National Weather Service United States Department of Commerce

Z/R Relationship Table

{ "timestamp":"Thu Jun 30 20:29:01 EDT 2016", "zrData":[ { "bgstyle":"row-even", "id":"BUF", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"300", "zrExp":"1.4", "icon":"Deep Convective ZR.png", "iconAlt":"Summer Deep Convection Z/R icon", "rate":"0.09", "formulaName":"Summer Deep Convection Z/R", "bcfTitle":"140 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.81", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"0.81", "bcfNumPairs":"140", "bcfDesc":"over-estimation" }, { "bgstyle":"row-odd", "id":"CCX", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"300", "zrExp":"1.4", "icon":"Deep Convective ZR.png", "iconAlt":"Summer Deep Convection Z/R icon", "rate":"0.09", "formulaName":"Summer Deep Convection Z/R", "bcfTitle":"379 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.75", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"0.75", "bcfNumPairs":"379", "bcfDesc":"over-estimation" }, { "bgstyle":"row-even", "id":"CLE", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"300", "zrExp":"1.4", "icon":"Deep Convective ZR.png", "iconAlt":"Summer Deep Convection Z/R icon", "rate":"0.09", "formulaName":"Summer Deep Convection Z/R", "bcfTitle":"758 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.00", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#00CC00", "bcf":"1.00", "bcfNumPairs":"758", "bcfDesc":"unbiased estimation" }, { "bgstyle":"row-odd", "id":"DTX", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"300", "zrExp":"1.4", "icon":"Deep Convective ZR.png", "iconAlt":"Summer Deep Convection Z/R icon", "rate":"0.09", "formulaName":"Summer Deep Convection Z/R", "bcfTitle":"82 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.27", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"1.27", "bcfNumPairs":"82", "bcfDesc":"under-estimation" }, { "bgstyle":"row-even", "id":"FCX", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"300", "zrExp":"1.4", "icon":"Deep Convective ZR.png", "iconAlt":"Summer Deep Convection Z/R icon", "rate":"0.09", "formulaName":"Summer Deep Convection Z/R", "bcfTitle":"16 positive gage-radar pairings found over the past 10 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.71", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"10-hr", "bcfColor":"#CC0000", "bcf":"0.71", "bcfNumPairs":"16", "bcfDesc":"over-estimation" }, { "bgstyle":"row-odd", "id":"GRR", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"300", "zrExp":"1.4", "icon":"Deep Convective ZR.png", "iconAlt":"Summer Deep Convection Z/R icon", "rate":"0.09", "formulaName":"Summer Deep Convection Z/R", "bcfTitle":"92 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.67", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"0.67", "bcfNumPairs":"92", "bcfDesc":"over-estimation" }, { "bgstyle":"row-even", "id":"HPX", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"200", "zrExp":"1.6", "icon":"Gen Stratiform ZR.png", "iconAlt":"Marshall/Palmer Stratiform Z/R icon", "rate":"0.11", "formulaName":"Marshall/Palmer Stratiform Z/R", "bcfTitle":"738 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.90", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#00CC00", "bcf":"0.90", "bcfNumPairs":"738", "bcfDesc":"over-estimation" }, { "bgstyle":"row-odd", "id":"HTX", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"300", "zrExp":"1.4", "icon":"Deep Convective ZR.png", "iconAlt":"Summer Deep Convection Z/R icon", "rate":"0.09", "formulaName":"Summer Deep Convection Z/R", "bcfTitle":"632 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.68", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"0.68", "bcfNumPairs":"632", "bcfDesc":"over-estimation" }, { "bgstyle":"row-even", "id":"ILN", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"300", "zrExp":"1.4", "icon":"Deep Convective ZR.png", "iconAlt":"Summer Deep Convection Z/R icon", "rate":"0.09", "formulaName":"Summer Deep Convection Z/R", "bcfTitle":"1201 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.76", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"0.76", "bcfNumPairs":"1201", "bcfDesc":"over-estimation" }, { "bgstyle":"row-odd", "id":"ILX", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"200", "zrExp":"1.6", "icon":"Gen Stratiform ZR.png", "iconAlt":"Marshall/Palmer Stratiform Z/R icon", "rate":"0.11", "formulaName":"Marshall/Palmer Stratiform Z/R", "bcfTitle":"11 positive gage-radar pairings found over the past 3 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.76", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"3-hr", "bcfColor":"#CC0000", "bcf":"0.76", "bcfNumPairs":"11", "bcfDesc":"over-estimation" }, { "bgstyle":"row-even", "id":"IND", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"200", "zrExp":"1.6", "icon":"Gen Stratiform ZR.png", "iconAlt":"Marshall/Palmer Stratiform Z/R icon", "rate":"0.11", "formulaName":"Marshall/Palmer Stratiform Z/R", "bcfTitle":"511 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.70", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"0.70", "bcfNumPairs":"511", "bcfDesc":"over-estimation" }, { "bgstyle":"row-odd", "id":"IWX", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"200", "zrExp":"1.6", "icon":"Gen Stratiform ZR.png", "iconAlt":"Marshall/Palmer Stratiform Z/R icon", "rate":"0.11", "formulaName":"Marshall/Palmer Stratiform Z/R", "bcfTitle":"338 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.76", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"0.76", "bcfNumPairs":"338", "bcfDesc":"over-estimation" }, { "bgstyle":"row-even", "id":"JKL", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"300", "zrExp":"1.4", "icon":"Deep Convective ZR.png", "iconAlt":"Summer Deep Convection Z/R icon", "rate":"0.09", "formulaName":"Summer Deep Convection Z/R", "bcfTitle":"1911 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.87", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#00CC00", "bcf":"0.87", "bcfNumPairs":"1911", "bcfDesc":"over-estimation" }, { "bgstyle":"row-odd", "id":"LOT", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"300", "zrExp":"1.4", "icon":"Deep Convective ZR.png", "iconAlt":"Summer Deep Convection Z/R icon", "rate":"0.09", "formulaName":"Summer Deep Convection Z/R", "bcfTitle":"250 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.61", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"0.61", "bcfNumPairs":"250", "bcfDesc":"over-estimation" }, { "bgstyle":"row-even", "id":"LSX", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"300", "zrExp":"1.4", "icon":"Deep Convective ZR.png", "iconAlt":"Summer Deep Convection Z/R icon", "rate":"0.09", "formulaName":"Summer Deep Convection Z/R", "bcfTitle":"17 positive gage-radar pairings found over the past 3 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.86", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"3-hr", "bcfColor":"#00CC00", "bcf":"0.86", "bcfNumPairs":"17", "bcfDesc":"over-estimation" }, { "bgstyle":"row-odd", "id":"LVX", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"300", "zrExp":"1.4", "icon":"Deep Convective ZR.png", "iconAlt":"Summer Deep Convection Z/R icon", "rate":"0.09", "formulaName":"Summer Deep Convection Z/R", "bcfTitle":"904 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.82", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"0.82", "bcfNumPairs":"904", "bcfDesc":"over-estimation" }, { "bgstyle":"row-even", "id":"LWX", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"300", "zrExp":"1.4", "icon":"Deep Convective ZR.png", "iconAlt":"Summer Deep Convection Z/R icon", "rate":"0.09", "formulaName":"Summer Deep Convection Z/R", "bcfTitle":"315 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.36", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"1.36", "bcfNumPairs":"315", "bcfDesc":"under-estimation" }, { "bgstyle":"row-odd", "id":"MRX", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"300", "zrExp":"1.4", "icon":"Deep Convective ZR.png", "iconAlt":"Summer Deep Convection Z/R icon", "rate":"0.09", "formulaName":"Summer Deep Convection Z/R", "bcfTitle":"10 positive gage-radar pairings found over the past 2 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.77", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"2-hr", "bcfColor":"#CC0000", "bcf":"0.77", "bcfNumPairs":"10", "bcfDesc":"over-estimation" }, { "bgstyle":"row-even", "id":"OHX", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"300", "zrExp":"1.4", "icon":"Deep Convective ZR.png", "iconAlt":"Summer Deep Convection Z/R icon", "rate":"0.09", "formulaName":"Summer Deep Convection Z/R", "bcfTitle":"823 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.85", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"0.85", "bcfNumPairs":"823", "bcfDesc":"over-estimation" }, { "bgstyle":"row-odd", "id":"PAH", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"200", "zrExp":"1.6", "icon":"Gen Stratiform ZR.png", "iconAlt":"Marshall/Palmer Stratiform Z/R icon", "rate":"0.11", "formulaName":"Marshall/Palmer Stratiform Z/R", "bcfTitle":"16 positive gage-radar pairings found over the past 3 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.78", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"3-hr", "bcfColor":"#CC0000", "bcf":"0.78", "bcfNumPairs":"16", "bcfDesc":"over-estimation" }, { "bgstyle":"row-even", "id":"PBZ", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"300", "zrExp":"1.4", "icon":"Deep Convective ZR.png", "iconAlt":"Summer Deep Convection Z/R icon", "rate":"0.09", "formulaName":"Summer Deep Convection Z/R", "bcfTitle":"1186 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.35", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"1.35", "bcfNumPairs":"1186", "bcfDesc":"under-estimation" }, { "bgstyle":"row-odd", "id":"RLX", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"200", "zrExp":"1.6", "icon":"Gen Stratiform ZR.png", "iconAlt":"Marshall/Palmer Stratiform Z/R icon", "rate":"0.11", "formulaName":"Marshall/Palmer Stratiform Z/R", "bcfTitle":"2576 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.06", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#00CC00", "bcf":"1.06", "bcfNumPairs":"2576", "bcfDesc":"under-estimation" }, { "bgstyle":"row-even", "id":"VWX", "cellbg":"", "update":"8pm EDT 30-Jun-2016", "zrCoef":"200", "zrExp":"1.6", "icon":"Gen Stratiform ZR.png", "iconAlt":"Marshall/Palmer Stratiform Z/R icon", "rate":"0.11", "formulaName":"Marshall/Palmer Stratiform Z/R", "bcfTitle":"14 positive gage-radar pairings found over the past 5 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.55", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"5-hr", "bcfColor":"#CC0000", "bcf":"0.55", "bcfNumPairs":"14", "bcfDesc":"over-estimation" }] }
 

 

The table above shows WSR-88D Z/R relationships for sites used in the OHRFC radar mosaic. 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.

Most stratiform rain events in the Ohio River Valley have a reflectivity signal strength of 20-40dBZ with occasional peaks to 45dBZ, but rarely anything higher (that isn't "brightbanding"). 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).