National Weather Service United States Department of Commerce

Z/R Relationship Table

{ "timestamp":"Fri Aug 28 13:29:01 EDT 2015", "zrData":[ { "bgstyle":"row-even", "id":"BUF", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"136 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.50", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"1.50", "bcfNumPairs":"136", "bcfDesc":"under-estimation" }, { "bgstyle":"row-odd", "id":"CCX", "cellbg":"yellow", "update":"9am EDT 28-Aug-2015", "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":"314 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.23", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"1.23", "bcfNumPairs":"314", "bcfDesc":"under-estimation" }, { "bgstyle":"row-even", "id":"CLE", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"461 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.22", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"1.22", "bcfNumPairs":"461", "bcfDesc":"under-estimation" }, { "bgstyle":"row-odd", "id":"DTX", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"87 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.53", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"1.53", "bcfNumPairs":"87", "bcfDesc":"under-estimation" }, { "bgstyle":"row-even", "id":"FCX", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"764 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.46", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"1.46", "bcfNumPairs":"764", "bcfDesc":"under-estimation" }, { "bgstyle":"row-odd", "id":"GRR", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"106 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.66", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"0.66", "bcfNumPairs":"106", "bcfDesc":"over-estimation" }, { "bgstyle":"row-even", "id":"HPX", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"644 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.11", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#00CC00", "bcf":"1.11", "bcfNumPairs":"644", "bcfDesc":"under-estimation" }, { "bgstyle":"row-odd", "id":"HTX", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"728 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.01", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#00CC00", "bcf":"1.01", "bcfNumPairs":"728", "bcfDesc":"unbiased estimation" }, { "bgstyle":"row-even", "id":"ILN", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"729 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.12", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#00CC00", "bcf":"1.12", "bcfNumPairs":"729", "bcfDesc":"under-estimation" }, { "bgstyle":"row-odd", "id":"ILX", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"267 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.91", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#00CC00", "bcf":"0.91", "bcfNumPairs":"267", "bcfDesc":"over-estimation" }, { "bgstyle":"row-even", "id":"IND", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"377 positive gage-radar pairings found over the past 168 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":"168-hr", "bcfColor":"#00CC00", "bcf":"0.86", "bcfNumPairs":"377", "bcfDesc":"over-estimation" }, { "bgstyle":"row-odd", "id":"IWX", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"254 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.99", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#00CC00", "bcf":"0.99", "bcfNumPairs":"254", "bcfDesc":"unbiased estimation" }, { "bgstyle":"row-even", "id":"JKL", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"1234 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.12", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#00CC00", "bcf":"1.12", "bcfNumPairs":"1234", "bcfDesc":"under-estimation" }, { "bgstyle":"row-odd", "id":"LOT", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"186 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.83", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"0.83", "bcfNumPairs":"186", "bcfDesc":"over-estimation" }, { "bgstyle":"row-even", "id":"LSX", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"242 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":"242", "bcfDesc":"over-estimation" }, { "bgstyle":"row-odd", "id":"LVX", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"596 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.11", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#00CC00", "bcf":"1.11", "bcfNumPairs":"596", "bcfDesc":"under-estimation" }, { "bgstyle":"row-even", "id":"LWX", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"126 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.30", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"1.30", "bcfNumPairs":"126", "bcfDesc":"under-estimation" }, { "bgstyle":"row-odd", "id":"MRX", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"1223 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.33", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"1.33", "bcfNumPairs":"1223", "bcfDesc":"under-estimation" }, { "bgstyle":"row-even", "id":"OHX", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"867 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.12", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#00CC00", "bcf":"1.12", "bcfNumPairs":"867", "bcfDesc":"under-estimation" }, { "bgstyle":"row-odd", "id":"PAH", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"462 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 0.80", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"0.80", "bcfNumPairs":"462", "bcfDesc":"over-estimation" }, { "bgstyle":"row-even", "id":"PBZ", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"506 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.59", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"1.59", "bcfNumPairs":"506", "bcfDesc":"under-estimation" }, { "bgstyle":"row-odd", "id":"RLX", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"1144 positive gage-radar pairings found over the past 168 hours", "bcfTitle2":" suggest that the radar estimates need to be multiplied by 1.32", "bcfTitle3":" to bring them in line with what the gages are reporting.", "bcfDur":"168-hr", "bcfColor":"#CC0000", "bcf":"1.32", "bcfNumPairs":"1144", "bcfDesc":"under-estimation" }, { "bgstyle":"row-even", "id":"VWX", "cellbg":"", "update":"1pm EDT 28-Aug-2015", "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":"391 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":"391", "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.)

OHRFC recommends using the Marshall/Palmer Stratiform Z/R for all rain events that are mostly stratiform in nature, including events with embedded thunderstorms. Also, we recommend this Z/R for convective events where significant stratification occurs downwind of convection (such as lines of thunderstorms with a stratiform rain area behind the front).

OHRFC recommends only using the Summertime Deep Convection Z/R for typical events in July and August when isolated convection occurs with little or no blow-off (anvil) precip. Many forecasters have the notion that anytime thunderstorms might occur in stratiform rain, then the radar should be in this Deep Convection mode. OHRFC strongly disagrees and recommends the Marshall/Palmer Z/R for most rain events except for the isolated thunderstorms that occur without stratification -- which occurs most often in July and August..

OHRFC recommends using the Cool Season Stratiform Z/R for wintry events which might contain frozen/freezing precipitation, or where brightbanding is a possibility, and where lightning would occur only in rare "thunder-snow" situations.

OHRFC recommends using the Tropical Z/R or the Marshall/Palmer Z/R for remnants of hurricanes or tropical storms that move into our basin.

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).