5.00
4.00
3.00
2.00
1.00
0.00
0.00
RAOB TPW versus GOES TPW RMSE
April - August 1999
9.00
8.00
7.00
April - August 1999
Using ETA as first guess
Using AVN as first guess
6.00
Retrieved TPW RMSE Using AVN First
Guess
Retrieved TPW RMSE Using ETA First
Guess
5.00
10.00
15.00
20.00
Raob TPW (mm)
25.00
RAOB TPW (mm)
30.00
35.00
40.00
45.00
50.00
Comparisons from Gary Gray and Jaime Daniels

RAOB TPW versus GOES TPW BIAS April - August 1999
-4.00
-5.00
-6.00
-7.00
2.00
1.00
0.00
0.00
-1.00
-2.00
-3.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
50.00
Using ETA as first guess
Using AVN as first guess
Raob TPW (mm) RAOB TPW
Comparisons from Gary Gray and Jaime Daniels
AVN BIAS
ETA BIAS

Overall AVN-based versus ETA-based GOES Soundings: The overall statistics from the GOES Soundings indicate that the AVN serves as a better first guess.
There are periods of performance when the ETA is the superior first guess, but these are less frequent and less dramatic than the AVN. The following table shows the complete statistics from the parallel study performed by FPDT. The study was run for 80 days
(beginning April 2 nd , 1999) with a sample of nearly 75,000 match-ups.
TPW RMSE
PW1 RMSE
PW2 RMSE
PW3 RMSE
TPW Bias
PW1 Bias
PW2 Bias
PW3 Bias
T950 RMSE
T850 RMSE
T700 RMSE
T500 RMSE
T950 Bias
T850 Bias
T700 Bias
T500 Bias
ETA Guess
3.75mm
1.70mm
2.16mm
1.34mm
-0.34mm
-0.65mm
-0.04mm
+0.32mm
2.20C
1.52C
1.38C
0.91C
-0.39C
-0.14C
-0.52C
+0.08C
ETA Retrieved
3.75mm
1.80mm
2.15mm
1.30mm
-0.70mm
-0.82mm
X
X
X
X
-0.34mm
+0.44mm
X
X
X
X
AVN Guess
3.92mm
1.77mm
2.25mm
1.45mm
-0.11mm
-0.67mm
+0.27mm
+0.26mm
1.84C
1.54C
1.20C
0.93C
-0.52C
+0.19C
+0.25C
+0.07C
AVN Retrieved
3.40mm
1.68mm
2.05mm
1.37mm
-0.13mm
-0.76mm
X
X
X
X
+0.07mm
+0.53mm
X
X
X
X

Summary:
The AVN clearly provides the superior first guess for this application, especially in more moist synoptic regimes.
Using the ETA first guess, the GOES retrieval algorithm is unable to improve the moisture profile. However, using the AVN first guess, the algorithm does an excellent job improving the profile; it reduces the TPW RMSE error by more than 0.5mm.
This ETA versus AVN discrepancy would be understandable if the
ETA first guess was simply too good to improve. However, even though the AVN first guess is, indeed, worse than the ETA first guess, the retrieval made using the AVN ends up considerably superior to retrievals using the ETA.