Fairmont
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fairmont clear sky chart from 2005-11-06 to 2024-12-09.

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	13% 8% 3 8% 5% 4 4 4 5% 7% 39%	101745
	Night	12% 8% 3 8% 5% 4 4 3 5% 6% 41%	98119
Transparency	Day	43% 7% 13% 24% 12% 1	105384
	Night	41% 6% 13% 24% 14% 2	102621
Seeing	Day	16% 10% 31% 28% 13% 3	16056
	Night	15% 9% 34% 31% 10% 1	25978

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	10% 15% 6% 20% 9% 5% 4 3 4 5% 19%	2527
	11th to 20th	Day	7% 14% 5% 11% 7% 6% 8% 5% 8% 6% 24%	2768
	21st to end	Day	8% 17% 8% 14% 7% 5% 4 3 5% 6% 22%	3135
February	1st to 10th	Day	8% 12% 5% 11% 8% 8% 6% 5% 6% 7% 25%	1710
	11th to 20th	Day	9% 11% 5% 9% 8% 7% 6% 4 6% 7% 28%	1664
	21st to end	Day	14% 10% 3 10% 7% 4 4 4 5% 7% 32%	1471
March	1st to 10th	Day	13% 9% 4 9% 4 4 3 3 5% 6% 40%	3436
	11th to 20th	Day	12% 8% 3 7% 4 4 4 4 5% 6% 43%	3480
	21st to end	Day	25% 13% 5% 11% 5% 3 4 3 4 4 22%	3814
April	1st to 10th	Day	19% 9% 3 8% 4 4 5% 4 5% 6% 33%	2244
	11th to 20th	Day	19% 9% 4 7% 4 4 4 3 5% 7% 33%	2304
	21st to end	Day	25% 10% 3 6% 4 3 3 4 5% 5% 32%	2470
May	1st to 10th	Day	19% 7% 2 6% 4 4 4 5% 7% 7% 34%	4082
	11th to 20th	Day	14% 6% 3 5% 4 4 4 3 5% 6% 46%	4365
	21st to end	Day	17% 6% 3 7% 4 4 5% 4 6% 7% 37%	4824
June	1st to 10th	Day	12% 5% 2 5% 4 5% 4 4 5% 8% 47%	2660
	11th to 20th	Day	13% 5% 2 6% 5% 4 4 3 7% 9% 42%	2660
	21st to end	Day	11% 5% 2 6% 4 5% 5% 4 6% 8% 44%	2660
July	1st to 10th	Day	10% 5% 2 6% 5% 5% 6% 5% 7% 9% 41%	4440
	11th to 20th	Day	7% 3 1 4 3 3 4 3 5% 8% 58%	4440
	21st to end	Day	5% 3 1 5% 4 4 5% 5% 7% 9% 50%	4497
August	1st to 10th	Day	12% 5% 2 7% 5% 4 5% 3 5% 7% 43%	4104
	11th to 20th	Day	13% 5% 2 7% 5% 5% 4 4 7% 9% 39%	4041
	21st to end	Day	9% 4 2 6% 4 5% 4 3 5% 7% 51%	4382
September	1st to 10th	Day	12% 5% 2 5% 3 4 3 4 5% 7% 51%	2280
	11th to 20th	Day	10% 6% 2 5% 4 3 3 4 4 7% 52%	2166
	21st to end	Day	13% 6% 2 5% 4 3 4 4 4 7% 49%	2050
October	1st to 10th	Day	15% 6% 2 5% 4 4 4 4 5% 5% 47%	1900
	11th to 20th	Day	14% 9% 2 5% 3 4 4 3 4 6% 46%	1900
	21st to end	Day	17% 10% 3 7% 4 4 3 2 4 5% 42%	2090
November	1st to 10th	Day	11% 8% 3 4 5% 4 5% 3 5% 7% 45%	1696
	11th to 20th	Day	11% 11% 4 12% 7% 3 4 3 4 5% 36%	1600
	21st to end	Day	13% 10% 4 8% 4 3 3 3 5% 9% 38%	1600
December	1st to 10th	Day	11% 11% 3 11% 8% 6% 5% 4 5% 7% 29%	1584
	11th to 20th	Day	10% 15% 5% 10% 6% 5% 4 3 6% 7% 30%	1918
	21st to end	Day	20% 14% 5% 18% 5% 3 4 3 4 5% 20%	2783
January	1st to 10th	Night	8% 13% 7% 22% 7% 5% 4 3 4 5% 22%	4428
	11th to 20th	Night	5% 12% 5% 13% 8% 6% 9% 6% 8% 6% 22%	4184
	21st to end	Night	11% 16% 9% 14% 6% 4 3 3 4 6% 24%	4532
February	1st to 10th	Night	9% 13% 4 9% 7% 5% 5% 4 6% 5% 33%	2470
	11th to 20th	Night	9% 10% 4 9% 5% 5% 5% 4 6% 6% 38%	2403
	21st to end	Night	12% 10% 3 9% 7% 4 4 3 5% 6% 36%	1996
March	1st to 10th	Night	11% 8% 3 8% 4 3 3 2 4 5% 49%	3419
	11th to 20th	Night	10% 7% 3 7% 4 4 5% 4 5% 7% 44%	3480
	21st to end	Night	28% 12% 4 9% 4 3 3 3 3 5% 26%	3817
April	1st to 10th	Night	15% 9% 2 7% 4 4 5% 4 5% 6% 39%	1935
	11th to 20th	Night	18% 8% 3 7% 4 4 4 4 4 5% 39%	1821
	21st to end	Night	20% 9% 2 6% 4 4 3 3 5% 6% 39%	1710
May	1st to 10th	Night	17% 7% 2 6% 4 3 4 3 5% 6% 43%	2823
	11th to 20th	Night	12% 4 2 6% 3 4 4 3 5% 6% 50%	2538
	21st to end	Night	16% 7% 2 6% 4 3 3 3 4 6% 45%	2743
June	1st to 10th	Night	9% 3 2 5% 4 3 3 4 6% 8% 52%	1520
	11th to 20th	Night	11% 3 1 5% 4 4 5% 5% 5% 8% 48%	1520
	21st to end	Night	10% 4 1 4 3 2 3 3 5% 9% 56%	1520
July	1st to 10th	Night	9% 5% 2 6% 4 3 5% 4 6% 8% 49%	2530
	11th to 20th	Night	3 2 1 3 3 4 4 3 6% 8% 62%	2530
	21st to end	Night	5% 2 1 4 3 4 4 3 6% 8% 60%	3061
August	1st to 10th	Night	12% 5% 2 6% 3 4 4 2 5% 7% 51%	2836
	11th to 20th	Night	12% 3 1 4 3 4 3 4 5% 8% 53%	2798
	21st to end	Night	9% 4 2 5% 4 3 3 3 4 6% 55%	3280
September	1st to 10th	Night	10% 4 1 4 2 3 2 2 5% 6% 61%	1900
	11th to 20th	Night	10% 5% 1 4 3 3 4 3 6% 8% 53%	2009
	21st to end	Night	10% 6% 2 5% 3 3 4 4 3 6% 55%	2110
October	1st to 10th	Night	13% 5% 2 5% 3 3 4 4 4 5% 50%	2280
	11th to 20th	Night	15% 7% 2 6% 3 3 3 3 4 5% 49%	2280
	21st to end	Night	15% 9% 3 6% 4 4 3 3 5% 5% 44%	2508
November	1st to 10th	Night	13% 8% 2 6% 4 4 4 4 5% 4 46%	2596
	11th to 20th	Night	11% 9% 4 10% 4 4 4 4 4 6% 41%	2800
	21st to end	Night	12% 9% 4 8% 5% 4 4 3 4 6% 41%	2800
December	1st to 10th	Night	10% 10% 4 11% 7% 6% 4 4 6% 6% 32%	2779
	11th to 20th	Night	12% 11% 4 10% 6% 5% 6% 4 5% 6% 31%	3279
	21st to end	Night	19% 13% 6% 14% 6% 4 4 3 4 4 22%	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	66% 6% 10% 12% 5%	2528
	11th to 20th	Day	56% 6% 10% 22% 6%	2768
	21st to end	Day	62% 7% 13% 13% 4	3135
February	1st to 10th	Day	57% 6% 13% 16% 8% 1	1710
	11th to 20th	Day	53% 8% 10% 20% 7% 2	1673
	21st to end	Day	52% 6% 13% 17% 10% 1	1471
March	1st to 10th	Day	44% 7% 11% 27% 11% 1	3436
	11th to 20th	Day	40% 6% 11% 29% 11% 3	3480
	21st to end	Day	65% 8% 10% 12% 5%	3814
April	1st to 10th	Day	49% 7% 14% 20% 8% 2	2244
	11th to 20th	Day	49% 8% 12% 19% 11% 1	2304
	21st to end	Day	52% 8% 10% 21% 8% 1	2470
May	1st to 10th	Day	43% 9% 13% 21% 12%	4120
	11th to 20th	Day	36% 8% 11% 27% 15% 2	4369
	21st to end	Day	43% 9% 12% 23% 13% 1	4837
June	1st to 10th	Day	34% 9% 15% 26% 15% 1	2660
	11th to 20th	Day	38% 8% 14% 22% 16% 2	2660
	21st to end	Day	36% 8% 16% 26% 13% 2	2660
July	1st to 10th	Day	37% 9% 18% 25% 9% 1	4371
	11th to 20th	Day	25% 6% 14% 34% 19% 2	4365
	21st to end	Day	27% 9% 16% 30% 17% 1	4356
August	1st to 10th	Day	39% 8% 11% 28% 12% 1	4090
	11th to 20th	Day	40% 8% 16% 28% 8%	4080
	21st to end	Day	33% 6% 16% 28% 15% 2	4381
September	1st to 10th	Day	32% 6% 14% 30% 17% 1	2280
	11th to 20th	Day	32% 7% 14% 32% 14% 1	2166
	21st to end	Day	35% 6% 11% 30% 17% 1	2050
October	1st to 10th	Day	26% 4 7% 32% 29% 1	3160
	11th to 20th	Day	34% 4 13% 26% 21% 2	3140
	21st to end	Day	41% 3 12% 29% 14% 1	3428
November	1st to 10th	Day	39% 7% 13% 21% 17% 3	1696
	11th to 20th	Day	51% 6% 11% 21% 11% 1	1600
	21st to end	Day	45% 5% 18% 20% 11% 1	1600
December	1st to 10th	Day	54% 7% 14% 15% 9% 2	1584
	11th to 20th	Day	53% 6% 20% 16% 5%	1915
	21st to end	Day	64% 6% 11% 13% 5% 1	2783
January	1st to 10th	Night	64% 6% 9% 14% 6%	4428
	11th to 20th	Night	56% 8% 12% 16% 7%	4184
	21st to end	Night	60% 6% 12% 14% 8%	4532
February	1st to 10th	Night	51% 6% 12% 21% 8% 1	2470
	11th to 20th	Night	45% 6% 13% 22% 11% 2	2404
	21st to end	Night	46% 6% 14% 19% 12% 3	1996
March	1st to 10th	Night	37% 5% 11% 29% 16% 1	3419
	11th to 20th	Night	37% 6% 11% 28% 17% 2	3480
	21st to end	Night	62% 5% 13% 14% 6% 1	3817
April	1st to 10th	Night	45% 7% 10% 25% 12% 1	1935
	11th to 20th	Night	47% 6% 9% 18% 18% 2	1821
	21st to end	Night	46% 5% 10% 23% 14% 2	1710
May	1st to 10th	Night	41% 7% 12% 19% 21% 1	2850
	11th to 20th	Night	33% 7% 11% 24% 19% 6%	2539
	21st to end	Night	39% 7% 10% 25% 16% 2	2751
June	1st to 10th	Night	29% 6% 16% 28% 18% 3	1520
	11th to 20th	Night	33% 8% 16% 20% 20% 3	1520
	21st to end	Night	26% 6% 18% 31% 17% 2	1520
July	1st to 10th	Night	31% 6% 21% 28% 12% 2	2490
	11th to 20th	Night	20% 6% 15% 36% 21% 3	2482
	21st to end	Night	21% 7% 18% 31% 21% 2	2964
August	1st to 10th	Night	34% 5% 13% 29% 17% 3	2826
	11th to 20th	Night	31% 7% 16% 32% 13% 1	2825
	21st to end	Night	30% 6% 18% 25% 19% 2	3280
September	1st to 10th	Night	25% 4 14% 32% 23% 2	1900
	11th to 20th	Night	27% 8% 17% 30% 17% 1	2009
	21st to end	Night	30% 6% 12% 29% 21% 2	2110
October	1st to 10th	Night	23% 3 7% 27% 36% 3	3800
	11th to 20th	Night	26% 4 13% 28% 24% 5%	3779
	21st to end	Night	41% 4 11% 29% 14% 1	4120
November	1st to 10th	Night	38% 6% 14% 22% 17% 3	2596
	11th to 20th	Night	45% 7% 12% 22% 13% 2	2800
	21st to end	Night	44% 5% 15% 24% 10% 1	2800
December	1st to 10th	Night	50% 7% 14% 21% 7%	2779
	11th to 20th	Night	50% 8% 17% 19% 6%	3281
	21st to end	Night	63% 7% 9% 16% 5%	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	16% 15% 31% 25% 10% 2	270
	11th to 20th	Day	20% 10% 38% 26% 5% 1	270
	21st to end	Day	14% 10% 40% 25% 9% 1	297
February	1st to 10th	Day	13% 16% 45% 21% 4 1	270
	11th to 20th	Day	14% 16% 38% 27% 4	270
	21st to end	Day	20% 15% 39% 23% 3	225
March	1st to 10th	Day	18% 13% 40% 24% 4	270
	11th to 20th	Day	22% 10% 39% 21% 7% 1	270
	21st to end	Day	33% 9% 28% 22% 5% 2	297
April	1st to 10th	Day	28% 13% 32% 23% 5%	424
	11th to 20th	Day	23% 17% 28% 23% 7% 1	502
	21st to end	Day	29% 14% 28% 19% 8% 3	650
May	1st to 10th	Day	22% 13% 32% 25% 6% 2	653
	11th to 20th	Day	22% 12% 27% 23% 12% 4	675
	21st to end	Day	20% 8% 26% 30% 13% 3	734
June	1st to 10th	Day	9% 6% 28% 32% 21% 5%	680
	11th to 20th	Day	13% 7% 35% 30% 12% 3	680
	21st to end	Day	12% 8% 32% 29% 15% 3	680
July	1st to 10th	Day	7% 4 23% 35% 24% 8%	671
	11th to 20th	Day	9% 4 29% 32% 18% 7%	668
	21st to end	Day	5% 4 26% 39% 22% 5%	739
August	1st to 10th	Day	10% 4 22% 37% 23% 5%	676
	11th to 20th	Day	12% 5% 22% 31% 24% 6%	665
	21st to end	Day	10% 4 28% 34% 18% 6%	663
September	1st to 10th	Day	16% 7% 26% 31% 16% 5%	490
	11th to 20th	Day	10% 5% 34% 32% 15% 4	376
	21st to end	Day	16% 9% 32% 28% 11% 3	300
October	1st to 10th	Day	17% 14% 29% 20% 16% 4	300
	11th to 20th	Day	16% 17% 39% 21% 6% 1	300
	21st to end	Day	22% 15% 36% 20% 5% 1	330
November	1st to 10th	Day	18% 14% 35% 24% 7% 2	300
	11th to 20th	Day	18% 21% 35% 19% 7%	300
	21st to end	Day	20% 15% 36% 23% 5%	300
December	1st to 10th	Day	13% 11% 42% 26% 9%	294
	11th to 20th	Day	16% 14% 37% 27% 6%	270
	21st to end	Day	25% 16% 36% 20% 3	297
January	1st to 10th	Night	12% 13% 40% 28% 7% 1	950
	11th to 20th	Night	13% 12% 40% 28% 6% 1	950
	21st to end	Night	18% 13% 35% 27% 7%	1045
February	1st to 10th	Night	15% 11% 41% 27% 5%	950
	11th to 20th	Night	14% 14% 40% 26% 5% 1	929
	21st to end	Night	16% 11% 39% 25% 7% 2	740
March	1st to 10th	Night	15% 11% 42% 25% 7% 1	570
	11th to 20th	Night	18% 11% 39% 25% 7%	570
	21st to end	Night	25% 10% 31% 26% 7% 1	627
April	1st to 10th	Night	20% 13% 38% 25% 4	570
	11th to 20th	Night	22% 13% 33% 25% 6% 1	563
	21st to end	Night	23% 11% 33% 24% 8% 1	570
May	1st to 10th	Night	18% 9% 34% 30% 8% 1	570
	11th to 20th	Night	18% 7% 33% 30% 10% 2	561
	21st to end	Night	19% 7% 30% 32% 12%	617
June	1st to 10th	Night	8% 6% 30% 40% 15% 1	570
	11th to 20th	Night	11% 3 32% 42% 11%	570
	21st to end	Night	11% 3 28% 41% 16%	570
July	1st to 10th	Night	6% 2 22% 43% 26% 2	555
	11th to 20th	Night	2 2 28% 43% 22% 2	552
	21st to end	Night	3 2 21% 51% 21% 2	624
August	1st to 10th	Night	9% 2 19% 46% 23% 2	567
	11th to 20th	Night	11% 2 19% 40% 26% 3	564
	21st to end	Night	8% 3 26% 41% 20% 3	627
September	1st to 10th	Night	12% 2 26% 42% 16% 2	570
	11th to 20th	Night	11% 4 33% 34% 15% 2	570
	21st to end	Night	9% 12% 32% 34% 13% 1	590
October	1st to 10th	Night	14% 10% 34% 29% 12% 1	760
	11th to 20th	Night	17% 11% 37% 28% 6%	760
	21st to end	Night	21% 11% 32% 29% 7%	836
November	1st to 10th	Night	17% 12% 37% 24% 9%	923
	11th to 20th	Night	14% 15% 42% 24% 5%	1000
	21st to end	Night	16% 13% 38% 25% 7%	1000
December	1st to 10th	Night	15% 10% 41% 28% 6% 1	993
	11th to 20th	Night	18% 9% 38% 28% 6% 1	950
	21st to end	Night	23% 12% 38% 22% 5%	1045

Page generated at 2024-12-06 02:54:49. Version ac07

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