GG101 - Introduction to Physical Geography Lab 5: Interpretation of Surface Weather Data Reference Materials:            Chapter 8 in Geosystems Environment Canada (web sites) Navigation Canada (web site) Hydrometeorological Prediction Center, US National Weather Service (web site) Meteorology, University of Cologne (web site) Weather Graphics (web site) NOAA Weather Prediction Center (web site) Introduction Making sense of the day to day variations in weather is greatly aided by an understanding of how air pressure, air masses, fronts and storm systems control much of the weather that we experience

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GG101 - Introduction to Physical Geography

Lab 5: Interpretation of Surface Weather Data

Reference Materials:            Chapter 8 in Geosystems

Environment Canada (web sites)

Navigation Canada (web site)

Hydrometeorological Prediction Center, US National Weather Service (web site)

Meteorology, University of Cologne (web site)

Weather Graphics (web site)

NOAA Weather Prediction Center (web site)

Introduction

Making sense of the day to day variations in weather is greatly aided by an understanding of how air pressure, air masses, fronts and storm systems control much of the weather that we experience. Surface weather data are commonly presented in map form. In this exercise, we will review the construction, use and interpretation of surface weather maps. These are the maps that depict the distribution of weather phenomena such as: (i) air pressure with centres of high (H) and low (L) , (ii) areas of precipitation, (iii) positions of fronts, (iv) temperature, and often (v) information on wind and clouds. Weather maps may be presented in many formats. It is important to differentiate between two main types of weather maps: Synoptic Charts and Forecast Maps.

 

A

Synoptic Chart

is a map

that shows the actual weather

c

onditions that were

r

ecorded across a reg

ion at

o

ne point in time (sy

noptic

means coincident in time).

T

he imag

e

to the left is an

e

x

ample of a sy

noptic chart

(

or weather map) (note the

imag

e is shown on this pag

e

a

t low resolution). This map

w

as g

e

nerated by

E

nvironment Canada. The

map shows the distribution

o

f air pressure, with centres

o

f Hig

h (

H

)

and L

ow (

L

)

p

ressure g

iven emphasis. The

p

ositions of fronts are also

shown. I

n

addition, there is

c

onsiderable information on

w

eather data from climate

stations.

 

Figure 1:        Example surface synoptic chart (weather map).

To find the detailed weather maps that are produced by Environment Canada go to the webpage:

https://weather.gc.ca/analysis/index_e.html. The surface weather maps are under the heading Surface Analysis: Mean Sea Level Pressure. Below that heading are links to two sets of maps, one set is under the sub-heading Preliminary (Canadian coverage) and the second below the sub-heading: Complete (Northern Hemisphere coverage). These synoptic charts are updated every six hours. When you open either the

Preliminary or Complete maps from Environment Canada the time and date are shown at the lower left of the map. Environment Canada posts synoptic charts produced daily that represent 00Z (0000 UTC), 06Z (0600 UTC), 12Z (1200 UTC), and 18Z (1800 UTC) time. The “Z” (Zulu) refers to the local time at the Prime

Meridian (Greenwich meridian). The Prime Meridian runs through Greenwich, England. The term Greenwich

Mean Time (GMT) was formerly used but is now obsolete. GMT has been replaced by Coordinated

Universal Time or Universal Time Coordinated (UTC). Zulu time and UTC are synonymous. Synoptic charts give the time using either a Z for Zulu or as UTC. For example, when it is 1200 UTC or 12Z, in the Eastern Time Zone (North America) it is 8 am in summer and 7 am in winter. To convert from UTC or Zulu to Eastern Daylight Time (EDT) or Eastern Standard Time (EST), see the table at the following URL: https://www.nhc.noaa.gov/aboututc.shtml.  

The Preliminary maps are published before the Complete maps and they cover Canada and the immediate surrounding areas, they do not show weather fronts. The Complete maps show a larger area and include weather fronts (e.g. cold and warm fronts). Figure 1 is an example of a Preliminary map. The Complete maps are very complex and much experience is required to easily interpret them. A version of the most recent Complete map is posted at the Navigation Canada website: https://flightplanning.navcanada.ca . At this webpage look under the heading Graphical Weather Products, select the box labelled SFC Analysis ( for surface analysis) and then select the link under the heading Latest. The Nav Canada map shows station observations, pressure, and fronts across Canada but it is of lower resolution and can be difficult to read the small symbols clearly.

Synoptic charts are produced from a global network of climate stations that report weather conditions to several World Meteorological Organization (WMO) data centres. From these station data, synoptic charts such as Figure 1 are generated.

There are a variety of other sources of synoptic charts (weather maps) that can be accessed online. An example is shown here. From the Hydrometeorological Prediction

Center (HPC) of the U.S. National Weather Service (NWS) a highly generalized daily weather map is shown for the US and southern Canada at: https://www.wpc.ncep.noaa.gov/dailywxmap/

Figure 2:   Example Synoptic chart produced by the U.S. National Weather Service (link is above)

Similar maps are available from:

            https://www.wpc.ncep.noaa.gov/#page=sfc   and   https://www.wpc.ncep.noaa.gov/html/sfc2.shtml  

A very useful version is a weather map that is updated every three hours and permits one to zoom and pan across North America, that map is available at:

https://www.wpc.ncep.noaa.gov/html/sfc-zoom.php

One limitation of the U.S. produced maps is the use of the Imperial measurement system, temperatures are given in degrees Fahrenheit not Celsius

The second type of weather map that is commonly used are Forecast Maps. These maps are simplified and may show the positions of pressure systems, fronts, precipitation, temperature and other variables at some point in the future. It is important to recognize that a forecast map is not the same as a synoptic chart. A synoptic chart shows the actual observations, a forecast map is the expected weather. The images below are examples of forecast maps produced daily by Environment Canada and the US National Weather Service (NWS) (shown at low resolution on this page). Figure 3 is called “Weather at a Glance” while Figure 4 shows the equivalent product from U.S. National Weather Surface.

 

Figure 3: Forecast map from Environment   Figure 4:  U.S. National Forecast Map

Canada, “Weather at a Glance” (https://www.wpc.ncep.noaa.gov//noaa/noaa.gif)

(http://weatheroffice.ec.gc.ca/jet_stream/index_e.html)   others at https://www.weather.gov/forecastmaps)

At the NWS webpage there are a series of other forecast maps that cover the US and southern Canada that can be found on the webpage  https://www.weather.gov/forecastmaps. A series of Short Range Forecast maps for the US can be found https://origin.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php. On that page, you can pan through several maps that depict the changes in the isobars, pressure systems and fronts at six hour intervals and they are placed together in an animated loop that can be viewed by passing your mouse over Loop on the right hand side (see: https://www.wpc.ncep.noaa.gov/basicwx/bwxloop_ndfd.html).

Station Model

To construct a synoptic chart, data are compiled from climate stations. Each climate station collects data on up to 18 different weather variables. On the synoptic chart, each station location is depicted as a circle. Within and around this circle the weather data are presented using a compact scheme of symbols that have been designed to portray that information. The Station Model is the WMO standard for symbolizing weather conditions. Figure 5 shows a simplified version of the WMO station model. The data that are not presented on this simplified version include: (i) visibility, (ii) height of base of lowest cloud, (iii) amount of lowest cloud, (iv) barometric tendency (graphical), (v) weather in the past six hours, (vi) time precipitation began or ended, and (vii) amount of precipitation in last 6 hours. A series of legend keys for the common symbols used on weather maps are included in this assignment. For a more complete set of codes and symbols see: http://www.weathergraphics.com/dl/wxchart.pdf.

Figure 5:    Simplified station model. To interpret the information on the model, use legend keys. The station location is shown by the circle. Within the circle the amount of shading indicates sky (cloud) cover. In the example above it is completely overcast.

Figure 6:

Sky (cloud) Cover. Sky cover is given in eights (as seen to the left) or tenths. The symbol for sky obscured could mean the sky cannot be observed due to smoke, haze or fog.

The Wind Direction is shown by a long stick that intersects the station circle. In the Figure 5 example, the wind direction is from the northwest (NW). Winds are named using the direction from which they blow.

Wind Speed is depicted by the number of flags attached to the stick, they are presented below.

Figure 7:

Wind scale in km/hr. If there is no wind, the station circle is surrounded by second larger circle.

To the left of the station circle a small symbol may be used to indicate the Present State of the Weather. In the example of Figure 5, the present state of the weather is a single dot which signifies light rain.

Alternatively a numerical code may be used. Figure 8 shows some of the common state of weather symbols.

Figure 8:     Present state of the weather symbols. The numeric codes that are commonly used are shown in the table below.

Sample of the commonly used state of the weather codes.

Code	State of the Weather	Code	State of the Weather
04	Smoke	65	Heavy continuous Rain
10	Mist	66	Slight Freezing Rain
13	Lightning	71	Continuous Slight Snow
40	Fog in Sight	75	Continuous Heavy Snow
45	Fog, Sky Obscured	80	Slight Rain Shower
50	Intermittent Drizzle	85	Slight Snow Shower
51	Continuous Drizzle	95	Thunderstorm, slight or moderate, with rain
60	Intermittent Slight Rain	97	Thunderstorm, heavy, with rain and or snow

The type of Clouds present are shown by up to three symbols, each denoting low, mid (alto) and high level clouds. In the example on Figure 5, there is cirrus, altostratus and stratus clouds. Figure 9 shows the symbols used for the common cloud types. In the table below are the cloud types and the letter codes used for each.

Figure 9:

Cloud types, symbol icons to left, legend below. For example, the symbol used to denote a low level cloud CL (row) that is type 6 ( column) is a solid horizontal line.  In the table, we see a CL 6 is called Stratus and the two letter code for that cloud type is St (in brackets).

	CL Low Level and Vertically Developed Clouds	CM Middle Level Clouds	CH High Level Clouds
1	Fair Weather Cumulus (Cu)	Altostratus (As), Thin	Cirrus (Ci), Filaments
2	Towering Cumulus (Cu)	Altostratus (As)	Cirrus (Ci), Dense
3	Cumulonimbus (no anvil) (Cb)	Altocumulus (Ac), Thin	Cirrus (Ci), from Cb
4	Stratocumulus (from Cu)	Altocumulus (Ac), Patchy	Cirrus (Ci), Hooks, Spreading
5	Stratocumulus (Sc)	Altocumulus (Ac),Thickening	Cirrostratus (Cs), Cirrus (Ci)
6	Stratus (St)	Altocumulus (Ac), from Cu	Cirrus (Ci), Cirrostratus (Cs)
7	Fractostratus (Fs)	Altocumulus (Ac), Thick	Cirrostratus (Cs)
8	Cumulus (Cu) and Stratocumulus (Sc)	Altocumulus (Ac), Turrents	Cirrostratus (Cs), Partial, Stable
9	Cumulonimbus (Cb)	Altocumulus (Ac), Chaotic	Cirrocumulus (Cc)

The Air Temperature is given as the numerical value to the upper left of the station circle, and the Dew Point Temperature is given as the numerical value to the lower left of the station circle.

The remaining information deals with Barometric Pressure. These data are corrected to sea level pressure and are provided using a three digit code. If the first digit in this code is a 6, 7, 8, or 9 then place a “9" in front of the three digits. If the first digit is a 0, 1, 2, 3, 4, or 5 then place a “10" in front of the three digits. The pressures can be given in either millibars (mb) or kilopascals (kPa). For example:

Code on Station Model	Barometric Pressure (mb)	Barometric Pressure (kPa)
834	983.4 mb	98.34  kPa
307	1030.7 mb	103.07  kPa
017	1001.7 mb	100.17  kPa

Information may also be given on changes to barometric pressure in the preceding three hours. These data are given to the right of the station model in tenths of a mb (hundredths of a kPa) and a positive sign (+) indicates a rising barometer, a negative sign (-) a falling barometer. Alternatively a graphical symbol is used.

Weather Map

A fully labelled weather map will normally show:

1. Centres of high (label with large H) and low (label with large L)  air pressure
2. The positions of fronts (cold, warm, occluded, stationary)
3. Isobars (lines of equal air pressure) at 4 mb intervals
4. Station models with data

There may be information on the movement of Low and High pressures areas, the positions of upper level features such as troughs and trowels may be shown, and areas of precipitation may be shaded (see Figure 10).

Figure 10:

Symbols used for fronts, centres of high and low pressure, isobars, and precipitation.

Construction of a Weather Map

When given a map showing data from a network of climate stations the steps below will assist in the construction of the isobars and locating the fronts.

1. Convert the three digit barometric pressure codes to barometric pressures in either millibars or kilopascals (depending upon which is desired).
2. Sketch in lightly (with a pencil) isobars (lines of equal air pressure) at 4 mb intervals (e.g., 992 mb, 996 mb, 1000 mb, 1004 mb etc). Use a technique similar to that used to produce contours from spot elevations (Lab 1).
3. Use the available temperature and wind data to locate frontal boundaries. There should be substantial temperature differences and changes in wind direction across fronts. Also there may be cloud and precipitation in the front area. Use the appropriate map symbols (Figure 10).
4. Once the fronts have been located, alter the isobars to indicate a slight trough of low pressure along each front (isobars are elongated along the front away from the direction of low pressure).
5. Add “L” and “H” in the areas of low and high air pressure.
6. If possible label the air masses involved.

Lab Preparation: Reading

1. Read the sections in Chapter 8 of Geosystems that are related to daily weather and focus on the sections that deal with frontal lifting, mid-latitude cyclones, and weather maps and forecasting.
2. Read this document and review the websites that are sourced in this document. Become familiar with the use of weather maps and the symbols that are used to depict information on weather maps.

Local Weather Data - Environment Canada

Environment Canada operates a network of over 2000 observation locations at which weather data are collected. The local Environment Canada weather station is at the Region of Waterloo Airport and is called Kitchener Waterloo station. Current weather conditions from that location are at available at: https://weather.gc.ca/city/pages/on-82_metric_e.html

Past weather data from this station may be examined by going to the Environment Canada web page called

Canadian Climate Data: https://climate.weather.gc.ca/historical_data/search_historic_data_e.html

Search for weather stations by using the “Search by Station Name” tab. In the middle of the page there is a box that is labelled "Name", type “Waterloo” into the name blank and click on Search. This will bring up a new page that lists the results, there should be several stations listed. One station is called "Region of Waterloo Int'l Airport". Data from this station covers the period 2002 to 2010. Under the column 'Data Interval' the data can be configured to display in hourly, daily, monthly or annual (almanac) intervals. The day, month and year may also be selected. To see the data in tabular format, click on the Go button.

The data may be displayed in graphical format by clicking on the graph icon below each variable heading (e.g. click on graph below Temperature). You can also select the “Kitchener Waterloo” station, which has the weather data from 2010 to present.

Explore the interface using data from Kitchener Waterloo. Pick some dates and display the hourly data and explore the graphing options. Repeat using daily data.