Low Clouds and Fog Alan Gerard MeteorologistinCharge National

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Low Clouds and Fog Alan Gerard Meteorologist-in-Charge National Weather Service Jackson, MS 5/21/2021 National

Low Clouds and Fog Alan Gerard Meteorologist-in-Charge National Weather Service Jackson, MS 5/21/2021 National Weather Service Jackson, MS 1

Weather Related Accidents Adverse Winds Reduced Visibilities Low Ceilings Turbulence High Density Altitude Icing

Weather Related Accidents Adverse Winds Reduced Visibilities Low Ceilings Turbulence High Density Altitude Icing Thunderstorms Obscurations 0 50 100 150 200 250 300 NTSB Accident Data for 1995 Fatal Accidents 5/21/2021 Non-Fatal Accidents National Weather Service Jackson, MS 2

TYPES OF PILOT VISIBILITY IN FLIGHT (AIR-TO-AIR) SLANT RANGE (AIR-TO-GROUND) SURFACE 5/21/2021 National Weather

TYPES OF PILOT VISIBILITY IN FLIGHT (AIR-TO-AIR) SLANT RANGE (AIR-TO-GROUND) SURFACE 5/21/2021 National Weather Service Jackson, MS 3

LOW CEILINGS CEILING 5/21/2021 National Weather Service Jackson, MS 4

LOW CEILINGS CEILING 5/21/2021 National Weather Service Jackson, MS 4

FLIGHT IN CLOUDS RESTRICTS VISIBILITY TO ZERO IN FLIGHT SL (AIR-TO-AIR) AN TR IR

FLIGHT IN CLOUDS RESTRICTS VISIBILITY TO ZERO IN FLIGHT SL (AIR-TO-AIR) AN TR IR -T AN OGE GR OU ND ) (A 5/21/2021 National Weather Service Jackson, MS 5

LOW CEILING EFFECTIVE PILOT CEILING 500’ REPORTED CEILING 500’ GOOD SLANT RANGE VISIBILITY POOR

LOW CEILING EFFECTIVE PILOT CEILING 500’ REPORTED CEILING 500’ GOOD SLANT RANGE VISIBILITY POOR SLANT RANGE LIMITS INDEFINITE CEILING VERTICAL VISIBILITY 500’ 5/21/2021 National Weather Service Jackson, MS 6

MOUNTAIN OBSCURATIONS TOPS = 12, 000 FEET 7, 000 FEET SEA LEVEL 5/21/2021 National

MOUNTAIN OBSCURATIONS TOPS = 12, 000 FEET 7, 000 FEET SEA LEVEL 5/21/2021 National Weather Service Jackson, MS 7

Quiz Question • A ceiling is the height of the lowest _____. • A.

Quiz Question • A ceiling is the height of the lowest _____. • A. broken or overcast layer above sea level • B. broken or overcast layer above ground level • C. scattered or broken layer above sea level

Quiz Question • _____ flights usually fly below broken to overcast cloud layers. •

Quiz Question • _____ flights usually fly below broken to overcast cloud layers. • A. VFR • B. MVFR • C. IFR

Quiz Question • Ceilings along rising terrain tend to ________. • A. increase •

Quiz Question • Ceilings along rising terrain tend to ________. • A. increase • B. decrease • C. remain the same

Quiz Question • VFR pilots must have good visibility ________. • A. only during

Quiz Question • VFR pilots must have good visibility ________. • A. only during takeoff and landing • B. only while en route • C. during all phases of flight

Quiz Question • IFR pilots generally require good visibility ___________. • A. during takeoff

Quiz Question • IFR pilots generally require good visibility ___________. • A. during takeoff and landing • B. only while en route • C. during all phases of flight 5/21/2021 National Weather Service Jackson, MS 12

Southeast U. S. • Two main types of low clouds and fog to be

Southeast U. S. • Two main types of low clouds and fog to be concerned with: – Radiation Fog and Stratus (any time of year) – Advection Fog and Stratus (mainly winter and spring) • Mountain obscuration also an issue in Appalachian region 5/21/2021 National Weather Service Jackson, MS 13

RADIATION FOG SHALLOW MOIST LAYER WIND LIGHT OR CALM 5/21/2021 National Weather Service Jackson,

RADIATION FOG SHALLOW MOIST LAYER WIND LIGHT OR CALM 5/21/2021 National Weather Service Jackson, MS 14

Radiation Fog and Stratus • Can form at any time of year • Typically

Radiation Fog and Stratus • Can form at any time of year • Typically “patchy” in nature, and can result in widely varying visibilities • Often more common in valleys and near bodies of water (rivers, lakes, etc. ) • Is most prevalent late at night and around sunrise; typically visibilities rapidly improve by mid to late morning – Usually “burns off” more quickly in summer than in winter 5/21/2021 National Weather Service Jackson, MS 15

Radiation Fog 5/21/2021 National Weather Service Jackson, MS 16

Radiation Fog 5/21/2021 National Weather Service Jackson, MS 16

ADVECTION FOG WIND 5 -15 KT COOL SURFACE 5/21/2021 WARM, MOIST AIR WARM SURFACE

ADVECTION FOG WIND 5 -15 KT COOL SURFACE 5/21/2021 WARM, MOIST AIR WARM SURFACE National Weather Service Jackson, MS 17

Advection Fog and Stratus • More common in winter and spring than summer/fall •

Advection Fog and Stratus • More common in winter and spring than summer/fall • Is usually much more widespread than radiation fog/stratus • Most prevalent at night and in morning, but can persist/form through day – In late winter/early spring months, stratus/fog more likely to cause long duration, persistent IFR conditions 5/21/2021 National Weather Service Jackson, MS 18

ADVECTION FOG L H L 5/21/2021 National Weather Service Jackson, MS 19

ADVECTION FOG L H L 5/21/2021 National Weather Service Jackson, MS 19

Rain Induced Fog • Similar to Advection Fog – Results in widespread low ceilings

Rain Induced Fog • Similar to Advection Fog – Results in widespread low ceilings and visibilities – Most common in cool season – While lowest visibilities/ceilings tend to be at night, can cause IFR conditions at any time of day 5/21/2021 National Weather Service Jackson, MS 20

RAIN INDUCED FOG COLDER, UNSATURTED AIR WARM AIR FAVORABLE CONDITIONS - WARM RAIN FALLS

RAIN INDUCED FOG COLDER, UNSATURTED AIR WARM AIR FAVORABLE CONDITIONS - WARM RAIN FALLS THROUGH COLDER, UNSATURATED AIR - LIGHT WINDS 5/21/2021 National Weather Service Jackson, MS 21

RAIN INDUCED FOG IN RA L H N RAI 5/21/2021 National Weather Service Jackson,

RAIN INDUCED FOG IN RA L H N RAI 5/21/2021 National Weather Service Jackson, MS 22

NWS Products • TAF Forecasts – Issued by local Weather Forecast Office – Ceiling/visibility

NWS Products • TAF Forecasts – Issued by local Weather Forecast Office – Ceiling/visibility for specific terminal point – 24 hour forecast • TWEB Forecasts – Issued by selected local Weather Forecast Offices – Ceiling/visibility for route or local vicinity of a terminal area – 12 hour forecast 5/21/2021 National Weather Service Jackson, MS 23

TAF/TWEB Examples FTUS 44 KJAN 181741 TAFJAN KJAN 181730 Z 181818 26006 KT P

TAF/TWEB Examples FTUS 44 KJAN 181741 TAFJAN KJAN 181730 Z 181818 26006 KT P 6 SM SCT 030 FM 2000 VRB 03 KT P 6 SM VCTS SCT 030 CB TEMPO 2024 BKN 030 CB FM 0000 VRB 03 KT P 6 SM SCT 035 TEMPO 0408 4 SM BR FM 0800 00000 KT 5 SM BR SKC TEMPO 0812 2 SM BR FM 1200 VRB 03 KT P 6 SM SCT 035 TEMPO 1214 4 SM BR= TWB 109 TWEB 182008 KCSG LCL VCNTY. ALL HGTS AGL XCP TOPS. TIL 02 Z 6 SM HZ SCT-BKN 040 WDLY SCT BLO 3 SM TSRA CIGS BKN 020 -030. . . AFT 02 Z P 6 SM SCT 060 AREAS 3 -5 SM HZ. 5/21/2021 National Weather Service Jackson, MS 24

NWS Products • Area Forecasts – Issued by National Centers for Environmental Prediction/Aviation Weather

NWS Products • Area Forecasts – Issued by National Centers for Environmental Prediction/Aviation Weather Center – Ceiling/visibility forecasts by states – 12 hour forecast – Additional 6 hour outlook period • Airmet – Issued by Aviation Weather Center – Hazard alert for IFR conditions 5/21/2021 National Weather Service Jackson, MS 25

Area Forecast Example FAUS 5 KDFW 181831 FA 4 W DFWC FA 181845 SYNOPSIS

Area Forecast Example FAUS 5 KDFW 181831 FA 4 W DFWC FA 181845 SYNOPSIS AND VFR CLDS/WX SYNOPSIS VALID UNTIL 191300 CLDS/WX VALID UNTIL 190700. . . OTLK VALID 190700 -191300 OK TX AR TN LA MS AL AND CSTL WTRS. SEE AIRMET SIERRA FOR IFR CONDS AND MTN OBSCN. TS IMPLY SEV OR GTR TURB SEV ICE LLWS AND IFR CONDS. NON MSL HGTS DENOTED BY AGL OR CIG. . SYNOPSIS. . . QUASI STNR BNDRY ARG-VUZ-ATL AND WK HI PRES OVR GLFMEX. AL N HLF. . . AGL SCT-BKN 040. WDLY SCT -TSRA/-SHRA. CB TOPS FL 420. 01 Z AGL SCT 040 BKN 120 LYRD TO FL 250. OTLK. . . VFR. ERN SXNS BECMG IFR BR 10 Z. S HLF. . . CIG BKN 030 LYRD TO FL 250. WDLY SCT -TSRA/-SHRA. CB TOPS FL 450. ISOL TS POSS SEV. 02 Z AGL FEW 040 SCT CI. OTLK. . . VFR BECMG IFR BR CIG 09 Z. . 5/21/2021 National Weather Service Jackson, MS 26

Acknowledgments • Several of the slides in this presentation are courtesy of the FAA

Acknowledgments • Several of the slides in this presentation are courtesy of the FAA and the National Air Traffic Training Program Course 50244 5/21/2021 National Weather Service Jackson, MS 27

Questions? ? 5/21/2021 National Weather Service Jackson, MS 28

Questions? ? 5/21/2021 National Weather Service Jackson, MS 28

CLOUDS clouds What are clouds made of CloudsCLOUDS clouds What are clouds made of Clouds
FOG Content Radiation Fog Advection Fog Stratus BuildFOG Content Radiation Fog Advection Fog Stratus Build
CLOUDS Clouds and Fog Key Ideas Describe theCLOUDS Clouds and Fog Key Ideas Describe the
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MA RS Clouds A B Clouds A CloudsMA RS Clouds A B Clouds A Clouds
TYPES of CLOUDS Stratocumulus Clouds Low lumpy layerTYPES of CLOUDS Stratocumulus Clouds Low lumpy layer
Clouds Low Altitude Clouds Form below 2000 metersClouds Low Altitude Clouds Form below 2000 meters
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FOG UPDATE STARTED PROGRAM IN 1991 ADOPTED FOGFOG UPDATE STARTED PROGRAM IN 1991 ADOPTED FOG
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