Hayfield Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hayfield Observatory clear sky chart from 2005-11-06 to 2025-01-07.

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% 6% 2 7% 5% 5% 5% 4 6% 8% 40%	105032
	Night	13% 6% 2 5% 4 4 4 4 6% 8% 45%	103814
Transparency	Day	39% 7% 11% 17% 18% 7%	108808
	Night	36% 7% 12% 18% 18% 9%	108178
Seeing	Day	14% 9% 21% 25% 21% 10%	14849
	Night	14% 7% 22% 29% 22% 6%	24302

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	17% 7% 2 5% 3 3 4 3 5% 7% 43%	3113
	11th to 20th	Day	13% 5% 2 5% 3 2 4 3 4 5% 56%	3131
	21st to end	Day	25% 8% 3 5% 3 3 3 2 4 5% 39%	3476
February	1st to 10th	Day	18% 9% 3 6% 5% 5% 5% 3 4 5% 38%	1900
	11th to 20th	Day	19% 6% 2 5% 3 4 4 3 5% 7% 42%	1848
	21st to end	Day	17% 8% 3 8% 5% 4 4 4 4 5% 38%	1570
March	1st to 10th	Day	22% 10% 3 7% 4 4 4 3 5% 6% 30%	3150
	11th to 20th	Day	16% 7% 2 7% 5% 5% 5% 4 5% 8% 36%	3480
	21st to end	Day	11% 7% 3 7% 5% 6% 5% 4 5% 6% 40%	4064
April	1st to 10th	Day	12% 7% 2 7% 4 5% 4 5% 6% 6% 41%	2280
	11th to 20th	Day	15% 6% 3 7% 4 4 5% 4 5% 7% 39%	2254
	21st to end	Day	9% 5% 2 6% 4 5% 5% 4 5% 7% 48%	2280
May	1st to 10th	Day	11% 5% 2 6% 5% 6% 7% 5% 8% 9% 37%	3765
	11th to 20th	Day	15% 6% 2 6% 4 5% 5% 4 5% 7% 41%	3764
	21st to end	Day	7% 4 2 6% 6% 4 6% 4 7% 12% 42%	4274
June	1st to 10th	Day	10% 6% 2 8% 7% 7% 8% 6% 8% 9% 29%	2470
	11th to 20th	Day	5% 5% 2 7% 8% 7% 6% 6% 8% 10% 35%	2537
	21st to end	Day	7% 7% 3 9% 7% 8% 8% 8% 9% 10% 25%	2576
July	1st to 10th	Day	7% 7% 3 9% 8% 9% 8% 7% 9% 11% 22%	4120
	11th to 20th	Day	7% 6% 2 8% 8% 8% 9% 7% 8% 9% 28%	3928
	21st to end	Day	8% 7% 3 9% 7% 8% 8% 6% 9% 11% 24%	4118
August	1st to 10th	Day	3 3 2 5% 5% 5% 5% 4 6% 8% 53%	3785
	11th to 20th	Day	7% 4 2 8% 5% 7% 6% 5% 7% 10% 39%	3729
	21st to end	Day	7% 7% 3 9% 7% 7% 8% 6% 7% 7% 33%	4180
September	1st to 10th	Day	10% 7% 3 9% 6% 7% 6% 5% 7% 7% 33%	2280
	11th to 20th	Day	11% 7% 3 8% 6% 4 5% 4 5% 8% 39%	2187
	21st to end	Day	9% 4 2 6% 5% 5% 5% 3 6% 6% 50%	2090
October	1st to 10th	Day	6% 6% 2 5% 4 4 4 4 4 7% 55%	2074
	11th to 20th	Day	8% 3 2 6% 4 5% 4 3 5% 7% 55%	1900
	21st to end	Day	9% 6% 2 4 4 3 3 2 5% 5% 56%	2090
November	1st to 10th	Day	10% 5% 2 6% 4 4 4 3 4 6% 52%	1956
	11th to 20th	Day	11% 5% 2 5% 3 3 3 3 4 5% 55%	1800
	21st to end	Day	13% 6% 3 7% 3 4 4 3 5% 6% 46%	1800
December	1st to 10th	Day	18% 7% 3 5% 4 3 4 3 4 6% 43%	2930
	11th to 20th	Day	11% 7% 2 6% 4 4 5% 3 6% 6% 46%	3373
	21st to end	Day	18% 8% 2 5% 3 3 4 2 4 6% 44%	4760
January	1st to 10th	Night	18% 8% 2 4 3 3 3 3 4 5% 48%	3862
	11th to 20th	Night	16% 7% 2 4 2 3 2 2 4 5% 53%	3800
	21st to end	Night	27% 9% 2 4 2 2 2 2 4 5% 40%	4180
February	1st to 10th	Night	18% 7% 3 6% 4 3 4 3 5% 5% 42%	2280
	11th to 20th	Night	20% 9% 3 5% 3 3 3 3 4 6% 41%	2218
	21st to end	Night	19% 9% 3 7% 4 3 3 3 5% 6% 37%	1884
March	1st to 10th	Night	24% 11% 4 7% 4 3 3 3 5% 5% 31%	3716
	11th to 20th	Night	15% 8% 2 6% 5% 5% 4 4 6% 7% 38%	3480
	21st to end	Night	15% 8% 2 5% 3 4 4 3 5% 6% 44%	3565
April	1st to 10th	Night	15% 7% 2 5% 4 4 4 3 5% 6% 44%	1900
	11th to 20th	Night	14% 5% 3 7% 4 4 4 4 4 6% 45%	1875
	21st to end	Night	8% 3 2 5% 4 3 3 4 5% 7% 56%	1900
May	1st to 10th	Night	14% 7% 2 5% 4 4 3 3 5% 7% 45%	3130
	11th to 20th	Night	14% 7% 2 7% 3 4 4 3 4 8% 43%	3129
	21st to end	Night	5% 4 2 5% 4 5% 5% 5% 7% 12% 46%	3277
June	1st to 10th	Night	7% 6% 2 6% 5% 5% 5% 5% 8% 11% 39%	1710
	11th to 20th	Night	3 3 2 5% 5% 4 5% 6% 9% 12% 45%	1632
	21st to end	Night	7% 6% 3 6% 6% 4 6% 5% 6% 11% 41%	1595
July	1st to 10th	Night	5% 6% 2 7% 6% 5% 6% 6% 8% 14% 34%	2850
	11th to 20th	Night	4 4 2 7% 5% 6% 5% 6% 10% 12% 39%	3026
	21st to end	Night	6% 5% 3 8% 6% 7% 7% 6% 9% 14% 30%	3435
August	1st to 10th	Night	2 3 1 3 3 4 4 5% 8% 12% 56%	3144
	11th to 20th	Night	3 3 2 5% 5% 5% 6% 5% 9% 14% 43%	3100
	21st to end	Night	5% 5% 2 7% 6% 6% 6% 6% 8% 10% 38%	3476
September	1st to 10th	Night	9% 7% 2 7% 6% 5% 4 4 6% 10% 39%	1900
	11th to 20th	Night	10% 5% 2 6% 5% 4 5% 4 7% 7% 44%	1971
	21st to end	Night	8% 4 3 5% 4 3 5% 4 6% 6% 52%	2090
October	1st to 10th	Night	6% 5% 2 5% 3 4 4 3 6% 7% 56%	2100
	11th to 20th	Night	7% 4 2 3 4 2 3 3 4 7% 60%	2280
	21st to end	Night	12% 4 2 4 3 3 3 2 4 4 59%	2508
November	1st to 10th	Night	10% 5% 3 5% 4 3 2 3 4 5% 57%	2340
	11th to 20th	Night	13% 5% 2 4 3 2 3 4 4 6% 54%	2598
	21st to end	Night	14% 6% 2 5% 4 3 4 4 5% 5% 49%	2600
December	1st to 10th	Night	16% 7% 2 5% 4 4 4 4 5% 5% 45%	4250
	11th to 20th	Night	14% 7% 2 5% 4 3 3 3 4 6% 47%	4822
	21st to end	Night	21% 8% 2 5% 3 3 3 2 3 5% 44%	6191

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	40% 4 5% 17% 23% 11%	3114
	11th to 20th	Day	31% 4 5% 19% 30% 11%	3131
	21st to end	Day	49% 3 5% 14% 21% 9%	3476
February	1st to 10th	Day	48% 4 7% 13% 19% 10%	1900
	11th to 20th	Day	42% 4 6% 16% 20% 11%	1858
	21st to end	Day	47% 4 7% 15% 17% 10%	1570
March	1st to 10th	Day	53% 5% 9% 15% 13% 5%	3150
	11th to 20th	Day	45% 6% 9% 17% 18% 5%	3480
	21st to end	Day	42% 7% 9% 14% 19% 9%	4064
April	1st to 10th	Day	40% 7% 9% 17% 18% 9%	2280
	11th to 20th	Day	42% 5% 8% 16% 20% 8%	2254
	21st to end	Day	35% 6% 9% 21% 22% 7%	2280
May	1st to 10th	Day	39% 9% 13% 21% 14% 4	3800
	11th to 20th	Day	41% 7% 11% 18% 21% 2	3768
	21st to end	Day	32% 8% 15% 32% 11% 2	4287
June	1st to 10th	Day	46% 10% 13% 20% 9% 2	2470
	11th to 20th	Day	39% 10% 16% 20% 13% 2	2537
	21st to end	Day	47% 12% 15% 17% 7% 1	2576
July	1st to 10th	Day	48% 15% 20% 14% 3	4056
	11th to 20th	Day	44% 15% 29% 10% 2	3861
	21st to end	Day	49% 15% 17% 15% 4 1	3987
August	1st to 10th	Day	27% 8% 13% 26% 25% 1	3773
	11th to 20th	Day	36% 9% 17% 24% 12% 1	3765
	21st to end	Day	45% 11% 13% 14% 14% 2	4179
September	1st to 10th	Day	46% 8% 13% 17% 11% 5%	2280
	11th to 20th	Day	43% 8% 11% 15% 16% 7%	2187
	21st to end	Day	33% 6% 10% 21% 19% 10%	2090
October	1st to 10th	Day	27% 3 6% 11% 22% 30%	3451
	11th to 20th	Day	18% 2 6% 16% 28% 30%	3140
	21st to end	Day	21% 4 4 13% 37% 21%	3428
November	1st to 10th	Day	32% 4 8% 19% 25% 12%	1956
	11th to 20th	Day	32% 4 6% 15% 30% 14%	1800
	21st to end	Day	39% 4 7% 17% 21% 12%	1800
December	1st to 10th	Day	43% 4 7% 15% 24% 7%	2930
	11th to 20th	Day	37% 5% 11% 14% 22% 10%	3370
	21st to end	Day	42% 5% 6% 18% 25% 5%	4760
January	1st to 10th	Night	38% 4 6% 14% 27% 10%	3862
	11th to 20th	Night	35% 4 5% 18% 26% 12%	3800
	21st to end	Night	47% 3 4 15% 23% 8%	4180
February	1st to 10th	Night	43% 5% 7% 17% 20% 9%	2280
	11th to 20th	Night	45% 4 5% 13% 20% 12%	2219
	21st to end	Night	47% 5% 9% 14% 13% 12%	1884
March	1st to 10th	Night	54% 5% 8% 13% 13% 6%	3716
	11th to 20th	Night	43% 7% 10% 15% 18% 7%	3480
	21st to end	Night	39% 7% 9% 19% 18% 7%	3565
April	1st to 10th	Night	40% 5% 10% 16% 18% 11%	1900
	11th to 20th	Night	39% 5% 9% 20% 17% 9%	1875
	21st to end	Night	27% 5% 12% 22% 26% 9%	1900
May	1st to 10th	Night	38% 7% 13% 21% 17% 4	3160
	11th to 20th	Night	38% 8% 11% 25% 16% 1	3130
	21st to end	Night	27% 10% 21% 27% 13% 2	3285
June	1st to 10th	Night	35% 9% 20% 25% 10% 2	1710
	11th to 20th	Night	27% 12% 21% 27% 11% 2	1632
	21st to end	Night	35% 11% 20% 24% 9% 2	1595
July	1st to 10th	Night	36% 16% 29% 15% 4	2805
	11th to 20th	Night	31% 16% 39% 10% 2 1	2971
	21st to end	Night	42% 18% 19% 19% 3	3325
August	1st to 10th	Night	16% 9% 22% 29% 21% 1	3132
	11th to 20th	Night	26% 14% 23% 27% 9% 1	3130
	21st to end	Night	37% 14% 18% 17% 10% 4	3476
September	1st to 10th	Night	40% 10% 18% 14% 13% 6%	1900
	11th to 20th	Night	36% 9% 17% 17% 13% 8%	1971
	21st to end	Night	31% 7% 11% 24% 16% 11%	2090
October	1st to 10th	Night	28% 4 7% 12% 23% 25%	3503
	11th to 20th	Night	15% 3 6% 20% 25% 31%	3779
	21st to end	Night	20% 3 5% 12% 36% 25%	4120
November	1st to 10th	Night	30% 4 8% 18% 24% 15%	2340
	11th to 20th	Night	31% 4 7% 16% 27% 16%	2598
	21st to end	Night	36% 4 7% 20% 20% 14%	2600
December	1st to 10th	Night	41% 4 6% 17% 24% 8%	4250
	11th to 20th	Night	38% 4 9% 18% 20% 10%	4824
	21st to end	Night	44% 4 6% 17% 22% 7%	6191

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% 15% 38% 16% 5% 1	288
	11th to 20th	Day	23% 17% 37% 18% 6%	270
	21st to end	Day	28% 24% 34% 12% 2	297
February	1st to 10th	Day	33% 18% 28% 16% 5%	270
	11th to 20th	Day	31% 16% 33% 15% 4	270
	21st to end	Day	20% 28% 40% 10% 1	225
March	1st to 10th	Day	23% 18% 38% 18% 3	270
	11th to 20th	Day	24% 22% 32% 17% 3 1	270
	21st to end	Day	21% 17% 33% 21% 8%	444
April	1st to 10th	Day	18% 15% 33% 25% 8% 1	460
	11th to 20th	Day	22% 13% 30% 24% 8% 3	452
	21st to end	Day	10% 12% 31% 28% 17% 2	460
May	1st to 10th	Day	13% 10% 29% 25% 20% 4	463
	11th to 20th	Day	14% 5% 23% 30% 20% 8%	487
	21st to end	Day	8% 3 19% 32% 26% 12%	529
June	1st to 10th	Day	14% 2 13% 32% 23% 15%	490
	11th to 20th	Day	8% 3 14% 32% 30% 14%	557
	21st to end	Day	10% 3 11% 30% 30% 16%	680
July	1st to 10th	Day	8% 3 7% 29% 33% 20%	671
	11th to 20th	Day	8% 1 4 21% 38% 27%	556
	21st to end	Day	9% 2 4 24% 38% 23%	532
August	1st to 10th	Day	4 2 6% 25% 34% 29%	486
	11th to 20th	Day	9% 2 3 18% 39% 29%	479
	21st to end	Day	11% 4 9% 20% 34% 22%	539
September	1st to 10th	Day	11% 2 9% 26% 34% 18%	490
	11th to 20th	Day	11% 5% 11% 26% 36% 12%	490
	21st to end	Day	10% 5% 11% 33% 31% 10%	490
October	1st to 10th	Day	7% 8% 21% 34% 23% 7%	474
	11th to 20th	Day	7% 8% 23% 35% 23% 5%	300
	21st to end	Day	16% 9% 23% 32% 17% 3	330
November	1st to 10th	Day	14% 9% 30% 33% 13% 1	300
	11th to 20th	Day	16% 15% 30% 25% 12% 1	300
	21st to end	Day	17% 13% 38% 19% 9% 3	300
December	1st to 10th	Day	22% 11% 35% 25% 7% 1	300
	11th to 20th	Day	24% 14% 38% 19% 6% 1	300
	21st to end	Day	25% 15% 31% 21% 7% 1	330
January	1st to 10th	Night	24% 11% 32% 28% 5%	785
	11th to 20th	Night	21% 12% 31% 30% 6%	760
	21st to end	Night	25% 13% 32% 26% 4	836
February	1st to 10th	Night	21% 12% 35% 26% 5%	760
	11th to 20th	Night	26% 15% 28% 25% 6%	743
	21st to end	Night	22% 18% 36% 21% 3	628
March	1st to 10th	Night	19% 14% 33% 27% 6%	756
	11th to 20th	Night	18% 8% 34% 31% 9%	570
	21st to end	Night	16% 10% 33% 31% 9%	627
April	1st to 10th	Night	19% 11% 29% 29% 12% 1	570
	11th to 20th	Night	17% 8% 32% 28% 14% 1	563
	21st to end	Night	9% 6% 29% 41% 15%	570
May	1st to 10th	Night	12% 5% 24% 40% 18% 1	570
	11th to 20th	Night	9% 4 22% 38% 23% 5%	561
	21st to end	Night	6% 2 14% 38% 34% 6%	617
June	1st to 10th	Night	10% 2 9% 37% 34% 8%	570
	11th to 20th	Night	4 1 8% 32% 44% 10%	570
	21st to end	Night	8% 2 7% 29% 42% 13%	570
July	1st to 10th	Night	6% 1 3 21% 48% 20%	555
	11th to 20th	Night	4 2 3 15% 49% 27%	552
	21st to end	Night	5% 1 3 22% 48% 20%	624
August	1st to 10th	Night	3 1 1 20% 49% 25%	567
	11th to 20th	Night	7% 4 16% 49% 24%	564
	21st to end	Night	7% 3 6% 20% 42% 22%	627
September	1st to 10th	Night	9% 3 7% 23% 40% 17%	570
	11th to 20th	Night	12% 4 7% 26% 41% 9%	641
	21st to end	Night	11% 3 10% 31% 39% 7%	760
October	1st to 10th	Night	8% 3 18% 38% 30% 4	760
	11th to 20th	Night	10% 5% 22% 36% 25% 3	760
	21st to end	Night	13% 6% 22% 36% 20% 2	836
November	1st to 10th	Night	13% 7% 21% 38% 19% 2	780
	11th to 20th	Night	14% 10% 28% 32% 15% 2	800
	21st to end	Night	17% 8% 28% 32% 14% 1	800
December	1st to 10th	Night	18% 12% 30% 28% 12% 1	800
	11th to 20th	Night	22% 7% 33% 30% 9%	800
	21st to end	Night	26% 11% 31% 25% 7%	880

Page generated at 2025-01-04 02:24:03. Version ac07

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