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 2025-02-06.

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	12% 11% 4 10% 7% 6% 6% 4 6% 7% 27%	108398
	Night	11% 11% 5% 12% 7% 6% 6% 4 6% 6% 26%	109858
Transparency	Day	52% 4 11% 21% 11% 1	111914
	Night	53% 4 11% 20% 11% 2	114506
Seeing	Day	25% 21% 31% 15% 6% 2	14896
	Night	22% 22% 27% 20% 8% 1	24052

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	6% 13% 7% 14% 10% 9% 6% 4 6% 6% 19%	3597
	11th to 20th	Day	6% 13% 7% 19% 12% 8% 5% 3 4 5% 18%	3570
	21st to end	Day	8% 11% 5% 15% 9% 7% 8% 5% 6% 6% 21%	3978
February	1st to 10th	Day	9% 14% 6% 12% 9% 6% 6% 5% 6% 6% 22%	1755
	11th to 20th	Day	6% 10% 6% 13% 10% 8% 7% 4 7% 6% 24%	1787
	21st to end	Day	10% 16% 4 12% 7% 6% 4 4 7% 6% 24%	1570
March	1st to 10th	Day	16% 14% 6% 13% 8% 5% 5% 4 4 4 21%	3116
	11th to 20th	Day	8% 17% 7% 12% 8% 6% 6% 4 5% 5% 22%	3286
	21st to end	Day	12% 12% 4 10% 7% 5% 4 4 5% 5% 32%	4160
April	1st to 10th	Day	15% 15% 4 8% 6% 4 5% 4 5% 6% 27%	2280
	11th to 20th	Day	14% 13% 4 10% 5% 6% 5% 4 5% 5% 31%	2254
	21st to end	Day	18% 15% 4 10% 4 5% 5% 2 5% 5% 27%	2400
May	1st to 10th	Day	19% 13% 4 10% 6% 5% 5% 4 5% 6% 25%	4288
	11th to 20th	Day	16% 11% 4 9% 6% 5% 5% 5% 6% 8% 25%	4398
	21st to end	Day	13% 6% 3 8% 6% 6% 6% 4 6% 8% 34%	4837
June	1st to 10th	Day	20% 9% 4 9% 6% 5% 5% 4 7% 6% 25%	2660
	11th to 20th	Day	15% 8% 4 8% 6% 5% 5% 5% 7% 7% 30%	2660
	21st to end	Day	19% 10% 3 8% 6% 5% 5% 5% 6% 7% 25%	2660
July	1st to 10th	Day	11% 7% 3 7% 6% 5% 6% 6% 7% 9% 31%	4440
	11th to 20th	Day	9% 6% 3 8% 7% 5% 7% 6% 8% 10% 30%	4440
	21st to end	Day	12% 7% 3 8% 6% 6% 6% 5% 8% 8% 31%	4814
August	1st to 10th	Day	14% 8% 3 9% 6% 5% 6% 5% 7% 8% 28%	4423
	11th to 20th	Day	11% 9% 4 10% 6% 6% 7% 6% 7% 8% 26%	3862
	21st to end	Day	11% 7% 3 7% 6% 5% 7% 5% 8% 9% 33%	4180
September	1st to 10th	Day	13% 7% 2 7% 5% 4 5% 4 6% 8% 39%	2280
	11th to 20th	Day	11% 7% 3 7% 4 5% 5% 4 6% 7% 43%	2198
	21st to end	Day	13% 8% 3 7% 5% 5% 5% 4 7% 8% 34%	2090
October	1st to 10th	Day	18% 11% 3 9% 5% 5% 5% 4 5% 6% 30%	1970
	11th to 20th	Day	14% 12% 4 9% 5% 4 5% 4 5% 5% 31%	1882
	21st to end	Day	18% 12% 5% 11% 6% 4 3 4 4 7% 26%	1881
November	1st to 10th	Day	10% 12% 5% 11% 7% 7% 6% 4 6% 6% 28%	1761
	11th to 20th	Day	11% 12% 5% 11% 8% 6% 5% 4 6% 5% 28%	1775
	21st to end	Day	12% 15% 5% 12% 7% 5% 6% 4 7% 7% 22%	1600
December	1st to 10th	Day	8% 18% 8% 22% 10% 6% 5% 3 4 4 12%	2600
	11th to 20th	Day	12% 12% 6% 16% 7% 6% 5% 4 5% 6% 21%	2986
	21st to end	Day	12% 13% 6% 12% 6% 6% 5% 3 6% 6% 24%	3960
January	1st to 10th	Night	9% 13% 6% 15% 9% 9% 7% 5% 6% 5% 16%	6349
	11th to 20th	Night	5% 13% 7% 21% 13% 8% 7% 4 6% 6% 11%	6315
	21st to end	Night	9% 8% 5% 15% 9% 8% 9% 6% 8% 7% 16%	6974
February	1st to 10th	Night	8% 11% 6% 13% 9% 8% 7% 5% 7% 7% 19%	2536
	11th to 20th	Night	6% 9% 6% 12% 10% 8% 7% 5% 6% 8% 22%	2279
	21st to end	Night	9% 12% 5% 12% 9% 6% 5% 6% 6% 6% 25%	1884
March	1st to 10th	Night	15% 12% 5% 11% 8% 6% 6% 4 5% 5% 24%	3724
	11th to 20th	Night	9% 14% 6% 12% 7% 6% 4 4 6% 5% 27%	3671
	21st to end	Night	11% 12% 6% 11% 6% 5% 4 3 5% 4 32%	3471
April	1st to 10th	Night	13% 12% 5% 11% 7% 6% 5% 4 5% 6% 27%	1900
	11th to 20th	Night	15% 12% 3 9% 6% 6% 5% 4 6% 7% 28%	1875
	21st to end	Night	17% 11% 4 10% 6% 4 4 3 4 5% 31%	1778
May	1st to 10th	Night	17% 15% 4 9% 6% 4 5% 5% 5% 6% 23%	2680
	11th to 20th	Night	17% 12% 4 8% 4 4 4 4 5% 6% 31%	2495
	21st to end	Night	11% 8% 3 7% 6% 5% 5% 4 7% 8% 36%	2738
June	1st to 10th	Night	18% 8% 3 7% 5% 5% 4 5% 6% 8% 32%	1520
	11th to 20th	Night	14% 8% 3 6% 4 4 4 5% 6% 8% 37%	1520
	21st to end	Night	17% 7% 3 7% 5% 5% 5% 4 7% 7% 34%	1520
July	1st to 10th	Night	9% 7% 4 9% 6% 5% 5% 5% 6% 7% 36%	2520
	11th to 20th	Night	10% 7% 2 7% 5% 6% 4 5% 6% 8% 40%	2520
	21st to end	Night	9% 7% 3 8% 5% 5% 5% 4 6% 8% 38%	2739
August	1st to 10th	Night	13% 8% 4 9% 5% 5% 4 4 5% 7% 36%	2506
	11th to 20th	Night	12% 9% 3 8% 5% 6% 5% 5% 6% 7% 34%	2932
	21st to end	Night	8% 6% 3 7% 6% 5% 5% 4 7% 9% 41%	3476
September	1st to 10th	Night	11% 6% 2 7% 5% 5% 4 5% 6% 7% 42%	1900
	11th to 20th	Night	11% 7% 2 7% 4 4 4 3 4 7% 46%	1981
	21st to end	Night	14% 8% 2 6% 5% 4 5% 4 7% 7% 38%	2090
October	1st to 10th	Night	16% 10% 3 8% 6% 5% 5% 4 5% 7% 29%	2208
	11th to 20th	Night	15% 10% 3 9% 6% 5% 5% 3 5% 8% 31%	2296
	21st to end	Night	18% 13% 4 11% 7% 6% 5% 3 5% 6% 23%	2717
November	1st to 10th	Night	11% 13% 5% 11% 7% 6% 6% 4 5% 6% 27%	2537
	11th to 20th	Night	12% 11% 5% 12% 7% 6% 5% 4 5% 6% 27%	2623
	21st to end	Night	11% 14% 5% 11% 8% 6% 5% 4 7% 7% 22%	2800
December	1st to 10th	Night	8% 13% 8% 21% 10% 8% 6% 4 5% 5% 11%	4580
	11th to 20th	Night	13% 14% 7% 15% 8% 6% 5% 3 5% 5% 20%	5208
	21st to end	Night	11% 16% 5% 14% 7% 5% 5% 4 6% 6% 22%	6996

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% 4 8% 22% 7% 1	3598
	11th to 20th	Day	66% 4 6% 12% 9% 4	3600
	21st to end	Day	58% 3 10% 16% 10% 2	3978
February	1st to 10th	Day	60% 3 8% 18% 8% 3	1755
	11th to 20th	Day	56% 4 8% 18% 13% 2	1796
	21st to end	Day	57% 2 10% 15% 13% 3	1570
March	1st to 10th	Day	67% 2 7% 11% 10% 2	3119
	11th to 20th	Day	61% 2 8% 15% 11% 3	3286
	21st to end	Day	54% 1 5% 14% 22% 3	4160
April	1st to 10th	Day	55% 3 9% 17% 14% 3	2280
	11th to 20th	Day	54% 4 7% 20% 14% 1	2254
	21st to end	Day	59% 2 9% 15% 12% 3	2400
May	1st to 10th	Day	60% 2 7% 21% 10% 1	4302
	11th to 20th	Day	56% 2 13% 19% 8% 1	4402
	21st to end	Day	47% 3 11% 27% 11% 1	4837
June	1st to 10th	Day	56% 4 12% 18% 10% 1	2660
	11th to 20th	Day	48% 4 11% 24% 11% 2	2660
	21st to end	Day	55% 4 11% 19% 9% 1	2660
July	1st to 10th	Day	43% 6% 15% 25% 10%	4370
	11th to 20th	Day	40% 7% 16% 30% 6%	4365
	21st to end	Day	46% 6% 11% 29% 8%	4661
August	1st to 10th	Day	48% 5% 14% 21% 10% 1	4409
	11th to 20th	Day	49% 7% 16% 23% 5%	3902
	21st to end	Day	42% 6% 17% 24% 10% 1	4180
September	1st to 10th	Day	41% 4 10% 31% 13% 1	2280
	11th to 20th	Day	40% 3 10% 29% 17% 1	2198
	21st to end	Day	46% 3 13% 24% 12% 2	2090
October	1st to 10th	Day	45% 7% 10% 25% 14%	3269
	11th to 20th	Day	44% 4 12% 22% 15% 3	3110
	21st to end	Day	43% 4 13% 31% 8% 1	3081
November	1st to 10th	Day	53% 4 11% 18% 12% 1	1761
	11th to 20th	Day	54% 4 9% 14% 16% 3	1775
	21st to end	Day	56% 4 12% 18% 9% 1	1600
December	1st to 10th	Day	70% 5% 8% 12% 4	2600
	11th to 20th	Day	59% 5% 9% 16% 10%	2986
	21st to end	Day	57% 3 6% 15% 16% 2	3960
January	1st to 10th	Night	60% 5% 10% 19% 7%	6349
	11th to 20th	Night	68% 4 8% 12% 7% 1	6360
	21st to end	Night	56% 5% 10% 15% 13% 2	6974
February	1st to 10th	Night	59% 4 10% 16% 10% 2	2536
	11th to 20th	Night	55% 5% 8% 18% 14% 1	2281
	21st to end	Night	56% 3 9% 18% 11% 2	1884
March	1st to 10th	Night	60% 2 7% 16% 12% 2	3734
	11th to 20th	Night	57% 1 10% 19% 11% 2	3672
	21st to end	Night	54% 2 4 18% 18% 4	3471
April	1st to 10th	Night	54% 3 8% 18% 15% 2	1900
	11th to 20th	Night	54% 2 11% 20% 12% 1	1875
	21st to end	Night	53% 2 9% 19% 13% 3	1778
May	1st to 10th	Night	61% 2 7% 20% 9% 1	2686
	11th to 20th	Night	53% 2 11% 24% 9% 1	2496
	21st to end	Night	44% 3 15% 22% 15% 1	2739
June	1st to 10th	Night	48% 4 13% 24% 10% 1	1520
	11th to 20th	Night	42% 4 15% 25% 13% 1	1520
	21st to end	Night	46% 4 15% 26% 9%	1520
July	1st to 10th	Night	43% 6% 16% 24% 12% 1	2480
	11th to 20th	Night	36% 6% 17% 31% 9%	2472
	21st to end	Night	38% 8% 16% 28% 9% 1	2651
August	1st to 10th	Night	43% 6% 18% 24% 9%	2496
	11th to 20th	Night	42% 5% 19% 25% 8%	2958
	21st to end	Night	33% 7% 18% 31% 11% 1	3476
September	1st to 10th	Night	36% 5% 15% 30% 12% 1	1900
	11th to 20th	Night	37% 3 13% 31% 15% 1	1981
	21st to end	Night	42% 4 12% 26% 13% 2	2090
October	1st to 10th	Night	48% 7% 10% 24% 11% 1	3689
	11th to 20th	Night	41% 6% 12% 25% 10% 6%	3807
	21st to end	Night	48% 5% 15% 24% 8% 1	4467
November	1st to 10th	Night	54% 4 10% 18% 12% 2	2537
	11th to 20th	Night	54% 4 7% 19% 12% 4	2623
	21st to end	Night	55% 4 13% 19% 9% 1	2800
December	1st to 10th	Night	65% 6% 11% 13% 4	4580
	11th to 20th	Night	61% 4 7% 13% 14% 1	5208
	21st to end	Night	60% 4 7% 13% 12% 4	6996

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% 6%	200
	11th to 20th	Day	27% 24% 40% 7% 3 1	200
	21st to end	Day	26% 26% 36% 8% 3 1	223
February	1st to 10th	Day	37% 37% 20% 5% 1	285
	11th to 20th	Day	30% 31% 30% 7% 1	395
	21st to end	Day	32% 27% 29% 10% 2	382
March	1st to 10th	Day	29% 24% 31% 13% 2	460
	11th to 20th	Day	31% 27% 28% 11% 3 1	460
	21st to end	Day	34% 25% 23% 11% 5% 1	506
April	1st to 10th	Day	34% 21% 28% 12% 4 1	460
	11th to 20th	Day	35% 25% 22% 12% 4 2	452
	21st to end	Day	33% 23% 26% 12% 5% 1	460
May	1st to 10th	Day	34% 21% 28% 10% 5% 3	463
	11th to 20th	Day	23% 20% 34% 17% 4 1	487
	21st to end	Day	23% 19% 34% 18% 5% 1	529
June	1st to 10th	Day	30% 14% 35% 15% 5% 1	490
	11th to 20th	Day	21% 17% 37% 18% 7% 1	490
	21st to end	Day	29% 18% 29% 17% 6% 1	490
July	1st to 10th	Day	18% 11% 39% 22% 8% 2	485
	11th to 20th	Day	15% 13% 41% 21% 7% 2	484
	21st to end	Day	17% 15% 42% 20% 5% 2	532
August	1st to 10th	Day	16% 15% 33% 23% 10% 3	486
	11th to 20th	Day	15% 11% 37% 23% 10% 4	479
	21st to end	Day	14% 17% 35% 19% 11% 5%	539
September	1st to 10th	Day	19% 14% 32% 18% 10% 7%	490
	11th to 20th	Day	15% 14% 26% 22% 13% 9%	490
	21st to end	Day	17% 19% 31% 19% 9% 5%	490
October	1st to 10th	Day	27% 18% 28% 14% 11% 2	490
	11th to 20th	Day	27% 24% 24% 17% 7% 1	480
	21st to end	Day	31% 21% 29% 15% 3	429
November	1st to 10th	Day	27% 22% 29% 15% 7%	395
	11th to 20th	Day	30% 28% 25% 12% 4 1	375
	21st to end	Day	31% 32% 26% 11% 2	200
December	1st to 10th	Day	27% 31% 27% 13% 3	200
	11th to 20th	Day	33% 36% 24% 8% 1	200
	21st to end	Day	32% 23% 32% 10% 3	220
January	1st to 10th	Night	22% 31% 29% 15% 4	800
	11th to 20th	Night	24% 26% 33% 14% 3	800
	21st to end	Night	14% 33% 33% 18% 3 1	880
February	1st to 10th	Night	20% 32% 32% 14% 2	781
	11th to 20th	Night	22% 30% 31% 15% 2	743
	21st to end	Night	23% 30% 30% 15% 3	628
March	1st to 10th	Night	26% 23% 30% 17% 3	760
	11th to 20th	Night	27% 26% 29% 13% 4 1	760
	21st to end	Night	26% 24% 27% 18% 4 1	836
April	1st to 10th	Night	26% 23% 31% 18% 3	760
	11th to 20th	Night	27% 23% 25% 17% 6% 1	751
	21st to end	Night	29% 20% 25% 20% 5% 1	638
May	1st to 10th	Night	28% 17% 27% 20% 8%	481
	11th to 20th	Night	21% 19% 28% 24% 6% 1	374
	21st to end	Night	17% 15% 35% 23% 10%	411
June	1st to 10th	Night	24% 12% 30% 22% 11% 1	380
	11th to 20th	Night	21% 11% 27% 30% 11% 1	380
	21st to end	Night	20% 13% 27% 30% 10% 1	380
July	1st to 10th	Night	13% 10% 30% 30% 15% 1	370
	11th to 20th	Night	11% 10% 29% 33% 15% 2	368
	21st to end	Night	13% 9% 31% 35% 10% 1	416
August	1st to 10th	Night	13% 8% 28% 33% 16% 1	378
	11th to 20th	Night	14% 7% 28% 32% 15% 4	645
	21st to end	Night	15% 10% 26% 30% 18% 1	836
September	1st to 10th	Night	16% 14% 23% 29% 14% 3	760
	11th to 20th	Night	17% 10% 23% 24% 21% 4	760
	21st to end	Night	21% 14% 23% 22% 18% 2	760
October	1st to 10th	Night	24% 16% 23% 22% 14% 2	760
	11th to 20th	Night	25% 22% 21% 21% 9% 1	760
	21st to end	Night	29% 26% 22% 17% 5%	836
November	1st to 10th	Night	25% 24% 27% 17% 6% 1	780
	11th to 20th	Night	26% 26% 25% 14% 7% 2	800
	21st to end	Night	23% 30% 24% 16% 5% 1	800
December	1st to 10th	Night	23% 32% 29% 13% 4	800
	11th to 20th	Night	26% 26% 26% 17% 4 1	800
	21st to end	Night	25% 28% 31% 13% 3	880

Page generated at 2025-02-03 03:05:55. Version ac07

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