Hilltop Homeschool Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hilltop Homeschool Observatory clear sky chart from 2005-11-06 to 2024-11-25.

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	13% 8% 3 8% 5% 4 4 4 6% 7% 38%	101659
	Night	13% 9% 3 8% 4 4 4 3 5% 6% 41%	97893
Transparency	Day	43% 5% 13% 23% 14% 1	105267
	Night	43% 5% 12% 23% 15% 2	102425
Seeing	Day	16% 10% 29% 27% 14% 4	15917
	Night	16% 9% 31% 31% 12% 1	25782

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	9% 11% 8% 20% 7% 7% 5% 4 5% 5% 20%	2527
	11th to 20th	Day	11% 12% 4 11% 10% 7% 5% 5% 6% 5% 24%	2608
	21st to end	Day	16% 18% 7% 16% 6% 5% 4 2 5% 5% 17%	3135
February	1st to 10th	Day	12% 12% 5% 9% 7% 5% 4 5% 5% 7% 29%	1710
	11th to 20th	Day	14% 11% 3 6% 4 6% 5% 5% 5% 7% 34%	1687
	21st to end	Day	14% 11% 4 11% 5% 4 4 4 6% 7% 33%	1570
March	1st to 10th	Day	17% 11% 4 7% 4 3 3 3 3 5% 41%	3267
	11th to 20th	Day	10% 7% 3 6% 4 4 4 4 6% 6% 45%	3480
	21st to end	Day	23% 14% 4 11% 5% 4 4 3 5% 6% 20%	3938
April	1st to 10th	Day	19% 12% 3 7% 5% 5% 4 3 4 6% 32%	2280
	11th to 20th	Day	17% 10% 3 7% 5% 5% 4 3 6% 7% 33%	2254
	21st to end	Day	22% 8% 3 6% 4 3 4 3 5% 7% 35%	2289
May	1st to 10th	Day	19% 7% 3 7% 5% 4 5% 4 6% 7% 34%	4237
	11th to 20th	Day	16% 7% 2 6% 4 4 5% 3 6% 5% 41%	4399
	21st to end	Day	15% 6% 2 6% 4 4 4 4 6% 7% 41%	4824
June	1st to 10th	Day	10% 6% 2 5% 4 5% 5% 5% 7% 9% 42%	2660
	11th to 20th	Day	11% 6% 2 6% 4 4 4 4 6% 7% 46%	2660
	21st to end	Day	11% 6% 2 7% 6% 4 5% 4 6% 9% 39%	2660
July	1st to 10th	Day	11% 7% 3 8% 5% 5% 6% 5% 7% 8% 36%	4440
	11th to 20th	Day	6% 4 1 5% 4 4 4 4 5% 9% 54%	4440
	21st to end	Day	6% 5% 2 7% 5% 5% 6% 5% 7% 11% 41%	4698
August	1st to 10th	Day	8% 5% 2 6% 5% 4 5% 4 7% 9% 45%	4104
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 5% 7% 10% 40%	3963
	21st to end	Day	7% 6% 2 6% 4 4 4 4 5% 8% 50%	4180
September	1st to 10th	Day	13% 5% 2 5% 4 3 4 3 5% 8% 50%	2280
	11th to 20th	Day	10% 5% 1 6% 4 4 4 4 6% 8% 50%	2280
	21st to end	Day	10% 5% 2 6% 5% 4 5% 3 7% 8% 45%	2009
October	1st to 10th	Day	15% 6% 2 6% 3 4 4 2 4 6% 47%	1900
	11th to 20th	Day	18% 7% 3 6% 4 4 4 3 5% 6% 42%	1900
	21st to end	Day	17% 9% 2 6% 4 3 3 3 5% 6% 40%	2060
November	1st to 10th	Day	12% 8% 2 6% 5% 4 4 4 5% 7% 43%	1762
	11th to 20th	Day	14% 12% 4 8% 5% 4 4 4 5% 6% 35%	1685
	21st to end	Day	16% 10% 3 7% 3 4 4 3 4 7% 38%	1552
December	1st to 10th	Day	14% 13% 4 10% 5% 5% 3 3 4 7% 32%	1520
	11th to 20th	Day	14% 11% 4 8% 6% 5% 5% 4 4 6% 32%	1918
	21st to end	Day	23% 20% 8% 11% 5% 3 3 3 3 4 16%	2783
January	1st to 10th	Night	12% 11% 7% 16% 5% 5% 5% 4 4 5% 26%	4428
	11th to 20th	Night	12% 16% 6% 13% 6% 4 5% 4 7% 6% 23%	4344
	21st to end	Night	17% 16% 7% 12% 6% 4 4 3 4 6% 22%	4532
February	1st to 10th	Night	12% 14% 5% 8% 6% 4 4 3 5% 5% 34%	2470
	11th to 20th	Night	11% 10% 2 8% 5% 5% 4 4 5% 6% 40%	2380
	21st to end	Night	14% 10% 3 9% 5% 4 3 3 4 5% 38%	1884
March	1st to 10th	Night	17% 8% 2 6% 4 4 3 2 4 5% 45%	3615
	11th to 20th	Night	10% 7% 2 7% 4 3 3 3 4 6% 51%	3480
	21st to end	Night	24% 12% 5% 11% 5% 5% 4 3 4 4 23%	3691
April	1st to 10th	Night	16% 9% 4 7% 5% 3 3 3 5% 5% 41%	1900
	11th to 20th	Night	17% 9% 3 7% 5% 4 3 3 5% 5% 40%	1875
	21st to end	Night	19% 8% 2 6% 4 4 4 3 6% 7% 39%	1886
May	1st to 10th	Night	18% 8% 2 6% 4 4 4 4 5% 6% 40%	2668
	11th to 20th	Night	12% 7% 2 6% 4 5% 5% 3 5% 6% 45%	2506
	21st to end	Night	9% 6% 2 6% 4 4 5% 3 6% 8% 47%	2743
June	1st to 10th	Night	8% 5% 2 6% 4 4 4 3 8% 9% 47%	1520
	11th to 20th	Night	9% 5% 2 5% 3 4 5% 4 9% 9% 45%	1520
	21st to end	Night	11% 4 2 6% 3 3 4 4 7% 8% 47%	1520
July	1st to 10th	Night	12% 5% 2 8% 4 4 5% 4 7% 7% 42%	2530
	11th to 20th	Night	4 4 1 4 3 3 4 3 6% 9% 59%	2530
	21st to end	Night	6% 4 2 5% 5% 4 5% 4 7% 8% 49%	2861
August	1st to 10th	Night	6% 3 2 5% 4 5% 4 4 6% 9% 53%	2836
	11th to 20th	Night	8% 4 2 5% 4 3 3 3 5% 7% 54%	2860
	21st to end	Night	9% 4 2 5% 4 3 4 4 5% 7% 53%	3476
September	1st to 10th	Night	10% 4 1 5% 3 3 3 3 4 6% 56%	1900
	11th to 20th	Night	11% 4 2 5% 4 3 3 3 4 7% 53%	1900
	21st to end	Night	8% 5% 1 5% 4 3 4 4 4 7% 55%	2147
October	1st to 10th	Night	12% 5% 2 5% 4 3 3 2 4 6% 54%	2280
	11th to 20th	Night	14% 7% 2 5% 4 4 4 3 4 5% 48%	2280
	21st to end	Night	17% 9% 3 6% 4 3 4 3 5% 5% 41%	2536
November	1st to 10th	Night	12% 6% 2 5% 3 3 4 3 4 6% 52%	2536
	11th to 20th	Night	13% 10% 3 7% 5% 4 3 3 5% 6% 41%	2713
	21st to end	Night	16% 10% 3 7% 5% 4 4 3 4 6% 40%	2723
December	1st to 10th	Night	13% 11% 4 10% 6% 4 4 4 4 6% 34%	2660
	11th to 20th	Night	14% 11% 4 9% 5% 5% 4 3 4 6% 34%	3279
	21st to end	Night	21% 16% 7% 11% 6% 4 4 4 4 5% 19%	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	65% 7% 10% 12% 6%	2528
	11th to 20th	Day	60% 3 12% 17% 7%	2608
	21st to end	Day	70% 4 11% 10% 5%	3135
February	1st to 10th	Day	53% 5% 15% 19% 8% 1	1710
	11th to 20th	Day	48% 6% 13% 22% 10% 1	1696
	21st to end	Day	50% 6% 14% 20% 8% 3	1570
March	1st to 10th	Day	47% 4 10% 24% 14% 1	3267
	11th to 20th	Day	38% 5% 13% 28% 15% 1	3480
	21st to end	Day	64% 5% 13% 13% 4 1	3938
April	1st to 10th	Day	53% 5% 11% 22% 9%	2280
	11th to 20th	Day	49% 6% 10% 22% 11% 2	2254
	21st to end	Day	49% 5% 11% 21% 13% 2	2289
May	1st to 10th	Day	48% 7% 12% 19% 13% 1	4275
	11th to 20th	Day	43% 6% 12% 26% 13%	4403
	21st to end	Day	39% 7% 11% 24% 17% 1	4837
June	1st to 10th	Day	35% 7% 16% 24% 16% 2	2660
	11th to 20th	Day	36% 7% 11% 22% 22% 3	2660
	21st to end	Day	40% 7% 13% 23% 14% 2	2660
July	1st to 10th	Day	44% 6% 13% 27% 9% 1	4371
	11th to 20th	Day	27% 6% 15% 32% 17% 2	4365
	21st to end	Day	34% 9% 18% 20% 18% 1	4550
August	1st to 10th	Day	35% 6% 17% 28% 13% 1	4090
	11th to 20th	Day	38% 6% 15% 25% 15% 1	4002
	21st to end	Day	32% 5% 14% 30% 17% 2	4179
September	1st to 10th	Day	34% 4 11% 26% 22% 3	2280
	11th to 20th	Day	32% 6% 12% 31% 18% 2	2280
	21st to end	Day	35% 5% 11% 29% 18% 2	2009
October	1st to 10th	Day	24% 3 5% 30% 36% 1	3160
	11th to 20th	Day	30% 3 11% 25% 26% 6%	3140
	21st to end	Day	40% 3 9% 30% 14% 3	3374
November	1st to 10th	Day	40% 5% 13% 26% 13% 3	1762
	11th to 20th	Day	49% 4 13% 20% 13% 1	1685
	21st to end	Day	47% 5% 16% 24% 8%	1552
December	1st to 10th	Day	53% 5% 14% 20% 8% 1	1520
	11th to 20th	Day	52% 5% 16% 17% 9% 1	1915
	21st to end	Day	72% 4 10% 10% 4	2783
January	1st to 10th	Night	58% 6% 12% 15% 9%	4428
	11th to 20th	Night	60% 4 12% 14% 10% 1	4344
	21st to end	Night	64% 5% 10% 15% 6% 1	4532
February	1st to 10th	Night	51% 4 10% 22% 11% 1	2470
	11th to 20th	Night	44% 5% 12% 25% 13% 2	2381
	21st to end	Night	47% 4 12% 21% 14% 2	1884
March	1st to 10th	Night	43% 3 11% 25% 16% 1	3615
	11th to 20th	Night	34% 5% 11% 32% 16% 3	3480
	21st to end	Night	64% 5% 13% 12% 5% 1	3691
April	1st to 10th	Night	45% 5% 9% 25% 13% 2	1900
	11th to 20th	Night	45% 5% 8% 23% 16% 4	1875
	21st to end	Night	44% 6% 11% 23% 14% 2	1886
May	1st to 10th	Night	44% 6% 10% 19% 18% 3	2695
	11th to 20th	Night	39% 7% 11% 28% 13% 2	2507
	21st to end	Night	33% 8% 12% 27% 18% 2	2751
June	1st to 10th	Night	31% 8% 14% 26% 17% 3	1520
	11th to 20th	Night	32% 7% 14% 24% 20% 4	1520
	21st to end	Night	32% 7% 17% 23% 16% 4	1520
July	1st to 10th	Night	39% 7% 13% 27% 12% 3	2490
	11th to 20th	Night	22% 5% 18% 34% 19% 2	2482
	21st to end	Night	29% 8% 19% 22% 19% 2	2770
August	1st to 10th	Night	27% 7% 18% 32% 15% 2	2826
	11th to 20th	Night	29% 6% 14% 33% 16% 1	2887
	21st to end	Night	30% 5% 12% 29% 18% 5%	3476
September	1st to 10th	Night	29% 5% 12% 26% 26% 3	1900
	11th to 20th	Night	32% 4 9% 32% 19% 3	1900
	21st to end	Night	29% 4 10% 30% 23% 2	2147
October	1st to 10th	Night	23% 3 6% 29% 36% 3	3800
	11th to 20th	Night	27% 3 10% 22% 31% 7%	3779
	21st to end	Night	46% 3 8% 23% 15% 4	4172
November	1st to 10th	Night	34% 5% 14% 26% 17% 4	2536
	11th to 20th	Night	44% 4 13% 24% 13% 2	2713
	21st to end	Night	47% 4 12% 25% 11% 1	2723
December	1st to 10th	Night	50% 5% 13% 23% 9% 1	2660
	11th to 20th	Night	51% 4 13% 24% 6% 1	3281
	21st to end	Night	67% 5% 9% 13% 6%	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	22% 10% 34% 23% 9% 2	270
	11th to 20th	Day	19% 16% 39% 21% 4 1	270
	21st to end	Day	22% 12% 36% 24% 4 1	297
February	1st to 10th	Day	20% 15% 40% 20% 4	270
	11th to 20th	Day	21% 17% 35% 21% 7%	270
	21st to end	Day	24% 14% 43% 14% 5%	225
March	1st to 10th	Day	17% 21% 40% 16% 5%	270
	11th to 20th	Day	21% 18% 31% 21% 7% 2	270
	21st to end	Day	32% 14% 29% 18% 6% 1	370
April	1st to 10th	Day	25% 12% 38% 17% 7%	460
	11th to 20th	Day	23% 17% 29% 21% 9%	452
	21st to end	Day	26% 12% 34% 17% 10% 1	469
May	1st to 10th	Day	20% 12% 36% 23% 7% 2	653
	11th to 20th	Day	20% 12% 27% 25% 13% 2	675
	21st to end	Day	14% 10% 28% 28% 14% 5%	734
June	1st to 10th	Day	8% 4 28% 34% 21% 5%	680
	11th to 20th	Day	13% 6% 30% 31% 17% 3	680
	21st to end	Day	11% 8% 32% 32% 12% 4	680
July	1st to 10th	Day	8% 4 19% 32% 25% 12%	671
	11th to 20th	Day	9% 3 25% 34% 22% 7%	668
	21st to end	Day	8% 2 23% 38% 24% 6%	739
August	1st to 10th	Day	7% 4 22% 37% 23% 8%	676
	11th to 20th	Day	12% 5% 20% 31% 24% 9%	626
	21st to end	Day	9% 3 18% 38% 25% 7%	539
September	1st to 10th	Day	13% 8% 19% 31% 22% 7%	490
	11th to 20th	Day	9% 4 22% 37% 21% 7%	490
	21st to end	Day	13% 10% 29% 24% 22% 3	374
October	1st to 10th	Day	18% 10% 26% 27% 14% 4	300
	11th to 20th	Day	21% 20% 34% 15% 9% 1	300
	21st to end	Day	26% 13% 35% 18% 5% 3	330
November	1st to 10th	Day	16% 10% 42% 21% 9% 2	300
	11th to 20th	Day	20% 19% 30% 23% 6% 2	300
	21st to end	Day	22% 12% 37% 22% 6%	282
December	1st to 10th	Day	14% 13% 43% 21% 7% 2	270
	11th to 20th	Day	16% 13% 39% 22% 9% 1	270
	21st to end	Day	28% 14% 39% 17% 2	297
January	1st to 10th	Night	14% 13% 38% 28% 7%	950
	11th to 20th	Night	19% 14% 33% 28% 6%	950
	21st to end	Night	19% 11% 36% 28% 6%	1045
February	1st to 10th	Night	19% 12% 38% 25% 5%	950
	11th to 20th	Night	16% 12% 38% 28% 5%	906
	21st to end	Night	21% 11% 41% 22% 4 1	628
March	1st to 10th	Night	19% 13% 38% 22% 7% 1	694
	11th to 20th	Night	17% 13% 33% 29% 8%	570
	21st to end	Night	22% 12% 36% 24% 5% 1	627
April	1st to 10th	Night	20% 14% 38% 24% 3	570
	11th to 20th	Night	22% 15% 31% 25% 6%	563
	21st to end	Night	21% 8% 33% 28% 9% 1	570
May	1st to 10th	Night	18% 6% 40% 28% 6% 1	570
	11th to 20th	Night	17% 10% 29% 33% 11% 1	561
	21st to end	Night	14% 4 30% 34% 17% 1	617
June	1st to 10th	Night	9% 4 27% 42% 16% 1	570
	11th to 20th	Night	10% 5% 28% 42% 14% 1	570
	21st to end	Night	13% 5% 28% 39% 15% 1	570
July	1st to 10th	Night	8% 1 14% 43% 31% 3	555
	11th to 20th	Night	5% 3 19% 43% 26% 3	552
	21st to end	Night	6% 3 19% 43% 27% 2	624
August	1st to 10th	Night	5% 3 16% 46% 28% 2	567
	11th to 20th	Night	7% 3 17% 43% 26% 4	564
	21st to end	Night	12% 2 14% 43% 27% 2	627
September	1st to 10th	Night	11% 4 19% 40% 22% 4	570
	11th to 20th	Night	11% 2 22% 35% 25% 4	570
	21st to end	Night	9% 7% 29% 35% 19% 2	705
October	1st to 10th	Night	14% 7% 28% 33% 17% 2	760
	11th to 20th	Night	19% 11% 32% 29% 9%	760
	21st to end	Night	21% 11% 32% 27% 8%	836
November	1st to 10th	Night	15% 9% 38% 29% 9% 1	780
	11th to 20th	Night	19% 14% 38% 22% 7%	913
	21st to end	Night	20% 11% 35% 26% 7%	973
December	1st to 10th	Night	18% 14% 36% 26% 6% 1	950
	11th to 20th	Night	23% 10% 34% 27% 6% 1	950
	21st to end	Night	25% 13% 34% 23% 4	1045

Page generated at 2024-11-22 07:02:25. Version ac07

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