Problem: A radar site recently contacted the Hotline with a problem concerning the display of a precipitation product. At the PUP, the forecaster observed a small area depicted as having received 0.5 inches of precipitation. Upon magnifying to 4x, the same area showed 0.2 inches of precipitation.

Affected Systems: This problem is restricted to PUPs only.

Affected Products: All base products (R, V, & SW), precipitation accumulation products (OHP, THP, STP, & USP), and the Hybrid Scan Reflectivity (HSR) product.

Cause: An investigation by the OSF Engineering and Applications Branches confirmed that the problem is caused by a known Ramtek firmware problem. It is manifested at the PUP as an incorrectly displayed partial radial of data.

The software for the precipitation products is written to accommodate this firmware problem. Put simply, the first radial containing valid data is copied and then "pasted" into the previous, adjacent radial. You can see this "copied radial" on precipitation products when your PUP is in screen draw mode ("<PASSWORD>,S,D"). The "copied" data will be the first radial displayed, and as the sweep completes, the copied data will be overwritten with real data. You will not see the "copied data" while the PUP is in "blank mode" ("<PASSWORD>,S,B") unless the following conditions are met:

• A feature must be located on the last/first radial (359/0 degrees for precipitation products but may be along any radial for base products)
• Range and magnification conditions as shown in the table below must be met.

The above conditions were met, in this case, when a forecaster zoomed on an item of interest located along the 359/0 degree radials. The resulting magnified precipitation product displayed pixels which were of a different value than they were prior to magnifying.

The effect of this problem on base products is slightly different than the effect on precipitation products. There is no copying of data. When in Screen Draw Mode, the first radial displayed will contain data from the beginning of the volume scan. When the screen draw completes, this first radial will be overwritten with data from the end of the current volume scan. Magnifying the products under the conditions indicated in the table may reveal these different radials in the form of different pixel data levels and features/pixels may be slightly displaced due to a small amount of feature movement.

Solution: How can you ensure you're seeing real, rather than copied data on the precipitation products and the latest data on base products? If you observe something you question, assuming you're in screen blank mode, put your PUP in screen draw mode ("<PASSWORD>,S,D"). This will NEVER show the copied data. If you'd like to learn more about this and see pictures of the specific event in question, check the OSF/OTB web page. As usual, contact the WSR-88D Hotline if you have any questions.