layers just above the ground. The layer with the highest theta-e is lifted. Recent additions are the mixed-layer and 300 mb best capes. The mixed-layer parcel is determined by averaging the T and q in the 3 lowest 30 mb deep layers (the true depth should be 100 mb instead of 90, but this was the simplest for us). The 300 mb best cape finds the level in the lowest 300 mb with the highest theta-e.

The 4 NAM capes can be compared at http://www.emc.ncep.noaa.gov/mmb/namsvrfcst/

When the new version of the RUC is implemented, the cape value currently labeled as "surfaced-base" will truly become a sfc-based computation. A 300 mb best cape will be added and will have the appropriate labeling.