
Iowa Forecast Contest 201112 Contest Rules
 Forecast Calendar
The contest will consist of 20 twoweek and oneweek periods over a
year, with the final period as the yearend tournament. Each twoweek
period will consist of 4 forecasts per week (Monday through Thursday),
for a total of 8 forecasts per period. Each oneweek period will
consist of 8 forecasts per week (two each day Monday through Thursday).
Forecasters must complete at least 12 of the 20 regularseason
periods to have their cumulative score count in the final standings. Forecasters' top 15
period scores will count toward the final overall score, so forecasters who
participate in more than 15 periods will have some of their worst scores
dropped from cosideration. Tournament eligibility for forecasters
who complete fewer than 12 periods will be determined by the
chairperson.
In each period,
forecasters must submit at least 6 of the 8 forecasts in the period to
have their forecasts counted for that period. In a twoweek period, this
would require forecasts on 6 of the 8 days. In a oneweek period,
forecasters must submit a forecast on at least 3 of the 4 days in the
period.
 Forecast Horizon and Interval
The forecast day will consist of a different forecast horizon,
ranging from Day 1 to Day 7, that will change from period to period and
potentially from day to day within a period. Temperature and
precipitation forecasts will consist
of a daytime period and a nighttime period. Aviation forecasts will
cover only a single period.
 For precipitation forecasts, the nighttime interval runs from
0000 to 1200 UTC. The daytime interval runs from 1200 to
0000 UTC.
 For temperature forecasts, the nighttime interval will consist of
the minimum temperature between 0100 and 1400 UTC. The daytime interval
will consist of the maximum temperature between 1300 and
0100 UTC.
 For aviation forecasts, the forecast interval will run from
0300 to 1800 UTC.
 Elements of the Forecast
The forecast will consist of two distinct types of forecast elements. The
majority of forecasts will be made for the basic public elements of
temperature and precipitation. A minority of forecasts will be made for
the basic aviation elements of wind, ceiling height, and visibility.
For the public forecast, depending on the time period the forecast is
for, the following elements may be forecast:
 The nighttime minimum and daytime maximum temperatures to the nearest
whole degree Fahrenheit
 The categorized probability of precipitation (POP)
POP categories are
Category 
Probability 
Category 
Probability 
0 
0% to 4% 
6 
55% to 64% 
1 
5% to 14% 
7 
65% to 74% 
2 
15% to 24% 
8 
75% to 84% 
3 
25% to 34% 
9 
85% to 94% 
4 
35% to 44% 
10 
95% to 100% 
5 
45% to 54% 


 The categorized quantitative precipitation forecast (QPF)
QPF categories are:
Category 
Precipitation 
Category 
Precipitation 
0 
0.00 in. or trace 
4 
0.50 in. to 0.99 in. 
1 
0.01 in. to 0.09 in. 
5 
1.00 in. to 1.99 in. 
2 
0.10 in. to 0.24 in. 
6 
≥ 2.00 in. 
3 
0.25 in. to 0.49 in. 


 The categorized amount of quantitative snowfall forecast (QSF).
QSF categories are:
Category 
Snowfall 
Category 
Snowfall 
0 
0.0 in. or trace 
3 
4.0 in. to 5.9 in. 
1 
0.1 in. to 1.9 in. 
4 
6.0 in. to 7.9 in. 
2 
2.1 in. to 3.9 in. 
5 
≥ 8.0 in. 
For the aviation forecast, the following elements will be forecast:
 The categorized highest sustained wind speed (HWS)
HWS categories are:
Category 
Wind Speed 
Category 
Wind Speed 
1 
0 kt. to 3 kt. 
5 
16 kt. to 19 kt. 
2 
4 kt. to 7 kt. 
6 
20 kt. to 23 kt. 
3 
8 kt. to 11 kt. 
7 
24 kt. to 27 kt. 
4 
12 kt. to 15 kt. 
8 
≥ 28 kt. 
 The categorized lowest reported prevailing ceiling (LRC)
LRC categories are:
Category 
Ceiling 
Category 
Ceiling 
1 
< 200 ft. 
5 
2000 ft. to 3000 ft. 
2 
200 ft. to 400 ft. 
6 
3100 ft. to 6500 ft. 
3 
500 ft. to 900 ft. 
7 
6600 ft. to 12000 ft. 
4 
1000 ft. to 1900 ft. 
8 
> 12000 ft. or no ceiling 
 The categorized lowest reported prevailing visibility (LRV)
LRV categories are:
Category 
Visibility 
Category 
Visibility 
1 
< 0.5 mi. 
5 
3.0 mi. to 5.4 mi. 
2 
0.5 mi. to 0.9 mi. 
6 
5.5 mi. to 6.4 mi. 
3 
1.0 mi. to 1.9 mi. 
7 
≥ 6.5 mi. 
4 
2.0 mi. to 2.9 mi. 


 Submission of Forecasts
Forecasts must be submitted to the chairperson by 2330 UTC using
the form on the contest website or email. There is a fiveminute grace
period for forecasts submitted by email after the deadline. Forecasts
submitted after 2335 UTC will be accepted at the discretion of the
chairperson.
 Failure to Forecast
Forecasters who do not make a forecast will be assigned consensus MOS
values and will be charged with absences as outlined in Rule 1.
 Occasional Planned Absences
If a forecaster knows in advance that he or she cannot forecast for the
next day (or days), two options are available:
 The forecaster may do nothing, and take consensus MOS as a forecast.
 The forecaster may make a planned guidancebased forecast. This option
requires an email to the chairperson, stating which numerical guidance (or
combination) to use and for which days the guidance will be used.
Either option will count toward the absence total for the period, and
eligibility for the period will be evaluated according to Rule 1.
 Computer Model Guidance Forecasters
Values for relevant model output statistics from the latest runs will be
entered by the chairperson or designee. The guidance that will be used
includes
 GFS MOS (MAV)
 GFS Extended MOS (MEX)
 Consensus GFS Ensemble MOS (MEC)
 Eta MOS (MET)
 Consensus MOS (CMO)
Since the MOS output may not directly correspond with the forecast horizon
and/or forecast elements for some periods, the MOS will be required to
optout of certain periods.
MAV and MET will forecast in all periods through day 2.5.
The MEX and MEC will not forecast in the
aviation forecast periods.
CMO will be the average of all eligible MOS forecasts rounded
to the same precision.
 National Weather Service Forecaster
The NWS official forecasts issued through 2340 UTC will be entered by
the chairperson or designee. The Point Forecast Matrix (PFM) will be
used for the temperature, POP, QPF, and QSF elements. The
Terminal Aerodrome Forecast (TAF) will be used for LRC and LRV elements.
The highest wind speed value
in either the PFM or TAF will be used for the HWS element.
 Average Forecast
The average of all human and guidance forecasts for each day, interval,
and element will be computed to the same precision as the individual
forecasts. This average forecast will serve as the baseline for scoring, as
outlined in Rule 11.
 Verification
All elements (except for snowfall) will be verified using the official
METAR reports produced at the forecast site. For snowfall,
National Weather Service cooperative observations for the site will be used.
Temperatures will be verified based on the sixhour maximum and minimum
temperature reported at standard synoptic observation times. Since the
forecast interval does not exactly match the 6 hour blocks, the
chairperson shall make a reasonable judgment based on hourly observations
and sixhour reports as necessary.
POP will be verified as either 0% or 100%. If at least 0.01 in. of
precipitation falls during the forecast interval, 100% POP will verify.
For both automated and manual sites, the 6 hour precipitation and snowfall
accumulation at standard synoptic observation times will be used for QPF
and QSF.
Both POP and QPF will be verified using the automated report during
rainfall events. When snow and/or sleet is reported at anytime by the
automated weather identifier during the time period, the NWS cooperative
observer site for will be used.
The HWS will be verified from the highest sustained wind speed reported
in the forecast interval. This does not apply to wind gusts or the peak wind
gust. Both hourly and special observations will be used for verification.
The LRC and LRV will be verified based on any observations (hourly or
special) reported in the forecast interval. However, if a variable ceiling
or visibility is reported in remarks, and this value is lower than any
nonvariable ceiling or visibility, the variable range will not be used.
Only the prevailing lowest reported ceiling or visibility will be
used.
In the event of failure with any of the automated equipment, maintenance
performed on the site sensors, any missing observations, or any value
deemed unrepresentative of what actually occurred, the chairperson shall
perform a reasonable decision regarding the parameter in question based on
the nearest weather data available. Questionable parameters will be
discussed via email with forecast participants, along with the
reasoning that necessitated the change. Any objection to a change should be
voiced or written via email to the chairperson.
 Scoring of Daily Forecasts
Raw forecast scores will be computed as the square of the difference
between a forecast and the verification value for each element and forecast
interval. Temperature errors will be capped at 15°. The sum of these raw square errors will be tabulated for each
combination of element and interval for each period. The raw scores for
each element and interval will be normalized according to Rule 12.
 Normalized Scores
An attempt will be made to adjust for any differences in difficulty
between different periods and elements by obtaining normalized scores. A
normalized score will be computed for each combination of forecast
element and interval. The normalization procedure is
 The standard deviation s of the raw squared errors of all
forecasters is computed.
 A forecaster's normalized score Z is computed according to the
formula
where X is the forecaster's raw squared error, Avg is the
raw squared error for the Average forecast, as defined in Rule 9, and
S is the standard deviation of all squared errors.
Each forecaster's normalized scores within a period are averaged to
give the normalized score for the period. The average of the
period averages gives the overall normalized score for the contest.
 YearEnd Tournament
The yearend tournament will follow the final (20th) period of the
contest. The tournament will consist of headtohead battles between two
forecasters. The winner will be determined by the better normalized score
during the round. Seeding is based on the final regular season cumulative
normalized score. The bracket and schedule will be drawn once the final list
of eligible forecasters is available. 
