108 lines
No EOL
4.4 KiB
HTML
108 lines
No EOL
4.4 KiB
HTML
<html>
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<title>GFESuite Documentation - Virtual ISC Weather Elements</title>
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<body>
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<!-- <hr width="100%"> -->
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<h2><a name="Virtual"></a>Virtual ISC Weather Elements</h2>
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The Show ISC capability simply compares one weather element against
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another. For certain elements, a virtual weather element is
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calculated and that is what is displayed against the Fcst
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database. For example, QPF is a rate-dependent weather
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element. It doesn't make sense to display your 12-hr QPF
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Fcst grid against a 1-hr QPF ISC grid, since the time periods are not
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equal. Using the virtual weather element capability in the GFE, a
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new weather element is calculated that will display your 12-hr QPF Fcst
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grid against a virtual 12-hr QPF ISC grid. The Virtual 12-hr QPF
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ISC grid was calculated from the multiple ISC grids in the
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database. For ISC, there are virtually calculated weather
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elements for QPF, SnowAmt, MaxT, MinT, and PoP as shown in the
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following table:<br>
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<br>
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<table style="text-align: left; width: 100%;" border="1" cellpadding="2"
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cellspacing="2">
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<tbody>
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<tr>
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<td style="vertical-align: top; font-weight: bold;">Weather
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Element<br>
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</td>
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<td style="vertical-align: top; font-weight: bold;">Algorithm<br>
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</td>
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</tr>
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<tr>
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<td style="vertical-align: top;">QPF<br>
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</td>
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<td style="vertical-align: top;">The virtual ISC grid is always
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the same duration as the Fcst QPF grid. The Virtual ISC
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grid is the rate-summation of the ISC QPF grid.<br>
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</td>
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</tr>
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<tr>
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<td style="vertical-align: top;">SnowAmt<br>
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</td>
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<td style="vertical-align: top;">The virtual ISC grid is always
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the same duration as the Fcst SnowAmt grid. The Virtual ISC grid
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is the rate-summation of the ISC SnowAmt grid.<br>
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</td>
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</tr>
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<tr>
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<td style="vertical-align: top;">MaxT<br>
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</td>
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<td style="vertical-align: top;">The virtual ISC grid is always
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the same duration as the Fcst MaxT grid. It contains the maximum MaxT
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value gridpoint by gridpoint from the ISC MaxT grids valid over the
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same period. Normally there is only 1 MaxT grid, except in cases
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where the office is in a different time zone or adjacent offices have
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configured their MaxT time constraints differently.<br>
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</td>
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</tr>
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<tr>
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<td style="vertical-align: top;">MinT<br>
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</td>
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<td style="vertical-align: top;">The virtual ISC grid is always
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the same duration as the Fcst MinT grid. It contains the minimum MinT
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value gridpoint by gridpoint from the ISC MinT grids valid over the
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same period. Normally there is only 1 MinT grid, except in cases where
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the office is
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in a different time zone or adjacent offices have configured their MinT
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time constraints differently.</td>
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</tr>
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<tr>
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<td style="vertical-align: top;">PoP<br>
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</td>
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<td style="vertical-align: top;">The virtual ISC grid is always
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the same duration as the Fcst PoP grid. It contains the maximum PoP
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value gridpoint by gridpoint from the ISC PoP grids valid over the same
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period.<br>
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</td>
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</tr>
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</tbody>
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</table>
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<br>
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The following illustration shows the purpose of the Virtual ISC weather
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elements. In the case on the left when the virtual weather
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element is not used, the forecaster will be comparing QPF from Fcst and
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ISC for different time periods. In the case on the right,
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the virtual ISC grid is calculated from the rates of all overlapping
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ISC QPF grids. The duration of the Virtual ISC grid is programmed
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to exact match the duration of the Fcst grid.<br>
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<img alt="" src="images/VirtualISC1.png"><br>
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<br>
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The illustration below assumes a constant rain rate of 0.10"/hour over
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the entire ISC and Fcst grid. The Fcst grid duration is 7
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hours, thus that grid will show 0.70" of precipitation. The
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three ISC grids are 2 hours, 3 hours, and 4 hours in duration, and at a
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constant rain rate of 0.10"/hour contain 0.20", 0.30", and 0.40"
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respectively.<br>
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<br>
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The virtual QPF grid is programmed to match the duration of the Fcst
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grid, and thus it is 7 hours in length. The precipitation rate
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for each overlapping ISC QPF grid is calculated and that portion of the
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time period that overlaps is summed into the virtual ISC grid.<br>
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<br>
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When the user enables "Show ISC Mode", they will be comparing the
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precipitation for the same duration as the Fcst grid. In this
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specific example, the Virtual ISC Grid will show 0.70" of precipitation
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due to the constant rain rate of 0.10".<br>
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<br>
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<img alt="" src="images/VirtualISC2.png"
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style="width: 909px; height: 496px;"><br> |