Low CloudsLow Cloudsandand

IFR ForecastingIFR Forecasting

Southwest Aviation Weather Southwest Aviation Weather Safety Workshop, Phoenix, AZSafety Workshop, Phoenix, AZ

Ken WidelskiKen WidelskiMeteorologistMeteorologistNWS: Lubbock, TXNWS: Lubbock, TX

ObjectivesObjectives

Low Cloud FormationLow Cloud FormationTypes of Fog: Types of Fog: AdvectionAdvection vs. vs. RadiationRadiationFlight Categories (Review)Flight Categories (Review)Applicable Pre-Flight Planning ToolsApplicable Pre-Flight Planning ToolsPre-Flight TipsPre-Flight TipsRecapRecapQuestions??Questions??

Low Cloud FormationLow Cloud Formation

Low Clouds Low Clouds (Stratiform and (Stratiform and Cumuliform at or Cumuliform at or below 6500 ft).below 6500 ft).

Can cause significant Can cause significant hazards to both hazards to both commercial and commercial and general aviation.general aviation.

Form from 4 main Form from 4 main processesprocesses

The 4 Main ProcessesThe 4 Main Processes

Low Level Moisture transport Low Level Moisture transport Warm air advection (Veering)Warm air advection (Veering) Low Level Jet (Band of stronger winds aloft)Low Level Jet (Band of stronger winds aloft)

Frontal PassagesFrontal Passages Cold Front (Shallow cold air advection)Cold Front (Shallow cold air advection) Warm Front (Warm air atop cooler air)Warm Front (Warm air atop cooler air)

Upslope Flow (No Penetration)Upslope Flow (No Penetration) Topographic influencesTopographic influences

PrecipitationPrecipitation Saturated low levelsSaturated low levels

Formation PerspectiveFormation Perspective

. . Clouds form when air Clouds form when air is cooled to its dew is cooled to its dew point. If the air is point. If the air is cooled to its dewpoint cooled to its dewpoint it reaches saturation. it reaches saturation.

Air can reach Air can reach saturation in a saturation in a number of ways. The number of ways. The most common way is most common way is through lifting. through lifting.

6 Low Cloud Types6 Low Cloud Types

Low Level Moisture TransportLow Level Moisture Transport -Warm Air Advection (Veer)-Warm Air Advection (Veer) -Low Level Jet-Low Level Jet

Frontal PassagesFrontal Passages

Upslope FlowUpslope Flow

PrecipitationPrecipitation

FogFogStratus cloud in contact with the groundStratus cloud in contact with the groundSaturated low levels of the atmosphereSaturated low levels of the atmosphere

Three Main Types of Fog:Three Main Types of Fog:

1)1) Advection FogAdvection Fog -Moisture transport over a relatively large area-Moisture transport over a relatively large area

2) Radiation Fog2) Radiation Fog -Clear skies, moist ground and light winds-Clear skies, moist ground and light winds -Localized dense fog-Localized dense fog

3) 3) Upslope FogUpslope Fog -Moist flow against topographic influence-Moist flow against topographic influence

Advection FogAdvection Fog

Flight CategoriesFlight CategoriesVFRVFR - - Visual Flight Rules; Visibility > 5 SMVisual Flight Rules; Visibility > 5 SM

Ceiling > 3000 feet Ceiling > 3000 feet

MVFRMVFR - Marginal Visual Flight Rules; Visibility 3 - Marginal Visual Flight Rules; Visibility 3 to 5 SM; Ceiling 1000 to 3000 feet to 5 SM; Ceiling 1000 to 3000 feet

IFRIFR - Instrument Flight Rules; Visibility 1 to <3 - Instrument Flight Rules; Visibility 1 to <3 statute miles; Ceiling 500 to 900 feet statute miles; Ceiling 500 to 900 feet

LIFRLIFR - Low Instrument Flight Rules; Visibility <1 - Low Instrument Flight Rules; Visibility <1 statute mile; Ceiling < 500 feetstatute mile; Ceiling < 500 feet

VLIFRVLIFR- Very Low Instrument Flight Rules; - Very Low Instrument Flight Rules; Visibility <1/2 mile; Ceiling <200 feetVisibility <1/2 mile; Ceiling <200 feet

Pre-Flight Planning ToolsPre-Flight Planning Tools

Advancements in technology over the past Advancements in technology over the past decade have allowed pilots to use reliable decade have allowed pilots to use reliable tools for pre-flight planning purposes.tools for pre-flight planning purposes.

Planning tools range from: Nationwide Planning tools range from: Nationwide Access to Access to TAFSTAFS, , TWEBSTWEBS, Area Forecast , Area Forecast Discussions, Model Output Statistics, Discussions, Model Output Statistics, Visible, Water Vapor and multi-channel Visible, Water Vapor and multi-channel satellite imagerysatellite imagery and Soundings. and Soundings.

TAF ForecastTAF Forecast TERMINAL AERODROME FORECASTTERMINAL AERODROME FORECAST

--The area within 5SM of the center ofThe area within 5SM of the center of

the runway complexthe runway complex

-FOUR ROUTINE ISSUANCES PER DAY -FOUR ROUTINE ISSUANCES PER DAY 12Z, 18Z, 00Z AND 06Z12Z, 18Z, 00Z AND 06Z

Nationwide TAF access is conveniently Nationwide TAF access is conveniently linked to one NWS website (Aviation linked to one NWS website (Aviation Weather Center)Weather Center)

Low Cloud TAF ExamplesLow Cloud TAF Examples

KLBBKLBB 101730Z 101818 25008KT P6SM SCT020 SCT200101730Z 101818 25008KT P6SM SCT020 SCT200 FM2200 03015G25KT 5SM BR BKN010FM2200 03015G25KT 5SM BR BKN010 FM0600 08010KT 1SM BR BKN005 FM0600 08010KT 1SM BR BKN005 FM1000 VRB04KT 1/2SM FG OVC003FM1000 VRB04KT 1/2SM FG OVC003 FM1400 20015KT P6SM SCT020 SCT120FM1400 20015KT P6SM SCT020 SCT120

KCDSKCDS 061730Z 061818 13015KT 3SM BR BKN010061730Z 061818 13015KT 3SM BR BKN010 FM2000 19022G32KT P6SM SCT030 SCT250FM2000 19022G32KT P6SM SCT030 SCT250 FM0000 16013KT P6SM SCT250FM0000 16013KT P6SM SCT250

NWS: Aviation Weather CenterNWS: Aviation Weather Centerhttp://adds.aviationweather.gov/tafs/http://adds.aviationweather.gov/tafs/

Raw FormatRaw Format

Translated FormatTranslated Format

TWEBTWEB

TTRANSCRIBED RANSCRIBED WEWEATHER ATHER BBROADCASTROADCAST

--TWEB ROUTETWEB ROUTE: : 50 NM WIDE CORRIDOR50 NM WIDE CORRIDOR

ALONG A LINE CONNECTING THE ALONG A LINE CONNECTING THE

ANCHOR POINTS OF THE ROUTEANCHOR POINTS OF THE ROUTE..

Example: Example: KAMA-KLBB-KMAFKAMA-KLBB-KMAF

--FOURFOUR ISSUANCES PER DAY ISSUANCES PER DAY

U.S. TWEB Routes

                                                                                                                                                                                                                 

     

Area Forecast DiscussionArea Forecast Discussionwww.weather.govwww.weather.gov

Aviation DiscussionAviation Discussion

Purpose: Better understand the forecast Purpose: Better understand the forecast reasoning in the TAF. reasoning in the TAF.

Experimental AFD PageExperimental AFD Pagehttp://aviationweather.gov/testbed/afd/http://aviationweather.gov/testbed/afd/

MOS: Model Output StatisticMOS: Model Output Statistichttp://www.nws.noaa.gov/mdl/synop/products.shtmlhttp://www.nws.noaa.gov/mdl/synop/products.shtml

MOS ExampleMOS Example

CIG 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 7 7 CIG 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 7 7 VIS 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7VIS 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7

OBV N N N N N N N N N N N N N N N N N NOBV N N N N N N N N N N N N N N N N N N

Satellite ImagerySatellite Imagery

RAOBRAOBhttp://www.spc.noaa.gov/exper/soundingshttp://www.spc.noaa.gov/exper/soundings

SoundingSounding: Vertical snapshot of the : Vertical snapshot of the atmosphere. (Twice daily)atmosphere. (Twice daily)

Pre-Flight TipsPre-Flight Tips

Know before you goKnow before you goDevelop a good knowledge ofDevelop a good knowledge of

forecast patterns ahead of time.forecast patterns ahead of time.Access the wide array of pre-flight Access the wide array of pre-flight

tools available.tools available.If Low Clouds and Fog are forecasted, be sure If Low Clouds and Fog are forecasted, be sure to make sound “go-no go” decisions. to make sound “go-no go” decisions.

-It can save your life-It can save your lifeFor further assistance…contact your local For further assistance…contact your local NWS Office 24/7/365NWS Office 24/7/365

ReferencesReferences

NWS Aviation Weather CenterNWS Aviation Weather CenterLocal NWS Weather OfficesLocal NWS Weather OfficesNWS Storm Prediction CenterNWS Storm Prediction CenterNWS Meteorological Development LaboratoryNWS Meteorological Development LaboratoryNASANASANWS Aviation Directive 813NWS Aviation Directive 813Geog.ucsb.eduGeog.ucsb.eduNWS SRH Jet stream ProjectNWS SRH Jet stream ProjectWikipedia.orgWikipedia.orgWeather Doctor: Island.netWeather Doctor: Island.net

Thank you for attendingThank you for attending

Any QuestionsAny Questions