Idaho Falls
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Idaho Falls clear sky chart from 2005-11-06 to 2025-07-06.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	7% 8% 3 6% 4 4 4 3 5% 6% 50%	123644
	Night	8% 10% 3 7% 4 4 4 3 5% 7% 45%	124030
Transparency	Day	35% 5% 10% 21% 19% 10%	123394
	Night	39% 5% 12% 20% 16% 8%	123866
Seeing	Day	12% 11% 25% 28% 18% 5%	16168
	Night	13% 7% 23% 37% 18% 2	25783

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	11% 22% 7% 10% 5% 5% 4 3 5% 6% 21%	3547
	11th to 20th	Day	8% 14% 7% 14% 7% 5% 4 3 3 5% 31%	3756
	21st to end	Day	11% 14% 5% 10% 4 3 3 3 4 5% 37%	4510
February	1st to 10th	Day	10% 16% 5% 13% 7% 5% 5% 4 5% 5% 26%	1800
	11th to 20th	Day	11% 14% 5% 10% 6% 5% 5% 4 6% 7% 27%	1772
	21st to end	Day	7% 13% 5% 10% 6% 4 4 4 6% 7% 33%	1650
March	1st to 10th	Day	8% 12% 5% 10% 5% 5% 4 4 5% 7% 35%	4753
	11th to 20th	Day	6% 13% 3 7% 5% 5% 5% 3 4 7% 43%	5000
	21st to end	Day	8% 13% 5% 10% 6% 6% 6% 5% 6% 7% 29%	5486
April	1st to 10th	Day	9% 11% 3 7% 5% 4 5% 4 7% 7% 38%	2271
	11th to 20th	Day	6% 10% 3 7% 4 4 4 4 5% 7% 45%	2567
	21st to end	Day	8% 9% 3 7% 5% 5% 5% 4 6% 8% 40%	2600
May	1st to 10th	Day	7% 8% 2 5% 3 3 4 3 5% 7% 52%	5880
	11th to 20th	Day	7% 6% 2 6% 4 5% 5% 4 6% 8% 47%	5841
	21st to end	Day	6% 6% 2 4 3 3 3 3 5% 6% 58%	6835
June	1st to 10th	Day	7% 5% 2 5% 4 4 5% 5% 7% 8% 50%	2929
	11th to 20th	Day	6% 5% 2 5% 4 3 3 4 5% 7% 55%	3000
	21st to end	Day	2 2 1 3 3 2 3 2 5% 6% 71%	3000
July	1st to 10th	Day	1 2 1 2 2 2 2 2 4 5% 77%	4758
	11th to 20th	Day	1 2 1 3 2 3 3 3 5% 6% 72%	4394
	21st to end	Day	2 3 1 4 3 3 3 3 4 6% 67%	4454
August	1st to 10th	Day	4 3 1 4 3 4 4 4 6% 7% 61%	4092
	11th to 20th	Day	2 2 1 2 3 3 3 3 4 7% 70%	4028
	21st to end	Day	2 2 1 2 2 2 3 3 4 6% 72%	4521
September	1st to 10th	Day	4 3 1 3 2 2 2 2 4 6% 71%	2203
	11th to 20th	Day	6% 4 1 3 3 3 3 3 5% 7% 63%	2090
	21st to end	Day	6% 3 1 3 3 2 3 2 5% 6% 65%	2090
October	1st to 10th	Day	6% 4 2 4 2 3 3 2 3 3 67%	3310
	11th to 20th	Day	5% 5% 2 5% 3 4 3 2 4 6% 62%	3150
	21st to end	Day	8% 8% 3 7% 4 4 4 4 6% 7% 46%	3286
November	1st to 10th	Day	12% 11% 3 6% 4 4 4 3 5% 6% 43%	1764
	11th to 20th	Day	10% 11% 3 6% 4 5% 4 4 7% 7% 39%	1678
	21st to end	Day	9% 13% 5% 8% 4 4 4 3 5% 5% 40%	1600
December	1st to 10th	Day	7% 9% 4 10% 4 2 2 3 5% 6% 48%	2620
	11th to 20th	Day	13% 18% 6% 11% 7% 5% 5% 4 5% 6% 21%	2911
	21st to end	Day	14% 16% 5% 10% 5% 4 5% 4 5% 7% 25%	3498
January	1st to 10th	Night	10% 17% 6% 14% 5% 5% 4 3 5% 8% 24%	6426
	11th to 20th	Night	12% 18% 6% 14% 5% 3 3 3 5% 7% 24%	6205
	21st to end	Night	12% 15% 4 7% 4 3 3 2 4 7% 38%	6468
February	1st to 10th	Night	12% 16% 4 10% 5% 4 4 5% 6% 7% 28%	2600
	11th to 20th	Night	13% 15% 4 9% 5% 4 4 2 5% 7% 33%	2512
	21st to end	Night	8% 13% 5% 12% 6% 5% 5% 5% 6% 7% 29%	1980
March	1st to 10th	Night	7% 14% 4 8% 5% 5% 4 4 6% 7% 36%	5140
	11th to 20th	Night	5% 9% 3 7% 5% 4 5% 3 6% 9% 43%	5000
	21st to end	Night	7% 10% 3 8% 5% 5% 5% 5% 7% 9% 37%	5489
April	1st to 10th	Night	9% 10% 3 7% 5% 4 4 4 7% 7% 40%	2125
	11th to 20th	Night	7% 11% 3 8% 5% 5% 4 4 5% 6% 43%	1781
	21st to end	Night	9% 8% 2 6% 5% 4 4 3 6% 6% 47%	1800
May	1st to 10th	Night	9% 9% 3 6% 4 3 3 3 5% 6% 48%	4100
	11th to 20th	Night	7% 5% 2 6% 4 5% 5% 4 7% 8% 48%	4074
	21st to end	Night	6% 5% 2 5% 4 4 5% 4 6% 9% 52%	4062
June	1st to 10th	Night	6% 4 1 5% 5% 4 4 5% 6% 9% 50%	1467
	11th to 20th	Night	7% 5% 1 5% 3 5% 3 3 6% 7% 55%	1400
	21st to end	Night	3 3 1 4 2 2 3 2 4 7% 70%	1400
July	1st to 10th	Night	3 2 1 2 2 3 3 3 4 6% 72%	2309
	11th to 20th	Night	1 1 1 2 3 4 3 3 5% 8% 70%	2565
	21st to end	Night	1 2 1 3 3 3 4 4 6% 8% 65%	3109
August	1st to 10th	Night	3 3 1 3 3 3 4 3 7% 8% 62%	2847
	11th to 20th	Night	2 2 1 3 4 3 4 4 5% 7% 65%	2811
	21st to end	Night	3 3 1 3 3 2 3 2 3 5% 73%	3146
September	1st to 10th	Night	4 3 1 3 2 3 3 3 4 5% 69%	1973
	11th to 20th	Night	6% 4 1 4 3 4 4 3 5% 7% 60%	2090
	21st to end	Night	7% 4 1 3 2 3 3 2 5% 5% 65%	2090
October	1st to 10th	Night	5% 3 1 3 2 2 3 2 3 5% 70%	3663
	11th to 20th	Night	9% 6% 2 5% 3 3 4 3 4 4 56%	3778
	21st to end	Night	7% 8% 3 6% 4 4 4 3 6% 7% 47%	4271
November	1st to 10th	Night	11% 9% 2 5% 4 3 5% 3 5% 7% 45%	2535
	11th to 20th	Night	10% 11% 3 6% 5% 4 4 4 5% 6% 39%	2700
	21st to end	Night	9% 11% 4 8% 5% 4 4 4 5% 7% 40%	2800
December	1st to 10th	Night	7% 11% 3 7% 5% 4 3 3 5% 7% 46%	4570
	11th to 20th	Night	12% 16% 5% 9% 5% 5% 4 4 6% 7% 27%	5286
	21st to end	Night	14% 15% 5% 11% 5% 5% 5% 4 5% 6% 25%	7458

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	62% 9% 11% 14% 4	3547
	11th to 20th	Day	56% 6% 15% 13% 7% 3	3756
	21st to end	Day	50% 7% 11% 21% 10% 1	4510
February	1st to 10th	Day	59% 8% 11% 16% 4 1	1800
	11th to 20th	Day	54% 9% 15% 16% 6% 1	1781
	21st to end	Day	52% 8% 14% 17% 9% 1	1650
March	1st to 10th	Day	47% 6% 14% 21% 10% 3	4753
	11th to 20th	Day	42% 5% 9% 31% 12% 1	5000
	21st to end	Day	52% 10% 15% 19% 4	5486
April	1st to 10th	Day	44% 8% 15% 18% 13% 2	2271
	11th to 20th	Day	39% 6% 11% 26% 15% 3	2570
	21st to end	Day	41% 7% 11% 25% 15% 1	2600
May	1st to 10th	Day	31% 5% 11% 25% 23% 5%	5880
	11th to 20th	Day	34% 6% 9% 27% 20% 5%	5844
	21st to end	Day	26% 6% 8% 35% 22% 3	6836
June	1st to 10th	Day	30% 6% 12% 30% 20% 1	2929
	11th to 20th	Day	28% 5% 10% 22% 23% 11%	3000
	21st to end	Day	15% 4 6% 22% 37% 18%	3000
July	1st to 10th	Day	11% 2 4 10% 27% 46%	4685
	11th to 20th	Day	15% 2 4 9% 25% 46%	4319
	21st to end	Day	18% 3 4 12% 32% 31%	4314
August	1st to 10th	Day	22% 3 5% 14% 29% 26%	4078
	11th to 20th	Day	15% 3 5% 19% 38% 20%	4067
	21st to end	Day	14% 3 4 20% 30% 28%	4520
September	1st to 10th	Day	17% 3 7% 17% 33% 23%	2203
	11th to 20th	Day	23% 5% 8% 24% 28% 13%	2090
	21st to end	Day	22% 4 7% 27% 30% 9%	2090
October	1st to 10th	Day	24% 3 6% 20% 34% 13%	3310
	11th to 20th	Day	26% 3 9% 37% 19% 6%	3150
	21st to end	Day	37% 5% 13% 27% 17% 1	3286
November	1st to 10th	Day	44% 6% 16% 22% 12% 1	1764
	11th to 20th	Day	43% 7% 18% 22% 7% 2	1678
	21st to end	Day	46% 5% 18% 21% 9% 2	1600
December	1st to 10th	Day	38% 7% 24% 26% 4 1	2620
	11th to 20th	Day	64% 7% 14% 13% 3	2909
	21st to end	Day	58% 7% 15% 13% 7%	3498
January	1st to 10th	Night	58% 7% 14% 16% 5%	6426
	11th to 20th	Night	60% 6% 14% 15% 4 2	6205
	21st to end	Night	46% 7% 14% 20% 10% 2	6468
February	1st to 10th	Night	54% 9% 14% 16% 7% 1	2600
	11th to 20th	Night	52% 6% 14% 18% 9% 1	2513
	21st to end	Night	53% 7% 14% 17% 7% 2	1980
March	1st to 10th	Night	44% 6% 15% 21% 11% 2	5140
	11th to 20th	Night	37% 5% 13% 27% 17% 1	5000
	21st to end	Night	41% 8% 16% 27% 7%	5489
April	1st to 10th	Night	42% 7% 13% 20% 14% 3	2125
	11th to 20th	Night	40% 5% 13% 23% 16% 2	1781
	21st to end	Night	37% 6% 12% 26% 18% 1	1800
May	1st to 10th	Night	35% 5% 11% 22% 24% 4	4097
	11th to 20th	Night	30% 6% 11% 28% 20% 5%	4075
	21st to end	Night	26% 5% 10% 26% 28% 5%	4062
June	1st to 10th	Night	30% 8% 12% 23% 25% 3	1467
	11th to 20th	Night	27% 5% 11% 19% 27% 12%	1400
	21st to end	Night	17% 3 6% 17% 31% 26%	1400
July	1st to 10th	Night	15% 2 5% 10% 23% 46%	2273
	11th to 20th	Night	14% 1 4 10% 22% 49%	2517
	21st to end	Night	16% 3 5% 12% 29% 34%	3011
August	1st to 10th	Night	19% 3 5% 11% 29% 32%	2838
	11th to 20th	Night	18% 3 5% 18% 32% 24%	2838
	21st to end	Night	16% 3 5% 16% 28% 32%	3146
September	1st to 10th	Night	18% 4 5% 11% 31% 30%	1973
	11th to 20th	Night	24% 5% 8% 21% 25% 17%	2090
	21st to end	Night	23% 3 7% 23% 32% 11%	2090
October	1st to 10th	Night	19% 2 7% 19% 37% 16%	3663
	11th to 20th	Night	33% 2 6% 33% 18% 7%	3778
	21st to end	Night	37% 5% 11% 28% 18% 2	4271
November	1st to 10th	Night	39% 7% 13% 25% 14% 2	2535
	11th to 20th	Night	45% 6% 16% 23% 9% 2	2700
	21st to end	Night	45% 5% 18% 22% 10% 1	2800
December	1st to 10th	Night	39% 6% 26% 24% 5% 1	4570
	11th to 20th	Night	56% 8% 21% 13% 3	5287
	21st to end	Night	58% 6% 14% 13% 7% 1	7458

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	24% 14% 20% 26% 13% 5%	200
	11th to 20th	Day	18% 7% 26% 28% 19% 2	226
	21st to end	Day	20% 7% 25% 31% 16% 2	330
February	1st to 10th	Day	21% 20% 29% 22% 8% 1	300
	11th to 20th	Day	21% 15% 28% 26% 9% 1	317
	21st to end	Day	16% 18% 29% 26% 9% 1	414
March	1st to 10th	Day	15% 21% 29% 25% 8% 2	500
	11th to 20th	Day	14% 16% 30% 27% 12% 1	500
	21st to end	Day	18% 20% 31% 23% 7% 1	550
April	1st to 10th	Day	17% 19% 26% 23% 12% 2	500
	11th to 20th	Day	14% 20% 34% 20% 11% 2	492
	21st to end	Day	14% 14% 29% 26% 13% 3	500
May	1st to 10th	Day	10% 15% 27% 27% 16% 4	503
	11th to 20th	Day	11% 15% 28% 26% 16% 4	528
	21st to end	Day	13% 8% 22% 28% 22% 7%	751
June	1st to 10th	Day	7% 11% 25% 28% 22% 7%	730
	11th to 20th	Day	13% 12% 28% 29% 16% 2	730
	21st to end	Day	5% 6% 26% 34% 24% 5%	730
July	1st to 10th	Day	3 6% 22% 35% 28% 6%	666
	11th to 20th	Day	2 6% 24% 40% 23% 5%	484
	21st to end	Day	3 3 20% 34% 30% 10%	531
August	1st to 10th	Day	5% 4 26% 31% 26% 8%	487
	11th to 20th	Day	4 4 22% 32% 27% 10%	477
	21st to end	Day	5% 9% 23% 30% 23% 10%	539
September	1st to 10th	Day	4 7% 23% 26% 29% 10%	490
	11th to 20th	Day	9% 10% 24% 29% 21% 7%	490
	21st to end	Day	9% 10% 22% 28% 24% 8%	490
October	1st to 10th	Day	12% 8% 18% 26% 27% 9%	388
	11th to 20th	Day	10% 14% 19% 21% 22% 13%	300
	21st to end	Day	16% 13% 22% 30% 16% 3	330
November	1st to 10th	Day	20% 10% 24% 24% 15% 7%	300
	11th to 20th	Day	16% 11% 22% 34% 13% 3	300
	21st to end	Day	15% 11% 25% 32% 16% 1	300
December	1st to 10th	Day	21% 8% 23% 26% 15% 6%	300
	11th to 20th	Day	25% 8% 27% 28% 11% 1	275
	21st to end	Day	24% 15% 20% 23% 14% 4	220
January	1st to 10th	Night	21% 8% 20% 32% 18% 1	855
	11th to 20th	Night	21% 7% 21% 33% 16% 3	800
	21st to end	Night	20% 5% 21% 37% 15% 2	880
February	1st to 10th	Night	20% 10% 28% 31% 12% 1	800
	11th to 20th	Night	21% 8% 26% 32% 11% 2	784
	21st to end	Night	13% 11% 29% 34% 11% 2	660
March	1st to 10th	Night	15% 9% 27% 35% 13% 1	800
	11th to 20th	Night	11% 8% 28% 36% 15% 2	800
	21st to end	Night	13% 9% 28% 38% 11% 1	880
April	1st to 10th	Night	15% 9% 26% 36% 15% 1	755
	11th to 20th	Night	13% 11% 31% 35% 9% 1	593
	21st to end	Night	12% 7% 25% 38% 17% 2	600
May	1st to 10th	Night	11% 8% 25% 36% 20% 1	600
	11th to 20th	Night	12% 6% 24% 34% 23% 3	591
	21st to end	Night	11% 6% 21% 41% 18% 3	650
June	1st to 10th	Night	8% 5% 23% 35% 25% 3	467
	11th to 20th	Night	9% 6% 27% 40% 18%	400
	21st to end	Night	4 3 19% 46% 24% 5%	400
July	1st to 10th	Night	3 1 17% 47% 28% 4	380
	11th to 20th	Night	2 1 17% 52% 26% 2	380
	21st to end	Night	3 1 17% 45% 30% 4	624
August	1st to 10th	Night	5% 3 16% 45% 28% 2	567
	11th to 20th	Night	3 2 17% 45% 31% 3	564
	21st to end	Night	4 3 21% 42% 28% 3	627
September	1st to 10th	Night	6% 2 21% 41% 26% 5%	670
	11th to 20th	Night	8% 3 17% 39% 27% 5%	760
	21st to end	Night	9% 3 18% 38% 24% 7%	760
October	1st to 10th	Night	12% 4 19% 39% 25% 2	760
	11th to 20th	Night	11% 7% 20% 36% 23% 3	760
	21st to end	Night	11% 8% 22% 41% 15% 4	836
November	1st to 10th	Night	15% 8% 24% 34% 17% 2	780
	11th to 20th	Night	15% 9% 28% 34% 14% 1	900
	21st to end	Night	14% 8% 22% 37% 18% 2	1000
December	1st to 10th	Night	19% 7% 24% 36% 12% 2	1000
	11th to 20th	Night	22% 8% 22% 35% 13% 1	1000
	21st to end	Night	26% 8% 27% 28% 10% 1	1100

Page generated at 2025-07-02 23:30:14. Version ac07

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