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 2024-01-27.

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% 5% 8% 8% 4 5% 5% 6% 7% 28%	74872
	Night	12% 10% 5% 9% 8% 4 6% 5% 6% 7% 28%	75169
Transparency	Day	53% 3 10% 20% 11% 2	74577
	Night	52% 4 11% 21% 12% 1	74998
Seeing	Day	25% 21% 31% 16% 6% 2	13598
	Night	22% 22% 27% 20% 8% 1	22762

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% 12% 7% 13% 11% 6% 7% 6% 6% 7% 20%	1517
	11th to 20th	Day	9% 12% 7% 10% 11% 5% 5% 6% 5% 7% 23%	1520
	21st to end	Day	8% 10% 6% 12% 10% 5% 8% 7% 6% 7% 22%	1636
February	1st to 10th	Day	10% 13% 6% 11% 11% 5% 6% 6% 6% 6% 20%	1620
	11th to 20th	Day	6% 10% 5% 11% 12% 6% 7% 5% 7% 6% 24%	1691
	21st to end	Day	11% 14% 4 11% 9% 4 5% 5% 7% 6% 24%	1480
March	1st to 10th	Day	10% 9% 6% 12% 11% 5% 5% 5% 5% 6% 27%	1797
	11th to 20th	Day	12% 13% 6% 8% 9% 5% 5% 5% 4 6% 26%	1870
	21st to end	Day	13% 12% 5% 9% 7% 4 5% 4 4 5% 31%	2370
April	1st to 10th	Day	15% 12% 5% 7% 7% 3 6% 5% 6% 6% 28%	2160
	11th to 20th	Day	14% 11% 5% 9% 6% 5% 4 5% 5% 5% 32%	2134
	21st to end	Day	19% 14% 5% 9% 5% 4 4 3 5% 5% 26%	2273
May	1st to 10th	Day	17% 11% 4 9% 7% 3 5% 5% 5% 6% 28%	2438
	11th to 20th	Day	17% 9% 4 6% 7% 3 4 5% 5% 8% 32%	2478
	21st to end	Day	15% 8% 3 8% 7% 4 6% 5% 5% 8% 32%	2725
June	1st to 10th	Day	21% 9% 4 7% 6% 4 5% 6% 7% 7% 25%	2520
	11th to 20th	Day	16% 7% 4 7% 6% 4 6% 6% 7% 8% 31%	2520
	21st to end	Day	19% 9% 4 7% 8% 4 6% 6% 6% 7% 26%	2520
July	1st to 10th	Day	14% 7% 4 7% 6% 4 5% 6% 5% 9% 33%	2520
	11th to 20th	Day	13% 6% 4 7% 8% 4 6% 6% 7% 9% 30%	2520
	21st to end	Day	14% 6% 3 6% 7% 5% 7% 8% 7% 8% 29%	2744
August	1st to 10th	Day	11% 7% 3 9% 8% 4 6% 7% 7% 8% 29%	2506
	11th to 20th	Day	11% 8% 4 7% 7% 5% 6% 7% 7% 9% 30%	2206
	21st to end	Day	12% 6% 4 7% 7% 4 6% 6% 7% 8% 32%	2376
September	1st to 10th	Day	14% 7% 3 6% 6% 3 4 6% 6% 8% 38%	2160
	11th to 20th	Day	12% 7% 3 6% 5% 3 5% 4 5% 7% 42%	2083
	21st to end	Day	13% 8% 3 6% 6% 4 5% 6% 7% 8% 35%	1980
October	1st to 10th	Day	19% 12% 3 8% 5% 4 5% 5% 4 6% 29%	1867
	11th to 20th	Day	15% 12% 4 8% 6% 3 5% 6% 5% 5% 30%	1783
	21st to end	Day	20% 12% 5% 10% 7% 3 4 4 4 6% 25%	1782
November	1st to 10th	Day	10% 11% 5% 10% 8% 5% 6% 5% 5% 6% 28%	1671
	11th to 20th	Day	12% 11% 5% 10% 9% 4 5% 5% 5% 6% 27%	1687
	21st to end	Day	12% 13% 6% 11% 7% 4 6% 5% 7% 8% 23%	1520
December	1st to 10th	Day	13% 17% 8% 13% 10% 5% 4 4 4 6% 16%	1520
	11th to 20th	Day	13% 12% 6% 12% 8% 4 5% 5% 5% 6% 23%	1906
	21st to end	Day	16% 15% 7% 9% 7% 4 5% 5% 6% 6% 19%	2772
January	1st to 10th	Night	9% 11% 6% 11% 11% 7% 7% 7% 6% 7% 18%	2649
	11th to 20th	Night	8% 13% 5% 11% 10% 6% 7% 7% 6% 8% 19%	2660
	21st to end	Night	7% 8% 5% 11% 12% 6% 7% 7% 6% 8% 23%	2860
February	1st to 10th	Night	8% 10% 7% 12% 10% 7% 8% 6% 7% 8% 17%	2340
	11th to 20th	Night	7% 9% 5% 10% 11% 6% 8% 7% 6% 8% 22%	2155
	21st to end	Night	9% 11% 6% 10% 10% 5% 5% 7% 6% 6% 25%	1776
March	1st to 10th	Night	10% 10% 6% 11% 9% 5% 7% 6% 6% 5% 24%	2150
	11th to 20th	Night	11% 12% 5% 9% 9% 4 6% 5% 6% 6% 28%	2087
	21st to end	Night	12% 11% 6% 8% 6% 4 5% 5% 5% 6% 32%	1985
April	1st to 10th	Night	14% 9% 6% 10% 7% 5% 5% 5% 5% 7% 28%	1800
	11th to 20th	Night	15% 10% 4 8% 7% 4 5% 5% 6% 7% 28%	1775
	21st to end	Night	17% 10% 4 9% 8% 3 5% 4 4 6% 31%	1685
May	1st to 10th	Night	18% 11% 4 8% 6% 3 4 5% 6% 6% 29%	1536
	11th to 20th	Night	16% 8% 4 6% 5% 3 6% 4 5% 7% 36%	1415
	21st to end	Night	12% 8% 4 6% 6% 3 5% 5% 7% 9% 35%	1550
June	1st to 10th	Night	19% 7% 3 6% 5% 4 4 6% 6% 8% 32%	1440
	11th to 20th	Night	15% 7% 3 5% 5% 3 4 6% 6% 8% 37%	1440
	21st to end	Night	16% 5% 3 6% 6% 4 5% 5% 7% 8% 35%	1440
July	1st to 10th	Night	11% 5% 3 6% 5% 4 5% 4 6% 8% 42%	1440
	11th to 20th	Night	9% 5% 3 5% 5% 4 6% 7% 6% 8% 41%	1440
	21st to end	Night	10% 6% 2 5% 5% 4 5% 6% 6% 11% 40%	1574
August	1st to 10th	Night	11% 4 2 5% 5% 3 6% 5% 7% 9% 42%	1432
	11th to 20th	Night	9% 7% 2 7% 6% 4 5% 7% 6% 8% 39%	1674
	21st to end	Night	10% 7% 3 6% 6% 3 5% 6% 6% 9% 39%	1980
September	1st to 10th	Night	11% 6% 2 6% 6% 3 5% 5% 6% 7% 41%	1800
	11th to 20th	Night	12% 7% 2 6% 5% 4 4 4 4 7% 45%	1876
	21st to end	Night	14% 8% 2 5% 6% 3 5% 4 6% 7% 39%	1980
October	1st to 10th	Night	17% 10% 3 7% 7% 4 5% 5% 5% 7% 29%	2091
	11th to 20th	Night	16% 9% 3 7% 7% 4 5% 5% 6% 8% 30%	2175
	21st to end	Night	19% 12% 5% 9% 8% 5% 5% 5% 5% 6% 22%	2574
November	1st to 10th	Night	11% 12% 5% 9% 8% 5% 5% 6% 5% 6% 27%	2407
	11th to 20th	Night	13% 10% 5% 10% 8% 4 6% 5% 5% 6% 27%	2491
	21st to end	Night	11% 12% 6% 10% 9% 5% 6% 5% 7% 8% 22%	2660
December	1st to 10th	Night	13% 13% 8% 13% 10% 5% 6% 5% 5% 6% 16%	2660
	11th to 20th	Night	13% 12% 6% 11% 10% 4 5% 5% 6% 6% 21%	3288
	21st to end	Night	15% 14% 5% 13% 8% 4 6% 5% 6% 6% 17%	4884

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	60% 3 7% 19% 10% 1	1518
	11th to 20th	Day	58% 4 8% 16% 10% 4	1520
	21st to end	Day	58% 4 8% 16% 13% 3	1636
February	1st to 10th	Day	62% 3 7% 17% 7% 3	1620
	11th to 20th	Day	56% 4 8% 18% 12% 2	1700
	21st to end	Day	58% 2 10% 14% 13% 3	1480
March	1st to 10th	Day	58% 3 9% 15% 11% 3	1800
	11th to 20th	Day	58% 3 8% 12% 15% 4	1870
	21st to end	Day	54% 2 6% 16% 16% 5%	2370
April	1st to 10th	Day	54% 3 9% 18% 13% 3	2160
	11th to 20th	Day	52% 4 8% 20% 15% 1	2134
	21st to end	Day	60% 2 8% 15% 12% 3	2273
May	1st to 10th	Day	56% 3 6% 20% 13% 1	2438
	11th to 20th	Day	50% 3 8% 23% 14% 2	2482
	21st to end	Day	50% 4 14% 20% 10% 1	2725
June	1st to 10th	Day	56% 4 12% 18% 10% 1	2520
	11th to 20th	Day	49% 4 11% 24% 11% 2	2520
	21st to end	Day	55% 4 12% 19% 10% 1	2520
July	1st to 10th	Day	46% 4 12% 26% 11% 1	2450
	11th to 20th	Day	46% 5% 13% 29% 7%	2445
	21st to end	Day	49% 5% 12% 24% 10%	2591
August	1st to 10th	Day	49% 4 14% 24% 10%	2492
	11th to 20th	Day	48% 3 14% 25% 9%	2206
	21st to end	Day	46% 4 12% 26% 11% 1	2376
September	1st to 10th	Day	42% 4 11% 30% 13% 1	2160
	11th to 20th	Day	41% 3 9% 29% 17% 2	2083
	21st to end	Day	46% 3 12% 24% 12% 2	1980
October	1st to 10th	Day	55% 4 9% 19% 13%	1867
	11th to 20th	Day	53% 4 12% 22% 9% 1	1783
	21st to end	Day	60% 2 10% 19% 8% 2	1782
November	1st to 10th	Day	54% 4 11% 18% 12% 1	1671
	11th to 20th	Day	56% 4 9% 15% 14% 3	1687
	21st to end	Day	56% 3 12% 18% 9% 1	1520
December	1st to 10th	Day	69% 3 9% 14% 6% 1	1520
	11th to 20th	Day	60% 3 10% 16% 10% 1	1906
	21st to end	Day	64% 2 7% 16% 12%	2772
January	1st to 10th	Night	59% 4 7% 18% 11% 1	2649
	11th to 20th	Night	59% 4 9% 16% 10% 2	2660
	21st to end	Night	52% 4 7% 17% 17% 3	2860
February	1st to 10th	Night	60% 4 10% 14% 10% 2	2340
	11th to 20th	Night	54% 5% 8% 18% 14% 1	2157
	21st to end	Night	56% 3 9% 18% 12% 2	1776
March	1st to 10th	Night	58% 3 8% 16% 12% 2	2160
	11th to 20th	Night	54% 2 8% 20% 13% 3	2088
	21st to end	Night	51% 4 7% 19% 16% 4	1985
April	1st to 10th	Night	53% 3 8% 19% 15% 2	1800
	11th to 20th	Night	53% 2 11% 20% 13% 1	1775
	21st to end	Night	54% 2 10% 19% 12% 3	1685
May	1st to 10th	Night	54% 3 7% 19% 16% 2	1536
	11th to 20th	Night	46% 3 9% 24% 16% 2	1416
	21st to end	Night	44% 4 16% 23% 12% 2	1551
June	1st to 10th	Night	48% 4 13% 24% 10% 1	1440
	11th to 20th	Night	43% 4 15% 25% 13% 1	1440
	21st to end	Night	44% 4 15% 27% 9%	1440
July	1st to 10th	Night	37% 4 16% 28% 13% 1	1400
	11th to 20th	Night	37% 5% 16% 32% 10%	1392
	21st to end	Night	36% 5% 18% 29% 11% 1	1486
August	1st to 10th	Night	35% 4 21% 30% 10%	1422
	11th to 20th	Night	39% 5% 15% 30% 11%	1674
	21st to end	Night	38% 4 15% 30% 12%	1980
September	1st to 10th	Night	37% 5% 16% 30% 12% 1	1800
	11th to 20th	Night	38% 3 13% 31% 15% 1	1876
	21st to end	Night	43% 4 12% 27% 13% 2	1980
October	1st to 10th	Night	53% 4 10% 19% 13% 1	2091
	11th to 20th	Night	50% 3 13% 23% 10% 1	2175
	21st to end	Night	59% 3 11% 15% 9% 2	2574
November	1st to 10th	Night	54% 4 10% 18% 12% 2	2407
	11th to 20th	Night	55% 3 8% 19% 12% 3	2491
	21st to end	Night	55% 4 13% 19% 9% 1	2660
December	1st to 10th	Night	65% 4 9% 15% 7%	2660
	11th to 20th	Night	60% 3 8% 15% 13% 1	3288
	21st to end	Night	65% 2 7% 15% 9%	4884

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% 27% 34% 16% 6%	180
	11th to 20th	Day	26% 24% 39% 7% 3 1	180
	21st to end	Day	22% 27% 38% 8% 3 1	190
February	1st to 10th	Day	37% 39% 19% 5%	240
	11th to 20th	Day	28% 31% 31% 7% 1	359
	21st to end	Day	31% 28% 29% 10% 2	346
March	1st to 10th	Day	27% 26% 32% 13% 2	420
	11th to 20th	Day	29% 28% 28% 11% 3 1	420
	21st to end	Day	32% 26% 23% 12% 5% 1	462
April	1st to 10th	Day	32% 22% 28% 13% 4 1	420
	11th to 20th	Day	33% 25% 23% 13% 4 2	412
	21st to end	Day	33% 21% 27% 12% 5% 1	420
May	1st to 10th	Day	32% 22% 28% 10% 6% 3	423
	11th to 20th	Day	23% 21% 35% 16% 3 1	447
	21st to end	Day	23% 19% 34% 19% 5% 1	485
June	1st to 10th	Day	30% 14% 34% 15% 5% 1	450
	11th to 20th	Day	21% 17% 36% 18% 7% 1	450
	21st to end	Day	26% 16% 31% 19% 7% 1	450
July	1st to 10th	Day	19% 10% 37% 23% 9% 2	445
	11th to 20th	Day	15% 13% 40% 22% 8% 2	444
	21st to end	Day	16% 14% 42% 19% 6% 2	488
August	1st to 10th	Day	14% 15% 34% 23% 11% 3	446
	11th to 20th	Day	15% 11% 36% 24% 11% 5%	439
	21st to end	Day	14% 17% 33% 20% 11% 5%	495
September	1st to 10th	Day	19% 13% 32% 18% 10% 8%	450
	11th to 20th	Day	17% 15% 26% 20% 12% 9%	450
	21st to end	Day	16% 20% 31% 19% 9% 5%	450
October	1st to 10th	Day	28% 17% 26% 14% 12% 2	450
	11th to 20th	Day	27% 23% 25% 17% 7% 1	441
	21st to end	Day	32% 20% 30% 16% 3	396
November	1st to 10th	Day	25% 22% 29% 16% 8%	365
	11th to 20th	Day	30% 29% 24% 12% 4 1	347
	21st to end	Day	26% 32% 28% 12% 2	180
December	1st to 10th	Day	26% 30% 27% 14% 3	180
	11th to 20th	Day	31% 37% 23% 8% 1	180
	21st to end	Day	34% 25% 31% 8% 2 1	198
January	1st to 10th	Night	22% 29% 30% 15% 4	760
	11th to 20th	Night	24% 25% 33% 14% 3	760
	21st to end	Night	13% 33% 32% 19% 3 1	820
February	1st to 10th	Night	20% 33% 31% 14% 2	720
	11th to 20th	Night	21% 31% 31% 16% 2	703
	21st to end	Night	23% 30% 29% 15% 3	592
March	1st to 10th	Night	26% 23% 30% 18% 3	720
	11th to 20th	Night	27% 26% 28% 14% 5% 1	720
	21st to end	Night	26% 23% 27% 19% 4 1	792
April	1st to 10th	Night	25% 23% 30% 18% 3	720
	11th to 20th	Night	26% 23% 25% 18% 7% 1	711
	21st to end	Night	28% 20% 26% 20% 5% 1	605
May	1st to 10th	Night	28% 17% 26% 20% 8%	456
	11th to 20th	Night	20% 20% 29% 24% 6% 1	354
	21st to end	Night	18% 15% 34% 23% 11%	389
June	1st to 10th	Night	24% 12% 30% 22% 12% 1	360
	11th to 20th	Night	20% 11% 26% 31% 11% 1	360
	21st to end	Night	19% 12% 27% 31% 10% 1	360
July	1st to 10th	Night	13% 9% 30% 30% 16% 1	350
	11th to 20th	Night	11% 9% 29% 33% 16% 2	348
	21st to end	Night	13% 9% 31% 35% 10% 1	394
August	1st to 10th	Night	12% 8% 28% 34% 17% 1	358
	11th to 20th	Night	13% 7% 28% 32% 16% 4	610
	21st to end	Night	15% 9% 26% 30% 19% 2	792
September	1st to 10th	Night	16% 14% 23% 30% 15% 3	720
	11th to 20th	Night	18% 11% 24% 23% 20% 4	720
	21st to end	Night	21% 14% 23% 21% 18% 2	720
October	1st to 10th	Night	24% 16% 22% 22% 14% 2	720
	11th to 20th	Night	24% 22% 22% 21% 10% 1	720
	21st to end	Night	29% 26% 21% 18% 6%	792
November	1st to 10th	Night	24% 23% 28% 18% 6% 1	740
	11th to 20th	Night	25% 27% 25% 14% 7% 2	760
	21st to end	Night	22% 30% 25% 17% 6% 1	760
December	1st to 10th	Night	23% 32% 28% 14% 4	760
	11th to 20th	Night	25% 26% 27% 17% 4 1	760
	21st to end	Night	26% 28% 31% 13% 3	836

Page generated at 2024-01-24 09:37:30. Version ac07

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