CHAPTER 5 MOISTURE, CLOUD FORMATION AND PRECIPITATION
HOMEWORK • READ CHAPTER 5 & 7 • COMPLETE AOPA’S WEATHER WISE CEILING AND VISIBILITY COURSE (DUE ON THURSDAY) • http://www.aopa.org/asf/online_courses/
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KMWH 171952Z 23023G30KT8SM FEW025 OVC090 06/M06 A2972 RMK AO2 PK WND 22030/1949 SLP073 T00561056 $KMWH 171852Z 20011KT 10SM CLR 03/M04 A2974 RMK AO2 SLP084 T00281044 $KMWH 171752Z 19013G19KT 10SM CLR 01/M05 A2975 RMK AO2 SLP088 T00111050 10017 21017 56010 $KMWH 171652Z 19012G19KT 10SM CLR 01/M05 A2977 RMK AO2 SLP094 T00061050 $KMWH 171552Z 18009KT 10SM CLR M01/M06 A2977 RMK AO2 SLP092 T10111056KMWH 171452Z 18011G18KT 10SM CLR M01/M07 A2978 RMK AO2 SLP098 T10061067 56022 $KMWH 171352Z 19013G23KT 10SM CLR 00/M07 A2981 RMK AO2 SLP105 T00001067 $KMWH 171252Z AUTO 18010KT 10SM CLR M01/M07 A2983 RMK AO2 SLP112 T10111072 $KMWH 171152Z AUTO 19014G21KT 10SM CLR 00/M07 A2985 RMK AO2 SLP119 T00001067 10000 21061 58020 $KMWH 171052Z AUTO 19012KT 10SM CLR M01/M07 A2988 RMK AO2 SLP129 T10061067 $KMWH 170952Z AUTO 19015G22KT 10SM CLR 00/M07 A2989 RMK AO2 SLP135 T00001067 $KMWH 170852Z AUTO 19008KT 10SM CLR M01/M07 A2991 RMK AO2 SLP142 T10111067 58018 $KMWH 170752Z AUTO 17006KT 10SM CLR M04/M08 A2993 RMK AO2 SLP152 T10441078 400111156 $KMWH 170652Z AUTO 16006KT 10SM CLR M06/M09 A2996 RMK AO2 SLP162 T10561089 $KMWH 170552Z AUTO 17006KT 10SM CLR M05/M09 A2997 RMK AO2 SLP166 T10501089 10006 21050 58009 $KMWH 170452Z 18006KT 10SM CLR M03/M08 A2998 RMK AO2 SLP171 T10331083 $KMWH 170352Z 18010KT 10SM BKN070 M02/M08 A2999 RMK AO2 SLP175 T10171078 $KMWH 170252Z 19009KT 10SM SCT095 M01/M08 A2999 RMK AO2 SLP176 T10111083 56006 $KMWH 170152Z 18009KT 10SM CLR M01/M09 A3000 RMK AO2 SLP178 T10111089 $KMWH 170052Z 19009KT 10SM FEW100 M01/M10 A3001 RMK AO2 SLP179 T10061100 $KMWH 162352Z 20012G18KT 10SM OVC085 01/M10 A3001 RMK AO2 SLP180 T00061100 10011 21089 56010 $KMWH 162252Z 19012KT 10SM BKN100 01/M10 A3001 RMK AO2 SLP181 T00061100 $KMWH 162152Z 20005KT 10SM BKN100 M02/M09 A3002 RMK AO2 SLP184 T10171089 $KMWH 162052Z 00000KT 10SM BKN100 M02/M09 A3004 RMK AO2 SLP191 T10221089 58009 $ KMWH 171739Z 1718/1818 20016G25KT P6SM VCSH BKN070 OVC150 FM181500 35016G24KT 1/2SM SN OVC020
WINTER STORM WARNINGin effect until Thursday, Jan 19, 4:00 PM ...WINTER STORM WARNING REMAINS IN EFFECT FROM 4 AM WEDNESDAY TO 4 PM PST THURSDAY... A WINTER STORM WARNING REMAINS IN EFFECT FROM 4 AM WEDNESDAY TO 4 PM PST THURSDAY. * SNOW ACCUMULATIONS: FOR THE UPPER COLUMBIA BASIN...THE WATERVILLE PLATEAU...THE WENATCHEE AREA...AND THE LEWISTON AREA...SNOW AMOUNTS OF 4 TO 7 INCHES WILL BE COMMON BY THURSDAY. * TIMING: HEAVY SNOW IS EXPECTED WEDNESDAY INTO THURSDAY. * LOCATIONS INCLUDE: MOSES LAKE...EPHRATA...OTHELLO...QUINCY... RITZVILLE...GRAND COULEE... ODESSA...WILBUR...COULEE CITY... WENATCHEE... CHELAN... ENTIAT... CASHMERE...WATERVILLE... MANSFIELD... BADGER MOUNTAIN ROAD PRECAUTIONARY/PREPAREDNESS ACTIONS... A WINTER STORM WARNING MEANS SIGNIFICANT AMOUNTS OF SNOW ARE EXPECTED OR OCCURRING. STRONG WINDS ARE ALSO POSSIBLE. THIS WILL MAKE TRAVEL VERY HAZARDOUS OR IMPOSSIBLE.
Plan for the Weather • You have control over most of the factors involved with flying, but you have no control over the weather. Good weather or bad weather, you must adapt your flying to it.
KMWH 132106Z 00000KT M1/4SM R32R/1000V1600FT FG OVC001 01/01 A2991 RMK AO2KMWH 132052Z 00000KT M1/4SM R32R/1800VP6000FT FG OVC003 00/00 A2992 RMK AO2 SLP144 T00000000 58004KMWH 132011Z 00000KT 1SM R32R/2400VP6000FT BR OVC003 01/01 A2992 RMK AO2KMWH 132003Z 23003KT 1 3/4SM R32R/4000VP6000FT BR OVC005 01/00 A2992 RMK AO2KMWH 131952Z 00000KT 4SM BR OVC005 01/00 A2993 RMK AO2 SLP147 T00060000KMWH 131852Z 00000KT 4SM BR OVC005 00/M01 A2993 RMK AO2 SLP151 T00001006KMWH 131752Z 00000KT 5SM BR OVC007 00/M01 A2993 RMK AO2 SLP149 60002 T00001011 10000 21011 50000KMWH 131652Z 00000KT 5SM BR OVC009 M01/M02 A2993 RMK AO2 SLP152 T10061017KMWH 131552Z 00000KT 6SM BR OVC009 M01/M02 A2994 RMK AO2 SLP154 T10111017KMWH 131452Z 24003KT 7SM OVC009 M01/M02 A2993 RMK AO2 SLP152 60002 T10111017 56030KMWH 131352Z 26005KT 5SM BR OVC009 M01/M02 A2997 RMK AO2 SLP163 T10111017KMWH 131252Z AUTO 27005KT 7SM OVC007 M01/M01 A2997 RMK AO2 UPB02E44FZRAE02 PRESFR SLP166 P0002 T10061011KMWH 131202Z AUTO 29004KT 5SM UP BR BKN009 OVC017 M01/M01 A3001 RMK AO2 UPB02FZRAE02 P0000KMWH 131152Z AUTO 31003KT 5SM -FZRA BR BKN011 OVC017 M01/M01 A3002 RMK AO2 SLP180 P0004 60008 70010 T10061011 11006 21050 58013KMWH 131052Z AUTO 34010KT 6SM -FZRA BR BKN023 OVC036 M01/M02 A3004 RMK AO2 UPE0959FZRAB0959 SLP187 P0004 T10111022KMWH 131044Z AUTO 34009KT 5SM -FZRA BR BKN025 OVC036 M01/M02 A3004 RMK AO2 UPE0959FZRAB0959 P0003KMWH 131005Z AUTO 34009KT 6SM -FZRA BR BKN036 OVC050 M02/M03 A3005 RMK AO2 UPE0959FZRAB0959 P0001KMWH 130952Z AUTO 33008KT 9SM UP FEW036 BKN060 OVC075 M02/M04 A3006 RMK AO2 UPB49 SLP194 P0000 T10221039
WHO IS BRAVE ENOUGH TO TRY? • KMWH 131152Z AUTO 31003KT 5SM -FZRA BR BKN011 OVC017 M01/M01 A3002 RMK AO2 SLP180 P0004 60008 70010 T10061011 11006 21050 58013 • Hopefully no one!!! –FZRA is a no go for most aircraft especially light training aircraft
KMWH 131152Z AUTO 31003KT 5SM -FZRA BR BKN011 OVC017 M01/M01 A3002 RMK AO2 SLP180 P0004 60008 70010 T10061011 11006 21050 58013 • Light freezing rain • P0004= hourly precip amount 4/100 of an inch precip. • 60008= .8 inches in last 6 hours can also be 3 hours • 70010=24 hour precip amount included in 12 UTC =1 inch in last 24 hours • T10061011=Temp -6.1 C / DPT -1.1 C • 11006= 6 hour max temp = -.6 C • 21050= 6 hour minimum temp = -5 C • 58013 = 3 hour pressure tendency = 8 is the character of pressure change (need chart = atmospheric pressure now lower than 3 hours ago. Steady or increasing, then decreasing; or decreasing then decreasing more rapidly) with a change of 1.3 hectopascals • Federal Meteorological Handbook No. 1 section 12 (search FMH-1) • http://www.ofcm.gov/fmh-1/pdf/L-CH12.pdf
CLOUDS & PRECIP. • Clouds and precipitation can obscure surface features and other aircraft. They can envelope high ground and may be associated with severe turbulence and ice formation. • Clouds form when water vapour gas condenses into liquid water droplets or sublimates into ice crystals
WATER VAPOR • Water Vapor is invisible just as oxygen.
WATER VAPOR • Two commonly used terms to express the amount of water vapor in the air are • Relative Humidity and • Specific Humidity.
DEFINITIONS • Relative Humidity = expressed as a % of actual water vapor present to that which could be present • If a given volume of air is cooled to some specific temp., it can hold no more water vapor than is actually present, relative humidity becomes 100% or saturated
DEFINITIONS • Specific Humidity =The ratio, by weight, of the water vapor in a sample of air to the combined weight of the water vapor and the dry air.
Type of Clouds/Precip. • The extent and type of cloud and precipitation produced will depend on the amount of water vapour available, the abundance of nuclei, stability of the air and the amount of cooling that the air undergoes.
DEFINITIONS • Dew Point Temperature = is the temperature to which air must be cooled to become saturated. • The higher the temp the more moisture it can hold • So, for the air to become saturated, either • 1. Cool the Temp, 2. Raise the Humidity
FOG • Temp/Dew Point Temp spread is 2ºC (4 ºF) and narrowing condensation/ fog/low clouds should be expected. • Water vapor must condense for fog to form. If there are no condensation nuclei present then even with 100% relative humidity, fog will not form. • Salt, dust combustion by products, smoke are all classified as condensation nuclei
FOG • Fog is a surface based cloud composed of either water droplets or ice crystals. • Less than 5/8 S.M. vis = FG • 5/8 S.M. or more = BR • With the right conditions fog can form very quickly (few minutes) VFR-IFR. • Be very cautious flying when the temp/ D.P.T. spread is close and getting closer. • Fog or a cloud may form: by cooling air to its dew point, by adding moisture to the air or condensation nuclei.
FOG • Several different types of fog: • Radiation Fog = Fog that forms on a clear calm night or day break when the surface of the earth is cooled by radiation until the temperature of the air near the the surface is below its initial dew point temp. Restricted to land because water surfaces cool little from nighttime radiation. Usually burns off rapidly after sunrise.
FOG • Advection Fog = forms when moist air moves over colder ground or water. Common along coastal areas. At sea it is called sea fog.
FOG • Upslope fog = forms as a result of moist, stable air being cooled adiabatically as it moves up sloping terrain. (as air rises it cools) • Precipitation-induced fog - forms when relatively warm rain or drizzle falls through cool air, and evaporation from the precip saturates the cool air.
FOG • Ice Fog = cold weather when the temp is below freezing and water vapor sublimates directly as ice crystals. Can be blinding flying into the sun. • Fog on a METAR is used to indicate visibility of less than 5/8 of a SM
CHANGE OF STATE • Sublimation - ice to vapor, vapor to ice • Evaporation - water to vapor • Condensation - vapor to water • Freezing -water to solid water • Melting - solid water (ice) to water • Virga - precipitation that never reaches the ground • Virga is a perfect example of condensation then evaporation
CHANGE OF STATE • Evaporation, condensation, freezing, melting, and sublimation are changes of state in water. The exchange of heat energy is required to change a substance from one state to another.
CHANGE OF STATE • The exchange of heat energy when a substance changes from one state to another is called latent (hidden) heat. • Latent heat of vaporization - when water changes to vapor it takes heat from the surrounding environment (hidden in the water vapor. • Like when you sweat it cools your body heat is taken
CHANGE OF STATE • Latent heat of fusion - when water changes to ice, it gives off heat to the surrounding environment • Like when farmers use water to keep crops or fruit from freezing. • Latent heat of condensation - when the water vapor condenses back into liquid water, this energy is released to the atmosphere. Thus condensation is a warming process.
SUPER COOLED WATER • Water droplets can exist below 32º F. We find them aloft between 0º C and -15º C. They may exist at temps lower than -15º C. They have been known to exist up to -40º C • Freezing is complex, and liquid water droplets often condense or persist at temperatures colder than 0º C because the molecular motion of the droplet remains large enough to weaken any formation of an ice crystal within the droplet . Striking an aircraft causes immediate freezing on impact.
DEW AND FROST • If the temp of a surface cools below the dew point, dew will form on that surface • Frost happens when the dew point is below freezing and the surface is colder than freezing
CLOUD FORMATION • Normally, air must become saturated for condensation or sublimation to occur. • The major cooling mechanism that causes condensation is adiabatic expansion. There are 5 processes which result in the ascent of air and adiabatic cooling and they are: • 1. Convection, 2. Mechanical turbulence, 3. Frontal lift, 4. Orographic lift, and 5. Convergence.
CLOUD FORMATION • Two other causes of cooling are, the evaporation of rain falling from higher cloud (rain partially evaporates as it falls through the air. The heat required for evaporation is taken from the air through which the rain is falling thus cooling the air • and with advection the movement of air over a surface colder than the air
#1. CLOUDS FORMED BY CONVECTION • Convection consistes of air rising rapidly in shafts or bubbles and it occurs in unstable air. A layer of air can be made unstable when it is heated from below either by moving over a portion of the earth’s surface warmer than itself or by the earth’s surface being heated by the sun.
CONVECTION DUE TO SOLAR HEATING • As the sun heats a land surface, the lower layers of the atmosphere warm and become unstable.
CONVECTION DUE TO SOLAR HEATING • DALR 3 degrees C/1000 feet • Air rises until it reaches air around it of a similar temp. Clouds form at saturation.
CONVECTION DUE TO ADVECTION • Movement of air over a surface warmer than itself (unstable)
CONVECTION CLOUD BASES • Same water vapor content, with an increase in temperature cloud bases rise (DALR 3 degrees per/1000ft)
ESTIMATING CUMULIFORM CLOUD BASES Pg. 51 • You can estimate height of cumuliform cloud bases using surface temperature-dew point spread. Unsaturated air in a convective current cools at about 3 degrees per 1000 feet; dew point decreases at about 1F or 5/9 degree C per 1000ft. Thus, in a convective current, temperature and dew point converge at about 2.5C per 1000/ft
ESTIMATING CUMULIFORM CLOUD BASES Pg. 51 • You can get a quick estimate of a convective cloud base in thousands of feet by rounding these values and dividing into the spread or by multiplying the spread by their reciprocals. When using Fahrenheit, divide by 4 or multiply by .25; when using Celsius, divide by 2.2 or multiply by .45
QUESTION • If the surface air temperature is 35 degrees C and the dew point is 26 degrees C. (assume standard lapse rates for a cumiliform cloud)what is the cloud base. • 9 degree spread/2.2 =4.0909 • *1000 = 4100 feet. • Read page 51!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!