Hillsboro
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hillsboro clear sky chart from 2005-11-06 to 2024-11-10.

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	9% 6% 2 6% 4 4 4 3 5% 7% 50%	101320
	Night	9% 6% 2 5% 4 3 4 3 5% 7% 53%	97923
Transparency	Day	31% 6% 12% 26% 20% 4	105050
	Night	29% 6% 12% 26% 22% 5%	102320
Seeing	Day	11% 10% 30% 30% 16% 3	15627
	Night	11% 10% 34% 34% 11% 1	25484

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% 8% 3 9% 7% 5% 5% 4 5% 7% 40%	2847
	11th to 20th	Day	8% 9% 4 8% 5% 6% 4 3 4 8% 42%	2850
	21st to end	Day	9% 13% 4 8% 4 3 3 2 4 6% 44%	3135
February	1st to 10th	Day	9% 11% 3 7% 5% 4 4 3 4 6% 45%	1710
	11th to 20th	Day	8% 6% 3 6% 5% 5% 5% 4 5% 6% 48%	1825
	21st to end	Day	8% 7% 3 6% 4 5% 4 3 5% 6% 50%	1570
March	1st to 10th	Day	10% 7% 2 5% 3 2 3 2 4 6% 56%	3359
	11th to 20th	Day	9% 6% 2 4 2 3 2 2 4 7% 59%	3480
	21st to end	Day	11% 7% 3 7% 4 4 4 3 5% 7% 44%	3814
April	1st to 10th	Day	11% 6% 1 6% 3 3 4 2 5% 7% 52%	2090
	11th to 20th	Day	12% 7% 2 6% 4 4 4 4 5% 7% 45%	2350
	21st to end	Day	16% 7% 2 5% 4 3 4 3 5% 7% 42%	2470
May	1st to 10th	Day	16% 10% 3 7% 4 4 4 3 5% 6% 38%	4082
	11th to 20th	Day	12% 7% 2 6% 4 4 4 4 5% 7% 45%	4082
	21st to end	Day	11% 6% 3 7% 5% 4 5% 4 6% 8% 42%	4477
June	1st to 10th	Day	5% 4 2 5% 4 4 4 4 6% 10% 54%	2470
	11th to 20th	Day	6% 4 1 4 4 4 4 4 6% 8% 54%	2470
	21st to end	Day	6% 3 2 4 4 4 4 4 6% 9% 55%	2470
July	1st to 10th	Day	10% 5% 2 5% 4 4 4 4 7% 8% 48%	4120
	11th to 20th	Day	6% 3 1 4 3 4 4 4 7% 9% 54%	4120
	21st to end	Day	5% 3 2 5% 4 4 5% 4 8% 10% 49%	4465
August	1st to 10th	Day	6% 5% 2 7% 4 4 4 3 5% 8% 52%	4104
	11th to 20th	Day	8% 4 2 6% 4 4 4 3 5% 8% 52%	4041
	21st to end	Day	3 3 1 4 3 3 3 3 5% 8% 62%	4427
September	1st to 10th	Day	11% 3 2 5% 3 3 3 3 5% 6% 55%	2090
	11th to 20th	Day	8% 5% 2 5% 3 3 4 4 5% 6% 55%	2090
	21st to end	Day	8% 5% 2 6% 3 4 3 3 4 7% 55%	2090
October	1st to 10th	Day	10% 5% 2 4 3 2 4 3 5% 6% 55%	2014
	11th to 20th	Day	9% 5% 2 3 2 2 3 2 4 4 65%	1900
	21st to end	Day	11% 6% 2 5% 2 3 3 2 4 5% 56%	2090
November	1st to 10th	Day	8% 5% 2 4 3 2 3 3 6% 7% 58%	1792
	11th to 20th	Day	8% 6% 2 4 3 3 4 2 3 7% 58%	1710
	21st to end	Day	12% 6% 2 3 3 3 2 2 4 6% 58%	1710
December	1st to 10th	Day	10% 5% 2 6% 3 4 4 4 6% 6% 52%	1710
	11th to 20th	Day	9% 7% 3 7% 5% 3 4 3 4 6% 49%	2161
	21st to end	Day	10% 10% 5% 14% 5% 4 4 3 4 7% 32%	3135
January	1st to 10th	Night	7% 9% 4 12% 5% 5% 4 3 4 5% 43%	4108
	11th to 20th	Night	6% 7% 3 6% 5% 5% 4 3 4 5% 51%	4120
	21st to end	Night	15% 12% 3 5% 3 2 2 2 4 4 47%	4532
February	1st to 10th	Night	10% 10% 3 6% 4 4 3 4 5% 5% 46%	2470
	11th to 20th	Night	9% 7% 3 6% 4 3 4 4 5% 7% 49%	2256
	21st to end	Night	8% 7% 2 6% 4 3 4 3 4 6% 53%	1884
March	1st to 10th	Night	9% 6% 2 4 3 2 3 3 5% 6% 57%	3495
	11th to 20th	Night	8% 4 2 5% 4 4 4 3 5% 7% 55%	3480
	21st to end	Night	12% 9% 2 6% 3 3 3 3 4 6% 48%	3817
April	1st to 10th	Night	10% 5% 1 5% 3 3 3 3 5% 8% 53%	2090
	11th to 20th	Night	9% 6% 3 5% 4 4 3 3 5% 7% 50%	1775
	21st to end	Night	13% 7% 3 6% 3 3 4 3 5% 6% 47%	1710
May	1st to 10th	Night	15% 8% 2 4 4 3 3 3 5% 7% 46%	2823
	11th to 20th	Night	12% 5% 2 5% 3 3 4 3 7% 8% 47%	2823
	21st to end	Night	9% 4 1 4 4 3 3 3 5% 8% 55%	3090
June	1st to 10th	Night	5% 3 1 4 3 3 4 4 7% 13% 54%	1710
	11th to 20th	Night	4 3 1 3 4 3 5% 4 8% 10% 53%	1710
	21st to end	Night	5% 2 1 3 4 4 4 4 5% 9% 58%	1710
July	1st to 10th	Night	7% 5% 2 5% 4 4 4 3 6% 7% 53%	2850
	11th to 20th	Night	2 2 1 4 3 3 4 5% 7% 11% 56%	2850
	21st to end	Night	6% 4 2 5% 4 5% 5% 5% 8% 11% 47%	3098
August	1st to 10th	Night	3 3 2 6% 5% 4 5% 4 7% 8% 55%	2836
	11th to 20th	Night	8% 5% 2 6% 4 4 4 4 5% 8% 51%	2798
	21st to end	Night	4 3 1 3 2 3 3 3 5% 8% 65%	3219
September	1st to 10th	Night	8% 3 1 4 3 3 3 2 6% 6% 59%	2090
	11th to 20th	Night	7% 5% 1 5% 3 3 3 2 4 7% 59%	2090
	21st to end	Night	6% 4 2 4 4 3 3 3 5% 6% 60%	2090
October	1st to 10th	Night	10% 5% 2 5% 3 4 3 3 4 6% 56%	2147
	11th to 20th	Night	10% 4 1 3 2 2 3 3 4 6% 63%	2280
	21st to end	Night	10% 5% 1 5% 3 3 3 3 3 6% 58%	2508
November	1st to 10th	Night	8% 4 1 4 2 3 3 2 4 6% 63%	2486
	11th to 20th	Night	8% 5% 2 3 2 2 3 3 5% 8% 59%	2470
	21st to end	Night	12% 7% 2 4 3 2 2 3 4 6% 56%	2470
December	1st to 10th	Night	8% 6% 3 5% 4 4 4 3 5% 6% 53%	2470
	11th to 20th	Night	9% 7% 3 5% 4 3 3 3 5% 7% 51%	3036
	21st to end	Night	15% 8% 4 10% 5% 4 3 3 4 6% 39%	4532

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	42% 7% 11% 24% 15% 1	2848
	11th to 20th	Day	41% 6% 15% 24% 10% 4	2850
	21st to end	Day	43% 5% 12% 24% 15% 1	3135
February	1st to 10th	Day	41% 5% 11% 25% 13% 5%	1710
	11th to 20th	Day	36% 6% 14% 25% 15% 5%	1835
	21st to end	Day	33% 5% 9% 25% 22% 5%	1570
March	1st to 10th	Day	30% 5% 8% 21% 28% 8%	3359
	11th to 20th	Day	25% 6% 13% 27% 28% 3	3480
	21st to end	Day	38% 8% 14% 29% 8% 2	3814
April	1st to 10th	Day	32% 6% 13% 25% 21% 4	2090
	11th to 20th	Day	36% 8% 13% 23% 17% 3	2350
	21st to end	Day	40% 7% 12% 27% 14% 1	2470
May	1st to 10th	Day	46% 7% 9% 19% 14% 4	4120
	11th to 20th	Day	35% 8% 12% 26% 18%	4086
	21st to end	Day	36% 10% 13% 23% 16% 2	4489
June	1st to 10th	Day	25% 8% 17% 31% 15% 3	2470
	11th to 20th	Day	26% 7% 14% 29% 20% 4	2470
	21st to end	Day	25% 7% 15% 26% 21% 6%	2470
July	1st to 10th	Day	32% 7% 12% 25% 20% 5%	4056
	11th to 20th	Day	24% 7% 13% 31% 21% 4	4051
	21st to end	Day	25% 8% 15% 29% 21% 1	4325
August	1st to 10th	Day	30% 6% 12% 25% 22% 4	4090
	11th to 20th	Day	31% 6% 17% 26% 18% 2	4080
	21st to end	Day	19% 6% 16% 34% 19% 5%	4426
September	1st to 10th	Day	29% 6% 12% 23% 22% 8%	2090
	11th to 20th	Day	27% 7% 12% 27% 24% 4	2090
	21st to end	Day	29% 6% 9% 24% 25% 7%	2090
October	1st to 10th	Day	19% 5% 8% 18% 41% 9%	3352
	11th to 20th	Day	16% 3 9% 31% 32% 9%	3140
	21st to end	Day	26% 3 8% 25% 31% 6%	3428
November	1st to 10th	Day	25% 5% 12% 28% 23% 7%	1792
	11th to 20th	Day	28% 4 9% 27% 27% 5%	1710
	21st to end	Day	29% 4 10% 29% 24% 4	1710
December	1st to 10th	Day	33% 4 12% 31% 19% 2	1710
	11th to 20th	Day	35% 5% 10% 29% 18% 2	2159
	21st to end	Day	49% 7% 10% 22% 10% 2	3135
January	1st to 10th	Night	41% 6% 11% 25% 15% 2	4108
	11th to 20th	Night	34% 7% 13% 26% 19% 2	4120
	21st to end	Night	41% 4 12% 22% 18% 2	4532
February	1st to 10th	Night	40% 6% 12% 23% 15% 4	2470
	11th to 20th	Night	33% 6% 13% 27% 18% 4	2256
	21st to end	Night	32% 5% 10% 22% 23% 9%	1884
March	1st to 10th	Night	26% 6% 8% 25% 27% 7%	3495
	11th to 20th	Night	27% 7% 10% 23% 30% 3	3480
	21st to end	Night	36% 8% 14% 30% 11% 2	3817
April	1st to 10th	Night	28% 7% 13% 23% 24% 6%	2090
	11th to 20th	Night	33% 6% 13% 24% 21% 3	1775
	21st to end	Night	37% 7% 12% 22% 18% 4	1710
May	1st to 10th	Night	36% 9% 13% 21% 15% 7%	2850
	11th to 20th	Night	31% 10% 15% 29% 14%	2824
	21st to end	Night	25% 10% 18% 29% 18% 1	3099
June	1st to 10th	Night	21% 10% 20% 30% 16% 3	1710
	11th to 20th	Night	23% 8% 14% 31% 20% 3	1710
	21st to end	Night	21% 8% 13% 31% 21% 7%	1710
July	1st to 10th	Night	28% 6% 14% 23% 22% 7%	2805
	11th to 20th	Night	19% 7% 12% 32% 26% 4	2796
	21st to end	Night	26% 9% 15% 31% 18% 1	2999
August	1st to 10th	Night	25% 7% 14% 26% 20% 8%	2826
	11th to 20th	Night	31% 6% 15% 24% 20% 3	2825
	21st to end	Night	18% 5% 15% 39% 18% 5%	3219
September	1st to 10th	Night	26% 5% 11% 25% 23% 10%	2090
	11th to 20th	Night	26% 6% 10% 25% 28% 5%	2090
	21st to end	Night	24% 6% 9% 24% 29% 8%	2090
October	1st to 10th	Night	20% 4 6% 16% 46% 9%	3576
	11th to 20th	Night	17% 3 6% 26% 34% 14%	3779
	21st to end	Night	25% 3 7% 24% 36% 5%	4120
November	1st to 10th	Night	25% 4 10% 27% 26% 9%	2486
	11th to 20th	Night	24% 5% 10% 29% 27% 5%	2470
	21st to end	Night	30% 4 11% 25% 23% 6%	2470
December	1st to 10th	Night	31% 5% 14% 26% 21% 2	2470
	11th to 20th	Night	33% 5% 9% 31% 19% 3	3037
	21st to end	Night	45% 7% 11% 23% 11% 3	4532

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	14% 14% 34% 27% 9% 1	270
	11th to 20th	Day	17% 19% 39% 22% 3	270
	21st to end	Day	10% 11% 52% 22% 4 1	297
February	1st to 10th	Day	19% 20% 39% 18% 3	270
	11th to 20th	Day	13% 17% 44% 20% 6%	270
	21st to end	Day	10% 20% 52% 14% 4 1	225
March	1st to 10th	Day	13% 18% 42% 23% 4	270
	11th to 20th	Day	20% 12% 44% 20% 4 1	270
	21st to end	Day	16% 21% 42% 18% 2 1	297
April	1st to 10th	Day	17% 20% 36% 20% 7%	270
	11th to 20th	Day	14% 16% 42% 23% 4	548
	21st to end	Day	18% 19% 35% 18% 8% 2	650
May	1st to 10th	Day	16% 14% 37% 24% 8% 1	653
	11th to 20th	Day	16% 12% 28% 26% 14% 3	675
	21st to end	Day	16% 10% 30% 26% 16% 3	734
June	1st to 10th	Day	5% 4 23% 39% 23% 6%	680
	11th to 20th	Day	7% 5% 30% 36% 19% 3	680
	21st to end	Day	5% 6% 33% 42% 12% 2	680
July	1st to 10th	Day	8% 2 16% 36% 31% 7%	671
	11th to 20th	Day	4 3 18% 41% 29% 6%	668
	21st to end	Day	7% 1 13% 40% 31% 7%	739
August	1st to 10th	Day	6% 2 19% 39% 30% 4	676
	11th to 20th	Day	8% 2 16% 42% 28% 5%	665
	21st to end	Day	6% 3 15% 37% 29% 10%	695
September	1st to 10th	Day	12% 1 11% 37% 33% 5%	300
	11th to 20th	Day	6% 3 20% 40% 28% 4	300
	21st to end	Day	12% 7% 27% 30% 19% 6%	300
October	1st to 10th	Day	15% 6% 30% 25% 16% 8%	300
	11th to 20th	Day	6% 13% 42% 26% 12% 1	300
	21st to end	Day	18% 12% 40% 19% 9% 2	330
November	1st to 10th	Day	12% 13% 35% 30% 9% 1	297
	11th to 20th	Day	14% 19% 33% 23% 10% 1	270
	21st to end	Day	19% 11% 35% 24% 9% 1	270
December	1st to 10th	Day	10% 11% 35% 32% 9% 3	270
	11th to 20th	Day	10% 16% 40% 29% 6%	270
	21st to end	Day	15% 20% 43% 19% 3	297
January	1st to 10th	Night	10% 11% 41% 31% 6%	950
	11th to 20th	Night	11% 12% 42% 28% 5% 1	950
	21st to end	Night	12% 12% 39% 34% 3	1045
February	1st to 10th	Night	15% 12% 43% 26% 4	950
	11th to 20th	Night	13% 13% 42% 28% 4	782
	21st to end	Night	12% 15% 44% 26% 3	628
March	1st to 10th	Night	11% 14% 43% 27% 4	624
	11th to 20th	Night	16% 13% 37% 27% 6%	570
	21st to end	Night	19% 14% 42% 21% 4	627
April	1st to 10th	Night	13% 15% 42% 24% 6%	570
	11th to 20th	Night	14% 16% 39% 28% 4	563
	21st to end	Night	16% 14% 37% 27% 6%	570
May	1st to 10th	Night	16% 12% 36% 29% 6%	570
	11th to 20th	Night	13% 9% 29% 37% 10% 1	561
	21st to end	Night	12% 7% 31% 35% 13% 2	617
June	1st to 10th	Night	5% 5% 31% 37% 22% 1	570
	11th to 20th	Night	4 4 38% 39% 14%	570
	21st to end	Night	4 4 36% 45% 9% 1	570
July	1st to 10th	Night	7% 2 18% 46% 27% 1	555
	11th to 20th	Night	2 2 20% 54% 21% 2	552
	21st to end	Night	6% 2 17% 44% 30% 1	624
August	1st to 10th	Night	5% 2 17% 51% 24% 1	567
	11th to 20th	Night	8% 3 16% 49% 22% 1	564
	21st to end	Night	6% 1 17% 44% 30% 2	627
September	1st to 10th	Night	9% 3 22% 44% 20% 2	570
	11th to 20th	Night	8% 3 28% 41% 20% 1	570
	21st to end	Night	8% 5% 28% 41% 17% 1	570
October	1st to 10th	Night	11% 7% 28% 32% 21% 1	627
	11th to 20th	Night	11% 9% 40% 32% 8%	760
	21st to end	Night	14% 11% 35% 32% 8%	836
November	1st to 10th	Night	10% 10% 36% 32% 11% 1	930
	11th to 20th	Night	9% 13% 40% 30% 7%	950
	21st to end	Night	14% 13% 32% 34% 7%	950
December	1st to 10th	Night	11% 12% 36% 33% 6% 1	950
	11th to 20th	Night	14% 11% 40% 29% 4	950
	21st to end	Night	13% 14% 40% 27% 5%	1045

Page generated at 2024-11-07 05:55:49. Version ac07

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