Robinson Preserve
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robinson Preserve clear sky chart from 2005-11-06 to 2026-06-16.

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	6% 4 2 6% 4 5% 5% 5% 8% 10% 45%	137641
	Night	7% 5% 2 6% 5% 5% 5% 4 7% 10% 44%	134385
Transparency	Day	32% 10% 20% 21% 13% 4	141414
	Night	34% 9% 17% 20% 14% 5%	138684
Seeing	Day	8% 4 18% 30% 26% 14%	17613
	Night	9% 4 17% 32% 28% 10%	27672

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	7% 5% 2 6% 4 4 4 4 5% 8% 53%	5258
	11th to 20th	Day	20% 8% 3 7% 4 4 4 4 5% 7% 34%	5280
	21st to end	Day	12% 6% 2 6% 3 3 4 3 6% 8% 47%	6411
February	1st to 10th	Day	10% 5% 2 5% 3 4 4 4 6% 7% 48%	2100
	11th to 20th	Day	6% 4 2 5% 4 3 4 3 6% 7% 56%	2048
	21st to end	Day	7% 4 2 5% 4 3 3 3 5% 7% 57%	1773
March	1st to 10th	Day	7% 4 2 6% 4 4 5% 4 6% 8% 50%	5045
	11th to 20th	Day	5% 3 2 4 3 3 3 3 6% 9% 60%	5090
	21st to end	Day	6% 4 2 5% 4 3 4 3 6% 9% 52%	5586
April	1st to 10th	Day	6% 3 1 4 4 3 4 5% 7% 10% 54%	2310
	11th to 20th	Day	7% 4 1 5% 4 4 4 4 6% 8% 53%	2286
	21st to end	Day	4 2 1 4 3 4 4 4 6% 8% 60%	2489
May	1st to 10th	Day	2 2 1 4 3 3 4 4 6% 11% 59%	7616
	11th to 20th	Day	7% 4 1 5% 4 4 4 4 6% 10% 51%	7626
	21st to end	Day	3 3 1 4 3 4 5% 4 8% 13% 54%	8391
June	1st to 10th	Day	10% 6% 3 7% 5% 4 6% 5% 8% 11% 35%	2730
	11th to 20th	Day	6% 5% 2 5% 5% 6% 7% 6% 10% 14% 35%	2665
	21st to end	Day	6% 5% 2 7% 6% 6% 7% 7% 10% 11% 33%	2600
July	1st to 10th	Day	5% 4 2 7% 6% 6% 8% 8% 11% 16% 28%	5900
	11th to 20th	Day	3 4 2 7% 6% 7% 9% 8% 12% 14% 28%	5900
	21st to end	Day	3 3 2 6% 6% 6% 8% 7% 11% 15% 33%	6424
August	1st to 10th	Day	6% 4 2 8% 6% 7% 8% 7% 10% 13% 29%	4109
	11th to 20th	Day	3 3 2 6% 4 5% 7% 6% 10% 13% 41%	3849
	21st to end	Day	6% 5% 2 7% 6% 7% 8% 7% 12% 14% 28%	3954
September	1st to 10th	Day	8% 5% 2 7% 7% 8% 7% 7% 10% 12% 27%	2200
	11th to 20th	Day	8% 6% 3 6% 6% 6% 7% 5% 9% 10% 33%	2200
	21st to end	Day	7% 5% 2 7% 5% 6% 6% 5% 8% 12% 37%	2200
October	1st to 10th	Day	8% 5% 3 7% 5% 6% 6% 5% 7% 11% 38%	2200
	11th to 20th	Day	6% 4 2 5% 5% 4 4 4 6% 8% 54%	2069
	21st to end	Day	7% 5% 2 5% 4 4 4 3 6% 9% 52%	2200
November	1st to 10th	Day	7% 4 1 5% 5% 3 5% 4 6% 8% 53%	2057
	11th to 20th	Day	7% 5% 2 5% 5% 4 5% 4 4 8% 52%	2100
	21st to end	Day	8% 5% 2 4 4 4 5% 3 7% 8% 51%	1927
December	1st to 10th	Day	4 3 1 4 3 4 4 3 6% 8% 60%	3020
	11th to 20th	Day	7% 6% 2 6% 5% 4 4 3 6% 7% 49%	3463
	21st to end	Day	10% 7% 3 8% 5% 4 5% 4 5% 9% 39%	4565
January	1st to 10th	Night	6% 5% 2 6% 4 4 4 4 6% 9% 51%	7635
	11th to 20th	Night	16% 10% 4 9% 5% 5% 4 3 6% 7% 32%	7680
	21st to end	Night	12% 5% 2 6% 4 4 5% 4 6% 8% 45%	7766
February	1st to 10th	Night	9% 8% 3 6% 4 4 3 4 6% 8% 47%	2520
	11th to 20th	Night	9% 6% 2 5% 3 4 4 4 5% 8% 51%	2458
	21st to end	Night	6% 4 1 5% 4 3 3 5% 5% 7% 54%	2030
March	1st to 10th	Night	7% 5% 2 7% 4 4 4 3 6% 7% 49%	5028
	11th to 20th	Night	4 3 1 3 3 4 4 4 7% 10% 56%	5090
	21st to end	Night	8% 6% 2 6% 4 4 4 4 5% 8% 50%	5588
April	1st to 10th	Night	5% 4 2 3 4 3 4 5% 7% 9% 53%	2310
	11th to 20th	Night	6% 3 2 4 3 4 5% 5% 6% 9% 53%	2283
	21st to end	Night	4 3 2 5% 3 4 4 4 6% 8% 58%	2143
May	1st to 10th	Night	3 3 1 5% 4 4 5% 4 7% 11% 52%	5237
	11th to 20th	Night	7% 5% 2 5% 4 4 5% 3 6% 9% 49%	5234
	21st to end	Night	3 4 2 5% 5% 5% 6% 4 8% 10% 48%	5761
June	1st to 10th	Night	10% 6% 2 7% 4 5% 5% 5% 6% 11% 38%	1890
	11th to 20th	Night	6% 4 2 5% 5% 5% 6% 6% 10% 12% 40%	1845
	21st to end	Night	6% 5% 2 7% 5% 6% 6% 5% 8% 14% 36%	1800
July	1st to 10th	Night	4 5% 2 9% 6% 7% 8% 8% 11% 14% 25%	4058
	11th to 20th	Night	3 4 2 7% 6% 7% 8% 7% 11% 15% 29%	4057
	21st to end	Night	3 5% 3 10% 7% 8% 9% 7% 10% 13% 24%	4427
August	1st to 10th	Night	5% 4 2 7% 5% 6% 6% 6% 10% 14% 34%	3034
	11th to 20th	Night	3 3 2 6% 5% 6% 6% 6% 11% 17% 35%	3200
	21st to end	Night	6% 5% 2 8% 6% 8% 8% 7% 10% 14% 26%	3907
September	1st to 10th	Night	5% 6% 2 7% 7% 8% 8% 7% 9% 13% 30%	2200
	11th to 20th	Night	8% 7% 3 8% 7% 7% 7% 5% 8% 10% 30%	2200
	21st to end	Night	7% 6% 3 9% 7% 6% 7% 5% 7% 11% 33%	2200
October	1st to 10th	Night	9% 6% 3 7% 5% 5% 6% 5% 7% 9% 39%	2200
	11th to 20th	Night	6% 5% 2 5% 4 5% 4 4 6% 8% 52%	2330
	21st to end	Night	8% 5% 1 6% 4 5% 4 4 6% 8% 48%	2640
November	1st to 10th	Night	7% 3 2 6% 5% 4 5% 4 6% 7% 51%	2461
	11th to 20th	Night	8% 5% 2 6% 5% 4 4 3 5% 8% 50%	2520
	21st to end	Night	7% 5% 2 7% 4 3 4 4 6% 9% 48%	2688
December	1st to 10th	Night	5% 3 1 3 3 3 3 4 5% 9% 61%	4380
	11th to 20th	Night	9% 6% 2 5% 3 4 4 3 5% 7% 50%	4952
	21st to end	Night	11% 8% 3 7% 5% 5% 5% 4 7% 9% 36%	6633

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	27% 7% 11% 24% 25% 7%	5259
	11th to 20th	Day	49% 5% 7% 17% 14% 8%	5280
	21st to end	Day	34% 5% 10% 29% 14% 9%	6411
February	1st to 10th	Day	32% 6% 12% 20% 19% 11%	2100
	11th to 20th	Day	25% 7% 13% 22% 25% 9%	2058
	21st to end	Day	27% 5% 13% 20% 27% 9%	1773
March	1st to 10th	Day	30% 9% 13% 22% 21% 6%	5045
	11th to 20th	Day	20% 7% 13% 25% 20% 16%	5090
	21st to end	Day	27% 5% 11% 30% 22% 6%	5586
April	1st to 10th	Day	24% 8% 20% 25% 18% 6%	2310
	11th to 20th	Day	28% 7% 15% 17% 24% 8%	2286
	21st to end	Day	20% 7% 15% 28% 26% 4	2489
May	1st to 10th	Day	18% 7% 28% 30% 14% 3	7651
	11th to 20th	Day	27% 9% 22% 26% 15% 1	7630
	21st to end	Day	21% 10% 29% 29% 10%	8405
June	1st to 10th	Day	40% 12% 24% 19% 5%	2730
	11th to 20th	Day	37% 14% 28% 18% 3	2665
	21st to end	Day	40% 17% 27% 14% 3	2600
July	1st to 10th	Day	41% 17% 34% 7% 1	5835
	11th to 20th	Day	41% 18% 33% 8%	5831
	21st to end	Day	35% 19% 28% 16% 1	6240
August	1st to 10th	Day	41% 17% 30% 9% 3	4096
	11th to 20th	Day	30% 17% 30% 18% 4	3885
	21st to end	Day	41% 18% 30% 10% 1	3954
September	1st to 10th	Day	45% 18% 25% 11% 1	2200
	11th to 20th	Day	44% 14% 25% 14% 4	2200
	21st to end	Day	38% 13% 19% 19% 9% 2	2200
October	1st to 10th	Day	50% 13% 14% 10% 8% 4	3590
	11th to 20th	Day	26% 6% 9% 22% 33% 4	3348
	21st to end	Day	27% 6% 8% 26% 27% 7%	3538
November	1st to 10th	Day	28% 7% 13% 23% 19% 10%	2057
	11th to 20th	Day	32% 6% 11% 22% 21% 9%	2100
	21st to end	Day	30% 7% 13% 22% 19% 9%	1927
December	1st to 10th	Day	22% 5% 16% 29% 20% 8%	3020
	11th to 20th	Day	33% 6% 10% 19% 21% 10%	3460
	21st to end	Day	41% 7% 12% 21% 15% 3	4565
January	1st to 10th	Night	29% 6% 10% 26% 24% 5%	7636
	11th to 20th	Night	51% 5% 9% 15% 13% 7%	7680
	21st to end	Night	35% 7% 11% 22% 16% 8%	7766
February	1st to 10th	Night	34% 5% 11% 19% 21% 9%	2520
	11th to 20th	Night	30% 6% 11% 21% 22% 9%	2459
	21st to end	Night	27% 6% 12% 21% 27% 7%	2030
March	1st to 10th	Night	32% 8% 13% 22% 18% 7%	5028
	11th to 20th	Night	21% 7% 17% 21% 19% 16%	5090
	21st to end	Night	31% 5% 10% 27% 22% 4	5588
April	1st to 10th	Night	25% 7% 19% 27% 16% 6%	2310
	11th to 20th	Night	24% 9% 16% 21% 23% 7%	2283
	21st to end	Night	22% 7% 14% 27% 26% 4	2143
May	1st to 10th	Night	23% 9% 25% 28% 12% 3	5264
	11th to 20th	Night	29% 9% 19% 28% 14% 1	5235
	21st to end	Night	28% 11% 21% 27% 12%	5771
June	1st to 10th	Night	39% 10% 25% 21% 6%	1890
	11th to 20th	Night	33% 13% 30% 21% 4	1845
	21st to end	Night	36% 17% 27% 15% 5%	1800
July	1st to 10th	Night	45% 17% 31% 7% 1	4015
	11th to 20th	Night	39% 19% 35% 7%	4006
	21st to end	Night	46% 15% 25% 13%	4297
August	1st to 10th	Night	36% 16% 31% 11% 6%	3023
	11th to 20th	Night	30% 16% 35% 17% 1	3230
	21st to end	Night	42% 19% 28% 9% 1	3907
September	1st to 10th	Night	41% 20% 25% 13% 2	2200
	11th to 20th	Night	46% 14% 24% 15% 2	2200
	21st to end	Night	42% 13% 19% 18% 8% 1	2200
October	1st to 10th	Night	54% 11% 13% 11% 8% 4	3590
	11th to 20th	Night	26% 6% 9% 28% 25% 5%	3790
	21st to end	Night	29% 6% 9% 26% 25% 5%	4252
November	1st to 10th	Night	29% 7% 13% 21% 20% 10%	2461
	11th to 20th	Night	32% 7% 11% 22% 20% 8%	2520
	21st to end	Night	31% 7% 12% 23% 19% 8%	2688
December	1st to 10th	Night	21% 5% 18% 29% 16% 11%	4380
	11th to 20th	Night	33% 6% 11% 21% 21% 8%	4954
	21st to end	Night	42% 9% 14% 18% 15% 3	6633

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	10% 9% 38% 33% 9% 1	330
	11th to 20th	Day	10% 15% 33% 30% 11% 2	330
	21st to end	Day	15% 11% 42% 26% 6%	363
February	1st to 10th	Day	6% 12% 32% 32% 16% 2	330
	11th to 20th	Day	5% 7% 38% 34% 15% 2	330
	21st to end	Day	8% 10% 29% 38% 14% 1	316
March	1st to 10th	Day	6% 7% 39% 32% 13% 1	540
	11th to 20th	Day	7% 10% 34% 30% 18% 1	540
	21st to end	Day	7% 7% 31% 35% 18% 3	594
April	1st to 10th	Day	8% 7% 33% 35% 15% 2	540
	11th to 20th	Day	7% 7% 31% 36% 15% 4	532
	21st to end	Day	4 4 25% 41% 22% 4	540
May	1st to 10th	Day	4 4 23% 41% 20% 7%	543
	11th to 20th	Day	10% 2 18% 38% 24% 8%	567
	21st to end	Day	5% 2 10% 35% 34% 15%	617
June	1st to 10th	Day	14% 3 8% 31% 30% 15%	570
	11th to 20th	Day	7% 2 5% 29% 34% 23%	550
	21st to end	Day	5% 1 4 17% 38% 35%	530
July	1st to 10th	Day	6% 2 1 14% 39% 38%	525
	11th to 20th	Day	4 1 2 15% 36% 41%	524
	21st to end	Day	7% 2 3 16% 36% 35%	576
August	1st to 10th	Day	8% 1 3 16% 40% 33%	526
	11th to 20th	Day	7% 2 1 13% 38% 39%	519
	21st to end	Day	7% 2 4 17% 38% 31%	583
September	1st to 10th	Day	8% 2 3 18% 37% 33%	530
	11th to 20th	Day	9% 2 3 28% 34% 24%	530
	21st to end	Day	7% 1 4 27% 37% 25%	530
October	1st to 10th	Day	12% 3 12% 35% 30% 8%	530
	11th to 20th	Day	7% 2 18% 35% 31% 8%	530
	21st to end	Day	9% 3 17% 42% 25% 4	583
November	1st to 10th	Day	8% 5% 19% 36% 27% 5%	535
	11th to 20th	Day	11% 4 22% 36% 21% 5%	540
	21st to end	Day	8% 5% 28% 36% 20% 4	367
December	1st to 10th	Day	5% 8% 33% 36% 15% 4	330
	11th to 20th	Day	8% 5% 35% 32% 17% 2	330
	21st to end	Day	7% 7% 31% 37% 15% 3	363
January	1st to 10th	Night	11% 8% 25% 37% 18% 1	840
	11th to 20th	Night	13% 7% 26% 37% 16% 1	840
	21st to end	Night	15% 10% 29% 33% 14%	924
February	1st to 10th	Night	13% 6% 29% 32% 19% 1	840
	11th to 20th	Night	11% 6% 24% 38% 19% 2	823
	21st to end	Night	8% 5% 24% 44% 19% 1	692
March	1st to 10th	Night	6% 6% 32% 41% 13% 2	840
	11th to 20th	Night	7% 6% 23% 41% 22% 1	840
	21st to end	Night	8% 5% 26% 38% 21% 2	924
April	1st to 10th	Night	7% 7% 24% 41% 20% 1	840
	11th to 20th	Night	7% 5% 27% 41% 18% 2	831
	21st to end	Night	6% 3 25% 45% 20% 1	809
May	1st to 10th	Night	4 2 13% 43% 34% 4	630
	11th to 20th	Night	8% 1 14% 41% 31% 6%	621
	21st to end	Night	6% 1 10% 35% 39% 10%	683
June	1st to 10th	Night	12% 1 4 26% 43% 14%	630
	11th to 20th	Night	7% 1 4 18% 41% 29%	615
	21st to end	Night	8% 1 3 12% 42% 34%	600
July	1st to 10th	Night	6% 1 2 9% 42% 40%	585
	11th to 20th	Night	4 2 1 9% 39% 45%	582
	21st to end	Night	4 2 1 10% 44% 38%	657
August	1st to 10th	Night	5% 1 1 10% 44% 39%	597
	11th to 20th	Night	6% 1 1 9% 39% 43%	594
	21st to end	Night	10% 2 3 21% 38% 26%	851
September	1st to 10th	Night	7% 2 3 21% 44% 24%	800
	11th to 20th	Night	11% 2 3 26% 39% 19%	800
	21st to end	Night	10% 2 6% 29% 39% 14%	800
October	1st to 10th	Night	12% 2 14% 35% 31% 6%	800
	11th to 20th	Night	9% 3 14% 37% 33% 4	800
	21st to end	Night	10% 4 20% 39% 24% 3	880
November	1st to 10th	Night	7% 3 26% 40% 20% 3	820
	11th to 20th	Night	10% 4 21% 41% 22% 2	840
	21st to end	Night	9% 5% 25% 39% 21% 2	840
December	1st to 10th	Night	9% 5% 23% 36% 24% 2	840
	11th to 20th	Night	10% 5% 23% 39% 21% 3	840
	21st to end	Night	12% 4 26% 35% 22% 2	924

Page generated at 2026-06-13 02:31:44. Version ac07

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