Dry Sandy Crossing
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dry Sandy Crossing clear sky chart from 2005-11-06 to 2026-09-14.

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	3 5% 2 6% 4 4 5% 4 6% 9% 52%	158288
	Night	3 5% 2 6% 5% 5% 5% 4 7% 8% 49%	150457
Transparency	Day	30% 3 11% 25% 20% 10%	153086
	Night	33% 3 13% 26% 18% 8%	146668
Seeing	Day	6% 8% 27% 32% 20% 6%	18216
	Night	6% 6% 31% 41% 15% 2	28250

By Month

Percentage Cloud Cover SW (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	1 6% 3 10% 7% 7% 9% 7% 10% 10% 30%	4755
	11th to 20th	Day	1 4 2 6% 6% 7% 8% 7% 8% 10% 42%	5340
	21st to end	Day	1 3 2 10% 10% 8% 7% 5% 7% 9% 38%	5844
February	1st to 10th	Day	2 7% 4 9% 5% 6% 6% 5% 7% 10% 40%	1890
	11th to 20th	Day	2 8% 4 9% 6% 6% 6% 4 7% 8% 41%	1845
	21st to end	Day	2 7% 3 8% 6% 6% 4 4 7% 9% 45%	1643
March	1st to 10th	Day	1 10% 3 8% 5% 5% 7% 7% 7% 9% 39%	5064
	11th to 20th	Day	1 6% 3 7% 5% 6% 7% 5% 7% 9% 44%	5110
	21st to end	Day	3 9% 3 9% 6% 5% 6% 5% 7% 11% 36%	5607
April	1st to 10th	Day	4 9% 3 7% 4 4 5% 4 7% 9% 45%	2486
	11th to 20th	Day	4 8% 2 6% 6% 5% 5% 5% 6% 8% 45%	2491
	21st to end	Day	5% 8% 2 7% 6% 4 5% 5% 7% 9% 42%	2727
May	1st to 10th	Day	5% 6% 2 5% 4 4 4 4 6% 8% 53%	7626
	11th to 20th	Day	6% 6% 2 5% 4 4 5% 4 6% 8% 49%	8011
	21st to end	Day	4 5% 2 6% 4 5% 5% 4 8% 11% 46%	9026
June	1st to 10th	Day	4 4 1 4 4 4 5% 5% 7% 10% 53%	2940
	11th to 20th	Day	3 3 1 4 3 3 4 3 5% 8% 61%	2940
	21st to end	Day	2 2 1 3 3 3 4 4 6% 7% 65%	2940
July	1st to 10th	Day	2 2 1 3 3 3 4 3 5% 6% 68%	8249
	11th to 20th	Day	2 1 1 3 3 3 4 4 6% 8% 63%	8116
	21st to end	Day	3 2 1 4 3 4 4 4 7% 9% 58%	8304
August	1st to 10th	Day	2 2 1 3 3 3 4 3 5% 7% 68%	7549
	11th to 20th	Day	2 2 1 4 3 4 4 4 7% 8% 59%	7565
	21st to end	Day	3 4 1 5% 4 4 5% 3 6% 9% 56%	7998
September	1st to 10th	Day	3 3 1 3 3 2 3 3 5% 7% 68%	2520
	11th to 20th	Day	3 3 1 4 3 3 4 4 5% 6% 64%	2332
	21st to end	Day	5% 4 1 4 2 3 3 2 4 5% 66%	2166
October	1st to 10th	Day	5% 3 1 3 2 2 2 2 4 5% 72%	3270
	11th to 20th	Day	7% 5% 1 4 3 3 3 4 5% 6% 59%	3250
	21st to end	Day	4 6% 2 6% 3 4 3 3 5% 7% 56%	3548
November	1st to 10th	Day	3 7% 2 5% 4 5% 5% 5% 6% 7% 51%	1878
	11th to 20th	Day	3 5% 2 7% 5% 5% 4 5% 6% 10% 49%	1680
	21st to end	Day	1 7% 1 7% 4 5% 4 4 7% 11% 49%	1680
December	1st to 10th	Day	1 4 2 5% 4 4 5% 5% 9% 9% 52%	2700
	11th to 20th	Day	2 5% 2 8% 8% 7% 8% 6% 9% 12% 35%	3106
	21st to end	Day	2 10% 4 11% 6% 7% 7% 6% 9% 10% 28%	4092
January	1st to 10th	Night	2 7% 3 9% 6% 7% 8% 8% 10% 9% 30%	8201
	11th to 20th	Night	1 4 3 9% 6% 8% 7% 5% 7% 8% 43%	7673
	21st to end	Night	1 5% 3 12% 9% 7% 6% 4 7% 8% 38%	8370
February	1st to 10th	Night	2 7% 4 8% 6% 5% 6% 5% 7% 8% 40%	2730
	11th to 20th	Night	2 8% 3 8% 6% 6% 6% 5% 6% 10% 41%	2662
	21st to end	Night	1 6% 3 9% 6% 5% 6% 5% 6% 9% 43%	2160
March	1st to 10th	Night	2 9% 3 8% 5% 4 5% 5% 9% 10% 40%	5050
	11th to 20th	Night	1 6% 3 8% 5% 4 5% 5% 6% 8% 49%	5110
	21st to end	Night	4 10% 4 9% 6% 5% 5% 4 6% 9% 37%	5610
April	1st to 10th	Night	4 8% 3 5% 4 5% 4 5% 5% 8% 49%	2133
	11th to 20th	Night	3 9% 2 7% 4 5% 5% 3 6% 9% 46%	2077
	21st to end	Night	5% 8% 2 6% 5% 4 5% 4 6% 9% 47%	1890
May	1st to 10th	Night	4 8% 3 6% 4 4 4 4 6% 8% 50%	5321
	11th to 20th	Night	4 5% 2 5% 4 4 4 4 5% 8% 55%	4879
	21st to end	Night	5% 5% 2 6% 4 5% 5% 5% 7% 9% 47%	5181
June	1st to 10th	Night	4 4 2 4 2 4 3 4 6% 10% 57%	1680
	11th to 20th	Night	3 3 2 4 5% 3 4 3 5% 7% 62%	1680
	21st to end	Night	3 2 1 3 3 3 3 4 4 7% 67%	1680
July	1st to 10th	Night	2 3 2 4 4 5% 6% 4 7% 8% 56%	4740
	11th to 20th	Night	1 2 1 4 4 5% 5% 4 7% 9% 57%	4856
	21st to end	Night	2 2 1 4 4 5% 5% 5% 8% 10% 53%	5805
August	1st to 10th	Night	1 1 1 3 2 3 3 3 5% 7% 70%	5273
	11th to 20th	Night	2 3 2 6% 4 4 4 3 6% 7% 57%	5291
	21st to end	Night	3 3 1 6% 5% 5% 5% 4 6% 10% 52%	6218
September	1st to 10th	Night	4 3 1 3 3 3 3 3 4 7% 68%	2100
	11th to 20th	Night	3 2 1 3 3 3 3 3 5% 8% 65%	2132
	21st to end	Night	5% 3 1 3 3 2 3 3 3 5% 68%	2233
October	1st to 10th	Night	4 4 1 3 2 2 2 2 3 5% 73%	3920
	11th to 20th	Night	4 5% 2 5% 3 3 4 3 5% 7% 59%	3898
	21st to end	Night	5% 6% 2 5% 4 4 4 3 5% 8% 54%	4252
November	1st to 10th	Night	3 5% 2 6% 4 5% 4 3 7% 9% 52%	2613
	11th to 20th	Night	3 5% 2 6% 5% 4 4 3 7% 8% 53%	2940
	21st to end	Night	2 7% 3 6% 4 4 4 4 6% 9% 51%	2940
December	1st to 10th	Night	2 5% 2 5% 4 4 5% 6% 8% 10% 50%	4710
	11th to 20th	Night	3 7% 2 6% 6% 5% 6% 6% 9% 10% 41%	5321
	21st to end	Night	2 9% 4 10% 7% 9% 8% 6% 9% 9% 28%	7128

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	47% 4 20% 19% 10% 1	4758
	11th to 20th	Day	36% 4 18% 25% 15% 3	5340
	21st to end	Day	44% 3 14% 26% 13% 1	5844
February	1st to 10th	Day	38% 7% 18% 25% 11% 1	1890
	11th to 20th	Day	39% 6% 19% 24% 9% 2	1854
	21st to end	Day	34% 5% 17% 26% 16% 2	1643
March	1st to 10th	Day	41% 4 13% 27% 11% 5%	5064
	11th to 20th	Day	37% 3 18% 28% 14%	5110
	21st to end	Day	43% 3 20% 29% 6%	5607
April	1st to 10th	Day	36% 6% 18% 26% 14% 2	2486
	11th to 20th	Day	36% 4 15% 28% 16% 1	2494
	21st to end	Day	37% 4 14% 32% 13%	2727
May	1st to 10th	Day	30% 2 13% 29% 20% 5%	7626
	11th to 20th	Day	33% 2 7% 27% 23% 7%	8015
	21st to end	Day	32% 2 10% 33% 20% 3	9027
June	1st to 10th	Day	26% 4 14% 29% 22% 4	2940
	11th to 20th	Day	22% 3 10% 22% 29% 15%	2940
	21st to end	Day	18% 2 4 22% 35% 18%	2940
July	1st to 10th	Day	18% 2 2 14% 29% 36%	8181
	11th to 20th	Day	19% 2 4 21% 26% 29%	8041
	21st to end	Day	23% 2 4 20% 30% 21%	8120
August	1st to 10th	Day	17% 2 3 16% 26% 36%	5978
	11th to 20th	Day	24% 2 8% 27% 26% 12%	5964
	21st to end	Day	21% 1 11% 24% 26% 16%	6277
September	1st to 10th	Day	17% 3 6% 21% 34% 19%	2520
	11th to 20th	Day	20% 3 8% 29% 27% 13%	2332
	21st to end	Day	21% 3 6% 30% 32% 8%	2166
October	1st to 10th	Day	18% 2 7% 23% 31% 19%	3270
	11th to 20th	Day	27% 2 10% 32% 22% 7%	3250
	21st to end	Day	30% 2 12% 38% 16% 2	3548
November	1st to 10th	Day	31% 5% 15% 29% 17% 2	1878
	11th to 20th	Day	31% 6% 21% 27% 13% 2	1680
	21st to end	Day	30% 6% 19% 28% 15% 2	1680
December	1st to 10th	Day	27% 5% 23% 31% 14% 1	2700
	11th to 20th	Day	40% 4 23% 26% 6%	3104
	21st to end	Day	49% 4 13% 17% 14% 3	4092
January	1st to 10th	Night	46% 5% 17% 21% 10% 1	8202
	11th to 20th	Night	39% 5% 19% 24% 11% 2	7673
	21st to end	Night	43% 4 14% 20% 16% 2	8370
February	1st to 10th	Night	40% 7% 18% 23% 11% 1	2730
	11th to 20th	Night	38% 6% 17% 25% 12% 2	2663
	21st to end	Night	37% 6% 16% 25% 14% 2	2160
March	1st to 10th	Night	38% 3 12% 30% 12% 5%	5050
	11th to 20th	Night	34% 3 14% 37% 11% 1	5110
	21st to end	Night	45% 3 15% 31% 6% 1	5610
April	1st to 10th	Night	33% 5% 17% 27% 15% 3	2133
	11th to 20th	Night	36% 3 16% 26% 18% 1	2077
	21st to end	Night	35% 3 14% 33% 14%	1890
May	1st to 10th	Night	33% 2 9% 30% 23% 3	5319
	11th to 20th	Night	30% 2 8% 31% 23% 7%	4880
	21st to end	Night	35% 2 11% 33% 17% 2	5182
June	1st to 10th	Night	24% 3 18% 28% 23% 5%	1680
	11th to 20th	Night	23% 2 9% 23% 27% 16%	1680
	21st to end	Night	19% 2 4 19% 35% 21%	1680
July	1st to 10th	Night	25% 3 3 13% 29% 27%	4700
	11th to 20th	Night	23% 2 4 16% 28% 27%	4808
	21st to end	Night	25% 2 6% 20% 29% 17%	5677
August	1st to 10th	Night	15% 2 3 21% 22% 38%	4168
	11th to 20th	Night	29% 2 9% 22% 24% 13%	4168
	21st to end	Night	22% 1 13% 24% 19% 20%	4870
September	1st to 10th	Night	17% 2 6% 22% 30% 22%	2100
	11th to 20th	Night	18% 3 8% 28% 30% 13%	2132
	21st to end	Night	20% 2 7% 29% 33% 9%	2233
October	1st to 10th	Night	18% 2 6% 22% 39% 14%	3920
	11th to 20th	Night	27% 2 9% 31% 23% 9%	3898
	21st to end	Night	30% 2 10% 36% 19% 3	4252
November	1st to 10th	Night	30% 5% 14% 29% 19% 3	2613
	11th to 20th	Night	29% 5% 20% 33% 12% 2	2940
	21st to end	Night	29% 5% 18% 31% 14% 2	2940
December	1st to 10th	Night	29% 4 22% 29% 14% 1	4710
	11th to 20th	Night	37% 4 24% 28% 7%	5322
	21st to end	Night	50% 4 13% 18% 12% 3	7128

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	7% 8% 29% 39% 11% 6%	330
	11th to 20th	Day	5% 5% 31% 38% 18% 4	330
	21st to end	Day	1 3 37% 39% 15% 4	363
February	1st to 10th	Day	8% 10% 41% 32% 8% 1	330
	11th to 20th	Day	4 6% 43% 34% 10% 3	330
	21st to end	Day	5% 11% 39% 34% 9% 1	299
March	1st to 10th	Day	6% 10% 33% 35% 15% 2	540
	11th to 20th	Day	5% 10% 28% 39% 16% 3	540
	21st to end	Day	8% 7% 29% 41% 14% 2	594
April	1st to 10th	Day	10% 9% 27% 35% 16% 4	540
	11th to 20th	Day	9% 13% 34% 29% 14% 2	532
	21st to end	Day	11% 13% 26% 27% 19% 4	540
May	1st to 10th	Day	11% 16% 23% 26% 19% 6%	543
	11th to 20th	Day	10% 10% 21% 31% 22% 5%	710
	21st to end	Day	9% 8% 23% 29% 21% 10%	844
June	1st to 10th	Day	5% 7% 24% 28% 27% 9%	780
	11th to 20th	Day	5% 9% 33% 33% 17% 3	780
	21st to end	Day	4 6% 25% 37% 23% 6%	780
July	1st to 10th	Day	3 4 17% 37% 30% 8%	771
	11th to 20th	Day	4 6% 17% 33% 32% 9%	725
	21st to end	Day	5% 4 17% 33% 28% 12%	619
August	1st to 10th	Day	3 4 21% 32% 30% 10%	567
	11th to 20th	Day	4 4 21% 29% 26% 15%	557
	21st to end	Day	4 4 24% 27% 29% 11%	627
September	1st to 10th	Day	5% 7% 22% 28% 25% 13%	570
	11th to 20th	Day	4 12% 27% 28% 19% 10%	543
	21st to end	Day	6% 8% 25% 29% 22% 10%	496
October	1st to 10th	Day	10% 6% 22% 28% 24% 9%	330
	11th to 20th	Day	10% 12% 28% 28% 16% 6%	330
	21st to end	Day	7% 13% 35% 29% 13% 3	363
November	1st to 10th	Day	9% 9% 32% 36% 12% 1	330
	11th to 20th	Day	6% 10% 35% 37% 9% 2	330
	21st to end	Day	5% 7% 37% 35% 13% 2	330
December	1st to 10th	Day	5% 7% 38% 35% 13% 2	330
	11th to 20th	Day	6% 7% 40% 35% 11% 1	330
	21st to end	Day	8% 8% 33% 33% 14% 5%	363
January	1st to 10th	Night	7% 6% 34% 42% 10% 2	1050
	11th to 20th	Night	4 8% 35% 38% 14% 2	850
	21st to end	Night	5% 5% 34% 42% 12% 2	924
February	1st to 10th	Night	5% 5% 45% 36% 8% 1	840
	11th to 20th	Night	6% 7% 36% 41% 9% 2	824
	21st to end	Night	5% 10% 43% 34% 8% 1	692
March	1st to 10th	Night	7% 5% 35% 39% 12% 1	840
	11th to 20th	Night	5% 7% 31% 44% 13% 1	840
	21st to end	Night	8% 4 32% 44% 10% 1	924
April	1st to 10th	Night	9% 8% 34% 39% 8% 1	663
	11th to 20th	Night	10% 9% 36% 36% 9% 1	623
	21st to end	Night	10% 8% 31% 37% 13% 1	630
May	1st to 10th	Night	9% 11% 31% 33% 15% 1	630
	11th to 20th	Night	8% 6% 30% 35% 19% 2	621
	21st to end	Night	8% 5% 27% 40% 17% 2	683
June	1st to 10th	Night	6% 5% 26% 39% 22% 2	630
	11th to 20th	Night	6% 8% 35% 41% 10%	630
	21st to end	Night	4 4 25% 45% 21% 1	630
July	1st to 10th	Night	3 2 21% 45% 29% 1	615
	11th to 20th	Night	2 3 17% 52% 25% 1	612
	21st to end	Night	3 1 13% 53% 29%	690
August	1st to 10th	Night	4 1 16% 51% 27% 1	627
	11th to 20th	Night	4 1 17% 51% 26% 1	624
	21st to end	Night	3 2 16% 48% 28% 3	693
September	1st to 10th	Night	5% 3 21% 47% 23% 2	630
	11th to 20th	Night	4 3 21% 48% 20% 5%	711
	21st to end	Night	6% 3 23% 39% 24% 6%	800
October	1st to 10th	Night	10% 5% 30% 34% 19% 2	800
	11th to 20th	Night	8% 7% 27% 40% 16% 2	800
	21st to end	Night	7% 7% 29% 41% 13% 3	880
November	1st to 10th	Night	7% 6% 37% 38% 11% 1	889
	11th to 20th	Night	5% 9% 37% 40% 8% 1	1050
	21st to end	Night	6% 7% 36% 39% 11% 1	1050
December	1st to 10th	Night	7% 9% 37% 37% 9% 1	1050
	11th to 20th	Night	8% 6% 38% 40% 7% 1	1050
	21st to end	Night	7% 8% 37% 36% 9% 2	1155

Page generated at 2026-09-11 02:11:57. Version ac07

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