Fort Mountain Scenic Overlook
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Mountain Scenic Overlook clear sky chart from 2005-11-06 to 2024-12-02.

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	15% 7% 2 6% 4 4 5% 4 6% 7% 39%	101198
	Night	15% 7% 2 6% 4 4 4 3 5% 7% 42%	98408
Transparency	Day	41% 7% 11% 20% 17% 4	105005
	Night	38% 7% 10% 20% 19% 5%	102727
Seeing	Day	21% 11% 22% 22% 16% 7%	14877
	Night	18% 10% 20% 28% 20% 4	24911

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	20% 12% 2 5% 4 3 3 4 4 5% 36%	2836
	11th to 20th	Day	20% 7% 4 8% 4 3 4 3 3 4 41%	2840
	21st to end	Day	25% 13% 2 5% 3 2 3 2 4 4 36%	3252
February	1st to 10th	Day	23% 11% 2 5% 4 2 4 3 4 6% 35%	1900
	11th to 20th	Day	24% 9% 2 6% 4 4 3 3 5% 5% 35%	1848
	21st to end	Day	26% 8% 2 6% 4 3 4 3 4 4 36%	1570
March	1st to 10th	Day	26% 9% 3 6% 3 3 3 3 5% 7% 32%	3172
	11th to 20th	Day	16% 6% 2 5% 3 3 3 3 5% 6% 47%	3480
	21st to end	Day	19% 7% 2 7% 5% 4 4 3 5% 7% 38%	3815
April	1st to 10th	Day	14% 6% 2 6% 5% 5% 5% 4 6% 7% 41%	2198
	11th to 20th	Day	14% 7% 3 7% 4 4 4 3 5% 5% 44%	2254
	21st to end	Day	13% 7% 2 6% 4 5% 5% 4 5% 7% 42%	2422
May	1st to 10th	Day	16% 6% 2 6% 5% 4 5% 4 6% 7% 39%	4082
	11th to 20th	Day	18% 8% 3 7% 5% 5% 4 3 6% 8% 33%	4081
	21st to end	Day	11% 6% 2 6% 4 4 5% 4 7% 9% 40%	4476
June	1st to 10th	Day	12% 7% 3 7% 5% 4 6% 5% 8% 9% 35%	2470
	11th to 20th	Day	7% 4 2 6% 5% 5% 6% 6% 9% 11% 40%	2470
	21st to end	Day	8% 5% 3 5% 5% 7% 6% 5% 8% 10% 38%	2470
July	1st to 10th	Day	7% 6% 2 7% 6% 7% 7% 7% 9% 11% 30%	4120
	11th to 20th	Day	10% 6% 3 7% 6% 6% 6% 5% 8% 10% 35%	4120
	21st to end	Day	15% 10% 4 10% 8% 7% 7% 6% 8% 8% 17%	4466
August	1st to 10th	Day	5% 4 2 6% 5% 6% 7% 6% 10% 12% 39%	4104
	11th to 20th	Day	9% 5% 2 5% 5% 4 6% 5% 8% 11% 39%	3768
	21st to end	Day	8% 4 1 6% 5% 5% 6% 5% 7% 8% 46%	4180
September	1st to 10th	Day	10% 6% 2 7% 5% 5% 7% 5% 7% 10% 36%	2128
	11th to 20th	Day	14% 7% 2 6% 4 5% 5% 4 6% 7% 40%	2090
	21st to end	Day	14% 5% 2 6% 4 4 5% 4 4 7% 45%	2090
October	1st to 10th	Day	10% 6% 2 5% 3 3 4 3 5% 5% 54%	2090
	11th to 20th	Day	12% 4 2 5% 3 3 4 3 4 5% 55%	2000
	21st to end	Day	14% 5% 2 4 3 2 3 3 5% 6% 53%	2048
November	1st to 10th	Day	13% 6% 1 4 2 3 3 4 4 6% 53%	1762
	11th to 20th	Day	16% 5% 2 4 3 4 3 3 5% 6% 50%	1800
	21st to end	Day	18% 6% 3 5% 4 3 3 3 4 6% 44%	1800
December	1st to 10th	Day	26% 8% 2 5% 3 4 3 3 5% 5% 35%	1719
	11th to 20th	Day	19% 8% 3 6% 4 4 4 3 5% 5% 40%	2153
	21st to end	Day	21% 11% 5% 7% 3 3 3 3 5% 6% 33%	3124
January	1st to 10th	Night	21% 11% 3 5% 3 4 3 3 3 6% 39%	4109
	11th to 20th	Night	20% 9% 3 5% 4 3 3 3 4 6% 40%	4120
	21st to end	Night	24% 13% 3 6% 3 3 3 2 3 4 37%	4400
February	1st to 10th	Night	19% 8% 2 6% 4 4 4 3 5% 5% 41%	2280
	11th to 20th	Night	23% 9% 3 6% 3 4 4 3 4 4 37%	2218
	21st to end	Night	24% 9% 2 6% 4 5% 4 3 4 5% 34%	1884
March	1st to 10th	Night	22% 9% 3 6% 4 4 4 4 5% 6% 33%	3680
	11th to 20th	Night	13% 5% 1 5% 3 4 4 3 6% 8% 47%	3480
	21st to end	Night	16% 8% 3 6% 4 4 4 4 5% 6% 41%	3817
April	1st to 10th	Night	14% 4 2 5% 4 4 4 3 6% 8% 47%	1996
	11th to 20th	Night	15% 7% 2 4 4 3 2 3 5% 8% 47%	1875
	21st to end	Night	12% 6% 2 5% 4 4 3 4 6% 7% 47%	1758
May	1st to 10th	Night	16% 7% 2 6% 4 4 4 4 6% 7% 39%	2813
	11th to 20th	Night	19% 7% 3 5% 4 4 3 4 6% 7% 38%	2812
	21st to end	Night	8% 5% 2 6% 5% 5% 5% 4 7% 11% 42%	3079
June	1st to 10th	Night	9% 5% 3 7% 6% 6% 5% 5% 7% 11% 36%	1710
	11th to 20th	Night	5% 4 2 4 4 4 5% 5% 9% 12% 46%	1710
	21st to end	Night	7% 4 2 5% 6% 4 5% 4 8% 10% 44%	1710
July	1st to 10th	Night	9% 6% 3 8% 6% 6% 7% 4 8% 11% 33%	2840
	11th to 20th	Night	8% 6% 2 6% 4 5% 5% 5% 8% 10% 41%	2840
	21st to end	Night	14% 10% 4 9% 6% 6% 6% 5% 9% 8% 23%	3087
August	1st to 10th	Night	5% 4 2 5% 4 4 6% 5% 8% 12% 44%	2825
	11th to 20th	Night	8% 6% 2 5% 4 4 4 4 6% 10% 47%	3057
	21st to end	Night	7% 4 2 6% 4 4 4 4 6% 9% 51%	3476
September	1st to 10th	Night	8% 6% 2 7% 5% 5% 4 5% 6% 8% 43%	2032
	11th to 20th	Night	11% 6% 2 7% 4 4 5% 3 6% 8% 43%	2090
	21st to end	Night	12% 6% 1 4 3 4 4 4 5% 7% 49%	2090
October	1st to 10th	Night	10% 5% 2 3 3 4 3 3 4 5% 58%	2090
	11th to 20th	Night	14% 4 2 5% 3 3 3 3 3 5% 55%	2179
	21st to end	Night	13% 6% 2 5% 3 3 3 2 4 5% 55%	2546
November	1st to 10th	Night	13% 6% 2 4 3 3 3 2 4 6% 54%	2536
	11th to 20th	Night	14% 7% 2 5% 3 3 3 2 5% 6% 51%	2600
	21st to end	Night	18% 6% 2 5% 4 3 4 4 4 6% 45%	2600
December	1st to 10th	Night	23% 8% 3 5% 4 4 3 3 5% 6% 35%	2495
	11th to 20th	Night	18% 9% 3 6% 4 3 3 3 4 5% 42%	3042
	21st to end	Night	21% 10% 4 7% 4 5% 4 2 5% 7% 31%	4532

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	49% 5% 6% 15% 22% 3	2837
	11th to 20th	Day	46% 6% 6% 16% 23% 3	2840
	21st to end	Day	51% 3 6% 17% 19% 3	3252
February	1st to 10th	Day	50% 4 6% 18% 19% 3	1900
	11th to 20th	Day	50% 5% 5% 18% 17% 5%	1858
	21st to end	Day	51% 5% 6% 13% 19% 6%	1570
March	1st to 10th	Day	50% 6% 9% 13% 13% 9%	3172
	11th to 20th	Day	38% 5% 8% 20% 22% 7%	3480
	21st to end	Day	46% 5% 9% 21% 16% 3	3815
April	1st to 10th	Day	40% 7% 12% 19% 18% 5%	2198
	11th to 20th	Day	41% 5% 6% 18% 24% 5%	2254
	21st to end	Day	38% 7% 10% 27% 15% 3	2422
May	1st to 10th	Day	41% 10% 12% 21% 14% 2	4120
	11th to 20th	Day	47% 9% 11% 24% 8% 1	4085
	21st to end	Day	37% 10% 12% 23% 17% 2	4489
June	1st to 10th	Day	43% 9% 16% 20% 10% 2	2470
	11th to 20th	Day	35% 9% 19% 24% 12% 2	2470
	21st to end	Day	38% 11% 17% 20% 12% 3	2470
July	1st to 10th	Day	40% 14% 20% 19% 6% 1	4055
	11th to 20th	Day	40% 11% 23% 19% 5% 2	4051
	21st to end	Day	60% 11% 13% 10% 5%	4324
August	1st to 10th	Day	32% 11% 18% 30% 9%	4091
	11th to 20th	Day	34% 9% 20% 22% 14% 2	3805
	21st to end	Day	33% 10% 12% 28% 15% 2	4179
September	1st to 10th	Day	40% 10% 14% 16% 16% 4	2128
	11th to 20th	Day	42% 8% 11% 20% 18% 1	2090
	21st to end	Day	37% 7% 13% 16% 21% 6%	2090
October	1st to 10th	Day	24% 4 7% 14% 38% 12%	3480
	11th to 20th	Day	22% 4 5% 18% 29% 22%	3305
	21st to end	Day	27% 4 6% 26% 26% 11%	3350
November	1st to 10th	Day	32% 5% 6% 17% 30% 10%	1762
	11th to 20th	Day	35% 4 6% 20% 25% 9%	1800
	21st to end	Day	41% 4 6% 18% 26% 5%	1800
December	1st to 10th	Day	51% 5% 6% 19% 16% 4	1719
	11th to 20th	Day	46% 4 7% 16% 22% 5%	2150
	21st to end	Day	50% 6% 7% 20% 15% 2	3124
January	1st to 10th	Night	47% 5% 5% 16% 22% 4	4109
	11th to 20th	Night	44% 6% 6% 19% 17% 8%	4120
	21st to end	Night	53% 3 5% 14% 21% 4	4400
February	1st to 10th	Night	44% 4 7% 18% 21% 5%	2280
	11th to 20th	Night	51% 5% 5% 16% 18% 6%	2219
	21st to end	Night	52% 5% 6% 15% 17% 6%	1884
March	1st to 10th	Night	50% 7% 9% 14% 15% 5%	3680
	11th to 20th	Night	34% 5% 8% 21% 21% 10%	3480
	21st to end	Night	43% 5% 8% 22% 18% 4	3817
April	1st to 10th	Night	34% 6% 12% 20% 23% 5%	1996
	11th to 20th	Night	36% 4 8% 22% 21% 8%	1875
	21st to end	Night	35% 6% 10% 28% 19% 3	1758
May	1st to 10th	Night	40% 11% 13% 20% 15% 1	2840
	11th to 20th	Night	43% 9% 15% 23% 10%	2813
	21st to end	Night	31% 12% 16% 25% 16% 1	3087
June	1st to 10th	Night	39% 11% 17% 20% 11% 2	1710
	11th to 20th	Night	26% 10% 23% 27% 13% 2	1710
	21st to end	Night	33% 9% 19% 20% 13% 5%	1710
July	1st to 10th	Night	42% 11% 19% 21% 7% 1	2795
	11th to 20th	Night	34% 11% 23% 23% 7% 2	2786
	21st to end	Night	54% 12% 13% 14% 5% 1	2988
August	1st to 10th	Night	29% 10% 17% 33% 10%	2814
	11th to 20th	Night	32% 8% 17% 28% 15% 1	3086
	21st to end	Night	29% 8% 14% 26% 22% 2	3476
September	1st to 10th	Night	35% 10% 16% 18% 15% 5%	2032
	11th to 20th	Night	37% 10% 13% 21% 18% 1	2090
	21st to end	Night	34% 7% 12% 21% 19% 8%	2090
October	1st to 10th	Night	20% 4 9% 17% 36% 14%	3480
	11th to 20th	Night	20% 3 4 17% 35% 20%	3613
	21st to end	Night	23% 3 4 28% 29% 13%	4182
November	1st to 10th	Night	32% 4 8% 20% 25% 10%	2536
	11th to 20th	Night	35% 3 6% 20% 27% 10%	2600
	21st to end	Night	40% 5% 6% 20% 24% 5%	2600
December	1st to 10th	Night	48% 5% 8% 18% 17% 4	2495
	11th to 20th	Night	43% 7% 6% 15% 25% 5%	3044
	21st to end	Night	51% 6% 7% 21% 13% 2	4532

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	37% 20% 33% 9% 2	270
	11th to 20th	Day	39% 22% 27% 9% 4	270
	21st to end	Day	30% 31% 28% 8% 2	297
February	1st to 10th	Day	37% 22% 31% 9% 1	270
	11th to 20th	Day	50% 20% 24% 4 1	270
	21st to end	Day	46% 24% 24% 5%	225
March	1st to 10th	Day	34% 20% 29% 15% 2	296
	11th to 20th	Day	31% 19% 27% 17% 5% 1	460
	21st to end	Day	29% 20% 27% 17% 7%	506
April	1st to 10th	Day	27% 16% 26% 19% 11% 2	460
	11th to 20th	Day	22% 17% 29% 20% 11% 2	452
	21st to end	Day	22% 12% 33% 18% 12% 3	460
May	1st to 10th	Day	20% 13% 30% 20% 12% 5%	463
	11th to 20th	Day	15% 9% 25% 26% 16% 8%	487
	21st to end	Day	15% 7% 22% 26% 19% 11%	529
June	1st to 10th	Day	18% 6% 18% 27% 20% 11%	490
	11th to 20th	Day	10% 5% 16% 29% 24% 17%	490
	21st to end	Day	11% 4 19% 29% 22% 15%	490
July	1st to 10th	Day	14% 3 11% 24% 29% 19%	485
	11th to 20th	Day	12% 4 9% 28% 27% 19%	484
	21st to end	Day	14% 4 6% 27% 30% 18%	532
August	1st to 10th	Day	12% 3 15% 26% 26% 18%	486
	11th to 20th	Day	14% 5% 13% 27% 28% 13%	479
	21st to end	Day	17% 2 9% 24% 33% 15%	539
September	1st to 10th	Day	11% 2 17% 29% 29% 12%	490
	11th to 20th	Day	18% 4 15% 28% 25% 10%	490
	21st to end	Day	17% 6% 14% 32% 27% 4	490
October	1st to 10th	Day	15% 6% 24% 30% 20% 6%	490
	11th to 20th	Day	17% 11% 27% 29% 15% 1	490
	21st to end	Day	19% 11% 27% 28% 14% 1	497
November	1st to 10th	Day	23% 16% 30% 21% 7% 3	300
	11th to 20th	Day	22% 21% 34% 18% 5%	300
	21st to end	Day	23% 22% 36% 13% 5% 1	300
December	1st to 10th	Day	36% 20% 27% 15% 1 1	273
	11th to 20th	Day	33% 16% 31% 16% 5%	270
	21st to end	Day	35% 23% 27% 12% 3	297
January	1st to 10th	Night	30% 19% 27% 20% 5%	760
	11th to 20th	Night	30% 16% 24% 23% 7%	760
	21st to end	Night	24% 18% 29% 25% 4	836
February	1st to 10th	Night	24% 16% 26% 29% 4	760
	11th to 20th	Night	29% 19% 28% 22% 3	743
	21st to end	Night	32% 16% 29% 19% 3	628
March	1st to 10th	Night	22% 17% 31% 25% 5%	760
	11th to 20th	Night	22% 18% 25% 26% 8% 1	760
	21st to end	Night	22% 14% 27% 26% 10%	836
April	1st to 10th	Night	18% 13% 27% 30% 11% 1	666
	11th to 20th	Night	20% 12% 30% 25% 12% 1	563
	21st to end	Night	17% 8% 25% 34% 15% 1	570
May	1st to 10th	Night	13% 10% 25% 32% 19% 1	570
	11th to 20th	Night	16% 5% 18% 33% 23% 5%	561
	21st to end	Night	11% 2 12% 35% 32% 7%	617
June	1st to 10th	Night	11% 4 12% 37% 31% 5%	570
	11th to 20th	Night	5% 3 12% 32% 36% 12%	570
	21st to end	Night	9% 2 6% 33% 40% 10%	570
July	1st to 10th	Night	12% 4 5% 23% 45% 11%	555
	11th to 20th	Night	10% 2 5% 26% 44% 13%	552
	21st to end	Night	11% 3 4 25% 46% 11%	624
August	1st to 10th	Night	8% 2 4 27% 47% 12%	567
	11th to 20th	Night	12% 2 8% 30% 39% 9%	564
	21st to end	Night	13% 2 7% 25% 43% 9%	627
September	1st to 10th	Night	10% 3 11% 26% 41% 9%	702
	11th to 20th	Night	14% 3 12% 31% 36% 4	760
	21st to end	Night	15% 4 14% 34% 31% 3	760
October	1st to 10th	Night	12% 6% 20% 33% 23% 6%	760
	11th to 20th	Night	16% 8% 25% 29% 20% 2	760
	21st to end	Night	16% 11% 20% 35% 16% 3	836
November	1st to 10th	Night	17% 8% 25% 31% 16% 3	780
	11th to 20th	Night	17% 16% 24% 29% 12% 2	800
	21st to end	Night	23% 15% 25% 26% 11% 1	800
December	1st to 10th	Night	28% 17% 22% 24% 8%	768
	11th to 20th	Night	25% 13% 25% 29% 8% 1	760
	21st to end	Night	28% 15% 24% 27% 6%	836

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