Probabilistic Decision Support

Overview

The probabilistic products are intended to provide a range of possibilities. This complements the existing NWS forecast in order to better communicate forecast uncertainties before and during weather events. For example, you may see your local forecast saying low temperature of 34°F. This is the official NWS forecast, but there is still uncertainty. The probabilistic information can help you understand more about this uncertainty to make informed decisions. This range of possibilities is important to consider when planning and making your decisions. For example, if the forecast low temperature for your location is 34°F, but there is still a possibility you could see a low of 30°F, then you may want to consider preparing to protect tender vegetation for a possible freeze. Traditional forecasts have only given a single forecast for temperature and precipitation, though they can change from day to day as the event approaches. The goal of this page is to provide the "Goal Posts", or range of possibilities for a specific event which we hope enables better decision-making. Another way to look at it for temperatures is we want to be able to say, "You can expect temperatures to be at least" - "This is the most likely temperature" - "You may want to prepare for the potential of this temperature". Graphics shown on this page are the official NWS forecast as well as those generated/derived from the NWS National Blend of Models (NBM) version 4.1. They are broken down into three parts: Expected - these are the official NWS Forecast temperatures and rainfall. Percentile - these graphics are generated/derived from the NWS NBM and represent the 10% and 90% percentiles for the temperature and rainfall. They depict the coolest/warmest possible temperatures and least/greatest possible rainfall amounts. Probability of Exceedance - these graphics are generated/derived from the NWS NBM and represent the probability that the temperature will exceed a certain value. Click on an image below for an interpretation of the different types of graphics. Expected Temp (Forecast) 90% Percentile Temp (High End) 10% Percentile Temp (Low End) Probability of Exceedance Expected Rain (Forecast) 90% Percentile Rain (High End) 10% Percentile Rain (Low End)   The graphics on these pages are updated at least twice per day, shortly after 3 AM EST/4 AM EDT and 3 PM EST/4 PM EDT. More detailed information about the NWS National Blend of Models (NBM) can be found here.

Expected High Temperature (°F)

These maps are the official NWS high temperature forecast in degrees Fahrenheit during the time period shown on the graphic. These high temperatures are determined by NWS forecasters to be the most likely outcome based on evaluation of data from computer models, satellite, radar, and other observations.

Day 1	Day 2	Day 3	Day 4
Day 5	Day 6	Day 7

Warmest Possible High Temperature (°F)

These maps depict a reasonable upper-end high temperature for the time period shown on the graphic, based on many computer model simulations of possible high temperatures. These higher temperatures are an unlikely scenario, with only a 1 in 10, or 10% chance that a temperature higher than this will occur, and a 9 in 10, or 90% chance that the temperatures will be lower. These temperatures can help serve as an upper-end scenario for planning purposes.

Day 1	Day 2	Day 3	Day 4
Day 5	Day 6	Day 7

Coolest Possible High Temperature (°F)

These maps depict a reasonable lower-end high temperature for the time period shown on the graphic, based on many computer model simulations of possible high temperatures. These lower temperatures are an unlikely scenario, with a 9 in 10, or 90% chance that a higher temperature will occur, and only a 1 in 10, or 10% chance that the temperatures will be lower. These temperatures can help serve as a lower-end scenario for planning purposes.

Day 1	Day 2	Day 3	Day 4
Day 5	Day 6	Day 7

Expected Low Temperature (°F)

These maps are the official NWS low temperature forecast in degrees Fahrenheit during the time period shown on the graphic. These low temperatures are determined by NWS forecasters to be the most likely outcome based on evaluation of data from computer models, satellite, radar, and other observations.

Night 1	Night 2	Night 3	Night 4
Night 5	Night 6	Night 7

Warmest Possible Low Temperature (°F)

These maps depict a reasonable upper-end low temperature for the time period shown on the graphic, based on many computer model simulations of possible low temperatures. These higher temperatures are an unlikely scenario, with only a 1 in 10, or 10% chance that a temperature higher than this will occur, and a 9 in 10, or 90% chance that the temperatures will be lower. These temperatures can help serve as an upper-end scenario for planning purposes.

Night 1	Night 2	Night 3	Night 4
Night 5	Night 6	Night 7

Coolest Possible Low Temperature (°F)

These maps depict a reasonable lower-end low temperature for the time period shown on the graphic, based on many computer model simulations of possible low temperatures. These lower temperatures are an unlikely scenario, with a 9 in 10, or 90% chance that a higher temperature will occur, and only a 1 in 10, or 10% chance that the temperatures will be lower. These temperatures can help serve as a lower-end scenario for planning purposes.

Night 1	Night 2	Night 3	Night 4
Night 5	Night 6	Night 7

Probability of Temperatures 90°F or greater

These maps represent the likelihood of the temperature meeting or exceeding 90°F for the time period shown on the graphic.

Day 1	Day 2	Day 3	Day 4
Day 5	Day 6	Day 7

Probability of Temperatures 100°F or greater

These maps represent the likelihood of the temperature meeting or exceeding 100°F for the time period shown on the graphic.

Day 1	Day 2	Day 3	Day 4
Day 5	Day 6	Day 7

Probability of Temperatures 32°F or less

These maps represent the likelihood of the temperature falling to or below 32°F for the time period shown on the graphic.

Night 1	Night 2	Night 3	Night 4
Night 5	Night 6	Night 7

Probability of Temperatures Below 28°F

These maps represent the likelihood of the temperature falling below 28°F for the time period shown on the graphic.

Night 1	Night 2	Night 3	Night 4
Night 5	Night 6	Night 7

Expected 12 Hour Rainfall (in.)

These maps are the official NWS rainfall forecast in inches during the time period shown on the graphic. These rainfall amounts are determined by NWS forecasters to be the most likely outcome based on evaluation of data from computer models, satellite, radar, and other observations.

Day 1	Night 1	Day 2	Night 2
Day 3	Night 3	Day 4	Night 4
Day 5	Night 5	Day 6	Night 6
Day 7	Night 7

Greatest 12 Hour Possible Rainfall (in.)

These maps depict a reasonable upper-end rainfall amount for the time period shown on the graphic, based on many computer model simulations of possible rainfall totals. These higher amounts are an unlikely scenario, with only a 1 in 10, or 10% chance that more rain will fall, and a 9 in 10, or 90% chance that less rain will fall. These amounts can help serve as an upper-end scenario for planning purposes.

Day 1	Night 1	Day 2	Night 2
Day 3	Night 3	Day 4	Night 4
Day 5	Night 5	Day 6	Night 6
Day 7	Night 7

Least Possible 12 Hour Rainfall (in.)

These maps depict a reasonable lower-end rainfall amount for the time period shown on the graphic, based on many computer model simulations of possible rainfall totals. These lower amounts are an unlikely scenario, with a 9 in 10, or 90% chance that more rain will fall, and only a 1 in 10, or 10% chance that less rain will fall. These amounts can help serve as a lower-end scenario for planning purposes. On many occasions these graphics will be blank, which depicts that the low end is for no measurable rainfall.

Day 1	Night 1	Day 2	Night 2
Day 3	Night 3	Day 4	Night 4
Day 5	Night 5	Day 6	Night 6
Day 7	Night 7

Expected 24 Hour Rainfall (in.)

These maps are the official NWS rainfall forecast in inches during the time period shown on the graphic. These rainfall amounts are determined by NWS forecasters to be the most likely outcome based on evaluation of data from computer models, satellite, radar, and other observations.

Day 1	Day 2	Day 3	Day 4
Day 5	Day 6	Day 7

Greatest 24 Hour Possible Rainfall (in.)

These maps depict a reasonable upper-end rainfall amount for the time period shown on the graphic, based on many computer model simulations of possible rainfall totals. These higher amounts are an unlikely scenario, with only a 1 in 10, or 10% chance that more rain will fall, and a 9 in 10, or 90% chance that less rain will fall. These amounts can help serve as an upper-end scenario for planning purposes.

Day 1	Day 2	Day 3	Day 4
Day 5	Day 6	Day 7

Least Possible 24 Hour Rainfall (in.)

These maps depict a reasonable lower-end rainfall amount for the time period shown on the graphic, based on many computer model simulations of possible rainfall totals. These lower amounts are an unlikely scenario, with a 9 in 10, or 90% chance that more rain will fall, and only a 1 in 10, or 10% chance that less rain will fall. These amounts can help serve as a lower-end scenario for planning purposes. On many occasions these graphics will be blank, which depicts that the low end is for no measurable rainfall.

Day 1	Day 2	Day 3	Day 4
Day 5	Day 6	Day 7

Expected Rainfall (in.)

These maps are the official NWS rainfall forecast in inches during the time period shown on the graphic. These rainfall amounts are determined by NWS forecasters to be the most likely outcome based on evaluation of data from computer models, satellite, radar, and other observations.

Day 1-2	Day 1-3	Day 1-5	Day 1-7
Day 2-3	Day 3-4	Day 4-5	Day 6-7

Greatest Possible Rainfall (in.)

These maps depict a reasonable upper-end rainfall amount for the time period shown on the graphic, based on many computer model simulations of possible rainfall totals. These higher amounts are an unlikely scenario, with only a 1 in 10, or 10% chance that more rain will fall, and a 9 in 10, or 90% chance that less rain will fall. These amounts can help serve as an upper-end scenario for planning purposes.

Day 1-2	Day 1-3	Day 1-5	Day 1-7
Day 2-3	Day 3-4	Day 4-5	Day 6-7

Least Possible Rainfall (in.)

These maps depict a reasonable lower-end rainfall amount for the time period shown on the graphic, based on many computer model simulations of possible rainfall totals. These lower amounts are an unlikely scenario, with a 9 in 10, or 90% chance that more rain will fall, and only a 1 in 10, or 10% chance that less rain will fall. These amounts can help serve as a lower-end scenario for planning purposes. On many occasions these graphics will be blank, which depicts that the low end is for no measurable rainfall.

Day 1-2	Day 1-3	Day 1-5	Day 1-7
Day 2-3	Day 3-4	Day 4-5	Day 6-7