OK, here's my sob-story: I am tired of beating my head against the "*Davis-induced* SLP Wall" and need an accurate method to "back" the 'raw' barometer sensor Station Pressure "out" of the VP2-calculated Sea Level Pressure (SLP) pressure data that WL-ISP sends to CWOP / MADIS / MesoWest, *et.al.*.

I read the **Barometer Pressure** section of **Davis Application Note #28, Rev. A**, dated 5/11/2006, with absolutely NO success because the humidity correction coefficient "C" isn't calculated, but rather comes from a "lookup table." The text wording says the lookup table is *"...(provided in the attached table)..."*; however, there is NO attached table! (I've e-mailed Davis about this omission) Most likely they meant use the "lookup table" found in one of the footnote referenced documents, but they forgot to specify *which* footnote document!

So, what I did was collect the last seven days of weather data for weather stations KTUS(NWS @ Tucson airport), KDMA(USAF @ DMAFB), CW5619, and DW6988(my station), into an Excel spreadsheet. Data from each station was collected into columnar rows: SLP, ALT, Sta.P, SLP/ALT-ratio, etc.. I then compared the columns of data against each other and found two sets of data pairs with very high correlation coefficients:

**• PART I** - What's Related to What?

1) **P**_{stn} vs. **P**_{alt} (both in "Hg):

**KTUS(2546'): P**_{alt} = 1.0764*(P_{stn}) + 0.5599; R^{2} = 0.9999

KDMA(2703'): P_{alt} = 1.0850*(P_{stn}) + 0.4952; R^{2} = 0.9999

2) **K** vs. **SLP/ALT**-ratio (K is mb/meter; SLP/ALT is dimensionless):

**KTUS(776m): (P**_{slp}/P_{alt}) = 1.0724 - 0.0085*(K); R^{2} = 0.9782

KDMA(824m): (P_{slp}/P_{alt}) = 1.0743 - 0.0087*(K); R^{2} = 0.9625

NOTE - "scale height" coefficient **K**, in mb/meter, is found in the following common equation:

**P**_{slp}_{(mb)} = P_{stn}_{(mb)} + (height_{(m)} / K ) ...where K-values range between 8.5 and 9.2

So, what did I learn so far from this exercise? (1) First, the NWS and USAF conversion of Sta.P into ALT is almost *perfectly* LINEAR! (2) Secondly, the "scale height" coefficient K is LINEARLY related to the ratio of the SLP and ALT values.

**• PART II** - Putting the Numbers to Work (...TBD...)