120 lines
7.9 KiB
HTML
120 lines
7.9 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
|
|
<html>
|
|
<head>
|
|
<meta http-equiv="CONTENT-TYPE" content="text/html; charset=utf-8">
|
|
<title>Collaborate_PoP_SnowAmt_QPF</title>
|
|
<meta name="GENERATOR" content="OpenOffice.org 1.1.3 (Linux)">
|
|
<meta name="CREATED" content="19951121;16410000">
|
|
<meta name="CHANGED" content="20050706;13040400">
|
|
<style>
|
|
<!--
|
|
@page { size: 8.5in 11in; margin-right: 1.25in; margin-top: 1in; margin-bottom: 1in }
|
|
P { margin-bottom: 0.08in; direction: ltr; color: #000000; text-align: left; widows: 0; orphans: 0 }
|
|
P.western { font-family: "Bitstream Vera Serif", "Times New Roman", serif; font-size: 12pt; so-language: en-US }
|
|
P.cjk { font-family: "Bitstream Vera Sans"; font-size: 12pt; so-language: }
|
|
P.ctl { font-family: "Lucidasans"; font-size: 12pt; so-language: }
|
|
-->
|
|
</style>
|
|
</head>
|
|
<body dir="ltr" lang="de-DE" text="#000000">
|
|
<font face="New Century Schoolbook, Times New Roman, serif"><font
|
|
size="5"><b>Collaborate_PoP_SnowAmt_QPF</b></font></font>
|
|
<br>
|
|
<br>
|
|
<font face="New Century Schoolbook, Times New Roman, serif"><font
|
|
size="3"><b>Introduction</b></font></font>
|
|
<br>
|
|
<br>
|
|
<font face="New Century Schoolbook, Times New Roman, serif">With the introduction of IFPS 11, the PoP,
|
|
SnowAmt, and QPF grids are now floating, i.e., they are no longer fixed to specific 6 or 12 hour intervals.
|
|
While this change allows for more flexibility in forecast preparation, it also creates two key problems
|
|
for forecasters. First, the duration of the PoP, SnowAmt, and QPF grids now varies considerably from
|
|
office to office, making the intersite coordination of these elements much more difficult. Second, the
|
|
NDFD Integrated Work Team has recommended that the graphics for these elements still need to be valid
|
|
for fixed durations (12 hours for the PoP graphics and 6 hours for the SnowAmt and QPF graphics).
|
|
<br><br>
|
|
The Collaborate_PoP_SnowAmt_QPF procedure addresses both of these forecast issues by creating fixed 12-hour
|
|
PoP (PoP12hr), 6-hour SnowAmt (SnowAmt6hr), and 6-hour QPF (QPF6hr) grids based on the values contained in
|
|
the floating PoP, SnowAmt, and QPF grids. These new grids may then be used for the purposes of intersite
|
|
coordination as well as web graphic generation.
|
|
<br><br>
|
|
In accordance with the NDFD, PoP12hr grids are created at 12-hour intervals through 7 days, QPF6hr grids
|
|
are created at 6-hour intervals through 72 hours, and the SnowAmt6hr grids are created at 6-hour intervals
|
|
through 36 hours.
|
|
<br><br>
|
|
The procedure calls several Smart Tools which populate the PoP12hr, SnowAmt6hr, and QPF6hr grids with
|
|
data from the floating PoP, SnowAmt, and QPF grids. The getMaxGrid Smart Tool reads the floating PoP
|
|
grids and assigns the maximum PoP value for each 12-hr period to the PoP12hr grids. The getSumGrids Smart
|
|
Tool is used to sum the SnowAmt and QPF grids into the SnowAmt6hr and QPF6hr grids. Note that these two
|
|
Smart Tools are designed to be called from a procedure and will generate an error if run interactively from
|
|
the Edit Actions dialog. A third SmartTool, MakeTmpGrid, is a generic SmartTool for creating a temporary
|
|
grid from the active grid. This is used in this procedure to copy and fragment the QPF and SnowAmt grids.
|
|
The procedure deletes these temporary grids when they are no longer needed within the tool.</font>
|
|
<br>
|
|
<br>
|
|
<br>
|
|
<big><big><font style="font-weight: bold;"
|
|
face="New Century Schoolbook, Times New Roman, serif">How
|
|
the Procedure Works</font><span style="font-weight: bold;">
|
|
</span></big></big><br>
|
|
<br>
|
|
<font face="New Century Schoolbook, Times New Roman, serif">All of the floating PoP, SnowAmt, and QPF
|
|
grids have been created before running the procedure/tools. The PoP12hr, SnowAmt6hr, and QPF6hr elements
|
|
exist in GFE. <br><br>
|
|
After creating and saving the floating PoP, SnowAmt, and QPF grids, the forecaster need only run the
|
|
Collaborate_PoP_SnowAmt_QPF procedure once to generate the PoP12hr, SnowAmt6hr, and QPF6hr grids needed
|
|
for intersite coordination.
|
|
<br><br>
|
|
When the forecaster runs the procedure, he/she is presented with a dialog box that allows a choice of
|
|
"All" or "Selected Time". If All is chosen, the procedure will generate the collaboration grids over
|
|
preset time ranges. These time ranges begin with the current time and extend out to 192 hours for the
|
|
PoP12hr grids, 60 hours for the SnowAmt6hr grids, and 96 hours for the QPF6hr grids. These ranges are
|
|
longer than the required minimum collaboration times to account for the different times during the day
|
|
when new grids may be added on to the end of the forecast database. If Selected Time is chosen, only
|
|
grids that intersect the active time selection in the grid manager will be used to compute PoP12hr,
|
|
SnowAmt6hr, and QPF6hr grids. Regardless of which option is selected, the procedure checks for the
|
|
existence of the source grids so errors will not be generated if grids are missing from the end of the
|
|
time range. Errors are generated if the floating grids are missing within a selected time range.
|
|
<br><br>
|
|
<b>Notable Methodology/Assumptions Used</b><br>
|
|
When the Collaborate_PoP_SnowAmt_QPF procedure is run by the forecaster, the floating SnowAmt and QPF
|
|
grids are first copied to two temporary elements, tmpSnowAmt and tmpQPF. The tmpSnowAmt and tmpQPF grids
|
|
are then automatically fragmented before being used by the getSumGrids Smart Tool to create the SnowAmt6hr
|
|
and QPF6hr grids. The usage of the temporary elements in this process allows the original floating SnowAmt
|
|
and QPF grids to be preserved; the fragmenting ensures that no tmpSnowAmt grid overlaps multiple SnowAmt6hr
|
|
grids/no tmpQPF grid overlaps multiple QPF6hr grids prior to running the getSumGrids tool. This latter
|
|
condition is important because such overlapping grids would cause the tool to produce inaccurate SnowAmt6hr
|
|
and QPF6hr grids. Once the getSumGrids Smart Tool has executed and the SnowAmt6hr and QPF6hr grids have been
|
|
produced, the temporary elements are automatically deleted.
|
|
<br><br>
|
|
To better illustrate the significance of fragmenting the tmpSnowAmt and tmpQPF grids, let=s consider a
|
|
simple example utilizing 3 forecast tmpSnowAmt grids. For the sake of simplicity, we will assume that the
|
|
default duration for the tmpSnowAmt grids is 3 hours, and that both the tmpSnowAmt and SnowAmt6hr grids are
|
|
based on Greenwich Mean Time (GMT). Note that the following also applies to tmpQPF even though it is not
|
|
discussed here. The forecast tmpSnowAmt grids are as follows:<br><br>
|
|
<i>Grid 1 - Valid 12-15 GMT, amount = 0" throughout<br>
|
|
Grid 2 - Valid 15-21 GMT, amount = 4" throughout<br>
|
|
Grid 3 - Valid 21-24 GMT, amount = 0" throughout</i>
|
|
<br><br>
|
|
If these grids are not fragmented before running the getSumGrids Smart Tool, the tool will see a
|
|
tmpSnowAmt grid with 4" accumulations that overlaps both the corresponding 12-18 GMT and 18- 24 GMT
|
|
SnowAmt6hr grids - and will therefore assign 4" accumulations to both SnowAmt6hr grids. This in turn
|
|
would imply an event total of 8" - not exactly what had been intended by the forecaster.
|
|
<br><br>
|
|
On the other hand, fragmenting the tmpSnowAmt grids before running the getSumGrids Smart Tool results
|
|
in the following grids as input to the tool:<br><br>
|
|
<i>Grid 1 - Valid 12-15 GMT, amount = 0" throughout<br>
|
|
Grid 2 - Valid 15-18 GMT, amount = 2" throughout<br>
|
|
Grid 3 - Valid 18-21 GMT, amount = 2" throughout<br>
|
|
Grid 4 - Valid 21-24 GMT, amount = 0" throughout</i><br><br>
|
|
Note that the 4" tmpSnowAmt grid valid from 15-21 GMT has been split into two three-hour grids containing
|
|
values of 2" throughout. This is because GFE assumes a constant snowfall rate when fragmenting the grids.
|
|
Naturally, this isn't always a valid assumption, but its currently the only one available for the software
|
|
to work with.
|
|
<br><br>
|
|
Executing the getSumGrids Smart Tool after fragmenting results in 2" accumulations in the corresponding
|
|
12-18 GMT and 18-24 GMT SnowAmt6hr grids, which would imply an event total of 4" - thereby matching the
|
|
original intent of the forecaster.
|
|
</font>
|
|
</body>
|
|
</html>
|