WMOD00564

• Title: Snow Accumulation Algorithm for the WSR-80D Radar: Supplemental Report
• Date: 11/1/1999
• Weather Modification - Doc Type: Report

o

60

100 160
Range. km

200

rawinsonde data are available only twice per day.
Altitudes of the melting level can vary signi-
ficantly in 12 hours, especially before and after
precipitating weather systems. The numerical
model (Eta, Rapid Update Cycle) can indicate the
melting level between the rawinsonde observation
times and can even identify gradients across the
field of view of a radar. However, it is beyond
the scope of this effort to modify the SAA code to
ingest melting level data. Such is needed to
distinguish some bright band effects from other
vertical gradient reversals. However, there needs
to be caution in the use of melting level data. I
have recently observed a case in which there was
a layer of air in a precipitating system that was
nearly isothermal at a temperature close to 0 oC
for a depth of over 1 km. Assuming a bright band
of only a few hundreds of meters depth based on
derived melting level data would be unreliable in
such a situation. Therefore, a bright band
warning could not be provided without further
study.

KDLH, dens.=O.085
x >=0.1"5;>=1.0.50
c >= 3.0"50

10

x )(
x x x
0 x
en x
~ " x
0
"'"
12. ..
"

0.1

Figure 6e.- The light precipitation data are offset from
unity in the opposite direction from the few heavier data
for KDLH.

7. ADDITIONAL EFFORTS

7.1 SAA Code Adjustments

In early November 1998, a bug was reported in the NOSPIKES subroutine. Reclamation determined
that the bug existed in all previous versions of the SAA. The bug was activated when a pixel had a
reflectivity exceeding the upper threshold (40 dBZ) and all 8 adjacent pixels had no detectable echo.
Such is a very rare occurrence. The coding was changed to prevent an ALOG 10 of numbers less than or
equal to zero.

Coding was further changed to avoid Y2K problems.

Additional coding modifications, shown in the appendices, were created for experimental investigations.
Appendix A presents coding modifications to the SAA to make the vertical profile graphs as shown in
figures 1 and 7. Appendix B presents a stand-alone program to add many days of SAA output (* .STP
files) to show blemishes in the hybrid scan and occultation files. Appendix C presents coding modifi-
cations to the SAA to attempt virga removal from the SAA products. The coding of appendices A and C
has not been incorporated into the operational versions of the SAA.

7.2 Support Code Development

A separate program (RESIDUAL.FOR, presented in appendix B) was written to ingest many days of
daily total (* .STP) files of S accumulations in order to identify residual ground clutter returns or bins
overcorrected for clutter. The daily files were partitioned, by the number of radar bins with non-zero
accumulations, into three categories of snow fall that might be termed trace-light, moderate, and wide

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