/*
This function opens and parses $html_file for $tag
and returns its content and its attributes to the
callback function $element_handler.
$element_handler is a custom funtion which acts upon
the content and the attributes of $tag and gets called
everytime $tag is closed.
It must accept the following parameters:
- $content (content of the element $tag)
- $attributes (attributes of $tag
*/
function html_parse($html_file, $element_handler, $tag)
{
$fd = fopen($html_file, "r") or die("Error: Unable to open file $html_file");
// Loop until we're at EOF of $fd
while (!feof($fd))
{
$char = fgetc($fd);
if ($open_tag != "")
{
$content .= $char;
}
if ($char == "<")
{
$inside_tag = true;
}
// We're inside a tag, so add $char to $element (for testing later if
// this is $tag)
if ($inside_tag)
{
$element .= $char;
}
if ($char == ">")
{
$inside_tag = false;
if (ereg ("\<$tag", $element))
{
$open_tag = $element;
}
else
{
if ($element == "</$tag>")
{
$tmp_array = ereg_replace("\<$tag", "",
$open_tag);
$tmp_array = ereg_replace(">", "", $tmp_array);
$tmp_array = split ("[$\"] +", $tmp_array);
for ($i=0; $i<count($tmp_array); $i++)
{
$tmp_array[$i] = trim($tmp_array[$i]);
$tmp_array[$i] = ereg_replace("\"", "", $tmp_array[$i]);
$tmp_attribs = split("=", $tmp_array[$i]);
for ($j=0; $j<count($tmp_attribs); $j++)
{
$attribs[trim($tmp_attribs[$j])] = trim($tmp_attribs
[$j+1]);
}
}
$content = eregi_replace("\<$tag([^>]*)([^>]*)>", "",
$content);
$content = eregi_replace("\</$tag>", "", $content);
$element_handler($attribs, $content);
$content = "";
$attribs = "";
$tmp_array = "";
$open_tag = "";
}
}
$element = "";
}
}
fclose( $fd );
}
A Terminal Aerodrome Forecast (TAF) is a concise statement of the expected
meteorological conditions at an airport during a specified period (usually
24 hours). Each ICAO state may modify the code as needed. The TAF code, as
described here, is the one used in the United States. TAFs use the same
weather code found in METAR weather reports.
A TAF report contains the following sequence of elements in the following
order:
*1. Type of Report
*2. ICAO Station Identifier
*3. Date and Time of Origin
*4. Valid Period Date and Time
*5. Forecast Meteorological Conditions
The international TAF also contains forecast temperature, icing, and
turbulence. These three elements are not included in National Weather
Service (NWS) prepared TAFs. The U.S. has no requirement to forecast
temperatures in an aerodrome forecast and the NWS will continue to forecast
icing and turbulence in AIRMETs and SIGMETs.
Type of Report
The report type header will always appear as the first element in the TAF
forecast. There are two types of TAF reports, a routine forecast, TAF, and
an amended forecast, TAF AMD. An amended TAF is issued when the current TAF
no longer adequately describes the ongoing weather or the forecaster feels
the TAF is not representative of the current or expected weather.
Corrected (COR) or delayed (RTD) TAFs are identified only in the
communications header which precedes the forecast text.
ICAO Station Identifier
The TAF code uses the ICAO four-letter location identifiers. In the
conterminous United States, the three-letter identifier is prefixed with a
K. For example SEA (Seattle) becomes KSEA. Elsewhere, the first one or two
letters of the ICAO identifier indicate in which region of the world and
country (or state) the station is. Pacific locations such as Alaska, Hawaii,
and the Marianas islands start with P followed by an A, H, or G
respectively. The last two letters reflect the specific station
identification. If the location`s three-letter identification begins with an
A, H, or G, the P is just added to the beginning. If the location`s
three-letter identification does not begin with an A, H, or G, the last
letter is dropped and the P is added to the beginning.
Canadian station identifiers start with C. Mexican and western Caribbean
station identifiers start with M. The identifier for the eastern Caribbean
is T, followed by the individual country`s letter.
Date and Time of Origin
This element is the UTC date and time the forecast is actually prepared. The
format is a two-digit date and four-digit time followed, without a space, by
the letter Z. Routine TAFs are prepared and filed approximately one-half
hour prior to scheduled issuance times. TAFs are scheduled for issuance
foure times daily at 0000Z, 0600Z, 1200Z, and 1800Z.
Example:
091050Z - Forecast prepared on the ninth day of the month at 1050Z.
Valid Period Date and Time
The UTC valid period of the forecast is a two-digit date followed by the
two-digit beginning hour and two-digit ending hour. Routine TAFs are valid
for 24-hours. Valid periods beginning at 0000Z shall be indicated as 00.
Valid periods ending at 0000Z shall be indicated as 24. The 24 indication
applies to all time group ending times.
In the case of an amended forecast, or a forecast which is corrected or
delayed, the valid period may be for less than 24 hours. Where an airport or
terminal operates on a part-time basis (less than 24 hours/day) the TAFs
issued for those locations will have the abbreviated statement NIL AMD SKED
AFT (closing time)Z, added to the end of the forecast. For the TAFS issued
while these locations are closed, the word NIL will appear in place of the
forecast text. A delayed (RTD) forecast will then be issued for these
locations after two complete observations are received.
Examples:
*091212 - Forecast valid from the ninth at 1200Z til the tenth at 1200Z.
*110024 - Forecast valid from the eleventh at 0000Z till the twelfth at
0000Z.
*010524 - Amended forecast valid from the first at 0500Z till the second at
0000Z.
The wind, visibility, and sky condition elements are always included in the
initial time group of the forecast. Weather is included in the initial time
group only if significant to aviation. If a significant, lasting change in
any of the elements is expected during the valid period, a new time period
with changes is included. It should be noted that, with the exception of a
FM group, the new time period will include only those elements which are
expected to change; i.e., if a lowering of the visibility is expected but
the wind is expected to remain the same, the new time period reflecting the
lower visibility would not include a forecast wind. The forecast wind would
remain the same as in the previous time period.
Any temporary conditions expected during a specific time period are included
with that time period.
Wind
The wind group includes forecast surface winds. The surface wind is the
expected wind direction (first three digits) and speed (last two or three
digits if 100 knots or greater). The contraction KT follows to denote the
units of wind speed in knots. Wind gusts are noted by the letter G appended
to the wind speed followed by the highest expected gust (two or three digits
if 100 knots or greater).
Calm winds (three knots or less) are encoded as 00000KT.
Variable winds are encoded when it is impossible to forecast a wind
direction due to winds associated with convective activity or low wind
speeds. A variable wind direction is noted by VRB where the three digit
direction usually appears.
Examples:
*18010KT - Wind one eight zero at one zero knots
*35012G20KT - Wind three five zero at one two gust two zero knots
*00000KT - Wind calm
*VRB16G28KT - Wind variable at one six gust two eight knots
Visibility
The expected prevailing visibility is forecast in statute miles and
fractions of statute miles followed by SM to note the units of measure.
Statute miles followed by fractions of statute miles are separated with a
space, for example, 1 1/2SM. Forecast visibility greater than 6 statute
miles is indicated by coding P6SM. Directional or variable visibility is not
forecasted and the visibility group is omitted if missing.
Examples:
*1/2SM - Visibility one-half statute mile
*2 1/4SM - Visibility two and one-quarter statute miles
*5SM - Visibility five statute miles
*P6SM - Visibility more than six statute miles
Weather
The expected weather phenomenon or phenomena is coded in TAF reports using
the same format, qualifiers, and phenomena contractions as METAR reports
(except UP).
Qualifiers of Intensity or Proximity
* - Light
* Moderate (no qualifier)
* + Heavy or well-developed
* VC in the Vicinity
Qualifier Descriptor
* MI Shallow
* BC Patches
* DR Low Drifting
* BL Blowing
* SH Showers
* TS Thunderstorm
* FZ Freezing
* PR Partial
Precipitation
* DZ Drizzle
* RA Rain
* SN Snow
* SG Snow Grains
* IC Ice Crystals
* PL Ice Pellets
* GR Hail
* GS Small Hail or Snow Pellets (less than 1/4 inch in diameter)
* UP Unknown precipitation (automated stations only)
Obscuration
* BR Mist (Foggy conditions with visibilities greater than 5/8 statute
mile)
* FG Fog (visibility 5/8 statute mile or less)
* FU Smoke
* DU Dust
* SA Sand
* HZ Haze
* PY Spray
* VA Volcanic Ash
Other
* PO Well-Developed Dust/Sand Whirls
* SQ Squalls
* FC Funnel Cloud
* +FC Well-Developed Funnel Cloud, Tornado or Waterspout
* SS Sandstorm
* DS Duststorm
Obscurations to vision will be forecast whenever the prevailing visibility
is forecast to be 6 statute miles or less.
If no significant weather is expected to occur during a specific time period
in the forecast, the weather group is omitted for that time period. If,
after a time period in which significant weather has been forecast, a change
to a forecast of no significant weather occurs, the contraction NSW (No
Significant Weather) will apear as the weather group in the new time period.
However, NSW is only included in the BECMG or TEMPO groups.
Sky Condition
TAF sky condition forecasts use the METAR format. Cumulonimbus clouds (CB)
are the only cloud type forecast in TAFs.
When the sky is obscured due to a surface-based phenomenon, vertical
visibility (VV) into the obscuration is forecast. The format for vertical
visibility is VV followed by a three-digit height in hundreds of feet.
Note: Ceiling layers are not designated in the TAF code. For aviation
purposes, the ceiling is the lowest broken or overcast layer or vertical
visibility into a complete obscuration.
Examples:
*SKC - Sky clear
*SCT005 BKN025CB BKN250 - Five hundred scattered, ceiling two thousand five
hundred broken cumulonimbus clouds, two five thousand broken.
*VV008 - Indefinite ceiling eight hundred
Optional Data (Wind Shear)
Wind shear is the forecast of non-convective low level winds (up to 2000
feet) and is entered after the sky conditions when wind shear is epxected.
The forecast includes the height of the wind shear followed by the wind
direction and wind speed at the indicated height. Height is given in
hundreds of feet AGL up to and including 2,000 feet. Wind shear is encoded
with the contraction WS followed by a three-digit height, slant character,
and winds at the height indicated in the same format as surface winds. The
wind shear element is omitted if not expected to occur.
Example:
WS010/18040KT - Low level wind shear at one thousand, wind one eight zero at
four zero.
Probability Forecast
The probability or chance of thunderstorms or other precipitation events
occuring, along with associated weather conditions (wind, visibility, and
sky conditions).
The PROB40 group is used when the occurrence of thunderstorms or
precipitation is in the 30% to less than 50% range, thus the probability
value 40 is appended to the PROB contraction. This is followed by a
four-digit group giving the beginning hour and ending hour of the time
period during which the thunderstorms or precipitation is expected.
Note: PROB40 will not be shown during the first six hours of a forecast.
Examples:
*PROB40 2102 1/2SM +TSRA - Chance between 2100Z and 0200Z of visibility
one-half thunderstorm, heavy rain.
*PROB40 1014 1SM RASN - Chance between 1000Z and 1400Z of visibility one
rain and snow.
*PROB40 2024 2SM FZRA - Chance between 2000Z and 0000Z of visibility two
freezing rain.
Forecast Change Indicators
The following change indicators are used when either a rapid, gradual, or
temporary change is expected in some or all of the forecast meteorological
conditions. Each change indicator marks a time group within the TAF report.
FROM Group
The FM group is used when a rapid change, usually occuring in less than one
hour, in prevailing conditions is expected. Typically, a rapid change of
prevailing conditions to more or less a completely new set of prevailing
conditions is associated with a synoptic feature passing through the
terminal area (cold or warm frontal passage). Appended to the FM indicator
is the four-digit hour and minute the change is expected to begin and
continues until the next change group or until the end of the current
forecast.
A FM group will mark the beginning of a new line in a TAF report. Each FM
group contains all the required elements -- wind, visibility, weather, and
sky condition. Weather will be omitted in FM groups when it is not
significant to aviation. FM groups will not include the contraction NSW.
Examples:
*FM0100 SKC - After 0100Z sky clear
*FM1430 OVC020 - After 1430Z ceiling two thousand overcast
BECOMING Group
The BECMG group is used when a gradual change in conditions is expected over
a longer time period, usually two hours. The time period when the change is
expected is a four-digit group with the beginning hour and ending hour of
the change period which follows the BECMG indicator. The gradual change will
occur at an unspecified time within this time period. Only the conditions
are carried over from the previous time group.
Example:
OVC012 BECMG 1416 BKN020 - Ceiling one thousand two hundred overcast. Then a
gradual change to ceiling two thousand broken between 1400Z and 1600Z.
TEMPORARY Group
The TEMPO group is used for any conditions in wind, visibility, weather, or
sky condition which are expected to last for generally less than an hour at
a time (occasional), and are expected to occur during less than half the
time period. The TEMPO indicator is followed by a four-digit group giving
the beginning hour and ending hour of the time period during which the
temporary conditions are expected. Only the changing forecast meteorological
conditions are included in TEMPO groups. The omitted conditions are carried
over from the previous time group.
Examples:
*SCT030 TEMPO 1923 BKN030 - Three thousand scattered with occasional
ceilings three thousand broken between 1900Z and 2300Z.
*4SM HZ TEMPO 0006 2SM BR HZ - Visibility four in haze with occasional
visibility two in mist and haze between 0000Z and 0600Z.
=
The = indicates the end of the individual TAF transmission. TAFs are bundled
together and transmitted as a single document. The = provides a convenient
means of separating this document into the individual TAF reports.
Source: FAA Training Center publication National Air Traffic Training
Program, Air Traffic Guide, Aviation Routine, Weather Report (METAR),
Aerodrome Forecast (TAF)
[Aviation Weather Center][U.S. Department of Commerce] [National Oceanic and Atmospheric Administration][National Weather Service][National Centers for Environmental Prediction] by:
