Monswath observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Monswath observatory clear sky chart from 2005-11-06 to 2025-07-21.

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	12% 8% 3 7% 4 4 4 4 5% 7% 42%	120178
	Night	13% 9% 3 7% 4 4 4 3 5% 6% 43%	119141
Transparency	Day	39% 6% 12% 24% 17% 3	123815
	Night	41% 5% 11% 23% 17% 3	123648
Seeing	Day	16% 12% 28% 26% 15% 4	16618
	Night	16% 11% 30% 29% 12% 1	26433

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	12% 13% 5% 14% 6% 3 4 3 4 6% 29%	3617
	11th to 20th	Day	9% 11% 3 9% 5% 6% 4 3 5% 6% 39%	4011
	21st to end	Day	16% 14% 6% 8% 4 3 3 2 4 5% 35%	4488
February	1st to 10th	Day	14% 12% 5% 8% 4 5% 4 3 5% 7% 33%	1800
	11th to 20th	Day	14% 11% 4 6% 5% 5% 4 3 5% 6% 38%	1877
	21st to end	Day	13% 12% 3 8% 4 3 3 3 4 6% 40%	1650
March	1st to 10th	Day	15% 11% 2 5% 3 3 2 2 3 4 50%	4664
	11th to 20th	Day	9% 7% 2 5% 3 4 4 3 6% 7% 52%	4980
	21st to end	Day	13% 9% 3 8% 5% 5% 5% 4 6% 8% 34%	5681
April	1st to 10th	Day	13% 7% 3 7% 5% 4 5% 4 5% 7% 41%	2400
	11th to 20th	Day	17% 9% 3 6% 4 4 4 3 5% 5% 41%	2374
	21st to end	Day	18% 8% 3 7% 5% 4 4 4 6% 8% 35%	2400
May	1st to 10th	Day	14% 8% 3 9% 5% 5% 4 4 7% 9% 32%	5533
	11th to 20th	Day	14% 8% 3 6% 4 5% 5% 4 6% 8% 37%	6319
	21st to end	Day	14% 7% 3 7% 5% 4 4 3 6% 6% 41%	6935
June	1st to 10th	Day	8% 5% 2 5% 4 4 4 4 8% 9% 46%	2800
	11th to 20th	Day	8% 5% 1 4 4 4 4 5% 7% 9% 49%	2800
	21st to end	Day	5% 4 2 5% 5% 5% 5% 6% 8% 9% 47%	2800
July	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 7% 9% 40%	4580
	11th to 20th	Day	5% 4 2 5% 4 4 5% 4 7% 10% 49%	4580
	21st to end	Day	6% 5% 2 6% 6% 6% 6% 6% 7% 11% 39%	4481
August	1st to 10th	Day	6% 3 1 6% 4 4 5% 5% 7% 10% 50%	4104
	11th to 20th	Day	13% 5% 2 5% 5% 4 5% 4 6% 9% 42%	3794
	21st to end	Day	5% 5% 1 5% 4 4 4 4 7% 9% 51%	4180
September	1st to 10th	Day	12% 5% 2 4 4 3 3 3 6% 8% 50%	2280
	11th to 20th	Day	9% 6% 1 5% 4 3 4 4 6% 8% 50%	2280
	21st to end	Day	8% 5% 2 6% 4 3 4 4 5% 8% 52%	2036
October	1st to 10th	Day	10% 5% 2 5% 3 3 4 3 5% 6% 56%	1900
	11th to 20th	Day	15% 6% 2 5% 3 3 3 2 4 5% 53%	1900
	21st to end	Day	16% 8% 2 6% 3 3 3 3 4 6% 46%	2090
November	1st to 10th	Day	11% 6% 2 5% 3 3 3 3 4 6% 53%	1783
	11th to 20th	Day	13% 8% 3 6% 3 3 3 3 5% 6% 46%	1800
	21st to end	Day	16% 11% 3 6% 4 3 3 3 3 6% 42%	1661
December	1st to 10th	Day	7% 11% 2 6% 4 3 3 3 4 6% 51%	2610
	11th to 20th	Day	12% 8% 5% 11% 4 4 4 3 4 6% 39%	3008
	21st to end	Day	20% 16% 5% 11% 6% 5% 4 3 4 4 22%	3982
January	1st to 10th	Night	14% 11% 7% 13% 6% 4 3 3 4 4 31%	6348
	11th to 20th	Night	11% 10% 5% 13% 6% 5% 5% 4 3 4 35%	5964
	21st to end	Night	17% 13% 4 8% 4 4 4 3 4 4 35%	6490
February	1st to 10th	Night	15% 13% 4 8% 5% 4 4 3 5% 6% 34%	2600
	11th to 20th	Night	16% 8% 3 8% 5% 4 3 3 4 6% 39%	2408
	21st to end	Night	15% 10% 3 7% 4 3 3 3 5% 5% 43%	1980
March	1st to 10th	Night	18% 13% 3 5% 3 3 3 2 3 4 43%	5217
	11th to 20th	Night	11% 9% 2 5% 3 3 3 3 5% 7% 49%	4980
	21st to end	Night	15% 10% 4 8% 5% 5% 4 3 5% 6% 35%	5246
April	1st to 10th	Night	11% 7% 3 6% 5% 4 4 3 6% 7% 45%	2000
	11th to 20th	Night	13% 7% 3 6% 4 4 3 3 5% 6% 45%	1975
	21st to end	Night	18% 8% 2 6% 4 3 4 3 4 7% 41%	2000
May	1st to 10th	Night	18% 9% 3 6% 4 4 4 3 6% 9% 35%	4349
	11th to 20th	Night	14% 7% 2 7% 4 3 4 3 6% 9% 41%	3596
	21st to end	Night	13% 7% 3 6% 4 4 4 3 6% 9% 40%	3942
June	1st to 10th	Night	8% 4 2 5% 4 4 4 5% 7% 8% 50%	1600
	11th to 20th	Night	6% 5% 2 4 5% 4 5% 4 6% 8% 52%	1600
	21st to end	Night	4 4 1 4 4 5% 4 5% 6% 11% 53%	1600
July	1st to 10th	Night	11% 6% 2 7% 4 4 4 3 6% 9% 45%	2610
	11th to 20th	Night	5% 3 1 4 3 3 4 3 7% 11% 56%	2610
	21st to end	Night	7% 5% 2 7% 5% 5% 5% 4 6% 11% 43%	3065
August	1st to 10th	Night	5% 3 2 4 3 4 3 3 6% 8% 59%	2836
	11th to 20th	Night	11% 6% 2 6% 3 3 4 3 4 7% 49%	3037
	21st to end	Night	5% 3 2 4 3 3 4 4 6% 10% 56%	3476
September	1st to 10th	Night	13% 4 2 4 3 2 3 3 5% 7% 55%	1900
	11th to 20th	Night	8% 5% 2 5% 4 4 4 3 6% 7% 53%	1900
	21st to end	Night	8% 5% 1 5% 4 4 4 3 5% 6% 55%	2122
October	1st to 10th	Night	8% 4 2 4 3 3 4 2 4 7% 59%	2280
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 4 6% 53%	2280
	21st to end	Night	16% 8% 2 5% 3 3 4 3 3 5% 47%	2508
November	1st to 10th	Night	11% 5% 2 5% 3 3 4 3 5% 5% 55%	2512
	11th to 20th	Night	12% 7% 2 6% 4 3 3 3 4 6% 50%	2600
	21st to end	Night	16% 9% 3 5% 4 3 3 3 4 6% 44%	2735
December	1st to 10th	Night	10% 9% 3 6% 4 4 4 3 5% 5% 47%	4580
	11th to 20th	Night	13% 8% 4 8% 4 4 3 4 5% 6% 40%	5199
	21st to end	Night	22% 18% 5% 9% 5% 4 4 3 4 4 21%	6996

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	55% 5% 10% 18% 10% 2	3618
	11th to 20th	Day	45% 5% 12% 19% 15% 5%	4011
	21st to end	Day	53% 3 8% 15% 17% 3	4488
February	1st to 10th	Day	51% 5% 13% 20% 10% 1	1800
	11th to 20th	Day	48% 5% 11% 19% 15% 3	1886
	21st to end	Day	46% 5% 8% 22% 15% 4	1650
March	1st to 10th	Day	40% 4 6% 22% 25% 3	4664
	11th to 20th	Day	31% 4 10% 24% 25% 5%	4980
	21st to end	Day	45% 8% 14% 25% 8%	5683
April	1st to 10th	Day	42% 6% 10% 24% 16% 1	2400
	11th to 20th	Day	45% 5% 10% 23% 14% 3	2374
	21st to end	Day	46% 6% 12% 21% 14% 1	2400
May	1st to 10th	Day	46% 9% 13% 20% 12%	5568
	11th to 20th	Day	43% 7% 10% 24% 14% 2	6323
	21st to end	Day	41% 7% 10% 22% 19% 1	6949
June	1st to 10th	Day	31% 9% 15% 28% 16% 2	2800
	11th to 20th	Day	30% 7% 15% 25% 20% 3	2800
	21st to end	Day	29% 10% 17% 25% 15% 5%	2800
July	1st to 10th	Day	38% 6% 13% 27% 13% 2	4511
	11th to 20th	Day	29% 7% 14% 31% 18% 2	4505
	21st to end	Day	35% 10% 19% 25% 10% 1	4340
August	1st to 10th	Day	28% 7% 15% 36% 14% 1	4090
	11th to 20th	Day	38% 7% 13% 24% 17% 1	3831
	21st to end	Day	28% 7% 15% 32% 14% 3	4179
September	1st to 10th	Day	33% 6% 11% 24% 21% 5%	2280
	11th to 20th	Day	31% 5% 11% 27% 23% 4	2280
	21st to end	Day	30% 6% 10% 27% 24% 3	2036
October	1st to 10th	Day	18% 3 6% 19% 46% 8%	3160
	11th to 20th	Day	24% 3 6% 20% 38% 8%	3140
	21st to end	Day	34% 4 8% 26% 26% 2	3428
November	1st to 10th	Day	33% 4 13% 25% 21% 5%	1783
	11th to 20th	Day	39% 4 10% 24% 20% 5%	1800
	21st to end	Day	46% 4 10% 26% 14%	1661
December	1st to 10th	Day	36% 3 14% 30% 16%	2610
	11th to 20th	Day	46% 5% 12% 22% 13% 1	3005
	21st to end	Day	65% 5% 11% 12% 6%	3982
January	1st to 10th	Night	57% 4 9% 21% 9% 1	6348
	11th to 20th	Night	54% 4 7% 21% 11% 3	5964
	21st to end	Night	53% 4 8% 18% 15% 2	6490
February	1st to 10th	Night	52% 6% 10% 19% 12% 2	2600
	11th to 20th	Night	47% 4 10% 21% 16% 3	2409
	21st to end	Night	44% 4 11% 23% 16% 3	1980
March	1st to 10th	Night	46% 4 6% 21% 21% 2	5217
	11th to 20th	Night	35% 4 9% 23% 22% 6%	4980
	21st to end	Night	48% 7% 10% 23% 10% 1	5246
April	1st to 10th	Night	37% 6% 11% 24% 17% 4	2000
	11th to 20th	Night	38% 6% 10% 23% 18% 5%	1975
	21st to end	Night	44% 5% 11% 23% 16% 1	2000
May	1st to 10th	Night	45% 8% 14% 19% 12% 1	4379
	11th to 20th	Night	39% 8% 12% 24% 13% 4	3597
	21st to end	Night	38% 8% 14% 21% 17% 1	3950
June	1st to 10th	Night	29% 8% 15% 27% 18% 3	1600
	11th to 20th	Night	29% 6% 11% 26% 24% 3	1600
	21st to end	Night	25% 7% 15% 27% 19% 7%	1600
July	1st to 10th	Night	36% 6% 11% 31% 13% 2	2570
	11th to 20th	Night	21% 5% 14% 37% 21% 2	2562
	21st to end	Night	34% 7% 20% 26% 12% 1	2968
August	1st to 10th	Night	23% 6% 17% 34% 19% 1	2826
	11th to 20th	Night	35% 5% 12% 27% 19% 2	3066
	21st to end	Night	23% 6% 19% 32% 17% 3	3476
September	1st to 10th	Night	29% 6% 10% 24% 25% 6%	1900
	11th to 20th	Night	30% 7% 10% 24% 25% 4	1900
	21st to end	Night	29% 6% 9% 25% 27% 4	2122
October	1st to 10th	Night	17% 4 7% 19% 47% 7%	3800
	11th to 20th	Night	23% 2 7% 23% 34% 11%	3779
	21st to end	Night	32% 4 8% 26% 26% 4	4120
November	1st to 10th	Night	32% 6% 12% 25% 21% 6%	2512
	11th to 20th	Night	36% 4 8% 26% 22% 4	2600
	21st to end	Night	43% 5% 11% 24% 16% 2	2735
December	1st to 10th	Night	40% 4 9% 33% 14% 1	4580
	11th to 20th	Night	44% 4 13% 21% 18% 1	5201
	21st to end	Night	66% 6% 12% 11% 5% 1	6996

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	22% 26% 33% 16% 3	300
	11th to 20th	Day	29% 24% 33% 13%	300
	21st to end	Day	18% 22% 44% 13% 2	330
February	1st to 10th	Day	25% 24% 36% 13% 2	300
	11th to 20th	Day	28% 24% 30% 15% 2 1	300
	21st to end	Day	28% 20% 37% 12% 2	249
March	1st to 10th	Day	22% 22% 41% 13% 2	300
	11th to 20th	Day	30% 22% 31% 14% 2 1	300
	21st to end	Day	33% 20% 31% 13% 2	420
April	1st to 10th	Day	22% 15% 38% 18% 6%	500
	11th to 20th	Day	26% 18% 29% 19% 7% 1	492
	21st to end	Day	25% 15% 36% 19% 5% 1	500
May	1st to 10th	Day	17% 17% 34% 25% 6% 1	543
	11th to 20th	Day	18% 13% 28% 26% 13% 2	725
	21st to end	Day	14% 12% 29% 27% 12% 6%	789
June	1st to 10th	Day	10% 6% 23% 32% 22% 6%	730
	11th to 20th	Day	10% 4 22% 37% 22% 4	730
	21st to end	Day	5% 6% 32% 37% 16% 4	730
July	1st to 10th	Day	11% 2 17% 29% 30% 11%	721
	11th to 20th	Day	5% 5% 24% 36% 25% 5%	718
	21st to end	Day	9% 4 18% 33% 30% 7%	740
August	1st to 10th	Day	8% 3 18% 38% 25% 7%	676
	11th to 20th	Day	10% 4 20% 34% 25% 7%	520
	21st to end	Day	9% 2 17% 33% 30% 9%	539
September	1st to 10th	Day	12% 4 17% 34% 25% 9%	490
	11th to 20th	Day	9% 3 17% 33% 28% 10%	490
	21st to end	Day	9% 10% 24% 28% 22% 8%	426
October	1st to 10th	Day	10% 13% 27% 30% 16% 5%	300
	11th to 20th	Day	20% 19% 29% 24% 7%	300
	21st to end	Day	28% 20% 32% 18% 3	330
November	1st to 10th	Day	15% 15% 34% 24% 9% 3	300
	11th to 20th	Day	22% 20% 32% 16% 8% 2	300
	21st to end	Day	28% 15% 31% 22% 3 1	300
December	1st to 10th	Day	16% 21% 39% 15% 6% 3	300
	11th to 20th	Day	23% 18% 36% 19% 5%	300
	21st to end	Day	27% 24% 35% 12% 3	330
January	1st to 10th	Night	19% 18% 39% 20% 5%	1000
	11th to 20th	Night	22% 20% 36% 19% 3 1	1000
	21st to end	Night	19% 19% 38% 22% 2	1100
February	1st to 10th	Night	21% 17% 38% 22% 2	1000
	11th to 20th	Night	23% 17% 37% 21% 2	853
	21st to end	Night	23% 18% 39% 18% 2	660
March	1st to 10th	Night	23% 16% 38% 20% 3	735
	11th to 20th	Night	22% 13% 35% 24% 6%	600
	21st to end	Night	25% 16% 34% 20% 4	660
April	1st to 10th	Night	16% 18% 37% 24% 5%	600
	11th to 20th	Night	18% 14% 34% 28% 7%	593
	21st to end	Night	20% 13% 39% 24% 5%	600
May	1st to 10th	Night	16% 11% 32% 32% 9% 1	600
	11th to 20th	Night	19% 8% 27% 31% 14% 1	591
	21st to end	Night	13% 4 27% 36% 18% 2	650
June	1st to 10th	Night	9% 3 22% 40% 25% 1	600
	11th to 20th	Night	9% 2 24% 44% 20% 1	600
	21st to end	Night	4 2 27% 47% 19% 1	600
July	1st to 10th	Night	11% 2 10% 40% 33% 5%	585
	11th to 20th	Night	5% 2 15% 43% 32% 2	582
	21st to end	Night	7% 2 16% 40% 34% 2	624
August	1st to 10th	Night	7% 1 14% 44% 32% 2	567
	11th to 20th	Night	8% 1 16% 41% 30% 4	564
	21st to end	Night	6% 1 15% 39% 36% 3	627
September	1st to 10th	Night	13% 2 17% 37% 26% 5%	570
	11th to 20th	Night	10% 4 16% 34% 32% 4	570
	21st to end	Night	9% 7% 23% 33% 23% 4	731
October	1st to 10th	Night	9% 6% 28% 33% 21% 4	760
	11th to 20th	Night	15% 13% 32% 29% 11% 1	760
	21st to end	Night	21% 13% 34% 25% 6%	836
November	1st to 10th	Night	12% 10% 39% 29% 10%	780
	11th to 20th	Night	17% 16% 34% 26% 7%	800
	21st to end	Night	23% 14% 35% 22% 5%	935
December	1st to 10th	Night	21% 15% 36% 23% 5% 1	1000
	11th to 20th	Night	22% 14% 32% 27% 4	1000
	21st to end	Night	26% 19% 33% 20% 2	1100

Page generated at 2025-07-18 00:10:05. Version ac07

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