Holt Rd. Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Holt Rd. Observatory clear sky chart from 2005-11-06 to 2026-06-01.

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	12% 11% 4 11% 7% 6% 6% 4 6% 7% 27%	132090
	Night	11% 11% 5% 12% 7% 6% 6% 4 6% 6% 25%	131067
Transparency	Day	53% 5% 10% 20% 11% 1	135558
	Night	52% 5% 11% 20% 10% 1	135686
Seeing	Day	26% 21% 30% 15% 6% 2	16618
	Night	23% 22% 28% 19% 7% 1	25696

By Month

Percentage Cloud Cover NE (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	5% 13% 7% 14% 11% 9% 7% 4 6% 6% 18%	4661
	11th to 20th	Day	5% 13% 8% 19% 12% 10% 6% 4 4 4 16%	4650
	21st to end	Day	7% 10% 5% 15% 9% 10% 8% 5% 6% 6% 20%	5142
February	1st to 10th	Day	9% 13% 5% 12% 10% 6% 6% 5% 6% 6% 21%	1890
	11th to 20th	Day	6% 10% 6% 12% 10% 8% 7% 4 7% 6% 24%	1981
	21st to end	Day	9% 15% 4 13% 7% 5% 5% 4 7% 6% 24%	1730
March	1st to 10th	Day	12% 12% 6% 15% 9% 6% 5% 4 4 4 23%	4576
	11th to 20th	Day	8% 14% 6% 11% 8% 6% 6% 4 5% 6% 27%	4806
	21st to end	Day	12% 13% 5% 12% 6% 6% 5% 4 4 5% 29%	6096
April	1st to 10th	Day	14% 14% 5% 9% 7% 5% 5% 4 6% 5% 27%	2520
	11th to 20th	Day	14% 12% 4 10% 5% 6% 4 4 5% 5% 31%	2494
	21st to end	Day	17% 14% 4 10% 4 5% 4 3 5% 6% 28%	2653
May	1st to 10th	Day	25% 15% 4 10% 5% 5% 4 3 4 4 19%	6287
	11th to 20th	Day	14% 14% 4 10% 6% 5% 5% 4 6% 7% 24%	6458
	21st to end	Day	18% 11% 4 9% 6% 6% 5% 4 5% 7% 26%	7103
June	1st to 10th	Day	20% 9% 4 9% 6% 5% 5% 4 6% 6% 25%	2800
	11th to 20th	Day	15% 8% 4 8% 6% 5% 6% 5% 7% 7% 30%	2800
	21st to end	Day	18% 10% 3 9% 6% 5% 5% 5% 6% 7% 26%	2800
July	1st to 10th	Day	11% 8% 3 8% 6% 6% 6% 6% 8% 9% 30%	6360
	11th to 20th	Day	8% 6% 3 8% 7% 6% 7% 6% 8% 10% 32%	6360
	21st to end	Day	11% 6% 3 7% 5% 5% 6% 5% 8% 8% 35%	6926
August	1st to 10th	Day	14% 7% 3 9% 6% 6% 6% 5% 7% 8% 29%	4563
	11th to 20th	Day	11% 9% 4 10% 6% 6% 7% 6% 6% 8% 26%	3986
	21st to end	Day	11% 6% 3 8% 6% 5% 7% 5% 8% 9% 33%	4312
September	1st to 10th	Day	13% 7% 2 7% 5% 4 5% 4 6% 8% 39%	2400
	11th to 20th	Day	11% 7% 3 7% 4 4 5% 4 6% 7% 43%	2313
	21st to end	Day	13% 9% 3 7% 5% 5% 5% 4 7% 8% 35%	2200
October	1st to 10th	Day	18% 11% 3 9% 4 4 5% 4 5% 6% 32%	2073
	11th to 20th	Day	14% 13% 4 8% 5% 4 5% 4 5% 5% 32%	1981
	21st to end	Day	18% 12% 5% 12% 6% 4 3 4 4 6% 26%	1980
November	1st to 10th	Day	10% 13% 5% 11% 7% 7% 5% 4 5% 6% 27%	1851
	11th to 20th	Day	11% 12% 5% 11% 8% 6% 5% 4 6% 5% 28%	1864
	21st to end	Day	11% 15% 5% 12% 6% 5% 6% 4 7% 7% 21%	1680
December	1st to 10th	Day	8% 18% 8% 22% 9% 6% 5% 3 4 4 13%	2680
	11th to 20th	Day	11% 12% 6% 16% 8% 6% 6% 4 5% 6% 21%	3066
	21st to end	Day	12% 13% 6% 12% 6% 6% 5% 3 6% 6% 24%	4048
January	1st to 10th	Night	8% 13% 6% 15% 9% 9% 7% 5% 6% 5% 16%	8234
	11th to 20th	Night	5% 13% 8% 21% 13% 10% 7% 4 5% 5% 10%	8235
	21st to end	Night	8% 7% 4 14% 9% 10% 10% 7% 9% 7% 15%	9021
February	1st to 10th	Night	7% 11% 5% 13% 9% 8% 7% 5% 7% 8% 19%	2730
	11th to 20th	Night	6% 9% 6% 13% 10% 9% 7% 5% 6% 7% 22%	2525
	21st to end	Night	8% 11% 5% 13% 9% 6% 5% 6% 6% 6% 24%	2076
March	1st to 10th	Night	12% 11% 5% 13% 9% 7% 7% 4 6% 5% 21%	5484
	11th to 20th	Night	9% 12% 5% 11% 7% 5% 5% 4 6% 6% 29%	5371
	21st to end	Night	12% 12% 6% 13% 7% 6% 5% 3 5% 4 26%	5077
April	1st to 10th	Night	13% 12% 5% 11% 6% 5% 5% 4 5% 6% 27%	2100
	11th to 20th	Night	15% 13% 3 9% 6% 6% 5% 4 6% 6% 27%	2075
	21st to end	Night	15% 11% 4 10% 6% 4 4 4 4 5% 33%	1965
May	1st to 10th	Night	24% 17% 5% 10% 5% 3 4 4 4 6% 18%	3915
	11th to 20th	Night	14% 13% 4 9% 4 5% 5% 4 5% 8% 29%	3655
	21st to end	Night	15% 11% 4 10% 6% 5% 5% 4 6% 7% 28%	4014
June	1st to 10th	Night	19% 8% 2 7% 5% 5% 4 5% 6% 7% 32%	1600
	11th to 20th	Night	14% 8% 3 6% 4 4 4 5% 6% 8% 37%	1600
	21st to end	Night	16% 7% 3 7% 5% 5% 5% 4 7% 7% 34%	1600
July	1st to 10th	Night	9% 7% 4 9% 6% 5% 5% 5% 7% 9% 35%	3600
	11th to 20th	Night	9% 7% 3 8% 5% 6% 5% 5% 6% 7% 39%	3600
	21st to end	Night	7% 7% 3 8% 5% 5% 5% 4 6% 8% 43%	3926
August	1st to 10th	Night	13% 8% 4 9% 5% 5% 4 3 5% 7% 37%	2586
	11th to 20th	Night	12% 9% 3 8% 5% 6% 5% 5% 6% 7% 35%	3026
	21st to end	Night	8% 7% 3 7% 6% 5% 5% 4 6% 9% 41%	3586
September	1st to 10th	Night	11% 6% 2 7% 5% 5% 4 5% 6% 7% 43%	2000
	11th to 20th	Night	11% 7% 2 7% 4 4 4 3 4 7% 46%	2086
	21st to end	Night	14% 8% 2 6% 5% 5% 5% 4 6% 7% 38%	2200
October	1st to 10th	Night	16% 10% 3 8% 6% 5% 5% 4 5% 7% 31%	2324
	11th to 20th	Night	15% 10% 3 9% 6% 5% 5% 4 5% 8% 32%	2417
	21st to end	Night	17% 12% 4 11% 7% 6% 5% 3 5% 6% 23%	2860
November	1st to 10th	Night	11% 13% 5% 11% 7% 6% 6% 4 5% 6% 26%	2667
	11th to 20th	Night	12% 11% 5% 12% 7% 6% 5% 4 5% 6% 27%	2754
	21st to end	Night	11% 13% 5% 12% 8% 6% 5% 4 7% 7% 22%	2940
December	1st to 10th	Night	8% 13% 8% 20% 10% 8% 6% 4 5% 5% 12%	4720
	11th to 20th	Night	12% 14% 7% 15% 8% 6% 5% 4 5% 5% 20%	5348
	21st to end	Night	11% 16% 5% 14% 7% 5% 5% 4 6% 6% 22%	7150

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	58% 6% 10% 20% 6% 1	4662
	11th to 20th	Day	67% 4 6% 10% 9% 3	4680
	21st to end	Day	58% 4 9% 17% 10% 2	5142
February	1st to 10th	Day	60% 3 8% 18% 9% 2	1890
	11th to 20th	Day	55% 4 8% 18% 12% 2	1990
	21st to end	Day	57% 3 10% 15% 13% 3	1730
March	1st to 10th	Day	61% 3 8% 12% 11% 5%	4579
	11th to 20th	Day	56% 2 11% 16% 10% 4	4806
	21st to end	Day	56% 3 5% 12% 20% 4	6096
April	1st to 10th	Day	55% 4 9% 17% 13% 3	2520
	11th to 20th	Day	54% 4 7% 19% 14% 1	2494
	21st to end	Day	57% 2 9% 17% 12% 3	2653
May	1st to 10th	Day	67% 3 6% 16% 8% 1	6298
	11th to 20th	Day	57% 4 13% 17% 8% 1	6462
	21st to end	Day	55% 5% 10% 22% 8% 1	7103
June	1st to 10th	Day	56% 4 11% 18% 10% 1	2800
	11th to 20th	Day	48% 5% 11% 23% 11% 2	2800
	21st to end	Day	54% 4 11% 19% 10% 1	2800
July	1st to 10th	Day	45% 7% 15% 23% 11%	6290
	11th to 20th	Day	39% 9% 14% 27% 10%	6285
	21st to end	Day	41% 6% 11% 34% 7%	6728
August	1st to 10th	Day	48% 5% 14% 22% 10% 1	4549
	11th to 20th	Day	49% 6% 16% 23% 6%	4026
	21st to end	Day	41% 7% 16% 25% 10% 1	4312
September	1st to 10th	Day	40% 4 10% 32% 13% 1	2400
	11th to 20th	Day	39% 3 9% 30% 17% 1	2313
	21st to end	Day	46% 4 13% 24% 13% 2	2200
October	1st to 10th	Day	43% 6% 10% 25% 14%	3372
	11th to 20th	Day	44% 4 12% 22% 16% 2	3209
	21st to end	Day	44% 4 13% 30% 8% 1	3180
November	1st to 10th	Day	53% 5% 11% 18% 12% 1	1851
	11th to 20th	Day	54% 4 9% 15% 15% 3	1864
	21st to end	Day	57% 4 12% 18% 8% 1	1680
December	1st to 10th	Day	70% 5% 8% 12% 5%	2680
	11th to 20th	Day	59% 5% 10% 16% 10%	3066
	21st to end	Day	58% 4 6% 15% 15% 2	4048
January	1st to 10th	Night	58% 6% 11% 18% 7% 1	8234
	11th to 20th	Night	69% 4 8% 11% 7% 2	8280
	21st to end	Night	55% 6% 10% 16% 11% 2	9021
February	1st to 10th	Night	58% 5% 9% 17% 10% 2	2730
	11th to 20th	Night	55% 5% 8% 18% 13% 1	2527
	21st to end	Night	55% 4 10% 18% 11% 2	2076
March	1st to 10th	Night	59% 4 8% 15% 13% 2	5494
	11th to 20th	Night	51% 4 14% 18% 10% 3	5372
	21st to end	Night	56% 4 5% 17% 16% 3	5077
April	1st to 10th	Night	54% 3 8% 18% 15% 2	2100
	11th to 20th	Night	54% 3 11% 19% 12%	2075
	21st to end	Night	51% 3 9% 21% 13% 3	1965
May	1st to 10th	Night	67% 2 7% 15% 8% 1	3921
	11th to 20th	Night	51% 5% 12% 24% 8% 1	3656
	21st to end	Night	53% 5% 13% 19% 11% 1	4015
June	1st to 10th	Night	49% 4 12% 23% 11% 1	1600
	11th to 20th	Night	42% 5% 15% 25% 13% 1	1600
	21st to end	Night	45% 4 15% 26% 9%	1600
July	1st to 10th	Night	40% 6% 18% 25% 10%	3560
	11th to 20th	Night	37% 7% 15% 28% 12%	3552
	21st to end	Night	33% 8% 15% 34% 9%	3809
August	1st to 10th	Night	43% 6% 18% 24% 10%	2576
	11th to 20th	Night	42% 5% 18% 26% 8%	3052
	21st to end	Night	33% 7% 18% 31% 10% 1	3586
September	1st to 10th	Night	36% 5% 15% 31% 13% 1	2000
	11th to 20th	Night	37% 3 13% 32% 15% 1	2086
	21st to end	Night	42% 4 12% 26% 14% 2	2200
October	1st to 10th	Night	47% 7% 10% 24% 12% 1	3805
	11th to 20th	Night	40% 6% 12% 26% 11% 6%	3928
	21st to end	Night	48% 5% 14% 24% 8% 1	4610
November	1st to 10th	Night	54% 4 10% 18% 12% 2	2667
	11th to 20th	Night	54% 4 8% 19% 12% 3	2754
	21st to end	Night	55% 4 13% 19% 9% 1	2940
December	1st to 10th	Night	64% 6% 11% 14% 5%	4720
	11th to 20th	Night	61% 5% 7% 14% 13% 1	5348
	21st to end	Night	60% 4 7% 13% 12% 4	7150

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	17% 30% 34% 14% 5%	220
	11th to 20th	Day	30% 25% 36% 6% 2 1	220
	21st to end	Day	29% 25% 36% 8% 2 1	245
February	1st to 10th	Day	36% 35% 22% 6% 1	330
	11th to 20th	Day	32% 30% 29% 8% 1	469
	21st to end	Day	32% 28% 29% 9% 2	446
March	1st to 10th	Day	30% 26% 31% 11% 2	540
	11th to 20th	Day	34% 26% 27% 9% 3 1	540
	21st to end	Day	36% 27% 21% 10% 4 1	594
April	1st to 10th	Day	38% 22% 26% 11% 3 1	540
	11th to 20th	Day	38% 24% 23% 11% 3 1	532
	21st to end	Day	33% 25% 25% 11% 5% 1	540
May	1st to 10th	Day	37% 22% 27% 8% 4 2	543
	11th to 20th	Day	26% 21% 33% 16% 3 1	567
	21st to end	Day	26% 20% 33% 16% 4 1	617
June	1st to 10th	Day	30% 16% 34% 15% 5% 1	530
	11th to 20th	Day	21% 18% 36% 17% 6% 1	530
	21st to end	Day	27% 19% 32% 16% 6% 1	530
July	1st to 10th	Day	19% 12% 39% 21% 8% 2	525
	11th to 20th	Day	15% 13% 41% 22% 7% 2	524
	21st to end	Day	17% 15% 41% 19% 5% 2	576
August	1st to 10th	Day	15% 14% 33% 24% 10% 3	526
	11th to 20th	Day	15% 11% 36% 22% 10% 4	519
	21st to end	Day	14% 18% 35% 19% 10% 4	583
September	1st to 10th	Day	19% 14% 33% 17% 10% 7%	530
	11th to 20th	Day	15% 14% 26% 23% 13% 9%	530
	21st to end	Day	18% 20% 31% 19% 8% 5%	530
October	1st to 10th	Day	26% 17% 28% 15% 11% 2	530
	11th to 20th	Day	28% 24% 24% 17% 7% 1	519
	21st to end	Day	31% 21% 30% 15% 3	462
November	1st to 10th	Day	29% 22% 28% 14% 7%	425
	11th to 20th	Day	29% 28% 26% 12% 4 1	404
	21st to end	Day	32% 31% 25% 10% 2	220
December	1st to 10th	Day	29% 30% 26% 12% 3	220
	11th to 20th	Day	35% 34% 24% 7% 1	220
	21st to end	Day	33% 24% 31% 9% 3	242
January	1st to 10th	Night	23% 30% 29% 14% 4	840
	11th to 20th	Night	26% 26% 32% 14% 3	840
	21st to end	Night	15% 33% 32% 17% 3 1	924
February	1st to 10th	Night	21% 30% 32% 15% 2	840
	11th to 20th	Night	23% 30% 31% 14% 2	823
	21st to end	Night	23% 30% 31% 14% 3	692
March	1st to 10th	Night	28% 24% 29% 16% 3	840
	11th to 20th	Night	30% 25% 29% 12% 4 1	840
	21st to end	Night	29% 24% 27% 17% 3 1	924
April	1st to 10th	Night	28% 24% 29% 16% 3	840
	11th to 20th	Night	29% 24% 24% 17% 6% 1	831
	21st to end	Night	29% 19% 27% 19% 5% 1	705
May	1st to 10th	Night	30% 18% 27% 18% 7%	531
	11th to 20th	Night	21% 19% 29% 23% 6% 1	414
	21st to end	Night	19% 16% 34% 21% 9%	455
June	1st to 10th	Night	25% 12% 30% 22% 11% 1	400
	11th to 20th	Night	21% 12% 27% 29% 10% 1	400
	21st to end	Night	20% 14% 27% 30% 9% 1	400
July	1st to 10th	Night	13% 11% 31% 29% 15% 1	390
	11th to 20th	Night	11% 10% 29% 33% 15% 2	388
	21st to end	Night	13% 10% 32% 35% 10% 1	438
August	1st to 10th	Night	13% 8% 28% 34% 16% 1	398
	11th to 20th	Night	14% 7% 27% 33% 15% 4	679
	21st to end	Night	15% 10% 27% 30% 17% 1	880
September	1st to 10th	Night	16% 14% 24% 29% 14% 3	800
	11th to 20th	Night	16% 10% 24% 24% 22% 4	800
	21st to end	Night	21% 14% 25% 21% 18% 2	800
October	1st to 10th	Night	23% 16% 23% 22% 14% 2	800
	11th to 20th	Night	24% 23% 22% 21% 9% 1	800
	21st to end	Night	29% 26% 23% 17% 5%	880
November	1st to 10th	Night	26% 24% 26% 17% 6% 1	820
	11th to 20th	Night	26% 27% 25% 14% 7% 2	840
	21st to end	Night	24% 30% 25% 16% 5% 1	840
December	1st to 10th	Night	23% 31% 29% 13% 3	840
	11th to 20th	Night	27% 27% 26% 16% 4	840
	21st to end	Night	27% 27% 30% 12% 3	924

Page generated at 2026-05-29 01:53:29. Version ac07

Copyright © 2026 Attilla Danko.