Salt Pond Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Salt Pond Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	19% 8% 2 6% 4 4 4 3 5% 7% 38%	101212
	Night	20% 9% 3 6% 4 4 4 3 5% 6% 36%	97844
Transparency	Day	46% 6% 13% 21% 13% 2	104752
	Night	48% 5% 12% 21% 13% 1	102394
Seeing	Day	25% 16% 32% 20% 7% 1	15801
	Night	25% 15% 29% 23% 8% 1	24104

By Month

Percentage Cloud Cover NE (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	18% 9% 2 6% 5% 4 4 2 4 6% 39%	2517
	11th to 20th	Day	19% 7% 2 4 3 3 4 3 4 6% 43%	2520
	21st to end	Day	18% 10% 3 7% 4 3 4 3 5% 7% 36%	2868
February	1st to 10th	Day	18% 12% 2 6% 5% 4 5% 4 6% 6% 33%	1710
	11th to 20th	Day	15% 9% 3 8% 5% 4 4 3 6% 6% 38%	1761
	21st to end	Day	14% 10% 3 8% 5% 4 4 4 6% 5% 37%	1570
March	1st to 10th	Day	26% 11% 3 6% 5% 4 4 3 4 5% 30%	3164
	11th to 20th	Day	19% 8% 3 6% 5% 4 4 3 5% 7% 37%	3480
	21st to end	Day	28% 9% 3 5% 4 3 5% 3 5% 6% 29%	3816
April	1st to 10th	Day	21% 10% 2 6% 5% 3 4 3 5% 6% 35%	2242
	11th to 20th	Day	20% 8% 2 5% 5% 3 3 2 5% 7% 40%	2424
	21st to end	Day	20% 9% 2 7% 4 4 4 3 5% 6% 37%	2470
May	1st to 10th	Day	20% 8% 2 7% 4 4 4 4 6% 8% 33%	4106
	11th to 20th	Day	18% 7% 3 6% 4 4 4 4 5% 7% 37%	4081
	21st to end	Day	18% 8% 3 6% 4 4 4 4 6% 7% 35%	4890
June	1st to 10th	Day	22% 8% 2 6% 5% 4 4 4 6% 7% 32%	2850
	11th to 20th	Day	19% 8% 2 5% 4 4 4 3 5% 6% 39%	2850
	21st to end	Day	26% 8% 2 6% 5% 3 4 4 5% 7% 31%	2850
July	1st to 10th	Day	19% 8% 2 7% 4 5% 4 4 6% 8% 33%	4569
	11th to 20th	Day	16% 6% 2 5% 3 4 3 4 6% 9% 41%	4440
	21st to end	Day	22% 7% 2 5% 4 4 4 4 5% 8% 37%	4699
August	1st to 10th	Day	19% 8% 2 7% 4 4 4 3 6% 7% 35%	4105
	11th to 20th	Day	18% 8% 3 7% 4 4 5% 4 6% 7% 36%	4045
	21st to end	Day	10% 4 2 5% 3 3 4 4 5% 8% 51%	4532
September	1st to 10th	Day	12% 6% 1 5% 3 3 3 3 5% 8% 50%	2177
	11th to 20th	Day	13% 6% 2 3 3 3 3 2 5% 6% 54%	2090
	21st to end	Day	18% 6% 2 5% 4 3 4 3 4 7% 43%	2090
October	1st to 10th	Day	17% 7% 2 5% 4 4 4 3 6% 7% 41%	2030
	11th to 20th	Day	18% 6% 2 5% 3 4 4 3 4 6% 43%	1900
	21st to end	Day	22% 8% 2 5% 3 4 3 3 5% 6% 39%	1886
November	1st to 10th	Day	17% 7% 2 6% 4 4 3 3 5% 6% 43%	1708
	11th to 20th	Day	21% 6% 2 4 3 3 3 4 5% 7% 42%	1673
	21st to end	Day	21% 9% 3 6% 4 3 3 3 4 5% 40%	1520
December	1st to 10th	Day	24% 8% 2 7% 4 4 3 3 4 6% 33%	1445
	11th to 20th	Day	24% 9% 2 6% 4 4 4 3 5% 6% 35%	1668
	21st to end	Day	25% 10% 3 6% 4 4 4 2 5% 5% 33%	2466
January	1st to 10th	Night	15% 9% 3 8% 4 4 4 3 4 7% 39%	4429
	11th to 20th	Night	14% 10% 3 9% 5% 4 4 3 5% 6% 36%	4440
	21st to end	Night	18% 11% 4 7% 4 4 4 3 6% 7% 32%	4787
February	1st to 10th	Night	18% 9% 3 7% 4 4 5% 4 5% 7% 32%	2470
	11th to 20th	Night	14% 9% 3 7% 5% 4 4 3 6% 6% 38%	2304
	21st to end	Night	15% 9% 3 7% 5% 5% 3 3 5% 6% 39%	1884
March	1st to 10th	Night	29% 12% 3 6% 3 3 3 2 4 4 31%	3676
	11th to 20th	Night	15% 10% 2 8% 5% 5% 6% 5% 7% 7% 29%	3479
	21st to end	Night	28% 9% 3 6% 4 4 4 4 5% 4 29%	3816
April	1st to 10th	Night	24% 11% 2 6% 4 4 4 3 3 5% 35%	1933
	11th to 20th	Night	21% 9% 3 5% 5% 4 3 3 5% 7% 35%	1704
	21st to end	Night	24% 9% 3 6% 3 4 3 3 4 6% 35%	1710
May	1st to 10th	Night	23% 8% 3 7% 4 3 4 3 6% 7% 31%	2834
	11th to 20th	Night	19% 7% 2 8% 6% 5% 5% 4 7% 8% 28%	2813
	21st to end	Night	17% 9% 4 6% 5% 4 5% 4 4 6% 35%	2704
June	1st to 10th	Night	26% 8% 2 6% 4 3 5% 3 5% 7% 30%	1330
	11th to 20th	Night	20% 8% 1 6% 4 4 4 4 4 8% 36%	1330
	21st to end	Night	28% 11% 2 6% 3 3 3 3 4 6% 30%	1330
July	1st to 10th	Night	19% 11% 3 7% 5% 4 6% 4 7% 7% 27%	2390
	11th to 20th	Night	20% 8% 2 6% 4 4 5% 4 6% 9% 33%	2520
	21st to end	Night	17% 9% 2 5% 5% 4 5% 4 6% 7% 36%	2822
August	1st to 10th	Night	24% 11% 3 8% 4 4 4 4 4 6% 28%	2825
	11th to 20th	Night	19% 9% 3 7% 5% 4 5% 4 5% 7% 31%	2782
	21st to end	Night	11% 6% 2 6% 5% 4 4 3 6% 8% 47%	3124
September	1st to 10th	Night	15% 5% 2 4 3 3 4 3 6% 6% 49%	1999
	11th to 20th	Night	17% 7% 2 4 3 2 3 2 4 6% 51%	2090
	21st to end	Night	18% 6% 2 4 3 3 4 3 4 6% 45%	2090
October	1st to 10th	Night	20% 6% 3 5% 4 4 4 3 4 5% 42%	2149
	11th to 20th	Night	18% 6% 2 5% 3 4 4 4 4 6% 44%	2280
	21st to end	Night	24% 9% 2 5% 3 4 3 2 3 6% 38%	2710
November	1st to 10th	Night	18% 7% 2 6% 4 4 4 4 5% 5% 42%	2470
	11th to 20th	Night	19% 7% 2 5% 4 4 4 3 4 6% 42%	2503
	21st to end	Night	19% 8% 2 4 4 4 4 3 5% 6% 39%	2660
December	1st to 10th	Night	25% 9% 3 6% 5% 4 4 3 5% 6% 32%	2731
	11th to 20th	Night	24% 8% 2 4 3 3 3 3 4 7% 38%	3531
	21st to end	Night	25% 9% 3 6% 3 3 3 3 5% 6% 35%	5195

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% 5% 14% 24% 9% 1	2518
	11th to 20th	Day	42% 6% 12% 25% 12% 2	2520
	21st to end	Day	48% 5% 14% 20% 12% 1	2868
February	1st to 10th	Day	50% 6% 12% 17% 13% 2	1710
	11th to 20th	Day	48% 5% 12% 19% 14% 1	1769
	21st to end	Day	48% 5% 12% 20% 10% 5%	1570
March	1st to 10th	Day	57% 4 9% 13% 13% 3	3168
	11th to 20th	Day	48% 5% 14% 19% 12% 2	3480
	21st to end	Day	56% 4 7% 14% 15% 4	3816
April	1st to 10th	Day	51% 5% 9% 17% 15% 4	2242
	11th to 20th	Day	45% 5% 11% 22% 15% 3	2424
	21st to end	Day	49% 4 9% 18% 16% 3	2470
May	1st to 10th	Day	49% 8% 14% 20% 8% 1	4120
	11th to 20th	Day	45% 7% 16% 22% 9% 1	4085
	21st to end	Day	45% 9% 14% 17% 14% 1	4890
June	1st to 10th	Day	51% 8% 12% 19% 9% 1	2850
	11th to 20th	Day	46% 6% 11% 20% 15% 2	2850
	21st to end	Day	52% 8% 11% 17% 10% 2	2850
July	1st to 10th	Day	48% 6% 11% 24% 11%	4499
	11th to 20th	Day	40% 7% 17% 25% 11%	4365
	21st to end	Day	47% 6% 12% 22% 12% 1	4549
August	1st to 10th	Day	48% 5% 15% 25% 6%	4092
	11th to 20th	Day	48% 6% 17% 20% 9%	4084
	21st to end	Day	31% 6% 14% 27% 21% 1	4532
September	1st to 10th	Day	33% 7% 13% 27% 19% 1	2177
	11th to 20th	Day	34% 6% 12% 27% 19% 3	2090
	21st to end	Day	42% 5% 10% 26% 16% 1	2090
October	1st to 10th	Day	48% 4 12% 22% 12% 1	3368
	11th to 20th	Day	33% 4 9% 33% 22%	3140
	21st to end	Day	35% 3 18% 23% 18% 3	3086
November	1st to 10th	Day	43% 5% 14% 23% 13% 1	1708
	11th to 20th	Day	42% 6% 10% 22% 18% 3	1673
	21st to end	Day	47% 4 16% 22% 10% 1	1520
December	1st to 10th	Day	52% 5% 13% 19% 10% 1	1445
	11th to 20th	Day	51% 5% 11% 18% 13% 2	1668
	21st to end	Day	53% 6% 12% 18% 8% 3	2466
January	1st to 10th	Night	45% 5% 14% 25% 10% 2	4429
	11th to 20th	Night	49% 5% 14% 20% 11% 2	4440
	21st to end	Night	51% 6% 11% 21% 10% 1	4787
February	1st to 10th	Night	52% 5% 12% 17% 12% 2	2470
	11th to 20th	Night	47% 5% 11% 20% 15% 2	2307
	21st to end	Night	46% 5% 10% 20% 14% 4	1884
March	1st to 10th	Night	59% 3 8% 15% 12% 4	3685
	11th to 20th	Night	49% 7% 16% 15% 10% 2	3480
	21st to end	Night	58% 3 7% 14% 15% 2	3816
April	1st to 10th	Night	54% 4 8% 14% 16% 3	1933
	11th to 20th	Night	49% 5% 9% 20% 15% 2	1704
	21st to end	Night	51% 4 10% 17% 15% 3	1710
May	1st to 10th	Night	49% 8% 15% 19% 8% 1	2840
	11th to 20th	Night	48% 10% 16% 17% 7% 1	2814
	21st to end	Night	47% 9% 13% 20% 11% 1	2705
June	1st to 10th	Night	54% 7% 10% 21% 8% 1	1330
	11th to 20th	Night	46% 7% 14% 20% 11% 2	1330
	21st to end	Night	57% 5% 9% 18% 9% 2	1330
July	1st to 10th	Night	54% 6% 11% 17% 11% 1	2350
	11th to 20th	Night	49% 5% 14% 24% 9%	2472
	21st to end	Night	47% 6% 13% 22% 12% 1	2732
August	1st to 10th	Night	57% 5% 12% 19% 7%	2813
	11th to 20th	Night	52% 6% 14% 20% 9%	2809
	21st to end	Night	36% 5% 12% 24% 21% 1	3124
September	1st to 10th	Night	36% 7% 12% 28% 17% 1	1999
	11th to 20th	Night	37% 4 12% 26% 19% 2	2090
	21st to end	Night	40% 5% 9% 28% 16% 1	2090
October	1st to 10th	Night	43% 4 13% 24% 15% 1	3591
	11th to 20th	Night	34% 3 10% 29% 23% 1	3779
	21st to end	Night	40% 3 10% 29% 15% 3	4460
November	1st to 10th	Night	43% 6% 12% 23% 15% 1	2470
	11th to 20th	Night	44% 6% 11% 22% 17% 2	2503
	21st to end	Night	45% 6% 13% 19% 15% 2	2660
December	1st to 10th	Night	54% 5% 10% 20% 11%	2731
	11th to 20th	Night	48% 5% 11% 20% 15% 1	3532
	21st to end	Night	51% 6% 13% 18% 11% 2	5195

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	29% 24% 29% 14% 3	180
	11th to 20th	Day	37% 18% 32% 10% 2 1	180
	21st to end	Day	25% 22% 35% 16% 2	255
February	1st to 10th	Day	29% 24% 29% 14% 4	370
	11th to 20th	Day	26% 32% 31% 9% 2	413
	21st to end	Day	27% 22% 31% 17% 2	382
March	1st to 10th	Day	28% 21% 34% 15% 2	460
	11th to 20th	Day	26% 25% 30% 16% 3	460
	21st to end	Day	32% 21% 27% 14% 6% 1	506
April	1st to 10th	Day	33% 20% 31% 10% 4 1	460
	11th to 20th	Day	27% 21% 33% 13% 5%	452
	21st to end	Day	25% 18% 37% 15% 4 1	460
May	1st to 10th	Day	28% 18% 32% 16% 4 1	463
	11th to 20th	Day	18% 20% 35% 21% 4 1	487
	21st to end	Day	25% 14% 36% 17% 7% 1	614
June	1st to 10th	Day	24% 13% 32% 21% 8% 1	680
	11th to 20th	Day	23% 11% 31% 22% 11% 2	680
	21st to end	Day	29% 8% 30% 24% 8% 2	680
July	1st to 10th	Day	24% 7% 34% 24% 10% 1	562
	11th to 20th	Day	19% 5% 35% 29% 10% 2	484
	21st to end	Day	19% 6% 36% 27% 10% 2	532
August	1st to 10th	Day	17% 7% 32% 29% 12% 1	486
	11th to 20th	Day	18% 8% 30% 28% 13% 3	479
	21st to end	Day	16% 10% 32% 28% 11% 2	539
September	1st to 10th	Day	16% 8% 37% 27% 10% 2	490
	11th to 20th	Day	18% 12% 30% 22% 11% 7%	490
	21st to end	Day	21% 10% 32% 23% 10% 4	490
October	1st to 10th	Day	19% 16% 28% 25% 11% 2	457
	11th to 20th	Day	23% 15% 32% 20% 9% 2	390
	21st to end	Day	30% 16% 31% 17% 6% 1	429
November	1st to 10th	Day	25% 18% 30% 20% 6% 1	378
	11th to 20th	Day	30% 18% 32% 15% 3 1	370
	21st to end	Day	32% 21% 28% 14% 4	370
December	1st to 10th	Day	28% 20% 34% 13% 4 1	295
	11th to 20th	Day	35% 30% 26% 8% 2	180
	21st to end	Day	40% 20% 24% 15% 2	198
January	1st to 10th	Night	26% 24% 32% 16% 3	760
	11th to 20th	Night	30% 22% 30% 14% 3	760
	21st to end	Night	21% 27% 30% 18% 4	836
February	1st to 10th	Night	28% 21% 34% 15% 3	760
	11th to 20th	Night	23% 29% 30% 15% 3 1	743
	21st to end	Night	26% 19% 33% 18% 4	628
March	1st to 10th	Night	27% 19% 35% 18% 2	760
	11th to 20th	Night	24% 20% 32% 19% 6%	760
	21st to end	Night	25% 17% 32% 20% 5% 1	836
April	1st to 10th	Night	32% 14% 32% 18% 4	760
	11th to 20th	Night	25% 13% 33% 23% 5%	580
	21st to end	Night	28% 14% 27% 24% 7% 1	570
May	1st to 10th	Night	27% 9% 31% 25% 8% 1	570
	11th to 20th	Night	25% 8% 33% 26% 7% 1	562
	21st to end	Night	26% 7% 26% 30% 9% 1	484
June	1st to 10th	Night	30% 8% 23% 30% 8% 2	380
	11th to 20th	Night	23% 6% 24% 33% 13% 1	380
	21st to end	Night	35% 4 17% 33% 10% 1	380
July	1st to 10th	Night	24% 4 21% 38% 13%	370
	11th to 20th	Night	23% 2 22% 37% 15% 1	368
	21st to end	Night	21% 3 22% 40% 13% 2	462
August	1st to 10th	Night	21% 5% 24% 36% 13% 1	568
	11th to 20th	Night	21% 4 22% 38% 13% 1	562
	21st to end	Night	19% 4 22% 35% 19% 1	627
September	1st to 10th	Night	17% 4 29% 34% 14% 2	755
	11th to 20th	Night	21% 8% 25% 26% 16% 4	760
	21st to end	Night	21% 8% 28% 27% 14% 3	760
October	1st to 10th	Night	24% 10% 24% 26% 15% 1	760
	11th to 20th	Night	21% 16% 29% 22% 11% 1	760
	21st to end	Night	30% 16% 29% 19% 5%	836
November	1st to 10th	Night	25% 15% 27% 24% 7% 1	760
	11th to 20th	Night	28% 20% 26% 19% 7% 1	775
	21st to end	Night	27% 22% 29% 16% 6%	850
December	1st to 10th	Night	31% 19% 33% 13% 4	850
	11th to 20th	Night	31% 24% 27% 15% 3	850
	21st to end	Night	31% 21% 30% 14% 4	922

Page generated at 2024-11-03 02:11:13. Version ac07

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