SCP Product Tutorials

Page last updated: 3/23/2016

This tutorial page is aimed to give users a full understanding of how to interpret the probability numbers.

Universities:

For a university opening campus on any particular day, there are five possibilities:

- Campus is open all day
- Campus is closed all day
- Campus opens at normal time, but closes early
- Campus opens late, but closes at normal time
- Campus opens late and closes early

These five events are mutually exclusive, meaning two of these events could not happen simultaneously.  Picture this as a spinner on any board game; one event must occur, and only one event can occur.

A forecaster will issue separate probabilities for these five events (in increments of 5%), and these probabilities will always add up to 100%.  See this example:

 Campus Opening Campus Closing Probability Normal Time Normal Time 25% Normal Time Early 10% Late Normal Time 5% Late Early 0% Closed All Day - 60%

Also, since these events are mutually exclusive, the probability of either of any two events is equal to their sum.  In the example above, to get the probability of campus either being closed all day or opening late, add up all events that include a late opening or a full closing.  5 + 0 + 60 = 65%

School Districts:

For a district opening schools on any particular day, there are three possibilities:

- School opens at normal time
- School opens late
- School does not open

These three events are mutually exclusive, meaning two of these events could not happen simultaneously.  Therefore, a forecaster will issue separate probabilities for these three events (in increments of 5%), and these probabilities will always add up to 100%.  See this example:

 Probability of a FULL CLOSING 15% Probability of a DELAYED OPENING 45% Probability of a FULL CLOSING OR DELAYED OPENING 60% Probability of school opening at NORMAL TIME 40%

Also, since these events are mutually exclusive, the probability of either of any two events is equal to their sum.  In the example above, the probability of a delayed opening or a normal time opening would be 45% + 40% = 85%.  The probability of a full closing or a delayed opening would be 45% + 15% = 60% (this probability is explicitly displayed due to its practicality for planning purposes).

For a district closing schools on any particular day, there are four possibilities:

- School closes for the entire day
- School closes early, prior to the end of the school day
- School closes at the end of the school day, or sometime later prior to after-school activities being complete
- School remains open the entire day

The possibility of school closing for the entire day has already been accounted for in the first set of probabilities for school openings.  The probabilities in the second set are conditional probabilities based on the assumption that school will be open.  Thus, the three remaining events become mutually exclusive, with probabilities that will add up to 100%.  See this example:

 Probability of an EARLY CLOSING 15% Probability of a CLOSING AFTER SCHOOL 5% Probability of an EARLY CLOSING OR CLOSING AFTER SCHOOL 20% Probability of school opening remaining open ALL DAY 80%

This graphic illustrates the above example:

It is worth stressing that the second set (closing after school vs. early closing vs. no early closings) consists of conditional probabilities instead of absolute probabilities.  To obtain absolute probabilities, multiply the listed probabilities by the probability of ANY opening (using the sum of the probabilities of a normal opening and delayed opening).   Usually, however, the timing of weather events are clear enough to indicate whether school operations would be affected in the morning or afternoon hours, and only one of the two sets contain significant probabilities.

Violations

This section is mainly to clairify that we do not interfere with or impede official decision making.  However, please contact us immediately if you notice any violations as described in this section.

If mutually exclusive probabilities do not add up to 100%, or a number within a module is not rounded to a 5% increment, the forecaster has made an error.

The design of our products requires forecasters to be capable of inputting a 0% chance for an abnormal event, and a 100% chance for a normal event.  As indicated in our disclaimer, this implies that there are negligible (not truly zero) odds for one or all listed abnormal events.  However, forecasters are not permitted to imply 100% certainty for any abnormal event, unless that event has already been officially announced.  As a result, in any forecast product, a forecaster must indicate a minimum 5% chance for the normal event in that product, unless a decision has already been announced.

Examples:

 Probability of a FULL CLOSING 100% Probability of a DELAYED OPENING 0% Probability of a FULL CLOSING OR DELAYED OPENING 0% Probability of school opening at NORMAL TIME (normal event - 5% minimum) 0%

Unacceptable: forecaster indicated 100% certainty of a full closing.

 Campus Opening Campus Closing Probability Normal Time Normal Time (normal event - 5% minimum) 0% Normal Time Early 0% Late Normal Time 50% Late Early 0% Closed All Day - 50%

Unacceptable: forecaster indicated 100% certainty of either an early closing or closing all day.  (Note however that this would be acceptable if the campus already announced a delayed opening.)

 Probability of an EARLY CLOSING 0% Probability of a CLOSING AFTER SCHOOL 0% Probability of an EARLY CLOSING OR CLOSING AFTER SCHOOL 0% Probability of school opening remaining open ALL DAY  (normal event - 5% minimum) 100%

OK: forecaster is letting us know that closings are no longer anticipated, and further updates will not be provided.

We do not announce decisions regarding school closings or delays prior to an official public source announcing the decision, unless we are given explicit permission to do so.  This is rare, but does happen on occasion.  If you see a decision announced on School Closing Probabilities before you see the decision announced on an official source, you may assume we were given permission to post this information.  However, as implied in our disclaimer, this site is not meant to serve as a substitute and you are fully responsible for checking official school sites for information on closings and delays.

Definitions

For purposes of this site, terms are defined as follows:

Full Closing - School is closed (or classes are not in session) the entire day.
Delayed Opening - School opens at a time such that the standard school day (not counting before-school activities for districts) begins late.
Early Closing - School closes any earlier than the standard end of the school day (not counting after-school activities for districts).
Closing After School - School closes any time later than the standard end of the school day, disrupting any after-school activities, even if not immediately after school.  This term is only used for districts.
Evacuation - School was evacuated due to a non-weather emergency.  This definition is met regardless of whether or not school resumed normal operations the same day.

Starting forecasts

Forecasts are initiated for a particular day and school if both of the following criteria are met:

- The beginning of the school day that would be affected is within 48 hours
- There is a 5% probability or greater of a closing or delay

As of 2015, forecasts are occasionally initiated prior to the 48 hour mark if confidence is sufficently high

For purposes of this site, the beginning times of school days are as follows:

Three Village Central School District: 7:05 AM Eastern Time
Stony Brook University: 8:00 AM Eastern Time
Suffolk County Community College: 7:30 AM Eastern Time

Hazard types

Typically, the only types of closings and delays that can be predicted ahead of time are ones directly related to weather conditions.  There are three general types of significant weather that could affect normal school operations:

- Winter Weather: A heavy snowfall and/or ice accumulation.  This is the most common cause for closings and delays.
- Tropical Weather: A landfall or close pass of a hurricane or tropical storm.
- Severe Weather: This includes threats associated with thunderstorms; including tornadoes, hail, high winds, and flash flooding.  A coastal storm where the main threat is damaging winds (as opposed to snow) would fit this category.

In addition, significant weather can cause power outages, structural damage, treacherous roads, and other lasting effects that could take time to clean up, well after the significant weather is over.  Post-storm cleanup is always accounted for in forecasts, as well as the decision to initiate forecasts for a particular day.  If there is a possibility of closings or delays on a day without significant weather, but significant remaining impacts from a previous weather event (eg. a hurricane knocking out power, a snowstorm leaving 2 feet of snow on roads), the label "impact recovery" will be added to the hazard tag.

Updating forecasts

In the event of a major change in anticipated weather conditions (for example, expected snowfall total increases from 3 inches to 12 inches), the probabilities will update rather quickly.  Otherwise, probabilities are actively re-assessed several times per day.  However, the products are not updated unless it is necessary to make a change in the numbers.  That is - if it is midnight and probabilities have not been updated since 10 am that morning, that does not mean the probabilities were being ignored throughout the day.  More likely, the forecaster feels that the probabilities issued that morning still hold.

Probabilities can continue to update even after a decision is made, but only for upgraded events.  For example, if a school announces a delayed opening, but the forecaster feels that conditions may pan out worse than expected and actually warrant a full closing, probabilities will continue to update for the probability of a delayed opening vs. full closing.  This is the one exception to the rule where a 5% minimum is required for the normal event, since an abnormal event has already been announced.  However, the forecaster must retain at least a 5% chance for the event announced by school authority (in this example, a delayed opening).

Updating forecasts after the school day starts

Once a school day has begun, if there is a possibility of early closings, probabilities may continue to update under fewer mutually exclusive possibilities.

For a university, there are two mutually exclusive possibilities:

- Classes end at normal time
- Classes end early

For a school district, there are three mutually exclusive possibilities:

- School remains open all day
- School buildings close early, affecting some or all after-school activities, but not the normal school day
- School closes early, prior to the end of the normal school day

Under these circumstances, probabilities are actively re-assessed every 1-2 hours, and updated as needed.

Archives

An archive of every forecast and school impact event since the start of this service (September 2010) is available under the archive links on the side panel.

For the purpose of keeping track of weather conditions that impact school activities, we also provide data on the storm that impacted the area, when available.  The storm totals provided are very specific to the Three Village area, and gathered from multiple Skywarn Spotters from villages in and near Three Village.  SCP estimates the following storm data:

Snowfall Total: The amount of snow that accumulated during an entire storm.  Rounded to 0.1" increments.

Rainfall Total: The amount of rain that fell during an entire storm.  Rounded to 0.01" increments.

Ice Total: The amount of freezing rain or ice that accumulated during an entire storm.  Rounded to 0.01" increments.

Peak Gusts: The gusts that were occurring during the windiest part of the storm.  Rounded to 5 mph increments.

Skywarn Spotter reports can be viewed online at http://www.erh.noaa.gov/okx/stormtotals.html