The following table is experimental and not an official forecast product. The table was created to display the Z-R (radar reflectivity to rain rate) relationships being used by individual NEXRAD sites throughout the LMRFC area. Bias correction values and selected ZR relationships are valid for the entire NEXRAD coverage area and are not necessarily valid for individual spot locations.
Experimental products may not always update in a timely manner and may be discontinued at a future date. Experimental products may not always reflect accurate, quality controlled information and should be used with caution.
Official rainfall estimates and observations remain available from the main LMRFC "Observed/Past Precipitation" page.
The table above shows WSR-88D Z/R relationships for radar sites within the LMRFC area. A Z/R relationship is a empirical formula that is used to estimate rainfall rates from reflectivity signal strength. Parameters that can be varied at each radar site are those shown in red.
Often times stratiform rain events have a reflectivity signal strength of 20-40dBZ. Convective rain events can often range from 40-55dBZ. For more information and recommendations regarding Z/R relationships, see the Radar Operations Center's Handbook. Refer to Section 7.7.2 Z-R Coefficients. (This handbook is for agency use only, and requires a NOAA LDAP login.)
The bias correction factor can only be computed if there are at least 10 gage-radar pairs with both values 0.03 inches or more. Sometimes, data has to be searched back several hours to find at least 10 such pairs. (The actual number of pairs used in computing this bias factor is shown following the # sign.) The number of hours searched is shown preceding the bias factor. Bias factors are color-coded green if the radar estimates are within 15% tolerance of what the gages verify, or red otherwise. Values over 1.0 mean the radar is under-estimating. Values under 1.0 means the radar is over-estimating. This may seem counter-intuitive. To get the radar estimates to verify well with the gage values, the radar estimates would have to be multiplied by this bias factor shown for each radar.
Any cells with a yellow background under the "Last Reported" column indicate that the latest report is not up-to-date (perhaps the radar is down for maintenance).