Online Phenology Models and Degree-day Calculator

INTRODUCTION: This phenology model/degree-day calculator uses weather data to calculate degree-days, also known as heat units that are used to estimate development of many organisms, such as insects and plants.

This app is essentially a wrapper around the newly re-designed, mobile-friendlier, online model/calculator at: - USPEST.ORG (home page). The numerous models served by this app are all driven only by daily maximum and minimum temperatures, using one of many different degree-day calculation formulas, many of which are described at this UC Davis IPM website. Note that this app requires wifi or cellular connectivity and will not work in airplane or off-line mode.

INSTRUCTIONS FOR USE: We split this app into tabbed sections in 1 or 2 rows near the top of the page. Use the tabs from left to right. This introduction is in the first tab "Intro". Notice while using this app, if you see the info icon, click on it to access more explanatory information via a pop-up help window.

station tab
The Station Tab
The second tab, "Station", allows selection of a weather station needed to run the models from a database of around 29,000 weather stations from hundreds of weather networks throughout the U.S., with more in Canada and Mexico and some other surrounding places. Most of our weather data comes from Mesowest in Utah. We also have data from participating agricultural weather networks (scroll to far bottom of this page and read the fine print to see some of these).

To find a weather station, enter a known weather station code (e.g. ARAO), a zip code, or a city and state abbreviation. Then click on the button "search for stations" to find 1 or more expandable lists (click on "+" sign to expand, "-" to contract) of the 4-8 nearest stations. Once you click on a station code and you see the text "Selected station:" with a station code and a place name, then you have selected a weather station. Be warned that not all weather stations have valid data so you may need to return to this step!

You may also click on the (MAP) link to open a Google map selection option. With this, you can zoom in, zoom out, pan, and click a station pin to select a station.


  model tab
The Model Tab
Once you have a station selected, click on the next tab, "Model". This tab begins with selection of a model category. For example, all models (ca. 115 models), insects (ca. 68 models), weeds (5 models), plant diseases (5 models), and crops (32 models), plus various combinations based on other criteria, such as invasive insects (22 models), apple and pear (16 models), stone fruits and nuts (12 models), etc. see current list.

Note that all categories include "generic degree-day calculator" (see below) as the first option. Also note that none of these models are driven by hourly weather, only by daily max and min temperatures. You may want to try MyPest Page at USPEST.ORG for hourly driven (most plant disease infection risk, plus other), models (not mobile-responsive however).

Model Options
Once you have selected a model, you may need to change the dates. The start date may be critical and require monitoring data. If the instructions indicate that the model starts on a fixed date (such as Jan 1 or Mar 1), then you generally do not need to enter a start date of your own determination.

The end date is usually not critical (as long as it is not set too early), and we have changed the graph output so that it only extends a couple of days beyond the last date of a model event.

Once a model is selected, you may scroll down to review the model information, helping you confirm that you have selected the appropriate model for your needs. Model inputs include information such as thresholds, region of known usage, model events, and links to extension pages and model source information. Many of the 100+ models were derived from one or more scientific publications and combined into a working model by OSU IPPC in the form of a spreadsheet converted to PDF format.

Forecast Options
We use different assumptions and strategies for predicting future weather and climate, past the usual 5 or 7-day forecasts that we access either from NWS or Fox Weather LLC. Current 8+ day forecast options include:
1) 10 year averages: uses most recent (updated every other month) 10-year average PRISM data localized to the currently selected weather station as the extended weather forecast.
2) 30 year averages: uses 30-year Normals (currently 1981-2010) as the extended forecast.
3) Last years data: uses data from last year (so you assume this year will be similar to last year). (May not be available for new weather stations)
4) Data from 2 years ago: uses data from the year before last (so you assume this year will be similar to 2 years ago). (May not be available for new weather stations)
5) NMME seasonal (7-month) forecast: uses the NOAA North American Multi-Model Ensemble (NMME) forecast system, which is an ensemble average of seven different extended (7-month) numerical models, all driven in part by scientific understanding of how ocean temperatures and other factors affect seasonal climate and weather patterns. Check the N. American NMME temperature and rainfall forecast anomaly maps, and the verification index to see how well their 1-7 month lead time forecasts have performed in the past. Use with caution.
6) CFSv2 seasonal (currently 3.5-month) forecast: uses the NOAA NCEP Coupled Forecast System model version 2 (CFSv2) forecast system, In contrast to our NMME forecast, this is a single model from NOAA, and Fox Weather LLC has customized it to attempt to reproduce realistic rainfall episodes rather than just smoothly interpolate temperatures and rainfall.

1) This forecast option will not be available if you run the model for prior years or you set the end date earlier than the current date.

2) All available forecast options will be used as future forecasts in the graph output (if the model end date is 6+ days later than the current date). See example image:

3) Three of these forecast options (past 1 year, 10- and 30-year averages) will be displayed as "comparison lines" versus current weather station observations if you run a model setting the end date earlier than the current date. See example image:

Celsius (temperature scale) Option
This calculator may be run in celsius or Fahrenheit. Brought back by popular demand!

DD Calculator Options
If you selected the degree-day calculator option, then you have additional options to consider:

Calculation Method
A variety of formulas are used to calculate degree-days. The most common method is the simple average/growing DD - this is the daily max plus min temps averaged together, (Tmax+Tmin)/2 minus the lower threshold (Tlow). Note that corn growing DDs in our system are the sweet corn formula and are not the same as simple average/growing DDs. Corn GDDs use a substitution rule: if the Tmin is less than the lower threshold (Tlow), we substitute Tlow instead of Tmin, and if the Tmax is greater than the upper threshold (Thi), we substitute Thi instead of Tmax in the formula.
The UC Davis recommended default formula is the single sine method. Models in our database usually use the calculation method used in the original modeling research study. For more complex formulas and more on degree-days, see this UC Davis IPM webpage.

Lower threshold
The lower developmental threshold is an approximate temperature below which, development has slowed to zero. This value varies depending on the type of organism and even the specific species. Usually the lower threshold is determined using laboratory or field data, and may be available in the scientific literature.

Upper threshold
The upper threshold is often not known or well studied. It is recommended that you use whatever guidelines are available for your organism. Otherwise just leave this at the default value (currently set at 130F).

output tab
The Output Tab
Once the Station and Model have been selected, click on the "Output" or "Graph" tabs back at the top of the page to see model predictions or output. The default "Output" consists of an expandable repeat of the Model Inputs, expandable Date Comparison (see below), and expandable table of Model Output with predicted dates (first column) and model events (last column). In between, are the daily max and min temperatures, rainfall, degree-days for the day, and the cumulative degree-days from the start date to indicated date. This "collapsed" table includes only rows for dates when a model event occurs.

full table
Check Data QA (Quality Assurance)
Click "show full table" to expand to the full table (rows for every day from the start to end dates) to review ALL of the temperature data used to drive the model, not just the small number of days when a model event occurrs. This is very important because, as mentioned above, not all weather stations have good data, so please examine the FULL set of temperatures used for the model, and watch for QA tags such as "Px" that indicate that the data was missing or in error, and a method ("Px" indicates PRISM map interpolation was used) was used to estimate the data. If you see numerous tags like these, you may want to run the model using a different nearby weather station (click on the "Station" tab again and expand the Google map to see nearby station locations). If only a few of these tags occur, then you may not expect much error in the degree-day accumulations (use at your own risk).

The QA column is also where a forecast is indicated, e.g. "Nm" reflects the selection of the NMME forecast. Click on the tag links to further investigate how the temperatures were estimated or forecasted.


  date comparison
Date Comparison
The Date Comparison expansion option allows you to see how, (for the current model inputs including the start date, threshold temperatures, and calculation method), the Current year degree-day accumulation compares to Past year degree-days, in particular the prior 2 years and to the 30-year Normals. For example (in the figure above), the 2018 to-date degree-day accumulation of 1377 DDs was reached 23 days earlier in 2017 and was reached 2 days later in 2016. That degree-day total was never reached using 30-yr Normal data. (note this is a slightly contrived example as the start date was Sept 1, 2018, but this could apply to fall-planted vegetables for example).


  graph tab
The Graph Tab
The Graph presents model output as a graph, with dates on the x-axis and cumulative degree-days on the y-axis. Predicted model events are displayed both with reference to the degree-days as horizontal lines of text, and with reference to dates as diagonal lines of text starting along the x-axis. Close-together events may overlap and be difficult to read. To help overcome this issue, the graph is interactive and allows for zooming in on only the portion of the output you wish to see. It will also display the data when you hover (lightly touch) a graph line or point, and has the option to turn off a data line by clicking on the legend item at the bottom of the graph. The options for displaying multiple forecasts are discussed above under Forecast options.

Degree-day model options not included in this version
To help simplify this version of the calculator for use on mobile devices, we have turned off two features available in an earlier version, at These include 1) Multiple start dates (added for vegetable phenology models), and 2) Daylength calculations (helpful for species that are photoperiod-responsive such as insects that use daylength to trigger diapause).


This app was funded primarily by a USDA NIFA CPPM EIP grant to support IPM at the state and regional level, and by the Oregon State IPM program at IPPC. Other sources of support include other NIFA funded grant programs, including the Western IPM Center, and from USDA APHIS PPQ support.

Location search using place names (geo-coding) by OpenCage, using data © OpenStreetMap contributors.

Weather Station


Species / Model

Select a model or species. (see list of models) To choose your own calculation method and threshold temperatures, chose "degree-day calculator".





Change some of the details, if you wish.

  • info : after 7 days, use

Ignore this blank; it's not supposed to be displayed.

Model Inputs

 show model inputs table

Date Comparison

 show Date Comparison table

Model Output

 show full table

All data provided "as is" and users assume all risk in its use - see full disclaimer. All NWS derived data is not subject to copyright protection.

This app is produced by at the Integrated Plant Protection Center at Oregon State University with support from the USDA National Plant Diagnostic Network, The OSU Agricultural Experiment Station, various USDA CSREES/NIFA grants, USDA SARE, USDA RMA, and USDA IPM Centers - Western Region. Climate map data provided by OSU PRISM Group, real-time public weather data provided by U. Utah Mesowest and other networks including WSU AgWeatherNET, AGRIMET, CPS Adcon Networks, IFPNet Automata, California CIMIS, California PestCast, and others. Geo-coding (location search using place names) by OpenCage, using data© OpenStreetMap contributors.

Previous versions online since May 16, 1997; this is app version 0.93, updated 28 Dec 2018

Contact Len Coop at or 541-737-5523 if you have any questions about this program.