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Winter Weather
Aviation Edition
Topics Covered
• Assessing Fog and Stratus• Forecast Funnel• Fog• Stratus• Writing a good TAF
Name that tune!
• Colored background indicates tune will be played
• Song title, artist• One point per element identified• Top 3 points leaders get a prize• Any ties will be broken by
“sudden death identification”
Assessing Fog and Low Stratus
• Forecast funnel• Upper air analysis• Current conditions
– trend
• Model analysis• Forecast
Assessing Fog and Stratus
Radiation Fog
• Little mixing within the boundary layer
• Large-scale subsidence • Low-level moisture source • Mechanism for rapid cooling
500mb & 700mb
• Dry air present?– Dry air above inversion favors fog
• Must have moist air below inversion
500mb & 700mb
• Windy?– winds 20-30kts mixes dry air at the
top of inversion– strong 700mb winds and light sfc
winds suggest decoupling • suggests inversion present• VWP good place to look
500mb & 700mb
• Exiting shortwave?– Area of subsidence– Mid level subsidence enhances
inversion development
Current Conditions
• Hand analysis • SPC mesoanalysis• Satellite analysis• Moisture availability
– advection– recent rain/snow
• Can you guess what I’ll say next?– ACARS!!!!!! You can get this in
AWIPS!
Point must be on IND or another ACARS airport!
Model Analysis
• Look at the forecast for the elements discussed previously
• RUC was designed with AVN forecasting in mind!– Uses ACARS data!– VWP data– GOES high density winds– Much more
http://rucsoundings.noaa.gov
RUC Cig
Model Analysis
• Tools for finding moisture– Time/height sections– Model Soundings
Model Analysis
• Model RH• 1000-900mb, 1000-950mb
– whatever is below the inversion level
– gradients– BUFKIT
Stratus
• Very common in winter• Mostly post frontal?• Surface cyclone
Stratus Formation
• Subsidence inversion behind front?– Hourly forecast soundings
• Low level moisture below inversion?– RH and specific humidity
Stratus Formation
• Moisture advection below inversion
• Cold advection at low levels?• Low level instability?
– Max cyclonic vorticity
• Boundary layer convergence– Preferably below inversion
Stratus Formation
• Nearly adiabatic process• Procedure – CLOUDS
– Cond pres def– isen adiabatic omega– sfc wind– RH
295K-305K Cond Pres Def (image), RH
290K-300K Cond Pres Def (image), RH
295K-305K Cond Pres Def (image), RH
290K-300K Cond Pres Def (image), RH
Stratus Maintenance
• Warm advection above inversion• Cold advection below inversion• Subsidence above inversion
– Weak sinking may cause cigs to lower
– Too strong?
Dissipation
• Important to ARTCC!• Especially in the AM
Fog Dissipation
• Moisture• Stability• Winds• Temperature
Fog Dissipation
• Other Factors• mid or high clouds
Stratus Dissipation
• Cold advection aloft• Warm advection at surface• Dry advection into low levels
Stratus Dissipation
• Solar heating• Subsidence forcing inversion to
ground• Mechanical mixing of moisture
Stratus Dissipation
• Forecast soundings– how fast is inversion lowering?– use ACARS to compare!
• If realistic– could begin thinning stratus from
top– even inefficient mixing could poke
holes
Stratus Dissipation
• East component to wind?– May maintain
• West component– Dry air advection, dissipation
What does this suggest?
10/17/06 15:56:02 METAR KIND 172054Z 25009KT 10SM OVC018 15/11 A2969 RMK AO2 SLP052 T01500111 53018 TEMP= 59 DWPT= 52 RELH= 77 WIND= 10 -------------------------------------------10/17/06 16:56:02 METAR KIND 172154Z 27010KT 10SM OVC018 14/11 A2972 RMK AO2 SLP062 T01440106 (CF) TEMP= 58 DWPT= 51 RELH= 78 WIND= 11 -------------------------------------------10/17/06 17:55:50 METAR KIND 172254Z 26006KT 10SM OVC018 14/11 A2974 RMK AO2 SLP068 T01390106 (CF) TEMP= 57 DWPT= 51 RELH= 80 WIND= 7 -------------------------------------------10/17/06 18:55:51 METAR KIND 172354Z 23005KT 10SM OVC020 14/11 A2976 RMK AO2 SLP075 T01390111 10156 20133 51024 (CF) TEMP= 57 DWPT= 52 RELH= 83 WIND= 6 -------------------------------------------10/17/06 19:55:51 METAR KIND 180054Z 20005KT 10SM BKN020 OVC026 14/11 A2978 RMK AO2 SLP081 T01390111 (CF) TEMP= 57 DWPT= 52 RELH= 83 WIND= 6 -------------------------------------------10/17/06 20:55:50 METAR KIND 180154Z 21005KT 10SM OVC028 13/11 A2979 RMK AO2 SLP085 T01330111 (CF) TEMP= 56 DWPT= 52 RELH= 86 WIND= 6 -------------------------------------------10/17/06 21:55:51 METAR KIND 180254Z 21004KT 10SM OVC024 13/12 A2981 RMK AO2 SLP092 T01330117 53017 (CF) TEMP= 56 DWPT= 53 RELH= 90 WIND= 5 -------------------------------------------10/17/06 22:55:50 METAR KIND 180354Z 21006KT 10SM OVC024 13/12 A2982 RMK AO2 SLP097 T01330117 (CMK) TEMP= 56 DWPT= 53 RELH= 90 WIND= 7 -------------------------------------------10/17/06 23:55:51 METAR KIND 180454Z 23004KT 10SM OVC022 13/12 A2982 RMK AO2 SLP097 T01330117 401670106 (CMK) TEMP= 56 DWPT= 53 RELH= 90 WIND= 5
TAF Writing
• Best practices from around the NWS
TAF Writing
• 5 lines or less• Link similar vis and cigs into
similar categories• Mention CI when there is nothing
else to mention• IF using TEMPO try not to jump
more than one category
TAF Writing
• It is not necessary to mention mid or high clouds if you have BKN low clouds
• No cat change? No extra lines!– Wind with FROPA the exception
• TEMPO?– Don’t use it if you aren’t changing
flight category
TAF WritingKXXX XX2325Z XX0024 27013KT P6SM SCT024 BKN045 OVC080
TEMPO 0002 -SHRA FM0500 29012KT P6SM SCT028 BKN080 FM0800 28008KT P6SM SCT060 BKN150 FM1500 26013KT P6SM BKN045 BKN100 FM1800 25017G25KT P6SM BKN045 BKN100
FM2100 25015G25KT P6SM BKN060=
What can be improved on this TAF?
3 cloud layers??
Necessary?
Concentrate on Ceilings
Write a concise TAF
Still VFR
Change groups should reflect cat change
SCT showers?If it’s organized, it should be prevailing
TAF WritingKIND XX2325Z XX0024 27013KT P6SM BKN045
FM0800 28008KT P6SM SCT060 FM1500 26013KT P6SM BKN045 FM1800 25017G25KT P6SM BKN045=
TAF Writing
KXXX XX1737Z XX1818 17010KT P6SM OVC120 FM2200 30008KT P6SM OVC080 TEMPO 2224 -SHRA OVC050 FM0000 31010KT P6SM OVC040 TEMPO 0002 5SM -SHRA OVC020 FM0600 30008KT P6SM SCT100 FM0900 30006KT P6SM SKC TEMPO 0913 2SM BR FM1600 20006KT P6SM SKC=
Where shall we start?
Why bother with a new FM group?
?????
KXXX XX1737Z XX1818 17010KT P6SM OVC120 FM2200 30008KT P6SM OVC080 TEMPO 2224 -SHRA OVC050 FM0000 31010KT P6SM OVC040 TEMPO 0002 5SM -SHRA OVC020 FM0600 30008KT P6SM SCT100 FM0900 30006KT P6SM SKC TEMPO 0913 2SM BR FM1600 20006KT P6SM SKC=
TAF Writing
KXXX XX1737Z XX1818 17010KT P6SM OVC120 FM2200 30008KT P6SM OVC080 FM0000 31010KT 5SM -SHRA OVC020 FM0200 31010KT P6SM OVC040FM0600 30008KT P6SM SCT100 FM1600 20006KT P6SM SKC=
TAF Amendments
• CR is watching!
TAF Amendments
• Amend if:– Conditions meeting criteria are
imminent or occurred– Conditions will persist
• 30 minutes?
– New guidance indicates a need for an update• Especially in the 0-6 time frame
What can you expect?
• Increase in TAF reviews• Looking for concise TAF• No more 3 cloud layers!• No more TEMPOs that don’t
change categories
The End!
