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 2026-10-29.

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	6% 7% 3 6% 4 4 4 3 5% 7% 52%	158336
	Night	7% 9% 3 7% 4 4 4 3 5% 7% 46%	151237
Transparency	Day	33% 5% 10% 21% 20% 12%	153043
	Night	37% 5% 12% 20% 17% 10%	147536
Seeing	Day	12% 11% 25% 28% 19% 5%	17945
	Night	13% 7% 23% 37% 18% 2	27480

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	12% 22% 6% 11% 5% 5% 4 3 4 6% 22%	4604
	11th to 20th	Day	6% 11% 5% 11% 6% 4 4 3 4 5% 42%	4898
	21st to end	Day	8% 13% 5% 10% 4 4 4 3 5% 6% 37%	5844
February	1st to 10th	Day	10% 15% 5% 13% 7% 5% 5% 4 5% 5% 27%	1890
	11th to 20th	Day	11% 14% 5% 10% 6% 5% 5% 4 6% 7% 27%	1863
	21st to end	Day	7% 13% 5% 9% 6% 4 4 4 6% 7% 34%	1730
March	1st to 10th	Day	8% 13% 5% 10% 5% 5% 4 4 5% 7% 35%	4858
	11th to 20th	Day	6% 12% 3 7% 5% 5% 4 3 4 7% 43%	5110
	21st to end	Day	7% 13% 4 10% 6% 6% 6% 5% 6% 7% 29%	5607
April	1st to 10th	Day	8% 11% 3 7% 5% 4 5% 4 7% 8% 39%	2384
	11th to 20th	Day	6% 10% 3 7% 4 4 4 4 5% 7% 44%	2697
	21st to end	Day	8% 9% 3 7% 5% 5% 5% 4 6% 9% 40%	2730
May	1st to 10th	Day	5% 6% 2 5% 3 3 3 3 5% 7% 58%	7626
	11th to 20th	Day	5% 6% 2 7% 5% 4 5% 4 6% 7% 49%	7596
	21st to end	Day	7% 6% 2 5% 3 3 4 3 5% 8% 54%	8908
June	1st to 10th	Day	7% 5% 2 5% 4 4 5% 5% 7% 8% 50%	3075
	11th to 20th	Day	6% 5% 1 5% 4 3 3 4 5% 7% 56%	3150
	21st to end	Day	3 2 1 3 3 2 3 2 5% 6% 70%	3150
July	1st to 10th	Day	1 2 1 3 3 3 3 3 5% 6% 71%	8705
	11th to 20th	Day	1 2 1 2 2 3 3 3 5% 7% 72%	8168
	21st to end	Day	2 2 1 4 3 3 4 4 5% 7% 64%	8304
August	1st to 10th	Day	2 2 1 3 2 3 3 3 4 5% 71%	7549
	11th to 20th	Day	3 2 1 4 3 4 4 3 5% 8% 63%	7565
	21st to end	Day	4 4 2 4 3 3 3 3 4 7% 62%	8374
September	1st to 10th	Day	3 3 1 3 2 2 3 2 4 6% 71%	2434
	11th to 20th	Day	6% 4 1 3 3 3 3 3 5% 7% 63%	2310
	21st to end	Day	6% 4 1 3 3 3 3 2 5% 6% 64%	2310
October	1st to 10th	Day	6% 4 2 4 2 3 3 2 3 3 67%	3519
	11th to 20th	Day	5% 5% 2 5% 3 4 3 3 4 6% 61%	3350
	21st to end	Day	8% 8% 3 6% 4 4 4 4 6% 7% 46%	3469
November	1st to 10th	Day	12% 11% 3 6% 3 4 4 3 5% 6% 43%	1854
	11th to 20th	Day	10% 10% 3 6% 4 5% 4 4 7% 7% 39%	1762
	21st to end	Day	9% 12% 5% 8% 4 4 4 3 5% 5% 41%	1680
December	1st to 10th	Day	8% 9% 4 10% 4 2 2 3 5% 6% 47%	2700
	11th to 20th	Day	13% 18% 6% 11% 7% 5% 5% 4 5% 6% 22%	2988
	21st to end	Day	14% 16% 5% 10% 5% 4 5% 4 5% 7% 25%	3575
January	1st to 10th	Night	12% 18% 6% 14% 5% 5% 4 3 5% 7% 21%	8330
	11th to 20th	Night	9% 14% 5% 11% 4 3 3 2 5% 8% 36%	8066
	21st to end	Night	9% 13% 5% 8% 4 3 3 3 5% 9% 38%	8370
February	1st to 10th	Night	11% 15% 4 9% 5% 4 4 5% 6% 7% 29%	2730
	11th to 20th	Night	12% 15% 4 9% 5% 4 4 3 5% 7% 32%	2641
	21st to end	Night	8% 12% 5% 11% 6% 5% 5% 5% 5% 8% 30%	2076
March	1st to 10th	Night	7% 14% 4 8% 5% 5% 4 4 6% 7% 36%	5255
	11th to 20th	Night	5% 9% 3 7% 5% 4 5% 3 6% 9% 43%	5110
	21st to end	Night	7% 9% 3 8% 5% 5% 5% 5% 7% 9% 37%	5610
April	1st to 10th	Night	9% 10% 3 7% 5% 4 4 4 7% 7% 40%	2232
	11th to 20th	Night	7% 10% 3 7% 5% 5% 4 4 5% 7% 43%	1871
	21st to end	Night	8% 8% 2 6% 5% 4 4 3 6% 7% 47%	1890
May	1st to 10th	Night	7% 7% 2 5% 3 3 3 3 5% 7% 53%	5321
	11th to 20th	Night	5% 5% 2 5% 4 4 4 3 6% 8% 53%	5296
	21st to end	Night	7% 5% 2 4 3 3 4 4 6% 9% 52%	5299
June	1st to 10th	Night	5% 4 2 6% 5% 4 4 5% 6% 8% 50%	1540
	11th to 20th	Night	7% 5% 1 5% 3 5% 3 3 6% 7% 56%	1470
	21st to end	Night	3 3 1 4 2 3 3 3 4 7% 68%	1470
July	1st to 10th	Night	2 2 1 3 3 4 4 4 5% 6% 66%	4236
	11th to 20th	Night	1 1 1 2 2 3 4 4 6% 8% 69%	4793
	21st to end	Night	1 1 1 4 3 4 4 4 6% 9% 62%	5805
August	1st to 10th	Night	2 2 1 2 2 2 3 3 5% 7% 70%	5273
	11th to 20th	Night	2 2 1 4 4 4 5% 4 6% 8% 61%	5291
	21st to end	Night	6% 4 2 5% 4 3 4 4 5% 7% 56%	5842
September	1st to 10th	Night	4 3 1 3 2 3 3 3 4 5% 69%	2181
	11th to 20th	Night	6% 4 1 4 3 4 4 3 5% 7% 59%	2310
	21st to end	Night	7% 4 1 4 3 3 3 2 5% 5% 65%	2310
October	1st to 10th	Night	5% 3 1 3 2 2 3 2 3 5% 70%	3894
	11th to 20th	Night	9% 6% 2 5% 3 3 4 3 4 4 56%	4018
	21st to end	Night	7% 8% 3 6% 4 4 4 3 6% 7% 47%	4506
November	1st to 10th	Night	11% 9% 2 5% 3 3 5% 3 5% 8% 45%	2665
	11th to 20th	Night	10% 11% 3 7% 6% 5% 4 4 5% 6% 39%	2835
	21st to end	Night	9% 11% 4 8% 5% 4 4 3 5% 7% 40%	2940
December	1st to 10th	Night	8% 11% 3 7% 5% 4 3 3 5% 7% 45%	4710
	11th to 20th	Night	12% 16% 5% 9% 5% 5% 4 4 5% 7% 27%	5428
	21st to end	Night	14% 15% 5% 11% 5% 5% 5% 4 5% 6% 25%	7623

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% 7% 16% 11% 3	4605
	11th to 20th	Day	44% 6% 22% 18% 8% 2	4898
	21st to end	Day	47% 7% 13% 22% 11% 1	5844
February	1st to 10th	Day	59% 8% 12% 16% 4 1	1890
	11th to 20th	Day	54% 9% 15% 15% 7% 1	1872
	21st to end	Day	50% 8% 13% 18% 9% 1	1730
March	1st to 10th	Day	47% 6% 13% 21% 10% 3	4858
	11th to 20th	Day	42% 5% 10% 30% 12% 1	5110
	21st to end	Day	51% 9% 15% 19% 5%	5607
April	1st to 10th	Day	43% 7% 14% 20% 13% 2	2384
	11th to 20th	Day	39% 6% 11% 26% 16% 3	2700
	21st to end	Day	41% 7% 11% 25% 15% 1	2730
May	1st to 10th	Day	26% 4 9% 25% 30% 5%	7626
	11th to 20th	Day	33% 4 7% 23% 24% 8%	7599
	21st to end	Day	28% 5% 8% 33% 23% 3	8909
June	1st to 10th	Day	30% 6% 12% 29% 21% 2	3075
	11th to 20th	Day	28% 5% 9% 22% 24% 12%	3150
	21st to end	Day	16% 4 6% 22% 37% 17%	3150
July	1st to 10th	Day	15% 2 4 12% 26% 41%	8633
	11th to 20th	Day	14% 1 3 15% 31% 37%	8093
	21st to end	Day	19% 3 5% 13% 35% 26%	8120
August	1st to 10th	Day	16% 2 4 11% 26% 40%	5978
	11th to 20th	Day	22% 4 8% 20% 32% 15%	5964
	21st to end	Day	19% 3 5% 25% 26% 20%	6569
September	1st to 10th	Day	16% 3 7% 18% 33% 22%	2434
	11th to 20th	Day	22% 4 8% 24% 29% 12%	2310
	21st to end	Day	23% 4 7% 28% 30% 9%	2310
October	1st to 10th	Day	24% 3 6% 21% 34% 12%	3519
	11th to 20th	Day	27% 3 9% 37% 19% 5%	3350
	21st to end	Day	37% 5% 13% 29% 16% 1	3469
November	1st to 10th	Day	43% 5% 16% 23% 11% 1	1854
	11th to 20th	Day	44% 7% 19% 22% 7% 2	1762
	21st to end	Day	45% 5% 18% 21% 9% 1	1680
December	1st to 10th	Day	39% 7% 23% 25% 4 1	2700
	11th to 20th	Day	63% 7% 14% 13% 3	2986
	21st to end	Day	58% 7% 15% 13% 7%	3575
January	1st to 10th	Night	61% 6% 13% 15% 4	8331
	11th to 20th	Night	47% 6% 23% 18% 5% 1	8066
	21st to end	Night	44% 7% 15% 21% 10% 3	8370
February	1st to 10th	Night	53% 9% 15% 16% 7% 1	2730
	11th to 20th	Night	52% 6% 14% 18% 9% 1	2642
	21st to end	Night	52% 7% 14% 17% 8% 1	2076
March	1st to 10th	Night	44% 6% 15% 21% 11% 2	5255
	11th to 20th	Night	37% 5% 13% 27% 17% 1	5110
	21st to end	Night	41% 8% 16% 27% 7% 1	5610
April	1st to 10th	Night	42% 7% 13% 21% 14% 3	2232
	11th to 20th	Night	40% 5% 14% 22% 17% 2	1871
	21st to end	Night	37% 6% 11% 26% 19% 1	1890
May	1st to 10th	Night	30% 4 9% 21% 31% 5%	5319
	11th to 20th	Night	28% 5% 8% 22% 27% 10%	5297
	21st to end	Night	26% 4 9% 26% 30% 4	5300
June	1st to 10th	Night	30% 7% 12% 22% 25% 4	1540
	11th to 20th	Night	27% 4 10% 18% 28% 13%	1470
	21st to end	Night	18% 3 6% 17% 31% 26%	1470
July	1st to 10th	Night	18% 2 4 11% 20% 44%	4200
	11th to 20th	Night	14% 2 4 12% 26% 42%	4745
	21st to end	Night	19% 3 5% 13% 30% 31%	5677
August	1st to 10th	Night	14% 2 4 8% 23% 49%	4168
	11th to 20th	Night	24% 4 9% 17% 27% 19%	4168
	21st to end	Night	24% 3 7% 19% 22% 24%	4578
September	1st to 10th	Night	19% 4 6% 11% 32% 28%	2181
	11th to 20th	Night	25% 5% 7% 21% 26% 16%	2310
	21st to end	Night	23% 4 7% 24% 32% 11%	2310
October	1st to 10th	Night	19% 2 7% 19% 37% 16%	3894
	11th to 20th	Night	33% 3 6% 33% 18% 7%	4018
	21st to end	Night	36% 5% 11% 29% 17% 1	4506
November	1st to 10th	Night	38% 6% 14% 26% 14% 2	2665
	11th to 20th	Night	46% 6% 16% 22% 9% 2	2835
	21st to end	Night	45% 5% 18% 22% 10% 1	2940
December	1st to 10th	Night	40% 6% 26% 23% 5% 1	4710
	11th to 20th	Night	55% 8% 21% 13% 3	5429
	21st to end	Night	58% 6% 14% 14% 7% 1	7623

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	26% 13% 20% 24% 12% 5%	220
	11th to 20th	Day	16% 6% 25% 28% 22% 2	249
	21st to end	Day	18% 6% 25% 33% 17% 2	363
February	1st to 10th	Day	20% 18% 28% 22% 9% 2	330
	11th to 20th	Day	20% 15% 27% 27% 10% 1	348
	21st to end	Day	17% 19% 29% 25% 10% 1	446
March	1st to 10th	Day	17% 21% 29% 24% 8% 1	540
	11th to 20th	Day	15% 16% 30% 26% 11% 1	540
	21st to end	Day	19% 20% 31% 22% 7% 1	594
April	1st to 10th	Day	17% 19% 27% 23% 13% 3	540
	11th to 20th	Day	15% 19% 33% 20% 11% 2	532
	21st to end	Day	15% 14% 28% 26% 13% 3	540
May	1st to 10th	Day	9% 15% 27% 28% 17% 4	543
	11th to 20th	Day	11% 16% 27% 26% 16% 4	568
	21st to end	Day	13% 8% 22% 28% 21% 7%	804
June	1st to 10th	Day	8% 11% 26% 27% 22% 7%	780
	11th to 20th	Day	13% 12% 28% 30% 15% 2	780
	21st to end	Day	5% 7% 26% 33% 24% 5%	780
July	1st to 10th	Day	3 5% 22% 36% 28% 5%	736
	11th to 20th	Day	2 6% 23% 39% 26% 5%	564
	21st to end	Day	3 3 20% 35% 28% 10%	619
August	1st to 10th	Day	5% 4 26% 32% 26% 7%	567
	11th to 20th	Day	5% 4 24% 32% 26% 10%	557
	21st to end	Day	5% 9% 23% 30% 23% 10%	627
September	1st to 10th	Day	4 8% 24% 26% 29% 10%	570
	11th to 20th	Day	9% 10% 24% 29% 21% 7%	570
	21st to end	Day	8% 9% 21% 27% 24% 10%	570
October	1st to 10th	Day	11% 7% 18% 27% 27% 10%	457
	11th to 20th	Day	10% 14% 20% 21% 23% 13%	360
	21st to end	Day	16% 13% 21% 29% 18% 4	387
November	1st to 10th	Day	20% 11% 23% 23% 16% 7%	330
	11th to 20th	Day	16% 11% 21% 35% 14% 4	330
	21st to end	Day	15% 10% 25% 31% 18% 1	330
December	1st to 10th	Day	22% 11% 23% 25% 14% 5%	330
	11th to 20th	Day	25% 9% 26% 27% 11% 1	302
	21st to end	Day	24% 15% 20% 23% 14% 3	242
January	1st to 10th	Night	21% 9% 21% 31% 17% 1	898
	11th to 20th	Night	20% 7% 20% 34% 17% 3	840
	21st to end	Night	19% 5% 21% 39% 14% 2	924
February	1st to 10th	Night	19% 10% 27% 30% 12% 1	840
	11th to 20th	Night	21% 8% 26% 33% 11% 2	824
	21st to end	Night	13% 12% 29% 34% 10% 2	692
March	1st to 10th	Night	15% 10% 26% 35% 13% 1	840
	11th to 20th	Night	12% 9% 29% 35% 15% 1	840
	21st to end	Night	13% 9% 28% 37% 11% 1	924
April	1st to 10th	Night	15% 9% 26% 35% 15% 1	793
	11th to 20th	Night	13% 12% 32% 34% 8% 1	623
	21st to end	Night	13% 7% 25% 37% 17% 1	630
May	1st to 10th	Night	11% 9% 25% 35% 19% 1	630
	11th to 20th	Night	12% 7% 24% 34% 22% 2	621
	21st to end	Night	12% 6% 22% 41% 17% 2	683
June	1st to 10th	Night	8% 6% 24% 35% 24% 3	490
	11th to 20th	Night	9% 6% 28% 40% 17%	420
	21st to end	Night	5% 3 19% 45% 23% 5%	420
July	1st to 10th	Night	3 1 17% 47% 28% 4	410
	11th to 20th	Night	2 18% 53% 25% 1	422
	21st to end	Night	2 1 18% 47% 29% 3	690
August	1st to 10th	Night	4 4 18% 46% 26% 2	627
	11th to 20th	Night	3 2 18% 45% 30% 3	624
	21st to end	Night	5% 3 20% 42% 27% 3	693
September	1st to 10th	Night	5% 3 21% 40% 26% 5%	740
	11th to 20th	Night	8% 4 17% 40% 26% 5%	840
	21st to end	Night	9% 4 18% 39% 24% 7%	840
October	1st to 10th	Night	11% 5% 19% 39% 25% 2	840
	11th to 20th	Night	12% 7% 20% 36% 22% 3	840
	21st to end	Night	11% 8% 21% 41% 15% 4	912
November	1st to 10th	Night	14% 8% 25% 34% 17% 2	820
	11th to 20th	Night	15% 8% 27% 35% 14% 1	945
	21st to end	Night	14% 7% 22% 37% 18% 2	1050
December	1st to 10th	Night	20% 8% 24% 34% 12% 2	1050
	11th to 20th	Night	22% 9% 22% 34% 12% 1	1050
	21st to end	Night	25% 9% 27% 28% 10% 1	1155

Page generated at 2026-10-26 02:37:47. Version ac07

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