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 2025-05-11.

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% 5% 5% 5% 5% 7% 8% 50%	118087
	Night	3 6% 2 7% 5% 5% 5% 5% 7% 8% 48%	119802
Transparency	Day	31% 3 12% 25% 20% 9%	117842
	Night	33% 4 13% 26% 18% 7%	119637
Seeing	Day	6% 8% 27% 32% 20% 6%	16272
	Night	6% 6% 30% 41% 15% 2	26515

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 4 2 9% 7% 7% 10% 9% 12% 11% 28%	3659
	11th to 20th	Day	1 5% 3 7% 7% 8% 10% 8% 9% 10% 32%	4100
	21st to end	Day	1 4 3 11% 12% 8% 8% 5% 7% 9% 32%	4510
February	1st to 10th	Day	2 7% 4 10% 5% 6% 6% 5% 6% 10% 39%	1800
	11th to 20th	Day	2 8% 4 9% 6% 5% 6% 4 7% 8% 42%	1755
	21st to end	Day	2 7% 3 8% 6% 6% 4 4 8% 9% 43%	1567
March	1st to 10th	Day	1 9% 3 8% 5% 5% 7% 7% 7% 9% 39%	4954
	11th to 20th	Day	1 6% 3 7% 6% 6% 7% 5% 7% 9% 44%	5000
	21st to end	Day	3 9% 4 9% 6% 6% 6% 5% 7% 11% 36%	5486
April	1st to 10th	Day	4 9% 3 8% 4 4 5% 4 7% 9% 45%	2368
	11th to 20th	Day	4 8% 2 6% 6% 5% 5% 5% 6% 8% 44%	2371
	21st to end	Day	5% 8% 2 7% 6% 4 5% 5% 7% 8% 43%	2597
May	1st to 10th	Day	6% 9% 3 7% 5% 5% 5% 5% 6% 8% 40%	4240
	11th to 20th	Day	6% 4 1 4 4 3 5% 4 6% 8% 53%	4292
	21st to end	Day	4 5% 2 5% 4 4 5% 4 7% 8% 51%	4825
June	1st to 10th	Day	4 4 1 4 4 5% 5% 5% 7% 10% 51%	2660
	11th to 20th	Day	4 4 1 4 3 4 4 3 6% 8% 60%	2660
	21st to end	Day	2 2 1 3 3 4 4 3 5% 7% 66%	2660
July	1st to 10th	Day	2 2 1 2 2 2 3 3 4 6% 74%	4430
	11th to 20th	Day	2 1 1 3 3 4 4 4 7% 9% 61%	4352
	21st to end	Day	3 2 1 4 3 4 4 4 6% 8% 60%	4454
August	1st to 10th	Day	2 2 1 4 3 4 5% 4 6% 8% 60%	4092
	11th to 20th	Day	3 2 1 3 3 3 4 4 6% 8% 63%	4028
	21st to end	Day	2 1 1 3 3 3 3 3 4 8% 70%	4314
September	1st to 10th	Day	3 3 1 3 3 2 3 3 5% 7% 67%	2280
	11th to 20th	Day	3 3 1 4 3 3 4 4 5% 6% 64%	2180
	21st to end	Day	5% 4 1 4 2 3 3 2 3 5% 67%	2058
October	1st to 10th	Day	4 3 1 3 2 2 2 2 4 5% 72%	3170
	11th to 20th	Day	7% 5% 1 4 3 3 3 4 5% 7% 59%	3150
	21st to end	Day	4 6% 2 7% 3 4 3 3 5% 7% 56%	3438
November	1st to 10th	Day	3 7% 2 6% 5% 5% 5% 5% 6% 7% 50%	1787
	11th to 20th	Day	2 5% 2 7% 5% 5% 5% 4 6% 10% 49%	1600
	21st to end	Day	1 7% 2 7% 4 5% 4 4 7% 10% 49%	1600
December	1st to 10th	Day	1 3 2 5% 4 4 5% 5% 10% 9% 52%	2620
	11th to 20th	Day	1 5% 2 8% 8% 7% 8% 6% 9% 12% 35%	3026
	21st to end	Day	2 10% 4 11% 6% 7% 7% 6% 9% 11% 28%	4004
January	1st to 10th	Night	1 5% 3 9% 6% 8% 9% 9% 12% 10% 28%	6327
	11th to 20th	Night	1 5% 4 12% 8% 10% 9% 7% 8% 9% 28%	5903
	21st to end	Night	1 7% 3 13% 10% 7% 6% 5% 7% 7% 32%	6468
February	1st to 10th	Night	2 7% 4 8% 7% 6% 7% 5% 7% 8% 39%	2600
	11th to 20th	Night	3 8% 3 8% 5% 6% 6% 4 6% 9% 42%	2532
	21st to end	Night	1 7% 4 10% 6% 5% 6% 5% 6% 9% 42%	2060
March	1st to 10th	Night	2 9% 3 8% 5% 4 5% 5% 9% 10% 40%	4940
	11th to 20th	Night	1 6% 3 8% 5% 4 5% 5% 6% 8% 48%	5000
	21st to end	Night	4 11% 4 10% 6% 6% 5% 4 6% 9% 37%	5489
April	1st to 10th	Night	4 9% 3 5% 4 5% 5% 5% 5% 8% 48%	2031
	11th to 20th	Night	3 9% 3 7% 5% 5% 5% 3 6% 9% 45%	1977
	21st to end	Night	5% 8% 2 6% 5% 4 5% 4 6% 9% 47%	1800
May	1st to 10th	Night	5% 11% 4 8% 4 4 5% 4 5% 8% 42%	2950
	11th to 20th	Night	4 4 1 5% 3 4 4 5% 5% 8% 57%	2617
	21st to end	Night	5% 5% 2 6% 4 4 4 4 6% 6% 54%	2762
June	1st to 10th	Night	4 4 2 3 2 4 3 4 6% 11% 56%	1520
	11th to 20th	Night	3 3 2 4 4 3 4 3 5% 8% 61%	1520
	21st to end	Night	2 2 1 3 3 3 3 4 4 7% 67%	1520
July	1st to 10th	Night	2 2 1 3 3 3 4 4 7% 7% 64%	2540
	11th to 20th	Night	1 2 1 3 3 4 5% 4 7% 10% 60%	2600
	21st to end	Night	1 1 1 3 3 3 4 5% 7% 9% 61%	3109
August	1st to 10th	Night	2 1 1 4 3 3 4 4 6% 8% 64%	2847
	11th to 20th	Night	2 2 1 5% 4 5% 4 3 5% 7% 62%	2811
	21st to end	Night	2 2 1 3 3 3 3 3 5% 8% 69%	3353
September	1st to 10th	Night	4 3 1 3 3 3 2 3 4 6% 69%	1900
	11th to 20th	Night	3 2 1 3 3 3 3 3 5% 9% 65%	1997
	21st to end	Night	5% 3 1 3 3 2 3 3 3 5% 69%	2121
October	1st to 10th	Night	4 4 1 3 2 2 2 2 3 5% 73%	3800
	11th to 20th	Night	4 5% 2 5% 3 3 4 3 5% 7% 59%	3778
	21st to end	Night	5% 6% 2 5% 4 4 4 3 5% 8% 53%	4120
November	1st to 10th	Night	4 6% 2 6% 4 5% 4 4 7% 9% 50%	2485
	11th to 20th	Night	3 5% 3 6% 4 4 4 3 6% 8% 53%	2800
	21st to end	Night	2 7% 3 6% 4 4 4 4 6% 9% 51%	2800
December	1st to 10th	Night	2 4 2 5% 4 4 5% 6% 8% 9% 51%	4570
	11th to 20th	Night	3 7% 2 6% 6% 5% 6% 5% 9% 10% 41%	5181
	21st to end	Night	2 9% 4 10% 7% 9% 8% 6% 9% 9% 28%	6974

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	46% 6% 17% 19% 11% 1	3660
	11th to 20th	Day	44% 5% 13% 20% 17% 1	4100
	21st to end	Day	49% 4 13% 21% 12% 1	4510
February	1st to 10th	Day	40% 7% 18% 24% 11% 1	1800
	11th to 20th	Day	39% 6% 19% 24% 9% 2	1764
	21st to end	Day	34% 5% 17% 26% 14% 3	1567
March	1st to 10th	Day	41% 4 13% 27% 11% 5%	4954
	11th to 20th	Day	37% 3 17% 28% 14%	5000
	21st to end	Day	43% 3 20% 29% 5%	5486
April	1st to 10th	Day	35% 6% 18% 24% 14% 2	2368
	11th to 20th	Day	37% 5% 15% 29% 14% 1	2374
	21st to end	Day	37% 4 14% 32% 12%	2597
May	1st to 10th	Day	41% 4 11% 26% 14% 5%	4240
	11th to 20th	Day	28% 2 10% 38% 16% 6%	4296
	21st to end	Day	31% 4 10% 32% 21% 3	4825
June	1st to 10th	Day	27% 5% 15% 30% 20% 4	2660
	11th to 20th	Day	24% 3 10% 22% 28% 14%	2660
	21st to end	Day	18% 3 4 22% 34% 19%	2660
July	1st to 10th	Day	12% 3 4 16% 29% 35%	4361
	11th to 20th	Day	19% 2 3 15% 30% 30%	4277
	21st to end	Day	22% 2 3 15% 34% 23%	4314
August	1st to 10th	Day	21% 2 5% 20% 30% 21%	4078
	11th to 20th	Day	20% 2 5% 24% 33% 16%	4067
	21st to end	Day	16% 2 6% 17% 36% 23%	4313
September	1st to 10th	Day	17% 3 6% 21% 33% 19%	2280
	11th to 20th	Day	20% 3 8% 27% 27% 14%	2180
	21st to end	Day	21% 3 6% 30% 32% 9%	2058
October	1st to 10th	Day	17% 2 7% 23% 31% 20%	3170
	11th to 20th	Day	27% 2 10% 32% 23% 7%	3150
	21st to end	Day	31% 2 12% 37% 16% 2	3438
November	1st to 10th	Day	32% 5% 15% 28% 17% 2	1787
	11th to 20th	Day	30% 6% 22% 27% 14% 2	1600
	21st to end	Day	30% 6% 19% 28% 15% 2	1600
December	1st to 10th	Day	26% 5% 23% 31% 14% 1	2620
	11th to 20th	Day	41% 4 23% 26% 6%	3024
	21st to end	Day	49% 4 12% 17% 14% 3	4004
January	1st to 10th	Night	46% 6% 13% 24% 10% 1	6327
	11th to 20th	Night	49% 6% 14% 18% 12% 1	5903
	21st to end	Night	50% 4 14% 17% 14% 2	6468
February	1st to 10th	Night	41% 8% 17% 22% 10% 2	2600
	11th to 20th	Night	38% 6% 17% 25% 12% 2	2533
	21st to end	Night	38% 6% 17% 23% 13% 2	2060
March	1st to 10th	Night	38% 3 11% 30% 12% 6%	4940
	11th to 20th	Night	35% 3 14% 37% 11% 1	5000
	21st to end	Night	46% 3 15% 30% 5% 1	5489
April	1st to 10th	Night	34% 5% 17% 26% 15% 3	2031
	11th to 20th	Night	36% 4 15% 27% 17%	1977
	21st to end	Night	35% 3 15% 33% 13%	1800
May	1st to 10th	Night	40% 3 11% 25% 18% 3	2950
	11th to 20th	Night	26% 3 13% 39% 12% 7%	2618
	21st to end	Night	31% 3 10% 37% 17% 2	2762
June	1st to 10th	Night	24% 3 20% 29% 21% 4	1520
	11th to 20th	Night	23% 3 10% 24% 27% 14%	1520
	21st to end	Night	19% 2 4 19% 34% 22%	1520
July	1st to 10th	Night	19% 3 4 15% 28% 31%	2500
	11th to 20th	Night	19% 3 3 15% 31% 29%	2552
	21st to end	Night	18% 2 5% 18% 36% 21%	3011
August	1st to 10th	Night	18% 2 4 28% 26% 22%	2838
	11th to 20th	Night	24% 1 6% 19% 32% 18%	2838
	21st to end	Night	15% 2 8% 20% 26% 29%	3353
September	1st to 10th	Night	17% 2 6% 22% 30% 23%	1900
	11th to 20th	Night	18% 3 9% 27% 30% 13%	1997
	21st to end	Night	19% 2 8% 29% 33% 9%	2121
October	1st to 10th	Night	17% 2 6% 21% 39% 14%	3800
	11th to 20th	Night	27% 2 9% 31% 22% 9%	3778
	21st to end	Night	31% 2 10% 35% 19% 3	4120
November	1st to 10th	Night	31% 5% 14% 28% 19% 3	2485
	11th to 20th	Night	28% 5% 19% 33% 12% 2	2800
	21st to end	Night	29% 5% 18% 30% 15% 2	2800
December	1st to 10th	Night	28% 5% 22% 30% 14% 1	4570
	11th to 20th	Night	37% 4 24% 28% 6%	5182
	21st to end	Night	50% 4 13% 18% 12% 3	6974

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% 7% 27% 40% 11% 6%	300
	11th to 20th	Day	5% 5% 30% 38% 19% 4	300
	21st to end	Day	2 3 34% 41% 15% 5%	330
February	1st to 10th	Day	9% 11% 41% 31% 8%	300
	11th to 20th	Day	4 6% 43% 33% 11% 3	300
	21st to end	Day	4 12% 39% 34% 9% 1	274
March	1st to 10th	Day	5% 10% 32% 36% 15% 2	500
	11th to 20th	Day	4 9% 27% 40% 17% 3	500
	21st to end	Day	8% 6% 28% 41% 14% 2	550
April	1st to 10th	Day	10% 9% 28% 34% 15% 4	500
	11th to 20th	Day	9% 13% 34% 29% 14% 1	492
	21st to end	Day	11% 13% 27% 26% 19% 4	500
May	1st to 10th	Day	11% 17% 25% 24% 17% 6%	503
	11th to 20th	Day	10% 10% 21% 31% 23% 5%	617
	21st to end	Day	9% 9% 24% 27% 21% 10%	734
June	1st to 10th	Day	5% 7% 24% 27% 27% 10%	680
	11th to 20th	Day	5% 9% 32% 32% 18% 3	680
	21st to end	Day	3 5% 24% 37% 24% 7%	680
July	1st to 10th	Day	3 4 17% 37% 31% 8%	671
	11th to 20th	Day	4 6% 18% 33% 31% 8%	629
	21st to end	Day	5% 4 17% 33% 29% 12%	531
August	1st to 10th	Day	3 3 20% 31% 32% 11%	487
	11th to 20th	Day	3 4 22% 28% 26% 16%	477
	21st to end	Day	4 4 25% 26% 29% 12%	539
September	1st to 10th	Day	5% 7% 22% 27% 26% 13%	490
	11th to 20th	Day	4 11% 27% 28% 19% 10%	490
	21st to end	Day	6% 9% 26% 29% 21% 9%	458
October	1st to 10th	Day	10% 6% 22% 28% 25% 9%	300
	11th to 20th	Day	9% 10% 27% 30% 18% 7%	300
	21st to end	Day	8% 13% 35% 29% 12% 2	330
November	1st to 10th	Day	9% 9% 32% 36% 13% 1	300
	11th to 20th	Day	6% 11% 36% 37% 8% 2	300
	21st to end	Day	6% 8% 36% 36% 12% 3	300
December	1st to 10th	Day	4 6% 35% 38% 14% 2	300
	11th to 20th	Day	5% 7% 39% 37% 11% 1	300
	21st to end	Day	7% 7% 33% 33% 14% 6%	330
January	1st to 10th	Night	6% 5% 33% 43% 11% 2	1000
	11th to 20th	Night	4 8% 34% 38% 14% 2	810
	21st to end	Night	5% 5% 33% 42% 13% 3	880
February	1st to 10th	Night	6% 5% 45% 35% 8% 1	800
	11th to 20th	Night	6% 7% 36% 40% 9% 2	784
	21st to end	Night	5% 10% 42% 34% 9% 1	660
March	1st to 10th	Night	7% 5% 35% 40% 12% 2	800
	11th to 20th	Night	5% 5% 30% 46% 14% 1	800
	21st to end	Night	9% 5% 31% 43% 11% 1	880
April	1st to 10th	Night	9% 8% 35% 40% 8% 1	631
	11th to 20th	Night	10% 9% 36% 35% 9% 1	593
	21st to end	Night	10% 8% 31% 37% 13% 1	600
May	1st to 10th	Night	10% 11% 31% 32% 15% 1	600
	11th to 20th	Night	8% 6% 29% 36% 20% 2	563
	21st to end	Night	8% 6% 27% 38% 18% 2	617
June	1st to 10th	Night	6% 5% 25% 39% 22% 2	570
	11th to 20th	Night	6% 8% 35% 41% 10%	570
	21st to end	Night	3 3 24% 46% 22% 1	570
July	1st to 10th	Night	3 2 21% 42% 30% 1	555
	11th to 20th	Night	1 3 17% 52% 25% 1	552
	21st to end	Night	3 1 12% 52% 31%	624
August	1st to 10th	Night	4 1 13% 51% 29% 1	567
	11th to 20th	Night	3 1 17% 51% 27% 1	564
	21st to end	Night	3 3 16% 46% 28% 4	627
September	1st to 10th	Night	5% 3 20% 46% 24% 2	570
	11th to 20th	Night	3 3 21% 47% 21% 5%	667
	21st to end	Night	6% 3 23% 39% 23% 6%	760
October	1st to 10th	Night	9% 5% 30% 34% 19% 2	760
	11th to 20th	Night	8% 7% 25% 41% 17% 2	760
	21st to end	Night	7% 7% 29% 41% 13% 3	836
November	1st to 10th	Night	7% 6% 36% 38% 11% 1	845
	11th to 20th	Night	5% 10% 38% 39% 8% 1	1000
	21st to end	Night	6% 7% 35% 40% 11% 1	1000
December	1st to 10th	Night	6% 9% 37% 38% 9% 1	1000
	11th to 20th	Night	8% 6% 36% 41% 7% 1	1000
	21st to end	Night	7% 9% 36% 36% 10% 2	1100

Page generated at 2025-05-08 07:34:00. Version ac07

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