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Z/R Relationships
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|
| WFO |
Last Reported |
Z/R Formula |
|
Rate @ 30dBZ |
Name of Formula |
Bias Correction Factor |
| BUF |
8am EDT 17-May-2008 |
Z=200R1.6 |
 |
0.11 in/hr |
Marshall/Palmer Stratiform Z/R | 3-hr: 1.26 #16 under-estimation |
| CCX |
8am EDT 17-May-2008 |
Z=300R1.4 |
 |
0.09 in/hr |
Summer Deep Convection Z/R | 2-hr: 0.88 #11 over-estimation |
| CLE |
8am EDT 17-May-2008 |
Z=200R1.6 |
|
0.11 in/hr |
Marshall/Palmer Stratiform Z/R | 5-hr: 1.17 #51 under-estimation |
| DTX |
8am EDT 17-May-2008 |
Z=200R1.6 |
|
0.11 in/hr |
Marshall/Palmer Stratiform Z/R | 10-hr: 1.87 #303 under-estimation |
| FCX |
8am EDT 17-May-2008 |
Z=300R1.4 |
|
0.09 in/hr |
Summer Deep Convection Z/R | 5-hr: 1.96 #45 under-estimation |
| GRR |
8am EDT 17-May-2008 |
Z=300R1.4 |
|
0.09 in/hr |
Summer Deep Convection Z/R | 10-hr: 1.28 #186 under-estimation |
| HPX |
8am EDT 17-May-2008 |
Z=300R1.4 |
|
0.09 in/hr |
Summer Deep Convection Z/R | 10-hr: 1.00 #1077 unbiased estimation |
| HTX |
8am EDT 17-May-2008 |
Z=300R1.4 |
|
0.09 in/hr |
Summer Deep Convection Z/R | 10-hr: 0.72 #830 over-estimation |
| ILN |
8am EDT 17-May-2008 |
Z=200R1.6 |
|
0.11 in/hr |
Marshall/Palmer Stratiform Z/R | 5-hr: 1.07 #75 under-estimation |
| ILX |
8am EDT 17-May-2008 |
Z=300R1.4 |
|
0.09 in/hr |
Summer Deep Convection Z/R | 10-hr: 0.70 #635 over-estimation |
| IND |
8am EDT 17-May-2008 |
Z=200R1.6 |
|
0.11 in/hr |
Marshall/Palmer Stratiform Z/R | 5-hr: 1.08 #27 under-estimation |
| IWX |
8am EDT 17-May-2008 |
Z=200R1.6 |
|
0.11 in/hr |
Marshall/Palmer Stratiform Z/R | 5-hr: 0.63 #10 over-estimation |
| JKL |
8am EDT 17-May-2008 |
Z=130R2 |
 |
0.11 in/hr |
Cool Season (East) Stratiform Z/R | 5-hr: 1.64 #65 under-estimation |
| LOT |
8am EDT 17-May-2008 |
Z=300R1.4 |
|
0.09 in/hr |
Summer Deep Convection Z/R | 10-hr: 0.93 #482 over-estimation |
| LSX |
8am EDT 17-May-2008 |
Z=300R1.4 |
|
0.09 in/hr |
Summer Deep Convection Z/R | 10-hr: 0.66 #395 over-estimation |
| LVX |
8am EDT 17-May-2008 |
Z=300R1.4 |
|
0.09 in/hr |
Summer Deep Convection Z/R | 5-hr: 1.83 #23 under-estimation |
| LWX |
8am EDT 17-May-2008 |
Z=300R1.4 |
|
0.09 in/hr |
Summer Deep Convection Z/R | 5-hr: 2.27 #31 under-estimation |
| MRX |
8am EDT 17-May-2008 |
Z=300R1.4 |
|
0.09 in/hr |
Summer Deep Convection Z/R | 5-hr: 2.38 #14 under-estimation |
| OHX |
8am EDT 17-May-2008 |
Z=300R1.4 |
|
0.09 in/hr |
Summer Deep Convection Z/R | 5-hr: 1.65 #11 under-estimation |
| PAH |
8am EDT 17-May-2008 |
Z=300R1.4 |
|
0.09 in/hr |
Summer Deep Convection Z/R | 10-hr: 0.74 #833 over-estimation |
| PBZ |
8am EDT 17-May-2008 |
Z=200R1.6 |
|
0.11 in/hr |
Marshall/Palmer Stratiform Z/R | 3-hr: 1.34 #30 under-estimation |
| RLX |
8am EDT 17-May-2008 |
Z=200R1.6 |
|
0.11 in/hr |
Marshall/Palmer Stratiform Z/R | 5-hr: 1.92 #92 under-estimation |
| VWX |
8am EDT 17-May-2008 |
Z=300R1.4 |
|
0.09 in/hr |
Summer Deep Convection Z/R | 5-hr: 1.81 #12 under-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,
authorization, instructions, and recommendations regarding Z/R relationships,
see the Radar Operations
Center's page.
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 following table lists the radars that OHRFC uses in the precipitation mosaic along with the Z/R relationship each radar is set to.
The bias correction factor can only be computed if there are at least 10 gage-radar pairs with values 0.01 inches or more. Sometimes, data has to be searched back several hours to find at least 10 pairs. (The actual number of pairs used in computing this bias factor is shown following the # sign.) This number of hours searched is shown preceding the bias factor. Bias factors are color-coded green if the radar estimates are within 15% 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.
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