Hazardous Weather Information

Andrew Doubleday

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Hazardous Weather Information
« on: May 26, 2012, 02:24:19 PM »
Initial article written for/posted at ZMP, but have received requests to have it more publicly available for interested parties.

Since we're reaching the time of year where severe weather can significantly impact ZMP, I figured now would be a good time to include information on the dissemination of weather information to aircraft on frequency.

What Information Needs to be Provided?
How do we know what types of weather information need to be disseminated to pilots? Chapter 2, Section 6 of the 7110 explains this:

Controllers must advise pilots of hazardous weather that may impact operations within 150 NM of their sector or area of jurisdiction. Hazardous weather information contained in HIWAS broadcasts includes Airmen's Meteorological Information (AIRMET), Significant Meteorological Information (SIGMET), Convective SIGMET (WST), Urgent Pilot Weather Reports (UUA), and Center Weather Advisories (CWA). Facilities must review alert messages to determine the geographical area and operational impact for hazardous weather information broadcasts. The broadcast is not required if aircraft on your frequency(s) will not be affected.

Another note to keep in mind for those of you providing terminal approach control services or ATCT services:

c. Terminal facilities have the option to limit hazardous weather information broadcasts as follows: Tower cab and approach control facilities may opt to broadcast hazardous weather information alerts only when any part of the area described is within 50 NM of the airspace under their jurisdiction.

What is this Information?
Now that we know the types of weather information we need to be on the look-out for as controllers, What exactly does this information mean?

- AIRMETs (AIRman's METeorological Information) include information about widespread (3000 square miles or larger areas) weather phenomenon associated with IFR conditions, turbulence, and icing conditions that primarily may affect VFR aircraft and sometimes larger operators. They are broken down into three sub-categories listed below:
         • AIRMET Sierra (IFR):
              Ceilings less than 1000 feet and/or visibility less than 3 miles affecting over 50% of the area at one time.
              Extensive mountain obscuration

         • AIRMET Tango (Turbulence):
              Moderate turbulence
              Sustained surface winds of 30 knots or more at the surface

         • AIRMET Zulu (Icing):
              Moderate icing
              Freezing levels

- SIGMETs (SIGnificant METeorological information) advise of weather potentially hazadous to all aircraft other than convective activity. In the conterminous U.S., items covered are:

         • Severe icing severe icing below 8,000 feet • Severe or extreme turbulence severe turbulence between FL100 and FL240
         • Duststorms lowering visibilities to less than three (3) sm
         • Volcanic Ash

- WST - Convective SIGMETs (SIGnificant METeorological information) are issued in the conterminous U.S. for any of the following:

         • Severe thunderstorm due to:
            Surface winds greater than or equal to 50 knots
            Hail at the surface greater than or equal to 3/4 inches in diameter

         • Embedded thunderstorms
            Line of thunderstorms
            Thunderstorms greater than or equal to VIP level 4 affecting 40% or more of an area at least 3000 square miles

- UUA - Urgent PIREPs (Urgent PIlot weather REPorts) include information reported directly from the pilot concerning turbulence and icing information.

- CWAs (Center Weather Advisories) are an aviation weather warning for thunderstorms, icing, turbulence, and low cloud ceilings and visibilities.

So now that we know the types of weather information we need to be on the look out for as controllers, where do we find this information?

AIRMET and SIGMET information can be found from sources such as ADDS (Aviation Digital Data Services) found at this link http://aviationweather.gov/adds/airmets/. On this page, you'll note a section labeled "Text AIRMETs/SIGMETs: Check at least one in each column:" followed by a series of check-boxes beneath that allow you to specify the types of weather information you are seeking and specific areas/area for that information with a map below that indicating which states fall within the given areas. See the below image for a visual:

[img]http://dl.dropbox.com/u/16162462/HWI/1.jpg\\\" border=\\\"0\\\" class=\\\"linked-image\\\" /]

You'll note that the ZMP falls within the Chicago area according to the map, so we'll want to specify that area when seeking hazardous weather information. Although AIRMETs (IFR, turbulence, icing information, primarily) are certainly important to pay attention to, they are generally not read as often on frequency as SIGMET/Convective SIGMET information/UUAs/CWAs. To pull up the SIGMET/CONVECTIVE SIGMET information, you'll want to check the following boxes for our area and then click the "Retrieve" button. See the below image for a visual:

[img]http://dl.dropbox.com/u/16162462/HWI/2.jpg\\\" border=\\\"0\\\" class=\\\"linked-image\\\" /]

Now a textual list of all current SIGMET information will display in a new window. See the below image for a visual:

[img]http://dl.dropbox.com/u/16162462/HWI/3.jpg\\\" border=\\\"0\\\" class=\\\"linked-image\\\" /]

Now that we have the textual list, we need to understand how to decode the information and read it on frequency to inform the pilots.

Convective SIGMETs are issues for the Western (W), Eastern (E) and Central © parts of the United States.  Each SIGMET report will begin with the place of issuance followed by the date and ZULU time in the very first line. They are generally issued at 55 minutes past each hour but can be issued at any time in between. The second line will show SIGW, SIGC or SIGE depending on the region it is for. The third line will read "CONVECTIVE SIGMET XXW/C/E" with the "XX" being a number (1 through 99) and the W/C/E following to indicate the affected region of the United States. The fourth line will indicate the time the SIGMET is valid till (2 hours from the time of issuance). The fifth line will indicate the affected States/areas. The sixth line will indicate the VORs, DME distances and directions for the affected geographic area (which makes it relatively easier for pilots/controllers to plot). The last line (which sometimes may be the seventh or eighth depending on the size of the previous section) then indicates the type of thunderstorms, size of the system, direction/speed of movement and cloud tops of the storms. Following the initial SIGMET report will be OUTLOOK information in which we should probably expect to see further SIGMETs issued for those specific geographic areas.

Something to keep in mind - I've noticed that the list will occasionally display SIGMET information for areas outside of the region we initially selected (you'll note this from the very first SIGMET in this list as it is an Eastern SIGMET for North Carolina, South Carolina and Coastal Waters). You'll have to browse down through the list to find the specific SIGMETs that concern the ZMP area (keeping in mind that it should be within 150nm of our sector). Pay attention to the affected States/water bodies as some of them will be for the South-Central U.S. outside of our coverage area.

[img]http://dl.dropbox.com/u/16162462/HWI/4.jpg\\\" border=\\\"0\\\" class=\\\"linked-image\\\" /]

Now that we understand how to decode the SIGMETs, we need to know how to read these on frequency. Below is the phraseology from the 7110 for reading the SIGMETs on frequency:

a. Controllers within commissioned HIWAS areas must broadcast a HIWAS alert on all frequencies, except emergency frequency, upon receipt of hazardous weather information. Controllers are required to disseminate data based on the operational impact on the sector or area of control jurisdiction.

The inclusion of the type and number of weather advisory responsible for the HIWAS advisory is optional.


So we'll take the example from our above textual list which indicates a SIGMET is out affecting the state of Iowa. Using the above phraseology, we would read that SIGMET on frequency as follows:

"Attention all aircraft, hazardous weather information, CONVECTIVE SIGMET Three-One Central out valid until two-one-five-five zulu for Iowa available on HIWAS, Flight Watch, or Flight Service Frequencies."

Since we are on VATSIM and those frequencies (HIWAS, Flight Watch, Flight Service Frequencies) are not readily available for use by most pilots not using some sort of addon weather programs, we are adding to the "realistic experience" we can provide to pilots on the network by stating this. To assist with this issue, I also like to add and additional phrase after the HIWAS, FlightWatch, Flight Service Frequencies line that would read on frequency as follows:

"Attention all aircraft, hazardous weather information, CONVECTIVE SIGMET Three-One Central is out valid until two-one-five-five zulu for Iowa available on HIWAS, Flight Watch, Flight Service Frequencies, or from air traffic control upon pilot request" which then indicates to the pilot that they can obtain a detailed reading of the SIGMET from us on frequency upon request. In this case, you would simply read the SIGMET in full detail (keeping in mind that you should work your traffic first and provide this information as second priority to that).

A full reading of the example report we are using would read as follows:

"CONVECTIVE SIGMET Three-One Central, out valid until two-one-five-five zulu, affecting Iowa, From 5-0 North-Northeast of Des Moines to 2-0 North-Northwest of Iowa City to 1-0 West-Northwest of Iowa City to 1-0 Southeast of Des Moines to 5-0 North-Northeast of Des Moines, an area of embedded thunderstorms moving from 2-3-0 at 3-0 knots. Tops to Flight Level 3-5-0."

There are, of course, other shortened words that you may see in the reports that need to be decoded but most are relatively simple to unlock using common sense as most of the vowels are simply removed to shorten the length of the report.

Keep in mind that there may be multiple SIGMETs out for our area, especially with the sheer size of ZMP's coverage area. You can read those off using the following phraseology:

"Attention all aircraft, hazardous weather information, CONVECTIVE SIGMETs Three-One Central, three-two central, and three-three central out valid until two-one-five-five zulu for Iowa, Nebraska, Kansas, North Dakota, South Dakota and Minnesota, available on HIWAS, Flight Watch, Flight Service Frequencies, or from Air Traffic Control upon pilot request."

Urgent PIREPs can be obtained from multiple online sources, but have no real applicability on VATSIM unless actually reported by a pilot flying on the network. Our IDS system will help you to keep track of that information and deliver this information to other pilots on frequency when/where applicable.

Some important information and phraseology from the 7110 should be noted for PIREPs:

Significant PIREP information includes reports of strong frontal activity, squall lines, thunderstorms, light to severe icing, wind shear and turbulence (including clear air turbulence) of moderate or greater intensity, volcanic eruptions and volcanic ash clouds, and other conditions pertinent to flight safety.

FAAO JO 7110.65, Para 3-1-8, Low Level Wind Shear/Microburst Advisories.
FAAO JO 7210.3, Para 6-3-1, Handling of SIGMETs, CWAs, and PIREPs.
AIM, Para 7-5-9, Flight Operations in Volcanic Ash.
FAAO JO 7210.3, Para 10-3-1, SIGMET and PIREP Handling.

a. Solicit PIREPs when requested or when one of the following conditions exists or is forecast for your area of jurisdiction:

1. Ceilings at or below 5,000 feet. These PIREPs must include cloud base/top reports when feasible.

TERMINAL. Ensure that at least one descent/climb-out PIREP, including cloud base/s, top/s, and other related phenomena, is obtained each hour.

EN ROUTE. When providing approach control services, the requirements stated in TERMINAL above apply.

2. Visibility (surface or aloft) at or less than 5 miles.

3. Thunderstorms and related phenomena.

4. Turbulence of moderate degree or greater.

5. Icing of light degree or greater.

6. Wind shear.

7. Volcanic ash clouds.

Pilots may forward PIREPs regarding volcanic activity using the format described in the Volcanic Activity Reporting Form (VAR) as depicted in the AIM, Appendix 2.

8. TERMINAL. Braking Action Advisories are in effect.

FAAO JO 7110.65, Para 3-3-5, Braking Action Advisories.
P/CG Term- Braking Action Advisories.

b. Record with the PIREPs:

1. Time.

2. Aircraft position.

3. Type aircraft.

4. Altitude.

5. When the PIREP involves icing include:

(a) Icing type and intensity.

( b ) Air temperature in which icing is occurring.

c. Obtain PIREPs directly from the pilot, or if the PIREP has been requested by another facility, you may instruct the pilot to deliver it directly to that facility.


Or if appropriate,

REQUEST/SAY (specific conditions; i.e., ride, cloud, visibility, etc.) CONDITIONS.

If necessary,

OVER (fix),




BETWEEN (fix) AND (fix).

d. Handle PIREPs as follows:

1. Relay pertinent PIREP information to concerned aircraft in a timely manner.

2. EN ROUTE. Relay all operationally significant PIREPs to the facility weather coordinator.

3. TERMINAL. Relay all operationally significant PIREPs to:

(a) The appropriate intrafacility positions.

( b ) The FSS serving the area in which the report was obtained.

The FSS is responsible for long line dissemination.

© Other concerned terminal or en route ATC facilities, including non-FAA facilities.

(d) Use the word gain and/or loss when describing to pilots the effects of wind shear on airspeed.

“Delta Seven Twenty-one, a Boeing Seven Twenty-seven, previously reported wind shear, loss of Two Five knots at Four Hundred feet.”

“U.S. Air Seventy-six, a D-C Niner, previously reported wind shear, gain of Twenty-Five knots between Niner Hundred and Six Hundred feet, followed by a loss of Five Zero knots between Five Hundred feet and the surface.”

AIM, Para 7-1-24, Wind Shear PIREPs.

Much of this information that we, as controllers, need to obtain from pilots is provided to you in the PIREP form via IDS. All you will need to do is fill in the blanks and submit the PIREP to the system. Use the above prescribed phraseology when disseminating the PIREPs to other pilots on frequency when necessary.

CWAs are read on frequency in a very similar fashion as the SIGMETs. What exactly is a CWA?

CWAs are unscheduled in-flight, flow control, air traffic, and aircrew advisory. By nature of its
short lead-time, the CWA is not a flight-planning product. It is generally a nowcast for conditions
beginning within the next two hours. CWAs will be issued:

        • As supplement to an existing SIGMET, Convective SIGMET, AIRMET, or FA.

        • When an In-flight Advisory has not been issued, but observed or expected weather
           conditions meet SIGMET/AIRMET criteria based on current PIREPs and reinforced by other
           sources of information about existing meteorological conditions.

        • When observed or developing weather conditions do not meet SIGMET, Convective
           SIGMET, or AIRMET criteria; e.g., in terms of intensity or area of coverage, but current Pilot
           Weather Reports or other weather information sources indicate existing or anticipated
           meteorological phenomena will adversely affect the safe flow of air traffic within the Air Route
           Control Center (ARTCC) area of responsibility.

Where can CWAs be found? Click the following link: http://aviationweather.gov/products/cwsu/. This will bring you to a page with a map showing all of the ARTCC boundaries within the U.S. Mouse over the ZMP area (which should highlight in a reddish color) and click. A new, smaller window should open that should then display the current CWA and MIS (Meteorological Impact Statement) information. MIS are for ATC planning purposes only and NOT read over the frequency to pilots.

Here is an example of a CWA:

[img]http://dl.dropbox.com/u/16162462/HWI/5.jpg\\\" border=\\\"0\\\" class=\\\"linked-image\\\" /]

The above example is a CWA issued from the Kansas City, Missouri ARTCC. The "3" after ZKC indicates this CWA has been issued for the third weather phenomenon to occur for the day. The "301" in the second line denotes the phenomenon number again (3) and the issuance number, "01," for this phenomenon. The CWA was issued at 2140Z and is valid until 2340Z.

This would be read on frequency as:

"Attention all aircraft, hazardous weather information, Center Weather Advisory Three-Zero-One out valid until two-three-four-zero concerning an isolated thunderstorm over the KCOU airport available on HIWAS, Flight Watch, Flight Service Frequencies, or from Air Traffic Control upon pilot request"

Weather Deviations
Something else to keep in mind on this topic is pilot deviations for weather. I've heard many controllers throughout VATUSA get completely tripped up and turn to mush when a pilot makes a request such as, "Hey Center, N123AB, we need to turn about 30 left for build-up..."

Handling weather deviations is actually quite simple (phraseology-wise). The phraseology for this is as followed:

2. When a deviation cannot be approved as requested and the situation permits, suggest an alternative course of action.

UNABLE DEVIATION (state possible alternate course of action).

FLY HEADING (heading),



b. In areas of significant weather, plan ahead and be prepared to suggest, upon pilot request, the use of alternative routes/altitudes.

DEVIATION APPROVED, (restrictions if necessary), ADVISE WHEN ABLE TO:

FLY HEADING (heading),

It may not always be possible to approve a weather deviation due to traffic or other factors. Keep in mind, the pilot has ultimate authority in making these deviations, however. It's more or less a "weather emergency" in this case as flying directly through the convective weather could present a massive risk to the safety of the flight. As a controller, you'll need to find a way to work around these situations.

Another way that I regularly seem to hear deviations for weather approved by ATC:

"Deviations left of course/right of course approved, when able proceed direct [VOR/FIX/AIRPORT]."

This about covers the dissemination of hazardous weather information to pilots on frequency and should help many of you to provide a more professional and realistic service to pilots operating within our sector.

Further information on weather information can be found in Chapter 2, Section 6 of the 7110: http://www.faa.gov/air_traffic/publication...#atc0206.html.1.

Additions from other ZMP controllers:

MT: Good stuff AJ. I personally also add aviationweather.gov in my broadcasts. ie. "hazardous weather info ....... Available on HIWAS, flight service, aviationweather.gov or controller time permitting."

JM: I'll also add in the terminal setting, the hazardous weather information is usually disseminated on the ATIS as well.  The short broadcast, "Attention all aircraft, Hazardous weather information Convective Sigmet 22 Central for Wisconsin and Lake Michigan available on HIWAS, Flight Watch, and Flight Service frequencies" is usually sufficient.  If a pilot has a question about weather not in my area of jurisdiction, I will generally refer them to flight watch/flight service, but of course that is not possible on VATSIM.

Wouldn't it be cool if there was a Flight Service position that we could staff during certain times?

DK: For the sake of not confusing network pilots any more than some stuff already does, I usually drop the "HIWAS/FlighWatch/AFSS" bit and just say:

"Hazardous weather, Convective SIGMET XXC valid until XX55z for MN/IA/ND/SD, etc. available from Air Traffic Controller on request."

For you terminal guys, when you're recording the KMSP voice ATIS and a convective SIGMET or CWA coverage area falls within 50nm of KMSP, add the following into the voice ATIS immediately after approaches/runways in use:

"ATTN ALL ACFT: HAZARDOUS WX INFO FOR KMSP AREA AVAIL FROM ATC ON REQ" (Read as: "Attention all aircraft: Hazardous weather information for Minneapolis-St. Paul Airport Area available from Air Traffic Control on request.").

To each his/her own, though. I strongly encourage all the enroute guys to disseminate these advisories, workload permitting!

Other comments, contributions welcome! Hope this provides a bit of insight and assistance to the rest of VATUSA...
« Last Edit: May 26, 2012, 02:26:53 PM by Andrew Doubleday »
Andrew James Doubleday (AJ)
Embry-Riddle | University of North Dakota CTI
Twitch Stream: Ground_Point_Niner

Brad Littlejohn

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« Reply #1 on: May 29, 2012, 01:10:55 PM »

AJ, This is really good stuff, and would help out just about everywhere in VATUSA (Hurricane season starting in the south, Monsoon season out west, Tornado season in the midwest), so this helps out just about everywhere. Depending on how much this is simulated, this may be worth posting in the VATSIM controller section, with parts in the pilots section to see what the equivalents are in the rest of the world.


Omer Varol

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« Reply #2 on: May 31, 2012, 07:52:51 PM »
One question and i always try to find it but i cant, Where can i find it for ZHN/HCF Honolulu Air Space
Omer Varol - 1141085 - C1
Atlanta ARTCC Facility Engineer

Rahul Parkar

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« Reply #3 on: June 01, 2012, 06:40:45 AM »
Haven't checked this in detail, but a 5 second google search brought this up,


Rahul Parkar,

On second thoughts Nappa, catch it, catch it with your teeth.

Harold Rutila

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« Reply #4 on: July 07, 2012, 11:11:42 PM »
Another tip...you can use the Java AIRMET/SIGMET viewer if you'd prefer not to scroll through a bunch of text. IRL the weather displays in towers and centers automatically grab the appropriate SIGMETs for the area and put them on the computer display or send it to the flight strip printer.

aviationweather.gov --> SIGMET/AIRMET --> Java Tool

Mouse over the SIGMET/AIRMET icons to get the full details on the advisories.