National Weather Service United States Department of Commerce

Z/R Relationship Table

{ "timestamp":"07/28/17 at 01:18:04 PM", "zrData":[ { "bgstyle":"row-odd", "id":"AKQ (Wakefield)", "cellbg":"", "update":"Jul 28, 2017 01:00 PM", "zrCoef":"300", "zrExp":"1.4", "icon":"DeepConvectiveZR.gif", "iconAlt":"Summertime Deep Convection Z/R", "rate":"0.09", "formulaName":"Summertime Deep Convection Z/R", "bcfTitle":"0 positive gage-radar pairings found over the past hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.00", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"0.001", "bcfColor":"red", "bcf":"0.00", "bcfNumPairs":"0", "bcfDesc":"over-" }, { "bgstyle":"row-even", "id":"BGM (Binghamton)", "cellbg":"", "update":"Jul 28, 2017 01:00 PM", "zrCoef":"300", "zrExp":"1.4", "icon":"DeepConvectiveZR.gif", "iconAlt":"Summertime Deep Convection Z/R", "rate":"0.09", "formulaName":"Summertime Deep Convection Z/R", "bcfTitle":"0 positive gage-radar pairings found over the past hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.00", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"0.001", "bcfColor":"red", "bcf":"0.00", "bcfNumPairs":"0", "bcfDesc":"over-" }, { "bgstyle":"row-odd", "id":"BUF (Buffalo)", "cellbg":"", "update":"Jul 28, 2017 01:00 PM", "zrCoef":"300", "zrExp":"1.4", "icon":"DeepConvectiveZR.gif", "iconAlt":"Summertime Deep Convection Z/R", "rate":"0.09", "formulaName":"Summertime Deep Convection Z/R", "bcfTitle":"0 positive gage-radar pairings found over the past hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.00", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"0.001", "bcfColor":"red", "bcf":"0.00", "bcfNumPairs":"0", "bcfDesc":"over-" }, { "bgstyle":"row-even", "id":"CCX (State College)", "cellbg":"", "update":"Jul 28, 2017 01:00 PM", "zrCoef":"300", "zrExp":"1.4", "icon":"DeepConvectiveZR.gif", "iconAlt":"Summertime Deep Convection Z/R", "rate":"0.09", "formulaName":"Summertime Deep Convection Z/R", "bcfTitle":"0 positive gage-radar pairings found over the past hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.00", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"0.001", "bcfColor":"red", "bcf":"0.00", "bcfNumPairs":"0", "bcfDesc":"over-" }, { "bgstyle":"row-odd", "id":"DIX (Mt. Holly)", "cellbg":"", "update":"Jul 28, 2017 01:00 PM", "zrCoef":"200", "zrExp":"1.6", "icon":"GenStratiformZR.gif", "iconAlt":"Marshall/Palmer General Stratiform Z/R", "rate":"0.11", "formulaName":"Marshall/Palmer General Stratiform Z/R", "bcfTitle":"0 positive gage-radar pairings found over the past hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.00", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"0.001", "bcfColor":"red", "bcf":"0.00", "bcfNumPairs":"0", "bcfDesc":"over-" }, { "bgstyle":"row-even", "id":"DOX (Dover)", "cellbg":"", "update":"Jul 28, 2017 01:00 PM", "zrCoef":"300", "zrExp":"1.4", "icon":"DeepConvectiveZR.gif", "iconAlt":"Summertime Deep Convection Z/R", "rate":"0.09", "formulaName":"Summertime Deep Convection Z/R", "bcfTitle":"0 positive gage-radar pairings found over the past hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.00", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"0.001", "bcfColor":"red", "bcf":"0.00", "bcfNumPairs":"0", "bcfDesc":"over-" }, { "bgstyle":"row-odd", "id":"ENX (Albany)", "cellbg":"", "update":"Jul 28, 2017 01:00 PM", "zrCoef":"300", "zrExp":"1.4", "icon":"DeepConvectiveZR.gif", "iconAlt":"Summertime Deep Convection Z/R", "rate":"0.09", "formulaName":"Summertime Deep Convection Z/R", "bcfTitle":"0 positive gage-radar pairings found over the past hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.00", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"0.001", "bcfColor":"red", "bcf":"0.00", "bcfNumPairs":"0", "bcfDesc":"over-" }, { "bgstyle":"row-even", "id":"FCX (Blacksburg)", "cellbg":"", "update":"Jul 28, 2017 01:00 PM", "zrCoef":"300", "zrExp":"1.4", "icon":"DeepConvectiveZR.gif", "iconAlt":"Summertime Deep Convection Z/R", "rate":"0.09", "formulaName":"Summertime Deep Convection Z/R", "bcfTitle":"0 positive gage-radar pairings found over the past hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.00", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"0.001", "bcfColor":"red", "bcf":"0.00", "bcfNumPairs":"0", "bcfDesc":"over-" }, { "bgstyle":"row-odd", "id":"LWX (Sterling)", "cellbg":"", "update":"Jul 28, 2017 01:00 PM", "zrCoef":"300", "zrExp":"1.4", "icon":"DeepConvectiveZR.gif", "iconAlt":"Summertime Deep Convection Z/R", "rate":"0.09", "formulaName":"Summertime Deep Convection Z/R", "bcfTitle":"0 positive gage-radar pairings found over the past hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.00", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"0.001", "bcfColor":"red", "bcf":"0.00", "bcfNumPairs":"0", "bcfDesc":"over-" }, { "bgstyle":"row-even", "id":"OKX (Brookhaven)", "cellbg":"", "update":"Jul 28, 2017 01:00 PM", "zrCoef":"300", "zrExp":"1.4", "icon":"DeepConvectiveZR.gif", "iconAlt":"Summertime Deep Convection Z/R", "rate":"0.09", "formulaName":"Summertime Deep Convection Z/R", "bcfTitle":"0 positive gage-radar pairings found over the past hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.00", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"0.001", "bcfColor":"red", "bcf":"0.00", "bcfNumPairs":"0", "bcfDesc":"over-" }, { "bgstyle":"row-odd", "id":"PBZ (Pittsburgh)", "cellbg":"", "update":"Jul 28, 2017 01:00 PM", "zrCoef":"250", "zrExp":"1.2", "icon":"TropicalZR.gif", "iconAlt":"Rosenfeld Tropical Z/R", "rate":"0.13", "formulaName":"Rosenfeld Tropical Z/R", "bcfTitle":"0 positive gage-radar pairings found over the past hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.00", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"0.001", "bcfColor":"red", "bcf":"0.00", "bcfNumPairs":"0", "bcfDesc":"over-" }, { "bgstyle":"row-even", "id":"RAX (Raleigh)", "cellbg":"", "update":"Jul 28, 2017 01:00 PM", "zrCoef":"300", "zrExp":"1.4", "icon":"DeepConvectiveZR.gif", "iconAlt":"Summertime Deep Convection Z/R", "rate":"0.09", "formulaName":"Summertime Deep Convection Z/R", "bcfTitle":"0 positive gage-radar pairings found over the past hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.00", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"0.001", "bcfColor":"red", "bcf":"0.00", "bcfNumPairs":"0", "bcfDesc":"over-" }, { "bgstyle":"row-odd", "id":"RLX (Charleston)", "cellbg":"", "update":"Jul 28, 2017 01:00 PM", "zrCoef":"300", "zrExp":"1.4", "icon":"DeepConvectiveZR.gif", "iconAlt":"Summertime Deep Convection Z/R", "rate":"0.09", "formulaName":"Summertime Deep Convection Z/R", "bcfTitle":"0 positive gage-radar pairings found over the past hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.00", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"0.001", "bcfColor":"red", "bcf":"0.00", "bcfNumPairs":"0", "bcfDesc":"over-" } ]}
 

 

The table above shows WSR-88D Z/R relationships for sites used in the MARFC radar mosaic. A Z/R relationship is a empirical formula that is used to estimate rainfall rates from reflectivity signal strength.

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 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 more than two hours old.  This most commonly occurs when the radar is down for maintenance.

Rainfall Rates for Each Relationship @ 30dBZ
Summertime Deep Convection 0.09 inches/hour
Rosenfeld Tropical 0.13 inches/hour
Marshal/Palmer General Stratiform 0.11 inches/hour
Cool Season (East) Stratiform 0.11 inches/hour

 

(Internal NWS Users Only: 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.)