Weather Defender Documentation

Page History: Forecasting Severe Weather

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Page Revision: 02/16/2009 10:20 AM

With your personalized map, with custom geography layers for reference, we can start making forecasts and predicting when severe weather will approach your site.

Because the weather is always changing, we are not able to practice forecasting a real severe weather event. So instead we will show you the forecasting tools and layers that are available in Weather Defender in order of the time range they can be used.

This tutorial assumes you have completed the Getting Started tutorial. It is recommended that you have also completed the Personalizing Your Map tutorial.

3 to 7 Days Out

Your event is 7 days away. Lets start by checking out the 7-day forecast.

Step 1
First, center your home location on screen.

Next, select the Forecast Tool from the toolbar.

You can also press CTRL+SHIFT+F on the keyboard to activate the Forecast Tool.
Now click on your home location.

An small window will pop-up with the 7-day Forecast for your location:


We've all seen 7-day forecasts before, that is nothing special. What is unique about this feature in Weather Defender is that the forecast is based on the exact position (latitude & longitude) of your mouse click:


This means that you are not getting the forecast of the nearest major city. You are getting the pinpoint forecast for your exact site.

The Forecast tool works on any location in the United States, except Alaska.

1 to 3 Days Out

Your event is just a few days away and there is a chance of thunderstorms according to the forecast. Lets find out what the experts are predicting.

Step 2
Open the Layer Browser (Add Layers > Browse All Layers).

Navigate to the Forecast category.

Add the following layers to your map:
  • Day 1 Convective Outlooks
  • Day 2 Convective Outlooks
  • Day 3 Convective Outlooks

About Convective Outlooks
The term 'convective' refers to thunderstorm-type weather, i.e., weather which can produce tornadoes, hail, and damaging winds. These outlooks are produced daily by the expert forecasters at the Storm Prediction Center in Norman, Oklahoma and serve as an excellect guide to those of us who want to be aware of damaging weather situations.

Outlooks are defined for broad regions and tiered in the following levels:
  • General Thunderstorms
  • Slight Risk of Severe Weather
  • Moderate Risk of Severe Weather
  • High Risk of Severe Weather

The periods cover the following ranges:
Day 1Today! (Forecast for the next 24 hours)
Day 2Tomorrow: Forecast for 24 to 48 hours
Day 3Forecast for 48 to 72 hours

More details can be found on the SPC's website.
Close the Layer Browser.

Step 3
The 3 layers you just added will appear under the Ungrouped layer group in the Map Layers window.

Edit the Ungrouped settings (click gearshaft icon).

Change the name of the group to Outlooks. Set the behavior to Single-Select.

Step 4
De-select Day 2 and Day 1 Outlooks, so that only Day 3 is active.

Now you may see an orange, green or other colored line drawn on your map. This line represents the area of concern.


Note: If you do not see any lines in the Continental U.S., it means no severe weather is forecasted for that period.

Step 5
If a forecast line is present on the map, you will also see a blue information icon near the description of the line:


Click the icon to review the full forecast text:


Note: SPC forecasts are very technical in nature and meant primarily for other forecasters and not the general public. However, if you practice reading these, over time you will begin to understand what elements forecasters look for when predicting severe weather and it can lead to better decision making on your own part.

For your reference, the SPC provides this glossary of abbreviations used in their forecasts:

1 Day Away

Your event is tomorrow. Severe weather is still expected, but how accurate are the forecasts? Lets take a look.

Step 6
Select Day 2 Outlooks from the Map Layers window. You will see that Day 3 is automatically de-selected per the group's behavior of Single-Select.

Review the Day 2 forecast. How does it compare with yesterday's Day 3 forecast? Have the threat levels increased or decreased? Are the areas of concern similar or different?

When forecasts "agree" with each other, that is worth noting because it means the prediction is more likely to be accurate.

For example, if yesterday's Day 3 Outlook was predicting a Slight Risk of Severe Weather for the midwest, and today's Day 2 Outlook was predicting the same, there is a fairly good chance that the midwest will in fact see some severe weather tomorrow.

Day of Event

Your event is today! The forecasts are in agreement that a Slight Risk of Severe Weather is expected for your region. Do you cancel or proceed?

Step 7
Review the Day 1 Outlook for today's and see if any Advisories are active for your county.

Plan accordingly:
At this point, all you know is that severe weather is expected for a relatively broad region. It would be premature to cancel your event. Many times the same ingredients that lead to severe weather (warm temperatures, lots of daytime heating) can also result in the most beautiful summer days.

But you can at least can be prepared with a contingency plan, such as an indoor alternative should the worst case happen.

4 to 8 Hours Out

''The event will proceed as scheduled. You are aware of the potential for severe weather, but when and where will it occur?

Open the Layer Browser.

Add the Mesoscale Discussions layer to your map, and close the Layer Browser.

About Mesoscale Discussions
Mesoscale Discussions (or MDs for short) are short-term, small-region forecasts issued about 2-6 hours before the expected event (also by the SPC). These are excellent forecasts because they cover a tighter region and are more specific about the threat expected.

Check every hour or so to see if any Mesoscale Discussions have been issued for your region.

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