Trout Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Trout Observatory clear sky chart from 2005-11-06 to 2026-06-16.

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	14% 10% 4 9% 5% 5% 5% 4 6% 7% 33%	137020
	Night	14% 11% 4 9% 5% 5% 5% 4 5% 7% 33%	135021
Transparency	Day	48% 6% 12% 21% 12% 1	140632
	Night	49% 6% 11% 20% 13% 1	139481
Seeing	Day	16% 7% 24% 29% 18% 6%	17493
	Night	19% 7% 27% 30% 15% 2	27453

By Month

Percentage Cloud Cover SE (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	14% 17% 7% 16% 6% 5% 4 3 6% 6% 16%	4691
	11th to 20th	Day	11% 17% 6% 15% 10% 6% 6% 3 3 4 17%	4992
	21st to end	Day	19% 15% 7% 13% 6% 6% 5% 4 5% 4 16%	5780
February	1st to 10th	Day	15% 15% 5% 13% 6% 5% 5% 3 5% 6% 21%	1890
	11th to 20th	Day	15% 12% 5% 12% 7% 6% 6% 3 5% 5% 24%	1999
	21st to end	Day	16% 14% 4 10% 6% 4 5% 4 5% 7% 25%	1730
March	1st to 10th	Day	17% 12% 6% 12% 5% 4 4 3 4 5% 28%	4738
	11th to 20th	Day	11% 11% 4 8% 5% 4 4 4 5% 7% 37%	5090
	21st to end	Day	17% 13% 5% 10% 6% 5% 4 3 5% 6% 25%	5586
April	1st to 10th	Day	14% 12% 4 9% 7% 4 4 5% 6% 6% 29%	2405
	11th to 20th	Day	15% 9% 3 8% 6% 5% 4 3 6% 7% 34%	2662
	21st to end	Day	17% 10% 3 6% 5% 4 4 4 5% 8% 35%	2730
May	1st to 10th	Day	20% 9% 3 8% 5% 4 5% 4 5% 7% 31%	7616
	11th to 20th	Day	14% 8% 3 8% 5% 5% 5% 4 6% 8% 34%	7626
	21st to end	Day	15% 7% 2 6% 5% 4 4 4 6% 7% 40%	8391
June	1st to 10th	Day	11% 6% 2 7% 4 5% 5% 5% 7% 8% 40%	2798
	11th to 20th	Day	10% 5% 2 7% 6% 4 5% 4 6% 8% 43%	2871
	21st to end	Day	10% 5% 3 6% 5% 5% 5% 5% 7% 10% 39%	2800
July	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 4 6% 10% 40%	6360
	11th to 20th	Day	7% 5% 2 7% 5% 5% 6% 5% 7% 10% 41%	6227
	21st to end	Day	8% 6% 2 7% 5% 5% 5% 4 6% 9% 41%	6424
August	1st to 10th	Day	10% 6% 2 6% 4 4 5% 4 7% 9% 43%	4234
	11th to 20th	Day	7% 6% 2 6% 5% 5% 7% 6% 8% 11% 37%	4174
	21st to end	Day	8% 5% 2 7% 5% 5% 5% 4 7% 10% 41%	4619
September	1st to 10th	Day	12% 5% 2 6% 4 4 4 3 7% 8% 46%	2236
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 5% 9% 47%	2200
	21st to end	Day	16% 8% 3 6% 4 4 4 3 6% 6% 41%	2200
October	1st to 10th	Day	11% 6% 3 6% 5% 5% 4 3 6% 7% 44%	2141
	11th to 20th	Day	17% 7% 2 7% 5% 4 4 3 5% 8% 38%	2000
	21st to end	Day	17% 9% 2 8% 5% 5% 5% 4 7% 7% 31%	2080
November	1st to 10th	Day	11% 10% 3 7% 4 4 4 4 6% 7% 40%	1852
	11th to 20th	Day	16% 12% 3 8% 6% 5% 3 3 5% 5% 34%	1890
	21st to end	Day	17% 14% 5% 9% 5% 4 5% 3 6% 6% 26%	1885
December	1st to 10th	Day	14% 14% 6% 12% 6% 5% 5% 4 5% 7% 23%	2680
	11th to 20th	Day	19% 19% 7% 9% 5% 4 4 3 5% 5% 19%	3280
	21st to end	Day	24% 21% 7% 12% 6% 5% 3 3 3 4 14%	4143
January	1st to 10th	Night	14% 16% 6% 16% 6% 6% 5% 3 5% 5% 19%	8232
	11th to 20th	Night	9% 17% 7% 14% 7% 6% 6% 4 5% 6% 19%	7964
	21st to end	Night	17% 14% 7% 10% 4 4 4 4 5% 6% 24%	8401
February	1st to 10th	Night	16% 15% 5% 10% 7% 5% 4 4 4 5% 24%	2730
	11th to 20th	Night	14% 13% 4 11% 6% 5% 5% 4 5% 6% 26%	2505
	21st to end	Night	19% 12% 4 9% 6% 5% 4 3 4 6% 28%	2076
March	1st to 10th	Night	18% 12% 3 7% 4 4 4 3 4 5% 36%	5334
	11th to 20th	Night	11% 7% 2 6% 4 5% 5% 4 6% 7% 42%	5090
	21st to end	Night	15% 11% 4 7% 5% 5% 4 3 5% 6% 36%	5588
April	1st to 10th	Night	16% 11% 3 8% 5% 4 4 4 5% 6% 33%	2231
	11th to 20th	Night	15% 7% 3 8% 6% 5% 4 4 5% 7% 36%	1905
	21st to end	Night	16% 9% 2 7% 5% 4 4 3 6% 7% 36%	1890
May	1st to 10th	Night	19% 10% 4 8% 6% 5% 5% 4 5% 6% 28%	5237
	11th to 20th	Night	15% 7% 3 8% 4 4 4 3 5% 7% 39%	5234
	21st to end	Night	13% 7% 2 6% 5% 4 5% 4 5% 8% 41%	5761
June	1st to 10th	Night	11% 6% 3 5% 5% 4 5% 4 5% 7% 45%	1817
	11th to 20th	Night	8% 6% 3 7% 4 4 4 5% 7% 9% 43%	1640
	21st to end	Night	9% 5% 2 4 5% 4 5% 4 7% 10% 45%	1600
July	1st to 10th	Night	8% 5% 2 6% 4 4 5% 5% 7% 9% 45%	3618
	11th to 20th	Night	8% 5% 2 6% 5% 5% 6% 4 7% 9% 43%	3739
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 7% 8% 47%	4427
August	1st to 10th	Night	11% 6% 3 6% 4 4 4 4 5% 10% 43%	2915
	11th to 20th	Night	8% 6% 2 6% 4 4 5% 4 6% 8% 47%	2875
	21st to end	Night	6% 5% 3 6% 5% 5% 6% 4 6% 8% 46%	3274
September	1st to 10th	Night	9% 6% 2 6% 4 3 4 3 5% 7% 50%	2142
	11th to 20th	Night	8% 5% 2 5% 4 4 4 3 4 8% 55%	2200
	21st to end	Night	13% 7% 3 7% 5% 4 4 3 5% 6% 43%	2200
October	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 5% 7% 48%	2257
	11th to 20th	Night	17% 9% 3 6% 4 4 3 4 5% 6% 40%	2400
	21st to end	Night	20% 8% 3 7% 5% 4 4 4 5% 6% 35%	2755
November	1st to 10th	Night	13% 8% 3 7% 4 4 4 3 4 7% 42%	2666
	11th to 20th	Night	15% 11% 4 8% 5% 4 5% 3 6% 7% 32%	2730
	21st to end	Night	20% 13% 4 8% 6% 5% 5% 4 5% 6% 26%	2730
December	1st to 10th	Night	12% 14% 5% 12% 6% 6% 5% 4 5% 6% 24%	4715
	11th to 20th	Night	16% 16% 6% 11% 5% 5% 4 3 4 6% 22%	5105
	21st to end	Night	25% 19% 5% 11% 5% 4 4 3 5% 5% 13%	7038

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	68% 5% 12% 12% 2	4692
	11th to 20th	Day	71% 4 8% 7% 10%	4992
	21st to end	Day	71% 4 9% 10% 6%	5780
February	1st to 10th	Day	63% 6% 11% 14% 6%	1890
	11th to 20th	Day	61% 6% 10% 16% 7% 1	2009
	21st to end	Day	57% 6% 14% 15% 6% 2	1730
March	1st to 10th	Day	58% 5% 11% 18% 7%	4738
	11th to 20th	Day	45% 6% 15% 24% 9% 1	5090
	21st to end	Day	57% 6% 11% 16% 9% 1	5586
April	1st to 10th	Day	52% 7% 13% 16% 12%	2405
	11th to 20th	Day	49% 6% 13% 19% 12% 2	2662
	21st to end	Day	47% 5% 14% 21% 10% 2	2730
May	1st to 10th	Day	51% 6% 11% 20% 12% 1	7651
	11th to 20th	Day	45% 7% 14% 21% 12% 2	7630
	21st to end	Day	42% 6% 9% 20% 18% 5%	8405
June	1st to 10th	Day	39% 8% 11% 26% 14% 3	2798
	11th to 20th	Day	37% 6% 15% 22% 16% 3	2871
	21st to end	Day	39% 7% 14% 21% 16% 4	2800
July	1st to 10th	Day	38% 6% 10% 27% 16% 2	6291
	11th to 20th	Day	35% 7% 15% 26% 16% 1	6152
	21st to end	Day	37% 7% 13% 21% 20% 2	6240
August	1st to 10th	Day	34% 8% 16% 26% 15% 1	4221
	11th to 20th	Day	36% 8% 14% 30% 11% 1	4213
	21st to end	Day	36% 7% 13% 31% 12% 2	4618
September	1st to 10th	Day	36% 6% 14% 24% 17% 3	2236
	11th to 20th	Day	32% 7% 11% 30% 19% 1	2200
	21st to end	Day	42% 6% 12% 22% 17%	2200
October	1st to 10th	Day	28% 5% 13% 32% 20% 1	3492
	11th to 20th	Day	39% 4 10% 27% 19% 1	3240
	21st to end	Day	42% 5% 12% 23% 18% 1	3343
November	1st to 10th	Day	42% 6% 11% 24% 15% 1	1852
	11th to 20th	Day	52% 5% 12% 19% 11% 1	1890
	21st to end	Day	57% 6% 12% 17% 7%	1885
December	1st to 10th	Day	61% 5% 15% 15% 4	2680
	11th to 20th	Day	65% 5% 11% 15% 5%	3277
	21st to end	Day	76% 4 7% 9% 5%	4143
January	1st to 10th	Night	66% 5% 9% 15% 4	8233
	11th to 20th	Night	66% 5% 10% 11% 9% 1	7964
	21st to end	Night	61% 4 12% 14% 9%	8401
February	1st to 10th	Night	61% 6% 11% 16% 6% 1	2730
	11th to 20th	Night	58% 5% 10% 18% 8% 1	2506
	21st to end	Night	57% 5% 11% 18% 8% 1	2076
March	1st to 10th	Night	51% 4 12% 23% 9% 1	5334
	11th to 20th	Night	38% 6% 15% 26% 13% 1	5090
	21st to end	Night	48% 6% 10% 21% 14% 1	5588
April	1st to 10th	Night	50% 6% 11% 17% 13% 2	2231
	11th to 20th	Night	47% 6% 11% 18% 17% 2	1905
	21st to end	Night	45% 7% 11% 21% 14% 3	1890
May	1st to 10th	Night	55% 6% 9% 14% 14% 2	5264
	11th to 20th	Night	43% 6% 11% 24% 14% 1	5235
	21st to end	Night	40% 6% 11% 22% 17% 3	5771
June	1st to 10th	Night	37% 6% 11% 24% 19% 3	1817
	11th to 20th	Night	35% 8% 13% 25% 16% 3	1640
	21st to end	Night	31% 8% 14% 25% 19% 2	1600
July	1st to 10th	Night	34% 7% 12% 25% 18% 4	3580
	11th to 20th	Night	34% 7% 16% 27% 14% 2	3694
	21st to end	Night	33% 6% 14% 23% 21% 4	4297
August	1st to 10th	Night	37% 7% 13% 26% 15% 2	2904
	11th to 20th	Night	33% 7% 12% 29% 17% 1	2902
	21st to end	Night	34% 6% 13% 29% 16% 2	3274
September	1st to 10th	Night	33% 7% 12% 27% 17% 4	2142
	11th to 20th	Night	28% 6% 11% 28% 25% 2	2200
	21st to end	Night	40% 7% 11% 22% 19% 2	2200
October	1st to 10th	Night	26% 4 9% 31% 29% 1	3686
	11th to 20th	Night	37% 4 10% 27% 20% 1	3899
	21st to end	Night	37% 5% 9% 31% 16% 3	4442
November	1st to 10th	Night	42% 6% 11% 24% 16% 1	2666
	11th to 20th	Night	49% 6% 12% 21% 11% 1	2730
	21st to end	Night	59% 5% 11% 18% 6%	2730
December	1st to 10th	Night	59% 5% 12% 17% 6%	4715
	11th to 20th	Night	62% 6% 12% 14% 5%	5107
	21st to end	Night	72% 6% 10% 9% 4	7038

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	21% 12% 34% 26% 5% 2	330
	11th to 20th	Day	22% 10% 45% 16% 5%	330
	21st to end	Day	24% 11% 31% 28% 6%	363
February	1st to 10th	Day	22% 11% 37% 22% 7% 1	330
	11th to 20th	Day	20% 16% 34% 25% 5%	330
	21st to end	Day	19% 15% 43% 19% 4	273
March	1st to 10th	Day	20% 11% 33% 28% 8%	397
	11th to 20th	Day	19% 11% 34% 28% 7% 1	540
	21st to end	Day	23% 10% 31% 29% 7% 1	594
April	1st to 10th	Day	19% 9% 32% 26% 11% 1	540
	11th to 20th	Day	18% 9% 33% 26% 10% 4	532
	21st to end	Day	21% 7% 29% 28% 12% 2	540
May	1st to 10th	Day	22% 6% 27% 28% 15% 2	543
	11th to 20th	Day	17% 5% 25% 30% 19% 4	567
	21st to end	Day	14% 2 21% 30% 25% 8%	617
June	1st to 10th	Day	11% 4 21% 37% 24% 4	638
	11th to 20th	Day	12% 3 19% 37% 24% 4	756
	21st to end	Day	11% 3 16% 38% 24% 6%	730
July	1st to 10th	Day	9% 2 13% 34% 29% 12%	721
	11th to 20th	Day	9% 3 15% 33% 29% 11%	663
	21st to end	Day	8% 2 13% 32% 34% 11%	576
August	1st to 10th	Day	10% 2 10% 32% 32% 14%	526
	11th to 20th	Day	12% 3 11% 33% 32% 11%	519
	21st to end	Day	10% 3 12% 30% 33% 13%	583
September	1st to 10th	Day	13% 2 16% 26% 28% 15%	530
	11th to 20th	Day	10% 1 10% 27% 32% 19%	530
	21st to end	Day	20% 4 21% 23% 21% 11%	530
October	1st to 10th	Day	11% 5% 20% 31% 22% 12%	530
	11th to 20th	Day	18% 12% 27% 28% 12% 3	530
	21st to end	Day	21% 11% 32% 27% 8% 2	463
November	1st to 10th	Day	15% 11% 27% 30% 14% 3	330
	11th to 20th	Day	21% 17% 28% 25% 8% 1	330
	21st to end	Day	24% 11% 35% 26% 4	327
December	1st to 10th	Day	18% 14% 35% 24% 9%	220
	11th to 20th	Day	20% 14% 40% 21% 4	272
	21st to end	Day	26% 12% 33% 25% 3	363
January	1st to 10th	Night	24% 11% 36% 23% 6%	1050
	11th to 20th	Night	26% 11% 37% 21% 5%	942
	21st to end	Night	22% 9% 36% 28% 4 1	924
February	1st to 10th	Night	23% 9% 36% 27% 6%	840
	11th to 20th	Night	22% 9% 35% 30% 4	823
	21st to end	Night	25% 11% 37% 24% 3	692
March	1st to 10th	Night	19% 9% 34% 29% 8%	840
	11th to 20th	Night	19% 11% 33% 27% 8% 1	840
	21st to end	Night	22% 8% 29% 31% 9% 1	924
April	1st to 10th	Night	22% 9% 32% 30% 6%	761
	11th to 20th	Night	18% 7% 34% 29% 11% 2	623
	21st to end	Night	21% 6% 29% 31% 12% 1	630
May	1st to 10th	Night	21% 5% 29% 32% 11% 3	630
	11th to 20th	Night	20% 4 25% 31% 17% 3	621
	21st to end	Night	12% 2 21% 37% 23% 5%	683
June	1st to 10th	Night	13% 3 20% 39% 23% 2	630
	11th to 20th	Night	11% 3 18% 41% 25% 2	615
	21st to end	Night	11% 2 19% 39% 27% 3	600
July	1st to 10th	Night	11% 2 10% 37% 36% 5%	585
	11th to 20th	Night	9% 3 13% 41% 27% 6%	582
	21st to end	Night	9% 1 11% 41% 33% 5%	657
August	1st to 10th	Night	9% 3 11% 40% 32% 6%	597
	11th to 20th	Night	10% 1 13% 34% 35% 7%	594
	21st to end	Night	9% 2 13% 34% 36% 5%	660
September	1st to 10th	Night	13% 3 17% 29% 31% 7%	742
	11th to 20th	Night	11% 3 12% 29% 36% 8%	800
	21st to end	Night	16% 5% 19% 32% 22% 6%	800
October	1st to 10th	Night	16% 6% 20% 32% 20% 6%	800
	11th to 20th	Night	21% 12% 26% 26% 12% 2	800
	21st to end	Night	25% 9% 30% 28% 7% 1	880
November	1st to 10th	Night	18% 11% 30% 27% 12% 2	820
	11th to 20th	Night	22% 12% 35% 22% 8% 1	840
	21st to end	Night	28% 11% 32% 22% 6%	840
December	1st to 10th	Night	25% 13% 35% 22% 6%	840
	11th to 20th	Night	24% 12% 37% 23% 4	840
	21st to end	Night	30% 10% 32% 24% 4	1108

Page generated at 2026-06-13 02:31:45. Version ac07

Copyright © 2026 Attilla Danko.