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

RUC Cig

Model Analysis Tools for finding moisture –Time/height sections –Model Soundings

Model Analysis Model RH mb, mb –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 Z 25009KT 10SM OVC018 15/11 A2969 RMK AO2 SLP052 T TEMP= 59 DWPT= 52 RELH= 77 WIND= /17/06 16:56:02 METAR KIND Z 27010KT 10SM OVC018 14/11 A2972 RMK AO2 SLP062 T (CF) TEMP= 58 DWPT= 51 RELH= 78 WIND= /17/06 17:55:50 METAR KIND Z 26006KT 10SM OVC018 14/11 A2974 RMK AO2 SLP068 T (CF) TEMP= 57 DWPT= 51 RELH= 80 WIND= /17/06 18:55:51 METAR KIND Z 23005KT 10SM OVC020 14/11 A2976 RMK AO2 SLP075 T (CF) TEMP= 57 DWPT= 52 RELH= 83 WIND= /17/06 19:55:51 METAR KIND Z 20005KT 10SM BKN020 OVC026 14/11 A2978 RMK AO2 SLP081 T (CF) TEMP= 57 DWPT= 52 RELH= 83 WIND= /17/06 20:55:50 METAR KIND Z 21005KT 10SM OVC028 13/11 A2979 RMK AO2 SLP085 T (CF) TEMP= 56 DWPT= 52 RELH= 86 WIND= /17/06 21:55:51 METAR KIND Z 21004KT 10SM OVC024 13/12 A2981 RMK AO2 SLP092 T (CF) TEMP= 56 DWPT= 53 RELH= 90 WIND= /17/06 22:55:50 METAR KIND Z 21006KT 10SM OVC024 13/12 A2982 RMK AO2 SLP097 T (CMK) TEMP= 56 DWPT= 53 RELH= 90 WIND= /17/06 23:55:51 METAR KIND Z 23004KT 10SM OVC022 13/12 A2982 RMK AO2 SLP097 T (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 Writing KXXX XX2325Z XX KT P6SM SCT024 BKN045 OVC080 TEMPO SHRA FM KT P6SM SCT028 BKN080 FM KT P6SM SCT060 BKN150 FM KT P6SM BKN045 BKN100 FM G25KT P6SM BKN045 BKN100 FM G25KT 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 Writing KIND XX2325Z XX KT P6SM BKN045 FM KT P6SM SCT060 FM KT P6SM BKN045 FM G25KT P6SM BKN045=

TAF Writing KXXX XX1737Z XX KT P6SM OVC120 FM KT P6SM OVC080 TEMPO SHRA OVC050 FM KT P6SM OVC040 TEMPO SM -SHRA OVC020 FM KT P6SM SCT100 FM KT P6SM SKC TEMPO SM BR FM KT P6SM SKC= Where shall we start? Why bother with a new FM group? ?????

KXXX XX1737Z XX KT P6SM OVC120 FM KT P6SM OVC080 TEMPO SHRA OVC050 FM KT P6SM OVC040 TEMPO SM -SHRA OVC020 FM KT P6SM SCT100 FM KT P6SM SKC TEMPO SM BR FM KT P6SM SKC= TAF Writing KXXX XX1737Z XX KT P6SM OVC120 FM KT P6SM OVC080 FM KT 5SM -SHRA OVC020 FM KT P6SM OVC040 FM KT P6SM SCT100 FM KT 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!