Geog. 321 -- Climatology
Exercise 5 -- Forecasts

This exercise examines some of the computer and human-generated "products" that are used make forecasts on a day-to-day basis.  Links to the various images and text can be found on the Current Weather & Climate web page, in the "Basic Information" and "NCEP Short-term and medium-range forecasts" sections.

Note:  The exercise once again makes use of "live" images, which might not be available at the time you work on the exercise.  Before starting the exercise, scroll down the page to make sure all images are being displayed.  There should be three images.  If some of the images are missing or the forecast-text pages don't open up, you could try doing the exercise later, or without losing any points, just type "image or page not available," and the time, into the answer form.

When you finish entering the answers, click on the "Submit" button at the bottom of the page.  If your name has not been entered or an answer is blank, an error message will appear.  Otherwise, you should get a message indicating that your answers have been submitted.

Please enter your Name before beginning (Last Name, First Name):

And your email address:

Open the Portland NWS Discussions, Forecasts, and Outlooks page by clicking here:  Oregon Forecast.  If a new window does not open, you can browse to this page by using links on the Current Weather & Climate page.

Click on "Eugene" in the "Selected Cities in Oregon" area of this web page.

Question 5-1:  This page contains a text summary of the forecast for the next few days that also appears on the more graphical "forecast-at-a-glance pages."  Briefly note the forecasts over the next two days, and in particular the temperature trends and likelihood of precipitation:

The next questions are below the following figure.  If there are no figures, try again in a little while, and if there are still no figures, enter "figures not available" in the answer boxes.

500mb Heights and Absolute Vorticity (colors are regions of positive (cyclonic) vorticity

700 mb Heights and Vertical Velocity (postive (green to red) = up, negative (blue to purple) = down)

Precipitation Forecast (no color = no precipiation; green and other colors = precipitation)

Take notice of the times of the forecast.  Times are UTC or "Z" -- Pacific Standard Time (PST) is 8 hours earlier, Pacific Daylight Time (PDT) is 7 hours earlier.

Question 5-2:  Using the 500mb and 700mb maps, describe the ridge and trough pattern of the upper level circulation over the eastern Pacific and western North America  (Describe where a ridge is and where a trough is.)  Remember:  1) the airstream moves parallel to the contour lines at these elevations, in a generally west-to-east direction; 2) ridges are regions were the airstream is turning in a clockwise direction, i.e., turning from heading toward the pole to heading toward the equator; and 3) troughs are regions where the airstream is turning in a counterclockwise direction, i.e., turning from heading toward the equator to heading toward the pole.

Question 5-3:  Now describe the correspondence among the ridges and troughs, regions of positive or cyclonic vorticity (on the 500mb map), rising motions (on the 700mb map), and precipitation.  You can do this by describing what's going on on the 500mb and 700mb maps where precipitation is being forecast.  Find an area of precipitation, then look at the corresponding area on the 700mb and 500mb maps to see what vertical velocity and vorticity are like, and then check the wave pattern.

 

Open the Portland NWS Oregon  forecast discussion page by clicking here:  Portland Area Forecast Discussion.  If a new window does not open, you can browse to this page by using links on the Current Weather & Climate page.

The forecast discussion page is written in fairly technical language, using some jagon and strange abbreviations.  Here are some hints:

  • POPS = probability of precipitation
  • ETA, GFS, and EURO are different numerical weather forecasting computer models.  The maps above are those from the ETA model.
  • UPR, LWR (or something like that) = upper and lower
  • retrograde means to move westward (instead of the usual eastward motion)
  • CWA = "county warning area" region around Portland that the forecast applies to
  • METAR = "meteorological airport report"  Reports from airports in the region.
  • "shortwave energy" has nothing to do with radiation!  It refers to "short" upper-level waves (ridges and troughs) -- those that look like wiggles on the maps above as opposed to the "long wave" troughs and ridges that are the principal features of those maps.

Question 5-4:  Read the synopsis, and short- and long-term discussions.  What seem to be the main controls of the forecasts of temperature and precipitation?  (This is rather vague, the main idea here is to see how the forecast, presented as text here, depends on the output of the computer models, presented as maps.)

When you are finished, and all answers have been completed, click on the "Submit" below to send us the exercise.  If you receive an error message, check to make sure that you've answered each question, and that your name has been filled in, and then click on "Submit" again.

Click on this button to turn in your completed exercise: