significant weather forecast

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Jasper Valero

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significant weather forecast or SIGWX are forecasts for the predominant weather conditions and its positions at a given time
there are three types of charts under SIGWX and those are low-level charts, mid-level charts, and high-level charts
low-level charts has an altitude cover of FL240 and below
low-level charts only provides an overview of selected aviation weather hazards 12 and 24 hours into the future
low-level charts are primarily used as a guidance for pre-flight briefings
low-level charts are issued four times per day by National Weather Service's Aviation Weather Center
there are two charts issued under low-level charts, the 12-hour and the 24-hour
the depictions under low-leve charts are weather flying categories, turbulence, and freezing levels
under weather flying categories, solid red line is for IFR
under weather flying categories, scalloped blue line is for marginal VFR
moderate or greater turbulence under depictions of low-level charts are enclosed by bold, dash, brown lines
the vertical extent is the specified top and base heights separated by a slant in low-level charts
intensity and height information may be located within or adjacent to the forecasted area
if adjacent to an area, an arrow will be depicted
freezing levels for low-level are labelled in hundreds of feet MSL beginning at 4000ft using 4000-foot intervals
freezing level in the surface are blue saw-tooth symbol
freezing level above the surface are blue dashed lines
mid-level charts has an altitude coverage of FL100 - FL450
mid-level charts are also called medium-level SIGWX
mid-level charts provides forecast to significant en route weather phenomena
mid-level charts are used by airline dispatchers for flight planning and weather briefing, and by flightcrew members during flight
the AWC issued a 24-hr mid-level SIGWX chart 4 times daily (0800, 1400, 2000, 0200)
mid and high-level SIGWX charts cover similar weather phenomenon using similar symbology
non-convective with moderate or severe icing and/or moderate or severe turbulence - enclosed red scalloped lines. (in which the type of icing is not forecasted)
in mid-level SIGWX chart, CB clouds are also depicted by enclosed red scalloped lines
XXX - bases extend below that level
the altitude coverage for high-level SIGWX chart is from FL250 to FL630
high-level SIGWX used by airline dispatchers for flight planning and weather brifings before departure and by flight crew members during flight
in accordance with the WAFS of the ICAO, high-level SIGWX forecasts are provided for the en route portion of international flights
high-level charts are issued as global data set in digital format by two WAFCs: the NWS's AWC and UK Met Office
contents of high-level SIGWX chart includes thunderstorm and cumulonimbus clouds, moderate or severe turbulence, moderate or severe icing, jet streams, tropopause heights, tropical cyclone, volcanic eruption sites, widespread sandstorm and duststorm
in high-level SIGWX chart, ts and cb are depicted as enclosed red scalloped lines and appears within or adjacent to the outlines area. if adjacent, arrow is depicted
in high-level, ts with cb are characterized by vertical extent and coverage
in high-level, CB are indicated only if there is a widespread cumulonimbus clouds, cumulonimbus along a line with little or no space between individual clouds, cumulonimbus embedded in cloud layers, cumulonimbus concealed by haze
CB coverage are only identified as ISOL, OCNL, and FRQ
ISOL are depicted only if EMBD in clouds or concelead by haze
the inclusion of CB shall be understood to include all weather phenomena normally associated with cumulonimbus: thunderstorm, moderate or serve icing, moderate or severe turbulence, and hail
in high-level, moderate or severe turbulence are depicted by enclosed by bold yellow dashed lines
moderate or severe turbulence - are associated with windshear zones and/or mountain waves
in high-level, turbulence is not identifies if convective or thunderstorm turbulence