Upper Air Analysis 850, 700, 500, 250 hPa charts

Upper Air Charts Objectives Review Upper Charts Identify features on Upper Charts 00Z CMC 850 hPa 30 Jul 2008

Why use Upper Air Charts? Weather usually develops throughout the depth of the Troposphere Most Synoptic weather is actually due to forcing aloft (upper lows/trofs/fronts) These features are often (but not always) reflected in the SFC analysis Upper charts are vital in overall analysis (3-D diagnosis)

Upper Air Charts Data displayed on a “horizontal slice” of the atmosphere For each radiosonde launch: one data point Horizontal slice can be taken at various heights of the atmosphere However instead of heights the norm is to use “constant pressure levels” - Ask students if they understand “Constant Pressure” levels… (Covered in Theory hour 3)

Why Pressure Levels? Historically A/C flew at Pressure Altitudes Still true for flights >18Tft (no Altimeter recalibration) Radiosondes report in terms of pressure (height is calculated from other parameters) Computation is easier using Pressure levels. This way: “the Pilot

H L 850 hPa Pressure Surface SEA LEVEL 1500 m > 1500 m < 1500 m Looking at the 850 hPa Pressure surface It usually sits near 1500 m / 5000 ft. ASL However, due to Lower than average pressure in the atmosphere the 850 hPa surface can dip below this. Similarly in an area of High pressure, the 850 hPa surface will be above 1500 m. So you can see that Heights on Pressure surfaces can be treated the same as Pressure on Height surfaces. SEA LEVEL

L   1380 m 1440 m 1500 m 12Z 29 Jul 2008 850 hPa Upper Air Stations So if we look at a plot of 850 hPa data we see varying Heights… YQD shows 1400 m, heights rise to above 1500 m in the SE. We can use this data to contour the changes in Height along a pressure surface… Wind blow || to contours just like Isobars 12Z 29 Jul 2008 850 hPa Upper Air Stations

Rejected Data Types of rejected data Reasons why data is rejected Discussion Exercise - find rejected data

Limitations What’s not represented Friction at low levels Sharpness/ Smoothing Like Td, heights

What’s typically analyzed The standard Pressure Levels used by most meteorlogical organizations (MSC): 850 hPa (near 5000 ft / 1500 m) Thermal advection, fronts, low level jets, moisture 700 hPa (near 10,000 ft / 3000 m) Thermal advection, fronts, moisture 500 hPa (near 18,000 ft / 5000 m) Steering flow, vorticity advection, fronts 250 hPa (near 34,000 ft / 10,000 m) Jet Streams Issued twice daily: 12Z (14-16Z) & 00Z (02-04Z)

Examples of height codes: Examples of height codes: CMC Upper Air Plots 850 hPa Examples of height codes: 79 means 1790 metres Height T 50 means 1500 metres T-Td 24 means 1240 metres 700 hPa Examples of height codes: T Height 30 means 3300 metres T-Td 00 means 3000 metres 74 means 2740 metres

Upper air plots WD - Wind direction (plotted to 36 compass points, or tens of degrees; indicates the direction from whence the wind originates). WS - Wind speed (knots, where a short barb indicates intervals of 5 knots, a long barb indicates 10 knot increments, and a flag indicates 50 knot increments). 

Upper air plots TT -Ambient air temperature rounded to the nearest whole °C; "-" for T < 0°C. DD - Dewpoint depression or spread = T - Td, rounded to the nearest whole °C. This nomenclature maybe only for the US rather than CMC. CMC includes temperatures and dewpoints less than -41C. [An "X" indicates air is too dry to measure dewpoint; normally used when DD exceeds 29°C. If TT < -41ºC, DD is left blank because the air is too dry at these temperatures]. This field is omitted in the 300mb and 200mb plots. 

K W K 10°C Isotherm 12Z CMC 850 hPa Temperature 29 Jul 2008 Exact same analysis as previous AMX plot 12Z CMC 850 hPa Temperature 29 Jul 2008

Exercise Draw the ___ degree isotherm on 850 Find thermal ridges on 850 hPa

500 hPa charts 500 hPa vorticity 500 hPa thickness

Examples of height codes: Fig. D1.2 Plots on upper charts. CMC Upper Air Plots Examples of height codes: 500 hPa (Vorticiy) 75 means 5750 metres T Height T-Td 40 means 5400 metres 96 means 4960 metres 500 hPa (Thickness) T Height T-Td Fig. D1.2 Plots on upper charts.

500 hPa Vorticity Troughs and ridges are most easily identified at this pressure level. Clouds and precipitation frequently accompany upper-level lows and troughs, even without surface frontal systems. Short-wave troughs, are often embedded in the Rossby flow, and will propagate at speeds of 20 to 40 knots. Most surface lows and fronts are associated with upper-level short-wave troughs. Rossby = wave pattern in the upper flow, usually the longer wave pattern Counted the Rossby waves. Low number = retrogression high # progression Changes around 5 or 6 when you count the #aroung the whole planet

CMC 500 hPa Vorticity Line of constant Vorticity

500 hPa Thickness The 534-540 dam thickness is an approximate RA/SN line This is indicative of the average temperature of the column of air under the 500 hPa pressure level. Larger thicknesses indicate warmer air.

W K Line of constant 1000-500 hPa Thickness 00Z CMC 500 hPa This chart can be found on the 0 hr 4 panel model run Line of constant 1000-500 hPa Thickness 00Z CMC 500 hPa 1000-500 Thkns 30 Jul 2008

00 Hr PROG MSLP & 1000-500 Thkns Valid 00Z 30 Jul 2008

250 hPa or 300 hpa Jet Streams

Examples of height codes: PLOTS ON UPPER CHARTS Examples of height codes: 250 hPa 80 means 10,800 metres 20 means 10,200 metres 90 means 9,900 metres Height T T-Td

Jet streams Normally, the greatest winds are found above the regions of strongest horizontal temperature contrasts, and hence, in the tightest contour packing. A “Jet” is often found in segments 1,000 to 3,000 miles long 100-400 miles wide. 3,000-7,000 feet deep Here we are basically at the top of the troposphere. The charts indicate the strength of features in the lower atmosphere - strong storm systems on the surface are reflected in the patterns contained in these charts. At middle latitudes, the jet stream can usually be found on the 300 hPa and 200 hPa charts. A "jet" (winds of 50 kts) is most frequently found in segments of 1,000 to 3,000 miles long, 100 to 400 miles wide, and 3,000 to 7,000 feet deep. Such dimensions vary with seasonal change. As a general rule, locations north of a jet associated with a surface front are likely to be cold and stormy; locations south - warm and dry.

Isotach (constant wind) Plotted for winds ≥ 60 kts CYQD – 10,530 m Isotach (constant wind) Plotted for winds ≥ 60 kts 12Z CMC 250 hPa Isotachs 29 Jul 2008

Enhancing Upper Charts and Exercises

Enhancing 850 hPa and 700 hPa CHARTS High (blue) & Low (red) symbols 0°C isotherm (red) Areas of moisture: Any stations reporting T-Td of 4 or less Highlight the station in Green Areas of Warm/Cold Advection

Thermal Advection Look for areas where the isotherms cross the contours and form closed “rectangles” (solenoids) An area of thermal advection is bordered by 2 separate Isotherms & 2 separate height contours The smaller the solenoid the more intense the advection

Thermal Advection Identifying advection type (warm or cold): Look at the height contours: find the direction of flow (“Low to your left wind at your back”) the wind will push the isotherms in that direction If air blows from warm to cold it is warm air advection If air blows from cold to warm it is cold air advection Identifying Warm and Cold “pools” will very helpful in this process

TEMPERATURE ADVECTION -10 -10 L L K -5  H H  5 15 10 W

L H W W K W 850 hPa 12Z

H L W W K L 700 hPa 12Z L

CMC 12Z 700 hPa Analysis L H K W

Enhancing 500 hPa Charts 500 hPa is referred to as the “Steering Flow” 500 hPa Vorticity chart: Analyze S/W Trofs and Ridges

250 hPa Upper level jets

Review Upper Air Charts 850 & 700 hPa Advections Moist/saturated stations (T-Td = 4 or less) 0 degree Isotherm 500 hPa (steering flow) Vorticity: S/W Trofs and Ridge Thickness: 534-540 dam thickness area 250 hPa Jet Isotachs (>60 kts) Jet Axis(es)

NEXT: Upper Chart Exercise

Exercises Highlight the following features on the upper air charts provided: 850 & 700 hPa Low/High labels 0°C Isotherm Saturated upper air stations Warm/Cold pools Thermal advections

Exercises Highlight the following features on the upper air charts provided: 500 hPa Vorticity chart: Analyze S/W Trofs and Ridges

Highlight the following features on the upper air charts provided: 250 hPa Isotachs Jet axes

Other websites for the description of upper air charts http://weather.unisys.com/upper_air/details.html http://www.gis.usu.edu/~av3250/BMET_3250_sp2001/lab12/UPPER_AIR_ANALYSIS_instructions_00.htm http://joseph-bartlo.net/articles/021799.htm

Online tools WeatherOffice http://www.weatheroffice.gc.ca/canada_e.html Aviation Digital Data Service (ADDS) www.adds.aviationweather.noaa.gov Storm Chaser Machine http://www.stormchaser.niu.edu/machine/