Frequently Asked Questions


Forecast Data

Who produces the forecasts that the StormwaterForecast alerts are based on?
Forecasts are produced by the U.S. National Oceanographic and Atmospheric Administration (NOAA)/National Weather Service (NWS), and are based on numerical weather prediction models and forecasts issued by local weather service forecast offices. What geographic region do the forecasts represent? StormwaterForecast provides alerts for the conterminous U.S. (CONUS). Future development may include areas such as Puerto Rico/the Virgin Islands, Hawaii, and Guam. Email us and let us know if these areas are of interest to you.

How often does the NWS update forecasts?
Forecasts are updated near the top of each hour, but may be delayed by a few minutes. Nationwide there may be a few locations where forecasts are not updated, and will vary depending on how rapidly weather evolves.

What type of alerts can I receive from
Two types of values are available from StormwaterForecast. The 12-hr probability of precipitation (PoP12), and the depth of precipitation for each 6-hr period called the quantitative precipitation forecast or QPF.

What is the probability of precipitation product?
The 12-hr probability of precipitation, or PoP12, is the likelihood, expressed as a percent, of a measurable precipitation event (1/100th of an inch or more) at a point during the 12-hr valid period. The 12-hr valid periods begin and end at 0000 and 1200 GMT.

What does the probability of precipitation mean in terms of NWS definitions?
The definition used by the U.S. NWS in the production of probability forecasts is defined as:
PoPExpression of UncertaintyAreal Coverage
0%None UsedNone Used
10%None UsedIsolated
20%Slight ChanceIsolated
80-100%None UsedNone Used

What does the quantitative precipitation forecast amount to?
The quantitative precipitation forecast, or QPF, is the expected amount of liquid precipitation (in hundredths of inches) accumulated over a six hourly period. A QPF will be specified when a measurable (1/100th of an inch or more) precipitation type is forecast for any hour during a QPF valid period. Valid periods for QPF are 6 hours long beginning and ending at 0000, 0600, 1200 and 1800 GMT.

Security and Privacy

How is my account information processsed and secured?
We use HTTPS for all browser interactions with our server. This helps ensure all information transmitted to and from our website remains secure and visible only to you. Our website and database are hosted on the Heroku platform. They document their extensive physical, environmental, data, network and other security measures on their website.

How is my credit card information processsed and secured?
Credit card services are provided by a third party service called Stripe. When you enter your credit card information, it is processed via their secure web service. For your security, credit card information is sent directly to Stripe; it is not sent to or stored on our servers. For more information on Stripe's rigorous security measures please visit their website.

Will Stormwater Forecast share my information with others?
No. User information is private and will not be sold or shared with third parties. Please see our privacy policy for details.

What happens to my data and history of notifications?
We maintain a log of rainfall events and notifications sent to aid in supporting and troubleshooting the service. Upon request, we can delete your account which removes all information about alerts that were configured, rainfall events that occurred, and credit card information (if any).


What can I do to ensure notification emails are not sent to my junk mail / spam folder?
We recommend that you add
to your address book.
What will a probability of precipitation (PoP12) notification look like?
The format of a typical notification is shown below.
From: Stormwater Forecast <>
Date: Mon, Jan 14, 2013 at 11:02 AM PST
Subject: Alert: Portland

Alert Details
Name Portland
Location 45.5235, -122.6762
Type Probability of Precipitation (12 Hour)
Threshold 50.0 %
Forecast Period 48 hours
Current Weather NWS

Time of Forecast Update
Time of Valid Forecast
Lead Time
Mon 14-Jan-2013 11:00 Mon 14-Jan-2013 16:00 05:00 54.00 %
Data Source: NOAA National Weather Service - National Digital Forecast Data

In 3 hours, another email notification will be sent if any period exceeds the threshold in the 48-hour forecast.

What will a quantitative precipitation forecast (QPF) notification look like?
The format of a typical QPF notification is shown below.
From: Stormwater Forecast <>
Date: Wed, Jan 9, 2013 at 8:02 AM CST
Subject: Alert: George R. Brown Convention Center

Alert Details
Name George R. Brown Convention Center
Location 30.2672, -97.7431
Type Quantitative Precipitation Forecast (6 Hour)
Threshold 0.5 in
Forecast Period 48 hours
Current Weather NWS

Time of Forecast Update
Time of Valid Forecast
Lead Time
Wed 09-Jan-2013 08:00 Wed 09-Jan-2013 12:00 04:00 0.98 in
Wed 09-Jan-2013 08:00 Wed 09-Jan-2013 18:00 10:00 0.68 in
Data Source: NOAA National Weather Service - National Digital Forecast Data

In 3 hours, another email notification will be sent if any period exceeds the threshold in the 48-hour forecast.

How often will I receive notifications from
By default, StormwaterForecast will send a notification no more than once every 24 hours during an active precipitation event that is exceeding your alert thresholds. You can modify this setting on each alert to be between 1 and 48 hours.

What is the time zone of the forecast times contained in an alert?
All times contained in an alert message reported by StormwaterForecast are converted to the time zone specified when the user signed up for an alert. Times are not adjusted for Daylight Savings time.

What do the times stated in the alert notification mean?
StormwaterForecast reports all times in the users selected time zone as an offset to Greenwich Mean Time (GMT). For example (GMT-6:00) is the Central Time zone, and GMT-8:00 is Pacific Time zone. These values are not adjusted for Daylight Savings time.

How much time is there to take action for a forecast rain event?
The ‘Lead Time (hh:mm)’ shown in the notification is the amount of time until the forecast threshold will be exceeded. It is measured from the time of the updated forecast that exceeded a threshold. Forecast updates usually occur a few minutes after the top of the hour. Since notifications are sent every three hours, the forecast update could be several hours in the past. If more time is needed, edit your alert duration to extend it beyond 48 hours.

Where can I find tabular NWS forecast values?
The forecast values and times are provided in the email notification. In the ‘Alert Details’ click on the NWS link, next to ‘Current Weather’, you can access their page where you can find the Tabular Forecast under ‘Additional Forecasts and Information’. Note that when you access the NWS page, the forecast may be updated and different from the forecast values that triggered the notification.

How do I verify the location shown in latitude and longitude in the email notification?
By clicking on the link next to Location in the ‘Alert Details’, the map location will display the location of the alert.

How do I sign up for an alert for more than one location?
You can configure as many alerts as your plan allows. Each alert configuration consists of a selected location, threshold, or type of alert, i.e. probability of precipitation or depth thresholds and forecast duration. If you need more alerts, please contact us by email or phone.


What type of account can I obtain?
We provide monthly and annual plans for 4 alerts. We also provide an Enterprise plan with additional features. Alerts can be changed at any time and have no limits on the number of email notifications. You can change or cancel your plan at any time. If you change or cancel a subscription, we will refund any pro-rated amount remaining.

Can Enterprise plan users bulk upload alerts?
We do not currently allow for a direct bulk upload of alerts on the website. However, you can fill out this spreadsheet and email us with your alerts to be loaded.

If I forgot which account type I have, how do I verify the subscription?
Sign in and select the Account menu in the upper right. The Subscription tab can then be selected to view your details.

How will the subscription charges appear on my credit card statement?
Paid subscriptions will show as "STORMWATER FORECAST" on your credit card statement.

How do I describe the service to my organization?
The StormwaterForecast subscription provides automated notifications for specified locations based on the NWS precipitation forecasts. The email notification service provides information that may be useful or required for protecting stormwater quality.