How to Read the NCSU Cucurbit Downy Mildew Forecasts

Step 1: Follow the highlighted labels to get to your FORECAST of interest.

Step 2: Note the DATE and DISEASE LOCATION at the top of each forecast.

Step 3: Page down on the large horizontal (xy) map showing the spore cloud pathway/trajectory. The SOURCE end of the trajectory is indicated by a green dot. Time/position nodes show six-hour segments along the pathway (up to 48+ hours). Latitude and longitude coordinates of the source are given on the left margin of the map. The small graphic below the xy map shows the vertical movement of the spore cloud center.

Step 4: Review the REGIONAL WEATHER and TRAJECTORY WEATHER information. TRAJECTORY CONFIDENCE is based upon the experience of the Forecaster and his/her assessment of atmospheric complexity pertaining to that case.

Step 5: Study the OUTLOOK carefully. The likelihood of disease spread along the forecast pathway is based on several things: weather favorable for sporulation at the source, survival of the spores during transport, and rain/favorable weather for deposition and infection. You should ALWAYS take into consideration your local weather and conditions.

Step 6: Click on the highlighted labels to find additional source forecasts for that date and other dates.

Each Downy Mildew Forecast includes descriptions of factors pertinent to the disease situation, a general outlook assessing the risk of disease development, and a map showing the flow away from an active area or region (i.e., a cluster of closely-grouped counties) with a single, centrally-located trajectory.

The maps show the motion of a floating particle that is released into the atmosphere on the date and time given in the third line of the map headings. The larger upper map shows the horizontal motion; the small rectangular lower map, the vertical motion. If you imagine the particle to be at the center of a spore cloud, then the forecast trajectory indicates the future pathway of the center of that spore cloud. The release time is in Universal Time on a 24-hour clock, and will be set to correspond to about 10AM local time. A green dot denotes the starting point for the trajectory (exact latitude and longitude are written along the left-hand side of the map). After the trajectory starts, there are time/position markers along the pathway at 00Z, 06Z, 12Z, and 18Z. A small triangle gives the position. The dot and triangles in the lower map correspond to the starting point and time/position stamps in the top map. In the headings, the THIRD line has the start date and time for the forecast trajectory. The right-hand side of the map has some information about the weather data used as input to the trajectory model, and it can be ignored for most purposes.

The Regional Weather section gives a broad view of the weather conditions existing immediately prior to and during the forecast period. Notes on jet stream winds, approaching fronts, temperatures, etc., will be found here. The Trajectory Weather section focuses on the conditions near the forecast track of the spore cloud center. This information is specific to each particular trajectory.

Trajectory Confidence describes the general quality of the forecast pathway, using the ratings of Low, Medium, and High. The 'Low' and 'High' categories are much smaller than the 'Medium' category and are reserved for the worst and best trajectories, respectively. Most trajectories are in between and described as 'Medium'. As the HY-SPLIT model undergoes improvements, you will likely see more "High" ratings. Sometimes there are combination ratings, such as 'High first 2 hours, then Low', but there is never an improvement from the initial rating. However, even the Low-rated trajectories may be helpful.

The Outlook portion of the Forecast combines all the biological and meteorological elements into an evaluation of the risk of disease development associated with that source or group of sources. There is a short general statement usually separated with several asterisks, followed by comments concerning sporulation at the source, survivability of the airborne spores, possibility of future deposition, opportunity for infection, etc.

THINGS TO REMEMBER: The forecast trajectories and the resulting Outlooks can vary from reality in a number of ways. They will be most useful if you keep in mind the following:

1. Sporulation occurs at night and the spores are released anytime from 8 AM through 1 PM. The trajectory start at 10 AM is just before maximum spore release. However, spores released at other times of the day may follow other tracks, especially if the weather situation is changing rapidly.
2. The pathway you see on the map is the anticipated path for the spore cloud CENTER. The spore cloud will actually spread away from the center. The areas on either side of the trajectory pathway will also be vulnerable.
3. There is a limit to the detail and accuracy of the weather forecasts. If you are in a potentially high risk area, be sure to pay close attention to your local conditions!
4. Finally, these forecasts can be viewed from a different perspective. They can't tell you exactly where the spores will go, what the exact weather will be, or if you'll definitely receive viable spores deposits on your fields. They can, however, do a very good job of telling you where the spores WON'T go, what the weather WON'T do, and when you likely WON'T have to worry about the inoculum arriving in your fields from known sources. This information should be helpful in making decisions about control strategies using protectant fungicides.

Web page last updated by Thomas Keever on 16 March 1999.