Low Clouds and IFR Forecasting Southwest Aviation Weather Safety Workshop, Phoenix, AZ Ken Widelski Meteorologist NWS: Lubbock, TX

Objectives Low Cloud Formation Types of Fog: Advection vs. Radiation Flight Categories (Review) Applicable Pre-Flight Planning Tools Pre-Flight Tips RecapQuestions??

Low Cloud Formation Low Clouds (Stratiform and Cumuliform at or below 6500 ft). Can cause significant hazards to both commercial and general aviation. Form from 4 main processes

The 4 Main Processes 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 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) Topographic influences Topographic influencesPrecipitation Saturated low levels Saturated low levels

Formation Perspective. Clouds form when air is cooled to its dew point. If the air is cooled to its dewpoint it reaches saturation. Air can reach saturation in a number of ways. The most common way is through lifting.

6 Low Cloud Types

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

Frontal Passages

Upslope Flow

Precipitation

Fog Stratus cloud in contact with the ground Saturated low levels of the atmosphere Three Main Types of Fog: 1) Advection Fog -Moisture transport over a relatively large area -Moisture transport over a relatively large area 2) Radiation Fog -Clear skies, moist ground and light winds -Clear skies, moist ground and light winds -Localized dense fog -Localized dense fog 3) Upslope Fog -Moist flow against topographic influence -Moist flow against topographic influence

Advection Fog

Flight Categories VFR - Visual Flight Rules; Visibility > 5 SM Ceiling > 3000 feet Ceiling > 3000 feet MVFR - Marginal Visual Flight Rules; Visibility 3 to 5 SM; Ceiling 1000 to 3000 feet IFR - Instrument Flight Rules; Visibility 1 to <3 statute miles; Ceiling 500 to 900 feet LIFR - Low Instrument Flight Rules; Visibility <1 statute mile; Ceiling < 500 feet VLIFR- Very Low Instrument Flight Rules; Visibility <1/2 mile; Ceiling <200 feet

Pre-Flight Planning Tools Advancements in technology over the past decade have allowed pilots to use reliable tools for pre-flight planning purposes. Planning tools range from: Nationwide Access to TAFS, TWEBS, Area Forecast Discussions, Model Output Statistics, Visible, Water Vapor and multi-channel satellite imagery and Soundings.

TAF Forecast TERMINAL AERODROME FORECAST TERMINAL AERODROME FORECAST -The area within 5SM of the center of -The area within 5SM of the center of the runway complex the runway complex -FOUR ROUTINE ISSUANCES PER DAY 12Z, 18Z, 00Z AND 06Z -FOUR ROUTINE ISSUANCES PER DAY 12Z, 18Z, 00Z AND 06Z Nationwide TAF access is conveniently linked to one NWS website (Aviation Weather Center)

Low Cloud TAF Examples KLBB Z KT P6SM SCT020 SCT200 FM G25KT 5SM BR BKN010 FM G25KT 5SM BR BKN010 FM KT 1SM BR BKN005 FM KT 1SM BR BKN005 FM1000 VRB04KT 1/2SM FG OVC003 FM1000 VRB04KT 1/2SM FG OVC003 FM KT P6SM SCT020 SCT120 FM KT P6SM SCT020 SCT120 KCDS Z KT 3SM BR BKN010 FM G32KT P6SM SCT030 SCT250 FM G32KT P6SM SCT030 SCT250 FM KT P6SM SCT250 FM KT P6SM SCT250

NWS: Aviation Weather Center

Raw Format

Translated Format

TWEB TRANSCRIBED WEATHER BROADCAST - TWEB ROUTE: 50 NM WIDE CORRIDOR - TWEB ROUTE: 50 NM WIDE CORRIDOR ALONG A LINE CONNECTING THE ALONG A LINE CONNECTING THE ANCHOR POINTS OF THE ROUTE. ANCHOR POINTS OF THE ROUTE. Example: KAMA-KLBB-KMAF Example: KAMA-KLBB-KMAF - FOUR ISSUANCES PER DAY - FOUR ISSUANCES PER DAY

U.S. TWEB Routes

Area Forecast Discussion

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

Experimental AFD Page

MOS: Model Output Statistic

MOS Example

CIG VIS OBV N N N N N N N N N N N N N N N N N N CIG VIS OBV N N N N N N N N N N N N N N N N N N

Satellite Imagery

RAOB Sounding: Vertical snapshot of the atmosphere. (Twice daily)

Pre-Flight Tips Know before you go Develop a good knowledge of forecast patterns ahead of time. forecast patterns ahead of time. Access the wide array of pre-flight tools available. tools available. If Low Clouds and Fog are forecasted, be sure to make sound “go-no go” decisions. -It can save your life -It can save your life For further assistance…contact your local NWS Office 24/7/365

References NWS Aviation Weather Center Local NWS Weather Offices NWS Storm Prediction Center NWS Meteorological Development Laboratory NASA NWS Aviation Directive 813 Geog.ucsb.edu NWS SRH Jet stream Project Wikipedia.org Weather Doctor: Island.net

Thank you for attending Any Questions