Current Weather
Return to Lab 9
Introduction
Recall our many reasons for following the weather regularly: to see real-time examples of concepts we've studied in the reading and video, to become comfortable with common weather maps, to observe the movement and development of weather systems, to see a broad range of weather patterns, to follow the change of seasons.
In this Unit we will continue to look at all of the weather products from previous Units. We will also discuss surface and 500-mb maps in a bit more detail and we will introduce the 1000-500 mb thickness map.
Objectives
Study several different surface maps
Study several different 500-mb maps
Introduce the 1000-500 mb thickness map
References
 | Surface and Upper-Air Charts in Chapter 6 of your text |
| Previous lab activities |
| Forces and Winds - an Online Meteorology Guide from the University of Illinois |
| Upper Air Data Details at Unisys - scroll down to "500-mb Height Contour" and "1000-500 mb Thickness Contour", |
Instruction
500-mb Maps
Read the comments below and then study the current 500-mb maps. As you do so, notice that the data and contours are identical at the different sites, but the formats are different.
| Station Plots, contours, isotherms: Most 500-mb maps have the contours, station plots, and isotherms. Notice again that the winds are nearly always parallel to the contours, the winds are stronger where the contours are closer together, and with your back to the wind, the contour values are lower to your left and higher to your right. |
| Movement of surface features: Surface pressure systems tend to move in the same direction as the 500-mb winds at about one half of the 500-mb wind speed. In the United States, this rule of thumb works best in the eastern two-thirds of the country east of the Rocky Mountains. Hence, a surface low located underneath a region of 50 knot southwesterly winds at 500-mb would be expected to move off toward the northeast at about 25 knots. |
| Highs and Lows: High and Low pressure systems with closed circular contours are not as common on upper-air charts, such as the 500-mb map, as they are at the surface. |
| Troughs and Ridges: In place of highs and lows, we tend to see a series of troughs and ridges on upper-maps. If you study a long series of 500-mb maps every 12 hours, you will notice that some of the troughs are very big in their latitudinal and longitudinal extent and tend to stay put for a long period of time. These are referred to as "longwaves". Others, much smaller and often associated with a surface low pressure system, move in a generally easterly direction at about the same speed as mid-latitude surface systems. |
| Zonal & Meridional flow: We refer to large regions in which the winds are blowing predominately from west to east as having "zonal flow." In regions of zonal flow, surface features tend to move fairly quickly from west to east. Meridional flow, associated with deep upper-air troughs, refers to upper-air patterns in which the north-south component is strongly enhanced. When the flow is meridional in the eastern half of the United States, storms cross the country more slowly, follow less of a directly west to east path, and are more likely to intensify. (with station plots & isotherms) |
500-mb Map from OSU
(Select Upper Air, Height/Temperature (U. S.), 500)
500-mb Map from
WSI (includes station plots & isotherms)
500-mb Map
from Unisys (includes station plots & isotherms)
Surface Maps
We have already encountered a variety of surface maps, many of which are composites. Review the maps at the sites below and notice which features they each have.
| Fronts: Some maps don't have fronts, so we will have to learn to identify where they are (in later Units) from the station plots. |
| Isobars: As long as we have the isobars we can infer wind direction and speed. |
| Station Plots: These use the station model we learned earlier. |
| Radar: |
| Satellite: |
Surface Map (with isobars
& satellite image - infer wind direction & speed)
Surface Map
(with radar summary, station plots, isobars, fronts)
Surface Map
from WSI
1000-500 mb Thickness Map
This is a map produced from the individual 1000-500 mb thicknesses from soundings (see 1000-500 mb thickness in the Unit 8 Lab). As you study the maps below, here are some facts to keep in mind.
| The contour interval is 60 meters: Also, the contours are labelled with the last digit dropped. Hence, 552 means 5520 meters, 558 means 5580 meters, and so on. |
| The thickness is related to average temperature: We observed this in Unit 8. So the lower the thickness value, the colder the air from 1000 mb (roughly the surface over much of the eastern half of the United States) to 500 mb. |
| Rain/snow rule of thumb: Thicknesses less than 5400 are associated with snow, thicknesses greater than 5460 are associated with rain, and thicknesses between 5400 and 5460 are in a rain/snow transition zone. Freezing rain and sleet are more complex to deal with. |
1000-500 mb Thickness
from OSU (select Upper Air & Thickness)
1000-500
mb Thickness from Unisys
The table below summarizes our process of assessing the current weather. It is identical to the previous Unit with additions added in bold, red type.
STEP |
WEATHER PRODUCTS |
PROCEDURES |
| 1. Review Large-Scale Weather Patterns | National Surface Weather Maps Temperature Contours Dew Point Contours 500-mb Map |
Identify highs, lows, fronts, areas of precipitation. Identify cold air, warm air, & temperature gradients Identify regions high & low moisture content and of rapid change Compare to features on the surface map. Compare to features on the surface map. Study pattern over U.S. Predict movement of surface systems. Identify the 5400-5460 band for rain/snow rule of thumb. |
| 2. Relate to Region of Interest (for example, a single state) | Regional Surface Maps Regional Radar Maps & Images Current Weather Observations Meteograms Soundings |
Look for relation between: winds, highs, & lows; precipitation,
fronts & radar Study observations for past 24 hours Study T, Td profiles; relate clouds & weather to local meteogram or surface observation at the same time |
| 3. Study Forecast Maps (Progs) | Surface Progs | How will highs, lows, fronts, areas of precipitation move? |
| 4. Make Forecasts | Zone forecasts | Based on relations from step 2 and forecast positions of highs, fronts, lows, and areas of precipitation, what is the forecast for your local area of interest? |
Web Examples
Follow our four-step procedure of assessing the current weather situation and imagine that you have the responsibility for making the weather forecast for Portland, ME for the next 24 hours.
1. Review the Large-Scale Weather Patterns: where are the major storm systems and areas of precipitation? Can they affect Maine within 24-hours?
2. Relate to Region of Interest (Maine)
| Northeast Simplified Surface Weather Map |
| Northeast Surface Weather Map with Data |
| Northeast Radar Summary |
| Gray, ME Doppler Radar |
| Caribou Doppler Radar |
| Current Weather Reports for Maine |
| Meteograms |
| Soundings (use either source)
|
3. Study Forecast Maps and make your forecast for winds, precipitation, and temperature for wherever you are located.
4. Make Forecast: In a very general sense, what would you expect for each of the following for the next 24 hours for Portland?
| temperature |
| precipitation |
| cloud conditions |
| winds |
Now that you've made your forecast, compare it with the National Weather Service forecast for Portland.
Maine Zone Forecasts (Portland is in Zone 24)
By the way, we're just doing this for fun and to learn Meteorology. However, with time, lots of observation, practice, and study you may become quite skilled at forecasting the weather a day or so into the future. I encourage you to repeat this exercise as regularly as you can throughout the course to develop your forecasting skills.
Don't forget to observe the weather over the next 24 hours and see how your forecast verifies.
Practice Questions
Use the surface, 500-mb, and 1000-500 mb maps to answer the following questions.
1. Using the 500-mb map, how would we expect the surface low centered over southeastern Ontario to move (direction and speed)?
2. Study the precipitation pattern on the surface map and the contours on the 1000-500 mb thickness map. Do the precipitation pattern and contour values agree in general with our rain/snow rule of thumb above?
Answers
The answers are given below the maps.
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Revised 06/16/04