Skip Navigation Links 
NOAA logo - Click to go to the NOAA home page National Weather Service   NWS logo - Click to go to the NWS home page
Climate Prediction Center

CPC Search
About Us
   Our Mission
   Who We Are

Contact Us
   CPC Information
   CPC Web Team

HOME > Outlooks > Monthly to Seasonal Outlooks > Probability of Exceedance Forecast > Outlooks for major Cities
Probability of Exceedance Banner
This experimental outlook product gives the probability that a temperature or precipitation quantity will be exceeded at the location in question, for the given season at the given lead time. The locations are one of 102 forecast divisions in the mainland U.S., or an individual station in other regions.
CPC Outlooks for Major U.S. Cities
Forecast Distribution File
File Names
cpcctytd.dat - Temperature Distribution file for most recent month
cpcctyhdd.dat - Heating degree day Distribution file for most recent month
cpcctycdd.dat - Cooling degree day Distribution file for most recent month

These tables give the climate outlook for 50 of the largest metropolitan areas in the U.S., with a few other cities included to provide even coverage. The tables give the forecast and climatological mean, and the exceedence threshold values for given probability levels. (98,95,90,80,70,60,50,40,30,20,10,5, and 2 percentile levels).The forecasts are for specific airport observation sites listed in the file: citydict.txt. Note that forecasts for Grand Rapids MI, Kansas City, MO, New Orleans, LA, Orlando FL, and Pittsburgh, PA, are for the metropolitan area averages, since the airport at these sites had data problems that prevented the derivation of a relationship between the CPC forecast division and the airport (Usually due to a change in airport location).

These data are derived from the outlooks issued monthly by CPC. Details of the relationships between each city and the CPC forecast division in which it resides, as well other information on the urban area temperatures can be found by following this link

The forecasts issued on a particular month are grouped together. There are 2 header records followed by multiple data records (Rows) per monthly forecast. Forecasts are for three month target seasons, defined by forecast issue time and lead.
The first line on the header record gives the month, day and year (mmdd yyyy) of forecast issue time, followed by the number of groups and the number of forecast locations in each group. The final number is a forecast type id flag. 950 is a number assigned to identify seasonal temperature forecasts, 962 identifies seasonal heating degree day forecasts, and 963 identifies cooling degree day forecasts.
The second header label gives column definitions. Each forecast issue time has its own 2 line header record.

Column: label: Definition
1-2: year mn Year and month number that the outlook was issued. 1=Jan, 2=Feb. Forecasts are issued around mid-month.
3: lead Approximate lead time of forecast in months - rounded upward, An actual lead time of about one-half month (the shortest lead on the outlook) is rounded to lead=1, for example. The valid target season can be found by adding lead months to the initial time listed in column 1 and 2, adjusting for year changes.
4: cd: The forecast location to which data apply. See citydict.txt for definitions.
5-17: 98,95,90,etc Values (Temperatures, or degree days) expected (Forecast) to be exceeded by the percent of time listed in the column label.
18: F mean: The forecast mean value for the target period.
19: C mean: The climatological mean value.

Data Set Use
These data are designed to be used in quantitative analysis of CPC forecasts. The forecasts are only estimates of the distribution implied by the long lead outlooks and are derived from the tercile probability anomalies (Forecasts for above, near, and below median). The distribution is most accurate in the vicinity of these tercile boundaries (33 and 66 percent probability of exceedence). Particular caution should be used in the interpretation probabilities below about 10% or above 90%.

This project is supported by Risk Prediction Initiative (

NOAA/ National Weather Service
National Centers for Environmental Prediction
Climate Prediction Center
5200 Auth Road
Camp Springs, Maryland 20746
Climate Prediction Center Web Team
Page last modified: December 12, 2002
Disclaimer Privacy Policy