Aviation Weather Products & Legends

Automated Weather reports generated by sensors
Some AWOS have verified observers “observed weather” who will provide visibility when < 7 miles Density Altitude when it exceeds the field elevation by >1000′

IN FLIGHT CONTINUOUS BROADCAST: ASOS / AWOS Frequencies listed on Navigational Charts

A weather observer’s interpretation of the weather conditions.
ASOS/AWSS is used to generate METARs
A Weather Depiction Chart contains a plot of weather conditions at METAR stations. See Example Tab

Altitudes are in MSL, Distances are in NM
AIREP – a routine, often automated report of in-flight weather conditions such as wind and temperature
PIREP – reported by a pilot to indicate encounters of hazardous weather
Both are transmitted in real-time via radio to a ground station.

PIREP Graphic Symbols:

Submit a PIREP to FSS, ATC,  or ARTCC:

SIERRA – IFR Conditions, Extensive Mountain Obscurations,
TANGO – Moderate Turbulence, Sustained Surface Winds 30+Kts, Non-Convective Low-Level Wind Shear
ZULU – Moderate Icing, Freezing Levels

IN FLIGHT: FSS, ATC, ARTCC
IN FLIGHT CONTINUOUS BROADCAST: Over HIWAS Frequency (H) – must be within 150NM of Nav Aide

• Severe Icing
• Severe or Extreme Turbulence
• Dust storms and/or sand storms lowering visibilities to less than three (3) miles
• Volcanic Ash
• Hawaii & Alaska Only:
  • Tornado
  • Lines of thunderstorms
  • Embedded thunderstorms
  • Hail greater than or equal to 3/4 inches in diameter

• Line of thunderstorms at least 60 miles long with thunderstorms affecting 40% of its length.
• Area of thunderstorms covering at least 40% of the area concerned and exhibiting a very strong radar reflectivity or a significant satellite or lightning signature.
• Embedded or severe thunderstorms expected to occur for more than 30 minutes.
• Special issuance criteria include:
  • Tornado
  • Hail greater than or equal to 3/4 inches in diameter
  • Wind gusts greater than or equal to 50 knots

IN FLIGHT: FSS, ATC, ARTCC
IN FLIGHT CONTINUOUS BROADCAST: Over HIWAS Frequency (H) – must be within 150NM of Nav Aide

L/H Pressure, Isobars, Radar Data,  Snow & Obstructions to Vision

Isobars closer together = stronger pressure gradients & stronger winds

• Wind missing within 1500’ of elevation
• Temp missing @ 3000 level or within 2500’ of elevation

2715-07    =   270°    15 kts    7°C

• 9900 = wind light and var <5kts
• For winds of 100+kts you add 50 to deg…Examples:
  • 771150 = (270°  111kts, -50°) put a 1 before the 11
  • 300° 220kts –54°  =  (809954) 199kts is the highest wind you can record
• wind missing within 1500’ of elevation
• temp missing @ 3000 level or within 2500’ of elevation
• temp above 24K is always negative

• Height Contours – representing altitude of various pressure levels
• Hatching indicates widspeed 70-110 Knots
• Troughts/Ridges
• Wind Contours

Jet streams, Cyclones, Volcanic Eruptions

Red Scalloped Lines: Depicts areas of Non-Convective clouds with moderate or severe icing and/or moderate or severe turbulence. It also depicts CB clouds.
The type of icing, i.e., rime, clear or mixed, is not forecast.

• OCNL CB 530 XXX (Occasional Cumulonimbus 53,000’ MSL top to below chart level)
• CB Coverage (thunderstorm, icing, turn, hail)
  • ISOL    less than 4/8
  • OCNL  4/8 – 6/8
  • FRQ   > 6/8
  • EMBD  embedded

1″ hail & Tornados

SPC AC 090048

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0748 PM CDT Wed May 08 2019

Valid 090100Z – 091200Z

…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM EAST TEXAS
INTO MISSISSIPPI AND PORTIONS OF SOUTHERN ARKANSAS…

…SUMMARY…
Damaging winds, a few tornadoes, and severe hail will be possible
this evening and tonight, particularly across central/eastern
Louisiana, southern Arkansas, and western Mississippi.

…01Z Outlook Update…
Most substantial change to the ongoing outlook was to extend severe
probabilities eastward into Mississippi. A well-organized MCS
continues to trek eastward along the Mississippi River. Sufficient
instability and shear within the pre-convective airmass ahead of the
complex will sustain its intensity into at least western portions of
Mississippi through tonight. Ref MCD 593 for more short-term
details.

This MCS has also interrupted the strong low-level flow in place
earlier across east Texas and Louisiana as evidenced by 50-kt 850 mb
west-southwesterly flow around 1km in latest VAD/Profiler and 00Z
RAOB at Shreveport. Until the MCS shifts farther east from this
region, return of very unstable air from southeast Texas and
vicinity will likely be hindered. Thus, severe probabilities have
been reduced in Arkansas behind the ongoing MCS with the expectation
that any re-development of convection will be confined to east
Texas/western Louisiana once the low-level jet can become
re-established. A conditional slight remains in place in the event
that convection does redevelop along any northward-retreating
boundary.

Marginal risk/severe probabilities remain in place across Deep South
Texas, where a low risk of convective development exists against
higher terrain of northeastern Mexico, although most guidance
suggests that this activity should hold off until after 12Z
Thursday. A marginal risk also remains in place from east-central
New Mexico eastward/northeastward through Oklahoma into northeastern
Kansas for a low risk of wind/hail with ongoing storms, although
these threats should lessen in most areas after dark with nocturnal
boundary layer cooling/stabilization. The only exception to this
scenario exists in east-central NM and vicinity dependent on any
upscale growth of ongoing storms in that area.

..Cook.. 05/09/2019

For the 00Z TAFS through 00Z Thursday

East of the Divide…KCOD/KCPR/KLND/KRIW/KWRL Terminals

The low pressure system is moving from eastern Idaho through Wyoming
this afternoon and evening. Showers and thunderstorms will
continue through central WY into the early evening hours
before becoming more widespread rain. Mostly MVFR conditions will
continue through the forecast time frame, with periods of IFR
expected as precipitation intensifies and ceilings lower. As the
surface low pressure moves to the southeast around 00Z/Wed,
northerly flow will strengthen east of the divide. Precipitation
around the northern Bighorn Basin will move southward into central
WY. 700mb temperatures of -6C are suggesting some snow fall from
KLND to KCPR from about 10Z/Wed to 16Z/Wed. Some upslope areas
could see moderate precipitation during the period. With the flow
continuing after 12Z/Wed, ceilings and visibilities will remain low
until after 18Z/Wed, particularly at KLND and KCPR where rain/snow
are possible into the afternoon hours. The mountains will be
predominantly obscured through the next 24 hours.

West of the Divide…KBPI/KJAC/KPNA/KRKS Terminals

The low pressure system is moving from eastern Idaho through Wyoming
this afternoon and evening. early afternoon showers and
thunderstorms have weakened late this afternoon, though
more widespread showers may return early this evening as activity
from eastern Idaho will move into western WY. Winds will be gusty
and variable through the afternoon, with stronger north-northwest
wind pushing in after 01-02Z/Wed while rain showers continue through
about 06Z. An easterly gusty wind push is expected to move into
Sweetwater County and SW WY after 06Z/Wed. Models are suggesting
continued precipitation across southwest WY after 12Z/Wed, with KBPI
having a chance of snow for a few hours. VFR/MVFR conditions this
afternoon will become more MVFR with localized IFR through the
afternoon and into the evening, becoming more MVFR/VFR overnight,
except for KBPI which should remain IFR/MVFR. Mountains will be
mostly obscured through the forecast period. Wednesday afternoon
should see partly cloudy skies with mid-level clouds and gusty
northeast wind, mostly due to downsloping off the mountains toward
KJAC and KPNA.

Visible
The visible images display the Earth similarly to how humans see it with their eyes or how typical cameras view it. Clouds and snow appear bright white (high albedo/reflectance) but oceans and trees are much dimmer.

IR
The infrared images display the Earth in a manner that correlates with temperature. Generally speaking, the warmer an object, the more infrared energy it emits (gives off). The satellite sensor measures this energy and calibrates it to temperature using a very simple physical relationship (Planck’s Law). In the real world, clouds that are very high in the atmosphere are generally quite cold (perhaps -50 °C) whereas clouds that are very near the earth’s surface can be quite warm (perhaps +5 °C). Likewise, the land may be even warmer than the lower clouds (perhaps +20 °C). Those colder clouds emit much less infrared energy than the warmer clouds and the land emits more than those warm clouds. The data measured by the satellite are calibrated and colorized according to the temperature with red shades representing higher (warmer) temperatures and blue shades representing lower (cooler) temperatures. If the temperature of the atmosphere decreases with height (which is typical), a user can get an idea of which clouds are high-level and which are low-level based on the cloud top temperature.

Water vapor
The water vapor images display the Earth in a manner that correlates to quantity of water vapor in the upper portions of the atmosphere (25,000 feet and higher in general). The actual numbers displayed on the water vapor images correspond to temperature but there is no direct relationship between these values and the temperatures of clouds (as is the case for infrared images) since this channel doesn’t really “see” clouds but “sees” high-level water vapor instead. The most useful information to be gained from the water vapor images is the locations of storm systems and the jet stream. The color scale on the images can be helpful in interpreting the water vapor images. In general, regions displayed in shades of red are VERY dry in the upper atmosphere and MAY correlate to crisp blue skies from a ground perspective. On the contrary, regions displayed in shades of blue or green are indicative of a significant amount of high-level moisture and may also indicate cloudiness. This cloudiness could be high-level cirrus types or serious storms. That determination can only be made when this image is used in conjunction with the other channels.

Vis/Fog
The visible images are very good at depicting the location of low clouds that won’t show up on infrared imagery. So if clouds show up in the visible and not the IR, they are likely low clouds or snow cover. But the visible image is not useful at night and thus can’t be used.

As mentioned, the basic IR image won’t depict low clouds. To resolve this problem, it’s best to look at multiple channels. The best solution is to difference the 3.9 and 11 micron channels. This highlights emissivity differences rather than temperature. Smaller droplets like those in fog will emit less whereas hogher clouds will emit more. Then by using the proper gray shading, the low clouds can be detected.

In the images on the Vis/Fog page, low clouds show up bright and higher clouds show up as dark. The ground shows up as gray. In addition, flight categories for various airports are plotted over the imagery as a secondary verification.

Preceipitation types, cell movements, maximum tops, lines & cells of hazardous thunderstorms