Clear Sky Confidence
Know Before You Open
Multiple Models. Clear Answers. Confident Imaging.
“Data you can trust.
Skies you can enjoy.”
ECMWF IFS  ·  GFS Seamless  ·  HRRR CONUS
Dark Sky New Mexico · 31.9508, -108.8675 · America/Denver
Retrieved Oct 10, 7:29 PM. All three models were returned.
Night Sat Oct 10, 9:00 PM – Sun 6:00 AM
Verdict
Uncertain
Confidence
Trend
First Run
Clear at Opening
No
All-Night Clear
No
Expected Clear Hours
3.5 h
Longest Clear Window
2 h
Agreement
Moderate
Deterioration
1:00 AM
Hourly Forecast Details
Values are cloud cover percentages from each model.
●  Clear  ≤ 20%
●  Uncertain
●  Cloudy  ≥ 60%
Model values  =  Total, Low, Mid, High cloud %
T Total (all clouds)   L Low (near ground)   M Mid (mid-level)   H High (high altitude)
Example
7700
TLMH
Total 7%  ·  Low 7%  ·  Mid 0%  ·  High 0%
Time State Consensus
avg cloud %
 ECMWF GFS HRRR
TLMH TLMH TLMH
9:00 PM ●  Cloudy 99% 9809813100086100100086100
10:00 PM ●  Uncertain 45% 530524410641410641
11:00 PM ●  Clear 11% 6060130113130113
12:00 AM ●  Clear 0% 000000000000
1:00 AM ●  Cloudy 70% 10101000100010001000
2:00 AM ●  Clear 6% 000099009900
3:00 AM ●  Cloudy 62% 202088138808813880
4:00 AM ●  Cloudy 71% 202010010010001001001000
5:00 AM ●  Cloudy 71% 422010013561001001356100
Clear Nights
Clear nights since Jan 1: 156 of 282 nights
Average clear hours per night: 4.3 h
Updated Oct 10, 9:36 AM.
MonthClearNights
Jan1631
Feb1728
Mar2231
Apr1830
May2131
Jun1830
Jul931
Aug1531
Sep1130
Oct99

A clear night has 4 or more clear hours (they need not be in a row) while the Sun is below −18°, using the same hour rules as the forecast. These figures come from archived model data (ECMWF, GFS and HRRR forecasts from the Open-Meteo history archive), not from direct sky observations. Weather data by Open-Meteo.com (CC BY 4.0).

About the Models
ECMWF IFS
High-resolution global model. Excellent for the middle and later hours of the night.
GFS Seamless
Global model. Good general guidance when you want a second opinion on the whole night.
HRRR CONUS
High-resolution, short-range model. Best for near-term conditions over the continental US.

Tip.  Look for strong agreement — hours where the three models show similar numbers — before treating the night as settled.

RetrievedVerdictConfidenceAgreementTrendClear hoursWindowData
Oct 10, 7:29 PMUncertain64 ModerateFirst Run3.52 hcomplete
Oct 03, 8:02 PMClear95 StrongStable9.09 hcomplete
Oct 03, 8:01 PMClear95 StrongStable9.09 hcomplete
Oct 02, 7:29 PMClear95 StrongStable9.09 hcomplete
Oct 02, 7:27 PMClear95 StrongFirst Run9.09 hcomplete

Tonight does not support a confident clear-sky decision. GFS predicts total cloud around 1:00 AM. The longest continuous clear stretch is 2 hours, and about 3.5 clear hours are expected. Model agreement is moderate. This is the first saved run, so a trend is not available yet.

The verdict and confidence are calculated in the app. This explanation does not change them. Hour rules A clear hour needs consensus cloud at or below 20%, no scoring model above 25% total cloud, no scoring model above 40% high cloud, and at least 2 models reporting. A cloudy hour needs consensus cloud at or above 60%. Every other reported hour is Uncertain. A missing model is never filled in from another model. Night window Only hours with the Sun at or below -18° are scored. That is astronomical night. Expected clear hours count a clear hour as 1 and an uncertain hour as 0.5. Model weights Under 18 hours of lead time: HRRR 45%, ECMWF 30%, GFS 25%. From 18 to 36 hours: HRRR 35%, ECMWF 35%, GFS 30%. After 36 hours, HRRR stays on screen but drops out of the consensus. ECMWF is 55% and GFS is 45%. Weights are rescaled across the models that actually reported that hour. This run Dominant risk: GFS predicts total cloud around 1:00 AM. Data quality: complete. Missing models: none. Agreement: moderate. Trend: first run. Confidence steps Base for Uncertain: 58 Data complete: +6 Confidence 64

Summary cards are the decision. Verdict, confidence, and whether the opening and the whole night are clear stay in front. The icons match the words.

Colors mean the same thing everywhere. Green is Clear (consensus cloud at or below 20%, no model above 25% total cloud, and no model above 40% high cloud). Amber is Uncertain (the hour is reported, but it is not clearly clear or clearly cloudy). Red is Cloudy (consensus cloud at or above 60%).

Each model has four numbers. T is total cloud, all levels together. L is low cloud, near the ground. M is mid-level cloud. H is high cloud. A dash means that model did not report the hour. The blank is never filled from another model.

Consensus is the weighted average of the models that reported that hour. HRRR carries more weight in the next 18 hours. After 36 hours it stays on screen but drops out of the average.

Forecast History is earlier retrievals of this same site, so you can see whether the night is holding, improving, or deteriorating. Why This Verdict is the exact scoring for the night on screen.

Clear Sky Confidence

Version: 1.0.0 Build Date: October 2026 Guide Version: 1.0

Developed by erhAstro

Copyright © 2026 Eric Horton All Rights Reserved.

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Forecast Advisory

Clear Sky Confidence is an advisory forecasting tool only.

Forecast information is provided for planning and informational purposes and should not be relied upon as the sole basis for observatory operations, roof control, equipment protection, or safety decisions.

Users remain responsible for independently verifying weather conditions and maintaining appropriate safety systems.

Data Sources

Forecast data provided by Open-Meteo.

Weather model availability, accuracy, and forecast content are subject to change by the underlying data providers.

Documentation

Clear Sky Confidence User Guide

Guide Version: 1.0