Site "M"
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Site "M" clear sky chart from 2005-11-06 to 2024-11-10.

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% 5% 4 5% 4 6% 8% 39%	101375
	Night	13% 9% 3 7% 4 4 4 3 5% 7% 41%	97841
Transparency	Day	42% 5% 12% 24% 16% 2	104940
	Night	42% 4 11% 24% 17% 2	102391
Seeing	Day	15% 10% 27% 27% 16% 5%	15736
	Night	17% 10% 30% 30% 13% 1	25554

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	11% 13% 7% 14% 6% 5% 5% 4 4 6% 26%	2527
	11th to 20th	Day	12% 11% 5% 11% 8% 7% 7% 6% 6% 5% 21%	2576
	21st to end	Day	18% 20% 9% 9% 5% 4 3 2 3 4 23%	3135
February	1st to 10th	Day	15% 12% 6% 10% 6% 6% 3 3 3 6% 31%	1710
	11th to 20th	Day	12% 11% 3 8% 7% 5% 5% 4 6% 7% 34%	1817
	21st to end	Day	15% 12% 4 10% 5% 4 3 3 4 7% 33%	1570
March	1st to 10th	Day	18% 14% 3 7% 4 3 3 2 4 5% 37%	3120
	11th to 20th	Day	9% 9% 2 5% 4 4 4 3 6% 8% 46%	3468
	21st to end	Day	17% 11% 3 9% 6% 4 5% 4 5% 7% 29%	4059
April	1st to 10th	Day	14% 8% 3 6% 5% 4 5% 4 6% 6% 37%	2280
	11th to 20th	Day	15% 9% 3 7% 4 4 4 4 5% 6% 39%	2254
	21st to end	Day	18% 7% 3 7% 5% 5% 5% 4 5% 5% 35%	2280
May	1st to 10th	Day	14% 8% 3 7% 5% 5% 6% 4 7% 10% 31%	3995
	11th to 20th	Day	17% 8% 2 7% 4 4 5% 4 5% 8% 37%	4399
	21st to end	Day	10% 5% 2 6% 5% 5% 4 4 7% 7% 44%	4824
June	1st to 10th	Day	8% 5% 2 7% 4 4 5% 5% 7% 9% 46%	2660
	11th to 20th	Day	8% 5% 2 5% 4 5% 5% 4 5% 8% 49%	2660
	21st to end	Day	7% 6% 2 6% 5% 5% 6% 5% 7% 9% 43%	2660
July	1st to 10th	Day	12% 6% 2 5% 5% 5% 5% 5% 7% 10% 38%	4440
	11th to 20th	Day	4 5% 2 6% 4 4 6% 5% 6% 10% 47%	4440
	21st to end	Day	8% 5% 2 6% 5% 4 5% 5% 9% 10% 40%	4755
August	1st to 10th	Day	6% 4 2 5% 4 4 4 4 7% 10% 48%	4104
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 6% 10% 42%	3738
	21st to end	Day	5% 4 2 5% 5% 5% 5% 4 7% 10% 48%	4180
September	1st to 10th	Day	11% 5% 2 5% 3 4 5% 3 5% 7% 50%	2280
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 6% 6% 51%	2240
	21st to end	Day	9% 6% 2 5% 4 4 4 3 5% 8% 49%	2090
October	1st to 10th	Day	11% 5% 2 5% 3 3 4 3 5% 6% 53%	1915
	11th to 20th	Day	16% 6% 2 7% 4 3 4 3 4 6% 46%	1900
	21st to end	Day	19% 9% 3 5% 4 4 3 3 4 6% 41%	2013
November	1st to 10th	Day	10% 7% 2 5% 3 3 4 4 5% 7% 49%	1753
	11th to 20th	Day	16% 9% 3 7% 5% 2 3 3 5% 6% 41%	1710
	21st to end	Day	15% 11% 4 9% 5% 3 3 3 4 4 38%	1602
December	1st to 10th	Day	13% 13% 5% 7% 6% 4 3 4 5% 7% 34%	1520
	11th to 20th	Day	14% 11% 3 7% 5% 4 4 3 6% 7% 35%	1918
	21st to end	Day	21% 17% 7% 13% 4 3 4 4 4 5% 19%	2783
January	1st to 10th	Night	13% 14% 6% 11% 5% 5% 4 3 5% 5% 31%	4428
	11th to 20th	Night	13% 17% 6% 10% 5% 5% 7% 4 5% 3 24%	4376
	21st to end	Night	21% 17% 6% 12% 4 3 3 2 3 6% 22%	4532
February	1st to 10th	Night	16% 12% 4 9% 6% 3 4 3 4 6% 33%	2470
	11th to 20th	Night	13% 10% 3 8% 5% 4 3 4 5% 6% 39%	2247
	21st to end	Night	16% 10% 3 7% 4 4 4 2 4 6% 38%	1884
March	1st to 10th	Night	19% 13% 3 5% 3 3 3 2 4 5% 39%	3733
	11th to 20th	Night	12% 7% 2 5% 4 3 3 3 4 6% 50%	3522
	21st to end	Night	18% 11% 4 8% 5% 4 4 4 4 6% 31%	3572
April	1st to 10th	Night	12% 8% 2 7% 4 5% 4 4 6% 7% 41%	1900
	11th to 20th	Night	15% 7% 2 5% 4 5% 4 4 5% 7% 43%	1875
	21st to end	Night	19% 8% 3 7% 4 3 4 3 5% 5% 39%	1900
May	1st to 10th	Night	17% 8% 3 7% 5% 4 5% 3 6% 8% 34%	2895
	11th to 20th	Night	14% 6% 3 6% 4 4 4 4 6% 8% 40%	2506
	21st to end	Night	8% 6% 2 6% 4 3 4 4 7% 8% 47%	2743
June	1st to 10th	Night	8% 5% 2 4 4 3 3 5% 6% 10% 51%	1520
	11th to 20th	Night	7% 5% 2 5% 4 3 4 4 7% 8% 51%	1520
	21st to end	Night	5% 6% 2 6% 5% 5% 4 4 6% 8% 49%	1520
July	1st to 10th	Night	12% 5% 3 6% 5% 5% 5% 3 5% 10% 41%	2530
	11th to 20th	Night	3 3 1 5% 4 4 4 4 7% 9% 56%	2530
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 6% 10% 45%	2804
August	1st to 10th	Night	5% 4 2 5% 3 3 4 4 6% 9% 57%	2836
	11th to 20th	Night	8% 4 2 4 4 4 4 4 6% 9% 52%	3091
	21st to end	Night	5% 3 1 4 4 4 5% 4 8% 10% 53%	3476
September	1st to 10th	Night	11% 5% 1 4 4 3 3 2 5% 6% 56%	1900
	11th to 20th	Night	7% 5% 2 5% 3 4 4 3 6% 7% 54%	1919
	21st to end	Night	8% 6% 2 5% 5% 4 4 4 5% 7% 51%	2090
October	1st to 10th	Night	10% 4 2 4 4 3 4 3 6% 6% 55%	2261
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 5% 6% 52%	2280
	21st to end	Night	17% 8% 2 6% 3 3 4 2 5% 5% 43%	2584
November	1st to 10th	Night	10% 6% 3 5% 4 3 3 3 5% 6% 53%	2530
	11th to 20th	Night	12% 8% 3 7% 4 4 3 3 5% 6% 46%	2470
	21st to end	Night	17% 9% 2 6% 5% 3 3 3 4 5% 41%	2574
December	1st to 10th	Night	15% 12% 3 7% 5% 4 4 4 5% 6% 34%	2660
	11th to 20th	Night	15% 10% 4 9% 5% 4 3 2 4 5% 38%	3279
	21st to end	Night	21% 18% 7% 12% 6% 4 4 3 3 4 19%	4884

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	59% 4 8% 20% 8%	2528
	11th to 20th	Day	63% 5% 12% 15% 6%	2576
	21st to end	Day	67% 3 9% 15% 6%	3135
February	1st to 10th	Day	56% 3 11% 19% 8% 2	1710
	11th to 20th	Day	49% 6% 12% 21% 12% 1	1827
	21st to end	Day	53% 4 10% 21% 10% 2	1570
March	1st to 10th	Day	51% 3 10% 19% 15% 2	3120
	11th to 20th	Day	36% 6% 14% 25% 18% 1	3468
	21st to end	Day	53% 7% 16% 19% 4 1	4059
April	1st to 10th	Day	45% 5% 12% 24% 13%	2280
	11th to 20th	Day	46% 4 9% 25% 14% 2	2254
	21st to end	Day	48% 6% 11% 20% 13% 2	2280
May	1st to 10th	Day	46% 7% 14% 23% 10%	4031
	11th to 20th	Day	45% 7% 11% 27% 9% 1	4403
	21st to end	Day	36% 7% 10% 22% 24% 2	4837
June	1st to 10th	Day	32% 8% 13% 27% 16% 3	2660
	11th to 20th	Day	33% 6% 10% 25% 23% 3	2660
	21st to end	Day	36% 8% 14% 22% 17% 3	2660
July	1st to 10th	Day	41% 5% 12% 26% 14% 2	4371
	11th to 20th	Day	32% 5% 15% 27% 20% 1	4365
	21st to end	Day	37% 5% 20% 25% 14% 1	4605
August	1st to 10th	Day	30% 6% 17% 35% 11% 1	4090
	11th to 20th	Day	38% 5% 12% 30% 14% 1	3774
	21st to end	Day	31% 5% 15% 30% 15% 4	4179
September	1st to 10th	Day	33% 6% 9% 26% 19% 6%	2280
	11th to 20th	Day	32% 5% 8% 26% 23% 5%	2240
	21st to end	Day	33% 4 9% 28% 23% 2	2090
October	1st to 10th	Day	24% 3 6% 18% 46% 3	3175
	11th to 20th	Day	27% 2 8% 23% 35% 5%	3140
	21st to end	Day	41% 2 6% 27% 22% 2	3290
November	1st to 10th	Day	35% 4 14% 25% 18% 4	1753
	11th to 20th	Day	44% 3 10% 25% 15% 3	1710
	21st to end	Day	50% 4 11% 23% 11%	1602
December	1st to 10th	Day	50% 4 15% 20% 10%	1520
	11th to 20th	Day	48% 4 10% 28% 8% 2	1915
	21st to end	Day	69% 4 9% 12% 6%	2783
January	1st to 10th	Night	54% 5% 12% 20% 9%	4428
	11th to 20th	Night	64% 3 8% 17% 8% 1	4376
	21st to end	Night	66% 3 8% 16% 6% 1	4532
February	1st to 10th	Night	53% 4 12% 18% 11% 2	2470
	11th to 20th	Night	46% 4 10% 23% 14% 2	2248
	21st to end	Night	48% 4 11% 23% 12% 3	1884
March	1st to 10th	Night	49% 4 8% 25% 13% 1	3733
	11th to 20th	Night	35% 5% 9% 27% 20% 4	3522
	21st to end	Night	54% 5% 11% 23% 6% 1	3572
April	1st to 10th	Night	42% 5% 12% 24% 14% 3	1900
	11th to 20th	Night	40% 5% 10% 25% 17% 4	1875
	21st to end	Night	47% 4 10% 20% 16% 3	1900
May	1st to 10th	Night	47% 7% 14% 22% 10% 1	2924
	11th to 20th	Night	40% 7% 14% 27% 11% 1	2507
	21st to end	Night	33% 7% 12% 21% 22% 4	2751
June	1st to 10th	Night	27% 7% 15% 28% 18% 5%	1520
	11th to 20th	Night	30% 5% 12% 24% 24% 5%	1520
	21st to end	Night	33% 7% 14% 23% 20% 4	1520
July	1st to 10th	Night	42% 4 11% 29% 13% 2	2490
	11th to 20th	Night	24% 4 13% 33% 24% 2	2482
	21st to end	Night	34% 4 18% 24% 17% 3	2715
August	1st to 10th	Night	25% 5% 18% 34% 18% 1	2826
	11th to 20th	Night	31% 4 12% 35% 18% 1	3121
	21st to end	Night	26% 5% 17% 33% 16% 4	3476
September	1st to 10th	Night	30% 4 10% 25% 23% 8%	1900
	11th to 20th	Night	30% 4 8% 25% 26% 6%	1919
	21st to end	Night	32% 4 9% 25% 25% 4	2090
October	1st to 10th	Night	22% 4 5% 22% 43% 4	3768
	11th to 20th	Night	25% 2 8% 23% 36% 6%	3779
	21st to end	Night	36% 2 10% 23% 24% 4	4244
November	1st to 10th	Night	33% 4 12% 27% 19% 5%	2530
	11th to 20th	Night	38% 3 12% 25% 19% 2	2470
	21st to end	Night	46% 3 10% 25% 15% 1	2574
December	1st to 10th	Night	50% 4 13% 22% 10% 1	2660
	11th to 20th	Night	49% 3 11% 24% 11% 1	3281
	21st to end	Night	70% 4 7% 12% 6% 1	4884

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	23% 20% 32% 17% 8% 1	270
	11th to 20th	Day	27% 18% 37% 16% 3	270
	21st to end	Day	18% 18% 36% 23% 5%	297
February	1st to 10th	Day	26% 16% 37% 18% 4	270
	11th to 20th	Day	20% 21% 32% 22% 5%	270
	21st to end	Day	24% 15% 44% 16% 1	225
March	1st to 10th	Day	23% 18% 41% 16% 1	270
	11th to 20th	Day	28% 15% 35% 16% 5%	270
	21st to end	Day	31% 15% 31% 16% 5% 1	439
April	1st to 10th	Day	21% 14% 34% 26% 5%	460
	11th to 20th	Day	18% 18% 32% 22% 9% 1	452
	21st to end	Day	22% 13% 36% 21% 7% 1	460
May	1st to 10th	Day	19% 14% 32% 25% 8% 2	464
	11th to 20th	Day	18% 12% 26% 26% 15% 3	675
	21st to end	Day	13% 8% 32% 26% 14% 8%	734
June	1st to 10th	Day	9% 6% 22% 32% 24% 7%	680
	11th to 20th	Day	10% 5% 24% 35% 21% 6%	680
	21st to end	Day	8% 7% 29% 34% 17% 5%	680
July	1st to 10th	Day	12% 3 15% 31% 26% 14%	671
	11th to 20th	Day	7% 3 21% 34% 26% 10%	668
	21st to end	Day	10% 1 18% 35% 29% 7%	739
August	1st to 10th	Day	8% 2 16% 39% 25% 10%	676
	11th to 20th	Day	11% 4 17% 28% 27% 13%	488
	21st to end	Day	7% 2 13% 33% 35% 10%	539
September	1st to 10th	Day	13% 5% 17% 28% 30% 7%	490
	11th to 20th	Day	9% 2 13% 34% 29% 12%	490
	21st to end	Day	11% 10% 22% 26% 23% 8%	490
October	1st to 10th	Day	13% 6% 28% 34% 13% 6%	315
	11th to 20th	Day	15% 21% 29% 26% 8% 1	300
	21st to end	Day	31% 13% 32% 20% 4	330
November	1st to 10th	Day	11% 14% 36% 23% 10% 5%	297
	11th to 20th	Day	23% 16% 31% 18% 11% 2	270
	21st to end	Day	25% 10% 39% 21% 5%	270
December	1st to 10th	Day	14% 21% 37% 18% 7% 3	270
	11th to 20th	Day	19% 16% 40% 20% 4	270
	21st to end	Day	26% 19% 38% 16% 2	297
January	1st to 10th	Night	17% 16% 39% 23% 5%	950
	11th to 20th	Night	21% 15% 37% 22% 5%	950
	21st to end	Night	22% 14% 34% 27% 3	1045
February	1st to 10th	Night	22% 13% 35% 25% 4	950
	11th to 20th	Night	20% 14% 35% 28% 3	772
	21st to end	Night	22% 18% 36% 22% 2	628
March	1st to 10th	Night	21% 13% 38% 23% 4	760
	11th to 20th	Night	21% 11% 34% 28% 5%	599
	21st to end	Night	26% 11% 35% 23% 5%	627
April	1st to 10th	Night	17% 14% 37% 26% 5%	570
	11th to 20th	Night	17% 13% 33% 27% 9%	563
	21st to end	Night	22% 9% 35% 27% 7%	570
May	1st to 10th	Night	21% 5% 35% 29% 8% 1	570
	11th to 20th	Night	17% 6% 26% 39% 12% 1	561
	21st to end	Night	11% 4 28% 35% 20% 3	617
June	1st to 10th	Night	9% 3 22% 45% 19%	570
	11th to 20th	Night	9% 3 23% 42% 20% 2	570
	21st to end	Night	9% 2 28% 40% 19% 1	570
July	1st to 10th	Night	10% 3 11% 37% 34% 5%	555
	11th to 20th	Night	4 1 18% 43% 31% 2	552
	21st to end	Night	8% 14% 44% 33% 1	624
August	1st to 10th	Night	7% 2 10% 47% 29% 4	567
	11th to 20th	Night	9% 2 13% 39% 32% 6%	564
	21st to end	Night	7% 1 13% 38% 40% 1	627
September	1st to 10th	Night	12% 3 15% 38% 27% 4	570
	11th to 20th	Night	8% 3 16% 40% 29% 4	589
	21st to end	Night	11% 8% 22% 32% 23% 4	760
October	1st to 10th	Night	11% 5% 28% 33% 20% 2	760
	11th to 20th	Night	17% 11% 30% 30% 11% 1	760
	21st to end	Night	23% 12% 34% 25% 7%	836
November	1st to 10th	Night	14% 11% 39% 28% 9% 1	779
	11th to 20th	Night	17% 14% 37% 26% 5% 1	760
	21st to end	Night	22% 13% 35% 24% 6%	864
December	1st to 10th	Night	21% 12% 39% 23% 5%	950
	11th to 20th	Night	23% 12% 33% 28% 5%	950
	21st to end	Night	26% 16% 34% 22% 2	1045

Page generated at 2024-11-07 05:55:44. Version ac07

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