July 2011
NOAA’s National Weather Service
Mission Statement
To enhance aviation safety
by increasing the pilot’s knowledge
of weather systems and processes
and National Weather Service
products and services.
Program Manager:
Michael Graf
Managing Editor:
Melody Magnus
Editor: Nancy Lee
Inside
Knowing the TAF: News
You Can Use
Page 5
Collaborative Decision
Making Meets
Volcanic Ash
Page 10
NWS Seeks Comments
on Future Service
Delivery Architecture
Through July 31, 2011
Page 12
When’s the Next Front?
Would you like an email
when a new edition of The
Front is published? Write
melody[email protected].
Thunderstorm Formation
and Aviation Hazards
By Ken Harding, Meteorologist in Charge, WFO Topeka, KS
Thunderstorms are one of the most beautiful atmospheric phenomenon. As
a pilot, however, thunderstorms are one of the most hazardous conditions you
can encounter. All thunderstorms can produce severe turbulence, low level wind
shear, low ceilings and visibilities, hail and lightning. Each of these hazards can
be difcult to cope with; if all these conditions arrive at once, it can be disastrous.
Understanding basic thunderstorm formation and structure can help you make
safe decisions.
Thunderstorms are formed by a process called convection, dened as the
transport of heat energy. Because the atmosphere is heated unevenly, an imbalance
can occur which thunderstorms attempt to correct. Three things are needed for
convection to be a signicant hazard to ight safety: moisture, lift and instability.
Moisture—Sufcient moisture must be present for clouds to form. Although
convection occurs in the atmosphere without visible clouds, think thermals
on a warm afternoon, moisture not only is the source of a visible cloud, but
also fuels the convection to continue. As the warm air rises, it cools, and the
water vapor in the air condenses into cloud droplets. The condensation releases
heat, allowing the rising air to stay buoyant and continue to move upward.
Lift—There are many ways for air to be lifted in the atmosphere. Convection,
or buoyancy, is one method. Other meteorological methods include fronts,
low pressure systems, interactions between thunderstorms, and interactions
between the jet stream and the surface weather systems. Air also can be lifted
by mechanical lift,
such as when it is
forced up and over
a mountain range.
Regardless of how
the air is lifted, if
the lift is enough to
make the air warmer
than the surrounding
air, convection can
continue.
Frontal lift
2
Next, We’ll look at the thunderstorm outow boundary, which can have a signicant impact
on aviation. This boundary marks the leading edge of rain-cooled air owing out from mature
thunderstorms. These outow boundaries can move many miles away from thunderstorms
and may be associated with clouds.
Instability—In general, as you increase in altitude, the air temperature cools up to the top of the
troposphere. Of course, around fronts, mountains and in shallow layers near the ground, this is
not always the case. How fast air cools is a measure of atmospheric stability. Meteorologists refer
to this vertical change in temperature as the lapse rate. Outside of extremes, the temperature
generally decreases from between 2.7
o
F - 5.4
o
F per 1000 feet. If the actual rising air cools
slower than the lapse rate, the air remains relatively warm compared to the surroundings, and
it continues to rise.
WSR-88D detection of multiple outow boundaries
Satellite picture of outow boundary
3
Three Stages of Thunderstorms
Towering Cumulus Stage: This is the stage of a
thunderstorm once convection has begun and a cloud is visible.
These building clouds are made entirely of liquid water. This
stage is characterized by upward motion throughout the entire
cloud. Aviation hazards from this stage include turbulence and
icing. Even though the cloud is composed of all liquid, some
of the liquid is “supercooled,” in other words, liquid water can
exist at temperatures below the normal freezing point.
Mature Stage: This stage is characterized by the production
of precipitation. Both updrafts and downdrafts are present.
Lightning is being produced. The mature thunderstorm contains
water, supercooled water and ice.
Dissipating Stage: During this nal stage, the updraft has
ceased and the storm is dominated by downdrafts. Precipitation
may still occur, but will decrease with time as moisture is depleted. This dissipating thunderstorm
contains mostly ice.
You can visually estimate the potential for convection to continue by looking at the texture of
the thunderstorms. If the cumulus tops are crisp and well dened—often looking like a cauliower,
the storm will continue to grow. The crisp texture occurs because the cloud is mostly made up of
water drops with little ice. As the storm becomes more vertical, these water drops will
change phase and freeze. This change will release heat, fueling the continued growth of
the cloud.
If the clouds appears fuzzy, it is likely because they are now composed mostly of ice
crystals As a result, the storm has much less energy available to grow signicantly taller.
Individual thunderstorms generally last less than one hour; however, if the storms are
being continually forced by a moving front outow boundary or from the same terrain
feature and area, thunderstorms can continue for many hours.
A special case of thunderstorms are known as supercell thunderstorms. Supercell
thunderstorms have a structure, driven primarily by the changing wind speed and direction
with height that allows the updrafts and downdrafts to remain separated. Thus, the
storm can remain in the mature phase for extended periods—several hours or more.
These supercell thunderstorms are often times associated with damaging winds, frequent
lightning, large hail, severe to extreme turbulence, and low level wind shear.
Supercell thunderstorm
Shown above are all three stages of thunderstorm
development.
Crisp clouds, (left) vs. fuzzy clouds (right) help you determine if a thunderstorm is
growing.
4
Hazards Associated with Thunderstorms
It is wise to avoid thunderstorms, as a ight instructor once said “A
thunderstorm is never as bad inside as it looks from the outside—it is worse.”
Thunderstorms contain many hazards to aviation such as the following:
Lightning: By denition, all thunderstorms contain lightning. Although
the NWS will mention lightning as a hazard in some warning products, lightning
is not a criteria used to determine if a thunderstorm is severe. As an aviator, you
should be aware that lightning can strike more than 10 miles from a thunderstorm.
Lightning
can strike
the ground,
another cloud or discharge into clear
air.
Turbulence: Pilot reports
from aircraft encountering
thunderstorms have noted up and
down drafts exceeding 6000 feet
per minute. Turbulence exceeding
the performance capability of most
aircraft can be found in and around
thunderstorms.
Wind Shear: Thunderstorm
outow can cause extreme changes in
wind speed and direction near the surface during critical phases of ight. Microbursts are possible
with many thunderstorms, as is heavy rain. Often virga and blowing dust on the surface are your
only clues to the presence of a microburst.
Icing: Because thunderstorms are driven, in part, from the conversion of liquid water to ice,
pilots can expect to nd airframe icing in all thunderstorms. Although
all forms of icing are possible, clear icing, caused by larger drops of
supercooled water, is the most common. Ice accumulation can be
rapid. Supercooled water and clear icing can extend to great heights
and to temperatures as low as -20
o
C.
The FAA publication, Thunderstorm Avoidance Tips puts it
succinctly: “To rely solely on Air Trafc Control (ATC) as a source for
weather avoidance is not entirely prudent. It is the pilot’s responsibility
to obtain a preight weather brieng. Any ATC reported weather
information, along with periodic contacts with Flight Watch while
airborne, will supplement what was learned during the preight
brieng. The ATC reports of precipitation areas are of value because
they can give you a global view of what is in the area. Pilots who have
onboard weather radar or lightning detection systems can benet from
the big picture that ATC can paint and can use the aircraft’s onboard
systems to pick the best tactical route to avoid severe weather.”
Source for More Pilot Information
The NWS Aviation Weather Center is one of your best sources for weather information. On the
Aviation Weather Center Website, you can nd preight information on thunderstorms and
other weather that may impact your ight. Before talking with Flight Service for your weather
brieng and ling a ight plan, educate yourself on the potential for thunderstorm, and identify
current SIGMETS and AIRMETS that may pertain to your route. Spend some time learning
about thunderstorms, study the current and forecast weather. The time you put into weather
study will greatly help your weather situational awareness. Q
Intense lightning
Microburst encounter
Example of icing on plane
5
Knowing the TAF: News You Can Use
By Mike Graf, NWS Aviation Services Branch
The Terminal Aerodrome Forecast (TAF) is an aviation forecast for the terminal area.
The area is dened as the 0-5 mile radius around the center of the airport. Guidance for how
a TAF is composed is available from the International Civilian Aviation Organization (ICAO)
Annex 3, Amendment 76; however, each country interprets this guidance a little differently.
This interpretation generates a slightly different looking TAF, depending on what country is
producing it.
Lets look at some examples of these differences by reviewing international TAFs and
U.S. Military TAFs and then comparing them to the typical U.S. TAF format. The differences may
surprise you. Below are TAFs from other countries, one U.S. military TAF and one typical U.S. TAF.
Keavik,Iceland…InternationalTAF
BIKF 201045Z 2012/2112 15012KT 9999 FEW025 BKN035
BECMG 2020/2022 VRB02KT
BECMG 2109/2112 33010KT
This TAF from Keavik uses the Becoming Group, BECMG, which is not used in the United
States except in military TAFs. The BECMG group allows a forecaster to infer a gradual or not so
gradual change over a period of usually 2 hours. For example, on the Iceland TAF above, the wind,
as of 2200 UTC, is variable at 2 knots. On the last line, the BECMG group indicates that sometime
between 0900 and 1200 UTC on the 21
st
the winds would change. As of the 1200 UTC, the winds
would be from the northwest at 10 knots.
Another common feature of international TAFs is the BECMG group usually includes only
the weather element that changes. You see this in the second and third lines where only the wind
is forecasted to change and the rest of the TAF carries 9999 FEW025 BKN035 throughout the
life of this TAF.
Cairo,Egypt…InternationalTAF
HECA 201000Z 2012/2118 34012KT CAVOK
TEMPO 2100/2106 VRB03KT 3000 BR NSC
The Cairo TAF makes use of several features we do not use in a U.S. TAF. In the rst line is
a remark Ceiling and Visibility OK, CAVOK, which is approximately Visual Flight Rules (VFR).
Also in the second line is the sky condition, NSC, which stands for no signicant clouds. Similar
to a sky clear, SKC, or scattered clouds, assuming the clouds are not convective.
Berlin,Germany…InternationalTAF
EDDB 201100Z 2012/2112 27015G25KT 9999 SCT020
BECMG 2012/2014 28010KT
PROB30
TEMPO 2014/2018 SHRA
BECMG 2018/2020 25005KT
Many international TAFs occasionally will use two conditional groups at one time. Look at the
third and forth line in the Berlin TAF above for example.
Before continuing, lets review two key terms: TEMPO and PROB.
6
TEMPO:indicates frequent or infrequent temporary uctuations in forecast meteorological
conditions expected to last less than 1 hour in each instance and, in the aggregate, cover less
than half of the period indicated.
PROB: indicates the probability of occurrence of forecast element(s) during a dened period
of time. Only the values 30 and 40 are used to indicate the probabilities of 30% and 40%,
respectively. The U.S.civilianTAFs useonlythePROB30remark.AndthePROB30
remarksarenotallowedintherst9hoursof aU.S.TAF.
Now let’s translate these terms to practical usage.
PROB30
TEMPO2014/2018SHRA
TEMPO straight-forward: SHRA is valid 1400-1800 UTC and indicates frequent or infrequent
temporary uctuations in forecast showers here, expected to last less than 1 hour in each instance
and, in the aggregate cover, less than half of the period indicated. Since this is a 4-hour period the
total time of showers should be less than 2 hours. If this was only a TEMPO group, you would
look for a greater than 50% chance of the showers.
Note, however, that you have the PROB30 remark preceding TEMPO, which means that there
is only a 30 percent chance of the airport getting a shower. Having said that, if they get the shower,
then it will be an on-and-off, 4-hour event as dened by the TEMPO rules above.
Moscow,Russia…InternationalTAF
UUWW 201050Z 2012/2112 20005G10MPS 9000 BKN020 SCT030CB
TEMPO 2012/2022 VRB18MPS 0800 +TSRAGR SQ BKN004 BKN010CB
BECMG 2022/2024 27007MPS
TEMPO 2022/2105 1100 SHRA BR BKN004 SCT015CB
The international TAF code recently made allowances for metric remarks. The Russian
TAFs, for example, use Meters Per Second (MPS) rather than Knots (KT). The conversion is
1 Meter Per Second = 1.9438444924406 Knots. So the rst line of the Moscow TAF above could
be converted by roughly doubling the MPS value: 20005G10MPS, which converts to 20010G20KT.
FtBragg,NorthCarolina…USMilitaryTAF (the format is the same for Marine/Navy/
Air Force
TAFs, Army TAFs are provided by the Air Force)
KFBG 2011/2109 26006KT 9999 SKC QNH2977INS
BECMG 2012/2013 31009KT 9999 OVC030 620304 50004 QNH2983INS
TEMPO 2100/2103 01015G30KT 8000 TSRA BKN030CB
BECMG 2103/2104 01005KT 9999 FEW050 QNH2993INS T33/2021Z T22/2109Z
In the U.S. military TAFs, you will notice some obvious differences from typical NWS civilian
TAFs. Most notable is the inclusion of barometric pressure adjusted to sea level, QNH, as well
as Icing and Turbulence forecasts below 10,000 feet and the common use of the BECMG group.
Icing and Turbulence can be decoded by using the information below. This data is helpful if
you are near a military installation with a TAF. Here’s an example from Air Force Pamphlet 11-238:
If forecasted, the icing group will be prexed by the number 6 and follows the cloud group in
the TAF. Look at the second line in the Ft Bragg TAF to decode, follow these instructions:
7
Using 620304:
1. Find the icing designator “6” following the cloud group:
620304
2. The next digit gives icing type and intensity: 620304.
See codes in Table1.
3. The next three digits give the base of the icing layer in
hundreds of feet: 620304.
4. The last digit provides the icing layer depth in thousands
of feet: 620304. Add this value to the base height to
determine the top limit of the icing conditions.
In the above example, the icing forecast will read,
“light rime icing (in cloud) from 3,000 to 7,000 feet.” If
forecasted, the turbulence code will be prefixed by the
Number 5 and will follow the cloud or icing group. Look
at the second line in the Ft Bragg TAF to decode the
turbulence group 520004 using these instructions:
1. Look for the turbulence designator “5” that
follows the cloud or icing group: 520004.
2. The next digit will determine the intensity:
520004. See Table2.
3. The next three digits will determine the base limit
of the turbulence layer in hundreds of feet Above
Ground Level (AGL): 520004.
4. The last digit will determine the turbulence layer
depth in thousands of feet: 520004. Add this
value to the base height to determine the top limit
of the turbulence conditions.
In the above example, the turbulence forecast will
read, “occasional moderate turbulence in clear air from
the surface to 4000 feet.”
Reagan Airport…Washington DC
KDCA 201137Z 2012/2112 06008KT 4SM -RA BR SCT018 BKN035 OVC050
FM201300 05008KT 6SM -SHRA BKN035 OVC050
FM201500 04009KT P6SM OVC060
FM202000 03007KT P6SM SCT050 BKN100
FM210000 16005KT P6SM FEW050 BKN250
The TAF above is a U.S. TAF. NWS Weather Forecast Offices (WFOs) produce
635 TAFs four times a day at in support of the National Air Space. The TAFs are issued between 20 and
40 minutes before the valid times of 1800/0000/0600/1200 UTC, and include amendments as
needed. Below are the major points to remember when planning and using NWS TAFs.
1. BECMG groups are not used.
2. Consecutive conditional groups are not used, i.e., PROB30 followed by a TEMPO group,
see example in the Berlin TAF.
3. TEMPO groups may only be 4 hours long.
4. At high impact airports, TAFs are routinely updated (amended) for critical push times; see
the following list.
Table 1. Icing Intensity Decode
0 Trace Icing or None (see note)
1 Light Mixed Icing
2 Light Rime Icing In Cloud
3 Light Clear Icing In Precipitation
4 Moderate Mixed Icing
5 Moderate Rime Icing In Cloud
6 Moderate Clear Icing In Precipitation
7 Severe Mixed Icing
8 Severe Rime Icing In Cloud
9 Severe Clear Icing In Precipitation
Note: Air Force code “0” means a trace of icing
Table 2. Turbulence Intensity Decode
CODE DECODE
0 None
1 Light turbulence
2 Moderate turbulence in clear air, frequent
3 Moderate turbulence in clear air, occasional
4 Moderate turbulence in cloud, occasional
5 Moderate turbulence in cloud, frequent
6 Severe turbulence in clear air, occasional
7 Severe turbulence in clear air, frequent
8 Severe turbulence in cloud, occasional
9 Severe turbulence in cloud, frequent
X Extreme turbulence
Note: Occasional is dened as occurring less than 1/3 of the time
8
5. All U.S. TAFs are valid for at least 24 hours. The following 32 TAFs are valid for 30 hours.
6. PROB groups are not allowed in the rst 9 hours of the TAF.
7. The U.S. TAFs allow the use of thunderstorm in the vicinity (TS VCNTY). No other countries
use this remark. And with no PROB30 allowed in the rst 9 hours of the TAF, forecasters
usually insert this remark for low probability convective events.
8. Given Points 6 and 7, it is imperative for you to look at other NWS convective services and
products such as:
NWS Storm Prediction Center: http://www.spc.noaa.gov/
LocalWFOinformation:http://www.weather.gov/
Aviation Forecast Discussions: http://aviationweather.gov/products/afd/
Q
ATL Hartseld-Jackson Atlanta Intl
BOS Boston Logan Intl
BWI Baltimore/Washington Intl
CLE Cleveland Hopkins Intl
CLT Charlotte Douglas Intl
CVG Cincinnati/Northern Kentucky Intl
DCA Reagan Washington National
DEN Denver Intl
DFW Dallas/Fort Worth Intl
DTW Detroit Metropolitan Wayne County
EWR Newark Liberty Intl
FLL Fort Lauderdale/Hollywood Intl
HNL Honolulu Intl
IAD Washington Dulles Intl
IAH Bush Houston Intercontinental
JFK New York John F. Kennedy Intl
LAS Las Vegas McCarran Intl
LAX Los Angeles Intl
LGA New York LaGuardia
MCO Orlando Intl
MDW Chicago Midway
MEM Memphis Intl
MIA Miami Intl
MSP Minneapolis/St. Paul Intl
ORD Chicago O’Hare Intl
PDX Portland Intl
PHL Philadelphia Intl
PHX Phoenix Sky Harbor Intl
PIT Pittsburgh Intl
SAN San Diego Intl
SEA Seattle/Tacoma Intl
SFO San Francisco Intl
SLC Salt Lake City Intl
STL Lambert Saint Louis Intl
TPA Tampa Intl
KATL William B. Hartseld Atlanta Intl
KBDL Bradley Intl
KBOS Gen. Edward Lawrence Logan Intl
KBWI Baltimore-Washington Intl
KCLE Cleveland Hopkins Intl
KCVG Covington/Cincinnati
KDEN Denver Intl
KDFW Dallas/Fort Worth Intl
KDTW Detroit Metro Wayne County
KEWR Newark Liberty Intl
KIAD Washington Dulles Intl
KIAH Houston-George Bush
KIND Indianapolis Intl
KJFK John F. Kennedy Intl
KLAX Los Angeles Intl
KMKE General Mitchell Intl
KMSP Minneapolis-St Paul Intl
KOAK Metropolitan Oakland Intl
KONT Ontario Intl
KORD Chicago-O’Hare International
KPHL Philadelphia Intl
KPIT Pittsburgh Intl
KSAN San Diego Intl–Lindbergh Field
KSDF Louisville, Intl Standford Field
KSEA Seattle-Tacoma Intl
KSFO San Francisco Intl
KSLC Salt Lake City Intl
KSTL Lambert-St Lewis Intl
KSWF Stewart Intl
PANC Ted Stevens Anchorage Intl
KAUS Austin-Bergstrom Intl Airport
KSAT San Antonio Intl Airport
9
KMSP Minneapolis-St Paul Intl
KOAK Metropolitan Oakland Intl
KONT Ontario Intl
KORD Chicago-O’Hare International
KPHL Philadelphia Intl
KPIT Pittsburgh Intl
KSAN San Diego Intl–Lindbergh Field
KSDF Louisville, Intl Standford Field
KSEA Seattle-Tacoma Intl
KSFO San Francisco Intl
KSLC Salt Lake City Intl
KSTL Lambert-St Lewis Intl
KSWF Stewart Intl
PANC Ted Stevens Anchorage Intl
KAUS Austin-Bergstrom Intl Airport
KSAT San Antonio Intl Airport
Collaborative Decision Making Meets Volcanic Ash
By Mike Graf, NWS Aviation Services Branch
As technology advances, the use of Collaborative Decision Making (CDM) improves. In a
nutshell, CDM happens when users of services have a chance to add their expertise to the decision
making process up front. For the process to work effectively, it helps to have tools to view the
information seamlessly and on the y.
One of the new CDM tools is available from the Anchorage VolcanicAshAdvisoryCenter
(VAAC). The site allows you to easily view Volcanic Ash Advisories (VAAs) anywhere in the world.
The information is a graphical representation of the VAA and is available for the current time
as well as a 6.12 and 18 hour forecast.
There are nine VAACs that cover the globe. By using this site, the VAACs can easily view their
counterpart’s products. This ability can improve coordination and collaboration between these
ofces as they prepare and update products.
Another example involves Airlines. The Anchorage VAAC works with Airlines in its region to
understand the impact of a VAA on airline operations. This in turn helps the VAAC understand
where to focus its attention with respect to levels and areal coverage during a Volcanic Eruption
and the resultant VAA. Below are some examples from the Anchorage VAAC’s new Webpage.
Q
Figure 1. Anchorage area of concern
10
Figure 2. Global view
Figure 3. Volcanic ash product from the Buenos Aires VAAC
11
NWS Seeks Comments on Future Service
Delivery Architecture Through July 31, 2011
NWS is currently looking at ways to improve its service delivery architecture to ensure it can
meet 21
st
century data requirements. To meet this goal, NWS is currently trying to determine user
requirements to develop a clear road map. The road map, in turn, will help NWS create a future-
facing service delivery architecture to better serve your needs.
NWS is requesting comments to better understand current and future service needs. The primary
goal is to fulll the NWS mission to protect life, property and the enhance the national economy.
NWS seeks to improve how it meets these goals by disseminating the necessary data using new and
emerging technology. Users, such as you, of NWS dissemination services are the most important
group affected by this process. User involvement is vital to the success of this effort.
NWS infrastructure includes all dissemination media currently supported, such as the NWS
Telecommunications Gateway, NOAA Weather Radio All Hazards, NOAA Weather Wire, Family
of Services, NOAAPORT, Emergency Managers Weather Information Network, NWSChat, iNWS,
as well as all web-based email and telephone services. As the NWS begins to consider how best
to improve and expand these current services through the new NWS Dissemination Architecture,
research will be conducted in the following areas:
Data Sets: Types required by users
Dissemination Methods: For example, the use of part of selected datasets through stable,
operational Web services (e.g., Simple Object Access Protocol, Representational State Transfer
services, Geographic Information System) or through complete datasets, i.e., traditional
meteorological formats
Best Practices of Existing Dissemination Systems: For example, NOAA’s National
Operational Model Archive and Distribution System, which is Web-based and provides both
real-time and retrospective format with independent access to climate and weather model data:
http://nomads.ncdc.noaa.gov/
OperationalLevel:For example, requirements to deliver time-critical information, e.g., within
1 minute of issuance, and to improve NWS’ ability to prioritize urgent information over
non-urgent information
Service level: Expansion of fee-for-service dissemination similar to the Family of Services
program, http://www.nws.noaa.gov/datamgmt/fos/fospage.html, adding stringent
delivery performance requirements for those customers
User input on these points will help NWS improve its services. If you have any information you
believe would help in this analysis, please provide your input by July 31, 2011 to the following address:
Robert Bunge
Chief, Telecommunication Software Branch
Telecommunication Operations Center
301-713-0882 x 114
[email protected]
You may also provide online input at:
NWSrearch.ideascale.com
Thank you for helping NWS improve its dissemination systems and apply techniques appropriate
for the 21st Century. Q